Rebarreling and Home-Shop Machining

I have been using a .475 inch thick Aluminum plate to adapt a Smithy Compound Rest to my Shoptask lathe which has a higher center height off the milling table. A .485 inch or so plate would be a little better, but I already had this plate. I needed some T-slots in this plate for a project with the Dremel Grinder, so I slotted the T from the back side with a .75 inch end mill and then elongated the slots with a .5 inch end mill. Note that T-slotting milling cutters are available to do this from the top side. I doubt you could use this tool on a small mill due to the huge cut that is involved in using it in one pass after the center slot has been cut to depth.

Photo 1. Mark the work with a Sharpie to color the Al. Layout the outline of the T-Nut with a scribe. Photo 2. Setup the work on the mill. I used V-blocks under the groove for maximum rigidity. I used the left side of the mill table away from the adjustable gib for maximum rigidity. Setup an indicator to run on the long edge of the work. 0 this indicator to the milling table travel by tapping the work around. This is a medium precision project so you can center the milling cutter by eye with your layout lines and a small magnifying glass. Find the top with the paper Method (Photo 3)

Photo 4. I milled at a 120 RPM, 3 inch/minute feed rate. I could Mill .025 inch deep with the soft Al. I used power feed and reversed the mill when it had reached a 0 point on a dial indicator mounted on the side of the milling table. I tried plunging and then reversing, but the mill did not like this, so I reversed with no feed.

Photo 5, I elongated the bolt slot in one pass with a .5 inch Endmill which I centered in the slightly narrower original slot, by eye. Then I widened the T-slot to fit a wider T-nut.

Photo 6. Test fit OK. Photo 7 Job Finished. Photo 8. I used three dedicated indicators to control the job. Indicator at left, slot width, Indicator at right, slot length. An indicator on the end mill drawbar (not shown), Slot Depth.