Milling an angle plate

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Oct 7, 2023
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Brighouse. Yorkshire, UK
Since it became rather obvious that I'll need some kind of angle plate fixture to make the Stuart engine that I've decided to build I got my son to weld up a thing that might be something close. The flycutting of a reasonable surface went well, leaving a finished surface that may need truing up after the rest of the machining, who knows?
To cut the slots I attempted to reach down using a very long 10mm end mill with an indexable insert. The quill is the part right at the top of the photo and is too large to get the cutter remotely close to the vertical plate. This was able to do only the lightest cuts without getting the rattles and breaking the insert. Chain drilling made things a whole lot worse as it caught on edges all the time and it wasn't going to work.
Angle 1.jpg

Next I attempted to do it the other way up. Using an 8mm carbide end mill, I thought that the setup might do, but it wasn't near to rigid enough and I ended up with some bits cut away that should still be there.
Angle 2.jpg

I added more clamping and, tediously, I was able to cut the first two slots.
Angle 3.jpg

It occurred to me that I might be able to mount the casting on a plate and simply grip the edge of the plate in the vice. I'm going to have a beer and ponder this. So far the plan is to drill the feet and use pins to locate the casting relative to the squared sides so it's datum centrelines align with the edges of the plate. I think I'm going to try to Rustinox the plate flat in the shaper, but after the beers and a sleep, maybe plans will change.Stuart plate.jpg
You could use a couple of 1-2-3 blocks as "angle plates" clamp one each end vertically to the mill table or even bolt right through. You can then either drill and tap your machining plate so it can be bolted to the blocks tapped holes or use sturdy G clamps

Vice may be OK as it is only the crank bearing holes that need doing from the side.

For larger engines I mount the machining plate on the lathe cross slide and pack up to ctr height


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In general when I want to machine some welded-up fixture I first stress relieve the fixture. To do this I put it at the end of the day in the dying fire of my workshop woodstove. Next morning it is fit for machining.
I probably would have bought an angle plate to machine the angle plate :). Makes no sense? ....yes that happens when I make my buying decisions....
Rubbish idea: mill slots first, weld another angle plate and then you can clamp one angle plate to the other angle plate. Improve the surfaces as you align and interchange the clamping setups between the two parts.

Clamping a big chunk of saw cut metal attached to the side with a big C-clamp helped a lot against chatter, when I had to mill pockets with a sketchy setup. The horrible chatter disappeared almost entirely.
A smallish 6 mm carbide endmill, light cuts and fairly high rpm did the trick.

Greetings Timo

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