Just a heads up to any of you smiths out there: All my references say that a Sako L579 is supposed to have 1.00X16 Standard threads .870 long on the tenon. I have a job I took in here to rebarrel such an action, and I accepted it based on this information. I was dismayed to discover that this L579 has metric 25mmX1.5mm threads after I had already threaded the barrel 1.00X16. Also, the length of the tenon is reported to be .870 in length, but I found that this action is .865 to the forward most face of the bolt, which means that the true tenon length should be .855 long. You might want to make a note in your references that it is very possible for a Sako L579 to have threads in this configuration! Again, the threads required by this action are: 25mm X 1.5mm pitch, .855 long. There is also the standard small action Sako extractor cut, but that is expected if you have ever rebarreled these actions before.
Sako L597 tenon threads
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Saw this about a year too late... There was an earlier action, the L57, made for only 2 years as I recall. It used the metric thread tenon. The later L579 was supposed to all have used 1.00X16TPI tenon. Maybe you had one made as they were changing over. There is an L57 rifle in .243 sitting in my safe that I wanted to rebarrel. Guess I need to get a metric gear for my old South Bend.
Keep your plowshare and your sword. Know how and when to use them.
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Actually, I ended up finding out that the L579 was indeed made with two thread pitches, and since I asked this question, I have seen another metric L579 that was used by Browning. It could be that the one that I was dealing with originally came from a Browning rifle as well. I wonder if Browning bought up a bunch of the metric ones for cheap and made rifles out of them? I don't know. The rifle ended up coming out excellent though and was capable of 1.2” 10 shot groups at 100 yards. It wasn't a totally happy ending though. The rifle only weighed 6.5 pounds when it was done, and the client had be chamber it in a warp speed heavy kicking caliber that made it very hard to control. I furnished him with the rifle and two ten shot groups. He then proceeded to burn 500 rounds of handloaded ammo trying to duplicate what I demonstrated and we had several conversations in which I tried to tell him that in order to shoot the rifle like I had done, his form must be excellent. He would get frustrated, insisting that he knew how to shoot and he ignored my advice. He ended up selling the rifle to another fellow who thought a 6.5lb rifle would be awfully handy for shooting prairie dogs at long range without all the bother of hauling a heavy rifle out there to do the job. (sigh) Oh well. Some projects are like that.
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p. t. barnum had a point ...
re:: southbend transposing gears ( 127/100 combo ) ::: since the tenon is only 0.8 inches ( 13 threads ?? ) long, you might be ok accepting a near miss pitch with standard gear combos. in fact, if it were my own rig, you really dont need 13 threads anyway ...
ken
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I've had several jobs that required a metric thread. I was using an Enco 13X40 lathe with a set of metric gears. It was capable of cutting a metric thread but there was a problem whenever I disengaged the half nuts. As soon as you do that you loose the thread timing.
The problem is that an American lathe usually comes with metric and ingh gears but still has an inch leadscrew. I don't like threading up to a shoulder without disengaging the half nuts. One slip and you've ruined a barrel. I did find that you could re-engage he half nuts in the same place again if you put a mark on the chuck and a matching mark on the headstock. Then put a mark on the leadscrew and a matching mark on the gearbox. In order to reengage the half nuts in time you simply lined up the marks on the headstock and leadscrew and then reengaged the half nuts after you took up the gear lash in the system. It worked but was slow.
You can cut a metric thread with an inch leadscrew if you don't disengage the half nuts. If you're really fast, you can withdraw the cross feed at the end of the thread and miss the shoulder. Then shut off the lathe and leaving the half nuts engaged back it up for another pass. I never wanted to take the chance of ruining a barrel.
Another way would to make up a left hand metric threading tool and run the lathe backwards away from the shoulder. Either way, it's a lot of extra work.
The last job I did I just bought an adjustable metric thread die. I mounted the die square in the headstock and placed the barrel in the steady rest and pushed with the tail stock. I held the barrel from turning and turned the headstock by hand. I kept tightening the die until it had a good thread fit in the action. I ended up with a nice straight set of threads that way. It was a PITA but I got it done.
No matter how you do it, if you don't have a metric lathe it's a lot more work than normal. Maybe somebody smarter than me can figger out how to do it easier. I dunno.
