A update on my DIY CNC project.
I consider using HTD5M pulleys and belt between the stepper motors and ballscrews and start with 1:2
(Have not designed new motor mount yet)
Using this i get:
- Less mechanical noise
- better hide the stepper motors
- Simple to alter reduction ratio if I need to.
https://www.facebook.com/mundsen/videos/10209642049868575/ (video showing my Z-axis - not finished yet)
What sounds do you think motor couplers make? Why would you want to hide your stepper motors? Stepper motors certainly don’t need a reduction.
Before you get too involved with elaborate designs I think you need to run something first. Then you’ll have a better understanding of the niggling little details that no one can tell you about. There’s no rule that says your first CNC build has to be your last. For most folks it usually isn’t too. For me the third time was a charm.
But I’ll build another machine someday.
I know my first do not have to be my last, but I try to use the advices I get to make my first ok.
One of the largest problems when building the first CNC or any other builds is all the different advices you get and then trying to figure out what to do or not to do…
The prevailing western philosophy is that it is better to do something wrong now, than waiting until things are perfect. Because we learn from our mistakes. You’ll never learn how to swim if you don’t jump in the water.
Skip all the advise. No one has built the CNC machine that you want yet. Or if they have, then get plans from them. Otherwise, just start putting stuff together.
I will give you this advise. Get all of your electronics, and get all of that working on a bench first. Because if you can’t get that working, then building the rest of the machine is pretty pointless. It really isn’t that hard. But it is something you should be somewhat familiar with ahead of time.
Some that skip that step regret it later on. It has to do with too many variables to deal with at once.
And actually building your electrical cabinet can be one of the more involved aspects of the whole project. It is also something you seem to have not addressed yet too.
But initially just having everything strewn on a bench is perfectly acceptable. You pretty much need to see everything in order to figure out how to house it all.
I use belts like that on my cnc, and it works well, my ratio is 1 to 3, but I am hitting a speed limit on my machines io’s, they can only pulse at 100khz, and that’s not a very fast jogging speed, with my micro stepping and pulley ratio combination. So maybe you should do the math before you decide to go with pulleys. I know I wish I had.
one of these will increase your I/O http://www.mesanet.com/fpgacardinfo.html
I think they go 50MHz at the low end.
@Paul_Frederick at 50 mhz im sure ill have other issues to deal with also im very happy with my current 24volt for my limit switches etc. from the looks of it i would have to run everything at 5volt with one of these cards.
50MHz is the maximum frequency they can output. They can of course run slower. There are ways of changing 24V to 5V. Or your switches would likely work fine at 5V too.
Mesa boards are what people that need more speed use. Like folks that run closed loop servos. I know they’re popular with that crowd.
I do not understand why I should ignore the advice about using a belt coupling like this compared to a alu coupling.
If using a belt like this I can use reduction if I want/need or use 1:1.
A more flexible setup, and I like the way I can mount the stepper motors better.
you’re not going to want to use a reduction. Stepper motors can go really slow. Heck they can even stand still. Pull out torque can be an issue with them sometimes, but control software has ramping built into it. So that takes care of that.
This is why I said you need to build something. Just so you know all of these gory little details.
My advise to you is bench run stepper motors. Then you’ll get somewhat familiar with the control software, and the motors themselves.
Seeing is understanding. Sometimes. With something like CNC you might have to see things a lot before it all begins to sink in.
Maybe even purposely get some undersized cheap junk to practice with. Because a lot of newbies end up cooking stuff. You can tell guys don’t disconnect the motors while the drive is on til you’re blue in the face. But until they actually blow up a couple drives no one ever listens.
BTW never disconnect the motor from the drive while the drive is on. You’ll blow the drive up. Now when you fry a drive don’t say no one ever told you.
Today you can get hardware so cheap it can be considered disposable. I’m running $10 drives on my machine. Those you can afford to blow up. Blow Geckos up and that might hurt a little more?
Soon ready to mount the base frame and the Y-rails (have to find a flat surface).
Have still not decided what stepper motors to use - Should I use 420 Oz low inductance motors (Nema23)? or lower Oz?
I guess the total CNC weight is going to be 70-100Kg so it`s not a small light weight desktop CNC.
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better to have too much power, than too little. 420 oz/in, or so, should be fine for you. That machine would likely run just fine on about 250 oz/in though I imagine.
Here’s a calculator http://www.orientalmotor.com/support/ballLeadScrew.html
Anyone having recommendations ? 300-420Oz
I have found that I should try to find a stepper with low inductance (1.8-2.5 mH) because motors with low inductance have better Oz value when the speed increase…
If using a motor with high impedance the motor have low torque when the speed increase…
Yeah what pitch screws are you using? I have 425 oz steppers and 10mm pitch screws. The problem I’m having is the high inductance of the 425 oz steppers hurts the torque as speed increases. I can only run about 3000mm/min. If any thing I’d run the ratio the other way around, steppers have heaps more torque at low speed. Look at what feeds you will need then pick your screw pitch, look at the torque curve at the speed you will need.
@Paul_Shaw I plan to use 1605 ballscrews
what are those?
@Paul_Frederick ball screw with diameter=16mm and pitch =5
So you have halfed your speed again there. You’ll be getting the drop in torque again. It was the one thing that I picked up from the forums was to use 10mm pitch. If you haven’t got them yet I’d recommend 10mm. But it does depend on what feeds you hope to get and the motors torque curve and even the voltage you run the drives at.
@Paul_Shaw what voltage do you run your motor drives at? I ask because at high step rates current drops. But if your voltage is high then that current drop does not affect power as much. Because power is volts times amps. Although lower inductance motors do exhibit less inductive reluctance than high induction motors do.
Usually you want a high current, low voltage rated motor for CNC. They suffer the least at high speed. Well, when they suffer is further up. All stepper motors suffer eventually.
Do you have a link to the 420 oz motors with the low inductance?