MAKERS: the machine shop at Make717 has all you need to easily mill square or hexagonal shapes on round stock. This before-and-after photo shows what I mean:
This document will give you some good hints on how to accomplish this. The tools in the shop that make it possible are a set of 5C collets to hold various size stock, and both square and hex collet blocks to hold the collet. Here are those components, along with the round nut to close the collet in the block:
The project at hand was a shaft measuring 0.810" in diameter. 13/16" is 0.813", so a 13/16" collet was the one to use. Install the stock in the collet, and then clamp the collet block in the milling machine vise, carefully aligning the face of the block with the edge of the vise.
Lower the head of the milling machine with the crank at the top until the bit is close to the work, and lock it on the column. Also lock the quill downfeed with the knob in the center. All the rest of the work is done with the fine feed on the front of the mill. Insert a piece of paper between the bit and the work, and lower the bit until the paper just snags.
Those hands belong to Phil Oles, Make717's primary guru on manual machining. If you are using this equipment, you already know him! Once the paper snags, move the Y-axis to bring the bit clear of the work, and lower the bit another 0.003" - the thickness of a typical piece of paper. Zero the DRO scale on the mill head (partially obscured by Phil's hand).
Now you can set the bit depth. In this example, our stock was 0.810" in diameter, and we wanted a hex of 3/4" = 0.750". Because we'll be removing stock from both sides of the rod, the depth of cut is (0.810 - 0.750) / 2 = 0.030". Easy to set with the fine feed:
For reasons that will become apparent in a minute, we also recommend that you zero all three axes of the X-Y-Z DRO for the milling machine:
Double-check that all appropriate locks are set, and start the spindle motor. Since our sample stock is a very tough steel (it was originally a large boring bar), we set the bit rotational speed rather slow, and used a very slow Y-axis feed to cut the flat.
Actually, you'll notice that the photo is of a second cut, because the bit wasn't wide enough to cut the desired length of flat. We used the X-axis DRO to move the table 0.500" for the second cut (blue circle):
But wait a minute! What happened on the Z-axis (red circle)? The previous photo clearly shows that it was set to zero. Clearly, the mill head drifted down. We didn't notice this, and it resulted in a bad cut that required the piece to be shortened and re-cut. The moral:
a) Don't forget to check the locks on all downfeeds and tables! Only the direction of travel should be free.
b) Every readout on these machines tell you important info. Don't ignore them!
Fortunately, this was a project that didn't suffer from this. We just cut off the bad and started over.
To use these collet blocks, you cut one flat, rotate the block (carefully realigning to the vise), and keep cutting until you've gone all the way around. For safety, stop the bit before rotating the stock. Here we are on the last pass:
The milling process raises some burrs that can scratch the collet if you don't remove them. We started that process with a file, removing or turning under the burrs so there would be no snags. You can see that it's still rather rough, but smooth enough to pull the work through the collet:
After that, we mounted the workpiece in the lathe, and faced, chamfered and filed to get it cleaned up and safe to handle:
Since this hex was to allow the shaft to be turned to by a 3/4" socket, the final check was to ensure that the socket fit well. And it did!
While this was a larger project, these tools can also be used to effectively make small parts. Here's a small tool called a "broach" with a square end that was made with exactly the same techniques:
Makers, if you want to try this, talk to Phil Oles or Emery DeWitt - we'll be glad to walk you through your first try!
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