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Center Slitting fixture


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I took the time to design a fixture for starting the slitting of stock right on center. By eye and chisel I am only able to do this so accurately, but mechanically it can be done within thousandths of an inch.

Once the split is started it can be finished off by a number of methods but the start of the split many times depicts how good and centered it ends up.

The following fixture can accommodate rectangular or square bar stock in a range of .30” to1.45” wide. It requires a bar that is parallel and having the edges being square helps for better results also.

All holes were precisely spaced and drilled using a mill. I didn’t have any reamers so I double drilled all the holes. A near press fit can be obtained on steel dowel pins by pre-drilling a hole .010 - .015” smaller before drilling the finish size of the dowel as long as your drills are sharp.

A small hole pattern was put in the middle of the fixture to hold a heat treated wedge made out of H13. One threaded hole in the middle and two dowel pins for location and stability. This piece can be replaced if another flavor of tool steel is ever deemed more optimal.

I TIG melted some washers to the top of the dowel pins so the disks wouldn’t pull off but rather stay in with the pins. The pins are easily assembled and seem to stay in place very well during use. The four corners would probably do the trick but I added the two middle disks also.

With three small springs there was enough clamping force to center the work piece by hand before hammering. The disks act as wheels for positioning the slit lengthwise along the bar.

This fixture worked extremely well on whatever I tried in it and with the work piece red hot places a beautiful 1” long groove right on center with very little effort in hammering. Spears.

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Have you seen one of the center markers? It's a sq bar with two vertical pins projecting from it and a carbide scribe point at the mid point between them. It works for different sized stock as you place it with one pin on each of opposing sides and drag it along scribing the exact center.

Go back over it with a cold chisel and you achieve the same result with a simpler set up!

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I've been kicking around the idea of a parallelogram setup like this for the flypress, but never got around to working out the details. It looks like a real handy tool. I can see where your adding 2 middle disks could help in positioning for marking near the end of stock. I dig your jig.

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OK I've seen another version used for hot metal where you take a piece of stock about twice as wide as the one you will be using. Cut a step halfway into the end such that a section will extend down the side of the piece you are working and then saw/file (or even drill if you are careful) so that the edge of the step is a protruding chisel. Harden in super quench if you used A36.

To use: place on hot piece with the protruding edge against the side of the work piece. Hit with hammer. You now have a dent exactly in middle.

Of course you have to make one of these for each size stock you use

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||_/| Bad ascii art--- lets see if this comes out...

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