Cutting threads onto shafts

[BobL]

This morning I was threading a number of 10 mm mild steel shafts/rods and ran across the usual problem of finding it very difficult to start and even once I got to going to put the 1.25 mm thread onto these shafts. Yes, I had tapered the end slightly and was using plenty of lube.

I then put the shaft on the lathe and took off 0.1 mm and the die cut the thread much easier. looking at the thread under some magnification I could see the thread was still fully formed.

I don't know how other people go such things but in contrast to the many readily available pre-threaded hole size charts for different size/pitch threads I have never seen charts showing recommend amounts of easing of the diameter before cutting a thread. Has anyone seen one of these?

[pipeclay]

Search for thread tolerance chart.

[RayG]

You might have scared it with a cutting threat Title corrected.

You aren't trying to start a thread with die nut, rather than a split button die by any chance?

Ray

1. Almost as bad as starting a thread with a mispelt title.

[welder]

Normally I turn the nominal size .05 to .1 mm under.

[Stustoys]

Asked a fitter the same question myself, "couple of tho under nominal size" was his answer.

But it would technically depend what class of thread you were after.

Found this http://www.amesweb.info/Screws/IsoMe...x#.VIkSstKUd2E

So even a 4h thread you could start at 9.9mm and still be in spec.


Stuart

[welder]

The Major diamter is not as Important as the pitch diameter.

E

[BobL]

You might have scared it with a cutting threat Title corrected.]

I just came back up from the shed to see if there were any replies and saw the original thread title so I went to edit the thread title and lo-and-behold it came up correct?

You aren't trying to start a thread with die nut, rather than a split button die by any chance?

Nope, split button full open.

Thanks for the responses.

[RayG]

I just came back up from the shed to see if there were any replies and saw the original thread title so I went to edit the thread title and lo-and-behold it came up correct?

Ah ha... I think you have a guardian angel behind the scenes correcting the thread titles..

Split button die, chamfer the end a little to help it start, drop of cutting fluid.. press down hard at the start, keep it square.. and away you go.

Ray

[chambezio]

I wanted to cut a thread on a 5mm shaft I had just made on the lathe. (The material was brass) I frigged around for an hour. Just COULD NOT get the button die to start. In sheer desperation I grabbed a 5mm bolt to be sure I was measuring right and lo and behold.....5mm thread/bolt was 4.7mm
Once I reduced the shaft diameter it threaded.
In the words of Julius Sumner Miller "Why is it so?"

[morrisman]

I have discovered that not all threading dies are the same nominal size . Some ( the asian ones ) are slightly smaller or larger than the size stamped on the die . Go from one brand to another brand and you will notice this . I dont think any of my dies are the split type , I have the cheaper brands .

When threading on the lathe , I start with the nominal OD , and after the threading I run a file over the thread , this takes a few thou off and also rounds the crests off

[wheelinround]

BobL thanks for starting this thread or was it a threat.

Ok have you guys got my shed on live feed.

I was always taught to chamfer a lead when threading for me in the past its always been die's used I hope to cut my first thread in over 40 yrs on a lathe soon have to play gear train organiser first.

forgetting the little screw on adjustable dies does wondrous things which can make life easy or hard

[BobL]

BobL thanks for starting this thread or was it a threat.

My treat

Earlier this year at the mens shed we were making something that involved threading dozens of ends of ~300 mm long pieces of 6mm rod. The guys were having a devil of a time used fixed size dies and started to turn the ends of the rod down on a lathe but as that was going to take some I went home and got an adjustable 6 mm die and that worked much better than the other one. This is why I was surprised this morning.

BTW, I just put everything away in the shed from this mornings job and realised the 10mm die I was using was nowhere near as opened up as I thought it was. I just tried it with the die opened up on some 10 mm rod and it was quite a bit easier. Next time I will remember to check this before I get carried away.

[KBs PensNmore]

Bob, were your nuts loose on the thread? I've found that MS bar varies quite a bit, seen it where it is 9.5 mm one way 10.5 mm the other, oval!
I was also going to ask if the die was opened for a start, as I've done similar, having it cut undersize, but you've answered it.
Kryn

[BobL]

Bob, were your nuts loose on the thread? I've found that MS bar varies quite a bit, seen it where it is 9.5 mm one way 10.5 mm the other, oval!

Ken, the threads were on two arms connected to the handle elbow of a set of cranks I wamas making for a log restraining device for the bandsaw mill I am sort of fixing up.

The big thread is 5/8 and passes through a 50 mm SHS support and then up against the log
The 5/8 is threaded into and locked to elbow "L" with am 8 mm high tensile sprung pin.

The 10 mm Galv arm is a loose fit on elbow L and threaded at Ti.
This one gave me no probs and I just measured it and it is 9.87mm in diameter

The SS tube rides on the 10.0mm diameter handle which is threaded into the lower elbow at T2.
T2 was the one that was giving me gip.
Yes it is a loose thread but it does up tight against the elbow and is not laid bearing so it's not a problem.

I was also going to ask if the die was opened for a start, as I've done similar, having it cut undersize, but you've answered it.

Yep not opened up enough.

I have two more cranks to make so I will now know what to do

[BaronJ]

Hi Guys,

FWIW If I'm using a die nut to thread a piece of rod I always put a two thread wide taper on the lead. Someone else also mentioned that the rod may not be truly round. Black bar is very likely more oval than round.