Table restoration - dowel screw woes

[paulrbarnard]

No, they screw in to an existing thread (often a damaged one).
I used one on my Jacob's chuck on my lathe. The threaded morse taper was 10mm, but I couldn't get a 10mm rod through the tailstock so had to use an 8mm one. They have an end bent across the diameter at the end which the insertion tool (screwdriver in my case) fits, which breaks off when the helicoil is in place. You can see it in the picture.
I guaranteed that never again will I need one - I bought a set.
View attachment 98182

I’ve got an identical set. I used one m8 insert from mine. I’ve had it for years now so works great as a prevention set.

 

[TheTiddles]

If it’s larger than M8 and smaller than M10, it’s probably 3/8” UNC.

Whilst M9 does technically exist, I’ve never seen one in my life and someone would have to go to a lot of trouble and expense to do something that odd

Aidan

 

[beech1948]

9mm converts to 23/64ths in or 0.354 inch. So only 1/64th short of 3/8ths. I would be looking for a 3/8ths UNC bolt as likely to be available in the UK.

M9 is something I also have never seen in my 72 yrs and should be considered a bit of an oddity.

Try asking Dieter Schmidt in Germany if they have any or ever heard of M9.

 

[--Tom--]

See post 5, 3/8 was tried and too small

 

[Camo16]

See post 5, 3/8 was tried and too small

Thanks all, yes 3/8 was just a bit too small - it was the closest one though. I was thinking of wrapping it in something to be honest - food for thought here!

 

[J-G]

9mm converts to 23/64ths in or 0.354 inch. So only 1/64th short of 3/8ths. I would be looking for a 3/8ths UNC bolt as likely to be available in the UK.

Even taking the lowest class (1A) the minimum O/D on a 3/8" UNC bolt is 0.3595" -- 4½ thou larger than 9mm

3/8" UNC is 16tpi so the pitch works out at 1.5875mm which is larger than M10 (1.5mm) so I suggest that before any 'alternative' thread is tried it is imperative to determine the pitch or tpi of the insert. I would take an impression of the thread with a small piece of plasticine and measure the pitch. Even with just a steel rule you ought to be able to distinguish between 16tpi (1/16") and 1.5mm as long as you can get an impression of at least 5 threads.

M9 is something I also have never seen in my 72 yrs and should be considered a bit of an oddity.

I also can't recall ever seeing - or being asked for - M9. It does exist, as Aidan has already said, it is 1.25mm pitch.

 

[TheTiddles]

See post 5, 3/8 was tried and too small

See post whatever number mine was and the person who gave the major diameter of a 3/8 UNC is... if it was too small M9 will also be too small... maybe it wasn’t a 3/8 UNC thread that was tried