Home made threading tap

[mars-red]

This is my most recent shop made tool, a tap for cutting 1/4 x 25tpi threads (that's not a typo, it's 25tpi). That's an odd thread size that I decided to use for a small leadscrew I made for another project (which I will also post about when it's done). This was the perfect excuse for trying my hand at making a tap.

I started with a length of O1 steel, center drilled one end and turned a male 60 degree center on the other end. I turned the business end to it's final diameter between centers:


I then transferred it to my watchmakers lathe to mill the flutes using the milling attachment. The headstock of the lathe conveniently indexes, so getting the flutes perfectly spaced was no problem.


This is the same setup for milling on the watchmakers lathe, but here a 6 degree relief angle is being milled behind the cutting edges of the flutes:


I returned the work to the bench lathe, blued it up, and cut the threads:






After the threads were cut, the shank was turned down to the final diameter (the flats at the end had already been milled), and finally the very end of the tap given its final point, removing the male center I had turned to work between centers. It was then polished and lightly deburred with a couple of stone slips. For polishing threads, I usually put some abrasive paste on a slip of wood and let it run along/in between the threads as the work is spun... the wood quickly conforms to the thread profile. In this case, I did the same but with the work spinning in reverse so that the cutting edges didn't immediately ruin the polishing stick.

Here is how it looked before heat treatment:


Being O1, heat treatment was straightforward. Lately I've been using a paste of boric acid (roach powder) and alcohol packed onto my parts while hardening. Especially when hardening in oil, it makes that nasty black scale chip of very easily. It leaves an attractive bright gray finish that polishes up quickly. After hardening (and testing with a file to make sure it was glass hard), I polished the shank and decided to try it out in a piece of aluminum before tempering it. It requires frequent chip clearing, as there's very little room for chips in the shallow flutes I milled, but it cut through just fine. Here is a pic of the heat treated tap, and another of the leadscrew threaded into the test hole:

[kbalch]

Thanks mars-red! I've added your Tap to our Tapping and Threading category, as well as to your builder page: mars-red's Homemade Tools. Your receipt:

Tap by mars-red

tags: tap & die, threading, heat treatment

[mars-red]

Thanks mars-red! I've added your Tap to our Tapping and Threading category, as well as to your builder page: mars-red's Homemade Tools.

Thanks!

Is there any way we could consolidate my two builder pages? I have one under "Max Phillips", and now this one under my registered forum name.

[PJs]

Very Impressive, Mars-Red! Have never considered making a custom tap and your write up makes perfect sense. Interesting threading tool, looks to be an old end mill reshaped...was it carbide? Thanks for sharing a great build. ~PJ

[mars-red]

Very Impressive, Mars-Red! Have never considered making a custom tap and your write up makes perfect sense. Interesting threading tool, looks to be an old end mill reshaped...was it carbide? Thanks for sharing a great build. ~PJ

Thanks PJ! Yes, you are spot on, the threading tool I'm using in there was indeed ground from a broken end mill. I use this one on those rare occasions that require small threads turned up close to a shoulder. It's not carbide, it's HSS. I don't generally care for carbide, I only use it when I need to cut steel that has been left tool-hard (for example, when I've accidentally broken off a tap in a work piece that I want to salvage, lol).

I keep broken HSS end mills and drills kicking around, you never know when they'll come in handy for something like this. Small broken center drills sometimes make great blanks for home made fly cutter inserts.

[PJs]

Most welcome! I too keep all the scrap bits and broken bits...even the sawed off jaws of the calipers for my DRO. You never know when you might be able to re-purpose them and don't take up a ton of room. The idea of end mills for special tool bits is great. I'll give it a try. I get it about carbide being a bit fragile but a must have for the tough stuff and the occasional "Bink"!

Thanks again for sharing! ~PJ