Threading questions - using tap/die

[underdog]

Tonight I was playing around with my tap and die set and seeing what kind of woods would tap easily. This was all done into end grain. I did no cross grain threading. I used a 17/64 drill (or smaller the 2nd time) and a 5/16 x 18 tap/die.

For tapping inside threads, Maple and Osage Orange seemed to do pretty well. The threads look nice and smooth. I didn't try anything else.

For outside threads I found that Maple, Crape Myrtle, Privet, and Walnut really sucked. They didn't make threads at all once I ran that die up on them..:mad:

The Bloodwood tried, but in the end it was too brittle and crumbly. The Osage Orange worked the best, but it still didn't make very nice threads...

My questions are these:

Is there a way to keep those outside threads from crumbling? Is there a trick to it? Can I apply CA glue and keep them together? Are some woods better than others? If so, what are they? Do I need to have really sharp taps and dies?

 

[john lucas]

Jim CA glue does work to some extent but it depends on the wood. Adding any kind of lubricant to the tap also works. I use Johnson's paste wax but some have recommended mineral oil. Some woods just won't hole a thread worth a darn. Osage Orange, Boxwood and Cocobolo all thread pretty well with hand taps.

 

[john lucas]

I forgot to tell you I tape the hole part way and then apply the CA. Then I tap some more. CA doesn't penetrate good wood very far so taping and CA in steps seems to toughen the threads better.

 

[GeorgeH]

Most of the threading I do involves making threaded face plates for my lathe and that involves threading the long grain rather than the ends. As a general rule, I use oak for that purpose and the tap is 1X8TPI. I have used smaller taps for various jobs and, for some varieties of wood, I find that an application of CA improves the chances for success. After drilling the initial "starter" hole, I soak the sides of the drill hole with thin CA (that watery stuff) and allow it to set before tapping the threads. I have had VERY poor results trying to run any kind of wood through a common threading die. For some reason they don't perform as well for me as a tap does. Wood threading dies are designed much differently than metal threading dies; I suppose that's because the folks who know how to do it correctly learned before I did that the metal threading dies aren't suitable for that job.

 

[Ken Grunke]

Part of the problem may be alignment. It's harder to get a die going on straight than a tap, unless you use some kind of alignment aid. A tap can usually correct itself as it goes in but if the die gets a crooked start, it will chew up the threads. .If you can have part of the shaft to be threaded at the minor diameter where the die will go on easy and align itself that will solve the problem.

 

[underdog]

As promised.... Here are pictures of my experiments.

The first picture is a shotgun shell sized box made of Osage Orange. It's open so you can see the threads. You can see they are pretty clean.

You can also see how I managed to use a steel cutting tap and die set on wood. The secret is I used a scrap piece turned cross grain for the threads. I first rough turned the box, parted off the lid, then drilled and tapped out the body. I used a little bigger drill than recommended as you want a little slop for wood threads. That goes pretty smoothly as you have plenty of support for the threads.

Then I chucked up the lid and estimated how thick I wanted the supporting "rod" for the cross grained piece I would use for threads. I think I used a 3/16 drill bit, so I sized the rod to that with dial calipers - within a couple thousandths of an inch so the glue joint would be strong. I then took a scrap piece of Osage Orange and drill it with the selected drill bit, and glued it in place. Then I turned it down to 1/2 inch or less (remember you want slop in the threads).

I was a little impatient so I used super glue, and didn't really wait long enough for it to dry, so the 1/2 x 13 die tended to twist the supporting rod a bit. If you look at the end grain of the lid, you'll see it stayed a little twisted. Once I got the threads cut, I cut a little relief at the shoulder, and cleaned up all the threads with a bit of sandpaper. I should add that I used CA glue to harden the threads a bit, and ran the tap back over it to clean it up. Then I applied some paste wax to lube the threads a bit.

I then screwed the lid on, and finished up the top since the bottom was still in the chuck. Once that was done I chucked up the original drill I used on the body and stuck that in the head stock and reversed the body onto the drill, and brought up the tails stock to finish off the bottom of the box. Once you have a little nubbin left you move the tails stock and finesse that nubbin off, sand and finish.

Next time I'll chuck up the thread stock and turn it round, face it off, and then drill it while it's still in the chuck. That way I can get it to fit a bit better. I'll also glue it on the rod, and let it dry before trying to thread it.

The second picture is of the box with lid on.
The third picture is the first box I tried threading. The threads are 5/16 x 18. The inside threads were great, but the outside threads were a little sad. Even though the outside threads are rough, the action is pretty smooth.

You can see why I made a box... I needed a place to keep this little things. And that's a bit of a gloat. The smallest goblet (errr... Martini glass) is 3/16 high...