As I mentioned in this thread
http://madmodder.net/index.php?topic=4830.0 that I would do a quick build log of making a temporary backplate for my new South Bend 6" 3-jaw chuck.
So here goes. I remember some one once saying he had to make a tool to make a tool. Well I wound up making 2 tools, one jig and an idea on how to repair an old chuck. The jig is a stub arbor that is the same as the nose of the spindle, 1 1/2" - 8 thread. The two tools were a boring bar for inside threading and a transfer punch. I made two parts that are welded together. They are made from aluminum jig plate. I never realized how gummy this stuff is. Sharp HSS tools worked the best at giving a good finish.
Lets get started. Here's a pic of the two chucks, 3 jaw 6" on right and 8" 4 jaw on left. The plate under the chucks is 1" thick. This will be made round to mount the chuck on.
I made the stub arbor first. Here I am setting up to cut the 1 1/2"-8 threads. I coated it with dye and did a scratch cut to make sure the pitch was right. This part is made from steal.
The finished threads. Looks a bit rough, but they aren't.
I used my old 4 jaw as a gage so I could tell when I got close to the size I needed. The chuck is shown here screwed on part way with a nice fit.
The finished stub arbor.
Next I used a piece of 5" round aluminum to make the first part of the backplate. Bored a hole in it for 1 1/2"-8 threads. Here I'm setting the internal thread cutting tool up. This is also the first tool I made for doing this job, the boring bar. The cutter is a piece #3 center drill ground to a thread profile.
The thread was cut untill the stub arobr had a nice smooth fit.
Then I turned it around without removing the chuck to make sure it fit the spindle nose. And it did.
After looking at this setup I realized that I could fix the old chuck to make it run truer. That'll be another project for later.
The first part is mounted on the spindle and faced off and a dia. of 3" is turned about 1" long that will fit inside the second part.
Work begins on the second part. The piece is first marked out and a center hole is drill so the part can be mounted on a rotary table. Notice the piece of MDF I have under the piece so I can drill all the way through without cutting into the table.
The part has been mounted to the rotary table with 1/4" HSS tool bit's to hold it up off the table. The center hole locating the part on the pin in the rotary table. This almost became a problem later when I cut the 3" center hole. The first of three cuts has been started. I needed to remove each clamp as I came to it to keep cutting around the outside.
The outside has been finished and so has the 3" center hole. The center hole was a bit of a problem. I set the cutter about ..05" away from the pin and chain drilled all around it with the end mill. I left a small amount of stock near the bottom to hold the center portion, milled everything round and then took a final cut to to remove the last of the stock holding what was left of the stock around the pin. When I broke through the part left on the pin spun around from the force of the cutter. I quickly pulled up the cutter before it grabbed hold of the scrap piece. The part was then milled to a 3" dia. so the first part would fit into it for welding.
A quick check to see if part one fits part two.
The front side. A bit of a counter bore for a weld fillet.
I did a bit of practicing on some scrap aluminum to set the welder up for aluminum before I tackled the part. Here it shows the counter bored weld. This is the front face.
The back side fillet. Was finally getting the hang of welding aluminum again. By the way that is a mig weld with argon gas sheild for aluminum.
The backplate was then mounted back on the spindle and cleaned up. A spigot was cut so the chuck could be mounted to the backplate. Once that was done I needed to locate the three holes that hold the chuck to the backplate. This involed making a second tool, a transfer puch the would fit sungly inside the drilled hole on the chuck. A piece of brass was turned to size and a piece of 1/8" tool steel was pressed in a reamed hole. The end was then turned to a nice sharp point.
The backplate and chuck were mounted in the lathe, a piece of 1" dia. steel was chucked up and the chuck was trued up. The unique thing about the South Bend arbor is that it has 4 set screws that allow you to tune in the chuck to "0" before tightening the mounting screws. Here I'm locating the holes.
This pic shows the backplate drilled for the mounting screws and the chuck. Notice how clean that weld is on the backplate.
This pic shows the setscrews that are used to center the chuck. This is the final setup. I trued up the chuck and drew up the three bolts that hold the chuck to the backplate.
I know what some of you are thinking, aluminum for a backplate?. Seems like aluminum plate is easier to find for me than a piece of steel. But I needed the chuck as soon as possible and I knew were to get the plate real fast. So why not. It's only temporary untill the cast iron plates arrive in September. I may just make the 4 jaw backplate out of steel since I don't need it right away. Also a suggestion was made 75Plus (Joe) of using a flywheel from a tread mill. I have several laying around, so I might look into that.
Bernd
