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Stepper motor

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Or look on CNCZone for ballscrews in their "For Sale" section.
I have similar misgivings about the chain drive. I'm sure it'll basically work, but the overall performance downsides I've heard described sound accurate.

Also I've seen some decent linear belt drives on eBay before that I almost got- and honestly should have gotten.

I've only got my CNC mill with a leadscrew personally. Ballscrews are much less backlash, and lower friction. But more important is that ballscrews are pitched with fewer turns/in. For a big router table, it means the screw doesn't have to turn at such high speeds to move the head around fast, thus the upper limit of what speeds are practical to run is much higher.

But note that for either leadscrew or ballscrew, that rod cross-connecting both sides to 1 motor wouldn't work. You'd need a pair of right-angle gearboxes which would increase backlash, friction, and cost, which is why a lot of tables use two motors stepped together. They cannot share a single driver, though. So you'd need a 4-axis drive for a simple XYZ router table.
 
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ACME threaded rod is readily available in about 8 turns/inch (3mm) and these days the machinery that makes ACME rod and most threaded rods is pretty precise. Even the developing countries that make cheap rod all have pretty good machinery now, it's not like the old days when Chinese threaded rod was hand carved by a gang of 10 year old kids with files. ;)

Anyway if you really wanted to tread the line between cheap and ok performance that would be my pick.

Personally I decided to spend a little more and bought 2 lengths of NSK ballscrew rod (8mm pitch) from the local bearing store. I think I paid about $90 USD for each length including shipping from Japan, and the lengths were 800mm if I remember right. I wanted the 8mm pitch so when using 800 step/rev steppers it would get exactly 100 steps to a mm.
 
Well I think I will go with the ballscrews but I will have to save up a little first, fixed income kind of limits me, but I did put a bid on ebay for one and I’ll keep looking.

But for now I think I have to go with the chain for now I picked up a 100 ft. of it for $10.00 - surplus “new – never used” still in the oily bag. I will upgrade to the ballscrews as soon as I able to.

Do you think by going to a bigger drive sprocket will decrease the cogging?

Oznog, if you can’t share the same driver for 2 steppers what about sharing part of the driver for the other stepper.

Would something like this work?

115-2step.jpg


Thanks shortbus= for the links.
 
Oznog, if you can’t share the same driver for 2 steppers what about sharing part of the driver for the other stepper.

Would something like this work?
Not really, because you generally can't separate the "logic" from the driver. For one, the logic does a current limit trigger and that's on a per-motor basis.
 
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But for now I think I have to go with the chain for now I picked up a 100 ft. of it for $10.00 - surplus “new – never used” still in the oily bag. I will upgrade to the ballscrews as soon as I able to.

Do you think by going to a bigger drive sprocket will decrease the cogging?
...

Well for one, if you are going with chains you no longer need 2 stepper motors for the gantry, the chain shaft will join one motor to 2 chains.

The cogging is a factor of the chain pitch, lets say you have 0.500" chain pitch you will get a cogging event every 0.500" of linear travel.

Bigger drive sprockets are bad. I have a couple of toothed belt driven slides here, they work pretty good but they miss steps if there is any large load on them or bad tool chatter. And their pulleys are only about 16mm diameter. If you have a cog of say 50 mm diameter it will be 3 times weaker.

If you steppers are 100 oz-inch and the cog is 2" diameter (1" radius) it will make at best 100 ounces of thrust. That's pretty poor, which is why chain drives normally use a motor/gearbox.

If that same 100 oz-in motor was on a 8 TPI ACME thread, it makes about 5000 ounces of thrust, and it is much better damped and less likely to break step from tool chatter.
 
I see I need to do some research now.

I want to thank you guys so much for all of the information and your time you provided for me, like I stated before I’m just a newbie and now with all this new information I’m dangerous lol…
I’m going to start putting the hardware together this week; I should have about 90% of the material some of it’s in storage at my son’s house I hope to get over there this week.
I think I’ll try to make drive section so it can easily be upgraded just in case I stumble into some extra money to get the ballscrews, meanwhile I have a lot to do before I’m ready for the drive section.

I’m really looking forward to building this.
 
If you think you might eventually go for ballscrews then it's probably a good idea to do the first build with cheap threaded rod, you can get that from the hardware store or steel supplier.

That will let you get the machine up and running, and sure it will be slow but most things you will cut will need to be slow anyway, and you can still test the rest of the system and find out what needs stiffening and adjusting etc. Then as your budget allows it's very easy to remove the threaded rods and nuts, and replace with ballscrews and ballnuts or leadscrews and polymer nuts etc.

Good luck with the build and if you don't mind please give us an update as it progresses. :)
 
I was thinking of taking some pictures at different stages of the build and maybe add some notes to it; I will be around I like the forums here, and I’ll most likely be popping in to pick your brain with problems I run into as I go along.
 
I’m having some medical issues so I’m working on possible improvements on my design and doing a little research until I able start the build
but anyway I’ve been fascinated with servo motor and how they work, ever since Oznog mentioned it, not that I’m going to use them in my design.
I’m a little confused; I know how the basic stepper motor controller receives commands from the computer “step/dir”
now what commands do a servo motor controller receive?
Does it get the physical location and does the controller send signals back like “ busy/ready/error”
is there anywhere I could find the information about on it.
 
IIRC, I think it depends. Some "smart" servo controllers take step/dir inputs and calculate how to satisfy the commanded position with the drive and encoder feedback. But Mach3 PC software has the ability to take encoder feedback and can "learn" how to control a servo based on on/off pulses to a dumb controller. It's certainly more complicated than a stepper- there's lag in getting the drive up to speed or stopping, and the pulses out have to be quantitized into the clock width used. It's not enough to simply leave the drive on until it reaches the desired location because it'll overshoot. And also it's not good enough to just run a basic, generic "slowdown" profile because as it moves in X and Y, it needs to have a very predictable location at all times. Otherwise you might command a move from 0,0 to x,y=1,10 and it wouldn't be a totally straight line if the y direction took longer to speed up and slow down.
 
Thanks for that info Oznog it's not as simple as I imagined.
I think I'll leave servo motors alone for awhile, it’s a little beyond me at this point at this time…
I have enough to do as it is…lol
 
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