Threading wood

[John Borgwardt]

I just bought a molding plane and the wooden nut is missing. The threaded rod is 3/4" - 8 thread. Can anyone tell me how to make the threads in this nut to match the shaft? I have seen it done but cannot remember where I saw it. Thanks in advance. John

[Jerome Hanby]

That sounds like a standard thread, could you pick a tough dense wood for the nut and use a standard tap?

[Robert Loss]

That sounds like a standard thread, could you pick a tough dense wood for the nut and use a standard tap?

3/4" standard taps for metal are 10 tpi although the 8 tpi are probably available at a price. The Standard Taiwanese wooden thread cutter boxes that are around are 6 TPI for the 3/4 size. You may have to cut one on a lathe.

The other way to do this is to find a 3/4" 8 tpi bolt and make your own tap. Using a bench grinder, grind a taper so that the tap can start easily and then make 4 cuts with an angle grinder perpendicular to the thread, this will serve to clear the swarf. This method works well and have done it a number of times for timber Aluminium and brass. When doing this in timber use a generous amount of linseed or tung oil as a lubricant.

[Robert Rozaieski]

Standard wood threading kits for 3/4" stock are 6 tpi:

http://www.woodcraft.com/family.aspx?familyid=792&productid=12T14

I have a similar problem with a wooden thumb screw for my plow plane (7/16" and I think 12 TPI). I think yours and mine will need to be carved as I don't believe any one makes these taps. Of course you could make a thread box and tap. Roy Underhill has several plans for several different designs. I may try this if I find myself unable to carve a satisfactory one.

[Tom Veatch]

...find a 3/4" 8 tpi bolt...

Not saying you can't, but it probably won't be at the local hardware store. 3/4" UNC is 10 tpi, and 3/4" UNF is 16 tpi. Those are the most likely to be commonly available. The UN, UNEF, and UNS series are all finer pitches and go up to 32 tpi in 3/4" diameter. The 8P series are all 8 tpi but don't cover anything smaller than 1" diameter.

Other than that, the suggestion sounds good and should work for making a tap for soft materials. If the OP knows anyone with a metal lathe, it wouldn't be difficult to turn 8tpi threads on a short piece of 3/4" steel rod.

Don't know how difficult it might be, but maybe replacing the shaft with one that matches a standard, available thread pitch may be another option.

[Wallis Hampson]

You could easily buy a die to cut the threads on the metal rod to a standard size that you can readily get a tap for even if you had to "die" it down to 11/16 or 5/8.