Was about to get a toy- then I did some research...

[NeoMorph]

I’ve got half a dozen or so helping hands that I use. Some are missing arms, some have been modded with mounts for plugs to be held without distortion. I usually make them out of wood as it doesn’t transfer the heat into the plastic that way.

Same goes for PCB holders. I used to lust after a decent pana-vice but they are crazy expensive for what they are. If you are any good at putting together a CNC then you could make a better one.

[Juranovich]

Hi again, I've been somewhat occupied with work lately, hence, the radio silence. I've got offers on nearly all main components and the intended design seems to be within budget. One loose end is the aluminium plates which I'll have to have made for me and to that end I wanted to ask a practical question (as I have very limited experience working with metals); what tolerances do you use on screw holes? More specifically, I'll probably end up using a combination of M5, M6 and M12 screws and 20mm aluminium plates.

[Doddy]

I think you probably mean clearance hole size rather than tolerance? Google "metric clearance hole chart"

Edit: Or if I've misunderstood then ignore the above.

[Juranovich]

I think you probably mean clearance hole size rather than tolerance? Google "metric clearance hole chart"

Edit: Or if I've misunderstood then ignore the above.

Precisely, tolerance, not clearance. And just for the record (and before anyone posts a lmgtfy-link :) ), I did try to google it before asking on here but using highly scientific terms like "screw hole sizes" did not yield me any useful info. Anyway cheers, I got exactly what I needed!

[NeoMorph]

I think Juranovich meant tolerance of holes being in the right location.

I’ve seen makers use the rails with hole transfer punches to make sure the holes are in the right place. Put the rail on the plate, loosely clamp down one end and then measure and tap to the right distance from the edge. Do the other end the same and then go back and forth until both end are perfectly aligned before clamping down hard... then one final measure to make sure the rail hasn’t moved.

Then if that is all correct, just go down the holes with the correct size hole punch and tap in the locations for the holes. Follow up with a drill press or a mag drill (you can even rent them according to my friend) and Bobbie’s your auntie.

This way, you won’t measure the hole spacing wrong and drop a hole out of position that would knock out the following holes too. Simples, as a certain Meercat would say.

[Juranovich]

I think Juranovich meant tolerance of holes being in the right location.

I actually meant tolerance as Doddy pointed out, but what you describe is also something I'd probably had come back to ask at some point :)

[Juranovich]

As I'm trying to get the whole picture I've had to dip into the electronic side of things. Now I've got offers for steppers, drives and torodial transformers, but I'm a bit unsure on how to size them properly, or specifically how to size the PSU. The specs are as follows:

- NEMA 24 closed loop steppers at 4.5Nm holding torque, 5A, 0.75ohms, 2.4mH (all phase values).
- Drives rated at 20-70VAC or 30-100VDC, 8A peak.
- 420W torodial transformer 220 to 70 VAC, 6 A

Firstly, as the drives can take AC, is there any need to convert the output current from the torodial transformer to DC? As I've understood in case I go for AC to AC I could simply connect the first winding to the mains (with fuse for safety) and the second directly to the drives? Also, assuming no DC conversion, is it safe to use a 70VAC rated torodial transformer to power the drives rated at max 70VAC?

Now, if I've understood correctly the total amps my 4 steppers will draw is roughly 2/3 of the sum of the rated amps of the steppers, i.e. 4*5A*2/3=13,33A. So the PSU would have to supply (rounded up) at least 14A? As the torodial transformer is rated at only 6A, should I consider wiring several in parallel to get more amps or would it be better to simply look for a beefier one to supply all the current i need?

And so the voltage. This has me the most confused, some recommend to not over do the voltage for fear of getting components burnt, while others prefer higher voltages in order to not lose out on max performance (however, in these cases drives usually have some sort of voltage regulators). Now, if I've done the math correctly the Vmax of my parallel wired steppers is 32*√(2.4mH) = 49.6V., so well within the 70VAC outputted by the torodial transformer so as to get the most out of the steppers, BUT (and see first question above) would I run the risk of overheating my drives/steppers with this setup? The drives I've been offered (Lichuan LCDA86H) do list "overvoltage protection", but this sounds to me more like a fuse type protection than active voltage regulation.

[AndyUK]

Firstly, as the drives can take AC, is there any need to convert the output current from the torodial transformer to DC? As I've understood in case I go for AC to AC I could simply connect the first winding to the mains (with fuse for safety) and the second directly to the drives? Also, assuming no DC conversion, is it safe to use a 70VAC rated torodial transformer to power the drives rated at max 70VAC?

