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Explain modified flank indeed threading

MazatrolMatrix

Aluminum
Joined
Sep 27, 2015
So I have a little difficulty visualizing what's actually happening here with a cnc machine. Is the Z starting point of the threading cycle starting further in each time so that the back edge gets clearence after the initial cut?
 
As said, the canned cycle simply adjusts the start point.

You can manually program any threading infeed you can envision using a one-pass thread cycle multiple times. Just change the start point each pass to chase down either thread flank however you want. This can be very useful for large or special profile threads.
 
Both Z and X start more negative each pass.
Yes, it's so only the leading edge of the insert "V" is cutting, this reduces cutting pressure considerably. It's equivalent to feeding in with the compound set to 29.5* on a manual lathe. The CNC just does it by increasing the Z start relative to the pitch.
There is also alternating flank infeed, where it alternates the Z offset + and - so you get the same effect, but it cuts on both flanks of the tool increasing tool life.
As said, the canned cycle simply adjusts the start point.

You can manually program any threading infeed you can envision using a one-pass thread cycle multiple times. Just change the start point each pass to chase down either thread flank however you want. This can be very useful for large or special profile threads.
Thanks guys!
 
Both Z and X start more negative each pass.
Not true for either axis. External thread X-minus, internal thread X-plus. Z-axis may or may not move more negative with each pass in Z depending on how the thread was programmed.

Also check out the threading technical information in an insert catalog to find out which shim to use for external threading tools and with internal threading bars large enough to have a shim. Shim used depends on thread diameter and pitch for that diameter.

Cutting on the leading edge only is normally the best way to help eliminate chatter. However, there are always exceptions to the rule.
 
Cutting on the leading edge only is normally the best way to help eliminate chatter. However, there are always exceptions to the rule.

I was a firm believer in this for years, literally. Then my Sandvik guy twisted my arm hard to try a straight-in approach, with their laydown fullform inserts.

It worked better. I was shocked. Now, this was with the laydown boys that probably have a slanted support base so they cut normal to the angle of the thread, which the on-edge type inserts don't do, but worth keeping in mind.

I would also say the 'modified flank infeed' refers to the back-and-forth type start points that's mostly good for larger threads, not just the standard 29* infeed angle.
 








 
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