Tom
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heh while showing off my vast 40 years of machining knowledge on a friend's smithy chinese lathe, i managed to cross thread a perfectly good shilen select match barrel ... seems the chinese wanted me to engage at exactly the same thread dial mark each time .... oops .
btw, it did good work ... especially after we rewired eveything and filed off the sharp edges . oh... and read the instruction manual ...
ken; slightly more humble now . ...
the shilen barrel ?? uh ...about an inch shorter now ... good for stiffness i told him ...
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Ken, It takes a big man to relate a story like that.
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For the record, I never disengage the half nut. Very very often the threads don't run right on a very worn lathe, and definitely when cutting metric threads. I engage the halfnut, and turn on the lathe to advance. When I get to the shoulder, I throw the lathe in reverse and withdraw the tool with the compound crank. Once trained to always do this, it becomes second nature and it seems wrong to do it any other way. Yes you have to wait for it to travel back to the starting point, but that's a great opportunity to brush on more cutting oil, advance your thread cut on the compound, or all sorts of simple tasks that the work waits on you to complete. Oh well, there's always another way to skin a cat.
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Yep, some mighty fine work can be done on a worn lathe if you know how to compensate for the wear.
My first lathe, purchased back in the late 60's, was setting in a bone yard near Detroit. It was a belt drive Clausing and had about .020” wear on the ways right in front of the headstock. The tailstock was worn so bad that I had to put shims under it to bring it up to level. If you wanted to do any real precise work with it you had to put a test bar in it at the length you were working at and adjust it up
It had belts in the headstock and only ran one way. I think those belts cushioned the vibrations in the lathe and it cut some of the prettiest looking threads in stainless barrels you ever saw. I used a hand ground high speed steel tool ground real sharp.
The hole in the headstock spindle was only 9/16 ths so I had to do all my barrel work between centers. I finally got rid of it when I couldn't find parts for it any longer. A guy gave me $500 for it and hauled it out himself.
I had made up a set of steady rest fingers with roller bearings mounted one the ends of the fingers so I could tighten up on the barrel and not scar it up. I pushed the chamber reamers with a live center in the tailstock. I got the barrel lined up with the tailstock by mounting a dial indicator on the barrel shank and indicated against the live center. By adjusting the steady rest fingers I could get the barrel running true with the tailstock. Thus a straight chamber the same size as the reamer.
When my barreling volume picked up, I spent the money for a modern gear drive lathe with a 1.5' spindle hole and never looked back. For this lathe, I made up a spider for the left end of the headstock spindle so I can get the skinny end of the barrel on center using a dial indicator mounted to the rear cover.
I'm skeered to slap my gear drive lathe from forward into reverse under power. I think it would bust something as there's nothing but that little plastic gear in there to give.
All those turning parts and the saddle can have a lot of inertia to overcome./images/emoticons/sad.gif');
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I might add that this old Clausing was almost as old a me. I started getting some chatter in it so I pulled the headstock out and replaced the bearings. One was marked 1945 and the other 1946. I replaced them and set it up for two tenths end play and it never chattered again.
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when i get bored i like to go to the gunsmith forums and watch the arguments on the best way to setup for chambering ... it can go on for months ...if it slows down someone will bring up reamer drivers ...i try to have some popcorn handy ...
ken
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Ken,
Just don't get me going on floating reamer holders. My pet peeve.
You'll need two bags of popcorn!! Ha
Tom
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My last reaming job, I made a “D” reamer and cut it by hand! Bring on the popcorn!
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My old Whitcome-Blasdale lathe never heard about metric. I would use my Starrett thread gauge and get as close to the metric thread as I could and cut a good snug thread. Not having a half nut dial I would cut a clearance gap next to the barrel shoulder to the thread root depth. In back gear plenty of time to stop and reverse wile nuts stayed clamped. Frank C.
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when i retired i put a cheap teco vfd ... variable frequency drive ... on my hobby sb 13-40 . such a fun toy ... i can adjust the rpm s down to a crawl .... being retired i can take a couple hours to cut a thread ....
i have cut some threads upside down and backwards, but it does seem strange .. i should practice that more. it does seem less scary . threading the regular way i always feel like i am playing on the interstate ...
ken
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This thread kind of got off course but we did all take notice of the problems with the Sako threads.
A VFD is what I need on my lathe. When I bought it, MSC gave the option of having an American motor substituted for the oriental motor. I opted for the American motor. Before I brought the lathe into my shop, I left it on the skid pallet and ran it for a half hour in different spindle speed to break in the gears and check it out. When I set it up in the shop, I started it up and it had a bad vibration. It shook so bad that if you tried to turn an OD on a piece of stock it would have a pattern on it that looked like fish scales.
