Internal screw cutting using tap

HI Guys
Here we are screw cutting an internal thread using a tap 3/4 x 18tpi .
Using a handle with half nut closed . and winding back etc any other idea,s
Nobby

At 18 tpi there is no reason why you couldn't screw cut this under power and also undo the half nuts wind back and drop in again at any numbered mark on the thread dial.

That's if it's a thru hole which isn't clear from the picture.

If it is a blind hole or with a step in it then yes go for the handle.

Hi Jason & John
Thank you for reply,s. The cutting edge is on the c/l I have a gauge for setting this . Its a through hole so i could
cut under power as John says It was just a demo for using the handle. The part is for a Drummond flat bed lathe its for adjusting the spindle .
Nobby

I've done this a few times but on a hole that is not much larger than the tap eg 1/2" tap to cut a 5/8" thread. Is there a rule of thumb as to when the helix angle on the tap becomes too steep compared with the one being cut and starts to rub and push the tool away?

J

Edited By JasonB on 15/05/2014 07:29:22

Hi J & Guys

That could be a problem When at work I used a screwing rotating screwing table fitted to a Bridgeport mill using a cutter with the thread form . as you know you had to tip the head to the helix angle . the table was fitted with nuts you could change to suite the pitch required . Used for internal threads on plastic mould inserts Cant list a photo
too long ago .
Nobby

If you have any die head chasers they are great for cutting multi start threads. Just grind them back to two teeth for a double start, three for a treble etc and set the gear box/change gears to two or three times the pitch and screw cut. Avoids any problems that can occur cutting the thread two or three times by advancing the compound slide.

I used this technique many years ago when I made some collets to take Clarkson end mills for an unidentified 2MT milling chuck

I'm using this method now to do 5/8" x 14 BSF for a topslide tee nut to anchor me new warco QCTP onto me 1236 lathe by using a 7/16" BSW tap. Jolly good in the absence of the correct tap to thread it by hand.

Rick

Hi dave , Rick & Guys
Using Clarkson auto lock collet's . A little tip if you want to use a plain cutter without the thread on the end .
Slice the threaded end off an old cutter grind a screwdriver slot across it and use it as a dummy centre . this works fine . If I can find one I will upload a photo.
Nobby