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Author Topic: Questions on Threading With Turn on Sherline - From Yahoo SherlineCNC Group  (Read 27821 times)

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Offline simpson36

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Rich,

Thx for the link. This excerpt from Art's explanation defines what I was talking about exactly:

"The second possability is a slightly varying index pulse in time.Ive seen
many sensors, ( my own included) that cause RPM variations due to being too
sensitive and varying in time from pulse to pulse. Adjusting sensitivity
solved my own issue with that."


I'll read thru the entire thread when I have more time.


Hood,

Thanks again! Obviously I have to do some more homework on the Smooth . . .  uh . . . 'driver' board before discounting it! Thinking a bit further thru the idea, the servo drivers from Gecko (for example)  take the same inputs as their stepper driver? And SS is generating those inputs, so it does not care what is being driven? Is that basically the crux of it?


BTW< I commend you both for infinite patience with an endless stream of stupid questions from we newbees.

Offline Hood

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Simpson,
 yes basically the SmoothStepper is just replacing two parallel ports and actually gives you an extra 6 inputs  on top of that, of which 3 are differential. Another great thing about the SS is that you can use the Index pulse from an encoder for the spindles Index and hopefully soon Greg will get a chance to work on full encoder integration which will tie the spindle and feed together, I think Art mentioned that in the write up but have not reread it in full for a while. The SS puts out a very nice pulse right up to 4MHz and I seem to remember Greg thinking 8MHz would even be possible, but dont quote me on that.
 
Hood
:) 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




Offline simpson36

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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.

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

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.
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. 

Quote
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.

Quote
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

Offline RICH

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Hi Bob,
Just a few comments for what they are worth.

Carbide has it's place, but for the wimpy and punny I'll go with razor sharp cobalt tools anyday.

Now that you got it running, play around with it some and a 1/4-20 thread requires small depth of cut.

Doing small threads can be a challenge because there is not much room for error becuse of your machine or setup.

To help with the spring of small diameters you may want to make a small live center like the attached.
The tip is replaceable or a custom one can be made ( ground rod was used). The one i made has three small bearings in it. Stock was placed in chuck, the front piece turned true on the outside, drilled and reamed thru for drill rod removable tip, match marked reversed in the collet chuck, and bored for the od of bearings, the beariings and tail shaft pressed in.
It is rigid and turns true. Better than some of the ones you can buy.

Now the one model maker at the model show last year does threading over 300 tpi and makes his owne taps and has written some articles in magazines about it. Small stuff and makes a 0-80 look big!

RICH

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


Offline RICH

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Bob,
Emco, Little Machine Shop, MSG, J&L Industrial supply.
Just a few places that come to mind.
 For internal threads i like the boring bars made by Bokum. You can regrind them  if your carefull and can find other manufactures which make similar.
RICH