PDA

View Full Version : Amae Design - 'AKITA' CNC Mill



damae
07-12-2005, 03:34 PM
Welcome to my new CNC Mill / Router project log!

The project is hereby named: "Akita" after the breed of Japanese bear hunting dogs. My wife loves to spend time training our Akita (it's her hobby) and now I have an "Akita" hobby too! Only my hobby can't fetch.

Here are some of my targets for this mill:

750 IPM (1500 rapid)
45" x 45" x 5" cutting area for metal (aluminum, steel)
45" x 45" x 10" cutting area for wood, light materials
45" x 45" x 30" cutting area when cutting foam
2hp spindle
Accuracy of about 0.002"
Moving gantry configuration with stationary table

The machine will be used to cut:

-foam (for investment casting in my garage foundry)
-aluminum (to build the second DIY CNC, of course!)
-wood (for the numerous and uncounted furniture projects I have on paper)
-large foam blocks (as a fiberglassed mold for a co-worker's composite canoe)

For the past 6 months, I've been fascinated by the people in the CNC community building DIY CNC machines. I recently joined this forum and have been soaking up ideas and advice ever since. To all of you who inspired and helped me, and to those who will, thank you!

Next post, I will include some pictures and particulars of the Design to-date.

damae
07-12-2005, 03:41 PM
A few threads of interest that I started, discussing components of my mill:

My big servo motors:
http://www.cnczone.com/forums/showthread.php?t=11454

Where to get cheap mil-spec connectors?
http://www.cnczone.com/forums/showthread.php?t=11760

How to get a breakout board to supply 25ma (instead of the usual 5ma):
http://www.cnczone.com/forums/showthread.php?t=11763

damae
07-12-2005, 04:02 PM
A few details about the Mill's configuration:

The mill will be configurable to 3 different Z cutting heights: 5", 10" and 30". This allows me to cut harder materials such as aluminum and steel (using 5" Z) and reconfigure later to build deep foam parts (30" Z). I plan to achieve this by creating three seperate mounting locations for my table. To cut deeper, I'll unbolt and lower the table to the next stop. I already have a THK Z axis that has around 32" of reach.

I have a moving gantry configuration, which means the table is simple and stationary. However, I haven't worked out the details of how I will acurately level and square the table at each stop position yet.

The Z axis is an all-in-one complete THK ballscrew assembly. It's got a really nice ground ballscrew. The other axes, X and Y, are using a pair of 56" long rolled ballscrews each. Each axis will have 2 linear rails from Star, also 56" long. I will eat up a substantial portion of that travel because I want a wide and rigid mounting to each axis, perhaps 8" worth. If I leave just 1.5" on each side for stopping distance before the limit switches, then I have effectively 45" travel in both X and Y.

Originally, I had planned to use 80/20 aluminum framing for the frame -- 3030 series extrusions, which are 3" x 3" in cross-section. But after reading advice from other DIY builders, it sounds like that will not be strong enough to handle my servo motors.

The motors are Emerson DX-455 3 phase AC brushless servo motors. Good stuff. But they are 2HP continuous rated (with at least 200% peak rating)! I have pretty fast ballscrews, just 2 TPI. Even if I don't gear down the motor, I can easily (in theory) get 750IPM. And at that speed, I get serveral hunderd pounds-force of side force. And with such high forces, it could be easy to bend even a 3" square aluminum frame.

So that leaves me with steel as a framing material of choice. The main drawback is that I don't have a welder and I am very concerned about getting the frame square and straight. If anyone has advice or experience here, I'd love to hear it!

One nice thing about a steel box frame would be that I could fill it with sand to dampen the vibration. An interesting thread on this idea is in the Mechanical Engineering forum:

http://www.cnczone.com/forums/showthread.php?t=11383&page=3&pp=10

damae
07-12-2005, 04:18 PM
Ok, I promised some pictures. First the motors -- 20 pounds each! I included a picture of my 7 year old son next to the motors for size reference.

And then the ballscrew assemblies. I count myself extremely fortunate to have found all the components (the ballscrew / linear rail / bearings / couplers, grease nipples, etc) all pre-mounted into one piece of heavy structural aluminum! I'll have to do some modifications, yes, but they are a good starting point! The long pieces of wood next to the assemblies are 10' dimensional lumber.

And last, a picture of me, scrounging at a local recyling yard.

mxtras
07-12-2005, 04:25 PM
This is a good read - it may offer insight. This guy did a fantastic job:

http://oneoceankayaks.com/madvac/madvac_index.htm

There are many ways to get a weldment close, but never perfect. That is where your design must allow for compensation. For example - design a completely welded structure then mount the guides on a adaptable arrangement so you can very finely adjust flatness, parallelism, etc to perfection.

Each weld will pull - so the trick is to forecast the amount of pull and compensate. Heavily tack everything then straighten and re-square before you start welding things up solidly. The difference in pull between a tack and a full weld is probably less than half but it depends on the type of weld and the thickness of the material - in other words, you may want to have an experienced individual give you a helping hand....it is an art to get weldments right. It is possible weld up a 4'X8' tube frame within 1/8" but it takes a journeyman, not a hobbyist.

BUT - you can remove most of the concerns through your design. See the link.

Scott

damae
07-12-2005, 04:36 PM
There are many ways to get a weldment close, but never perfect. That is where your design must allow for compensation. For example - design a completely welded structure then mount the guides on a adaptable arrangement so you can very finely adjust flatness, parallelism, etc to perfection.
Scott

Fantastic! I am still reading through his technique and it sounds like the way to go. As you said, welding so precicely will be tricky for anyone less than a journeyman. I had budgeted almost $1000 for the aluminum framing... maybe I'll see what a local shop would charge to build the beginnings of a precision frame.

Then again, it may be the excuse to pour that money into a nice TIG rig. That wasn't in the budget, so I'll go check some local shops first.

damae
07-12-2005, 06:32 PM
For posterity, here is the original frame design, when I planned to use the 80/20 framing.

damae
07-13-2005, 01:33 PM
Last night I finally got the computer to talk to the controller/motor!

