FC Posted January 25, 2007 Report Share Posted January 25, 2007 From an old American Rifleman Q&A: The V threads on Mauser 98 barrels are of British Whitworth form with a rounded crest and root, and the included angle is 55 degrees, not 60. Threads on three German Mauser 98 military barrels were measured with an optical comparator by the American Rifleman technical staff. Two of these barrels were from model 98 infantry rifles of WW1, and the other was from a carbine 98k barrel produced during WW2. All three barrels have 12 threads per inch, and the diameter over the threaded portion is 1.10 inch. Many Mauser 98 replacement barrels produced in the U.S. have threads with 60 degrees included angle. While these barrels are not an ideal fit, they are generally serviceable. Such barrels, when screwed part way into the receiver, can usually be moved from side to side somewhat since the threads are not mated perfectly with those in the receiver. There is almost no side ward movement with Mauser 98 issue barrels and others having proper fitting 55 degree threads. Link to comment Share on other sites More sharing options...
cold shot Posted January 27, 2007 Report Share Posted January 27, 2007 FC If the OEM barrels have a different degree of pitch, then how come the aftermarket doesn't do the same? Is there a reason they do it that way? Dave Link to comment Share on other sites More sharing options...
BobVZ Posted January 27, 2007 Report Share Posted January 27, 2007 I read once that the reason has to do with the loose fit remark in the preceeding quote. There is such a variance between different manufacturers that the looser fit allows aftermarket barrels to be attached to most actions without trouble. If the angle were 60 degrees the fit would be too tight. The other reason is(I believe) that in the US, 55 degrees is the standard for thread cutting bits. Now if I was having a blank turned, I think I would have the receiver threads measured and duplicated on the blank for a snug fit. Link to comment Share on other sites More sharing options...
ken98k Posted January 28, 2007 Report Share Posted January 28, 2007 I read once that the reason has to do with the loose fit remark in the preceeding quote. There is such a variance between different manufacturers that the looser fit allows aftermarket barrels to be attached to most actions without trouble. If the angle were 60 degrees the fit would be too tight. The other reason is(I believe) that in the US, 55 degrees is the standard for thread cutting bits. Now if I was having a blank turned, I think I would have the receiver threads measured and duplicated on the blank for a snug fit. I think you've got it turned around. Standard US threads are 60 degree. Link to comment Share on other sites More sharing options...
BobVZ Posted January 28, 2007 Report Share Posted January 28, 2007 kenak2, You are correct. I got my degrees flip-flopped. Thanks for the clarification. Bob Link to comment Share on other sites More sharing options...
Vladymere Posted January 28, 2007 Report Share Posted January 28, 2007 The article was true when written and is still true today. The US manufacturers use a 60 degree thread as it requires no special tooling. The manufacturers by cutting tools of the shelf. They do not make there own. Specialty made cutting toolls would be an extra costs to the barrel manufacturers. As I recall Brownells sells a 55 degree Whitworth cutting tool. I wonder what thread design Lothat Walther uses? You could probably get a properly threaded barrel from them. Vlad Link to comment Share on other sites More sharing options...
machinist1 Posted January 28, 2007 Report Share Posted January 28, 2007 I cut my barrel threads at 55 degrees. Just grind the tool bit to 55 degrees and change the compound angle to 27 1/2 degrees. The tighter the threads are the better the alignment of the barrel. I try to get the threads tight enough that the barrel stops short of contaction the front of the ring. If you buy prethreaded barrels you have no choice. Link to comment Share on other sites More sharing options...
donmarkey Posted January 28, 2007 Report Share Posted January 28, 2007 As I recall Brownells sells a 55 degree Whitworth cutting tool. Vlad Yes they do. Also one for straight threads like the enfield. -Don Link to comment Share on other sites More sharing options...
ken98k Posted January 29, 2007 Report Share Posted January 29, 2007 Does anyone have photos of a barrel being threaded? I just can't seem to figure out this 29 degree thing. Kenny Link to comment Share on other sites More sharing options...
donmarkey Posted January 29, 2007 Report Share Posted January 29, 2007 Does anyone have photos of a barrel being threaded? I just can't seem to figure out this 29 degree thing. Kenny If you leave your compound at 90 deg you would be cutting with both sides of the bit as you advance. With the compound angled you only cut with the front of the bit which produces a nicer finish. If that makes any sense? -Don Link to comment Share on other sites More sharing options...
ken98k Posted January 29, 2007 Report Share Posted January 29, 2007 If you leave your compound at 90 deg you would be cutting with both sides of the bit as you advance. With the compound angled you only cut with the front of the bit which produces a nicer finish. If that makes any sense? -Don I'm sure I must be doing something wrong because when I set my compound to 29 degrees it looks like this 29_degree.bmp Link to comment Share on other sites More sharing options...
gun nutty Posted January 29, 2007 Report Share Posted January 29, 2007 Wrong 29.5 degrees... You need to set it 29.5 degrees from the perpendicular, with perpendicular being with the compound rest set to do a straight plunge cut. Set the compound rest to a straight plunge cut. Read the indicator on the rest. It might be 0 degrees, it might be 90 degrees. Move the tail of the rest 29.5 degrees to the right. The indicators on the compound rest are reference points, and that's about it. You'll need to track things on your own. Link to comment Share on other sites More sharing options...
