Advice requested

[docsteve66]

Need advice from anyone on how to makea tap. 1 15/16 by 14 TPI. Two time use in aluminum, old Henderson motor cycle (4 cylinder in line) crankcase. Advise materials, and construction. Want to avoid heat treating problems if practical.
Steve

[spope14]

Can you internal single point thread this unit? This would be the best method. Just a thought.

I have made taps that act like those form taps, but with limited success. I will see if I can find some info. I always have to look this stuf up.

It is not fun.

A second suggestion, and this can work....

Get a lathe setup for the part, and use one flute of a 7/16 - 14 tap set up like a boring bar, the compound set right parallel to the direction of the cut. Use the tap like a boring bar, and set the machine up to 14 TPI. Chase it in. Taper taps work best for this operation. Slight negative rake on the flute, best use a two flute tap.

I have done this a few more times than to admit, it works great. The compound rest set parallel to puse the backlash forward, and I use the carriage running back like a bore, and make passes at about .003 or so.

Try this on scrap first.

Get the bore size for the thread right before starting, formula: bore diameter = major diameter -(pitch of thread x.541 x2)

The pitch is the distance between points on a thread for those who do not know, or 1 divided by the number of threads per inch. Pitch is NOT the number of threads per inch.

[kgarver]

Are you going to tap a brand new thread (twice) in the aluminum crankcase or just clean up ones already there? If its the later use 4340 and thread it to size using the three wire method. Flute it on your mill (someones mill!) square off the end and have at it! You can hand grind the undercut on the ends of the flutes. If you want to be high class you need to center drill both ends of the tap off from the
centerline about .050" to .060". Using that set of centers will give you the relief that you'll need when you turn it on your lathe. BTW there was an article about a year ago in HSM by a person that did this (made his own tap). He used some really tuff aluminum/silicon/bronze bearing material out of a big trucks differential bearing to make a split crossfeed nut for his small lathe. I'd get it and read it first. I can't recall what material he used to make his tap out of. I hope like H_ _ _ that this is a through hole.

Now if you are going to make new holes, after TIG welding up the old ones, I'd make two taps. The above one and one that was about .020 -.025" smaller on the PD (pitch diameter). That way you'd have a roughing and finishing tap. No heat treat and it could be done in one (long) evening of play!

I assume that its one of the through holes that either attaches the motor to the steering head or the rear suspension. Let us all know. FYI I used to have a '46 Indian Chief w/a '48 motor many moons ago.

[docn8as]

O1 heat rx not a problem ..very forgiving....heat to lt cherry red ,plunge vertical in oil ....put in wifes oven @400 deg. for one hour ,turn off & let cool ...ur done .............after fluting ( a regular end mill , horiz. convex cutter or ball point end mill, last two providing some rake ), u can( and should) on a large tap, back off abt 3/4 of thrd ..magic mark it & file relief .have also , as suggested , successfully used a small tap of same thrd for single pointing many times

best wishes
docn8as

[SJorgensen]

I spent my Sunday removing an old Ramsey PTO winch from a 1969 J3000 pickup I bought in December. (I'll get to taps soon) Sure enough every time you have steel bolts in old aluminum housings you have a bad situation. The heads of 7 of 8 bolts snapped off, leaving 1/4" studs holding the winch in a welded up tight heavy steel frame. I was screwed. No way to drill them out either. God I'm glad I have some neat tools now (in my old age of collecting tools.) I got out my hydralic tools and was able to rig up a ram and stretched the frame enough to slip a hacksaw blade between the winch and the frame and cut off the studs (I need a sawsall!) Got my first chance to use my Harbor Freight sand blaster too. So on Sunday I had to drill out and tap those holes. Easy outs didn't have a chance. I have a tap set, so I didn't have to make one. Aluminum is so soft that I would just get a piece of steel pipe that has the thread you need. Assuming you aren't tapping a blind hole, I would taper the end of the threaded pipe and then cut some sharp groves across the threads. Do this all the way around the pipe piece. If you can get it to guide into the existing threads in your piece it will chase the threads and might solve the problem. If that isn't workable step up to the next thread size. IMHO I don't suggest that anyone follow my advice but me, because I've screwed up lots of stuff with my methods and its only ok because it is mine.

Spence