First attempt at threading

[EmeraldPenn]

Well, I took the leap and bought the basics for kitless pen making. My first attempt at a section for a rollerball never quite got off the ground. I turned a 9mm tenon and cut exterior threads with a 9x.75 die, but when I went to thread it into a mandrel cut with a 9x.75 tap (in aluminum), the blank just spun - too small. The exterior threads on the blank and the interior threads on the mandrel look good, they just don't mate. I'm assuming it's operator error, but I'm looking for any advice before I start wrecking more blanks. Thanks!

 

[bmachin]

What was the hole size for your female thread? In theory it should've been 8.25mm. Practically 8.35 to 8.4 would be a little better. I would also probably undersize the tenon to maybe 8.9.

Theoretical hole size for tapping is diameter minus the thread pitch. In practice this is always too tight unless you way undersize your tenon.

Hope this helps.

Bill

 

[EmeraldPenn]

I seem to be having the opposite problem - the hole was either too big, or the tenon was too small - but I thought if that was the case, there wouldn't be any threads because there would be nothing to cut....

 

[bmachin]

You're right. Either the hole was too big or the tenon was too small--or both.

Your tap is going to cut threads from the smallest possible hole size--in this case 8.25mm--all the way out to its maximum thread depth--in this case 9mm. The only thing is that the threads will keep getting shallower as the hole size gets larger.

Your die is going to cut threads on a tenon from the largest possible size--in this case 9mm--all the way down to (guessing here) about 8.5mm. Again the treads are just going to get shallower as the tenon gets smaller

So if you drill an oversize hole and cut an undersize tenon, you can have two threaded parts that will not thread together or possible even touch each other.

My guess is that this is your problem. You might want to measure your tenon and if it is in the range of 8.9-9mm then it should be good to go and I would try remaking the female thread with a 8.3-8.4mm hole.

Hope this wasn't too murky

 

[magpens]

@EmeraldPenn

Hi Steve, and welcome to IAP (just in case I missed your Introduction when you joined) !!

You say above: " Well, I took the leap and bought the basics for kitless pen making. "

I assume that your set of "basics" includes calipers, one of the most essential tools.

It's not clear why you are having a problem. . But it is always a good idea to double check your drill and tenon sizes with the calipers.

 

[EmeraldPenn]

Thank you for all the replies! And that was the clearest explanation of the tap/die size relationship I've heard - I was wondering about exactly that.