Thread Milling

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Bill Shields
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Re: Thread Milling

Post by Bill Shields » Wed Sep 19, 2018 6:24 am

motion repetition is not something supported by all software or controls.

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ctwo
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Re: Thread Milling

Post by ctwo » Wed Sep 19, 2018 8:16 am

If I recall, I think I had to put the repetitious code in a subroutine and call that. Have to look it up. Mach was doing some strange things with cutter comp until I added a Y motion. I never tried that feature before so need to look into it. I might actually try cutting some threads before January now :D
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Bill Shields
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Re: Thread Milling

Post by Bill Shields » Wed Sep 19, 2018 10:43 am

SOME controls, when activating G41/G42 and going directly into a series of more than 2 arcs (as you are here) at a sharp included corner, 'loose track' of where they need to begin without having a Y component in the initiation line.

It is better (for the general control case), to initialize cutter comp on a short line, then have a small TANGENT ARC that joins the G41 line to the thread milling arc series...

If you do this, you will RARELY find a control that chokes on the code.

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ctwo
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Re: Thread Milling

Post by ctwo » Wed Sep 19, 2018 2:34 pm

I could not figure it out because the tool would follow most of the initial small arc, but get closer to the edge and finally cross before it got to the large arc. Then, it fully reversed direction to pick up the large arc where it would cross at the left side...here is a figure I recreated from memory.

And not intending to derail the thread into a discussion about mach, but at least it's somewhat thread related. I figured I'd try to change the lead in and small arc to be tangent, so only 1/4 of a circle lead-in, especially since I'd expect my cutters to be closer to the hole diameter. Proposed paths shown in the figure, right side. My goal is to set up an Excel spreadsheet that takes the cutter diameter, hole diameter, and thread pitch and will produce the g-code. I could either rely on mach's cutter comp, or build it into my spreadsheet. My spreadsheet would produce a result as shown in the image. Mach will likely steer the cutter up (Y) from the lead in at the start to observe compensation on that path.
Attachments
mach3-g41-misfit.PNG
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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Bill Shields
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Re: Thread Milling

Post by Bill Shields » Wed Sep 19, 2018 4:43 pm

This is a case of the control not knowing what to do with cutter comp as described earlier.

You might find it easier tp use G42 and put in a negative value for the offset. Some controls will handle it better.

Another way to handle this is to break it into quadrants..some controls handle the LOOK AHEAD better if you do.

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Re: Thread Milling

Post by Geezer » Wed Sep 19, 2018 7:31 pm

This is just a sample, It works with my Mach3

%
O0
G17 G40 G80 G90
T1 M6
S2500 M3
G0 G90 G54 X0 Y0
G43 Z1. H1 M8
G0 Z-0.9833
G1 Z-1.0833 F30.
X0.0003
G41 X0.0002 D1
G3 X0.9496 Y-0.0287 I0.4747 J-0.0143 F21.509
Z-1. I-0.9496 J0.0287
Z-0.9167 I-0.9496 J0.0287
Z-0.8334 I-0.9496 J0.0287
Z-0.7501 I-0.9496 J0.0287
Z-0.6668 I-0.9496 J0.0287
Z-0.5835 I-0.9496 J0.0287
Z-0.5002 I-0.9496 J0.0287
Z-0.4169 I-0.9496 J0.0287
Z-0.3336 I-0.9496 J0.0287
Z-0.2503 I-0.9496 J0.0287
Z-0.167 I-0.9496 J0.0287
Z-0.0837 I-0.9496 J0.0287
Z-0.0004 I-0.9496 J0.0287
Z0.0829 I-0.9496 J0.0287
X0.95 Y0 Z0.0833 I-0.9496 J0.0287
X0.0002 I-0.4749 J0
G1 G40 X0.0003
G0 Z0
Z1.
M9
G28 G91 Z0
M30
%




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Bill Shields
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Re: Thread Milling

Post by Bill Shields » Wed Sep 19, 2018 8:56 pm

That's a good example of tangencies...but care that you wear offset cannot exceed 0.0001 -> which may not be enough

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Re: Thread Milling

Post by neanderman » Thu Sep 20, 2018 5:25 pm

A short video of this in use would be super cool. ;)
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Re: Thread Milling

Post by Geezer » Thu Sep 20, 2018 6:06 pm

I don’t have a video cutting the part.
Here’s the simulation and finished parts

https://www.youtube.com/watch?v=WWC3AjgiFd4

Leg Assy.JPG
Leg Assy.JPG (23.51 KiB) Viewed 489 times
Upper mount.JPG
Upper mount.JPG (22.85 KiB) Viewed 489 times
Foots.jpg

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