This has been a little struggle for me, a surprising one. I expected to just hook up the correct step and direction pins from the breakout board to the controller. TTL is TTL right? After carefully checking the connections, I turned everything on, fired up TurboCNC and ..... nothing. Very disappointing!

I've tried swapping cables, changing my port settings, remapping the parallel port pins, even changing power supplies to the breakout board. Nothing worked, so I came to the conclusion that I wasn't getting enough current out of the breakout board. I'm using a CNC4PC board, by the way.

The board I am using claims 8ma per pin.
http://www.cnc4pc.com/Parallel_Port_Interface_Card.htm

Looking for a link, I just discovered that they offer two breakout boards. The "Bidirectional" board has a specification of 35ma per pin!
http://www.cnc4pc.com/Bidirectional_Breakout_Board.htm

The Emerson manual says the controller needs 25ma per pin. I reasoned this is because the TTL lines go directly into a opto-isolator, which need the higher current. So I thought I needed more current from my breakout board.

It turns out to be much simpler! There are two DB25 ports on my computer, one male, one female. My parallel cable, of course, only plugs into one of the ports. I never checked if it was the right one! On opening the PC case, I discovered it was actually hooked up to a serial port. Man, did I feel dumb.

After shelling out $8 (yikes!) to Radio Shack for a gender changer, I plugged everything in and it actually worked! It's silly how gratifying it was, just watching the motor respond as I used the jog controls in TurboCNC.

It wasn't perfect though. I am running TurboCNC in a DOS window within Win98, and I think windows is messing with the timing, making it pause between pulses and limiting the maximum speed. Funny thing is that when I try to run TurboCNC in DOS only mode, it just sends the computer into a reboot.

damae
07-15-2005, 06:24 AM
My project is taking over the garage!

Fortunately my wife hardly notices since the garage was already overgrown with junk. Funny how she didn't even notice how much I cleaned it up. ... of course, I cleaned it up just enough to squeeze my CNC bits in there!

So I invite any comments about the components I spent my hard earned cash on, especially if you think it won't be suitable for the kind of machine I'm trying to build!

-New Z axis from THK. I remeasured this and it has about 20" of Z travel, not the 30" I was imagining. hehe. I guess I have to revise my goal of reaching 30" of Z depth for cutting foam. 20" will have to do for now.

-1" hubless timing pulleys, 0.375" pitch. These are pretty beefy and weigh about a pound each, without the hub.

-Collet nuts. I don't know what the technical name is, but they're fantastic! I when I turn the nut, the OD increases and the ID decreases at the same time. I just slip them onto a smooth shaft and tighten -- no keyways. Supposedly, these should handle the 110 in-lb of torque (at 200% peak load) that the motors put out.

-Bucket-o-belts. Miscellaneous widths and lengths, all 0.375" pitch, but none of the correct length.

-Ballscrew assemblies. There are now 4 of them (I originally had just 3). I decided to buy a fourth one to make the gantry stronger.

-Motors. I have 3 DC servos of 1/2 HP, 3 Emersons (455 series) and 2 smaller emersons (316 series). The picture shows the big Emersons next to the smaller ones. The Z axis has a smaller DX-316 Emerson mounted.

-Miscellaneous. I have a buckets of 1" Idlers, t-slot mounting hardware, energy chain, mismatched steppers, small induction motors, mounting hardware, etc.

Does anyone else feel like their CNC has "feature creep?" I can't be the only one who buys too many parts, can I? Once I get the motors figured out, I will probably sell the extras. In fact, I'll probably have to sell the DC Servos soon to get the $600 (or slightly less) back out of them.

That money can go into the frame. I am hoping to build a steel frame for around $1000. Building this frame is going to be the hardest part of the whole machine. I feel like I'm at the foot of a mountain right now, looking way, way up. When people ask me why I'm building a CNC in my garage, my answer probably sounds not much better than what mountain climbers say, "Because it's there."

So in the spirit of creativity and challenge, I say I build it "because I can!"

DieGuy
07-15-2005, 09:22 AM
Last night I finally got the computer to talk to the controller/motor!

It wasn't perfect though. I am running TurboCNC in a DOS window within Win98, and I think windows is messing with the timing, making it pause between pulses and limiting the maximum speed. Funny thing is that when I try to run TurboCNC in DOS only mode, it just sends the computer into a reboot.

This is a fantasic setup! Where did you get those motors and controllers?

TurboCNC needs to have pure DOS to run in as it needs to have direct access to the parallel port. No stinking Winders in between.

you can get one here. (http://www.bootdisk.com/) :cheers:

damae
07-15-2005, 12:03 PM
This is a fantasic setup! Where did you get those motors and controllers?


A local junkyard, believe it or not! Actually, it is a recycling business that sometimes deals in high tech junk. They are smart enough to know what controllers and motors are worth, but realistic enough to sell them for ebay prices.

There are a lot of high tech businesses around here (Portland) so when they disgard their previously expensive equipment, it often ends up at scrap prices.



TurboCNC needs to have pure DOS to run in as it needs to have direct access to the parallel port. No stinking Winders in between.

you can get one here. (http://www.bootdisk.com/) :cheers:

I've been wanting to get TurboCNC running in DOS-only mode. Thanks for the great link; I'll make a DOS boot disk and try it again. Hopefully TurboCNC will cooperate (instead of rebooting my PC when run!).

damae
07-15-2005, 07:20 PM
Good news! My workplace decided to purchase a small CNC mill for prototype work. It's a Roland MDX-500 and while it's not big, it is big enough to help me cut some miscellaneous brackets (after hours) for my homebrew CNC!

http://www.rolanddga.com/products/3D/modelers/MDX-500/

Otherwise, I was going to build all the parts on a smaller machine -- a little MaxNC-10 I bought some years ago. That would have been ok, but some of the brackets will be too big to put on the little MaxNC - the parts would have to been indexed to finish milling. So needless to say, I'm excited!

I'll attach pictures to show both machines. Also, there's a picture of the workshop at my workplace, where I may build some of the parts for the machine.

Jason Marsha
07-16-2005, 11:24 PM
That's one clean and tidy workshop.

Jason

damae
07-17-2005, 04:12 AM
That's one clean and tidy workshop.

