[Pete Stenabaugh]

Raynorj:

The best advice I have for you is to use Nema 34 motors, not Nema 23. You will be too limited in motor size choices. With Nema 34 (about 3" square or round) you can have motors down in the 500 oz range or up to over 2000 oz and they will all fit the same bolt patterns.

I recommend that you go with motors heavier than 500 oz in. The cost is very little more, and you will have a lot more margin for power drop off. I would recommend at least 600 to 900 range. The prices for the motors can be seen on the www.homeshopcnc.com web page. I also recommend gecko 202 drivers, not the older 201 drivers.

If you have not already checked, talk to Stephen at Logitrol, www.lowcostcncretrofits.com about his stepper controllers and power supplies, he is right in your back yard in Aussie.

You can also go with the Xylotex controllers, these are very good as well (I have one and I am very happy with it, but it is not heavy enough for me), but they are limited to 2.5 amps, unless Jeff has some new stuff, so the Xylotex will not drive the bigger motors. Even the 500 oz in motors will be limited in power as they draw more amperage than the Xylotex can deliver.

If you are going to be cutting thin plastics, you will need fairly high machining speeds, in the range of maybe 60 to 100 ipm, depending of course on the rpm of the router. With aluminum sheet, you can slow the feeds down to maybe 20 ipm, but you will have to experiment. At these feed rates, your little motors may not deliver enough torque. It is a bit of a crap shoot, you may be fine with little motors, but why not be safe, it is better to have too much power.....

Pete

[raynorj]

Thank you guys for all the replies,
Working on the basis of plastics needing of order 100 ins/min with the 5 mm ball screws from homeshopcnc that means I need about 508 rpm. Comment that torque drops "dramatically" above 400 rpms suggests that I may have a problem with NEMA 34 at 425 oz/ins rate. Maybe the actual torque requirement is minimal for the plastics anyway. i would think that would be the case.
What about the next one up the RS34-960 at 960 oz/ins. I guess I need to know what the torque drop off is with it.
At the moment I see the bulk of my cutting being acrylic and styrene sheet 1 thru 4 mm thicknesses, and thin ply like 1.5mm.
I would imagine the 100 ins /min is the max so other machining would all be significantly slower than that.
So if not the 425 oz unit the 960 oz model.
With the gecko 201 or 202. I see suggestions that the 202 is a better deal. the homeshop people offer a deal with the motors for the Gecko 201.
Still somewhat confused but getting there.
I am assuming that one can mix and match torque rated servos with the 3 pack controllers. With the geckos one for each motor that is no prob.
Thanks again all continue the input much appreciated.
Raynor J

[Pete Stenabaugh]

Raynor,

Homeshop will supply you with gecko 202's in place of the 201's if you ask him. The 202's are the new design and have some new built in safety features.

I think the 960 motors would be fine for you. The idea is that they will also start to drop off in torque at the higher speeds, but when they do, they have to loose 1/2 of their torque before they even equal what the smaller motors have for max torque. This is where you get some safety margin for torque loss.

I would recommend getting the stepper controller from Logitrol as I mentioned earlier, it will save you a lot of time. You should ask him though if he can supply gecko 202 drivers for the controller, as he may only use gecko 201 drivers by default. There might be a slight price difference to do that, but it would be worth it. You should also look at his new ver 3.0 controller pendant, it is a cool device, I use one on my milling machine, I wouldnt be without it now.

If you have not already purchased your ball screws, I would recommend that you go with the larger ball screws that homeshop has, they are .631 diameter and will give you more rigidity for the higher speeds. Once again the cost difference is not that bad either. Plan on using 2 ball nuts per axis, so that you can preload one against the other to remove any backlash.....one ball nut is mounted to the moving part of the router, and the second ball nut is preloaded against that one, such that it cannot rotate. You can preload them with a couple of setscrews between them (lightly) to remove backlash. You will get much more accurate machining that way.

Pete