Cutting a Large diameter using mini-mill

[12bolts]

+1 on Jim's suggestion

You could probably get away with making it from heavy plywood. Secure the base board to your mill, with the pivot point 7" from your cutter and sweep the pivoting arm back and forth manually.

Cheers Phil

 

[willthedancer]

+1 on Jim's suggestion
View attachment 227434
You could probably get away with making it from heavy plywood. Secure the base board to your mill, with the pivot point 7" from your cutter and sweep the pivoting arm back and forth manually.

Cheers Phil

Seen a fixture like this made of iron with multiple fulcrum holes as an attachment for a shaper.....

Sent from my Moto G Play using Tapatalk

 

[coherent]

A few thoughts on your project... I'll try to avoid repeating the other good ideas...

4. Router bits will work on aluminum. I've used them in my mini-mill. In your case, maybe actually use a router, guided by a template jig, making a series of passes until reaching the final depth.
Greg

That would work pretty well. I've used a jig with a router to cut a convex in hardwood. Great results.
I too use carbide router bits ocassionaly in my mill. They work surprisingly well on aluminum. Especially the roundover bits that cost a fortune if you buy round over end mills. On the other hand I've used end mills in a router with so so results. RPMs too fast for the cutter profile I'd guess.

 

[brino]

Also a little "out of the box", but.......If you could find a ~14" carbide-tipped blade and use a big table saw, I could picture a hinged jig to lower it onto the blade (or raise the blade into it?), move over one kerf width and repeat. I doubt you could find a dado blade that diameter.

Oh hey, here's a 14" blade that's made for metal.....reasonable price too....
http://www.princessauto.com/en/detail/14-in-dry-cut-metal-saw-blade/A-p8141756e

-brino

EDIT: just remember to respect the max RPM on the blade!

 

[GarageGuy]

In spite of the two thick blocks I am getting too much of chatter. If I run the mill at low speeds I can see heavy vibration of the piece being machined. So I am not sure how a rotating jig would perform. I am looking at reducing the depth of cut/penetration next and try doing it in two passes. So far it was done in just one pass.

You could use a smaller diameter cutter and speed up the spindle. Since you're taking light cuts anyway, you could use a 1/4" or 3/8" mill instead of 3/4". In aluminum, I've had good luck with 2 flute end mills, but that also depends on the alloy. If it is gummy aluminum, slower speed with lots of WD-40 as a cutting fluid.

Also a little "out of the box", but.......If you could find a ~14" carbide-tipped blade and use a big table saw, I could picture a hinged jig to lower it onto the blade (or raise the blade into it?), move over one kerf width and repeat. I doubt you could find a dado blade that diameter.

That is a relatively quick and easy solution. If you used a radial arm saw, or compound mitre saw and carefully mounted the work piece to the table, any carbide tipped wood cutting blade will do a nice job cutting aluminum as long as you take it slow and easy. Clamp or hold your work very securely so it can't get away from you. Slow and safe.

GG

 

[prasad]

Thanks all for your advice and encouragement. I went ahead and completed the radius milling. The pieces fit quite good. The assembly is almost ready. I had to make a dedicated drill and tap jig for drilling a large 14 inch diameter cast aluminum ring using a hand held drill as was simply too big for any of my machines. It too worked great. I will share pictures in a couple of days.

 

[brino]

The pieces fit quite good.

Congratulations on the success!
Did you continue with your original method or use one of the proposed solutions?

I had to make a dedicated drill and tap jig for drilling a large 14 inch diameter cast aluminum ring using a hand held drill as was simply too big for any of my machines. It too worked great. I will share pictures in a couple of days.

Great, looking forward to it.

-brino

 

[gjmontll]

Great to hear that you worked it out. If I'd known that it was a drilling jig when I replied 3 weeks ago, I'd have shown the jig I made last year to drill radial holes through the wooden/steel rims of the cannon model I've been working on for 2 years. (and chronicled here in my "Greg's French 75 Mm Field Artillery Model" thread. This was about a 7" diameter, my Mini Mill was big enough - but not in your case! I'll be interested to see your setup. Greg