Messages

11

LazyTurn / Re: LazyTurn

« on: December 20, 2009, 06:31:20 PM »

Art,

The X-axis feed rate helped a lot.  I dropped from 7-1/2 minutes to 3-3/4 minutes with the separate X feed rate.  Thanks!!!

 Only, I don't understand why you called it "plunge rate" instead of simply "X-feed rate."  If performing a facing or boring operation wouldn't "plunge rate" be a misnomer, since the roles of X and Z are reversed when compared to turning operations?

Dave

12

LazyTurn / Re: LazyTurn

« on: December 13, 2009, 06:36:19 PM »

Art,

I'm really eager to have a finish pass.  I'm supposed to cut 1000 wood pincushion bases by February and, of course, I'm using the roughing pass in lieu of a finish pass.  It works, but I'm sure that having a finish pass will let me rough it out much faster and save a lot of time.  Multiplied by 1000 of these things, the time savings would be significant.

I'd be happy to test a pre-release with my project. 

Dave

13

LazyTurn / Re: LazyTurn

« on: November 22, 2009, 11:34:57 AM »

I'm using LT to do a real job, in wood, turning out pincushion bases from red oak for my wife's company.  Everything is working well enough.  The thing I'm wishing for, most of all, is a feed rate for X that is different than Z. 

Here's why:  when the tool is moved (X direction) into the stock to begin the next (Z direction) cut, it plunges into the material and initially has to cut a lot of material all at once.  After it starts traveling in the Z direction it's only cutting from half of the cutter tip and I've chosen a feed rate that's appropriate for this.  But every time it plunges in for another cut it cuts from both sides of the tip simultaneously, removing too much material too fast.  If I slow the feed rate to match this X cut, I waste too much time on the Z cuts.   I need different, independently set feed rates for cuts in the X and Z directions.

Is there some other way to solve this problem?

Thanks,
Dave

14

General Mach Discussion / Re: Need help with resonance problem

« on: November 05, 2009, 02:06:19 AM »

I found out my controller supports 1/8 steps, so I used it and indeed, it solved the problem.

And, now that I see it in operation, it makes perfect sense.  While I was still at full steps I watched the motor as it ramped up and down.  There was a discrete speed, fairly slow, where I could actually see the motor stumble and reverse briefly.  Made more noise too.  Thinking about it, it makes perfect sense.  Those full steps were huge slugs of torque that were exciting the resonance of the system.  Using smaller steps avoids that excitation.  Everything is smoother and quieter.

Thanks for the advice.

Dave

15

General Mach Discussion / Re: Need help with resonance problem

« on: November 04, 2009, 09:38:25 PM »

This motor is German, Nanotec - Munich, 4H5618C0408, 3.4V, 2.85A, 1.8deg.  NEMA 23. 

 I'm not microstepping it.  The controller can do half and quarter steps if that will help.

The error is always the same direction.  I.e., when I stop it to check position, the carriage is always farther away from home than it should be.

In playing around with jog mode, I was able to run the stepper at 900 and acceleration of 120 without obvious stalling.  But in actual use I was still seeing errors down at 250 and 40. So I cut it to 25 and 2 and the errors stopped.

I'll generate some code to run it back and forth short distances, lots of reversals, for use in determining the velocity and acceleration at which the errors begin.  Given the mass of the leadscrew relative to the size of the stepper, I'm expecting that acceleration is going to be the problem.

Should I be half-stepping to improve performance?

Dave

16

General Mach Discussion / Need help with resonance problem

« on: November 04, 2009, 05:42:17 PM »

Hello all,

I've converted a Grizzly wood lathe to CNC by adding some scrounged actuators with step motors.  I'm having a problem with the Z-axis.  It gets a few steps out of sync with Mach3 and starts cutting where it shouldn't.  In a run of 15 minutes it gets off maybe as much as a dozen steps.  Computer is fine.  Electronics is fine.  These are my background and I wish the problem was here because I could deal with it.  It's not.  It's mechanical.

