Internal Threading Tool ?

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GeneT
Posts: 177
Joined: Sat Jan 04, 2003 9:36 am
Location: Albany, Oregon

Post by GeneT »

My most frequently used internal threading tool is just a normal tip, same as you'd grind for an external, held in a boring bar. This system works great.

Grinding HSS comes to you as soon as you relax and stop trying to make it harder than it is.

If your thread is rough you may be feeding in too much - a threading tool is a form tool, so forces are higher than you might expect. Feed slowly - maybe only a couple thousandths to start. Make sure your cutter is on center. Use lots of cutting fluid. If you're still cutting a rough thread your cutter doesn't have proper side clearance, or you're cutting some nasty junk metal.

GsT
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GadgetBuilder
Posts: 139
Joined: Thu Apr 12, 2007 2:34 pm
Location: Newtown, CT

Post by GadgetBuilder »

"Screwcutting in the Lathe" by Martin Cleeve has lots of good, readable info on threading.

I built Cleeve's simple jig to sharpen internal and external threading bits, shown here: http://www.gadgetbuilder.com/ThreadingTools.html

It takes about as long to build the jig and sharpen a bit as it does to sharpen a threading bit without the jig so it's well worth the effort. Resharpening a threading bit in the jig is quick, only a couple minutes.

The book also provides plans for a boring bar suitable for threading. It uses round HSS as an insert and this can be sharpened with the above jig.

John
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BadDog
Posts: 5131
Joined: Wed May 17, 2006 8:21 pm
Location: Phoenix, AZ

Post by BadDog »

I wouldn't say that an internal is just like an external, particularly one for a moderately smallish diameter. I also use the old style bars with square holes and small ground bars. But for ID work, only the top 60* profile remains the same as outside. For outside, the end clearance clears the thread fairly quickly, so a single tool can generally handle multiple pitches and diameters. For ID, the side clearance can be hard to manage. And especially for diameters below 1", the resulting point can generally only manage a limited range of pitches while stile retaining it's ability to support the cutting edge. I've got a 7/8-18 ID thread to do, both L and R. In spite of having several made up, none of my existing ID bits would manage this fine pitch at the ID. So I ground yet another. Maybe I work to hard to keep support, but with the exception of needing several, it has served me well enough so far. Sadly, my legs were killing me by the time I face the tube, bored the hole to within tolerance, cut a run-out with a specially ground bit, and then ground a new threading bit. So, I didn't get it done that night, but it's top of my list tomorrow.
Russ
Master Floor Sweeper
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