I spent hours shimming up the motor on the motor plate and adding O rings on the mounting bolts etc.. I finally got it to turn an acceptable finish. Later I burnt up the start windings in the motor doing something too repetitive too fast. I went to see about having it rebuilt and found that it was a throw-away motor and it was cheaper to just buy a new one. I looked around and found a 1 1/2 hp American motor off an old air compressor in my shed so I put it on the lathe. It ran fine with no harmonic vibrations simply bolted to the motor plate.
When I went to mount the original Enco motor pulley on the motor I found that the motor I paid extra for had a metric size shaft in it. I had thought that I'd have an inch shaft in it if it was an American motor. To get it to work with the air compressor motor I had to turn a bushing for the motor to match the pulley.
Later, I found that if I had purchased a VFD and put it on the lathe I could have tuned the motor frequency to null out the harmonic vibrations in the lathe very easily.
Had I bought the lathe with the original china motor on it it probably would have run smooth with no jacking around.
You pays your money and you takes your chances....
Tom
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Off topic maybe but I learned a bit.. I have a 3/4HP DC motor and a controller that I want to put on my 9” SB. Infinite smooth variable power and I already have it. Still not sure I feel comfortable threading to a shoulder without disengaging the half-nuts though. On occasion, I'm easily distracted at the wrong time... The idea of choosing a thread that's close? Never considered it but I might just give it a try on a piece of scrap and see. Another thread I'd like to cut is 30TPI, as used on the Lyman 310 dies. I'm sure there is a combination of gears that will do it. So far, I just use the quick change gearbox. If it ain't on the box, I don't do it. BTW, I'm a self taught cobbler for the most part, didn't have a machinist around to bug.
Keep your plowshare and your sword. Know how and when to use them.
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Hello ?
Glad to hear you got something out of this discussion. That's what we're here for.
I've theaded maybe a hundred barrels in my career. I consider the barrel fit-up to be critical to the rifle accuracy. Studies like the one that Harold Vaughn in his book Rifle Accuracy Facts show that the thread quality and fit has a lot to do with accuracy. If there is any movement in the barrel/action joint it shows up in the group size. He found that a specialty thread called Spira Loc was the best for pulling the barrel shoulder into the receiver shoulder. Some accuracy gunsmiths have changed over to this type thread.
Having a good square barrel shoulder and a good clean shoulder on the action at a perfect right angle to the boltway is critical to good barrel lock up. A tight thread is of no advantage as the threads are not there to steer the barrel into the action but simply to pull the two locating shoulders together with sufficient force to withstand the strain that occurs with the gun fires.
It takes a minimum of 4 to 6 threads all acting equally in concert to achieve the tension that is needed. More threads may be better. Having a thread fit that is close but not exactly the correct pitch or thread angle is OK if you just want something to go bang. But if you do it right your chances of making a good shooter are much higher. Having the correct pitch on the barrel threads is important so that they all work do their share of the pulling. With mis-matched threads who knows how many are really working threads.
I have a switch barrel gun where I can swap barrels on it. I've found that I can remove one barrel and replace it with another. Then put the first one back on and find that the scope will only require one click to sight it in again. I don't make a tight fit on the threads and make sure that the crest of the male thread does not bottom out in the root of the female thread.
The correct tension on the joint achieved by torquing to a specific value is also important as Vaughn also proved. At one time we used to simply snap the barrel on tight using the barrel on a Stolle custom action. They shot OK but one time my buddy next to me had his come loose during a cast bullet benchrest match. It shot low all of a sudden. We tightened it up by hand and he finished the match but from that time on, we put them on tight and never looked back. Sometimes we have to learn the hard way.
Tightening up to a mark on the action and barrel is not a good way to replace a barrel. Every time the barrel is tightened the threads stretch a little and some metal on miniature high and low spots on the threads flatten out. Soon you will see that it will go past the mark before the tension is achieved. I had one customer who insisted I put marks on his switch barrel benchrest barrel and action. No amount of explaining could sway him. So I did it like he wanted. If the two surfaces that come in contact are true and smooth, the barrel can be turned past the marks but the headspace will always remain the same. Your simply looking at thread wear and stretch. The two surfaces on the barrel shoulder and receiver set the headspace.
