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How to mill concave radius on scope rail for round action

cbailey1956

Silver $$ Contributor
I have a 1.350 diameter round action (10x 22lr) that I would like to mount a one piece pic rail on. I would like to set my scope farther back and higher than I'm able with the traditional dovetail setup. I have a manual mill and did achieve this thru trial and error (4 hours). I used a small fly cutter and tilted the head at 50 deg in the x axis. Initially I set the fly cutter to cut a 1.350 diameter circle but that did not cut the proper concave for the action. Kept making the flycutter smaller and smaller untill there was a good fit to the action. But is there a formula for this,, or easier way. Have looked but failed to find. Dro installed has no program for this so its basically a 3 axis counter. Thanks,
 
Have thought about leaving it with rough ridges and bedding it. It actualy turned out fairly smooth and fits good but who wants to spend 4 hours and then retramming the head. Nice way to spend a hot day though.
 
There's a formula that takes the cutter diameter and the desired radius then gives you a number. Then there's a chart that takes that number and gives you the angle to set the milling machine head. For 1.350" I think it's a 1" diameter cutter and 44 1/2 degrees. I always make a trial cut on a piece of scrape. I'm headed out of town in a few minutes but someone remind me next week and I'll scan and post the chart.
 
 
But is there a formula for this,
Marc Klotz website has a program that’ll calculate tilt and cutter diameter. I’ve posted the link on this forum before.

Dave Tooley posted a formula on this forum awhile back. I have it saved but you can probably search and find it faster than I’ll get to it.

FWIW This method cuts an ellipse, not a perfect radius. You want to (and it will) create an ellipse where the outside edges touch first rather than the center.

Edit: Doh! Tooley posted above :)

Edit: The Marc Klotz website is down, not available. Hopefully it’s temporary. I have the radius.zip file saved.

IMG_3734.jpeg
 

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