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Author Topic: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group  (Read 28379 times)

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Rich,


I guess it really isn't that important to my threading issue, I just wanted to understand what I saw.  I turned off the backlash compensation and commanded the X axis to go 0.2" so it would go one full revolution on my 0.100" per turn DTI.  I measured it being about .0022" off, entered that in the backlash compensation, and now it hits the indicator "dead nuts" on 0.100" every time, each way. 

So I started wondering did I have .0022" or .0011" and Mach was outsmarting me?  No big deal, because (like I say) I know by watching my DTI that I can go back and forth and that needle never misses the zero mark by a tenth (.0001).  I think X axis has to matter less than Z for threading.  Yes, the depth of the thread may be wrong, but you can make more cuts if they're in the right place every time.

Now off to look for a way of shielding or filtering that feedback wire....



Thanks,
Bob

Offline RICH

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Bob,
Try wrapping some Al foil neatly around the wires or slipping some brade over them, also twisted pair adds
impedence to noise, and a tight loop over a pencil or such can assist also.

As far as the X axis not as important as compared to the Z. Not when you start cutting some of the small stuff as
there's not much room for error in a nice thread. And I don't know how to pick-up a thread in CNC threading.
RICH

Offline Hood

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Rich, running the thread again if you have it still in the chuck is not a problem, if its been removed from the chuck then that is not going to be an easy task to get set up for a re-run.

Hood
Bob,
Try wrapping some Al foil neatly around the wires or slipping some brade over them, also twisted pair adds
impedence to noise, and a tight loop over a pencil or such can assist also.

As far as the X axis not as important as compared to the Z. Not when you start cutting some of the small stuff as
there's not much room for error in a nice thread. And I don't know how to pick-up a thread in CNC threading.
RICH

Not much difference. 

Rummaging around the house, I found I had a MIDI cable that I haven't used in ages.  This is 4 conductor, with a shield wire (5 conductors in all) and aluminumized Mylar ground shield around it all.  So I hooked up three ground wires, power and signal.  Brought them up to the other end of the harness (plugs into my box) and spliced it there. 

I just don't see much difference.  Maybe a bit cleaner, but nothing to write home about. 

I guess I'll plug the motor into a completely different outlet.  I had to do that once before.  Right now, everything is plugged into an UPS. 


Bob

Offline RICH

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Bob,
The easiest way to check it would be with a scope to see if progress is being made, as you do only .....ONE .....
change at a time, .....even minor....., otherwise you may be chasing you tail around ( sometimes just black magic works and i can't explain that ). The best approach is to eliminate the source but then sometimes that's not even possible. For the amount of time invested, i would just change to the simple index as stated before, get it running, and then go back and see if you can get your pick up working.
That's my nickle,
RICH

Offline RICH

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Hood
After removing from the chuck is what i ment.  One of these days i'll fool around and try post removal.
Fortunately, for what i do, only a penny of material is wasted. Pretty soon i will have enough for
ball screws.  :)
RICH
Bob,
The easiest way to check it would be with a scope to see if progress is being made, as you do only .....ONE .....
change at a time, .....even minor....., otherwise you may be chasing you tail around ( sometimes just black magic works and i can't explain that ). The best approach is to eliminate the source but then sometimes that's not even possible. For the amount of time invested, i would just change to the simple index as stated before, get it running, and then go back and see if you can get your pick up working.
That's my nickle,
RICH

Rich,

I think I spotted something odd.  You said a while back

1.In config>input signals> index is checked and port & pin iis assigned along with proper pulse setting
            "  >spindle setup> in special functions box, the spindle feedback in sync is checked and  also
                                       spindle speed averaging

I did not have the "spindle feedback in sync" button clicked.  When I did this, running your 78 line program, it moved very oddly.  Sort of step, sit a while, step, sit a while, and so on.  It was so odd I stopped it without running it any length of time. 

Any idea what might be going on??


Bob

Offline simpson36

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Wow, this is turning in to quite a thread . . . yuck, yuck.

There are two ways to single point threads; a straight plunge, or cutting only one side of the 'V', which I would imagine would be far better for the 'puny' lathes. In either case, backlash is irrelevant as you always cut in the same direction. Your error far exceeds the backlash so it would be an academic discussion even if you were improperly cutting the 'near' side of the 'V' where backlash might come into play.

Having seen the picture of your pulse trigger setup, I believe that is your suspect. The color is not as relevant as the surface, I would imagine. You have shiny tape on a small radius. It is probably only slightly less reflective than the shaft itself. Perhaps even more so to IR light.  You can see the highlight on the shiny black tape even in your photo. That's also probably what the sensor is seeing.

To support the consensus, I'll add that I also use a slotted disk. Single round hole of about 1/4" dia. Mach seems extremely accurate picking up deviations of a few RPM at speeds over 6,000 and also reading steady at slow speeds.

My sense is that at very low speeds like 100RPM, more than one slot would be beneficial, but it appears from several people who have posted their successful threading experience, that one pulse is sufficient.

There is enough information now to suggest that moving your black area to the face of the disk instead of the shaft as suggested by RC (Overloaded) would probably solve your problem. You also should use flat black, and not something shiny. Even better, as has also been suggested, go with a slot or blade arrangement for the most positive trigger. 

As a minimum, strip off that shiny tape and spray some flat back paint in it's place,( and you might consider making it significantly narrower as well) - or - (for diagnostics and not as a permanent solution) take some 600 or finer grit wet/dry and at least scuff off that shine!
« Last Edit: January 24, 2009, 07:15:38 PM by simpson36 »

Offline Hood

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Bob
Sounds like Mach is not seeing the Index properly if it is jittering about like that.

Simpson
 Art did a bit of a write up regarding Index versus Timing , if I remember correctly ,  it all boiled down to if anything Index was best.

Hood
Bob
Sounds like Mach is not seeing the Index properly if it is jittering about like that.

Simpson
 Art did a bit of a write up regarding Index versus Timing , if I remember correctly ,  it all boiled down to if anything Index was best.

Hood

But Mach reports a solid RPM reading, and the threading diagnostic plug in says 1.39% maximum speed error.  Does that report properly if the pulse is missing? 

BTW, the jump does seem to occur every RPM. 


Bob