FC Posted January 29, 2007 Author Report Share Posted January 29, 2007 Yes, there are pictures here of a barrel being threaded. Try the search feature, top right. It is under the archives. I'll try to find it. I don't see it on a quick look, but I have those pictures, but can't get at them right now. Please remind me if I don't get this done today. Link to comment Share on other sites More sharing options...
ken98k Posted January 29, 2007 Report Share Posted January 29, 2007 I found some photos elsewhere on the web. I think I've got it now. Link to comment Share on other sites More sharing options...
gun nutty Posted January 29, 2007 Report Share Posted January 29, 2007 The first picture you have is correct for INTERNAL threads (please note the bore thread tool). Rather than driving the bit into the stock from the outside, you are pulling the bit into the stock from the inside. The second and third pictures have the rest set correctly for EXTERNAL threads. Link to comment Share on other sites More sharing options...
ken98k Posted January 30, 2007 Report Share Posted January 30, 2007 Gun Nutty, Don, Tony, Thanks guys, I got it now. I'm going to do some practicing this weekend. Kenny Link to comment Share on other sites More sharing options...
FC Posted January 30, 2007 Author Report Share Posted January 30, 2007 I wish I had written down who to credit for these pictures. Was it Belk? http://i39.photobucket.com/albums/e174/Ton...ns/machine1.jpg Link to comment Share on other sites More sharing options...
Limpid Lizard Posted January 30, 2007 Report Share Posted January 30, 2007 In the first set of pictures, the pictured first setting would be correct not only for threading internally but also for threading externally away from the headstock. LL Link to comment Share on other sites More sharing options...
sonic1 Posted January 30, 2007 Report Share Posted January 30, 2007 this thread goes along with the one about how to hold a rem. barrel..... this is the setup i use...you can take it out put it in the vice check the threads and if your tring to time the sights and you need a little more off the top ...just put the dog back in the same hole and you can pick the threads right back up.. lot easyer than tring to reclamp it and set the cut tool back in the right place... Link to comment Share on other sites More sharing options...
odies dad Posted January 31, 2007 Report Share Posted January 31, 2007 Excellent thread and excellent pictures! I have a Southbend lathe that doesn't have the thread index dial. Do I need this for a 12 TPI cut? I heard a rumor that I don't. So far for threading, I make a cut and reverse the motor to take the carriage back for the next cut while leaving the half nuts engaged. Putsy way of doing it but it does work. Do I dare unlock the half nuts and move back with the carriage then just relock the half nuts? Link to comment Share on other sites More sharing options...
Clemson Posted January 31, 2007 Report Share Posted January 31, 2007 Excellent thread and excellent pictures! I have a Southbend lathe that doesn't have the thread index dial. Do I need this for a 12 TPI cut? I heard a rumor that I don't. So far for threading, I make a cut and reverse the motor to take the carriage back for the next cut while leaving the half nuts engaged. Putsy way of doing it but it does work. Do I dare unlock the half nuts and move back with the carriage then just relock the half nuts? You can disengage the split nut and reengage it at will if you are cutting a thread that is a multiple of the lead screw pitch. In other words, if your lathe has a 6 tpi lead screw, you can cut 6 tpi, 12 tpi, 18 tpi, 24 tpi, ad nauseum, without worrying about when to engage the spit nuts. Any other thread requires you to use your system of leaving the nuts engaged, reversing the lathe to back the bit up, and then reversing direction again to make the next pass. For what it's worth, you can probably purchase a threading dial for a fairly reasonable price on ebay, etc. I have a 13" South Bend lathe, and it DOES have a 6 tpi lead screw. I can't speak for the other SB lathe sizes. Clemson Link to comment Share on other sites More sharing options...
milsurpcollector Posted February 1, 2007 Report Share Posted February 1, 2007 Im sort of confused, If you put the compound at 29.5 deg but the tool holder is still 90 deg to the work what have you acoumplished. I have a lathe and have cut threads and have had problems with the tools cutting both sides of the V at the same time. Whats the trick? Link to comment Share on other sites More sharing options...
sonic1 Posted February 1, 2007 Report Share Posted February 1, 2007 when you advance the tool for the next cut you advance the compound not the tool hold dial..this make the tool only contact on one side...making a better cut .......the tool goes in at an angle..... not straight into the part.. would n"t this be 27 1/2 ....half of 55 Link to comment Share on other sites More sharing options...
gun nutty Posted February 1, 2007 Report Share Posted February 1, 2007 There are two ways of increasing the depth: With the cross-saddle and with the compound rest. Feeding-in directly in at 90 degrees with the saddle (or the compound rest) is quick and a good way to do rough or quick thread work. Feeding-in at 29.5 degrees with the compound rest imparts a smoother finish on the threads. That 0.5 degree relief alieveates the roughness by putting pressure on one side of the thread only (I think it benefits by cutting in only one direction - direct feed is actually cutting on both sides of the bit and thus in two directions). I've done it both ways and prefer the compound rest for finished threads. If I am chasing threads afterward with a die for final form, I just use the 90 degree plunge cut. Link to comment Share on other sites More sharing options...
gun nutty Posted February 1, 2007 Report Share Posted February 1, 2007 OK... Technical answer from the Navy... "Ordinarily on threads of fine lead, you feed the tool straight into the work in sucessive cuts. For coarse threads, it is better to set the compound rest at one-half of the included angle of the thread and feed along the side of the thread. For the last few finishing cuts, you should feed the tool straight in with the crossfeed of the lathe to make a smooth, even finish on both sides of the thread." "When you set the compound rest in this position.... This permits the chip to curl straight in, and it prevents the tearing of the thread. since the angle on the side of the threading tool is 30 degrees, the right side of the tool will shave the thread smooth and produce a smoother finish..." So, feeding in with the compound rest limits tearing of the threads by improving cutting action. Link to comment Share on other sites More sharing options...
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