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Messages - RICH

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5681
General Mach Discussion / Re: Problems threading on the lathe
« on: September 28, 2009, 10:53:12 AM »
Hood,
Thanks,
The TURN  DIAGNOSTICS dosen't work for the SS.
I can turn off the drives and  check it out as if i was using the PP and get some info and then will repost
shortly.

RICH

 

5682
General Mach Discussion / Re: Problems threading on the lathe
« on: September 28, 2009, 09:50:54 AM »
Art,
I assume that the variance will carry over to the SS. Is that true?
During the driver test for my pc i get 22000 for 25KhZ and it varies by 200.
RICH

5683
Show"N"Tell ( Your Machines) / Re: CNC CONVERSION - 6" ATLAS LATHE
« on: September 28, 2009, 09:05:18 AM »
The work kind of stopped as there was only Chip and I trying some things out that Art was testing.
It was difficult testing to do. I just posted in Problems Threading on the Lathe thread, so you may want to follow along in that thread. The combination Z X move that your seeing has been around a long time, it is a bear to really
see / define the actual movements when it happens. Haven't tried lastest versions and don't really know if there are any threading changes in them.
RICH

5684
General Mach Discussion / Re: Problems threading on the lathe
« on: September 28, 2009, 08:54:15 AM »
Hood,
Mine has never been rock solid and varies. This is true for four different computers i have tried.
You can have a good consistant index input, but, as you elude too, if Mach has a bum
input for controlling the steps then you can end up with the lead problem and even when
the the start of the threading cycle should start. 

I'm thinking and that is dangerous.  ;)
RICH

5685
General Mach Discussion / Re: Problems threading on the lathe
« on: September 28, 2009, 08:22:00 AM »
Not using a VFD, but have a 1 hp DC motor and VFD drive for it. Figured I would just use the AC motor and see how all worked and maybe later try out VFD. Not sure on the motor though since i have no info on it.

Can change the Z over to a servo and replace the gecko dirve. My controller ( four drives in it ) is set up and used for multiple machines as it is portable along with the computer and sits on a cart. Thus that option would be a pain and really don't care to do it.

I can say that compared to other testing from the Sherline that the lead relative to length was improved some.

I also narrow it down to the index and computer. If the machanical spindle rpm is solid ( i wathced it during regular cutting and took measurements ) and it stayed within 1 rpm / the accuracy of my indicator consistently.

I know Graig can slave an encoder to the Z axis and provide for slowdown in one direction of a stepper. I was more interested at that time for both directions.
Agree that an encoder would be the ticket. We have used one for threading using DeskCNC. In fact you can turn the motor off and turn the system by hand, even go back and forth on a very small thread and it would just track whatever the encoder movement was doing. Maybe i will try and contact Graig again.

The thread testing back some months ago never came to closure. Art seemed to think it could be computer, but those tests were strickly for the PP.

One thing for sure is that the problem is not going away, it's a tuff one, and a lot of users will experience it.
RICH




5686
General Mach Discussion / Re: Web Cam not working
« on: September 28, 2009, 12:23:19 AM »
Dan,
If it worked before it should work again ( you would think ).
I have some cameras that will not work in MACH. In fact i bought two web cams from Radio Shack, same models,
 and the one required a different driver to work in both Windows and MACH. You figure and sorry don't have an
suggestions other than the driver.
RICH

5687
General Mach Discussion / Re: Problems threading on the lathe
« on: September 28, 2009, 12:15:36 AM »
HI ALL,
I know there were problems with the lead changing when threading. Take a look at this thread as i just did some thread testing on the converted lathe.

http://www.machsupport.com/forum/index.php/topic,12484.msg82874.html#msg82874

The lead error and heavier cut ( somewhere during the cycle ) still exist as I have shown.
I know it is not mechanical.
Any thoughts on the matter?

RICH

BTW.........1/2 a good thread is better than none!  ;D

5688
Show"N"Tell ( Your Machines) / Re: CNC CONVERSION - 6" ATLAS LATHE
« on: September 28, 2009, 12:01:44 AM »
THREADING CHECK – LONGER THREADING
Mach3 version 3.042.27 and using a SmoothStepper.

