Tight threads

[Laurenr]

I am using a 12mm triple start tap and die for the cap to barrel connection. Is there a way to loosen the fit? I drill 11mm in the cap, and a 12mm tenon on the barrel. If I went to 11.5mm and say 11.75, would I get a looser fit, or just shallower threads?

 

[Carl Fisher]

Does your die have an adjustment screw on it? Most of mine have a small grub screw that you can fine tune the cut.

A smaller tenon would give you flatter profile threads but may not loosen up the fit. Worth a try though.

 

[duncsuss]

I am using a 12mm triple start tap and die for the cap to barrel connection. Is there a way to loosen the fit? I drill 11mm in the cap, and a 12mm tenon on the barrel. If I went to 11.5mm and say 11.75, would I get a looser fit, or just shallower threads?

I'm guessing your tap/die set is 12mm x 0.8 x 3 -- which would call for a hole drilled at 11.2mm for a "full" female thread.

I'd be inclined to drill 11.3mm (simply because that's a drill size I have!) but wouldn't go any larger than that.

On the tenon, I'd aim for 11.9mm to 12mm. As Carl said, there's usually an adjustment screw, if you back it out slightly it will let the die cut a smaller diameter thread.

A safer option is to put a little fine-grit polishing compound on the threads and work the two mating pieces against each other for a while. As a bonus, this will polish the threads so they look better once you wash the compound off :biggrin:

 

[mredburn]

The actual hole should be more towards 11.2mm or around .442 to .444 I make the tenon 11.88 to 11.9 Cutting the threads smaller may make it work but you would be better off to make the hole a little larger. If the threaded area is not very long on the tenon you can reverse the die after cutting the first pass the right way. I like Duncan drill the hole out to 11.3mm or its decimal equivalent. Although I bore mine after the 7/16ths drill.

 

[Laurenr]

Reverse the die? Explain?

 

[plantman]

Reverse the die? Explain?

If you look at your die, the side with the numbers on has a bevel to make starting easier, and the full threads don't go all the way to the end. The other side has the threads running all the way to the end. By reversing the die, after running it in correctly first, you will be able to run your threads all the way to the end of your tenon. I would also suggest putting a slight bevel on the end of your threads to make starting easier, and take a parting tool and make a small releaf on the other end so your threads seat properly and don't tighten up on you. A little silicon spray will help also on tight threads, Jim S

 

[duncsuss]

Reverse the die? Explain?

First cut using the die in its correct orientation. Typically, the etched size information is the "front face", and it has a taper on the first couple of threads.

After cutting the threads that way, reverse the die off the threads you've just cut, and flip the die in the die holder.

Then run through the threads again, leading with the "back face" -- which doesn't usually have any taper on the threads.

This will let you cut at full-depth closer to the end of the threads (rather than have them get shallower in the last couple of turns because of the taper.)

(or ... "what Jim just wrote!")

 

[Laurenr]

I will definitely reverse the die. Thanks to Victor, I have a 11.25mm drill bit on the way.

Thanks guys. You never disappoint.

 

[yort81]

I get all my Metric Taps and Dies from Victor Machine....The Dies are beveled on both sides of the die... but they are single point.. and not triples... should that make a difference?

 

[mredburn]

no its the way the dies are cut when they are made. I have the same dies from Victor and and on short threaded tenons I have to reverse the die to cut the threads. THe dies are cut with a taper to them inside so the full cut of the threads is at the back of the die.

 

[Robert111]

If the tightness occurs in just the last turn or two before the barrel is screwed all the way into the cap, the usual cure is to "kill" the first 1/16" to 1/8" of threads inside the cap using a drill bit about a millimeter larger than you used to drill out the cap for threading. For example, if you drilled the cap with a 11.25, kill some threads with something close to a 12.25 bit.

This of course requires a little preplanning so that your cap wall is thick enough to allow you to kill threads without seriously weakening the lip of the cap.