Rebarreling and Home-Shop Machining

Transfer Punch

Photo 1. I am using a 3/4 inch slotted plate bolted to my fifth column. This plate will be attached by ½ by 13 thread per inch socket head capscrews that go through the Drilled and Counterbored one inch square Bars whose preparation is described in my Journal. I needed to accurately transfer the locations of the four holes to the 3/4 inch plate. I used a ½ inch transfer punch which is shown in the photo from an inexpensive set that I purchased at Harbor Freight Tools ( Do a Keyword search for Transfer Punch in the top left column of the Harbor Freight Web site.) A transfer punch fits the hole closely and has a small raised point that will not interfere with the centering of the punch. I added a strip of tape to the bottom of the plate and placed it in the opening. This tape will allow clearance on the paint film. I punched the location of the four holes. The plate will then be drilled and tapped ½ x 13 thread per inch. After the mill is back on the table I plan to mill the slot in the plate to test the rigidity of the new fifth column. An alternative approach would be to cut the slot a little small with a Sawsall and a course metal cutting bimetallic blade, and then clean up the slot with the mill.

Wiggler

Photo 2. After the holes are accurately center punched, I clamped the plate to the milling table and used a wiggler to align the center punched hole with the milling spindle. Lower the Wiggler into the punched hole then run the mill and lift the wiggler with the mill running. If it does not wiggle or is not out of focus then you are centered. I used an SPI brand precision chuck with the wiggler and center drill. This chuck is longer than the standard chuck which helps finish the drilling without moving the quadralift.

Center Drill

Photo 3. I used a fat center drill to start the hole. I set up the quadralift height using the center drill at maximum quill extension. Use of a Wiggler and Center Drill will achieve an accuracy of about .003 inch or less which is suitable for this project.

Drill to Size

I used a 27/64 ths inch drill with cutting fluid to drill the hole. I used a hand assisted power feed set to cut .010 inch per revolution of the tooth. This gives a feed rate of .010 inch/tooth x 2 teeth/revolution x 125 revolution/minute = 2.5 inch per minute. This produced good chips. Photo 4. Alignment should be good from the center drilled hole. Using the standard chuck preserves the precision of the SPI precision chuck.

Tap

Photo 5. I decided to drill all the way through instead of using a blind hole and tap 1/2 x 13 thread per Inch to avoid having to buy a bottom tap which I did not have on hand. I had a tapered plug tap. I used a Morse #3 Center in the milling spindle to guide the tap which has homemade handles.

Do this complete set of operations to one hole then align the mill with the next hole.

Chamfer

Photo 5. I used this inexpensive 82 degree counter sink bit item #07939 from www.Harborfreight.com to chamfer the holes by hand until I could feel no lip on the hole with my finger. Harbor Freight also has a set of countersinks starting at 1.5 inch available just recently that I have ordered item # 91373-0BMA. Also at a good price. I could have used the larger set on my 3/4 inch holes in the 1 inch uprights. The largest tool in this set is 3/4 inch.

Installed Plate

I installed the plate with the ½ inch socket head capscrews. (Photo 6) The screws started by hand with no difficulty. This is the result of the accurate placement ofthe threaded holes. Theplate is coated with DoAll’s Steel Ink Spray. The transfer screw described below is installed in the cross arm to make a scratch as I lower the quadralift. I will use this line to mill the slot in the proper place. Since I had the lathe supported by the milling arm and off the bench, I retrammed the mill head and made a small adjustment. Tramming the mill head is discussed in a topic in this set of folders.

|  Add to del.icio.us |  digg this