Amae Design - 'AKITA' CNC Mill

[damae]

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]

A few threads of interest that I started, discussing components of my mill:

My big servo motors:
BIG servos! (is there such a thing as too much power? =)

Where to get cheap mil-spec connectors?
Where can a guy find cheap mil-spec connectors?

How to get a breakout board to supply 25ma (instead of the usual 5ma):
Need a breakout board that can supply 25ma

[damae]

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:

Why is a heavy iron base vital for a good machine?

[damae]

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]

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]

Originally Posted by mxtras 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]

For posterity, here is the original frame design, when I planned to use the 80/20 framing.

[damae]

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]

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]

Originally Posted by damae 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.

[damae]

Originally Posted by DieGuy 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.

Originally Posted by DieGuy 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.

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]

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.