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Author Topic: can threading be done in mach without an index pulse?.  (Read 4939 times)

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can threading be done in mach without an index pulse?.
« on: December 23, 2010, 08:24:42 PM »
I am dying to figure this out.

I want to know if I can thread without an index pulse just "relying" on the spindle to keep in correct position. I have a lathe that has a stepper motor on the spindle for indexing and threading (if I can figure this out)

Originally, I thought that I would use the stepper on the spindle as an A axis and write the code for threading and indexing by hand.

Is there a way to run the stepper as the spindle motor (yes, I can configure it this way, I know) and then use the threading wizard? I have tried just this, and I cant keep the thread synced... I have a powerful enough stepper running on the spindle, I dont know why mach cant just assume that when I tell the stepper (spindle) to do 30 rpm, it does exactly 30 rpm. when I run the threading wizards program, the thread looses position.

How can I get mach to believe that the rpm is 30 without an index pulse?

Is their a setting that would allow me to not be reliant on an index pulse? and for mach to just believe that the rpm is as it should be?

before you ask, my index pulse generator is cooked.

Additionally, how would I write code that would work in machlathe that would use A as the spindle and as an indexer (rotation in degrees) I assume that I would have to write the code as "circular interpolation" can this type of code be read by mach lathe? or do I have to execute it in mach mill?

any ideas???

Offline RICH

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Re: can threading be done in mach without an index pulse?.
« Reply #1 on: December 23, 2010, 09:06:37 PM »
natefoerg,

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my index pulse generator is cooked
Buy a new index pusle generator, CNC4PC has one which is not very expensive or make one up from parts. I use a Halls effect sensor to get the index pulse.
Save yourself a lot of a trouble.

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thread without an index pulse just "relying" on the spindle to keep in correct position
anything is possible, but, the answer on my end is NO / won't work since there is a lot more going on than you think

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stepper motor on the spindle for indexing

no problem

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stepper motor on the spindle for  threading

servo ok, but stepper is not good ...... even bad

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How can I get mach to believe that the rpm is 30 without an index pulse?

You need an index pulse in order for the threading cycle ( G32 or G76 ) to work and without it you will get an error and the program will stop .
How can Mach ever know what true rpm your running at if you never telll Mach via an input? Hope the question makes sense.

use A as the spindle and as an indexer (rotation in degrees)
Use two different configurations for the lathe one as linear ( step per unit ) and one for indexing ( angular / degrees ).

Suggest reading section 2 in Threading on The Lathe which can be found in Members Docs.
A stepper is bad for driving the spindle because as it's rpm goes up it will loose torque, the speed will not be linear as you increase it.
The speed is limited thus you wont get the spindle rpm's your after for turning work.

RICH





Re: can threading be done in mach without an index pulse?.
« Reply #2 on: December 23, 2010, 09:30:31 PM »
Yes, it all makes sense.

I did have a cnc4pc index pulse unit, which I somehow fried. I will have to buy a new one.

I think that I now know that I must have an index pulse.

I actually have this stepper running on a hardinge lathe. I normally use a vfd and 3 phase motor for turning ops. The motor is under powered and I have never been able to thread due to the spindle slowing so drasticly when taking a threading cut.

because I wanted to be able to index on the lathe anyway for milling flats etc... i decided to retrofit a stepper to the spindle that I can engage/disengage when I need to. (disengaged for regular turning, engaged when i need to index or thread)

I can just upgrade the motor and have enough power to thread with the lathes spindle motor, but that upgrade will cost me about a grand. I dont have 3 phase power and so all the spindle control options I have are sub-optimal and expensive.

I actually am running the spindle indexing stepper with a 3to1 reduction, so it takes a threading cut fairly well. I know it would suck for regular turning, so thats why I made it disengageable.

Offline BR549

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Re: can threading be done in mach without an index pulse?.
« Reply #3 on: December 23, 2010, 10:35:13 PM »
IF you have a big enough stepper threading is not a problem BUT you will have to LONGHAND the code. THe reason it won't stay synced using the thread cycle is mach relies on the index pulse to know where to start the thread. Useing the SPindle as A axis YOU program where you want the thread to start so it requires NO indexing. BUT remember you cannot use the threading cycles.

You can also use Swappaxis() to swap back and forth between Aaxis and Spindle on the fly.

Justa thought, (;-) TP

Offline RICH

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Re: can threading be done in mach without an index pulse?.
« Reply #4 on: December 24, 2010, 09:29:55 AM »
Planning is built into the threading cycle such that variations in spindle rpm are monitored and the Z axis movement is modified to maintain the lead.
It automaticaly adjusts the feed should there be spindle slow down to a fairly large % but no longer can it do a stopped spindle ( 100%).
That was done to help the hobby users with punny lathes and works, but......, accuracy of thread cutting will vary. Nothing beats a stable rpm and good lathe system.

The user should really experiment by trying different cutting methods to find out what THEIR lathe system is capable and adjust accordingly.
I won't go on as all is in the write up.

CNC thread cycle is complex in what it needs to accomplish and if the user pursues a work around he is on his owne.
 I say that since we spent a lot of hours fixing & refiining  the threading cycle and I just don't have any energy to address work arounds to something that works in the first place.

RICH
Re: can threading be done in mach without an index pulse?.
« Reply #5 on: December 24, 2010, 10:57:33 AM »
I will add some useful info

I was having some issues with my lathe and i was putting the blame on the Smooth Stepper (Mach freezing)

I changed to the PP well what can i say the RPM which was rock steady on the SS was all over the place with the PP the machine sounded much rougher using the PP also.

I finally found the problem, i had a USB pci card that was a magnet for all the crud floating in the workshop air and had built up over all the ports and circuit board.  >:(

So if you want good threading get a SS

Phil

The Good Thing About Mach3, Is It's very Configurable

The Bad Thing About Mach3, Is It's Too Configurable
Re: can threading be done in mach without an index pulse?.
« Reply #6 on: January 16, 2011, 03:13:51 PM »
set the spindle stepper up as a rotary indexer as A axis. if its 20 threads per inch then program z axis to move 1 inch while the the index axis is turning 20 revolutions along with a feed rate you can live with..
Re: can threading be done in mach without an index pulse?.
« Reply #7 on: July 01, 2012, 04:32:54 AM »
I have done threading with a stepper driven spindle before and it works.   However, it is slow and the stepper motor I used
did not have enoiugh power to thread steel threads.

Setting up my lathe to send Mach3  one pulse per revolution.
Jim
Re: can threading be done in mach without an index pulse?.
« Reply #8 on: July 01, 2012, 04:39:46 AM »
We are using the proximity switch which is fixed near the spindle and on spindle one steel material is fixed in such way that it
comes near the proximity switch once in one rotation and proximity switch generates one pulse for one rotation. On time of
pulse is 10% as compare of  OFF time of pulse. further these pulses are optically isolated and feed to MACH3 to measure the
Speed of spindle rotations.
but i cant thread properly up to 500mm length.

Offline Hood

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Re: can threading be done in mach without an index pulse?.
« Reply #9 on: July 01, 2012, 06:43:09 AM »
Santosh, Please stick to one thread instead of posting all over the place.
Hood