cutting threads question

[Flat Tire]

Go easy on me
So I am new to owning a lathe and and when I started cutting threads I started with the tube already being a fixed size of 1.5" OD and .065 wall so ID of 1.37. I cut the threads on the tube first and I am cutting 24 TPI and then started cutting my end caps to fit the tube. I cut down the material to 1.40 before I started cutting the threads and then keep cutting the threads on the end cap until it fit tight, does the 1.40 sound like the right measurement ? The threads seem to be pretty tight but I am just seeking more info on doing it better. Thanks, I am just self taught.
When I did a final assemble I used epoxy everywhere to glue this thing together. I might crush it and make another just to get better at this game.

How deep does a 24TPI thread end up , if measured on one side ?

[jfk]

If you cut both of the caps first, you can use them to test fit the tube rather than the other way around. .140 sounds about right.

[Enfield577]

If you cut both of the caps first, you can use them to test fit the tube rather than the other way around. .140 sounds about right.

Yep that is what I do and I have made at least 50 cans now. It is amazing how cutting that last .002"-.003" frees up the thread.

I would say don't trash what you have done so far, I have had to sort out a few that have tightened up and have usually got away with using a bit of car valve grinding paste and metal polish (carefully) to just work the threads together and free it off

Cheers

[300sniper]

Machinery's Handbook, get a copy.

[T-Rex]

I do this
Tube ID + .01 (.005 a side) + 2(.868 * TPI) = Cap OD.
I skim (bore) the ID .005, a side, to make baffle entry a bit easier.

Example:
1.5" x .065 Tubing
1.5-.065-.065=1.37ID

1.37 + .01 + 2(.868 * 1/24) = 1.452 for OD of Cap

If you do it this way, you can make ONE cap first. Use this as your blank to fit both ends of the tube. Then, you can make the other cap and use the tube to fit it.
You can, also, make some blanks, from bar stock, for thread patterns. Depends on how dedicated or deep into suppressor building you plan on getting.

[sillycon]

http://www.efunda.com/designstandards/s ... finish=396

Assuming you're trying to use a "standard" thread, you can find the thread specs you require at the above link.

If you're a visual person, this (in conjunction with the data at the link above) may help: http://www.roymech.co.uk/images/Iso_thread_5.gif

Don't forget the correct root radius on your cutting tool. You can calculate the minimum radius here: http://theoreticalmachinist.com/Threads ... erial.aspx

Also, if you're using a "custom" thread pitch, you can use the above calculator to figure out min and max for both your internal and external parts.

Screw thread micrometers are also very useful here. The Starrett model you'd want for this application is a 585EP or a Lufkin 611. They can be found on ebay for under $60 if you keep your eye out (sometimes WELL under $60).

[Flat Tire]

Thanks

[V8Astro]

I do this
Tube ID + .01 (.005 a side) + 2(.868 * TPI) = Cap OD.
I skim (bore) the ID .005, a side, to make baffle entry a bit easier.

Example:
1.5" x .065 Tubing
1.5-.065-.065=1.37ID

1.37 + .01 + 2(.868 * 1/24) = 1.452 for OD of Cap

If you do it this way, you can make ONE cap first. Use this as your blank to fit both ends of the tube. Then, you can make the other cap and use the tube to fit it.
You can, also, make some blanks, from bar stock, for thread patterns. Depends on how dedicated or deep into suppressor building you plan on getting.

So trim the OD to 1.452 then start cutting threads?

[300sniper]

I personally would probably use a 1-7/16 20 for that tube size.

Start with the boy part about 1.43" od and thread it to the correct pitch diameter. Bore the girl part to about 1.385 and thread until the boy part fits the way you want it to.

Either way, you should have some sort of a spec to work toward before you start cutting. You really need to be able to measure thread pitch.

[yondering]

20 tpi is pretty coarse for a .065" wall tube. I'd be going the other way, and use 28 tpi, or even finer. I use 28 tpi myself.

[Flat Tire]

I personally would probably use a 1-7/16 20 for that tube size.

Start with the boy part about 1.43" od and thread it to the correct pitch diameter. Bore the girl part to about 1.385 and thread until the boy part fits the way you want it to.

Either way, you should have some sort of a spec to work toward before you start cutting. You really need to be able to measure thread pitch.

After reading this I am tempted to go 1 5/8" so I can catch more air not less.

[Scared_of_zombies]

20 tpi is pretty coarse for a .065" wall tube. I'd be going the other way, and use 28 tpi, or even finer. I use 28 tpi myself.

I agree and use the same TPI.