off the wall nooobie design ideas

[project5k]

First I'd like to say howdy to everyone, and thanks for making all this information available.. I have learned so much and haven’t even touched the welder or soldering iron yet...

Oh, and please let me apologize for the monster post... but it's my first, so I have lots of stuff to cover...

Now, in all my reading I remember seeing something said that I should start off smaller and then work up. This just isn’t an option for me as 1) I'm impatient, 2) I just don’t have the resources to do something twice, and 3) I really don’t see that big of a difference in a small machine vs. a large one, everything is just bigger... ok, so at this point I think I have the perfect recipe for disaster... perfect, time to push forward...

So as the title says, I'm a total nooooobie to cnc. I work around cnc machines at work all day, but never have the chance to "crawl inside" to see what makes one tick. I have been doing lots of research, and for what I want (a 4' x 8' usable cutting area) I think I have decided to go with bipolar steppers and drives... I think that this will fall in my budget, and I feel confident that I can make it work for the accuracy I need.

Goals of my cnc machine:
1)Be able to cut and contour in 3d a full 4x8 sheet of mdf/ply for signs, speaker boxes, cabinets, and anything else I can dream up
2)Convert the machine from a router to a plasma table and have the ability to cut at most 1/2" mild plate steel for some prefab kits in designing
3)Have the ability in the future to add a 4th axis for doing all that nifty stuff, chess pieces, baseball bats, table legs, and so on...
4)Do it on the cheap, and I mean on the super cheap, I’m talking maybe $500 to $750 give or take to get the 3 axis running...

What I see that I need
1)A legal full copy of mach 3
2)The parts to build the driver circuits
3)Stepper motors
4)Steel for the table
5)Linear drive components
6)Steel
7)Bearings, linear slides, bolts wire, and a bunch of other little stuff….

What I don’t have and wish I did
1)Milling machine for making the parts to get my cnc going
2)More money

What I have at this point:
1)A large shop (2400sq-ft) to build, test, and run the machine
2)Computers, that will run mach 3 with no problems
3)Electronics background in design, and prototyping
4)Mig welders
5)A plasma cutter than can more than handle the 1/2" plate
6)A steel yard about 4 miles away from my shop
7)The ability (knowledge) in structural design to build pretty much anything that I can dream up given enough time
8)2 metal working lathes, one a mini 7x12 with 3 jaw chuck, an the other a 100 year old 10x24 lathe with 3 jaw chuck and independent 4 jaw
9)The demo version of mach 3
10)Rhino version 2
11)Some crazy ideas
12)Someone that just might pay for the mach3 for me
13)A boss (at my regular job) that is into this and wants to help (and is cool too!!) yea I know that’s a first
14)Someone that can mechanically or photo etch the driver boards for me for nothing more than the cost of materials
15)A design for the driver boards and sources for the parts that I don’t already have in house (I’m planning to use the l297/l298 design)
16)A 3/4 hp router and some bits
17)Lots of empty spaces in my breaker box, and the knowledge and ability to add more circuits as needed, and a “proper” amount of fear!
18)An austron 35amp 13.8v supply in a 24 space cabinet on wheels with 2 17Ah gell cell batteris for backup and momentary current draws over the 35amps..(im planning to put the drivers, computer and any other electronics in this cabinet as well)

My plan
1)Learn a bunch more
2)Finalize the design I want to use
3)Get the motors that I’m going to use
4)Build the driver circuits
5)Test the drivers and motors on the desk with mach3
6)Begin building the table
7)Assemble
8)Troubleshoot, troubleshoot, repair, redesign, build, troubleshoot, repair
9)Use the machine and giggle like a schoolgirl when it finally works
10)Upgrade the stereo in the shop so that it’s loud enough to be heard over the router. (and really annoy the neighbors at 3am) TURNABOUT IS FAIR PLAY!!!

