Circle cuting

[motorworks]

I have to cut out several 7 7/8" cirles in 3/4" mild steel plate.
I saw somewhere a guy cut circles on his bandsaw with a subplate on the table and a dowel pin in the subplate.He would drill a hole in the centre of the square that he was cutting the circle out of and place over the dowel pin on the subplate on the bandsaw table.Then turning the square,he cut out the circle.
Only HE was doing this with wood.
Think it would work in 3/4" plate
These DO NOT have to be perfect.

[lenord]

Motorworks,

Unless you have the plate already, why not just have them cut from 8" rod stock at the local metal supplier ?

If I had to do it out of plate, I'd use the rotary table on the mill.

I would think you could use a bandsaw if you had the blade vertical too. It can, is and has be done in 3/4" wood on a wood bandsaw.

FWIW
Lenord

[wierdscience]

3-15/16" radius means 3/8" wide blade,yes you can do it,I have done it,just be sure that the bottom of the tooth gullet is exactly on the centerline of the the guide pin,otherwise you will be cutting cams.

[lynnl]

weird, how'd you arrive at that blade width? Did you calculate it as a chord length? I've seen that calculation done, but don't remember it.

[DR]

lynnl,

Don't the band saw blade catalogs have this info, minimum radius for blade widths, etc.?

IMO, unless the poster has a very heavy duty saw this is not going to be an easy thing to do, especially in 3/4" stock.

[Mike W]

I would use my torch with a circle cutting attachment.

[lynnl]

DR, maybe you're right...I may be thinking of a chart(s) I've seen. Of course they (charts) would probably have originally been derived from calculations of the chords of the corresponding arcs. Maybe with an emperical fudge factor thrown in.
And, as has been pointed out before, radiusing the back edge of the blades help to make the turning cut, if you're cutting near the limit for the blade width.

[wierdscience]

Its in nearly every catalog that sells blades,every bandsaw thats intended to cut circles and it really helps if you have two Doall,two Tannawitz and one Grob bandsaw

[Derek13]

I would put a 7 7/8" drill bit in my drill press and go at it.

[gglines]

Derek13:

Make sure you're using a 7/78" hole saw bit, not a regular drill bit. Frankly, on a 1110v circuit, only a Sears drill press would have the necessary horsepower. I believe Sears can get about 75HP out of 15 amps.

George