About 30 people share that lab and it can actually get messy. It was cleaned up for a VIP tour not too long before I took the picture.

Anyway, that's at work. Check out my garage, where I am building the CNC! The rack in the background takes full 4' x 8' sheets of particleboard for shelves and I still have stuff sitting on the floor. So I planned a garage sale for next weekend because I can't even build a my mockup of the CNC frame -- there's not enough room!

A thread titled "My Poor Wife!" talks about messy work areas:
http://www.cnczone.com/forums/showthread.php?t=11746

damae
07-17-2005, 04:27 AM
The next two things I want to sort out:

1. Get the CAD model and spec sheets for my THK actuator. But the model number is partially rubbed off. I'm guessing it reads "GL15S160600L." Anyone familiar with this slide assembly?

2. The thrust bearing arrangement on the larger ballscrew assemblies seems a bit weak. The bearing is held in place with two washers screwed into the endcap to overlap the outer race of the bearing. To me, this seems far too weak.

And what do you guys think about the overall rigidity of these parts anyway?

damae
07-17-2005, 07:17 PM
The guys in the TurboCNC forum set me straight!

http://www.cnczone.com/forums/showthread.php?p=91959#post91959

I pruned back all the fluff in autoexec.bat, config.sys and now it runs in pure DOS mode, without rebooting my computer. It's faster and rotates very smoothly -- no popping and jerking like it had under windows!

800RPM seems to be the fastest I can get it to run under TurboCNC, about 50kHz pulse speed. I'll reprogram the Emerson servo amp to act like it has 800 pulses per revolution instead of 4096. That should let me reach the 4000 rpm that these DX-316 series motors are rated for.

Yikes, the garage is getting hot today! But it's time to pull everything out and start getting organized for a garage sale; into the furnace I go!

Jason Marsha
07-17-2005, 09:04 PM
Wow that garage is even worse than my CNC work space. Good luck with your garage sale.

Jason

damae
07-18-2005, 09:30 PM
Anyone want to guess (or suggest) how much thrust those washers (picture in post #15) will handle? I need to handle 200-400 pounds of thrust!

jimbo
07-18-2005, 10:20 PM
they should be fine, a google search of "gl15s" turned up the following site,
http://www.arsales.com/pages/thk/products/gl.htm
middle of page shows ballscrew speces for gl15s16 dynamic load at 12.9KN or ~2900 lbs.

damae
07-19-2005, 01:46 AM
they should be fine, a google search of "gl15s" turned up the following site,
http://www.arsales.com/pages/thk/products/gl.htm
middle of page shows ballscrew speces for gl15s16 dynamic load at 12.9KN or ~2900 lbs.

Thanks Jimbo!

That site seems to contain better information that THK's own site. The moment load ratings and the thrust rating you mention is very helpful! I also didn't have the repeatability and accuracy ratings until I saw that page. Looks like it's good to within about 4 tenths!

From THK's site, I was able to download part of the 3D model for the actuator (could only get the carriage to import into my CAD for some reason).

In my question (post #18) I was wondering about the other ballscrew assemblies (56" long ones) not the THK.

At the end of the aluminum extrusion, there is a bearing mounted in a stainless steel plate (first picture in post #15). The bearing is pressed down into a recess and sits flush with the outside surface of the block. It looks like two washers are the only thing holding the bearing in place, and they only overlap the outer bearing race just slightly!

The Nook ballscrews are 3/4" diameter and are rated at 2700 lbf (dynamic) and 17,400 lbf (static). So I know the screws can handle plenty of thrust. What worries me is how much force the washers holding the bearing in place can handle!

Come to think of it, I don't know for sure if that's a thrust bearing. How would I be able to tell? Is it common to have only one thrust bearing on a ballscrew?

Jason Marsha
07-19-2005, 07:19 AM
Damae,
Check out the first post in this thread by swede it may have what you want in it.
It has a bit about supporting the ballscrew.

http://www.cnczone.com/forums/showthread.php?t=8813

Jason

jimbo
07-19-2005, 08:04 AM
my bad, i got the pictures mixed up. I looked at the picture again with the bearing. It looks like this end of the ballscrew just floats in the bearing and the bearing is only used to support it, no thrust on this end. There is probably another bearing(s) on the driven side of the actuator that handles the thrust duty.

damae
07-19-2005, 12:47 PM
Damae,
Check out the first post in this thread by swede it may have what you want in it.
It has a bit about supporting the ballscrew.

http://www.cnczone.com/forums/showthread.php?t=8813

Jason

Perfect, this was just what I needed! Here's a quote from his article:




"With the driven end fixed, why not REALLY fix the ballscrew in place by using another pair at the opposite end of the ballscrew? Don't do that! The far end of the ballscrew must be free to float axially. This is due to temperature variations. "


So the conclusion is my setup is OK. With the real thrust bearings mounted on the other end of the ballscrew, I can leave the bearings on this end alone because they are most likely just radial bearings, not thrust bearings.

Thanks to all who helped!

damae
07-20-2005, 02:40 PM
Tiernyn, the Akita, is the official mascot for this mill/router project. Here's a picture of her overseeing the work:

damae
07-21-2005, 07:27 PM
I've had some time to model up the pulleys, idlers, controllers, and the main extrusions that hold the Nook ballscrews.

For the gantry (the Y axis), I am planning to use two ballscrew assemblies linked together with timing belts and driven by one motor. Attached is a screenshot of the general idea. Unfortunately, I don't yet have the Nook ballscrew, Star rails, or any of the other 'guts' modeled. So the image just shows the empty extrusions. (for clarification, the ballscrew mounted vertically is the Z axis)

What do you guys think? Help me out by pointing out any pitfalls I may need to dodge. For instance, I just realized I'll probably need a tensioner in there.

damae
07-22-2005, 09:38 PM
I guess I need to make it easier to poke holes in the design -- nobody had anything to say about the Y axis belt drive.

So I whipped up a concept for driving both ballscrews on the X axis at the same time that has some problems to solve! I jogged the whole belt downward below the level of the table, with the idea that I can lift my workpiece out from either side and make the table more accessable.

