Making taps

There was recently a thread with instructions on how to make taps "the old fashioned way". In the past I've tried to grind homemade taps in the same manner as commercial ones and had no success at all. I needed a M6x0.35 tap, so decided to give it a try. Cut the appropriate sized thread on a piece of O1, heated the tip to red and quenched it. Then I ground four 30 degree flats, a bit hollow from the wheel actually. I was skeptical, but by gosh, the thing cuts like a dream. Can't remember the thread, but my thanks to whomever suggested this.

Any pics buddy?? Sounds great.

I was the guy who put up the information. I have to make odd taps all the time to do antique repairs like the spinning wheel flyers I posted pictures of weeks ago. they are frequently left handed taps.

Glad it helped you out. My work mates were always trying to avoid making taps,but it is less trouble to make 1 up than to look all day for 1 or spend money,sometimes big money on one.

Good plan.

I have always actually fluted them, but there really isn't likely any reason to have cutting edges anywhere but at the front end, like a machine reamer, or a "gun tap".

Gwilson- thanks! I didn't see the photos, so I hope mine look about right. The flats could be deeper, but these threads are so small that what's there seems adequate. It motored through that brass test piece with no problem and it's hard enough I'd expect equally good results with steel.

Conrad Hoffman said:

Gwilson- thanks! I didn't see the photos, so I hope mine look about right. The flats could be deeper, but these threads are so small that what's there seems adequate. It motored through that brass test piece with no problem and it's hard enough I'd expect equally good results with steel.

Click to expand...

Thanks guys.
Knowing this effectively gives me the entire range of 60° taps in both RH and LH configurations. Heck a person could even make a progressive Acme tap.

Raymond

I'm curious, if you don't mind, as to what you were using that thread for?
Payson.

There's a small off-the-shelf optical component (special lens) that has a M6x0.35 external thread that we needed to mount. It seems they could have picked a more standard thread, but that's the one they chose to use.

Stupid question.......

Looking at the tip of that tap. I see that all the "cutting edges" have a very definite and large "negative rake".

It seems that the tap so "sharpened" would be much more of a "forming tap" than a "cutting tap".

Do you find that to be the case? Or do you get actual swarf from it?

I rehair and restore / repair, instrument bows in my off hours. We see a lot of fine and coarse metric threads. The .35 is not uncommon to me. I too make my own taps out of necessity. Sometimes on the +, and sometimes on the -.
All the best.
Payson

Conrad Hoffman said:

Gwilson- thanks! I didn't see the photos, so I hope mine look about right. The flats could be deeper, but these threads are so small that what's there seems adequate. It motored through that brass test piece with no problem and it's hard enough I'd expect equally good results with steel.

Click to expand...

Wow, I'd never even have tried that, cut or formed, those brass threads look great! I'm with JST, much swarf?

Bob

It used to be common here to find commercial taps ground flat on three sides in small sizes. I think the idea was that they were stronger than fluted taps. The little spiral taps you can get now cut so well you can't get the three sided ones anymore. Easy to make in a pinch though. They do 'cut', and make a very nice thread.

This is a 1.5mm commercial tap:





You can see that in addition to the three main flats along the body they've ground a taper on the thread a little more than one diameter long.

JST said:

Stupid question.......

Looking at the tip of that tap. I see that all the "cutting edges" have a very definite and large "negative rake".

It seems that the tap so "sharpened" would be much more of a "forming tap" than a "cutting tap".

Do you find that to be the case? Or do you get actual swarf from it?

Click to expand...

Could it be that they are actually almost "zero rake" for the commercial one and a combination of positive on one face & negative rake on the other face for the home made one? That is looking axially rather than radially.

These old taps served for hundreds of years. Conrad,you did just fine. So long as the squared up end of the tap goes below the minor diameter of the threads,plus a bit smaller,just as you have done,the tap will cut just fine. Your tap looks just like I make them. I have also made the tips triangular. I have bought small diameter taps that were made commercially,and are triangular,like the Swiss ones show.

These taps definitely do cut,and eject chips out ahead of the tap. The chips have no where else to go.

If you looked at the pictures of 2 dovetailed planes I made,I did make special "Acme" styled 19th.C. thread taps to put in the cap screws with. They aren't exactly modern form acme threads,but similar. I also made a short Acme left hand tap when I had to make a new tailstock quill for a 12" Rockwell lathe I once rebuilt. It tapped the steel quill just fine so I could use the original handwheel and its screw.

