Threading Help Please!
i am working on a suppressor for my Ar15, 5.56 x 45.
& yes i have the stamp in hand
i am using 316 stainless 1.5" x .065" seamless tubing.
here is the kicker, the tubing from onlinemetals does not seem to be perfectly round. i have been trying to get it to indicate & it seems impossible!
i have only been turning for about a year now so it could be me but if not what can i do to get it threaded right?
I suggest that you purchase a piece of slightly oversize bar stock and start from there.
Turn, bore and thread without removing the said piece from your chuck.
You will need to turn a mandrel to fit the ID. This will support the tube and hold the outside concentric with the centerline to allow it to be threaded.
If you are not sure of the EXACT outside diameter, since it is out of round, measure the OD at a number of points and average them to get the real OD, mike the wall thickness and use the estimated OD obtained the readings and subtract (2X) the wall thickness to get an idea of the correct mandrel diameter. As you get close, verify the fit.
The method used to make those tubes results in a pretty consistent circumference, but will not be precise, as in 1.500" diameter, but will likely be within 5 thou plus or minus.
thanks for the help guys.
while i could handle twice the $ for the solid bar (ouch!) i have a small, 9" x 24" or so i can't turn it in 1 setup so that kinda screws that approch.
i have cut a "mandrel" for the chuck, but i didn't go to the extent you suggested, will try that. but what can i do if i want to thread the other end ID?
i have thought about cutting a peice of stock for a press fit, pressing it into the end, heating it & maybe doing some lite "hammering" with a mallet or something soft. also would it be ok to thread it if it was only 1-2 thousanths off seeing that my lathe has some "flex" to it?
to help reshape it. what are your thoughts on something like this?
Could part of the problem be, over tightening the chuck jaws and distorting the work. Two short pieces turned to fit in each end with a shoulder and accurate center in each. Glued in place. Work then set between centers and a steady rest set to the work. Use a lathe dog on headstock end. Wire or otherwise Tye the dog so it does not move and effect the threading operation. To do the other end you will need to make a plug that threads into the threads and has a accurate center, then reverse ends in the lathe and bore thread the other end. These threads will be concentric with each other. This is but one way to do the job.
Cylinder tubing is consistant in both id and od. The only thing is its alum.
Thread both ends
If you make the mandrel with a taper you can knock the piece onto it, thread the end you need and then knock it off and end for end it and repeat.
You could also forgo the threading operation and turn an end piece that is threaded for the barrel then turn the OD of the adapter to match the ID of the tube, leave a shoulder on it, then heat the tube and press it on up to the shoulder, when it shrinks it will be on to stay. You could pin or screw the two together after just to be sure. If you make the barrel end out of stainless steel as well, just TIG the two together after the shrink fit. It will look like one piece for sure then.
Look here for a shrink fit demo:
not quite what you are doing but it's a start.
I adapted a .22 LR rifle barrel to fit my High Standard pistol. Needed a little larger diameter for the chamber end to fit the frame. I heat shrunk a sleeve onto the barrel. The first time I did not have the outer sleeve quite hot enough and had to saw it off by cutting a slit in it... there was no way it was coming off manually.... I tried. The next time I heated the sleeve more evenly and it is now one piece as far anyone could every tell.
here is an idea i am pondering.
how about i drill & tap the end piece 1/2x28 tpi & thread it onto a mandral i threaded. then turn it to fit the tube? would this give me a concentric line up?
thanks for the advice;
When I make sight extension tubes (bloop tubes) for target rifles I am using 6061 DOM tubing. There is usually several thou runout inside to outside and the ID/OD are not perfectly round. I really only care about the inside so I dial in the ID in the four jaw with "light" clamping pressure so I don't distort it. I then cut the profiles or threads required and put a 60 degree chamfer on the ID for a live center to run on. Repeat on opposite end. I do as much as possible in one setup. When the ID ends are done I mount the tube between centers and cut the OD so that it is now concetric to the ID, at least it is on the ends. If the ID hole wanders or is significantly out of round then the first operation would be to bore or ream the ID to a consistent dimension and then proceed. I've never had to do that and my tubes have only a small amount of runout if rotated on the muzzle tenon. Not enough to affect accuracy.