Another threading question

I’m having trouble with another thread.

I’ve used a better quality steel, threading at 305rpm now, got a nice thread.

I am trying to thread, M20 x 2.5mm pitch.

My OD started at 20.06.

My OD is now 19.88 and my threads are the full depth of the 2.5mm insert.

I still can’t get a nut on?

Any ideas?

 

You've cut a left-hand thread?

 

I would advice investing in thread wires they are the only method i know of for proper sizing of threads.

 

I took another two almost spring passes and the nut winds right on now

some sort of thread measuring gear is definitely needed.

 

Running a square file along the thread can help knock of any last burrs

Well done for persevering

 

Move along a couple of thou on the compound and take another cut

 

This is what I should of done to narrow the crests.

know for next time now

 

I measure all of my external threads, takes seconds, easy thanks to DrAl's calculator, here, www.cgtk.co.uk/metalwork/calculators/screwmeasurement

Measure the OD before starting. Choose a suitable drill bit from the calculator wire size. Deburr the part and measure with your drill/peice of mig wire. Subtract the original radius and double the result. That is the easy way to do it.

Youd be looking for 20.3mm with a single 1.5mm drill bit/wire

Internal threads I have not worked out yet. It should be easy enough to turn pitch specific tips for a bore gauge.

 

Internal threads either buy or make a guage