How to Turn a Wood Cap Nut? - Woodworking Talk - Woodworkers Forum
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post #1 of 14 Old 09-12-2020, 02:40 PM Thread Starter
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How to Turn a Wood Cap Nut?

I bought a used machinist vise at a great price. I needed one for a long time. The only issue with it is that one end cap nut on the handle is missing. I figured that I could turn a replacement cap nut easily enough, right?

Here are the specs:
* The metal rod is exactly 5/8 inch in diameter.
* I used a ruler, and counted ~2 threads per 1/8 inch. That makes 16 TPI. My guess is that the cap nut is 5/8-18 which seems to be a common size.

-> Do metal thread specifications use the outer (uncut) diameter of the rod?

After 10 tries, it isn't working out. My problem is limited tooling. I don't have a matching thread tap. I have Forstner bits, 1/16 inch apart. Here is what I tried that didn't work:

WHAT DIDN'T WORK:
* Drilled a shallow 5/8 inch hole as a guide to keep the rod straight.
* Drilled a deeper 9/16 inch hole inside it for the rod.
* Did a rough rounding of the outside on the scroll saw and bandsaw, whichever was handy for the next try.
* Used the rod threads as a tap for screwing the rod into the wood. It was VERY tight; too tight, really. Despite the 5/8 inch guide hole, the rod didn't always go on straight.
* Inserted the rod in a four-jaw chuck on the lathe and stabilized the wood piece with a live center. It looks straight and good. The rod end has no visible runout when I turn on the lathe, live center or not.
* Using sharp tools and the lightest cuts I could master, I tried to turn the cap.
* I tried it on softwood, "medium wood" (poplar), and hardwood (maple). I drilled the holes in side grain, not end grain. The turning was like a bowl blank, not an end grain "cookie".
-> There were various failure modes, but the cap consistently failed with large pieces cracking off. My hunch is that there is too much internal stress from screwing the rod into the way-too-tight 9/16 inch hole.

I could buy the correct tap. I could buy a nut or pay a lot for a cap nut (the ones I found are chrome plated for Harleys). I prefer to make something myself, using materials on hand, and I am enjoying the challenge. I want the cap to be removable, so I can replace it in case something cracks or breaks later.

I thought about wrapping the end of the rod in teflon tape, drilling the larger hole, and using hot melt glue or epoxy. The teflon tape would keep the glue from bonding to the rod, so I could unscrew it later.

-> Would teflon tape prevent hot melt glue or epoxy from adhering to the rod so I can remove it later?

-> What would you do? How would you make this replacement cap nut?
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post #2 of 14 Old 09-12-2020, 02:44 PM
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Quote:
Originally Posted by Tool Agnostic View Post

-> What would you do? How would you make this replacement cap nut?
I would purchase the replacement nut (and any other part needed) until I figured out
how to operate the lathe or get the needed tooling. (that's what I would do).

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post #3 of 14 Old 09-12-2020, 04:41 PM
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post #4 of 14 Old 09-12-2020, 04:50 PM Thread Starter
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Quote:
Originally Posted by John Smith_inFL View Post
I would purchase the replacement nut (and any other part needed) until I figured out
how to operate the lathe. (that's what I would do).
Thanks for the advice. Purchasing a metal cap nut (or the correct tap) would work just fine, but I want to make it myself for many reasons.

As far as I can tell, I am not having any issues operating the lathe. I have made many similar turnings of that size. I won't claim to be a great woodturner, but I beg to differ that operating the lathe is the issue here. I gave turning demos to groups before (by request), so I must know something about it. When I said, "Using sharp tools and the lightest cuts I could master..." I meant "The tools were freshly sharpened and very sharp, and I used as light a touch as humanly possible." Perhaps that is the cause of confusion here.

Using the rod itself as a mandrel seems to be a good lathe mounting option. It is strong and there is no visually apparent runout. It may be unorthodox, I have seen similar techniques before.

-> I believe that these caps are cracking apart from the inside. I think that there is too much internal stress caused by too-tight threading. The stress is released during turning. Some parts cracked before I could turn them, too.

What I am trying to say is that I tried forcing it and it didn't work, so I am looking to change my approach. That is why I posted my issues here.

-> I am looking for a better way to mount the part on the end of the rod with the tools I have at hand.

-> I am also looking for additional suggestions and ideas of how to create a removable cap nut from the tools and materials I have at hand.
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post #5 of 14 Old 09-12-2020, 05:58 PM
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Rather than cut threads in your wood why not use an insert which can be epoxied into a drilled hole?

Drill a blind 7/8 hole in your blank, thoroughly clean the OD. of the thread insert, glue it in the hole with a two part epoxy. *** keeping the epoxy from the internal threads*** packing the ID with plumbers putty should work well for keeping the internal threads epoxy free.

