If I am sent to a bad place when I die, I am certain it will be filled with bockety threadboxes.
Today I spent the entire afternoon preparing for a class at the Melbourne Guild of Fine Woodworking and prepared the stock so every student could make a Moxon vise. I started by making the blanks for the screws.
While I was turning these spindles, I threaded one with my generic “Made in Taiwan” threadbox that is available everywhere.
The spindle jammed in the tapped hole.
I adjusted the threadbox and made another spindle. It jammed in the hole. I made another. Jam. Alastair Boell, who owns the school, sensed my despair (it might have been the fact that I was screaming and peeing myself) so he came to take a look.
He made some adjustments. Jam.
Then he had the brilliant idea to cut open the threaded hole to see if we could diagnose the cause of the jamming. The problem was obvious. The tap and the thread box each cut different a tpi.
I had heard there was a batch of bad threadboxes last year. But the suppliers assured me that the problem had been resolved.
I don’t think it has been fixed entirely. There are still bad threadboxes in the pipeline. This was a new, unused threadbox I’d purchased recently with another threadbox (which worked perfectly). I brought the unused one to Australia to make sure I had a cutter that was in good shape.
If you buy a threadbox, keep your receipt. If the results from your threadbox won’t work, cut open a threaded hole you’ve made and check out the tpi.
— Christopher Schwarz
Sounds like someone needs to do an article on making thread boxes. There’s this guy that lives in an old mill…
Sounds like the expensive thread cutter from Dictum may not be such a bad deal after all?
I wish that Beall Tool Company made a massive 3″ threader.
This is how we learn where to save money and where not to try it – “experience”.
Thanks for taking one for the team and telling the story.
(A new deli opened in Forth Smith – not bad. “River City Deli” I think it’s called)
There is no such a thing as perfection. The thicker the nut, the greater is the chance the mismatch conducts to jamming. I see on your picture that the nut is about 11 threads thick: That is not useful. On the vise from my great-grandfather’s workbench, the wooden nut is about 6 or 7 threads thick. With ordinary metal screws and nuts, due to elastic deformation of the metal, the first 3 threads are taking nearly all of the stress, so there is no point to make nuts more thick (standard 0.8Xdiameter), it is just wasted metal (and looking for mismatch). Of course wood is not metal and my great-grand father’s vise is probably right with its 6 thread thickness.
On your picture, 5 or 6 threads might be working in spite of the gross tolerance.
Look at the last picture on the page “tolerancing of screw threads” on this site :
http://www.boltscience.com/pages/screw8.htm
Wooden screw saga here :
http://lumberjocks.com/mochoa/blog/33045
Sylvain
The threadbox is actually 7 tpi, with the tap close – but no cigar.
I don’t understand the relation of your reply with my comment, so probably my command of English was not good enough.
With 7 TPI, a 6 threads nut-thickness would give a nut thickness of 6/7″ (~0.86″).
Yours seems to be about 1.75″. Twice as much; increasing the chance of jamming.
That is not to say that the box and tap should not be better matched.
Sylvain
Chris,
What will you use for the class? It sounds like this thread box is unfixable.
Chris
We have a stopgap solution. Clamps.
Here are the trials and tribulations of a young guy’s experimentation on making large wooden threads. His work puts me to shame.
http://lumberjocks.com/mochoa/blog/series/4912
Eric