Using the Cross Slide for Threading

I get much better thread form if I use the cross slide instead of the compound. I've changed the compound angle, changed inserts nothing seems to work better than using the cross slide.
 
I get much better thread form if I use the cross slide instead of the compound. I've changed the compound angle, changed inserts nothing seems to work better than using the cross slide.

Acme as well?

Paul
 
Acme as well?

Paul
Using the cross slide for Acme should cause no problems. The angle is much narrower than 60 degree threads. The cutter should probably be ground a little differently, though, so it does not rub on the trailing portion of the cut. Get your head deeply into both types of cuts and think about how the cutting tool is following the thread form with different tool advances.
 
Using the cross slide for Acme should cause no problems. The angle is much narrower than 60 degree threads. The cutter should probably be ground a little differently, though, so it does not rub on the trailing portion of the cut. Get your head deeply into both types of cuts and think about how the cutting tool is following the thread form with different tool advances.

Is that 5 degree on leading edge and 5 degree on trailing?
Bob could you just move up this way for a month or so....with your equipment . I think we could get some stuff done:)
 
Some of your Acme threads can have a high helix angle on the thread, thus requiring the cutting tool relief angles to be much steeper on the leading edge and nearly perpendicular on the trailing edge. Most of your preformed threading inserts available for cutting Acme threads have plenty of clearance ground on them to take care of most threads on most diameters. I have once or twice gone in and ground a bit off the bottom of the leading edge of the insert off to give it additional clearance if it was dragging. And you can tell if it was dragging by the finish on the thread flank and shiny spots/areas on the lower edge of the insert. And it will not feel right when cutting!
 
Is that 5 degree on leading edge and 5 degree on trailing? ..........

5 degrees should be fine Paul for most Acme threads. Again, it depends on the helix angle of the thread. You can calculate the angle. I'm rusty on the exact formula to use. If you get out your Machinery's Handbook and do some looking under "Thread Milling" I believe it is, the formula is at the bottom of one of the charts. Don't quote me on it, it's something like (pitch diameter) times pi times (1/2 pitch) = angle. Seems like there is a Tangent that is part of the equation. You guys can look and correct me on this.
 
Lead angle= Arc tan( Thread lead/Thread circumference)

For a single lead screw, Lead= pitch Double lead, 2xPitich etc.

So
Lead angle= Arc tan( Pitch/(pi*pitch diameter))
 
If you're cutting Acme or square threads, remember that at the root the angle's a lot bigger - lead angle will be arctan (pitch/(pi*ROOT diameter)) - this can catch out the unwary! Certainly caught me out...
You'll need to find the root angle then add a few degrees clearance on the leading edge.

Dave H. (the other one)
 
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