For checking of how longer threading is functioning in Mach ( or my lathe ? ) a microscope was attached to the carriage for viewing and measurements.
The tube was finished down to a .7500” diameter, then the surface was colored blue with a permanent marker. A very pointed sharp tool ( no radius ) was used to scribe the lines on the shaft as it was cut.
The threading was as follows:
PITCH:  0.050”  and 29 degree angle ( basically there is no step change in the Gcode for Z as it just cutting radial)
PASSES: 60 @ 0.0001”
TOTAL DEPTH OF CUT: 0.003”
RPM: 402 / 20 IPM
Picture #57, 58 show the setup and scribed material after the threading cycle.

Now it is quite obvious that the pitch is changing as the threading is progressively getting longer.
I guess that has not been fixed yet in MACH! On the starting end of the thread there are five cuts in a space
0.005”, then in the middle there are 5 cuts in 0.011”, and at the end of the 2” thread there are 5 cuts
in 0.019”. This is shown in picture #60 and then enlarged to show the cutting grooves at the end of the threading as shown on picture #61.

Each groove measured 0.003” deep ( I have .0003” backlash in the X ) but the widening / changing of pitch is not do to the Z mechanically ( I have 0.0006 to 0.0008” backlash in the Z ). The rpm is not changing.
The steps per unit a correct.

In the last post a ¾-13 x ¾” long thread was cut and there were no lead problems. If this thread was
cut was 2” long only ¾” or  maybe 1” would have been usable. I didn’t get any X & Z combination moves,
but, as shown in the pictures, somewhere in the threading cycle there is still something causing a change in the Z such that one bigger cut is “always” done somewhere in  the cycle. On a punny lathe the thread may be ruined but on bigger machine you would just have a wider cut and may not even notice that quirk!

More threading tests need to be done but did notice that the affect is not as pronounced as in a smaller
thread. Maybe Mach4 will have have it fixed, but until then, there are still problems with threading on the lathe.
 
Till next time…….keep the threading short,
RICH

5689
Newfangled Solutions Mach3 Wizards / Re: MachTurn wizards
« on: September 27, 2009, 03:55:41 PM »
Ian,
When in Mach Turn just click the Wizard tab at the top of the screen and select the threading or the turning.
RICH

5690
Show"N"Tell ( Your Machines) / Re: CNC CONVERSION - 6" ATLAS LATHE
« on: September 27, 2009, 09:24:29 AM »
Daniel,
The material is AL 6061. No chatter, but i did have that "crackling sound" at times which indicates that the
chip was breaking and there was work hardening of the material.  The tool is somewhat hung in front of the carriage
so you get some flex of the carriage. ( moment about the carriage Z axis, so whatever play is in the gibs was happening under load) You could see the tool  ( top part and tool mounting slide ) spring down, but again i wanted to see what she would do. I wanted to see if the belt would slip or rpm  or feed rate would change.

There is a fair amount of force when doing this thread. I  have broken a 3/8" diameter  diameter boring bars when doing a 1-8 thread on the 11" manual lathe. I would guess that the tangental force is 100 to 150# ( which is a lot for a little lathe ). Put that load on small part of you toe and you would really feel pain!

The little sherline would never be able to what the converted lathe did. Alll you need is a little backlash
say .002" in the Z, and making a cut it could be 0.005" instead of .003" and you would have disaster as the load
really increases.

Threading is a real true test of the lathe as you need to have accuracy, repeatablity, torque, and overall a good system.
Loads from cutting  are transmitted back into the components of the system. A good example from, a design point of view , would be how many and what size set screws should be put into the collar that acts as a retainer for  preloading of the Z anchor bearing.  Or notice that i deliberately didn't put any screw holes into the top carriage slide where the
tool gets anchored as it is rather thin in section, but, i can bridge across the slide with an adapter piece or plate.

This thread is about more than just here's the conversion. In the beginning there were posts about initial considerations
on components. I didn't take it to any high level of engnineering, but as a designer, the engineering stuff is of interest
to me. I may go into some calc's just for the fun and educational part for some. Then it went into each system and how it was done.

Sorry for rambling on but trying to add some perspective to the conversion.
RICH

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