Hi al.
Im trying to retro fit a bridgeport sized vertical miller
My leadscrews will be 5mm pitch ball screws
I am not looking for very high speeds, just home shop use and reliable / acurate

What sized stepper motors should I aim for (I think I would prefer to go steppers rather than servo)

What would be a decent driver size to use

Are any of the multi axis boards, max seems to be 3amp per axis, worth considdering.

Thanks for any advice

John

John,
If you can give an indication of the size of your machine / model then someone will be able relate to theirs and make a better suggestion. You can also go to DanaherMotion site and download a sizing program, and after defining all the parameters, it will give you torque requirements etc for motors.
RICH

I have Geckos and 916 Ozin steppers on my Bridgeport Interact series 1, works well enough. Gearing between motor and ballscrew is 2.5:1 and I get about 2500mm/min (100 ipm)
Hood

I have used one brand of multi axis drivers. I would never consider going that route again. Mine did not perform well at all, blew chips like crazy, and was really more of a science project than a reliable driver.

I have to second the notion to avoid multi axis setups.

For steppers, I have to also second using big steppers as noted by Hood on his machine. Definitely 900 oz-in or better.

For stepper drives, I can confidently recommend the Gecko203V (their top-of-the-line). My preference from those I have used is the Centent commercial drives. Noticeably better than the Gecko  . . .  and noticeably more expensive as well.

DC brush Servo setups are now comparable in price to steppers for mid to larger machines if you accurately compare the real world performance power wise. In my opinion, there is no reasonable comparison performance wise. The two types are worlds apart in their characteristics. 

Hi John,

I have a Gorton 1-22 mill, a little bigger than the bridgeport.  It has really old NEMA 42 Pacific Scientific motors with Geckos on X and Y and a big DC servo on the knee, Gecko drives all-around.  I would avoid going with a knee-drive, it is slow, heavy, and it was pretty difficult retro-fitting a ball screw in there....  I run 80IPM rapids all around and can take heavy cuts at 30IPM no problem.  Gecko's are superb stepper drives, I have a small preference for Vipers for servo (the preference gets bigger as the motor gets bigger :-))

Hope that helps,
Dustin

P.S-  Direct drive on the steppers, .2in pitch ballscrews.

The mill is a cincinati toolmaster, the same size as a basic bridgeport.  4foot by 10" table approx,  travel about 18"  by 10",   Quill about 4" travel.

Motor at present is 1.5HP 1000rpm with 8 speeds via pullys, driven by an inverter drive.

Thanks for the replys so far.
I was planning to avoid the knee and have Z on the Quill.

I have already got on order 5mm pitch ballscrews which is 0.2 inch

If I were to go servo instead what size and type of motor would work

Thanks for the replys so far.
I was planning to avoid the knee and have Z on the Quill.

I have already got on order 5mm pitch ballscrews which is 0.2 inch

If I were to go servo instead what size and type of motor would work

I did my BP clone with 850oz-in peak/170 oz-in continuous, 72V,  4200RPM NENA 34 servos from www.homeshopcnc.com, and Gecko G320s.  The X/Y drives go through 2.5:2 GT2 belt reducers to 4-pitch 1" Nook XPR ballscrews.  The knee goes through a 4.8:1 XL belt reducer to the stock bevel gears and leadscrew.  I'll have a quill drive on it in a few days, at which point the knee will be used only for tool length compensation.  X/Y will do at least 350IPM (I don't have the nerve to go faster than that, but the hardware does....), the knee does 75 IPM.  All three axes are almost unstoppable - they'll snap off a 1/2" tool without losing position.

If you go with steppers, something in the 1000-1200 oz-in range (NEMA34) should be plenty, especially with 5-pitch screws, and direct drive will be fine, making the hardware a bit simpler.

Regards,
Ray L.

I can second the recommendation for the HomeshopCNC servo motor. Note that is it similar to the Keling drive, but 72V instead of 90V. USdigital or Aveco encoders work well.

My enthusiasm for the Gecko stepper drives does not extend to their servo drives. The Geckos have very crude tuning and they 'sing' or bounce between encoder counts constantly, which is quite annoying. The functional problem is that their low bandwidth chokes the motor RPM with a high resolution encoder.

In any case, a 20A drive is not the best match for that motor (in my opinion), as you loose a lot of acceleration with the 20A limit. I ran that very motor thru its paces with the Gecko320/340 and several other drives and there is a very big difference in the preformance. You can read the review here: http://www.thecubestudio.com/ServoDriveReview.htm Pay particular attention to the braking resistor issue with larger motors.

My preference is for the CNCdrive Dugong servo drive, which I use with the NEMA34 motor referenced earlier.  I have 5 of them now and am quite happy with the features, especially the tuning software. The only issue is availability. They are often sold out.