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Author Topic: Perfect Lathe threading  (Read 12235 times)

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Offline Hood

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Re: Perfect Lathe threading
« Reply #30 on: August 08, 2015, 08:05:21 AM »
Oh Terry you are funny indeed.
 You said what I was showing in the vid was simply Z synchronised to spindle, well there was a bit more to it than that. What I was demonstrating was something that was shown in the video you initially posted and hailed a massive breakthrough, now it seems because it has already been done, and for many years, then it is not so much of a wonder ;)

Ok using the spindle with an encoder and making the Z axis the follower, yes it can almost certainly be done. That would make rigid tapping  fairly good but you may hit snags with encoder resolution. My memory is a bit hazy as it is a long time since I messed with encoders and the parallel port but I seem to recall 25KHz was about your limit for the input frequency, that would mean either low RPM or low count encoders. Rigid tapping tends to be relatively slow RPMs but lathe threading is normally a lot faster, especially  if using carbide.
Now threading on a lathe, well it is, as I am sure you are aware, not just a matter of synchronising Z to spindle, you have to also start the synchronising at an exact point in relation to the Index and have to then de-synchronise at a defined point on the Z axis, you then again have to synch with the index on the next pass but also have to advance the X and Z axes the defined amounts to take the correct amount of material off.
Could it be done via the PP using the spindle as the master and the Z as the follower?
Yes of course it could.
Would it be easy?
No it would not.
Would it be a reliable method for Mach to do lathe threading?
Probably not as if it were then Art would have done so a long time ago.

Anyway looking forward to the video you are going to post showing exactly what the initial video, and the one I posted, are doing but all via your master/follower method via the PP ;)

BTW no rush, I likely won't be around for at least a  few days.

Offline BR549

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Re: Perfect Lathe threading
« Reply #31 on: August 08, 2015, 12:25:49 PM »
hIYA hood I was not implying that what you showed was trivial it is not.  What I described with M3 was exactly that a magic trick. Can it be done in mach3 sure the magic trick can be done.. I even explained how it could be done.   Can encoder threading be done from Mach3. I fully believe it can BUT it would be a BEAST to make it all work reliably as you stated WITH dedicated exact hardware and really NOT worth the effort to develope it for the 10 people that might actually use it. Mach3 is dead and will never be revived or worked on again so what would be the point(;-).

The odd thing is every since Mach3 allowed outside controllers every OEM said oh yea we will have encoder threading out next week. THAT was what 10 years ago ??

I guess next week FINALLY showed up at a very high price for a hobby lathe.

I think Art saw it the same way.  Single index threading CAN work depending on the machine and the precision of the thread that is required.  Hobby threads sure Precision Gauged threads not so much.

Same with rigid tapping in mach3 it CAN be done but not easily with a normal spindle setup as you do not have full control of the spindle. EVEN if you have spindle following you do not have TRUE rigid tapping as you can NOT control the exact stopping point of the spindle rotation so you cannot predict the EXACT depth it will stop at. You can get close but that is not true ridgid tapping.

Move to a step/direction SERVO spindle then it becomes a piece of cake for Mill or Turn. 1 Mcode to set from RPM mode to index mode function ( no swap axis involved)  and I can USE canned Gcode cycles to do the drilling and do the tapping. We have already made that work years ago.

I can do peck tapping and return from anywhere and retap the same hole again EXACTLY true and never tweak a thread.  BUT it also takes a properly setup machine to do it.  

 AND just a note I garrenty you it does not work in the way one would think it does (;-). It to is a magic trick.

SOME magic tricks are best left a secret. (;-)

(;-) TP

« Last Edit: August 08, 2015, 12:29:33 PM by BR549 »
Re: Perfect Lathe threading
« Reply #32 on: August 13, 2015, 01:28:59 PM »
there are really 2 types of controlled tapping.  

rigid tapping -> the z axis is geared to the spindle rotation and follows.
synchronous tapping -> the spindle is in effect a rotary axis and the spindle and z axis do synchronized move (exactly like a z - a move.)

Mach seems to use synchronous tapping.  (having a servo spindle that can position well enough to tap)

Linuxcnc can do both - although most use rigid tapping.  A spindle that can reverse quickly really doesn't over shoot much.  (but you do have to take it into account..)


how about gear hobbing...  :)



Offline BR549

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Re: Perfect Lathe threading
« Reply #33 on: August 13, 2015, 01:55:36 PM »
Mach3 can do gear hobbing as described in the Video and can do true Rigid tapping IF you have the hardware. Not just Z following the spindle down and back. True rigid tapping will have FULL control of Z depth not just a best guess.

Just a thought, (;-)