Tuesday, February 23, 2010

Mini Mill Modifications / Shumatech DRO

I have not yet modified my Mini Mill to the extent I have the lathe, but I have added the upgrades I consider most essential:  Belt Drive conversion, Gas Spring mod, and most importantly, a Shumatech DRO.  My previous experience with mills was on Bridgeports with DRO's and I really missed having one. Especially on the Harbor Freight Mini Mill, with it's non-standard dials and considerable backlash.
Fortunately, Scott Shumate had created the affordable Shumatech DRO-350.  Also fortunate, the Chinese developed amazingly cheap digital calipers with a data output port.  Put them together, and the hobby machinist can have a DRO that rivals commercial units for a fraction of the cost.

The Shumatech is a fun to assemble kit.  It takes about 4 hours to solder.  It is more than just a simple readout, with several built in functions like finding centers, drilling bolt hole circles and compensating for tool diameters.  It has made me a much better mini-machinist.
       Kits are available from Wildhorse Innovations in the USA and Model Engineers Digital Workshop in the UK.

Adding the scales is fairly easy. There are many ways of accomplishing this, and every installation I've seen is different. Here is my way. My Z axis mount is different than most, for the scale beam moves while the caliper head is stationary. I prefer stationary heads where possible, because the wires do not have to move with the head.
  While there are many ways to mount the scales, I recommend you attach the wires my way.  Out the bottom of the scale.  Why?  Three reasons:  It is a much stronger arrangement.  The bottom of the readout head is thick and makes a great strain relief.  Also, the wires run through the head, instead of exiting immediately.  The solder pads are fragile and having the extra wire inside reduces the chances for fatigue.  Finally, wires exiting the top are often in the way.  I could not have mounted my X scale so compactly if the wires exited the top.

My latest acquisition is a rotary table.  With a 5 inch lathe chuck attached using clamps of my own design, it has been a valuable addition.  I could not have made my lathe modification without it.
      This Rotary Table and many other fine accessories are available from Little Machine Shop.

My brackets.  This photo shows two which are complete, and two which still need holes drilled.  The brackets are a few thousands lower than the table surface when tightened. This ensures that the chuck is firmly clamped to the rotary table.  A centering plug may be fabricated to ensure exact centering, but since this is a 4 jaw independent chuck, I haven't bothered.  It is necessary to use round head cap screws because the heads are slightly inside the T slots.  Because of this, each screw can be turned only two turns at a time, making installation and removal a little slow.

Update:  For information on my solid column conversion, click here.
For info on upgrading to a larger table, click here.

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