Of course, this leaves long stretches (maybe literally!) of belt that aren't well supported. I don't have any experience in syncing two ballscrews and I certainly don't have much of a feel for the strength and flex of belts.

So what do you guys think? (I'm sure someone has an idea if this will work or not..)

Edit: Yikes! I just measured, and it's almost 5m of belt!

damae
07-22-2005, 09:51 PM
Having a big CNC machine in my garage is one thing. But I have to be considerate for the WAF (Wife Acceptance Factor)!

So in the interest of keeping the sprawl of materials and accessories down, I thought I would try to store the extra materials on a shelf below the working surface (see picture).

Also, I've been on the hunt for a good NEMA encosure to hold all the servo amps, power supplies and PC. Well, my junkyard came through again -- and in a BIG way! This encolusre is 175 lbs! And that's empty! 40" x 36" x 16" I think. $60 makes it around $.035 per pound.

Anyway, I modeled up the controllers (rough model) and placed them in the cabinet. There's certainly room to spare!

The top is about bar-counter height, perhaps a good height to mount the LCD monitor. The keyboard would still have enough of a shelf to sit in front of the monitor.

The downside is that it's so big, it kind of restrics access to the machine table from one side.

randyf1965
07-23-2005, 01:00 AM
Is the cabinet structrual enough to become part of the table? IE replace the leg(s) on 1 side

damae
07-23-2005, 04:22 AM
Is the cabinet structrual enough to become part of the table? IE replace the leg(s) on 1 side

See, that's why I love this forum -- always thinking "outside the box!" Hehe.

To figure out the wall thickness of the metal, I had Pro/E calculate the mass for me, then kept changing the wall thickness until it weighed 175 lbs. Turns out it's pretty close to a 1/8" wall. Surprising, isn't it? It seems like it should be much thicker for that weight.

So given a 1/8" wall, I'm a little nervous about how rigid that box will be. Next trip to the junkyard is to pick it up, so I'll soon be able to tell.

Ken_Shea
07-23-2005, 10:14 AM
damae,
From a purely non-technical point of view, thinking mechanically only, all that belt looks like trouble, especially since I know you are wanting to build a fast IPM machine.

Ken

damae
07-25-2005, 01:52 PM
damae,
From a purely non-technical point of view, thinking mechanically only, all that belt looks like trouble, especially since I know you are wanting to build a fast IPM machine.

You're right, there's just too much belt. I can just see the belt starting to twang like a guitar string!

So here's another concept where I mount the whole belt drive above the table. Having a variable height table, this may be a much better arangement anyway.

What do you guys think? It's still 3.3m of belt. Is this too long? How should I go about maintaining tension? How much belt flex can be allowed before the belt will cog (skip on the pulley)?

[edit: Please ignore the Y axis belt and pulleys on the gantry -- I moved things out of place and didn't put them back yet. Focus on the X axis]

ViperTX
07-25-2005, 01:59 PM
What is your reason for wanting to drive 2 ballscrews on the axis?

damae
07-25-2005, 02:11 PM
What is your reason for wanting to drive 2 ballscrews on the axis?

Actually, I would do it with just one ballscrew, but I want the table to be of variable heights.

The target is up to 20" of Z cutting area for foam and about 5" of Z for cutting metals. I'll move the table to different stops to use the minimum Z height I need for a particular job.

Because of this, I don't see any good way to mount the ballscrews under the table. If I mount below the lowest table, it seems like I'd be fighting a lot of leverage. And I was planning to use the area below the table to store extra materials, precut 4' x 4' sheets of birch plywood mostly.

ViperTX
07-25-2005, 07:25 PM
damae,

Have you seen the small wood planers?? So, what you want to do is to have an adjustable gantry (just the center section or the x-axis). You would adjust the center section up/down and then lock it in place to the vertical risers. If you use the approach of having twin screws to assist in the raising / lowering like in the wood planers you'll have what you want in a much nicer package.

damae
07-25-2005, 07:51 PM
damae,

Have you seen the small wood planers?? So, what you want to do is to have an adjustable gantry (just the center section or the x-axis). You would adjust the center section up/down and then lock it in place to the vertical risers. If you use the approach of having twin screws to assist in the raising / lowering like in the wood planers you'll have what you want in a much nicer package.

Interesting idea. I've thought about automating the table adjustment. But making the gantry have a second Z height adjustment is a new idea to me. I'll take a trip to Home Depot to see the way it's done in a planer.

So if I understand your suggestion correctly, it would allow me to have a fixed table. The whole gantry would move down toward the table on a second Z height adjustment that can be positioned and locked before each job. And the Z axis would, of course, still move automatically. Is that the idea?

ViperTX
07-25-2005, 08:44 PM
Damae...you got it....it will become clearer once you see the planers at Home Depot.

10bulls
07-26-2005, 05:13 AM
Wouldn't this increase the risk of the gantry flexing? In effect you're increasing the lever distance of the tool from the x bearings.
I suppose in properly built machines like you guys this isn't such an issue :)

I like the flexibility of having no obstructions under the gantry. Although my gantry is small and shonky, I could (in a moment of boredom or whimsy), sit the mill on top of a large door, or table (..or car?!) and machine an entire mill work area's worth at a time.
...Given time I may even think of something useful you could do like this! ;)

Also (again probably not such an issue with quality components like yours), I find 2 screws does help increase the rigidity of my machine.

Another benefit - when you build mark II, you could then use this one as a plasma table!

Rather than timing belt, what about getting another servo (or pair of smaller servos) and use one per lead screw (master/slave)?

ViperTX
07-26-2005, 10:02 AM
True 10bulls....but at the upper gantry heights he is only cutting foam....so, not a problem.

damae
07-26-2005, 01:01 PM
Wouldn't this increase the risk of the gantry flexing? I like the flexibility of having no obstructions under the gantry.

Either way, I have the same amount of torque being applied to the gantry. The difference is how the two different gantry structures handle the forces. As ViperTX said, I am really only planning to machine foam at 20" of Z, so hopefully the foam won't offer much resistance at large Z heights.

The difference will be when handling large forces, when I'm cutting metal. Or when I'm cutting wood very fast. So the question is which arrangement will be better?

