Making a 5/32 * 16 TPI butress tap

[sbwhart]

A friend bought a very nice completed model of 1 1/2" to the ft Alchine traction engine which he was delighted with, the only blot was that the break drum wouldn't work, he found out that the nut that tightens the break drum was not threaded, the bolt was nicely made with a butress thread but for some reason or other the builder nadn't completed the job and made a tap and tapped the nut.

So I offered to do the job for him.

First thing it pays to measure up the job and sketch up how the threads will fit together as you have to think inside out and back to front  .

Making a 5/32 * 16 TPI butress tap

From this I worked out the sizes for the tap, then by hand ground up the tool for the job this is just like a parting tool but you have to give the leading edge enough rake to clear the thread helix.

Making a 5/32 * 16 TPI butress tap

This pic also shows the bolt, and nut.

I turned a couple of blank taps up, then set the change gears of my lathe to cut 16 tpi.

Making a 5/32 * 16 TPI butress tap

Making a 5/32 * 16 TPI butress tap

My lathe is not that friendly when it comes to thread cutting, even though its got a split but its got lots of back lash so I find the best way is to keep the nut engauged and power the sadle back and two winding the cut off and the end of each pass.

Making a 5/32 * 16 TPI butress tap

The biggest problem was from the tool wanting to dive under the thin rod as the thread was cut I got round this by slightly setting the tool above centre.

Next I got to try out my new power feed on my mill.

Making a 5/32 * 16 TPI butress tap

The threaded tap was set up in the spin indexer with the tail stop and supported with a jack to stop it flexing, and three flutes cut.

Making a 5/32 * 16 TPI butress tap

By hand I filed a small amount of radial releaf, then heated them up to cherry red and quenched them in water, gave them a wire brushing and a quick hone with a stone.

Making a 5/32 * 16 TPI butress tap

This is what happend to my first attemp of cutting a thread.

Making a 5/32 * 16 TPI butress tap

For the second attempt I tempered the remaining tap and increased the size of the tapping drill.

This time it worked like a dream, I'm going to bush the square nut with the nut that I've made.

Making a 5/32 * 16 TPI butress tap


Stew

[Stilldrillin]

Well done, that Man! 

A nice feeling, when you can work "magic" for someone else. 

Even better...... When the tension subsides, 'cos it's gone right second time! 

Nice one Stew. 

David D

[andyf]

Hi Stew,
I've only ever made one tap, the M10x1 lefthander shown below.One thing I did find useful was to cut the flats for the tap wrench in the middle, rather than at the end of the shank. This was to enable the tap to be used on a drill press and turned by hand with a wrench on the flats, without the shank slipping in the drill chuck, which is apt to happen if the spindle is turned.

Making a 5/32 * 16 TPI butress tap

Andy

[sbwhart]

Thats a neat idea andy 

Stew

[ieezitin]

Great!1

now why don't they make them in the commercial world like that.  superb idea Andy

Anthony.

[arnoldb]

Nice job Stew 
Good idea Andy!

Regards, Arnold

[andyf]

now why don't they make them in the commercial world like that. 
Anthony.

I wish they did, Anthony, because there would be no need for a dedicated tapping stand - just use a drill press. The ideal would be flats at each end of the shank, so the tap could also be used freehand.

But it isn't going to happen... .

Andy

[Bogstandard]

Nice job Stew.

I thought it wouldn't be long before you got around to sorting it, when you showed me the problem the other day.

Single point threading rules the day, yet again 


John

[Dean W]

Nice job of that, Stew.  Thanks for the show 'n tell.  Good info here.