threading question

[mike thomas]

If one is external threading at an angle different than 60, does one change the setting of the compound infeed from 29.5. How is this setting arrived at, and what would be the optimum infeed angle for a 55 degree thread. Thanks, Mike

[Ron LaDow]

Mike,
The 29.5* setting is to make sure that nearly all of the cutting is done on one side of the cutter, with just a 'skim' on the other side.
For a 55* thread, the same rule would apply, half the included angle minus a touch, so half is 27.5*, make it 27*. Obviously, the tool needs to be ground to the 55* total angle.
BTW, what sort of thread is 55*?
Ron LaDow

[mike thomas]

Ron, That is what I figured, I just wanted another opinion prior to running the bit in. I have been know to outsmart myself in the past. It is a Mauser receiver. It is common to just run the barrel threads at 60* and live with the slop, but I wanted to do it right. I picked up a 55* center gage from Starrett. Thanks, Mike

[artificer in metal]

The 55 degree thread sounds like a British Witworth thread form.

[Randy]

Yes, British Standard Whitworth threads are 55*. I believe it's pretty much obsolete now. Also, some Italian bicycle components have 55* threads. There are three sets of "standard" for threads in the bicycle industry. British (probably the most common) which is all inch, French is metric of course, and Italian, in which diameters are in mm and pitches are in TPI! Go figure.

[halfnut]

Yes, the 29.5 degrees is for a skim cut on one side of tool, taking most of cut with other side, chip curls out better that way. Yes 27 or 26.5 should work nicely. I do 29 degrees, not 29.5 myself, works fine.

Them englishmen, got them away from the whitworth threads with the unified standard threads, I have a BSA motorcycle which has mostly unified threads. It does have a few whitworths lurking here and there.

I've heard tell that when they adopted the metric system they went back to the whitworth thread form of 55 degrees for their metric bolts. Or so I have heard. My newer machineries is at work, I'd look it up, not in my 15th here at home.

[halfnut]

Looked at original post, Mike, are you sure it is 55 degree thread, got my copy of Gunsmithing out by R Dunlap. He doesn't specify just says vee thread. He also warns that these threads vary sometimes from one to another. Only time I have ever cut threads for a Mauser was on a Siamese Mauser that a friend of mine converted over to 45-70. I cut at 60, maybe it should have been 55.

I'll have to ask my friend Scotty about this one, he's a German relic enthusiast, mostly Lugers. Have a couple 3 around here, don't even want to unscrew the barrel to have a look.

[Ron LaDow]

Halfnut,
Racers get to deal with BSP tubing threads. The hexes are Whitworth, which means a 1/4" nominal is about 7/16". They're commonly refered to as British Stupid Parts.
Ron LaDow

[docn8as]

Halfnut ,et al the last 1/2dozen military mausers i have rebarelled were 55deg.whitworth looking threads....have cut both 55deg & 60 when couldnt find thrd bit /too rushed/lazy to grind another....felt better abt 55's but dont think any practical difference.....thrd must be easy enuf to allow barrel to register properly.........a lot of smiths in 60's cut 12 pitch 60's rather than metric thrd 55's ...12 pitch is 2 1/8 mmm .083333 & if i emember right, military mausers are 2mm. pitch .078
best wishes
docn8as

[docn8as]

mike ...maybe should mention ,98's are designed to butt up to INTERNAL shoulder ...because of that ,shd have .001 clearance on front face ......dont forget to allow for .0015 crush when wrenching up( unless u are godzilla ,) .001 is enuf....does not need to be near as tight as the one that came off!....check to see if both lugs bearing evenly, if not get out the valve grinding compound......if u want to get really involved there is trueing up thrds,lug seats ,shldrs,faces....bolt faces
best wishes
docn8as