Comments are moderated. Please be patient. It may take some time for your comments to appear.

Wednesday, January 2, 2008

Turning a (Short) #2 Morse Taper

I've recently purchased a 6" rotary table. One of the first things I'm going to do is make a chuck adapter that will allow me to use the chuck from my lathe on the rotary table. The plan is to make a part with a #2 Morse taper on one end, and a straight stub on the other to center the adapter on the rotary table.

There are two ways to turn a taper (or maybe more). One is to turn a piece of stock between centers with the tailstock offset just the right amount to get the taper you're after. The other is to use your compound mount turned to just the right angle. The problem to solve is how much is just the right amount.

I decided to turn a short version of a #2 morse taper using my compound mount. It's short because the compound travel on most 9x20 lathes is in the neighborhood of an inch and a half. As long as you can live with a short taper, it's the easier of the two methods.

The photo shows me setting the angle on the compound. I used a MT#2 dead center to provide the proper angle for the compound. I installed the left end in a piece of drill rod that had been center drilled and clamped in the lathe chuck. The right end fit in a live center installed in the tail stock. This procedure works if your subject taper has a countersink in the end. Mine did. I used a 1-2-3 block held against the side of the compound slide to extend a surface parallel to the slide up to the subject taper. Yes, 1-2-3 blocks are flat, square and parallel. Then all you have to do is crank in the cross slide till the block touches the taper, and tighten your compound clamp. This is a little fiddly, and you might have to do it a couple times to get it right, but it can be done.

Once you've got the compound set, use it to turn your work to the desired diameter. I was turning the large end of the taper. The only problem was that it didn't work. After three tries, and setting up three times, I still had a wobbly taper when I installed it in the socket in the center of my rotary table.

I finally got out my dial test indicator and set it up to measure the distance from the tool rest to the subject taper as I moved the compound slide back and forth to see how far off I was. As it turned out, the problem wasn't the setup, it was the compound slide. There was .005" play in the slide at the far right end of travel. That's too much for turning a taper.

The short term solution was to tighten the gib screws to the point that operating the compound slide was difficult as a result of the screw tension, and then turn the taper. This time it worked as planned. When I installed my QCTP I wrote that the weak link in the compound rest was the gib and gib screws. This just reinforced that opinion. Shortly I will be building a new gib and new gib screws, but that's a post for another day. It's time to finish my adapter.

1 comment:

FleaCircusDirector said...

Saw an nice article on Home Metal Shop that uses a boring head to offset a live centre for taper turning.