Messages

1

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 26, 2009, 10:30:41 PM »

Rich,


I need to get an internal threading tool, so where would I find the cobalt steel tools you refer to?  Enco? 

That live center is a neat project.  Strange is at may seem, I sometimes forget I have these tools that can make other tools.  As my wife says, "we can do _any_ thing".  Well, anything that fits in the puny/wimpy work envelope.   



Bob

2

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 26, 2009, 06:07:48 PM »

Hi, Simpson36,

Thanks for you inputs.  I'll answer one at a time.

Bob,

Couple tips . . .

To reduce the power needed and the flex on your single point cuts:

1) Sharpen the tool. Your photo shows a tool sharpened with a pretty rough wheel. You need a razor edge and a min 7 degree negative rake for that brass. While it is not a necessity, but you could benefit from using some cutting fluid also.

The tool is a brazed carbide cutter (not that negates what you're saying), and that's the way it came.  I didn't attempt to sharpen it, but have gotten some diamond polishing stones so that I can try.  I do use cutting fluid (Tap Magic), but usually make a point to clean it up before photos. 

2) increase the spindle speed . . . a lot . . . . I mean . . . .  a LOT

That's where this all started, wondering whether or not my wimpy steppers were able to keep up with faster spindle speeds.  They aren't.  But I wanted to make sure I could thread slowly with light cuts so I didn't blow $500 on better steppers and drivers only to find it still didn't work.  I have confidence I can get the more macho steppers and go faster now. 

Having said that, I'm a hobbyist and if I my lathe takes 2 minutes to cut a thread rather than 30 seconds, I really don't care.  A lathe doesn't seem very practical to me for things I can go get in the hardware store.  If I need some 1/4-20 screws, I'll go buy them.  I have some things that I will probably want to thread, but they're things I can't just go get, or get a tap and die for, like camera filter sizes.  If I need to thread a portion of some other assembly I'm making I want to be sure I can do that.  It isn't my main interest.

3) I don't know how the wizards or the Gcode macros function, but you can reduce thepower required significantly by only cutting one side of the 'V', if that is doable with the wizard/macro.


For cutting those tiny threads on soft material, unless you are doing it for the pleasure and/or the challenge, you should consider just getting a die holder for your tail stock and cut your threads with a die . . . much easier and faster.

My reference to something like an inch long 2-56 was for emphasis.  I have seen the pieces I'm working on deflecting under cutter load and I figure I need to find a way to fix that in the long term.  Some day I'll see it for real in a part I care about and want to make sure I can work around the bending.


All the best,
Bob

3

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 25, 2009, 12:27:28 PM »

Good for you Bob and have fun. 
You may want to check out the Canned Cycle - Threading G76 item 10.7.18 on page 10-16 of
Using Mach3Turn.
 
RICH
 

Thanks Rich, and especially thanks for all your help. 

I've put a few shots up on my pbase account to show a little of the process: 

http://www.pbase.com/montana_aardvark/image/108518311  is a scope shot of my RPM sensor output
http://www.pbase.com/montana_aardvark/image/108518321  is a "backed out" shot showing how the scope probe was attached http://www.pbase.com/montana_aardvark/image/108518327  is a gratuitous close-up inside the box.
http://www.pbase.com/montana_aardvark/image/108518329  shows my first successful pass of your GCode, 78-pass file. 

I need to read that section and not rely on the threading wizard.  I really don't know enough about this subject.  I need to learn everything I need to know to sit down with hunk of raw material and end up with a finished threaded "part".  That 1/4-20 screw I made last night was too wide at the far end, probably due to deflecting at the far end because of the force from the cutter.  So I need to use my live center - or some kind of center - and still get enough room at the end of the screw to do everything. 

The guys that cut tiny screws, 2-56s and smaller, have to know this.  If 1/4" inch brass rod bends, a 2-56 has to be like overcooked spaghetti. 


All the best,
Bob

4

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 24, 2009, 11:43:17 PM »

Hi All,

This is going to be a bit long, and I'm going to address a bunch of things.  

The big news:  I got it working.  

One of Rich's "78 passes" tests yielded a bunch of nice parallel grooves.  Then I did a 1/4-20 bolt.  I started with .250" rod and didn't realize that's too big, but I was able to cut the threads and it looked great.  When I turned the finished screw down to the same size as a bolt I had, that (of course) buggered up the thread profile.  So a nut doesn't fit it, but it looks gorgeous compared to everything I've been getting up till now.  