My current design and thoughts:
Build the table pretty much like the one that I saw on http://www.inshorepowerboats.com/cnc.../CNCROUTER.htm
With a few changes… I like the y and z-axis setups, so I will probably replicate this. But the x-axis is using rack and pinions and that’s a little outside my budget, so here’s my thought. I have some and can easily get more #40 drive chain. My thought was to either lay the chain along the top rail of the table frame and have the gears ride in that (still need to investigate this and how much slop there would be) and use that like a rack and pinion. The other idea I had was to suspend the chain along the insides of the rails, and have the x-axis drive gears interface the chain there. The chain would be pulled taught and would make an upside down “U” where the drive gear would be at the top, and then 2 idlers would make the other bends, this way the chain is around 180deg of the pinion gear. Either system would be replicated on both sides with a connecting shaft between, so there would be no chance of the gantry racking diagonally… then use one of the 500oz*in motors I found on the net geared 10:1… figuring 300rpm max (I have no idea what this should be, I just picked a # outta the air) on the motor and a 1” diameter gear for the pinion, my math says that I should get a max speed of about 90ipm. So, if ya’ll will, please rip this design to shreds and show me what I’m missing…

Project5k

[project5k]

oh, while im thinking about it, i was considering using something like 2"x2"x1/4" angle top and bottom on the x axis for the long slides.. i could turn some v groove wheels on the lathe... my worrie is how much variance will there be in the angle iron that will cause the slides to not be absolutely true straight and flat, and how much will i cause when i weld it all down...

[ger21]

Well,, at least you know you have a recipe for disaster. Most people building an 18"x24" machine will spend $750. Building a 4x8 machine for that is totally unrealistic, unless you get virtually everything for free.

It's likely that chain drive will have far too much slop. You'll quickly find out that 90ipm is painfully slow for a 4x8 machine. A 3/4HP router is really too small. If you plan on running your stepers on 13V, you won't get anywhere near 90ipm. While a lot of people want to use their machines for both routers and plasma, I'm not sure if I've really seen anyone that does. They have different requirements.

Good Luck. (you're going to need it)

[project5k]

Ok fair enough. This is exactly why I'm on here, to pull from the vast experience that every one has. If you noticed, the #1 item in my plan is to learn a bunch more before going any further...
One thing that I had considered, but was leaving as a fall back plan was to build the table 48x48 with support wings to either end, so that I could index my stock, cut half, move it, and then continue. This is of course not my preferred method, but I think with enough careful planning, I might be able to make it work good enough for what I’m going to use it for...maby not.. anyone got experience doing it this way?

Regardless of what the final table size, my main interest at this point is to see if some of the principals of my design are flawed, and I’m seeing that they are. If the chain has too much slack in it, then I will have to figure another method... that’s fine, that’s what I’m trying to do, is to learn.

Ok, so let’s go through this, one step at a time....
Chain, bad idea....

How about the angle iron "tracks" and v groove wheels for the x-axis? I can see the potential for there to be some slack in this as well, but I was wondering if anyone had ever done this, considered it, and so on…

12v isn’t enough... ok, here’s my thinking on this... I figure to have any kind of margin, I need at least a 30amp supply... (I like to design my electronics with at least 25% extra capacity) so what should I be shooting for minimally? 24? 48? I’ve seen lots of different #'s on this...

90ipm did seem a bit slow, but I was using this figure more to see if people agreed with my math, and how I got to that #... having it take over a min to travel the length of a 4x8 sheet would be aggravating, but would work, yes?
What kind of ipm should I be shooting for? In my example I have the motor geared 10:1. Figuring that I’m guessing my gantry will be around 50# and working the math backwards, I would need 1600oz*in on the x-axis shaft with a 1" pinion. 1600/10=160. Now, this should accelerate the gantry at 1g. Not accounting for frictional losses and so forth. So lets call it 200 to make the math easier. If I use one of the 500oz*in motors, that would mean that I could cut my 10:1 gearing down to 5:1. This would make the motor minimum 320oz*in plus friction. And would make my feed rate 180ipm...now I understand that the faster you run a stepper, the less torque that it can produce at high speeds. Increasing the feed V will help with this some, but not totally overcome the torque curve...

