Necessary to tap for knife thread inserts?

silky smoove

silky smoove

Supporting Member
May 19, 2004
12,575
16,544
6,351
42
Seattle, WA
www.aroguestory.com
#1
I picked up some inserts for use in a Warmoth neck. I've used these before on basses (this build is a guitar), but did them when I was younger, more brash and without much forethought. They both turned out well, but here's what I'm wondering: With a knife thread insert, is it better to simply drill and allow the threads on the insert to cut into the wood, or is it better to tap the hole first so that the threads don't have to cut into as much wood?

These are the inserts in question:
10-24 Stainless Wood Knife Thread Insert | Fastenal

There's a misprint on the specs. It says that the external thread size is 0.35" and the drill size is 0.375". It doesn't take a rocket scientist to understand that the drill should probably not be larger than the external thread diameter. I checked with EZ-Lok (the manufacturer) and the external thread size is actually 0.453" (29/64"), but they couldn't offer me much on which tap would work well with these, which lead me to my question here.

So luthiers, or woodworking pros: Would you pre-tap the 0.375" hole, or would you simply drill it and allow the threads themselves to do the tapping as they were inserted. If you would pre-tap, which specific tap would you use, and would you go along with Fastenal's suggestion of a 0.375" drill as well?

Thanks!
 
#2
I don't always use threaded inserts, but when I do, I don't tap.

I spread some System 3 T-88 epoxy into the whole, then drive the insert in with a 1/2" socket-cap screw and a T-handle Allen wrench.
 
#6
silky smoove said:
Do you drop the epoxy into the hole, or apply it to the threads?
Click to expand...

I smear it on the side-walls of the hole, into which the threads will cut. The wet epoxy seems to have a lubricant effect, as it is markedly easier to drive them in with epoxy than without. Of course, once it cures, it isn't coming out, for love or money.
 
#8
On the original question, I don't think there is an off-the-shelf tap made that would work with those inserts because they have knife threads.

Knife thread = Wood Screw (not ever tapped)

Machine thread = Machine Screw (always tapped)

If you're interested in seeing the process for using a machine-threaded insert tapped into a hardwood neck, I posted a thread a while back:

Guitar and Bass Neck Threaded Inserts
 
  • Like
Reactions: okcrum
#9
I did something like hammerhed mentioned.
I was worried about it being square in the neck so I held the screw in a chuck on a mill and started threading the insert into the neck by turning the chuck by hand. Once it was started and had a few threads created I used a wrench.

When I was testing it on another piece of wood I tried the suggested hole size and increased it until it screwed in comfortably.

insert1.jpg

Most important part of this besides taking my time was making sure the neck was clamped firm when drilling.
 
#11
Did some test runs in a scrap of maple last night. The manufacturer's suggested 3/8" diameter drill size was considerably too small. I could get the insert in, but not without significantly high torque that caused the wood to creak more than I would think safe when I transition over to the actual neck. I'm going to try some different bits tonight to try and find the "right" one.

Three cheers for scrap maple and spare inserts :p
 
You must log in or register to reply here.
Top Bottom
Back