You can use an M6 x 1mm tap to thread a 30mm hole with a 1mm thread. The tap is held in the toolpost in the same manner as an internal threading tool. The only difference is the tap gives you (in theory) the perfect thread form. I've been using taps this way for a while now and is my preferred method.

Edited By Chris Trice on 15/05/2012 00:05:19

Yes the change gears are set to suit the pitch of the thread.

I've only done it without angleing the topslide, tool parallel to lathe axis, set the cut with the cross slide.

I can mock it up tonight and take a photo.

Whats the "fish"

Thats what 'Chasers' are for, only trouble is I never have the one I need to cut the thread in large diameter components.

I can see the problem with large pitch threads abd clearance would be needed, possibly a three flute tap would be OK.

Clive

When you disengage the feed at the end of the thread do you not then get a series of radial grooves corresponding to the taps pitch as the tap will have teeth in contact all the way along the job/

best wishes,

Tony

Yes, its best used for through holes or if blind machine a small undercut at the end of the thread and just stop the machine when the tool runs out, back it out of the cut and then withdraw the carrage.

If you can't get an undercut in and the part is not tool large then the spindle can be turned by hand stopping as the tap touches the bottom of the hole.

On the one in my photo because I had a valve seating face right at the end of the thread that I did not want to damage I managed to get a very fine undercut and then rotated the spindle by hand and left the feed engaged for the whole job, just disengaging the tap from the thread with half a turn of the cross slide before with drawing under power with the machine in reverse.

J