Let cure and then mount on your "mandrel" and turn the desired shape.

https://www.amazon.com/Z-Externally-...strial&sr=1-11


The linked insert is actually designed to be used in metal, hence, the locking locktite visible on the OD threads will need removed. Similar inserts are made for wood but I could not find those in the size you need.
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post #6 of 14 Old 09-12-2020, 06:34 PM
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if you can get a bolt that matches the thread, make your own tap.


cut/grin a slot in the bolt, file down the lead side of the threads to create a cutting edge.
pattern files . . . careful work cleaning up threads, etc etc


you'll probably need to grind the end of the bolt down to eliminate the lead in threads - for that nut you need a 'bottoming tap'
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post #7 of 14 Old 09-12-2020, 07:04 PM
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T/A: ~ I am very sorry for the confusion here.
I had about a dozen things going on in my feeble brain and I was thinking that you had a metal machinist's lathe.
I guess seeing the metal bar and the word cap nut just didn't register for me.
now, I think I understand that you want to make an end cap nut out of wood - vs metal.
having just used a couple dozen "cap nuts" over the past few months, the image sticks in my mind.
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sorry for the confusion on my part. and yes, I know you know how to turn on a wood lathe.

deepest apologies,
John

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post #8 of 14 Old 09-12-2020, 09:10 PM
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A couple of ideas come to mind. You might see if you can find a hex nut that would fit the size and threads. If you didn't like the appearance you could grind off the corners of the nut. You might also thread the rod to a standard pipe fitting and then screw a union on the end of the rod. A plug could be put in the other end to fill the hole. Another option if you have a metal lathe is to turn a cap without the threads and either glue or weld a cap on one end. The other end that has the correct cap would allow you to remove the rod.
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post #9 of 14 Old 09-12-2020, 11:33 PM
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Quote:
Originally Posted by Tool Agnostic View Post

I thought about wrapping the end of the rod in teflon tape, drilling the larger hole, and using hot melt glue or epoxy. The teflon tape would keep the glue from bonding to the rod, so I could unscrew it later.

-> Would teflon tape prevent hot melt glue or epoxy from adhering to the rod so I can remove it later?


I think you could glue the cap on there with or without the Teflon tape. If/when you decide to remove the tape, some heat on the rod will loosen the glue right up.

You could also cast a thread by coating the threads with a thin coat of mold release and placing the rod into an epoxy filled hole. The mold release should allow the rod to unscrew easily.

Last edited by Quickstep; 09-12-2020 at 11:35 PM.
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post #10 of 14 Old 09-13-2020, 09:59 AM Thread Starter
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Thank you to everyone for their great ideas. Like most of us, I have a drawer full of loose nuts and bolts. None of the nuts on hand is large enough.

I could buy a cap nut that fits, a threaded insert, the right tap, or something else. For multiple reasons, I seek a no-cost, do-it-myself-at-home option:

-> Make the cap nut out of wood with materials on hand.

We don't have "mold release" on hand, but we have:
* teflon tape
* non-stick cooking sprays (vegetable oil)
* furniture polish with silicone (always stored and used inside the house!!)
* petroleum jelly
* various oils like 3-in-1, air tool oil, etc.
* beeswax and carnauba chunks
* soft waxes like Renaissance Wax, Johnson paste wax, and carnauba (for cars)
* WD-40 and Boeshield T-9
* Wood finishes like mineral oil, Howard's butcher block finish (mineral oil and waxes), Tried and True (linseed oil with beeswax)

Which would you try first as a mold release for epoxy?
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post #11 of 14 Old 09-13-2020, 10:56 AM
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what kind of epoxy are you using ?
JB Weld - takes an overnight cure to be fully hard.
WestMarine G/Flex takes 24 hours to cure, and it remains somewhat flexible/soft.
some casting resins dry hard, but certain brands are pretty brittle. while others are pretty soft.
even if you get a mold release to work, you may still have issues with the type of epoxy you use.
not trying to discourage your DIY project, just trying to lessen the experimentation level.
your other options would be to drill some holes in the type of wood you are using.
if you have a few bolts of approximately the size as the shaft, try some of the methods
with the materials you have on hand to see which mold release would work for your project.
it is looking like not many (or none) of us are experienced in this area.
I am leaning towards the teflon tape and bees wax myself. (but have never tried it).
keep chugging away on it.

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post #12 of 14 Old 09-13-2020, 12:02 PM Thread Starter
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I have the 5 minute clear in the syringe (JB Weld and an unopened Gorilla brand). I also have small bottles of the G-Flex. I have hot melt glue, which is probably similar in cured texture to the G-Flex, though not nearly as strong.

The only drills larger than 1/2 inch are Forstner bits (spade bits won't work), which is what I used before. The 9/16 inch is too tight and resulted in the cracking issues I described above.

My eventual plan is to use the 5/8 inch bit. The rod slides in, but the gap is tight. I'll spread the epoxy inside the hole before inserting the rod.

Before any of that, I'll run a test or two with spare "scrap" bolts to see what happens. I'll let y'all know when I learn anything new. At some point, it becomes more trouble than it is worth. For any reasonable person (including most of you), it is way past that point already. :-)
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post #13 of 14 Old 09-13-2020, 08:46 PM
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You could do this several ways. Epoxy a 5/8" nut into a wood knob, make a tap by grinding 3 or 4 flutes with a Dremel tool. I'm assuming your lathe is a wood lathe. Chuck the bolt and file a small bevel on the first and second threads.
Bore the hole in the knob 9/16" and then tap. Run the tail stock up to the knob and turn the knob or the chuck while keeping light pressure on the tail stock spindle. This will help to keep the tapped hole straight.
If all else fails then bore the knob for a sliding fit and use hot hide glue, or even hot glue from a glue gun. Either will can removed with a heat gun.
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post #14 of 14 Old 09-14-2020, 07:22 AM
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I've read that hairspray (the old style) will serve as mold release.
I bet the beeswax or carnauba would work fine. Be sure to just coat the threads, not fill them.

Last edited by Quickstep; 09-14-2020 at 07:31 AM.
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