peanut Posted June 30, 2007 Report Share Posted June 30, 2007 Hello All, I am close to getting my SB Heavy 10 back together. Here is a link to the photos I have taken thus far. It is a mix of parts. It is on casters until I find a permanent place in the garage for it. http://s158.photobucket.com/albums/t88/Hugh98/?start=all I made the spider on the tail of the spindle, nothing fancy, but it works great. The second thing I want to make is a mandrel for a LR small thread receiver. On page 179 of "Mauser Bolt Actions", Mr. Kuhnhausen refers to an inside thread caliper to measure the inside threads. Is he referring to a spring caliper? Any guidance will be greatly appreciated! Thank you, Hugh Link to comment Share on other sites More sharing options...
Ron J Posted June 30, 2007 Report Share Posted June 30, 2007 When I get home I'll check the book and try to figure it out. I may be able to help. Being in the threading industry for 20+ years I'll be surprised if even Kuhnhausen has an accurate way of checking an inside thread that any of us could afford. You mentioned LR recvr with SR threads. I am working on a Turk, my first Mauser. The threads were so bad inside, we made a fixture, bored it out and single pointed large ring threads in it. You can move forward quicker by threading a short plug on the lathe with a shoulder big enough to seat against the recvr face but not hit the inner torque shoulder. Maybe .500" from face to shoulder. Thread this until the recvr screws on with a good fit. You can get a cheap set of thread wires to measure the plug. They have instructions. You'll need a 1-2 inch mic to mic over the wires. You do not need to do all the math in the instructions to figure P.D. Just make your mandel to the same measurements. Now if you want to find out if the thread is drunk like mine was, take a light skin cut off the recvr face while fixtured on the mandrel you made. Put the plug back in the lathe and indicate it so the shoulder is running true. Screw the recvr on and see if it touches all the way around with a feeler gage. If it does you're luckier than I. If it's out more than you can live with, mark the plug shoulder & recvr where the gap shows. Unsrew off and face .040" off the shoulder of the plug (1/2 turn of a 12 pitch thread). Screw the recvr back on and see if the gap is in the same place on the plug. If it is, the thread is running on an angle to the center line. If the gap moves 180 degrees like mine the thread has a bad lead and I could not figure out a good way to repair it. Mine had about a .004" gap. Taking about .015" off the P.D. of the plug only lowered it to .003". The barrel thread would have to be very undersize for the shoulders to square themselves. A thread with a drunken lead can fit tight on something, with only 25% contact in spotty areas of the flanks. It's a b!t&h! FYI we did everything with a 55 degree bit. That's why I feel that a caliper type gage that measures inside threads is almost useless. It tells you one thing about one spot. This is alot of crap, I know. I hope it helps and I didn't waste your time telling you things you already know. Ron Link to comment Share on other sites More sharing options...
peanut Posted July 1, 2007 Author Report Share Posted July 1, 2007 Walnut, Thanks for the great info. Not a waste of time at all. I am just a novice, and learning all the time. How did your threads turn out? Have any pictures? So the fixture held the receiver in the chuck? I would like to see the jig. As soon as I get my idler gear mounted (waiting on a stud and bushing) I will be able to run the gearbox and feeds. I will probably then discover a whole new set of issues that have to be addressed. I'll cross my fingers. By the way, do you know of an online source for a 55 degree screw cutting tool bit gauge? Enco sells a 60 degree, but I can not seem to find a 55 degree. Thank you for the reply. I will start hunting for the threading wires and let you know how it turns out. Hugh Link to comment Share on other sites More sharing options...
z1r Posted July 1, 2007 Report Share Posted July 1, 2007 Starrett makes the 55 degree gage. Brownells sells em. Nice job on the lathe. Link to comment Share on other sites More sharing options...
Ron J Posted July 1, 2007 Report Share Posted July 1, 2007 We got the 55 deg tool from Brownells like Z said. The thread wires will be cheapest at Enco. Probably 20 bucks a set. You'll curse me to death until you get the feel of holding 3 wires spaced correctly and mic over them at the same time. I'll try to sketch up something as I don't know how to post pictures yet. It's not the easiest thing to make and cut internal threads, but if you can build a lathe from the ground up as nice as yours is coming, you'll do fine. Link to comment Share on other sites More sharing options...
Vladymere Posted July 1, 2007 Report Share Posted July 1, 2007 Could you make a casting of the inside threads using cerosafe, unscrew it when it cools and then measure the casting? Vlad Link to comment Share on other sites More sharing options...
z1r Posted July 1, 2007 Report Share Posted July 1, 2007 You guys are making this much harder than needed. You know the maximum thread size, now using your machinery's handbook, calculate the minimum. be sure to use the formulas for 55 degree whitworth form. Link to comment Share on other sites More sharing options...
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