There is no need to make the flats as long as the Swiss examples shown. They are stronger if you don't. I also do not make these taps any longer that is needed to tap the required hole,to keep them from being weaker and possibly snapping off.

I also make taps that have just 1 flat,tapering out to nothing as you have done. The end has to be relief ground,so that the cutting edge can bite into the metal,else it won't cut. The single flat tap actually offers a more acute cutting edge than the other 2 options. All of them seem to cut,though,improbable as it seems.

I hope more folks see this useful and quick way to make a tap.

As a note,these taps are fully hardened,then drawn to a dark brown or purple color. They will do steel just fine. You can grind the flats a bit to resharpen them. But these are special taps that I only ever use for a few holes on a special job in antique mechanism repair. I save them,but being non standard back then,the taps probably won't fit another of my jobs.

As I said, I was skeptical, but they cut like crazy, sending fine chips right out the front. It's hard to see, but the "flats" are somewhat hollow from the wheel radius, which helps the rake slightly. Now I'm thinking about trying an Acme, maybe with a shallower angle on the grind. If I could avoid buying those very expensive Acme taps to repair lead screw nuts and such, that would be great.

As said,Conrad,I have made acme taps. I caution you to not make the taps ANY LONGER than needed to tap the hole. Even HSS acme taps are easy to break if used too hard,and they USED to come in sets of 3,to gradually enlarge the hole. At least,I have some old ones that are like that.So,do use caution. Draw them to purple.

To get the most accurately square holes with these old style taps,I drill the holes in the lathe,and tap them in the lathe if possible.

One last remark: I don't even strive to grind the 4 ,or 3 flats on center. If just 1 corner cuts,thy have done just fine,and I haven't made them for producing lots of tapped holes anyway. Most of my taps haven't even got a hollow grind. I just hit them on the belt grinder. If I feel I need to,I might hone them sharper afterwards. Usually I don't even do that. I WOULD HONE THE ACME TAPS.They have a much greater amount of metal to remove.

I think you'd be best off grinding a 1 sided cutting edge as I did for my lathe tailstock quill,which was tapped into steel. Grind just the same as you did for the 4 sides tap,letting the 1 side taper out pretty quickly,say,in 1 1/2 diameters of the tap. Then,grind the end of the tap to below minor diameter,and rotate the tap,grinding ever deeper as you go around,to provide clearance. I say this because I think this tap style has a better,more acute cutting edge.

I don't know what steel,or how deep you intend to tap,but it might be a good idea to make 2 taps with the same MINOR diameter,but with the first tap cutting perhaps 1/2 the full thread depth. Then,of course,you will have to feel your way into the first thread when you use the 2nd. tap.

I'm not sure making the taper of your tap longer would be good or not. You still end up cutting just as much metal away when tapping anyway,but the tap would be longer,and prone to twist more and snap off.

I had made a pair of acme taps about 1" diameter to make new nuts for a milling machine's leadscrews. I had cut flutes in these just with the corner of an end mill,to make 4 flutes. I wound up not needing the mill and sold it along with the taps. The person has not yet gotten into making the new nuts,though. These taps would have been relief ground just like commercial taps,except the flutes were not circular.

I advise you to test your acme taps on something unimportant before you use them for the real part where you've invested a lot of work. Good luck!!!

George, have you ever turned a minor diameter pilot on a shop made tap, to use on a part that will not fit on a lathe, on a drill press table or under a hand tapper?

Just curious, seems like second best, got a situation coming up. I realize that it would require a chip relief section, emerges from the hole to drop the chips, after several threads have been cut square.

Bob

Robert, great minds run in the same channel, or is it rut? I was thinking about exactly the same thing, as I've got some parts that would be very difficult to fixture, and I don't want to start the thread at an angle. I have a commercial tap with a pilot, but it's fluted in the usual way.

I haven't done that.Of course you'd have to make a place for the chips to go. Maybe you could tap a few threads with it,and use a normal tap to finish up.

Bringing back my necro-thread, are there any tricks to making your own forming taps? I know Balax has some special patented/proprietary grind they use, but anything else? I'm thinking a bit of taper so the threads are largest at the tip might help. Or are DIY formers a bad idea?