On the original design, I have to worry about the movable table -- if it will move under the large loads (not too worried about that, since it'll be bolted) or if it will be hard to level and set up, which is likely.

To follow ViperTX's suggestion, I will have a fixed table and will be almost guaranteed not to have trouble with the table moving or being out of level. But when I am cutting metal especially, even if I'm using a small Z height, the forces must be transmitted through an extra set of linear slides/ballscrews. But setup time would be much shorter with this arrangement.

I haven't gone to Home Depot yet and don't know exaclty what these planers look like inside. Maybe that will make me more confidant in that design ... =)

damae
07-26-2005, 01:16 PM
Another benefit - when you build mark II, you could then use this one as a plasma table!


Hehe. I can just see it now, TWO CNC machines in my garage! =) My wife would more than just raise an eyebrow at that! hehe.

A funny thing about that -- I have thought about buying an empty lot across the street from my house as an investment. And then someone jokingly suggested I could put a shop on it temporarily until I decide to build a house there.

They thought it was funny, but I like the idea! Ok, it's more of a dream than an idea....




Rather than timing belt, what about getting another servo (or pair of smaller servos) and use one per lead screw (master/slave)?

Good point! Because either design still requires that I drive the gantry with the two ballscrews. So I still haven't solved the problem of how to drive the ballscrews together.

Yes, I could use a second servo. Actually, I have 5 sets of motors/controllers right now! I have three of the DX-455 motors (2hp each) and two of the DX-316 motors (about 3/4 HP).

One of the DX-316 motors is already mounted on the Z stage, so that pair of motors is already split up. I can drive the X axis with two of the DX-455 motors, but that is really really overkill! It would be 4HP nominal, at least 8HP peak driving that axis! I can really see something getting bent up!

Which method is safer? To drive both ballscrews mechanically with the timing belt (stretch and cogging problems)? Or is it better to mount one motor to each screw and hope that they don't get out of sync?

In the case of the Emersons, I think I can just send the same step/direction signal to both controllers and they should be able to automatically compensate for any extra load or lag. But if somehow one of the controllers shuts down, or loses the step/direction signal, I can see it bending the frame real fast!

By the way, can someone tell me, is X axis this the right term for the axis that moves the most components? I figure X axis is the first one, the one that moves the other two axes. The Y moves the gantry and the Z. And, of course, the Z is just the Z stage. If i'm saying it wrong, someone set me straight! =)

damae
07-27-2005, 03:14 PM
Well, I finally made it to Home Depot to see how wood planer machines make the Z height adjustment.

I actually managed to get the inspection covers off without any employees telling me not to disassemble the machines in the store. Hehe. It looks like they use one threaded rod and two rod-style guides on each side.

The two screws are chain-driven by a crankhandle and surprisingly didn't seem to have any backlash or play.

There is one catch to this design, at least for me. It would allow me to reach large Z heights, but only manually, between setups. So I won't be able to cut the full 20" Z height for foam parts...

Uh oh.. I was just told by a coworker that Mt. St. Helens is going off again... I'll add to my post later. (I want to go peer out the window)

ViperTX
07-27-2005, 06:08 PM
Well you want to have your cake and eat it also. How will you be machining the foam parts....hot wire or ?

damae
07-27-2005, 07:44 PM
Well you want to have your cake and eat it also. How will you be machining the foam parts....hot wire or ?

I was planning to cut the foam with regular endmills and I'd like to do it in one pass. The foam is 2lb urethane, surfboard style foam.

So I would secure the 20" tall block of foam to the table and cut the whole 20" depth at once. I realize I'll still be limited as to what shapes I can cut -- for instance I can't cut a 20" vertical wall. But as long as the part has enough draft on it to allow the spindle to clear, I hope to cut to the full 20" depth.

10bulls
07-28-2005, 04:57 AM
I don't know about TurboCNC, but Mach2/3 supports the notion of master/slave dual lead screw motors. I think it pretty much just sends the same pulse and step to both, but handles the limit and home switch logic more intelligently.
Speaking of which, I would have thought it would be pretty straight forward to rig up an emergency cutoff switch on your gantry that would trip under excessive twist...

ViperTX
07-28-2005, 12:04 PM
damae....well both the spindle and the gantry portion supporting the x-axis will have to clear.....so, you would never be able to cut a "v" shape that was deeper then the travel of your z-axis, or a vertical wall as you stated. It almost seems that you need the gantry to be adjustable on the fly...if you really want the complete 20 inch travel without any manual adjustment.

10bulls
07-28-2005, 12:31 PM
Perhaps another alternative is to go with a moderate Z travel for now (say 10"), then when you've got this machine built and working tidy, for your next project, make a 4th rotation axis. You'd get more detail like this rather than just being able to plunge down into the foam. Of course it would limit you to the diameter of the foam object you could mill. Are you wanting to make garden gnomes...or scale models of local volcanos?
...Oh! just read the 'composite canoe' bit....hmmmm....
How 'bout cutting out cross sections from 6" foam and glueing them all together?

damae
07-28-2005, 05:48 PM
Lots of good ideas, thanks guys! I was working until 6am this morning and only got 2 hours of sleep. Instead of napping during lunch today, I worked on the CAD design a little. This CNC stuff is kind of addictive!

Hopefully my replies make sense!


damae....well both the spindle and the gantry portion supporting the x-axis will have to clear.....so, you would never be able to cut a "v" shape that was deeper then the travel of your z-axis, or a vertical wall as you stated. It almost seems that you need the gantry to be adjustable on the fly...if you really want the complete 20 inch travel without any manual adjustment.

I made a quick sketch showing the clearances I was talking about. The THK slide can move about 20". As long as the spindle and THK slide clear the part, I should be able to cut parts this deep.

You're right that I'm going to be stuck with a manual adjustment of one kind or another. I don't plan to swich often between tall Z foam parts and low Z wood or aluminum parts. Realistically, I'll be stuck in one mode or another most of the time.

So I'll have to figure out what minimum draft angle I need on the hull. Looking at some of the other posts in this forum (and videos of commercial equipment) I realize I would really need to make this a 5 axis to do anything but the most simple boat shapes. Hehe. Perhaps that will be Mark II.


