Hi Peter

Most I have seen have been home made, a 55 or 60 degree raised shape on the end, a 90 degree segment cut or ground out to provide the cutting edge for threading.

Emgee

Its a circular chaser,I found some in a box at a second hand tool dealers years ago,they are very good for internal screwcutting in small bores,and lathe backplates.

One of my favourite tools ever bought Martin the PH Horn internal grooving/interpolating milling cutter with interchangeable heads. Not cheap £30-£45 for two tips in a box but do they cut well in a lathe.

Not the one but gives the idea OP was after **LINK**

Really a 1950s thing when we made a squillion widgets a year per machine to feed the empire

Have no clue if there's anywhere left that does these things nowadays

Ady1

I have one of those pre-insert days external threading tools marked up as Eskilstuna – Sweden. I will upload a photo and post it. The circular die is about Ø42mm so it would be hard to use for any small internal threads if a suitable holder was made. It has a screw at the front for small adjustments to the stick out and the head can be swiveled on the body to allow for different helix angles. As I say it was pre-inserts. I think they have been replaced with throw away inserts now. Reduces the need for someone to sharpen it and then for the tool to be re-set.

Jon

I have a thread milling tool I made with Horn inserts in it. Could be used for internal threads if there is a big enough bore.

You can see it in action here.

**LINK**

Martin

Hi all, during my apprenticeship I did shedloads of large bosses with BSP threads in them for hydraulic tanks, we used Alfred Herbert circular cutters with a 1 inch round shank in a holder specifically for them in the 4 way tool post, have not seen one in years although I do have a holder. Can't even find a picture, but I would suggest that anyone thinking of going down that road, HSS, easy to offhand sharpen, easy to set, could do worse than to use orphan circular dies from BSA / NAMCO dieheads still made in modern times, world probably waist deep in them especially odds & sods. Attach to boring bar along front of toolpost with single screw etc etc. Take side trip to gear cutting section, fill Fairy Liquid bottle with viciously politically incorrect sulphurised cutting oil apply as necessary, wash hands occasionally, get beautiful shiny finish on thread, job done.

Bob.

I have some by MESA Tools in the US

Same holder holds the insert side, front for external threading and across the rear face for internal threading.

Works well for me.

Edited By John Stevenson on 18/12/2015 10:46:05

Simtek DX – German system, available with threading inserts, available from Cutwel.

Nice idea. Looks like it could be turned out out of silver steel and hardened. The cutout could maybe be done on the offhand grinder.