Rebarreling and Home-Shop Machining

Lathing Plastic/ Machine Table Feet

            I have a suspicion that half the wiggle on my Shoptask machine is flex in the feet and thin plates to which they are attached on the stand. The feet are also a bit small for a Linoleum floor. I looked at http://www.northwesterntools.com/ to see what they made that was suitable, mostly to get ideas. They sell machine pads out of PVC (polyvinylchloride). This material is also used for Schedule 40 cold water pipe (the white pipe). I got some 2" plugs made by Lasco with a large wrench flat (as opposed to small square flats) to make my pads. I found some at my hardware store.

             Northwestern tools also sells some 3/4 inch bolt diameter self leveling feet. I decided to use 1 inch diameter by 2 inch long bolts and weld a nut to the bottom of 3/8 plate as these parts are readily available locally at the steel supplies and hardware stores. The bolt head will bear directly on my PVC pads. This sturdy foot will allow the stand and milling machine to borrow rigidity from the slab. The larger diameter pads will keep the machine from sinking through the Linoleum over time. See photo 4 for a finished pad and the raw materials.

            Lathe turning plastic requires a sharp bit unlike the roundnose tips found on most inexpensive indexable carbide tipped tools. When you turn metal the surface is torn. A slightly rounded tip does a good job here as it tends to burnish the metal back smooth. On plastic this same tip will create a lot of heat and melt the plastic creating an ugly surface finish. I tried my indexable tip, that is shown in photo 1 ( but not against the work) just for grins and, as expected, the finish was horrible with lots of melted ridges in the work. The plastic needs to be cut, not torn. I switched to a brazed on tip tool that is shown facing the plastic and got a nice almost shiny smooth finish. The edge of the bit is not rounded over from the top to the face at all. The nose does have a radius. It produces a nice continuous thin ribbon of plastic with no melting. On a back pass with no feed it shaves a very thin layer of plastic away. That is how clean the edge needs to be to get a good finish on plastic. It is out of the box. I have not modified it. Note that indexable tips with a smaller nose radius are available, but not by most hobby type suppliers.

            Photo 2 shows the finish left by the indexable carbide tipped tool on this PVC plastic on the left. On the right is the finish left by the brazed on carbide tipped tool. I kid you not. The finish on the right is right off the lathe, no sanding.

            Photo 3 shows the parting operation. I have not had much luck with this parting tool holder as it seems to have way too much flex. This is to protect the blade, I imagine, as parting is a very strenuous operation. I first stuffed the slot with leather. Still not much improvement. Most of the time, I use a brazed on carbide grooving/parting tool, that works much better on steel. It will not go to the center of a steel rod, though, so I finish the part with a hacksaw with the lathe turning and then face it clean.

             Now I have used a 3/32 inch nickel welding rod to weld up the slot. This is visible in photo 3. Worked great on the plastic. There is still probably enough flex in the setup as this is a small lathe and tool holder, but I have not tried it on steel or brass.

Finished Foot

Photo 5 shows the finished machine table foot upside down. The strap is 2 inch wide x 3/8 inch thick.

Examining the Nub/ Cutting Tool Height

            You can tell if your cutting tools are at the right height by examining the nub left on the center of faced work. If the nub is a cylinder the tool is too low. If the nub is rounded off the tool is too high. If there is no nub then your tool is at a good height on a small lathe. Run the bit slightly low for a big cut turning the diameter on a larger lathe. 

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