AC setscrew taper?

Anyone with access to an optical comparator out there?

I'm a foot away from one 5 days a week(at this minute), which screw, I am sure a have a loose one or can take one off.

Never heard of set screw tapers but could be. Some greese fittings and pipe thread are all 3/4in per ft. AC use some pipe thread on hyd.

They were used to hold the starter in, the belt pulley has one and the front crankshaft pulley has one. What have I missed?

Like this one? From McMaster-Carr?


Gerald J.

Steering arms on spindles,brake pedals on G,bearings lock on G axle,hand clutch lever shaft on several to name few.I have several made to make the reproduction brake pedal shafts for G and WD. HTH Tracy Martin

Unless the mating parts have a tapered hole to match, the taper angle is there to force alignment of a straight hole with the straight threads, and is not terribly critical. Changes in the slope change the side force multiplier from the thread motion. Much like a Gib key, but in this case round and perpendicular.

Since set screws tend to be very hard, a machine shop would probably need to start with a long screw and set up a tool post grinder to make the shape. They'd lock two nuts near the middle of the screw to drive it, with a loose one near the head to center it in a 3 or 6 jaw chuck and grind away. Several minutes per screw. Sounds expensive. If you have one in good shape, they can mount it the same way with a dial indicator in the tool post and swing the feed until its parallel to the existing screw and don't need to know the measured angle. Its probably too steep to use the taper attachment and using the dial indicator on a good part is the best way to set it. The angle they'd start with is the angle from the axis, not the included angle which is what Steve M tried to measure.

Grabbing the screw threads directly isn't great for the threads or the chuck. A threaded collet would be used for production work.

Rather than the complication of two strips of metal, why not two THIN feeler gauges, or cut a slot in one strip of metal, then adjust the angle until it fits the taper. Either takes out most of the uncertainty.

Otherwise measure the diameter at two points having carefully marked them and then measure the distance between them, and put a scientific calculator to work to get the angle, or just give the machine shop the three measurements. E.g. .127" from the end the taper diameter is .364" and .637" from the end the diameter is .567". That's 21 degrees included angle, or 11.5 degrees to turn the tool post feed. formula. tool post angle = inverse sin ((bigradius - smallradius) / spacing) where the radii are half the measured diameter. The included angle is twice the tool post angle.

Gerald J.

Gerald, I've turned a lot of hardened bolts and set screws in a lathe. The easiest way is a 5C collet. Chuck right on the OD. Carbide inserts are not effected by hardened bolts and I have never had a problem with the threads spinning in the collet.
 Steve, if the set screw was reshaped, the hole it goes into will be more effected than the setscrew. Unless you can redrill the hole to make it round, I don't think the angle on the screw would matter much.

Charlie this cheap little fix has turned into full blown major O/H with line boring,decking block/head and a NEW crankshaft  so I'm counting on a "good" hole in the crank.

Gerald; AC tapered setscrews allways fit in a tapered matching hole.