I don't know about TurboCNC, but Mach2/3 supports the notion of master/slave dual lead screw motors. I think it pretty much just sends the same pulse and step to both, but handles the limit and home switch logic more intelligently.
Speaking of which, I would have thought it would be pretty straight forward to rig up an emergency cutoff switch on your gantry that would trip under excessive twist...

Couldn't find the way to do it in TurboCNC yet. Eventually, I hope to switch to Mach 2, when I get a better computer to run the machine. When you say it handles the limit switches more intelligently, what do you mean? I thought most people hook all their limit switches in parallel...

I thought about the limit switch that would detect racking or crabbing of the gantry. Maybe an insulated feeler arm that closes a circuit with the X axis rails? Hmm.. or maybe a strain gage on the gantry?


Perhaps another alternative is to go with a moderate Z travel for now (say 10"), then when you've got this machine built and working tidy, for your next project, make a 4th rotation axis. ...


I have some parts I eventually want to convert into a 4th axis. Wow, that would be a big swing -- almost 2 feet! I'll post the picture. It's got a globe motor on it now, but I will upgrade later.

My friend with the canoe project has also suggested using 6" slices of foam. It sure would be easier, but maybe not faster. I guess I'll build with the 20" Z travel and see how useful it is. If the spindle and Zaxis get in the way too much to cut useful parts, I'll have to do something else.

But in the meantime, it's a fun challenge!

damae
07-28-2005, 06:05 PM
Here's what I did during lunch.

Nothing too exciting, just added the motor mount and end plates on the Y axis and played with driving the X with two servos, one on each ballscrew.

Critiques and ideas welcome!

ViperTX
07-28-2005, 10:59 PM
Ooohhhhh...ohhhh...10bulls hit on something.....what if when you did the foam that required 20 inches.....10 inches was above the table and 10 inches was below the table surface and the 4th axis rotated the "whole enchillida".......

damae
07-29-2005, 02:44 AM
Ooohhhhh...ohhhh...10bulls hit on something.....what if when you did the foam that required 20 inches.....10 inches was above the table and 10 inches was below the table surface and the 4th axis rotated the "whole enchillida".......

Haha! Allright, you guys are convincing me! I can build a fixed table at 10" depth -- and design it with a removable center panel to allow the 4th axis to make the large swings like you described. Wow, that will look cool!

Do you guys ever take a step back, look at your ever growing project, and wonder "How did this all happen anyway?" Hehe!. When I got bit by the whole "build stuff in your garage" bug, I imagined I'd only be melting metal in my garage. Now look at this! What a monster of a project!

Oh, I almost forgot to mention the garage sale this last weekend. I netted $136 and about 250 square feet of garage floor space! I have space for the CNC now! Woohoo!

10bulls
07-29-2005, 04:45 AM
Lots of good ideas, thanks guys! I was working until 6am this morning and only got 2 hours of sleep. Instead of napping during lunch today, I worked on the CAD design a little. This CNC stuff is kind of addictive!
He He. I was rewiring my driver box till 3AM this morning, then got kicked out of bed by 6AM by little 'un. Fun isn't it?


...When you say it handles the limit switches more intelligently, what do you mean? I thought most people hook all their limit switches in parallel...

Sorry, I just RFTFM again ;)...it doesn't do anything clever with the limit switches, just the home switches. When you reference the axis (ie tell it to go to it's home position), it treats the master and slave axis seperately...This way you correct minor skewing/racking caused by missed steps, or when you first turn on the machine and it's in an unknown state...Check out the big brain on Art!!!

My thought for a simple cutoff switch would be to have single PCB pin headers on the bottom corners of the gantry. Push a wire into/onto the header, loop it around the gantry (perhaps on guide pegs) then connect it to the pin header on the opposite corner (as it's the corners that will move most relative to each other if the poop hits the twirly thing). keep the wire under tension so that a couple of mm deflection should pop the wire from the header. Rig another wire on the other 2 diagonal corners and wire them in series so that either of them popping would break the circuit.

10bulls
07-29-2005, 06:16 AM
My thought for a simple cutoff switch...
Oh scrub that, just looked at your latest drawing...I'd just put a couple of microswitches (with the roller contact) on each side so they are just touching the outside of the slides so any twisting *should* trip them. I suppose it all depends on which part of the machine would 'give' first !?

ViperTX
07-29-2005, 10:39 AM
Well if you are looking for minute amounts of deflection...then a strain gauge is the way to go...microswitches take an inordinate amount of movement to actuate.

dama.....isn't our brand of brainstorming cool!

damae
07-29-2005, 04:01 PM
Well if you are looking for minute amounts of deflection...then a strain gauge is the way to go...microswitches take an inordinate amount of movement to actuate.

dama.....isn't our brand of brainstorming cool!

Very!

This forum is a huge help in designing so far! Going it alone, I'm sure I'd build something backwards or catch myself on fire or something! At the least, you guys are helping me to avoid building, scratching my head, and then tearing it apart to build it right the second time!

It's been ages since I've wired up a strain gage. I'll have to figure some way to interface that with TTL signals. The PCB idea was very interesting too, but I agree that regular limit switches may not be sensitive enough.

...Unless I have optical ones? The Mach 2 home switch functionality to correct askew gantries makes it worth doing that even if I do go with a strain gage.

Thanks again guys!

ViperTX
07-29-2005, 05:57 PM
Maxim's 1452 & 1455 make it easy to adapt a strain gauge...and they usually have free samples. Boy, this could take some time....experimentation....I didn't check any of the strain gauges...I suspect they have some with calibration tables, etc.

damae
07-29-2005, 06:31 PM
ViperTX, This must be the Maxim IC you were talking about?:

http://www.machinedesign.com/ASP/strArticleID/56672/strSite/MDSite/viewSelectedArticle.asp

I'm going to do a little reading up a little on wheatstone bridges and conditioning. Maybe I can convince an EE here at work to help me out!