I slowed the Z-axis *waaay* down to speed of 25 and acceleration of 2 and the problem went away.  So, now I have to figure out how to identify the resonance and how to deal with it.  This is an area I have no experience in.  Can someone point me to a recipe or tutorial on how to identify, measure and compensate for resonance?  I'm hoping I don't have to do this by trial and error because that could take forever.

Now, there's a Lovejoy-style coupler between the step motor and leadscrew.  I'm suspicious of the rubber spider between the two halves.  Seems to me that this could exacerbate resonance problems.   The leadscrew is almost 30" long and at least 1/2" dia., pretty massive.  The stepper's 1/4" shaft looks puny next to the leadscrew, and it is probably twisting under the torque and contributing also.  Would a larger stepper with a more robust shaft help?

Any help will be appreciated.

Dave

17

LazyTurn / Re: Is this a bug in LazyTurn?

« on: November 04, 2009, 05:32:00 PM »

Dave / Rich,

Wilco. I'll post in "General."

I do have two more identical motors.  I just have to put on my connectors in order to use them.  I don't expect it will make a difference though, because this is a small step motor driving a large leadscrew and the original design didn't require high performance.  If I want performance I'll probably have to spend money.

Dave

18

LazyTurn / Re: Is this a bug in LazyTurn?

« on: November 04, 2009, 03:04:18 PM »

Rich / Dave

I found my hardware problem.  It isn't the Dell laptop.  It's worse.  Apparently, I'm fighting a resonance in my Z-axis actuator.

I slowed the Z-axis *waaay* down and the problem went away.  Now I have to figure out how to identify the resonance and how to deal with it.  This is an area I have no experience in.  Can you point me to a recipe or tutorial on how to measure and compensate for resonance?  I'm hoping I don't have to do this by trial and error because that could take forever. 

Now, there's a Lovejoy-style coupler between the step motor and leadscrew.  I'm suspicious of the rubber spider between the two halves.  Seems to me that this could invite resonance problems.  Yes? No?  The leadscrew is almost 30" long and at least 1/2" dia., pretty massive.  And the stepper shaft is only 1/4" and is probably twisting under the torque and contributing also.  Would a larger stepper with a more robust shaft help?

Should I post this on a different part of the forum?

regards,
Dave   

19

LazyTurn / Re: Is this a bug in LazyTurn?

« on: November 02, 2009, 11:45:02 AM »

Rich / Bud,

I double checked.  Yes, I'm using the May 28 LT.

The Z-offset is at 0.1.  I don't remember if I put that in, but if I did it was a long time ago.  I haven't been doing anything to it for the last two weeks at least.  I haven't touched either the Z-offset pointer or stock location pointer on the ruler.  That's why it's a mystery to me, that the profile moves on the stock even though AutoCAD always shows the profile at the UCS origin.  This is not a showstopper.  I can work around it, now that I'm aware of it

My showstopper is:  I apparently have some hardware problems after all.  As I am cutting the profile, Z-axis stepper acts like it is briefly sticking or something, i.e., getting slightly offset.  I don't think the problem is mechanical.  I cut the Z-axis speed and acceleration in half and I'm still seeing the same problem.  I am suspicious of my Dell laptop.  I'm going to switch to a different platform, running a fresh install of Win2K, my favorite Windows version.

I'll be back after I get a handle on my hardware problems.

I must say, it is gratifying and reassuring to get the level of attention you guys are giving.  I saw this forum and this process before I chose Mach3, and this was a major factor in my decision to go with Mach3 instead of the alternatives.

Thanks!
Dave

20

LazyTurn / Re: Is this a bug in LazyTurn?

« on: November 02, 2009, 12:19:50 AM »

Rich,

I think what you just described is equivalent to what I normally do, which is: "Tools,"  "UCS," "Origin," then I snap-to whatever point I want to be 0,0 and left-click it.  That makes the point 0,0 in the UCS, but somehow that's not what LT wants.  Because if I move the profile a little left or right and then fix the origin like I just described, to keep the profile at 0,0 in every case, LT will still move the profile on the on the Z-axis.  As though there's an underlying coordinate system that AutoCAD and LT are using, and LT is ignoring the UCS.

By trial and error I can figure out where LT thinks its origin is.  I just wish I knew what's going on.

Thanks,
Dave