If the drives take AC, don't bother rectifying it into DC. Go straight from the transformer to the drives. Don't daisy chain them though. Size the transformer by taking the max motor current (e.g. 4A) times the number of motors (3 or 4), so lets say 12A, then reducing by 1/3rd, so 8A. Don't go too overboard on the VA of the transformer, get what you need. Bigger transformers can suffer from large amounts of inrush current which can trip the power and just be a pain without other compensation.

Now, if I've understood correctly the total amps my 4 steppers will draw is roughly 2/3 of the sum of the rated amps of the steppers, i.e. 4*5A*2/3=13,33A. So the PSU would have to supply (rounded up) at least 14A? As the torodial transformer is rated at only 6A, should I consider wiring several in parallel to get more amps or would it be better to simply look for a beefier one to supply all the current i need?

Well clearly I should have read ahead because you already know the method. Oh well, not editing it now. No just get a larger VA transformer. You probably need 1000VA based on your 13.3A current, but that seems a little high? Most of us have 500-600VA transformers when turning into DC, perhaps someone can shed more light on this.

And so the voltage. This has me the most confused, some recommend to not over do the voltage for fear of getting components burnt, while others prefer higher voltages in order to not lose out on max performance (however, in these cases drives usually have some sort of voltage regulators). Now, if I've done the math correctly the Vmax of my parallel wired steppers is 32*√(2.4mH) = 49.6V., so well within the 70VAC outputted by the torodial transformer so as to get the most out of the steppers, BUT (and see first question above) would I run the risk of overheating my drives/steppers with this setup? The drives I've been offered (Lichuan LCDA86H) do list "overvoltage protection", but this sounds to me more like a fuse type protection than active voltage regulation.

I think most people tend to ignore Vmax and just give them as much as the drivers can manage, then limit the current on the drives so they don't burn. Typically with 3.2mH motors with a Vmax around 58V people use 68V (convenient toroidals are available). Basically I think you want the motors to be warm but not burny hot (demagnetisation occurs when they hit a certain temp).

The overvoltage protection you talk about is interesting though - what do the drives spec for the voltage?

[NeoMorph]

What AndyUK said about larger transformers tending to pop breakers and blow fuses due to high inrush current is right. The less is said about the time I was working on a DIY boost converter for my electronics course, and blew out the power to an entire wing of the YMCA I was living in, the better. That was back in mid 86 so they might have forgiven me now lol.

That was down to high inrush current as well.

But the good news is inrush current can be reduced pretty easily. See here...

http://www.ti.com/lit/an/slva670a/slva670a.pdf

[Juranovich]

Well clearly I should have read ahead because you already know the method. Oh well, not editing it now. No just get a larger VA transformer. You probably need 1000VA based on your 13.3A current, but that seems a little high? Most of us have 500-600VA transformers when turning into DC, perhaps someone can shed more light on this.

Yes! Pretty please! The problem seems to be (assuming 1000VA is an issue- as I'm quite unqualified to judge) that 4-4.5nm steppers seem to be rated at 4-5A and with 4pcs that quickly adds up.

I think most people tend to ignore Vmax and just give them as much as the drivers can manage, then limit the current on the drives so they don't burn. Typically with 3.2mH motors with a Vmax around 58V people use 68V (convenient toroidals are available). Basically I think you want the motors to be warm but not burny hot (demagnetisation occurs when they hit a certain temp).

The overvoltage protection you talk about is interesting though - what do the drives spec for the voltage?

For the record it also lists overcurrent protection. If you're after the input rating it's 20-70VAC and 30-100VDC. Is that what you were looking for?

When your're saying to max the voltage, shouldn't there be some room for the transformer to fluctuate (upwards) from the rated voltage? In this case the transformer outputs 70V which is also the max of the drives. Also regarding overheating, is it the wattage/VA that is the decisive factor or can voltage alone cause over heating? I'm thinking if higher than rated voltage is passed through a circuit but at lower than rated current (i.e. less than rated watts are being fed), shouldn't there then be "unused" resistance in the circuit to avoid overheating? If so, is higher than rated voltage more a question of the structural integrity of the circuit? Or does it maybe manifest in the same way in the end, i.e. burning components...? In the current case the transformer outputs 70V at 6A = 420VA and the drivers can take 70V at 8Apeak = 560VA. Even if I had 4 transformers in parallel and 4 drives in parallel, respectively, the total wattage would still not exceed that of the drives' capabilities. So getting back to what you said about maxing voltage and limiting current, as the drives can take more current than the transformer outputs, I should be on the safe side?

sorry, for the ramblings, my thinking hat came on while writing this...also b/c curious!