The problem?  The big problem was that I believe it was using the wrong polarity for my sync pulse!  It was "active low" and my pulse is active high.  Sheeeeshhh.  But to get to the point where I found that I had to take everything apart again and test all the hardware.  I got to the point where I was absolutely sure the hardware was right - or as sure as I could be.  Then I was convinced it was software or configuration.  I just didn't know what it was.  

Not having the "spindle feedback in sync" in software setup was a complication.  That didn't work, and threading would not have worked without it.  When I set the sync pulse active high, it started to work properly.  

I have a good oscilloscope, a Tektronix 475 if that means anything to you.  I looked at the pulse train out of my sync pulse encoder and it was as clean as can be.  No extra pulses, no glitches, no noise - nothing but clean square waves.  While I'm sure the kind of pulse encoder many were recommending would be really good, this one works as well as it needs to.  When I set the RPM rate low enough, I could watch the tape go past the sensor and see the pulse hit on the o'scope.  When I set the speed to 60 rpm in Mach (1 rev per second), I can measure 1 pulse per second on my oscilloscope.  When I set it to 600 RPM (10 PPS), I measured 10 pulses per second on the scope.  Likewise for other easily figured out speeds in RPMs.  Since Mach was telling me the right numbers, numbers I can verify at the spindle sensor, I had to conclude the whole path from the IR sensor through my Xylotex controller and into Mach must be good.  

So I dug back into all the configuration menus and found that "active low" thing.  I must have looked at it a thousand times.  I actually threaded some screws about a year ago, so it must have all been right then.  I have no idea how it changed.  

Right now, I'm pretty tired.  I will try to put up some interesting pictures tomorrow.  I'm hoping if anyone needs to learn about threading, this message "thread" might be helpful, especially if it's complete.



Bob

5

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 24, 2009, 08:50:34 PM »

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

6

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 24, 2009, 06:27:23 PM »

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

7

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 24, 2009, 03:11:22 PM »

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

8

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 24, 2009, 12:05:06 PM »

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

9

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 23, 2009, 10:00:14 PM »

RC,
Pulse setup here is just like in the manual with a single  slotted disc and the opening width based on the calculation they gave in the manual ( slightly under ). For the thread test i just posted, the max variation in rpm was 1.46%  and the turn readout will just flicker once in a while from the 100 to 99 rpm in the display. I don't even do an rpm check anymore with the speed indicator anymore as I trust what Mach is telling me.

I can fool wiith my punny lathe manualy, by hand,slowi ng the spindle down and seeing what happens and must say that Art took care of the hobbiest. As you well know, when it comes to thread tolerance, we haven't gone there yet in this thread.

I tend to agree with you that Bob's problem may be the index pulse. I am only quessing, but if the pulse triggers Z start at say a diifferent point of the mark on the shaft, then you will see it by the change of the scribed line. Will need to waite for Bob to get back from the garage.
In the mean time wine and pitza, moma's nice, so i hope he dosn't take too long.
RICH  

Rich,


I'm back.  

The final result looked like a frosted rod.  It did a thorough job of removing all of the marker, not a clean little spiral.  

Now to figure out why.

I readjusted my lathe Z axis and got it down to .001 backlash.  I take that out with backlash compensation.  My x axis had .0022 backlash (I'm in diameter mode - does that mean .0011 radius, or does diameter not matter in backlash??).  Whichever, I'm able to crank that out in backlash compensation so that a dozen back and forth moves on each axis (one at a time, of course) doesn't end up with the needle of my DTI off at all.  

But I did move the wires from the power cord and sensor apart and it was a noticeable difference.  The first few turns were everywhere, moving them made a difference and slowed down the wander.  It's still intolerable, but it did get better.  I did one wrap of the power cord on a big ferrite toroid I had lying around, but that didn't do much.  

I opened up the diagnostic panel, and it never showed my RPM off by more than 1%.  It never showed the pulse missing or anything.  It seemed perfect.  

Tomorrow, I'll re-wire that sensor.  I think I put a simple filter on the board, but I'll double check and add one if I need to.  


Thanks for all the help.
Bob

10

General Mach Discussion / Re: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group

« on: January 23, 2009, 08:06:35 PM »

BOB,
POST#2 MORE PIC'S

RICH

Rich,


Thanks a million for this.  It's fantastic.  I am carrying the file out to the garage to give this a try. 


Bob