jon's homemade cnc

[jonbabbz]

Not criticism but slight concerns.? @72V on what I think are 75V drives then your very close to Max with not much room for back EMF. Hopefully you'll be ok but if the drives start tripping then chances are that will be the prob.! . . . I wouldn't be running silly high velocity's just to be on the safe side.

The drives are 982's, 80v max so should be ok.

The difference between 2Nm or 3Nm weight wise won't make a jot of difference with these drives/voltages running on ball-screws because the mechanical torque ball-screws produce is awesome and really both are more than enough if all your attaching is a router or WC spindle etc. Also with a Z axis you tend not to run high velocity but more acceleration so the available torque is higher has your not so close to the motors corner speed.
Personally I'd use 3Nm for continuity with rest of machine.

Thanks for that, guess ill just use the 3nm ones then.

Looking good and soon be cutting.?

Was hoping within the next couple of weeks, but I damaged (or may have been defective) a linear bearing while assembling it(a couple balls dropped out), so im now waiting for some bearings to arrive.

Tip: cover them sides before you start cutting else all the crap gets onto ballscrews and shoots every where in all directions. Amazing how much sides really help contain the mess.

Thanks, never even thought of that!!

Edit:
Just spotted that the top box section with rails on is only supported at it's ends. I think you'll find you could suffer from resonance problems at certain depths or feeds esp in harder materials. I Know it certainly will show an effect on finish quality in Aluminium.
Know you've painted it now but I would seriously consider adding some support in the middle, it will pay back in quality of cut believe me.

It will be a real pain in the ass to add these now, so I think ill see what its like before I commit to stripping it completely down. Do you think a strut bolted to the underside of the top box section and bolted to the side of the bed would be adequate for this? i could do that while its still up and still have a few bits of box left over from when I cut up the last bed.

Edit 2: Eh eh sorry about the add-on's.!! Just spotted that you have the bridge rectifier on a bracket. Really It wants to be on a heat sink, stick it on an old PC CPU heat sink and then fasten that to bracket.

Dont worry mate, happy for the info. This one was recommended by Jonathan in another thread. Apparently it doesn't require one, (MB256)? I wasn't so sure - especially with the high amount of current that will be running through it. I suppose its better to be safe than sorry. Ill get one added. Cheeeeeeers

[Jonathan]

Dont worry mate, happy for the info. This one was recommended by Jonathan in another thread. Apparently it doesn't require one, (MB256)? I wasn't so sure - especially with the high amount of current that will be running through it. I suppose its better to be safe than sorry. Ill get one added. Cheeeeeeers

I use the same one and it gets warm, but not hot or anywhere near it's temperature rating so I've not put a heatsink on mine. The peak current running through it is quite high, but here it's the mean current that matters (as that determines the power dissipation) and that is much lower. However if you've got a suitable heatsink lying around then you might as well use it.

Here I'm running one stepper driver with a 3Nm motor at 4.09A from my lab PSU for testing, note the current:

[JAZZCNC]

Was hoping within the next couple of weeks, but I damaged (or may have been defective) a linear bearing while assembling it(a couple balls dropped out), so im now waiting for some bearings to arrive.

Ye it's a bitch when your balls drop out and before ye know it you have an ASBO. .

Regards the frame then it's not a big job to do really. Just take 2 diagonal lengths off each leg with brackets at each end that bolt into leg and top rail. . . Simplizz really.
Doing it like this will also allow some adjustment for centre if when testing you find the top rail is slightly bowed.?

[Jonathan]

Just take 2 diagonal lengths off each leg with brackets at each end that bolt into leg and top rail. . . Simplizz really

I agree ... it's well worth it.

[JAZZCNC]

I agree ... it's well worth it.

Yep I agree with that has well.!!! . . . Steel box is nice and cheap but if it hits the right resonance it can sing like that annoying twat off Go compare Advert. So anything you can do to help minimise this will show in the finish.