Sherline Spindle Mounting Block

5 Bears Home Homebrew CNC bench mill

The basics of the Z axis are now complete. I did fashion a simple motor mount plate which is seen here. The plate itself is bored 1.5" and has a standard NEMA 23 hole pattern. The motor in this picture is, however, a much more powerful NEMA 34 brushed servo. I'll go into the why's and hows of this motor swap later.

Essentially then I could power up the Z and move the spindle backplate up and down at a nice clip. Due to the geometry of the column in relation to the table, there was no way to directly mount the Sherline spindle directly to the spindle backplate. An additional 2" or so was needed between the spindle centerline and the backplate, so that the spindle would be in the heart of the Y-axis envelope, and the motion generated by the controller would allow machining over 90% of the table, as well as possibly machining overhanging work on the Y-axis.

To do this, I decided to make a fairly large additional standoff block which would handle both the Sherline and the KAVO HF spindle, as well as possibly mounting the R8 mini-mill spindle... basically a "jack of all trades" standoff block.

I was getting concerned with the overall weight of the spindle. I have only one motor with a brake. A motor brake is a 24VDC device which clamps the motor spindle in place when the power is off. This is needed with ballscrew assemblies mounted vertically. The ballscrew is so efficient that the weight of the assembly will cause the spindle to slowly drop with the power removed, ultimately colliding the spindle with either the table or the vise. Not good. I took care of that problem which you will see in a later installment.

This page, then, deals with a simple block standoff. Since the spindle area draws the eye, I wanted it to have a nice finish.

PostScript: With this module complete and mounted, over a few weeks, I began to slowly hate its appearance! It looks like a wedding cake, with the base being the spindle backplate. While functional, it just flat-out looked like crap, and it has since been replaced with what I call a spindle foreplate, a slab of aluminum with dimensions similar to the spindle backplate, offset from the backplate with 2 heavy aluminum standoffs.

To get to this point, a large block of aluminum was face milled and trued on all sides. The four corner holes have been drilled and countersunk for 3/8 x 16 SHCS... probably overkill there.

The back side of the Sherline spindle, where it mates to this block, has only two 1/4" X 20 holes and a keyway to secure it. Two holes then are drilled at the correct location.

Oddly, I couldn't derive any offest dimension for the keyway slot on the Sherline spindle back. Usually, you'll find such a cut in a commercial product at one of the major imperial system dimensions (3/8", 1/2") or at least a metric dimension in whole mm. The English offset of the keyway slot relative to the bolt holes was something like 0.484", or 12.3mm. Likewise, I got equally nonsensical dimensions from the edge of the spindle housing. So I milled the slot as best as I could measure it in the correct location.

The keyway is 0.187", or 3/16".

The keyway is set in place to test the fit. It is tight in the spindle, and looser on this plate, as I wanted.
Here is the mating of the spindle housing to the mounting block. The entire assembly is flipped and a pair of long SHCS does the job.
  One solid unit!

This spacer block is intentionally large so that I can use it for the KAVO 4041 spindle. I will simply have to drill a few more holes in the block to mount a clamp-ring type of spindle mount.