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Author Topic: lathe threading problem  (Read 3917 times)

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lathe threading problem
« on: October 18, 2016, 03:07:57 PM »
Hi
i have a problem with my denford orac cnc lathe that i hope the people on
this forum can help me solve this problem
the lathe was converted to mach 3 about 3 years ago and has been a very reliable machine
until easter sunday this year when it decided that it would no longer do external or internal
threads , but still works very on normal turning jobs
the machine is using mach 3 version 062
i have tried a new cnc4pc spindle index board but this has not solved my problem as well a
few other ideas found on internet , the latest being a proximinty switch which i bought from
cnc4you this gives a very stable spindle speed but still no threading .
the problem when threading it is not picking the pitchin the same every time so all it
ends up with is alot of grooves
i have changed to a new copy of mach 3 on about 6 times just in case the program is corrupted
but still no joy
i have been stuggling with this problem for 7 months and have now run out of idea's so please
can anybody help me
thank you
robert

Offline RICH

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Re: lathe threading problem
« Reply #1 on: October 18, 2016, 07:11:16 PM »
Post your xml file that you are using.

A few questions:
Are you using steppers?
Are you sure that the spindle index is working / checked it?
How are you generating the threading code?
 - Are you allowing for 3 to 5x pitch movement so the axis can accelerate?
 - If using the wizard did you "calc the number of passes Button " to check if your velocity and accel is appropriate for the thread?
Try just scribing  as a check to see  how well it's following the pitch.

Again post your xml file.

Till Then,

RICH
Re: lathe threading problem
« Reply #2 on: October 19, 2016, 01:27:09 AM »
rich
thank you for your reply

yes i am using stepper motors and using the parrallel port

i have checked the spindle index board with a meter and i am getting 5.08 volts when it sees the slot
and 0.8 when not seeing the slot , the disc has a single slot which is 20mm wide

the threads are done by hand coding

i always start any thread 15 mm from the front of the job
thank you
robert

Offline Hood

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Re: lathe threading problem
« Reply #3 on: October 19, 2016, 02:47:06 AM »
Config menu then Ports and Pins then Spindle Setup, enable the Use Spindle Feedback in Sync mode option

Hood

Offline RICH

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Re: lathe threading problem
« Reply #4 on: October 19, 2016, 06:05:59 AM »
Assume Hood already looked at your xml and found the problem. ;)

Note that a  thin disc  on the end of a shaft with the edges blackened in the spindle provides a surface to check repeatability  
of the indexing during threading.

RICH
Re: lathe threading problem
« Reply #5 on: October 19, 2016, 11:22:45 AM »
hi
thank you to rich and hood for help with trying to solve my problem , i will try both idea's tomorrow morning
when i go to my workshop
robert
Re: lathe threading problem
« Reply #6 on: October 20, 2016, 02:58:19 PM »
hood
i altered my machine settings to 'spindle feedback in sync mode' when it came round to the threading cycle the machine moved to the starting position & didn't move any further
help please , have i got a corrupt version of the thread code , anybody got any idea's as to what is happening
all the best
robert

Offline RICH

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Re: lathe threading problem
« Reply #7 on: October 20, 2016, 04:00:54 PM »
Threading ,the start of the Z motion, will not begin if the index pulse is not  seen by Mach.
What is your Index Debounce value set to in configuration?
The debounce is defines how many times Mach must see the index before it accepts it if memory serves me.
I asked you to check / confirm the index was functional..........

(See page 9 of Threading On The Lathe - Mach 3 Turn write up which you will find in Members Doc's.)

RICH
Re: lathe threading problem
« Reply #8 on: October 21, 2016, 01:30:01 AM »
rich
the index debouce is set to 10
i have checked the index signal with a meter , i am getting 5.08 volts working & 0.8 volts not working this at index pulse board
at the input pin connection i am getting the same voltage readings , i have also checked the parallel cable to make sure i haven't got a broken wire in the cable
if i tick the spindle speed averaging box i get threading movement but if i tick the use spindle feedback as well as the machine just hangs when it gets to the threading cycle
robert

Offline Hood

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Re: lathe threading problem
« Reply #9 on: October 21, 2016, 07:36:28 AM »
As Rich says it would seem Mach is not seeing the index pulse  clearly. Try Zero for the Index Debounce and see if that helps. If not, and if you have another spare input try and swap to that and see if it helps.

Hood