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Re: general problems with mach3
« Reply #10 on: May 22, 2008, 11:37:45 PM »
Thanks for all the suggestions. I think I have determined that my problem is mechanical, probably related to ball screw. The screw is driven by a direct Oldham style coupling. It's aligned well, and feels smooth by hand, but grumbles when stepper driven. I  did some manual screw mapping, with power off, turning the motor by hand, referencing to a mark in the motor shaft and "dial".   My lead is very close to its stated 20mm. Turning it 30 revolutions by hand and measuring the resulting 23.6 odd inches of travel with a steel rule gave me a number a few thousandths of an inch shy of 20 mm. So the step number I've been using to get very close to the travel I'm asking for is apparently inflated to compensate for the missing steps, which you all probably knew all along. I'm still learning here. I am amazed at the machines ability to miss steps in such a nearly consistant manner.
I then switched drivers on x and the perfectly performing z, which have different drivers. Same results though, making me think perhaps x stepper was the problem. I switched steppers, and same results. So I"m left to conclude that despite the smooth feel to me, the ball screw is causing missing steps.I should say that in motor tuning the axis sounds horrible, especially at very slow speeds. The smoothest travel came from using high microstep values, 1/25 or 1/32, but it's still usually a bit grumbly, and in consistant in its smoothness, which I guess is a clue. It's weird, because it feels smooth when turned by hand. 
I"m going to disassemble and clean the ball nut, and I might have some issues with its bearings...a long story.
As for accuracy of high lead screw, this machine is to be used for woodworking, so accuracy to within a couple thousandths would be fine.  The screw is a high quality THK four start, 20 mm diameter, 20 mm lead.Do I need to use a pulley and belt arrangement, gearing things down to achieve that?

Offline Chip

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Re: general problems with mach3
« Reply #11 on: May 23, 2008, 03:21:32 AM »
Hi, Endgrainguy

Check your setting in Config, Motor Tuning, Step and Dir Pulses, If there at 0 set them to 5 and see if this Helps.

Some control boards need a little more time to see Mach's pulses.

Also if you used Ports and Pins, Motor Outputs, Active Lows/Highs to change Directions of your axises, It should be done in Home & Limits page, "Reversed" box.

Some control boards don't like that ether. If your cont. boards are all the same thy should be all the same, Active Low or High for Step and Direction.

Chip
 
Re: general problems with mach3
« Reply #12 on: May 23, 2008, 07:33:12 AM »
Thanks, I'll try that when I get scew back together. I do have those set at 0 and noticed yestrday that might not be correct. A little paragraph in Mach set up I had overlooked. Tried a couple other settings to no avail, but not 5,5.

Offline jimpinder

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Re: general problems with mach3
« Reply #13 on: May 23, 2008, 07:48:55 AM »
Once you have found the reason - the rest should be fairly simple.

I have great respect for Art and the Mach software, but I cannot agree with allowing Mach 3 to determine you number of pulses per inch. The only trouble is - if the answer is wrong, how do you know. I appreciate Art was probably trying to simplify things, and he has done in so many other respects.

Steps per inch is not difficult to calculate - so calculate it. The either use Mach 3 system, or a set of digital calipers to confirm what you knew all along.

Endgrainguy - well done - but wait til you get going with backlash, offsets etc etc. It's great fun.

Was my calcu;ation of your steps per inch correct - or am I far too low - your accuracy will suffer if it is too low. There is also the problem, that if you miss any steps - each step is a greater distance, so your error is worse.
« Last Edit: May 23, 2008, 07:52:07 AM by jimpinder »
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Re: general problems with mach3
« Reply #14 on: May 23, 2008, 12:13:34 PM »
Keling recommends using Sherline 1/2 pulse mode, which according to Art will give you a 40us step/direction pulse regardless of the other pulse width settings.

http://www.kelinginc.net/Mach3Tutorial.doc
Re: general problems with mach3
« Reply #15 on: May 23, 2008, 12:33:12 PM »

I have great respect for Art and the Mach software, but I cannot agree with allowing Mach 3 to determine you number of pulses per inch. The only trouble is - if the answer is wrong, how do you know. I appreciate Art was probably trying to simplify things, and he has done in so many other respects.

Jim- are you referring to the 'Set steps per unit' button on the settings page?  If so, I don't really understand why you don't think this is a good method?  Have you ever checked out that process?  It's such an easy way to determine your steps per unit which I have found to be accurate.  I have always used this method and never had any problems.  Is there some kind of flaw that I'm not aware of?

