Issues threading with dies

[PAturner]

Hi,
Attempted my first kitless pen and ended up screwing up every single part. Section, body, and cap. Luckily the material I was planning on using for the cap and body can be salvaged for a re-try later.
Anyway, what I kept having an issue with was threading the tenons using a die.
On the section I used acrylic, and had less trouble. However, starting it was still an issue. I'm holding the die in a homemade fixture chucked in a Jacobs chuck. It's quite stable, so that's not an issue. I just can't seem to start threads right. On the acrylic, the beginning is rough, but then the threads cut fine so I just part off the nasty stuff. When I tried threading ebonite, the die ended up just grinding the tenon down, creating no threads to speak of. Plenty of lubricant was used. Any idea what's causing this?
I did some reading and found that dies are supposedly "designed to cut 75% of a thread", and so to make the tenon smaller than the intended thread diameter. I was using a 1/2" die, and the tenon was a couple thousandths under. Could that be the issue, and all I need to do is cut the tenon a little smaller?

 

[magpens]

I believe that would help, Sam

 

[thewishman]

My tools and notes are across town, so this is from memory (haven't cut threads since the 2015 MPG demo.)
There is a front and a back to the die - the front is the side with the writing on it - it will have a slight concave area where the threads are cut back just a little. If you thread with the other side, it starts right out with regular threads.

Could it be a die made to cut left hand threads?

 

[plano_harry]

If you are threading from the face side, as Chris mentioned, then your tenon is probably too large. Imagine that if it were undersize, the die would thread on effortlessly, so you need to cut your diameter down a little until you can get a good starting bite.

 

[farmer]

Treading

Use bag balm on the threads to lubricate the wood to keep it from tearing ....

Or buy a metal lathe and cut the threads with a live cutter..

 

[frank123]

Smaller tenon diameter (even a few thousandth makes a difference) and it doesn't hurt to put a slight chamfer on the end of it so the die isn't making a full diameter from the start, just sort of gradually engages the full diameter (I'm not talking about a large taper, just a small chamfer like you would see on the end of a bolt if you looked closely).

Some brittler materials are more prone to chipping out when you thread them, but Ebonite has always threaded easily and beautifully for me.

 

[KenV]

Sam,

If your die is "cocked" just a bit, it will shear off the threads. The chance of that happening with a Jacobs Chuck is good unless you are carefully setting and checking with a dial indicator.

 

[low_48]

I have no idea what your skill levels are with fixture making, but "homemade" would be the first thing I check. Plenty of references on line for cutting the threads by percent of engagement. That will also tell you what diameter to turn the tenon.

 

[Curly]

In addition to what's been said I think the main reason you may be having issues is the thread you picked is it's more coarse than those usually used. A 1/2 x 20 UNF is approximately .050" from crest to crest where a metric of 12mm x .8 or .75 is approximately.030" from crest to crest. That means the Imperial die is removing 60% more material than the metric die. Even worse if you are using a 1/2 X 13 UNC die.

If you want to try with what you have before investing money in special taps and dies try making the tenon .008 undersize or even a little more if testing indicates the need. Also do the 1/2" die work before tapping the smaller thread in the part.

 

[JLL]

Have a look at this - should help http://content.penturners.org/library/general_reference/taps_dies_kitless.pdf

 

[mredburn]

Also are you beveling the end of the tenon 45 degrees? If not use a file or other tool to form a 45 degree bevel at the tip of the tenon and if possible round it just a bit.
cut your tenon about 98% of stated diameter.

 

[Penultimate]

Greetings
If you want to use a half inch die I recommend changing to a fine pitch like 32 tpi. I tried a 1/2-20 and the threads were too course making a deep thread. When I switched to 32 tpi it worked great. If you have to make an internal thread under the 1/2 thread both need to be fine pitch.
Good luck

A real die holder may be a good investment.

 

[farmer]

Wood threads

This weird .
If you look up wood taps and dies that are all coarse.
I do wood threads inside the shafts on my pool cues with custom made 3/8 x 10 taps
Some taps are 3/8 x 8 .

As long as I lube the tap or die and work the tap back and forth . 1/4 turn at a time then work the tap or die back and forth .

make sure the tap or die doesn't load up with saw dust .

 

[Curly]

Farmer I believe, from the original post, that the OP is working with acrylics and ebonite and not wood to make his pen.

 

[More4dan]

I've had much better luck getting the die to bite by reversing the die with the face with the writing turned away from the work. Coupled with a 45 chamber on the end this seems to work better for acrylic and ebonite. Try it on some scrap.

Danny

 

[Joey-Nieves]

Well there are many videos out there, but They sort of miss some minor details that if you don't catch them while your watching well you don't get concept.

Here is a tip, for my example lets make a 10mm thread. I use a 10mm wrench to gauge the size of the tenon I'm making for my male thread. Now if you are going to do a fine thread , .75 or .5 you need to be just a hair shy on 10mm. A wrench is 10.2 or 10.25 mm because it has to fit easily on the nut, so this is where you use your calipers. I cut a small tenon about 1/32" at the beginning of my tenon, this serves the purpose of allowing the die and any other thread an alignment before you actually star threading, if you look at most sections on the kits you will notice this to. At the end of were my threads will end I make a small tenon, less than 1/16 because the die will not butt perfectly with the end and the cap will not go in all the way, also I do it before I thread because if you do it after there is the chance that the waste and the excess waste will ruin all the work you just did.

For there cap, there is some info you need First the 1mm less drill bit rule is only for threads that are x 1, Ex. a 10mm x 1 would require a 9mm drill bit if you use a 9mm drill bit on a 10mm x .5 thread it will be to lose. The proper drill bit at 75% would be 9.5mm (100% thread specification is only 5% stronger than a 75% thread specification but requires 3 times the torque to produce.) once you drill your hole cut a small notch to fit the small tenon you made on the male thread, go slowly, backing out every 1/4 of a turn and use plenty of lubricant, No matter how much time takes it will be much faster than having to start over again.

For more information on drill sizes this calculator should help.Guhring, Inc. - Tap-Drill

Joey

 

[farmer]

Well shoot

Farmer I believe, from the original post, that the OP is working with acrylics and ebonite and not wood to make his pen.

I thought he was talking about wood too.

I can only say sorry, if it makes any difference it is solid info for threading wood .

 

[Curly]

No apologies needed. It doesn't diminish your advice in anyway.

 

[PAturner]

Well, tried some of the suggestions mentioned with little success. I was able to thread an acrylic tenon with a 3/8" x 24 die by reducing the tenon size. Worked out great. I was also able to tap the same thread in ebonite. However, the 1/2" x 20 tap and die both are too stubborn to take in ebonite *or* acrylic. So, I've come to the conclusion that everyone is probably right that I should be looking into some metric threading tools. I'll try to keep updating if I'm finally able to finish something!