M3.5 thread with 1mm pitch, very non standard

The picture is a Nickel-Silver stanchion-like component that supports the keywork on a woodwind instrument. It has a thread that measures 3.4mm diameter over the crests and as far as I can tell, the 3.5mm length has the same pitch and thread profile as an M6 bolt. The spherical part is 4.8mm diameter.

After extensive searching I have come to the conclusion that it is impossible to buy a ready made tap so I'm wondering whether anyone thinks its feasible to make one? It is not something that will ever be heavily used and its not tapping into hardened steel although African Blackwood is probably not far off!

Ian P

Perhaps possible to find a wood screw with similar thread and use that as tap. Niko.

For wood, I use (and make) roll taps. That works better than my taps for steel.

Just make a M3.5 x 1 thread on a peace of hex steel and use that to tap the hole in wood.

Drill diameter should be the same as for a M3.5 x1 metal tap 2.53 mm (2.5)

Crest diameter for the tap should be 3.5 mm

Cutting depth for a sharp, self grind threading tool should be 0.704 mm

Cutting depth for an insert 60°, for 0.5 mm pitch should be 0.65

Edited By Huub on 13/07/2023 23:12:15

Hi Ian

Some time ago I made a tap from silver steel and hardened it for use in wood, it had 45 degree flanks so thread form was 90 degrees, the person it was made for reported it worked OK.
The part in your pic seems to have rounded crests, can you measure accurately crest to crest to confirm the pitch is 1mm ?

What is the minor diameter ?

Emgee

Depending on how old and where manufactured it could be a No6 American thread

Edited By bernard towers on 13/07/2023 23:23:28

The part is almost certainly metric, made in France and is 1mm pitch (USA No 6 is 32tpi).

A roll tap would make sense but the wood used for oboes is so hard and dense its virtually incompressable that I think a tap would have to cut most of the thread form. The hole is blind and only 4mm deep so I think I will need to do lots of experimenting

Ian P

The grain direction of the wood will probably be a consideration.

Using a roll tap M3.5 x 1 for steel requires a drilled hole of 3 mm.

Making/turning a tap isn't that difficult but takes some time. This video shows how I make a tap from round steel Turning a tap. It is easier if you use hex steel.
For a roll tap, I use the same procedure but without milling the flutes. For wood, I use mild steel without hardening.

Taps aren't difficult to make. Don't last as long or cut as well as commercial taps, but OK for specials.

First cut the required thread pitch in a rod. Silver Steel is best because it can be hardened and holds an edge, but mild-steel copes with softer materials for a short while.

Then cut 4 slots along the thread to create teeth: I normally mill them, but a file works too. Finish, by filing off the flank, non-cutting, side of the teeth to provide relief. Not shown in the CAD pic, but the rod should be chamfered to lead the teeth into the hole.

That's a basic tap. Can be improved, for example by cutting the thread into a mildly tapered rod. As this type of tap doesn't cut brilliantly, it might pay to make three with gradually deepening threads. (A first, second and third set.)

I guess the main difficulty is the job will be a bit fiddly and delicate, at least by my clumsy standards. M3.5 x 1.0 is a relatively coarse pitch for a small diameter rod.

Dave

Hi Ian I have made special taps mainly for cutting metal parts but the same could be done for your wooden part.

I screw cut the thread on a piece of silver steel , then using a ball nosed cutter cut the cutting edge. It was then flame hardened.

These were similar items I made for a friend but made from bronze for an unknown musical instrument.

David

Time flies, I made the tap in 2015 which I mentioned in my last reply, video link below shows the turning, milling, hardening and flute finish grinding process.
**LINK**

Emgee