lathe_feedscrew_modifications

lathe_feedscrew modifications

Threaded rod feedscrew:

What, you mean you never thought of this? I guess some people actually enjoy cutting long lengths of threaded rod with a die... Doubled up nut and washer act as a thrust bearing, wingnut is a simple crank handle.

Ball bearing modification:

Feedscrew is turned down to .245" while held in headstock chuck for approx 1.5" of its length to accept 1/4-20 threads on its end. I held it in a drill chuck screwed onto my spindle. I also rigged up a temporary steady rest out of wood to hold the other end while machining. Doesn't have to be very accurate, just so it doesn't hit you in the face. The cleaned up portion of the feedscrew is then cut off of the stub being held in the chuck with a hacksaw, then turned around in the chuck and threads cut with a die aligned in the tailstock.
I used rollerblade bearings which came with 1/4" to 5/16" plastic inserts. The preload keeps the bearings from slipping radially when cranking on the handle, but too much preload makes it crunchy and stiff. Probably could have used better bearings to begin with. The radius on the ball handle was turned using my modified compound slide. The handle itself is a 1/2"x1" nylon spacer on a 1/4" button head screw in a partially tapped hole, with washers to remove axial play.

micrometer collars:

That is a terrible picture. You can't see anything! Let's try again.

Ah much better. Look at those exquisite lines. Lines were cut with a threading tool turned on its side. Carriage was cranked back and forth, 2 turns of the handwheel for 1's, 3 turns for 5's, 5 turns for 10's. I indexed off of my drill chuck keyring which just happens to have 31 teeth. Adjusted the height halfway between the marks and went around again to make 62 divisions, which is close enough to the 62.5 divisions needed for my 3/8-16 feedscrew.

At the bottom of the page, along with it's accompanying explanation, is a postscript file that is easily modified to print out the desired number of divisions in a straight line. The printout is then wrapped around a cylinder to make a graduated dial, like Dave_Gingery's measuring tape trick. This might be easier to do than making your dials on a rotary table. Props go to Thomas Gardner for this one. Edit the file with notepad equivalent and display it using adobe illustrator or ghostscript.

fenn