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View Full Version : New steppers on the mill, Who wants to race?



JFettig
01-02-2005, 09:03 PM
I just finally got around to putting my new steppers on my mill. The ones I am selling in the classifieds currently. Out of my amasement, I managed to hit 250ipm on my mini with 5tpi ballscrews. This is under the rated current and at ~30v(24v transformer).
The funny part is that it only actually travels about 3" on my x axis wich has about 8" of travel at top speed, the rest is accelerating or decelerating and keeping a margin of error :eek: I think I can push it more with my new 67v power supply and correct current, although its quite scarry and I dont like to mess with it. In order to hit that speed I sometimes sacrafice some steps while its trying to stop. The funny part is that turbocnc says my 10% jitter is at 21000hz and Im pushing 42000hz.

Here is a short video, its from my olympus camera that doesnt have a mic and only records quicktime format, dowload the 'quicktime alternative' which is quite nice to view it if you dont already have quicktime.
http://jfettig.wc101.com/cnc/newsteppers/250ipm.MOV

http://jfettig.wc101.com/cnc/newsteppers/nsright.JPG

http://jfettig.wc101.com/cnc/newsteppers/nsleft.JPG

What kinds of speeds are others getting out of their machines? Im sure I wont keep mine like at these speeds, Ill probably leave it where I can trust it, Ill see when I get my new ballnuts and new controll box set up. Probably 120ipm.

Jon

JFettig
01-02-2005, 09:47 PM
wow, funny thing is that I got both axes to move at the same time at 210ipm then I try again and it starts missing steps, then I cant now get one axis to move at 120ipm. Something is weird, I lubed the screws and dovetails when I started this, I have the gibs pretty tight. Im going to have to figure something out to get it moving fast again.

Jon

ESjaavik
01-03-2005, 04:28 AM
@JFettig: This reminds me of some words about the tail wagging the dog! http://www.sjaavik.com/images/lol.gif

I think your main problem is way too big motors for the poor machine.

With this setup your resonances will be quite close to the motor's, and not appreciably damped at all. This because the mass of your leadscrew make a very small addition to the moving mass of your (huge!) motor.

Do you have a lathe chuck? As your motor has a tail shaft, try to hang some rotational mass onto it, like a lathe chuck. That will move your resonance speed.

You should also try to lower the motor current. That will make your resonances less violent.

But really I think you should try to find the resonance speed(s), and teach your controller not to use them. When dealing with resonance problems you can get quite puzzled if you don't realize what's going on. One example is that it may behave better at high accelerations, but miss steps or stall out at low acceleration. Keep in mind you cannot command it to use lower accelerations, as that also depends on your program.


Edit: On second look, I also see another problem. Your motors are mounted with very low torsional stiffness! The 4 long bolts used as a motor mount will not at all hold back on torsional vibrations. Swap them with 2 flat pieces. One top and one bottom is fine, as that aslo help keep swarf out. With your mount the motors are more or less free to vibrate as they like. The thing I mentioned with the chuck: forget it. With your mounting it will just transfer the movements to the motor itself.

JFettig
01-03-2005, 07:39 AM
The motors may be a little big, the current is already about an amp too low and I will try the full current. Im really not looking for super speed like this, just had to brag about it a little;)
What I am mostly looking to do is crank down on the gibs to tighten up the machine a bit so it doesnt chatter quite so much so I can take large cuts easier. the column is probably not stiff enough but I will try.
I threw these motors on here because I wanted the other ones for my lathe and to try these ones out.

Another problem is that I am having a problem with my ballnuts binding from the previous mount, the slots for the nuts were slightly angled to remove backlash when tightened when there were leadnuts, but it just screwed up the ballnuts. I will be putting new ones in there soon.

Jon

fpworks
01-03-2005, 11:25 AM
...and I thought I was doing well with 120 ipm.

Jon,
Now you just need a high speed spindle ;)

JFettig
01-03-2005, 01:17 PM
lol, fpworks, 8000rpm isnt high enough?;)

My overall goal for stability and repeatability and all is 120ipm. Ill see what happens with 2x the voltage.

Jon

Torsten
01-03-2005, 04:16 PM
I just downloaded your movie file, I don't know how well this
represents your actual speed but when looking at the movie
it looks more like about 30 IPM.
Pretty big motors are those steppers?

JFettig
01-03-2005, 04:20 PM
Yes, they are steppers, nema 34 aproximately 300-400oz/in.

In that movie, the table moves aproximately 7.5" in less than 2.5 seconds. It moves about 1.5" before it reaches top speed and takes that long to slow down to stop.

Jon

ESjaavik
01-03-2005, 06:23 PM
Don't tighten down the gibs too much! You need space for lubricant or wear will be greatly accelerated.
Check with leadscrew disconnected when tightening gibs. Then you can feel tight spots much better. This also goes for manual mills/lathes.