Rebarreling and Home-Shop Machining

Transfer Screw Scratch

Photo 1 & 2 shows the transfer screw making a scratch when I lowered the Quadralift (The making of this screw is described in the topic Transfer Screw in this Journal). I plan to mill a 3/4 inch slot centered on this scratch.

Milling Slot, Setup

I planned to test the rigidity of the fifth column supported mill head by finding the maximum depth of cut that can be cut with a 3/4 inch two flute mill. I prepared some bars similar to the 1 inch square bars in the topic Drill and Counterbore 1 inch square stock in this Journal. The plate is screwed to the bars with recessed socket head cap screws and then these bars clamped to the bed. This will produce a rigid setup of the workpiece to test the mill head. I plan to use flood coolant. This arrangement of the plate will produce a convenient flow path for the fluid into the stock pan. I center punched each end of the scratch and then used the wiggler alternately in each hole to align the plate on the bed. Photo 3. I also plan to surface the plate with the mill, but may have to use a different setup due to interference with the lathe spindle flange.

Hard Stops, Coolant Hose

Photo 3 shows the coolant hose and brass nipple coming in from the right. The hose is supported by a clamp on a magnetic indicator stand and directed at the milling cutter. I have placed two temporary stops on the lathe. One is attached to the lathe spindle flange. I adjusted the bolt so the power feed would stop the milling when an indicator that has been removed indicated 0. This indicator was zeroed with a wiggler centered on the punch mark at the end of the slot. On the right I have used a bolt near the bed on the carriage which will hit the tailstock and stop the movement in the other direction. I was using temporary clamps on the fifth column which are shown in photo 4.

Milling Plunging

Photo 5 & 6. I first Plunged the 3./4 inch two flute center cutting mill at each end of the slot. This provided a good exit for the coolant and chips and easy depth changes at the end of each milling pass. This particular Chinese import two flute mill was not very even cutting (one tooth bit harder) while plunging and made large demands of the setup rigidity. I locked the milling table and carriage and made the plunge at 2 inch per minute. This produces about a .008 inch thick chip which is suitable for this large size mill. In the future I would drill the ends which will make for an easier plunge.

Milling Depth Test

Photo 7 & 8. I made a short pass at .020 depth. No Problem. I then made a full pass at .100 inch depth. No problem. I made a full pass with .150 inch depth. Again no problem; slight rattling at the end of the pass when the milling cutter passed the edges of the holes. I decided that .1 inch was a good depth for this 3/4 inch cutter. I made all the following passes at .1 inch depth and 2 inch per minute which produces chips about .008 inch thick. The mill produced huge volumes of chips. This depth of cut was 21 times deeper than I have cut previously in steel (with no fifth column). The rigid fifth column was really doing its job well. I was very pleased with the depth of cut possible in steel. It should be a little stiffer still when the slotted plate is mounted up.

Milling Sides at Full Depth

Photo 9. I took a couple of .010 inch wide passes on the sides of the slot at full depth to widen the slot just a bit for good clearance on my 3\4 inch cross arm clamping bolt. I got a really nice surface finish on these passes with coolant. No complaints from the mill

Modified Drip Pan Test

Photo 10 & 11. The drip pan modification on the right to catch coolant on the end of the lathe worked great. It was deep enough at 1/4 inch to catch all the coolant that could run under the tailstock. Allowing the bed to drain provided more coolant at the pump than sealing the area under the tailstock.

Milling the Face of the Plate

Photo 12 & 13. I had a 2 inch shell end mill that I used to Face the Surface of my plate. I solved my setup problem by taking a cross pass on the end. This way I avoided the lathe spindle flange. I used 4.5 inch per minute at 125 RPM and made two passes about .005 deep. The finished surface was pretty flat when tested against a straight edge by eye while still clamped down. It stayed flat along the long dimension of the plate when I remove the clamps. I had some small unevenness across the plate. Doing two passes should have helped removed some curl. I will touch up the surface by testing on the surface plate and scraping any high spots. The finish feels good to the finger. Photo 14 shows the finished plate.

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