Hi, all!
For the last few weeks I had been putting some effort into machining the additional parts to convert my Sears Craftsman from a wood lathe into a jewelery lathe.
I ran into a very bad snag, when I discovered that the pulleys I was going to bolt onto my end support inserts to support the X axis ways screw were made of such hard steel as to be undrillable!
Can’t bolt ‘em! Sorry!
So, I had to figure out how to fashion substitute parts to support the ways screw. I tried several things mostly involving using the keyless chuck and the rotary table. But without a 3-jaw clamp for the rotary table I was stuck, because I haven’t figured out how to properly indicate a 4-jaw clamp yet!
It finally got to where I was considering spending another $20 just to buy a 1/2 inch cobalt drill bit (the only kind certain to drill into 6061 Aluminum), when I thought to myself… Doofus! Doesn’t your milling machine have codes to cut circles?!?!?
I never did that before, but I was now sufficiently frustrated with my drill press and rotary table to give it an honest try. Once I figured out how to locate a circle’s corner and then mill the circle’s arc, it was easy to create perfectly aligned concentric circles.
Which meant, I could now create a combination stop nut and screw support. It took several tries, but here’s how.
Preparation:
Mr. Ryobi helped me cut a small amount of aluminum barstock as needed for 4 stop nuts. BE SURE TO KEEP BOTH THE BLADE AND THE WORK WELL OILED!
True the vise on your mill table using a precision square.
Four sides of the bar stock are completely square as it comes out of the factory, this fact can be used to define a fifth surface normal to them all.
X axis touchoff using a .0015 feeler gauge
Next, the Y axis touchoff.
Use a cube of same squareness as bar stock to ensure the stock is normal with respect to the vise.
After centering X and Y (compensating for feeler gauge thickness), touch off Z axis.
Compensate Z axis by thickness of feeler gauge. The endmill is now centered with respect to X and Y axis and is at zero vertical distance with respect to surface of stock.
Creation:
1) I moved my 1/4 inch roughing endmill to the first quadrant just beyond the corner of 0.625 square bar stock, a few inches that were mounted vertically in my vise.
2) I plunged Z axis down 0.26 inches. I allow about .01 inches to remove later.
3) I used G1 X0.24 Y0.24, to move the endmill to the circle’s corner for a 0.5 inch width cylindrical plug at 0.1 inches per minute, making allowance for the rougher’s apparent extra cutting width. This is intended to mate with a 0.5 inch width hole in the end support.
4) I then used G2 I-0.24 J-0.24 to create the cylinder.
5) I then lifted the endmill above the work, then plunged straight down to make a hole at 0.26 inches deep at 0.1 inches per minute, adding fresh EVOO for lubricant every 0.01 inches to prevent fouling.
6) I then used the G1 X0.015625 Y0.015625 command to move the endmill INSIDE the hole about 1/64 of an inch on both X and Y.
7) I then used the G2 I-0.015625 J-0.015625 to bore the extra diameter around the endmill’s normal thickness. This would create a hole to later guide a 9/32 drill bit on my drill press.
The entire part is intended to be threaded throughout for a 5/16 inch diameter way screw. The purpose of the part is to hold the screw as the round part, about 1/4 inch long, rotates in place inside the aluminum support. The square part, also 1/4 inch long, will be of use as a square stop nut, with set screw holes to be later drilled and threaded. It seems to me to make sense not only to provide set screws but also to thread the part throughout for an firmer grip on the way screw.
Aftermath:
After practicing to find the right sequence as documented above I finally created a set of 4 parts that were nearly perfectly radially symmetrical. But during the entire exercise I learned that I had to compensate about .01 inch in radius for the rougher to create the outside diameter.
I really wanted to determine just what radius relative to the rougher’s center that I needed to create a hole that would be a snug yet effortless fit for the round part of the stop nut to rotate within the end support.
Several holes later, I determined that to be 0.95 inches radius [final measurement pending] that would fit 3 out of 4 parts. I’ll cheat, and sand the fourth part to fit.
Here are all the end supports, ready for drilling. Note also the stop nuts to hold the way screw in place rather than using the undrillable steel casters.
‘Till next time,
Aulë
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