I always thread up to a shoulder and don't have a run off area at minor thread diameter. I simply stop the cutter travel at the same spot each time and it forms a groove with no pitch to it at the end of the threads. Most actions have the first one or two threads relieved so it doesn't matter if you let the tool stop in that part of the barrel shank. The way I stop in the same spot is I set up a dial indicator on the ways that indicates against the saddle. As the saddle comes in contact with the indicator stem and the needle starts to move, you watch it and throw out the half nuts at the same spot. With some practice, you can throw it out within a couple of thousandths every time. Just try to stop it at the same spot in the indicator each time.
There's lots of ways to skin a cat but if someone is paying you to do it right, close enough is not good enough.
Tom
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Tom, Good posts! So what is your opinion of square threads, i.e. 1903 Springfields and model 70's? Ric
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Hello ?
Glad to hear you got something out of this discussion. That's what we're here for.
I've theaded maybe a hundred barrels in my career. I consider the barrel fit-up to be critical to the rifle accuracy. Studies like the one that Harold Vaughn in his book Rifle Accuracy Facts show that the thread quality and fit has a lot to do with accuracy. If there is any movement in the barrel/action joint it shows up in the group size. He found that a specialty thread called Spira Loc was the best for pulling the barrel shoulder into the receiver shoulder. Some accuracy gunsmiths have changed over to this type thread.
Having a good square barrel shoulder and a good clean shoulder on the action at a perfect right angle to the boltway is critical to good barrel lock up. A tight thread is of no advantage as the threads are not there to steer the barrel into the action but simply to pull the two locating shoulders together with sufficient force to withstand the strain that occurs with the gun fires.
It takes a minimum of 4 to 6 threads all acting equally in concert to achieve the tension that is needed. More threads may be better. Having a thread fit that is close but not exactly the correct pitch or thread angle is OK if you just want something to go bang. But if you do it right your chances of making a good shooter are much higher. Having the correct pitch on the barrel threads is important so that they all work do their share of the pulling. With mis-matched threads who knows how many are really working threads.
I have a switch barrel gun where I can swap barrels on it. I've found that I can remove one barrel and replace it with another. Then put the first one back on and find that the scope will only require one click to sight it in again. I don't make a tight fit on the threads and make sure that the crest of the male thread does not bottom out in the root of the female thread.
The correct tension on the joint achieved by torquing to a specific value is also important as Vaughn also proved. At one time we used to simply snap the barrel on tight using the barrel on a Stolle custom action. They shot OK but one time my buddy next to me had his come loose during a cast bullet benchrest match. It shot low all of a sudden. We tightened it up by hand and he finished the match but from that time on, we put them on tight and never looked back. Sometimes we have to learn the hard way.
Tightening up to a mark on the action and barrel is not a good way to replace a barrel. Every time the barrel is tightened the threads stretch a little and some metal on miniature high and low spots on the threads flatten out. Soon you will see that it will go past the mark before the tension is achieved. I had one customer who insisted I put marks on his switch barrel benchrest barrel and action. No amount of explaining could sway him. So I did it like he wanted. If the two surfaces that come in contact are true and smooth, the barrel can be turned past the marks but the headspace will always remain the same. Your simply looking at thread wear and stretch. The two surfaces on the barrel shoulder and receiver set the headspace.
I always thread up to a shoulder and don't have a run off area at minor thread diameter. I simply stop the cutter travel at the same spot each time and it forms a groove with no pitch to it at the end of the threads. Most actions have the first one or two threads relieved so it doesn't matter if you let the tool stop in that part of the barrel shank. The way I stop in the same spot is I set up a dial indicator on the ways that indicates against the saddle. As the saddle comes in contact with the indicator stem and the needle starts to move, you watch it and throw out the half nuts at the same spot. With some practice, you can throw it out within a couple of thousandths every time. Just try to stop it at the same spot in the indicator each time.
There's lots of ways to skin a cat but if someone is paying you to do it right, close enough is not good enough.
Tom Excellent post! I agree completely, although I have not read the book you mention, I have come to all the same conclusions on my own (except that Spira-loc thread. Never heard of that one, but I'll check it out). This is how you build an accurate rifle for sure.
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Ric,
I really don't know much about the design of them. If they were better than a standard thread I think you'd see them used more rather than an a few old design guns. I've cut them and they worked. Try to google acme threads vs. SAE threads that may shed some light. I don't recall Mod. 70's having square threads.
I'm not at home for the winter. Staying in my RV in AZ so I don't have access to my library at home.
Tom
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