I thought it should be 60 degree for uts or metric

55 degree for whitworth or bsp

I could be wrong of course

55 is the included angle so you set teh topslide to half that so the tool runs down one side of the thread, look at the following pinched from a post on another forum

Are you sure that the original thread is 22 tpi? I would start fault finding with that, measure over a few threads and do some calculations. 22 tpi would measure .136" across 3 threads.

Also, are you sure it's an imperial thread? This pitch is close to 1mm pitch!?

Andy.

Only screwing on 3/4 of a turn could be caused by one or more of several factors.

First I would establish what thread the original was. If you know the OD and aproximate pitch then by looking in some thread charts you can establish if its metric or imperial, Whitworth, UNF or whatever. If you have cut a close fitting thread but the pitch is only slightly out then it wont screw on very far.

Using a micrometer and two wires that is a diameter which sits on the flank of the threads, compare the original with the one you made to see if there is any clearance at all.

From a practical point of view, if this part is only for a lever that is going be fixed permanently in place then go with what you have got and get BRUTAL! Use vice grips to install it and you wont need any threadlocking compound.

Ian P

Edited to correct poor spelling

Edited By Ian Phillips on 12/03/2012 21:04:35

There are some other catches too. You say spot on diameter and are probably comparing original and copy but often people forget the crests should not be pointed and are flat or rounded depending on thread by about 1/8 depth. So the starting diameter is less than nominal. If not the nut can bind on the crests.

Then the depth you cut depends on that starting point and whether your tool is pointed, flat, or rounded. The flat and round depend on pitch so every one is different and you may be using a random ground tool. This affects the infeed.

Since the calculations still don't account for the quality of your nut it is easiest to start right, get close, then just try the nut until it fits knowing the binding is not the crests but the roots so you just need to cut a little deeper.

I think you would have less trouble if you set up, and go straight in,as Nobby says, rather than setting over, make absolutly sure that the tool is correctly set, take your time, and if you can find a nut that has the same thread, it will make it easy to check your progress.

You don't have to be too fancy, my first thread was a 1" whitworth one, and the tool was a bit off an old sqare file, the only problem with whitworth is the round creston the thread, quite noticable with 1", I remember at school we were taught to use a chaser to finish the thread, this is not needed with SAE, or Metric threads. Ian S C

The first photo looks like a square thread to me, a white background would help a lot, if you offer your cutting tool up to the original thread does it fit well?

Andy

For W.W. form threads I always set the top slide to 25 deg. as recommended by Geo. Thomas. This makes the trailing edge of the tool take a fine skim and results in a smoother thread. It also makes the calculation of the feed depth easier!

Capnahab, if you want a reference book with a good treatment of screwcutting I can recommend Geo. Thomas "The Model Engineers Workshop Manual".

Russell.

Hi
It could be 10 x 1mm pitch witch is close to 1/8 bsp We used 1/8 bsp for water plugs on plastic moulds Until metric Now 10 x 1 mm fine not to be confused with M10 .
Nobby

My late father taught me when screw cutting a standard thread to stop when nearly to the correct depth of thread and to finish it with a die or a dienut. This technique gives a finished thread to size and the correct thread form. Obviosly this cannot be done with a non-standard thread.

My screw cutting tips are; to make sure the tool has the correct clearance angles to take account of the thread helix, set it dead on centre height and square to the job when using the straight-in method. Use a screw cutting template to get this right.

Always cut a run-out groove to the correct thread depth using a parting tool. If possible on small diameter work use tailstock support.

To get screw cutting down to a fine art practice, practice and practice!