Screwcutting

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16 Jun 2009 22:19 #435 by welderfabrod
Replied by welderfabrod on topic Re:Screwcutting
Yes Alan your quite right, but surely the software has no idea what my tool tip radius is unless I define it in the tool table, which I have'nt as most of the time the thread pitch's that I use are quite small because I am often more concerned with thread depth and calculate my pitch accordingly much of the time my thread depth is 0.5mm so the point radius is not really worth worrying about and a rub with a stone on the cutter is adequate. (metric for a bolt Rad.= 0.1443 x Pitch the nut has no radius just a flat at the core= pitch/8). Also this should have no effect on the pitch I cut. When I say the pitch is too small at 500revs. it is less than 1mm instead of 1.25mm. This is just a test to get syncronization right.
And as I said when running the G76 sample from the live CD in simulation the odd toolpath is still there. I'll download 2.3.1 tomorrow and have a try with that as you suggest.
I'm sure we'll get there in the end, just wish I had more knowledge of hal though. Rod

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17 Jun 2009 03:55 - 17 Jun 2009 03:57 #436 by acondit
Replied by acondit on topic Re:Screwcutting
Are you sure you scale is correct for both axii? One of the ways to get incorrect pitch is to have the wrong scale set up. The other thing that can cause problems, is if you don't have enough acceleration for the distance away from the starting thread. Also on coarser pitches, there can be a problem with whether the z-axis actually can move fast enough to cut the thread at a given rpm.

Alan
Last edit: 17 Jun 2009 03:57 by acondit.

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19 Jun 2009 09:50 #446 by welderfabrod
Replied by welderfabrod on topic Re:Screwcutting
Alan my scales are correct, I did think of acceleration when I first set up the encoders and tried G76 which is why I started at a low revs (150). Anyway I decided to bite the bullet and upgrade to 2.3. Nothing is ever that simple though is it. Went to the Installing off-line (32-bit systems) downloaded the Emc2 deb ok but when I tried to download the the two Ubuntu debs I.E. reports that the web pages cannot be found. So I had to download the live CD and have now installed that and this all appears to be running ok I hope now to get into the workshop this weekend and have a go with that.

Let you know how I get on in the next couple of days

Thanks again for persevering with me on this, I did think with the number of views this topic has had that we would have had a little more input from others as we can't be the only two people that have set up encoders for thread cutting.

Rod.

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19 Jun 2009 11:02 - 19 Jun 2009 11:03 #447 by BigJohnT
Replied by BigJohnT on topic Re:Screwcutting
welderfabrod wrote:

Thanks again for persevering with me on this, I did think with the number of views this topic has had that we would have had a little more input from others as we can't be the only two people that have set up encoders for thread cutting.

Rod.


Hi Rod,

The forum is rather new so there is not a lot of users posting in the forum yet. I hope as people like Alan and yourself join in we can have a broad base of users on this forum to draw knowlage from.

Regards
John
Last edit: 19 Jun 2009 11:03 by BigJohnT.

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21 Jun 2009 18:47 #465 by welderfabrod
Replied by welderfabrod on topic Re:Screwcutting
Yes it is a bit new John but I thought a few more from CNC zone would have popped across. Plenty of time yet though. I don't contribute much to any sites really as I normally find there are far more knowledgable guys out there than me. But if I do get a problem I'll ask because there is probably someone else out there with the same problem, so hopefully it'll help them as well.

Guys I have been playing around with the new Live CD install and have had mixed results. The good news is that I can now use my USB sticks for transferring files to and from my Linux box in the workshop. That makes life a lot easier.

As far as EMC2 is concerned I still have the same problems, but I have discovered why I'm getting pitch varition depending on spindle speed, Don't know why I did'nt notice it before, what is happening is that it simply is'nt syncronizing along the cutting pass. It travels along Z at maximum velocity all the time both in the rapid passes and cutting passes, If I adjust the Max Velocity slider on the Axis screen it slows or increases the velocity along the rapid passes but has no effect on the cutting passes they are still at max velocity.
Also I'm still getting what I feel is the odd motion of the rapids outside the drive line. Now the point is, is this how the G76 in EMC2 has been implemented or is it just me having this problem.
The other bit of good news is I have managed to get a digital read out for the revs on the Axis screen and that is working fine, seems to be reading the encoders OK. I tested this by swapping the pins over in the hal file. When I put phase A on pin 11 and set spindle speed to 500 I got 5 on the readout (500/100) swapped it back to Pin 10 and got 500, this more or less tallied with the Emco readout,so there does'nt seem to be a problem with reading the encoders. So it appears to me that the motion controller is'nt getting the information to syncronize the z axis with the spindle speed.

I'm still a bit bemused as to why the stepconf wizard could not set this up as in the manual it all seems a simple proccess.

Any thoughts on this.

