Milling a curved slot in 3/8 steel bar.

RB72 said:
...need to mill a slightly curved slot on each end of the plate the guide bar...... I am doing this on a mini mill machine.
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chuckorlando said:
Maybe I'm just misunderstanding what he wants. I am thinking of a rounded key slot. Half moon type. Which t slot cutter would create a half moon if plunged in on one side.
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Picture a flat bar about 18 or so inches long that pivots about the center. The curved slots are on either end, and the curve matches the radius of the distance from the center to the slot, and are used to secure the bar at the desired angle for the taper.
 
Jim great description of what it's for. Thanks
Tom I like your idea also. Not sure I have enough table to be able to attempt that approach. Sounds like there could only be two bolts holding the plate to the table and both would need to allow the plate to move in order to mill the slot. I will check into that further but I'm not sure I am comfortable not having the plate secured while milling. You don't get any kick back or other movement?
 
Actually it is more stable than you might think. I don't know what your mill table size is, but if you have 3 t-slots it's pretty easy to anchor the work piece down. The center pivot bolt will be pretty tight, and then put a bar across the work piece near where you are cutting the slot, and secure it with the outside t-slots. Now you have the piece captured in the X and Z plane. Put stops at each end of the Y travel (rotational), now you are limited in 3 axis. Position everything, and lock the table locks.

Attach a lever to the work (maybe a 18 inch crescent wrench?), and use that to move the work. First drill holes at each end of the cut, slightly smaller than the final width. You can also drill a series of holes to reduce the amount of material removal by milling.

If your mill table is not long enough to do this, then bolt a plate to the table to extend the center point off of the table if you need to. Also you will want to have something under your work anyway, just to protect the table.
 
Sorry guys. I have been tied up on another project and have not been able to respond.

The pictures in the supplied link helped me get a better understanding of the setup. I won't be able to try this until I get a little further into the project.

The milling option should / will eliminate the filing.

thanks everyone for your input.

Rick
 
As someone mentioned, use a fulcrum. If you know diameter you want it's easy enough to set up. Couple of months ago I was making an 'Egli Style' fork brace from 1/2" thick 6061 for a 1968 Suzuki. Outside diameter 26.5" so way outside capabilities of rotary table (kinda sorta) I bolted two 5/16" thick about 2ft long steel plates together (didn't have anything thicker handy) and mounted 5" wide 6061 to it at 13.25". Set some bolts as stops and carved away. I know I have pictures of 'finished product' but grandson thought it was hilarious to pull flash drive from USB port so a lot of pictures were 'corrupted' (He's two in a couple of weeks)
 
A safer way to do this pivot thing (than trying to pivot it with leverage by hand) is to start with a undersized drilled hole at one end, then using a full sized end mill, size the hole, then step over a small distance and re clamp the part and feed down into the cut until the end mill is through; repeat until the other end of the slot-to-be is reached. This is also a good way to machine deep slots without so much tendency of the end mill to deflect and cut off to one side; it would be best to do with an undersized cutter, then finish with a full sized cutter or, offset the undersized cutter to get the finished width..
 
Your quest to make the part aesthetically pleasing is laudable yet unnecessary, as long as the clamping device functions do it any way that works.
 
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