Sid

Offline Chip

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Re: general problems with mach3
« Reply #16 on: May 23, 2008, 02:01:31 PM »
Hi, Endgrainguy

In Ports & Pins, Are you using the Sherline 1/2 Pulse mode.

Thanks, Fiero Addiction, For the document: That, Keling recommends using Sherline 1/2 pulse mode, This gives your control boards even more time to see Mach's

Pulses and bypasses the settings in Motor Tuning, "Dir/Step Pulse" settings.

Thanks, Chip

Offline jimpinder

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Re: general problems with mach3
« Reply #17 on: May 24, 2008, 03:53:11 AM »
Sid -

No - what I am saying is - it is a bit like shop sales people on an electronic till. If they make a mistake they have no idea and charge you just the same. I always have a rough idea how much the items I have bought are.

By all means use Arts software - but I think you should have an idea of the answer before you start, just to make sure that if you make a mistake inputting the information (say by a factor of 10) or your fingure hits the wrong key and it comes up with a different result to the one you were expecting, you know to have a second look.

I suppose the same can be said of me- I should calculate - then use Arts Software to confirm it - just in case I have made a mistake.

Endgrainguy -

Yes if you are using this for woodwork - and are only looking for a couple of thou in accuracy, then you should be alright once you have got over this hiccup. You must excuse me, I work in steel where 1/2 thou is the difference between fitting and not fitting. Yes - if you understand the point I was making, gearing down the drive between motor and leadscrew will give you that much more accuracy - and your motors should be capable of (to a point) speeding up to compensate. It is a question of compromise for the job in hand.

Jim
« Last Edit: May 24, 2008, 04:00:14 AM by jimpinder »
Not me driving the engine - I'm better looking.
Re: general problems with mach3
« Reply #18 on: May 24, 2008, 02:01:35 PM »
Well it wasn't the ball screw. And towards the end of the four hour procedure of taking the x and z axis sufficiently apart to disect the ball nut, sort the balls, and reinstall them, methodically sorting and spacing the 15 of 212 that are smaller, and then putting it all back together, I realized there was a much easier test. I should have simply decoupled the motor from the screw, and used a tick mark in the outboard motor shaft to see if it was still losing steps even without the motor connected to axis. This would have revealed to me ,as it did,that the problem was not the ball screw, or anything in the axis, but electronics or settings. So, wasted time, but knowledge gained.
And  the answer is : Motor Tuning, Step and Dir Pulses, If they're at 0 set them to 5. Thanks  Chip! It also smoothed things out a bit to enable "Sherline 1/2 pulse mode" in ports and pins.
I still have annoying resonance issues at mid speed, I guess the notorious "midband resonance." I'm using Keling drivers and steppers and BOB, the 640 OZ/inch motors and KL-6050 driver on x and y, with the KL-8078 on Z.
 It's not really a problem on Z, where it midband, expresses itself dramatically. With its 2 mm lead, it runs very smoothly from 1-38 IPM or so, and then stalls completely up to about 50, then smooth at higher speeds,  but I"d not want to go faster than 50 anyway on Z, and a reliable 35 IPM is actually fine speed, even for the joint cutting work with router horizontal I'll be doing.
On X, with its 20 mm lead, I get best results microstepping to 1/16 th, and then it runs smoothly up to about 60 inches minute, and smoothly again at about 90, and can go to 300 IPM fine, even at 1/16th mictrostep.
Y, with a .5 lead two start "no name" screw with a little roughness in the screw in a couple spots is good to about 18 IPM, and then bad to about 35 IPM, really atrocious in the middle of that range. Then it runs better, smoothing out beautifully at about 50, and can go to at least 120 IPM, far faster than I'd expect to use it. A little  more experimenting with settings, trying switching the drivers on Y and Z, to se if that helps quiet the Y at its resonant speeds. This is amzing stuff-- not exactly intuitive, is it?

Offline Chip

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Re: general problems with mach3
« Reply #19 on: May 24, 2008, 05:39:58 PM »
Hi, Endgrainguy

What's your power supply Volts and Amp's, Stepper Volts and Amp's rating and current setting on Driver boxes.

Check that your Dir & Step "Low Actives" are All Checked, Axis reversing/direction changes should be done in Home & Limits page, "Reversed"  box.

Your Keling boards may not operate properly if not set this way. http://www.kelinginc.net/Mach3Tutorial.doc

Chip