Tapered taps

[mikechoochoo]

I don’t have a picture of them but I saw some taps that look like blacksmith taps but have a very fine thread. They are about three inches long and tapered their whole length. The thread size is 7/16 - 80 on one and 9/16 - 20 on another. The size marked appears to be the big end because the point is less that 1/4 diameter. There are several smaller ones also. What are they used for and do they have any hobby value?
M.Nix

[Bill Shields]

Only if you start them square.

Start them crooked and the become much shorter very quickly

[tornitore45]

7/16 80 TPI ? That is quite a fine pitch for a 7/16 the tread is so small it won't take much taper before the threads disappear.

[mikechoochoo]

The fine thread and the taper is the weird thing, you would almost need to start with a tapered hole. And why so long, they are marked with the size and for a short hole they would not need to be that long.

[mikechoochoo]

The first photo is the taps, the 2nd is on a box of similar taps and dies, so maybe bicycle building, but why the long taps?

[Bill Shields]

I have seen them used in cases where you want to thread both walls of a tube such that a single long screw can engage both threads in walls....like a bicycle frame

[Charles T. McCullough]

"BOTH WALLS of a TUBE?"??? Please explain that to me. Every circle has two sides, inside and outside... is that what you mean? How can a TAP thread the outer wall" Or a screw contact the resultant outside threads? it is just tooooo early in the AM to understand that.

[Bill Shields]

1" diameter tube with 1/16" walls. Drill a hole straight through on the diameter...in one wall.out the other.

Now put the tap in one side and straight through and out the other.

Pot a long screw in the hole that you want to engage both walls.

This describes use of a long tap. Having the long needle point on it mades getting started on the back side a lot easier

[Charles T. McCullough]

ACH! When you said "both walls" I was thinking inside wall and outside wall, lengthwise of the tube, not drilling a hole through the diameter to have holes opposite each other. Sorry!

[Bill Shields]

I was not being clear...nuddin' to apologize fer