My question is this. Since I don’t have that much experience with this, what would be a decent ball park RPM# to plan for on a nema 23 motor at say 24V or 48V? This is one thing that I haven’t found enough information on... My original guess was something like 300RPM. Is this too fast? On a 200 step/rev motor this would be 1000 steps per second. My electronics should be able to handle this. But will the motor do this with any torque?

If I figure 150RPM motor speed, the 5:1 gearing, 1” pinion then I’m back to roughly 90ipm rapids… I could go to a larger motor and less gearing, but I’m trying to get a baseline so start from…. If you all agree with the math and how I’m getting my #’s then I can make adjustments to the design once I get some kind of ballpark figures… While speed is an important factor, its not nearly as important to me as it might be to some…

One thing that I think I understand is that a lead screw would take less torque to move the same load than the rack and pinion, but will require a higher drive speed… a 50# gantry accelerated at 1g on a 5tpi screw would require approx 25oz*in not allowing for losses. But to get 90 ipm I would have to turn the screw(or nut) at 450rpm…. Ok this seems a little fast to me… but at 25oz*in, couldn’t I get away with say 1:2 gearing on the 500oz motor…that would then put the motor speed at 225rpm and the input torque at 50oz*in…but would also reduce my move per step accuracy from .001” to .002”

As for the cost, the $750 is a target, but is not the absolute final #. The software will most likely be paid for, and the steel is one thing that I have quite a bit of.. and can get more at a somewhat decent price. 2x2 box tubing comes in 24’ sticks and is $28 for 16ga and $47 for 11ga. I figure I’ll need something like 6 sticks to make the table frame, and then I can use something else for the actual bed… so lets just call that $300, the motors im figuring will cost something like $200, so that’s $500, the drivers are going to cost me $20 each to build (I have most of the parts already) so that’s $60, so $560 total, so that leaves 190 for everything else…so $750 does come up short… and that’s fine, it was just a ballpark # to aim for… Even if I end up putting $2k into it to get it going.. that’s ok, it will just take more weeks to do it…I’m really aiming for a up and running date of the first of next year.. so I have a little time to get my plan together, save up some $$$ and build it…

[ger21]

I have seen a router driven by chain, and the builder claimed it worked well for him. But it's the only one I've seen. (It's not on this site, I don't think)

Shopbot's use V-Rollers on angle iron, or at least the older ones did. www.shopbottools.com

Also, see this: Linear bearing compromise

Motor supply voltage. At least 10 times the motors rated voltage, up to maybe 20 times. More voltage = more speed, up to a point. To much voltage = too much heat.

What speed (ipm) shold you shoot for? As much as possible. The router motor you use as a spindle will probably be the limiting factor in how fast you can cut, and 90ipm might be adequate, but I'd try to shoot for rapid postioning moves of 200ipm or more, the faster the better.


Your gantry will probably end up weighing close to 150lbs., if not a lot more. Mine is a wood torsion box with about 32" of travel (40" overall length) and with the Z-axis, probably weighs about 70lbs.

How fast can you spin a Nema 23motor? Depends on the torque curve for that particular motor, drives, and supplied voltage. Maybe 200rpm, maybe 1000 or more. Can vary greatly. You need to consider the entire drivetrain package, and optimise everything to work together.

$2K is a lot more than $500 to $750. To build a decent 4x8 router (not good, just decent), figure $2K minimum. Jmo

[project5k]

Thanks for the information... i'm still doing more research.. and i started drawing this whole thing in rhino, so i'll try and post some renderings of it for yall to take a look at...
also while im thinking about it.. i found this site that has some guide rails for sale, and wanted to see what ya'll thought....
http://www.cadcamcadcam.com/index.as...ROD&ProdID=133

i dont know why, but 1/4" wide seems a bit narrow to me, but what do i know....