Another interesting problem will be how to distinguish between gantry flex underload and flex due to racking. I guess I should work on getthe gantry built in the first place! =)

damae
08-16-2005, 04:12 AM
I find it somewhat funny that I set out to build a CNC machine and end up shopping for a welder, eyeing a mini lathe, buying a master precision level, and so on.

My coworkers reminded me that originally I only set out to do some fancy concrete work in my garage, which led to the home foundry, which led to the idea to do a foam cutting CNC (for lost foam casting) which led to building a full size CNC! Was there something before all that?

I gave them permission to intervene if they saw a truck unloading an injection molding machine into my garage! Haha!


Work has required a lot more of my time these past two weeks, but I managed to do some research on MIG welders. I spent a lot of time trolling craigslist and ebay trying to find a good deal. Craigslist is great, but I've had at least three welders bought up from under me (before I could get there). I want a decent MIG rig, Lincoln or Miller. TIG sounds like fun, but there's no way I can afford it!

Has anyone tried the Lincoln 3200HD? It seems to be the right welder for the right price. I'll need to weld 1/4" tube steel, so my only worry is that the 135 amp supply may not be enough.

I also snagged a 10" master precision level on ebay, 'cause I can't afford retail! The frame is definately my next target and I realize the machine won't be worth scrap steel if the frame isn't straight. I hope to get it level to within 0.0005".

What I don't know how to do (yet) is how to get it nice and parallel. My idea is to partially disassemble the linear slides on the two Y axis assemblies. Each rail has two cars on it. I'll move one bearing car to each end of the slide and bolt them to temporary fixture bars that spans the distance. The bars will have to be carefully machined so that they span the exact same distance. This fixture arrangement should allow me to shim up the balllscrew assemblies and secure the rails using Madvac's aluminum filled epoxy method.

What else. Oh, I checked my e-chain that I bought and it looks like they are perfectly sized for my 4' of travel. I bought 6 of them, thinking I may have to splice several together to get enough travel out of them. So the three extra segments will become part of Mark II!

damae
08-18-2005, 12:39 PM
Woohoo!! I sold my extra motors (the DC servos) on ebay! Listed them at 2am and they were sold before 9am this morning!

Now i have the cash to buy the steel for my frame!

ViperTX
08-18-2005, 01:03 PM
Personally, I'd stick with the Miller....135 Amps....yes that is sufficient for 1/4 inch steel.

0.0005 on a welded steel frame....that will probably be a first for a home hobbyist! I would plan on learning about 'scraping ways'...isn't it funny that the only difference with scrape and scrap is the vowel....interesting....

damae
08-18-2005, 01:34 PM
Personally, I'd stick with the Miller....135 Amps....yes that is sufficient for 1/4 inch steel.

Thanks for the advice! The 135 amp welders look pretty small (you can carry them) so I was worried they couldn't handle it.



0.0005 on a welded steel frame....that will probably be a first for a home hobbyist! I would plan on learning about 'scraping ways'...isn't it funny that the only difference with scrape and scrap is the vowel....interesting....

I don't expect the steel frame to be within 0.0005 as welded, but plan on using MadVac's technique to inject an epoxy/metal powder mixture to take-up the difference. He has a pretty good technique where you adjust the rail (or ballscrew assembly in my case) at each location using machine screws. Then when everything's flat and parallel, you seal the deal with epoxy.

Hehe. You'll know I messed it up if you see me post with the title "Can I buy a vowel?"

damae
08-25-2005, 02:35 PM
Just got my Porter Cable model 690 router motor, another component courtesy of ebay. Here's a link to a thread about this router:

http://www.cnczone.com/forums/showthread.php?t=10297&page=3

Although the motor is only 1.75HP, it's enough to get me started. This forum is fantastic! So many people trying out their crazy ideas, it's easy to mine for good ideas, especially since you can see how it turned out for them!

Another thread pointed me to an easy way to add ER16 collet capability, using a "straight shank collet chuck."

Here's the thread:
http://www.cnczone.com/forums/showthread.php?t=9925

Edit: I posted a link to an ER11 holder. Here's a link to the ER16, for about $95:
http://www1.mscdirect.com/CGI/N2DRVSH

Oh, the pictures -- I went a bit overboard with the 3D modeling of this part. hehe.

damae
08-30-2005, 05:17 AM
No matter which way I looked at it, the twin aluminum extrusions just weren't cutting it for the gantry. Here's why:

1. Too many cutouts machined into the side of the extrusions. I'm sure they served a purpose when they were part of another machine. But for me, it just violates the strength of the extrusions.

2. Tall, thin portions of the extrusion were not really adding to the structure, but they did waste space. I think they were originally inteded to guard the ballscrew and rails from dirt and such.

3. Connecting the two extrusions was a problem. It looks like it will require a lot of plate and adjustment to attach the two rigidly.

For less effort, I can demount the rails and one ballscrew (ditching the second ballscrew) and attach them to a large steel beam. This simplifies and shrinks my pulley arrangement, not to mention the chore of getting two ballscrews in sync with each other. The beam weighs in at around 150lbs! That's reduced from the 220lbs I started at with 12mm (1/4") walls.

I figure I have to at least be able to lift each individual part of the machine on by myself! Speaking of which, I just had a backyard 'accident' this weekend. A 6" steel C-Clamp fell about 4 feet onto my noggin and ripped a small hole. (ouch!)

After a trip to the emergency room, I'm sporting 4 stainless steel staples in my head. They're a good reminder how little steel it takes to do serious damage. So out with the 220 pound beam and in with the 150 pound one!

Actually, I'm sure it's still overkill as it is. Hmm. In light of the staples in my head, maybe I should say it's 'overdoing' it instead!

The second image shows the progress on the Z-Axis design. The first image shows the cutting envelope as a red outline box.

damae
08-30-2005, 01:47 PM
I hacked out a motor mount design for the Porter-Cable spindle. It's crude and rude, but a good placeholder. The tabs on the clamp plates are intended to align the clamp to the mounting plate while I drill into the clamp plate, using the mounting plate as a drill guide.

