The following is further evidence why probing for the center of a cylinder is preferred over using traditional indicator methods for a Sherline mill due to space constraints.
My Sherline mill is a
2010 model with a
2" column riser added to increase vertical clearance. I made a tool to allow using a test indicator to zero the X/Y axis against the cylindrical work piece. Due to the length of a test indicator the Z axis is only 5 mm to 10 mm from the maximum Z axis position. By comparison the Drewtronics touch probe when mounted in the Sherline
3/8" Endmill Holder is about 30 mm shorter. Potentially the back plate of the Drewtronics touch probe could be replaced with an aluminium plate with a 3/4" 16 TPI thread mouting for the Sherline spindle nose, this would provide an additional 40 mm clearance. To put this in perspective the total mill Z axis travel is 140 mm (30 mm is 21% of the Z axis travel)
The mounting tool for the test indicator was made using two 3D printed parts, a M6 x 40 mm hand bolt from Bunnings, a 3/8" x 1-3/4" x 0.035 compression spring (Bunnings), a 100 mm length of 6mm harden ground linear shaft rail (eBay) that was cut by hacksaw into 2 x 40 mm + 1 x 20 mm lengths. I found cutting the hardened ground shaft was an excellent way to remove the teeth from the hacksaw blade ( *grumble* ).
Using a test indicator was challenging as the range of the indicator was 0.4 mm, this means that the position of the axis needs to be within 0.4 mm of the true center before the probe remains in contact with the cylinder for a complete revolution. Once the touch probe was properly in contact with cylinder making the final correction to center the spindle over the cylinder was fairly quick. Total time from mounting the indicator in the spindle to zeroing the work was about 5 minutes.
Summary:
Using a touch probe has advantages of both clearance (21% additional Z axis clearance) and speed (30 seconds vs 5 minutes).