[ger21]

That #2 track will work fine. Keep in mind you'll need 2 tracks per side, at about $100 per track. $400 + 8 wheels = $500 for just the X axis.

If you think you'll need bigger, go to www.bwc.com

[project5k]

ok, so here are a couple of the renderings that i have done in rhino so you can more easily see what im planning, the cavities in the v groove wheels is where the bearings will go, right now the plan is that the outter flange of the wheels is 3" diameter(its what stock i have) and the bearings will be 2"OD... all of the frame is 2x2 box tubing, and the y axis slider is 1x2.. i still have to work up all the propultion stuff, but im still thinking that i might just try and go a different route with the chain drive, im starting to think that maby crossing the chains is the way to go... this would put the x axis drive motor on the gantry, which may be a weight issue, but its just a thought.. at least doing it that way would eliminate any chance of it racking...

ok, question, 2 tracks per side? im guessing thats so you have rollers on top and on bottom.. well thats a thought, but i was thinking more like 1 track per side, and then just have a flat "follower" wheel under the rail... maby on a spring loaded arm with some really stiff springs, and some form of adjustable mechanical limiting...
i'll draw up what im thinking later on....

ok, so this is the first time im going to try and attach images... so i put the web address where they are, and also i inserted the images... forgive me if it dosent work correctly.. and there are larger images on the website as well...

http://www.jpcustomcrafts.com/shopmachines.htm

[project5k]

oops... wrong button

[spalm]

Hey,

I somewhat successfully used those V-bearings on angle iron, so did Benny (Ynneb). It is on my third machine, first being a JGRO, second was a torsion box – skate bearing machine. It works quite well and is a magnitude cheaper than using the proper rails. My machine is a 24” X 48” and mostly wood. If you can figure out how to support the angle iron for the length you have in mind, you might want to give it a thought. You can see my build at:
Vbearings and Ply

You can see Benny’s larger metal machine at:
Built on a foundation of past mistakes.

My recommendations: start a bit smaller until you get the hang of this. Large machines are a PITA to build and costs get large very quickly. You can always build a second machine and re-use many of the components. Chain drive seems scary to me (too loose).

Steve

[project5k]

yea i hear ya, actually after pricing some of the parts that im looking at using, i'm really thinking about cutting this thing in half.. it would be cheaper, take up less room in the shop, and would let me see if i'm really gonna use it as much as i think that i am.. im thinking about actually building it to work a 4x4 or half sheet... my buddy/boss, has a tiny unit that we've been trying to get to work, but theres no communication from his parallel port, so im gonna take the machine that im planning to use over to his place and see what happens....

one of the things that i first noticed about your machine is that you used the angle on its edge.. thats not something that had thought about... i had been planning to put it down open side against the 2x2 frame and spot welding it into place, the one thing that really scares me about that is that theres not adjustability and the other thing is that im afraid that the welding might cause the angle to pull and not be straight... bolting it down like you guys did would allow some adjustability, and i really like that....

the v grove bearings just dont appeal to me... im going to machine my own wheels and then use standard issue bearings, that way i can change out any one part of any one truck if it wears or gets damaged... plus its an excuse to be out in the shop and on my lathe... which in and of itself is a great joy for me...

[project5k]

ok, so it might be a mistake, but i did it anyway, i ordered my electronics for to build the drivers, l297's and l298's and some diodes... and then just now i ordered my motors.. i got 3 nema 23 500oz-in 4 wire bipolars for $175... so how'd i do??

the way i figure it, ill spend the weekend building the driver boards, then early next week the motors will get here from california and i can test both them and the drivers... pluss then i can see what the no load speed of the motors is, and that will give me some kind of an idea as to what i need as for the rest of the drive train...

I did have this thought... what if i mount one of the motors onto something solid, and then mount a large set of fan blades.. i know theres not really a way to measure the amount of load, but it would allow me to see how much the rpm's fall off and or if it starts cogging, and give me some idea as to what kind of ramp up to play with.... Ideas? suggestions??