Actually, that's something I've been wondering about for a while. What is a good way to drill into the ends of plate? Designs requiring two plates to be joined at right angles are not new. How do most people get the precision they need? After all, it's the placement of these holes that determine if everything will be square when you tighten up the assembly. But many of the plates are longer than the Z axis of a CNC. So are most people using a drill press?

ViperTX
08-30-2005, 02:04 PM
the endplates are too long for a mill ?? Do you have a drill press? if not then make youself a drill block or guide block....I'm facing the same problem on my gantry uprights.

damae
08-30-2005, 03:45 PM
the endplates are too long for a mill ??

The mill I have access to right now has a max Z height of under 5". The gantry mount plates will be up to 12" tall.

At work, I have access to a drill press, center punches, measuring equipment, etc. However, I've never thought of drill presses as high precision machines. The round columns never seem to clamp down tight enough to make me believe in it.

Viper, let me know how your gantry parts turn out when you get it figured out.

Unless I find a better way, I'll be doing the layout for these holes by hand. And how accurate can that be anyway? =)

ViperTX
08-30-2005, 04:17 PM
The main thing is for the mounting surface to be square with the vertical sides and the holes drilled and tapped as square to the mounting surface as possible.

damae
09-03-2005, 06:47 PM
Just for fun, I traced a picture and cut it out. Perhaps I'll refine the logo design and cut it into the gantry endplates.

DOMDEC
09-04-2005, 05:32 AM
I like your logo very much, it looks very cool and is nicely made.
Witch program did you use to write the G code ?
Now you got me thinking to design my own logo.
:cheers:

damae
09-04-2005, 11:13 AM
Witch program did you use to write the G code ?
Now you got me thinking to design my own logo.

Thank you! I used Pro/Engineer to design the shape and Modella 4 from Roland to generate the toolpaths. You can see that the lettering isn't finished; I had to do another pass with a smaller end mill, but ran out of time.

I've also thought of decorating various parts of the mill, following the Akita theme. As cool as most industrial CNC machines look, they don't have the freedom to put any kind of theme or decoration on them. They have to look business-like.

Well, not my CNC! I hope to do some interesting things to dress it up a bit.

ViperTX
09-05-2005, 12:20 AM
Well, I had to design and build a drill guide block to drill the ends of the gantry uprights...my uprights are 12.5 inches long. Anyway, I've got the guide block done....wish I had ordered some hardened guide bushings....but what I have will work for the 14 holes that I need to drill. I'll drill and tap 8 of those holes in the morning those will will be the holes in the gantry uprights.

damae
09-06-2005, 06:37 PM
Meet Arnaldo, the gantry drivetrain. Mr. Arnaldo to you.

Mr. Arnaldo is fully equipped to handle all of the acceleration and abuse he will surely have to endure. He laughs at the mere 110 in-lbs (9 ft-lbs) peak torque from the Emerson DXM455 motor. "Go ahead, accelerate me to full speed and crash my Ganyry into a wall! You'll see who survives, me or the gantry!"

Now, Mr. Arnaldo is not totally insensitive as you may imagine. He is strong, yes, but he has feelings too. In fact, he prides himself on being sensitive to other's needs. For instance, he will ignore the poorly welded bracket and misalignment due to Mr. Amae's poor welding skills. He feels the same tenderness toward the nook ballscrew, not wanting any angular misalignment of his output shaft to cause it any discomfort.

Mr. Arnaldo even cares about the motor manufacturer's feelings. They want him to go easy on the motor. So he has promised not to exert more than 100lbs of radial, or 50lbs of axial force, just like their spec sheet says.

Yes, Mr. Arnaldo is strong, but is he the best design? Or is another mysterious design, Ms. Kaya, lurking in the background, waiting for Mr. Amae to come to his senses?

ViperTX
09-06-2005, 06:45 PM
Well my vote is with Ms. Kaya....'cause she's a woman and has intuition! *chuckle*

10bulls
09-06-2005, 06:51 PM
Yes, it's about this stage that anthropomorphism kicks in...maybe due to sleep deprivation ;)
Anyway...I think Ms Kaya will just end up 'screwing around'...it'll all end in tears!

damae
09-08-2005, 03:25 AM
Well, I had to design and build a drill guide block to drill the ends of the gantry uprights...my uprights are 12.5 inches long. Anyway, I've got the guide block done....wish I had ordered some hardened guide bushings....but what I have will work for the 14 holes that I need to drill. I'll drill and tap 8 of those holes in the morning those will will be the holes in the gantry uprights.

Hey ViperTX, do you have a project log? If so, can you post a link? I'd love to see pictures of your drill jig and setup!

ViperTX
09-08-2005, 11:03 AM
I'll have a project log up on my website sometime in the next couple of days and will post at that time. Last night I milled the piece of aluminum where the Y-axis rails will be mounted, I'll drill the ends tonight and attach to the gantry uprights.

damae
10-30-2005, 04:55 AM
Just a quick update on this machine. I bought a Bridgeport mill, which I am retrofitting with the huge servos previously slated for my CNC router. Actually, I just bought a second Bridgeport and will be retrofitting that one too.

These two Bridgeport mills will now handle all my parts requiring high precision, power, rigidity and to cut any metal harder than aluminum..

http://www.cnczone.com/forums/showthread.php?t=13821

So there's a bit of a scope change on this project. I am going to relax my tolerances and limit this machine to cutting primarily wood, foam, plastic, and occasionally sheetmetal. I'll aim for high speed, but no longer need to have the frame perfectly straight and level.


New spec:

-750 IPM
-Repeatability of 0.002"
-Accuracy of 0.005" per foot
-Cut Wood and Plastic within 10" Z height
-Cut Foam within 30" Z height
-4th axis is now a must
-Welded frame is no longer a requirement. The frame can be bolted together for final alignment.
-Tool changer (pick-n-place style) is now back in the plans
-Will be movable, on metal casters. This was not an option back when I wanted this machine to do everything, including high accuracy.
-2HP servos are gone. (the Bridgeport gets them). Instead, I'll use 1kw Sanyo Denki motors:

http://www.cnczone.com/forums/showthread.php?t=13909

So in general terms, the Bridgeport mills are for high-precision metal (within 12" x 18"). The router is for wood and foam with a larger cutting area and faster movement.