I have asked several folks how they cut their threads when the barrel and action and also several guys i work with and have heard a few differant ways to do it , I was just wondering if any of you other builders would mind posting how you cut your threads.
I personaly use the method I was tought in school by setting the compound to 29.5deg and useing only the compound to make the depth adjustments. I use two dial indicators , one setup to read off the back of the tool post that I use to ensure correct cut depth (don't trust the dials) and one setup on the back side of the lathe bed so that after I make a cut , pull out and bring the carriage back to the start point I go back past the origionla start point and come back to the part where the dial is set at 0 , this ensures that their is no slack in the screws and will start at the exact same place. I pick a number to drop in on and stay with that number the whole process ,my reasoning is that your enguaging gears and that one could have more wear than another and this could have some change on the thread , trying to make everything exacttly the same as the last cut except the cut depth , I also keep a log as to which number I dropped in on last and rotate the numbers so that they all get equal use (i'm very O.C.D. and this helps me sleep at night). when I get to the end of my cut I take the carriage out of gear and let it sit their before I pull the tool out , I don't make an undercut in the barrel I come back at the end and cut the raised portion to the same diameter as the bottom of the thread so that the action will mate up square.
I'm probably wasteing time with this process but like I said in my mind this is giving me as close to perfect threads as possible.
JJ, I too have a very similar way of threading. The only thing I could say that would make your threads a little more accurate, would be to leave the feed engaged through the whole process. Just when you get close to the end of the tenon you will need to have a good idea on when to turn off the lathe and let the tool bit coast, then use your hand to turn spindle until the desired length is cut.
Do you happen to cut a thread relief inside the action?
I was also taught in high school to use the 29.5 degree method. The teacher who was a retired journeyman machinist also taught us the straight in method.
This is where you use the carriage instead of the compound rest and just turn the dial in.
I have the luxury of having digital readout so I do not watch my dials.
If youre using HSS then the 29.5 degree method should probably be used, if youre using carbide you can go straight in.
I cant remember why he said or taught us both ways been a long time since high school.
Your dial method if you dont have dro is perfect keep using it.
Most of the lathes I have used have +/-.0005 some have even had +/-.001~.0015 chuck play when a force is applied perpendicular to the axis of the lathe bore.
The carriage also has some minute play +/-.0002 or so usually but you can adjust it so that its so tight you remove it all but then you wear out your way rub strips and way surface prematurely.
You can of course remove all play by tightening the way rub strips on the cross feed and compound rest.
I dont worry about it as I take around 7 spring passes to remove what imperfects are caused by tool deflection, part spring, and machine tolerances.
The biggest thing I worry about is getting the tooling bit perfectly perpendicular to the axis of the lathe bore. This ensures proper thread engagement.
If you are using the threading dial which it sounds like you are youre using it correctly and staying on the same number for the whole threading process in most cases.
I work on a very high precision lathe at work and cut on any even number or odd depending on what the call out is on the lathe plate, but the lathe is 75k so its tolerances and play are a lot more tighter. I only wish it had a larger bore its 1.5 now maybe a bit bigger 1.55.
Yep you are getting as close to perfect threads as you can barring the use of a thread grinder.
James; Good thread. (no pun intended) I'm self taught, so have always assumed that my instructor was a dummy. I set the tool angle with the little arrow shaped threading cutter grinding and centering gage. (Don't know what it's name is). Then set the compound dial to zero, run the crossfeed in to just barely touch the tenon, and zero the crossfeed dial. I use the #1 on my threading clock, and always wait for it to come back around. No reason. I've been told that you can use odds or evens, but haven't. When I have reset the crossfeed and compound for the next cut, I set the carriage about 1/2" to 1" away from the end of the tenon so that if I catch a crab engaging the leadscrew, I have time to pull it out before it can touch.
I do cut a thread relief with a parting off tool to just below the thread root diameter. I cut threads at 40 - 100 rpm. I use 40 rpm. 40 rpm gives me time to disengage the carriage without nicking the shoulder. I do just feed with my compound dial and I try the receiver a lot. I also record the compound dial reading when the thread reaches depth. A good machinest told me that he makes the last pass by feeding straight in with the crossfeed, but I haven't tried it.
I've been told that high speed tools will make a slicker cut, but I use a carbide tool and then lightly dress with a thread file.
I haven't had to recut a receiver thread, but I did make up a thread chaser tap for Remingtons from an old factory barrel that was a tight fit.
Probably more than you wanted to know. I do get long-winded.
On edit: added threads
Good hunting, Tom
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A big fast bullet will beat a little fast bullet every time
Last edited by specweldtom; 08-20-2008 at 06:01 PM.
I cut threads about the same way as you and Specweldtom
except for the 29.5 degree tool position.
I use carbide tools so I use 30 degrees on the compound and grind
a chip breaker on the threading tool so I can see the cut better.
Also I like cutting the tenon about a 1/4" long so that when the tool
contacts the tenon if there is any chater or slack it is taken up
before it reaches the finished threads. and this extra tenon is removed
when threading is completed.
Part of the relief is under the recoil lug giving me the most threads
possible.And once the action will start on the tenon(It still will not
make up) I chase the threads without any feed (Cross feed or
compound) normaly all I get is about .001" and if this is not enough
I will feed the crossfeed (not the compound) in .001" and chase 2 or
3 more times.
And I use 44rpm to 70rpm ( my lathe will not go to 40rpm).
I forgot to mention that I use the slowest RPM possible generaly 40-60 RPMs with a Kennametal top notch insert (NPR3-KC850) this makes for a very clean glassy thread.
I also like to use the older style Aloris threading blades but the Carbide makes superior threads in my oppinion an their is no worry about regrinding a tip to match what you had if you chip one , just turn the insert over or replace it ,they are setup with the optimal rake and chip breaker , kind like cheating !!
I love to watch CNC's run , never stops impressing me how fast and accurate they cut things.
Chad , Nesika uses CNC's to thread their barrels? , that must realy speed up building time huh?