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Author Topic: Problems threading on the lathe  (Read 330206 times)

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Offline ART

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Re: Problems threading on the lathe
« Reply #300 on: May 19, 2009, 10:11:35 AM »
Hi Guys:

  New version, shoudl show steady RPM's on your displays in encoder or slot input.
Let me know if your RPM's are now accurate and stable if you can.. Ill then start working on the actual threading speed correction algorithm, which will complete ( hopefully) slot based or encoder threading. Then, finally, we get to see
if this all actually makes better and more pitch accurate threads. :)

Art

Offline RICH

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Re: Problems threading on the lathe
« Reply #301 on: May 19, 2009, 01:01:55 PM »
ART,
Hopefully, I'll get the  pulse generator today, so i can simulate either the slot or encoder while actually
using what is mounted to the spindle. Can't be of much help until that happens.
RICH
 

Offline Chip

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Re: Problems threading on the lathe
« Reply #302 on: May 20, 2009, 05:08:11 PM »
Hi, Art

Hears a couple of pic's, I'll post more info later.

Chip

Offline ART

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Re: Problems threading on the lathe
« Reply #303 on: May 20, 2009, 05:54:52 PM »
Hi Guys:

 Found a problem with encoder input, nSlots was counting slots properly. Hopefully thi swill fix that if your using an encoder input..

Chip: Any idea why the number of slots is zero on your? Other than that the numbers look great.

Art

Offline ART

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Re: Problems threading on the lathe
« Reply #304 on: May 20, 2009, 05:55:35 PM »
oopss..

Here the files..

Art

Offline Chip

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Re: Problems threading on the lathe
« Reply #305 on: May 21, 2009, 12:35:45 AM »
Hi, Art

Hears 2 pic's, First is from my problem computer and Second is from the stable one.

The signal is from simulated pulses, Both computers are tied to the test pulses at the same time, Index/RPM was used to set Index & Timing values, Index set to 200 & Timing set to 400.

Both computers show  close to 200 rpm for Index Base RPM's but that's about all that's common to both, Number of Slot's are working now also.

Threading only start's if Advanced Threading Enabled is Checked.

Chip
« Last Edit: May 21, 2009, 03:40:34 AM by Chip »
Re: Problems threading on the lathe
« Reply #306 on: May 21, 2009, 09:43:12 PM »
Wow I am glad to see this thread has taken hold and there has been positive progress on lathe threading .
I am still having problems threaading with the lathe from page one.
I dont think spindle HP is an issue , motor is 30hp , Rpm never varies more than 1 rpm no matter how heavy the cut. machine is equiped with ballscrews and has almost zero backlash . Was new one year ago when this project started and has less than 200 hours on it t date. Motors are 2kw ac servos. In my original configuration I was alternating between a single slotted disk and the factory encoders index pulse. The results with both were the same , threads would overlap and starts were random.

After talking with Hood about his threading success I decided the smooth stepper might be the key . I have it up and running nicely , but I am still having problems with threading. The problem now each time a new pass starts, it starts just a few degrees later . On a 3-4 pass thread 40 tpi or so you can only see the problem under a microscope. With course threads like 10 tpi that require 12 or so passes it quite obvious. The valley ends up flat bottom as if the tool has started slightly later or at aprox z-.001 deeper on pass one, z-.002 deeper on pass two and so on.

My rpms appear very stable, all the motors are strong enough there is no mechanical loss. No backlash . I am not getting the variable pitch problems as some folks earlier in the thread, doesnt matter if i thread .5" or 8 inches in length.

What really has me confused is I have a crappy 13x40 enco lathe I purchased in the 80's , very well worn, with dc servos , 2 hp spindle motor and cheap ball screws that turns perfect threads. This one drops 10-15 rpms everytime it makes a new pass but still cuts perffect threads . I have threaded both ends of hundreds of suppressor tubes and thousands of end caps and barrels and it turns perfect threads everytime. The only things I can think of that might be an issue is i am using version 2.54 on this machine, I dont know that the computer has made a difference , I was using a 2.2ghz p4 for most of a year and a few months ago started using an older p3 , and its cut perfect threads with both.

All the above rambling aside , are we getting pretty close to having a workable plugin for threading?

 Anyone have any thoughts on what I might try with my big lathe , I have more help in the shop now and plenty of time to get this lathe threading properly and i am willing to try /experiment with just about anything to get the threading ironed out. As far as HP , accuracy and rigidity this thing is a perfect test bed so feel free to throw out suggestions.


Offline Hood

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Re: Problems threading on the lathe
« Reply #307 on: May 22, 2009, 02:07:41 AM »
Richard
 I would say by your description you have not checked "Use Spindle Feedback in Sync Mode" you will find that from Config menu, Ports and Pins, Spindle Setup, its over at the top right.
Hood

Offline ART

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Re: Problems threading on the lathe
« Reply #308 on: May 22, 2009, 07:59:37 AM »
Hi:

>>The problem now each time a new pass starts, it starts just a few degrees later . On a 3-4 pass thread 40 tpi or so you can only see the problem under a microscope.

  This is an odd problem to have. (Though Im pleased pitch and such isnt a problem on either lathe, but then it really shouldnt be.). This new thrust is really meant to help
in compensating for computers that vary their internal timing , it is thought ( primarily by me. :) ), that many of the issues with threading are a result of internal clocking
differences in some CPU types and motherbaords. The new plugin is goign to try to address those by getting more accurate data from the cpu and motherbaord and
allowing a better averageing of these random frequency changes. When you average a true random event, you average to zero displacement. So a multi slot
system ( say 90 slots in a rotation ) should be 64 times as stable ( I average over 64 slots in the driver ), and more responsive as its correction algorithm will use a rolling
avergae over the 64 slots so even one slot timing changing from a load will compensate. In theory all this will help.. a lot if Im right, not at all if Im wrong.

  Your problem though.. cant see it. Either the license file is acting up ( make sure it doesnt read demo..) or the "Use Spindle Feedback for sync" isnt checked. The only
other possability is a floating time on the trigger (index) pulse or a computer that is internally floating more than most. Almost no reports have ever been made of start
trigger fluctuations though.. normally errors are in the pitch realm, but from variations during cut, not from the start, on 99% of systems the first several threads are
near perfect.  There arent enough users to give you stats on how many have issues with threads, but I hear from fewer with problems that I do from people with
threads that are good. Within a short period though I will turn on the compensator algortithm with this current testing.. and we'll see if all is well , better, or worse
with this theory.

Thx
Art
Re: Problems threading on the lathe
« Reply #309 on: May 22, 2009, 08:45:51 AM »
That was it, I checked use spindle feedback and the threads look great.... so many settings , buttons and things to configure I just cant keep up. I am glad for this group and all the help.

 I have run half a dozen test cuts at 20 tpi , all look great at 40x on the microscope, and more importantly they mesh properly with tubes threaded on the other lathe running mach and the tubes threaded on the Haas . I am going to work with course threads next . Thanks