Rod

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21 Jun 2009 21:45 #466 by BigJohnT
Replied by BigJohnT on topic Re:Screwcutting
welderfabrod wrote:

As far as EMC2 is concerned I still have the same problems, but I have discovered why I'm getting pitch varition depending on spindle speed, Don't know why I did'nt notice it before, what is happening is that it simply is'nt syncronizing along the cutting pass. It travels along Z at maximum velocity all the time both in the rapid passes and cutting passes, If I adjust the Max Velocity slider on the Axis screen it slows or increases the velocity along the rapid passes but has no effect on the cutting passes they are still at max velocity.
Also I'm still getting what I feel is the odd motion of the rapids outside the drive line. Now the point is, is this how the G76 in EMC2 has been implemented or is it just me having this problem.
The other bit of good news is I have managed to get a digital read out for the revs on the Axis screen and that is working fine, seems to be reading the encoders OK. I tested this by swapping the pins over in the hal file. When I put phase A on pin 11 and set spindle speed to 500 I got 5 on the readout (500/100) swapped it back to Pin 10 and got 500, this more or less tallied with the Emco readout,so there does'nt seem to be a problem with reading the encoders. So it appears to me that the motion controller is'nt getting the information to syncronize the z axis with the spindle speed.


Rod,

It sounds like your asking for a spindle speed/pitch combination that exceeds the maximum velocity of the Z axis.

Good to hear you got the spindle speed part worked out.

John

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21 Jun 2009 22:02 #467 by acondit
Replied by acondit on topic Re:Screwcutting
Rod,

I am more or less in agreement with John. So, the question I have is, what is the pitch of your z-axis screw and is it geared or direct drive? Also what is your "scale" number for the z-axis?

Alan

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30 Jul 2009 10:08 #653 by welderfabrod
Replied by welderfabrod on topic Re:Screwcutting
Hi Alan and John I,m back again. Sorry its been a while but sad family business has occupied me for a while.

Back to the matter in hand i.e. scewcutting. The other reason I,ve not been online is I decided to build a new power supply for the lathe as the Emco one only delivered 16v to the steppers which limited my Max Velocity to 360mm per min. I now have 31v to the steppers giving 780mm per min which should be ample for threads up to about 1.25 pitch. Plenty for what I intend to do.
I have also installed a seperate 5v regulated supply for the spindle encoders and now have really strong pulses when veiwed on the HalScope. However I still have the problem i.e. the Z axis appears to stop start along the length of the thread. When watching the velocity on the Axis screen what appears to be happening is that when the index pulse is seen the Z axis will ramp up to max velocity (780mm p.m.) then drop back again, it will do this a few times along the length of the thread. If I reduce the spindle speed it will do this more often along the thread, if I increase the spindle speed it does it fewer times along the length of the thread. Its like its not seeing the spindle speed pulse and does'nt syncronize. All this is done with a 1mm pitch thread in the G76.

I also now have the rev. counter on Axis and this is working fine.

Here is my Mechanical info:
Screw pitch = 2.5mm
Motor pulley 16T Screw pulley 40T (2.5:1)
Motors 200 step HalfStepping i.e. scale 400
Max Vel. 780mm per. min.
My spindle speed is set manually and not controlled by software.

I also now have two set ups one with the spindle speed halfile that you kindly gave and another done with the stepconf. wizard and both give the same result.
Today I,m going to change the pins on the port just to see if anything changes. Desperation really.

Rod.

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30 Jul 2009 12:04 #654 by BigJohnT
Replied by BigJohnT on topic Re:Screwcutting
I did complete my spindle with encoder feedback for testing here. Just to be sure you have the right HAL connections compare it to the manual which now has the connections needed for spindle feedback.

www.linuxcnc.org/docview/html//examples_spindle.html#r2

When running my spindle at 50 RPM using the g76 line from the sample program g76.ngc and increasing the length of the thread to 1.5" I notice the velocity readout from Axis kinda bounces around. I'm using a Mesa 5i20 card with a 2500 line encoder. The motion seems smooth to the eye and it does wait at the begining of each pass for the index pulse. Running at 300 RPM the velocity is much smoother.

Run your spindle and take a look at the encoder velocity with halscope at different RPM's. Just looking at my encoder velocity at 300 RPM it is a slightly lumpy but regular spaced pattern and at 1000 RPM it is smooth.

John

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30 Jul 2009 18:20 - 30 Jul 2009 18:23 #658 by welderfabrod
Replied by welderfabrod on topic Re:Screwcutting
John thanks for coming back. Just a bit more info, as the apparent stop start motion tended to reduce with increased spindle revs I wondered if it would get to a point where it would disappear altogether so I did a pulley change to get more revs and sure enough it did eventually disappear. this seemed to be at about 700 revs. in this case.

The Spindle Feedback as shown in the manual is basicaly what you get if you use the Stepconf Wizard to set it up.

I did as you suggested and watched the encoder velocity at different revs. The results are below. I,m not sure what the info HalScope is giving means so does it look like yours at all.

Encoder velocity at 8000 samples.

1) At 900revs


2) At 600revs


3) At 300revs


Pulses on Pins 10 and 11 at 900revs

Hope this works have,nt done this before.

Rod

Nope did,nt work got the same on them all not sure why ?????
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Last edit: 30 Jul 2009 18:23 by welderfabrod.

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