Concave arched beam.

[JMN]

I need to mill a 16. 078" concave arch down the length of a 18" x 3" x 1.5" thick length of 4140.

See attachment.

Can I use a fly cutter and simply tilt the mill head to creat the needed radius?


JMN

View attachment radiusbeamcopy.pdf

 

[Bill Gruby]

I don't see any reason why you can't. I have used the flycutter to plunge cut many time. You won't need the starter hole like I did. Go for it.

"Billy G"

 

[Tony Wells]

Well, sort of. It's really not a true radius, it's a segment of an ellipse, but for most things, close enough. Here's how to calculate the angle:

http://www.angelfire.com/ks/mcguirk/generatingradius.html

 

[DMS]

It will be a true radius if the head is 90deg to the base, but if you're gonna do that you might as well mount your part on an angle plate.

I have done similar things with shorter pieces, how long is yours?

 

[jmarkwolf]

I wondered the same thing when I wanted to make a saddle bracket for mounting the DRO arm to the hoist ring hole on my new-to-me Bridgeport ram.

I didn't have either a flycutter or a boring head, or any other tooling for that matter, so I used a 5" diameter hole saw! I clamped the 1.75" diameter round stock horizontally and took a skim cut with the hole saw.

It worked, but not well. I used an extremely slow manual feed, but still broke a tooth on the hole saw which gouged the concave surface somewhat.

Turns out the top surface of the ram is not very semi-circular, but it doesn't fit too bad.