While milling some stainless steel I noticed that the spindle was vibrating a fair bit. After poking around with a dial indicator I found I could move the plate the spindle was mounted on by about 10 thou of an inch just by pushing and pulling on it by hand. The other axises I could only move about 1 thou.

I found the holes drilled into the plate to be awful, the holes were very over sized and the bottoms were not flat. I think several of the bolts were not actually fastening the plate to the linear ways. The cast iron was also a bit porous and the screw heads were squishing the metal underneath. Here they also had to grind the head on the socket head screw so that it would fit, some of the holes were out by about 1mm.

So began the process of building a new Z axis plate. This is the raw hot rolled steel plate, 1.25 inch thick. This plate weighed about 60 lbs.

Cutting the plate close to size on the bandsaw.

After cutting the plate I used a face mill to finish the top and bottom. The face mill is a bit beat up, it left deeper machining marks than I would prefer but the surface was flat according to the dial indicator.

After surfacing the top and bottom I squared and cleaned up the sides. Did this with a single full depth pass of a 5/8 endmill, the chips it left were like thousands of razor sharp needles.

The surface finish on the sides was quite nice.

Next step was to set the plate up in my milling machine and pocket the holes.

After a bit, all the holes are milled. Besides the two small holes in the bottom left corner everything was done with a 4mm endmill. I had to take this slow to prevent vibrations due to still using the old Z axis plate at this point.

Manually tapped the M8 holes for the Spindle mount.

Here is the back of the plate, I lightly sanded the surface.

Here is the new plate, installed. Fit perfectly. Now I can only move the dial indicator about 1 thou of an inch.

So far so good, there is less vibration and when it does vibrate they are lower frequency. Will be interesting to see how deep I can cut in a single pass now.

TTFN,

GrantM.