I have mulled this problem many times and have yet to get the correct or workable answer. What do the majority of you fellas do when you need to have a radius cut to fit a certain diameter? I normally use a boring head and do it with that, and that is usually quite adequate. However, on occasion I need to cut a radius that is fairly long, say 5-6 inches, and have to use the old "tip the head" on the mill. I have a formula that specifies a ratio of the cutter diameter to the diameter needed equals the, and here is the problem, Secant of the angle to tip the head. Do you tip the angle of the head from the vertical or the reciprocal? Is the secant correct or is it the co-secant? When I do this for, say two different radii, sometimes one comes out but not the other. Why not? Come on guys help me out here. This one was not covered during my apprenticeship.

Jim--

Did you get that formula from my article in the Gunmaker?

For it to work the endmill must be BIGGER in diameter than than the part you're cutting and SMALLER in diameter than the circle you're fitting to. SO-- If you're putting a .500 wide ramp an a .700 barrel, a .625 endmill will work.

DIVIDE the diameter of the barrel into the diameter of the cutter. The result is the SINE of the angle (from verticle) to offset the mill head.

26 degrees 46 min.

(Sine/co-sine tables on page 179 in the 17th edition of Machinery Handbook)

I usually screw up two or three parts before I get it right.

I've made barrel blocks as long as 15" in aluminum for a 1.45" dia. barrel, using a 1.250 dia. ball endmill. A friend, Gerry Geske, came up with a formula that uses an Excel spreadsheet and it works great. You end up with a number of overlapping scallops but a few passes with some abrasive paper over a 1.430 dia. bar makes the radius just about perfect. The "tilt the head" trick will not work when you are going a full radius deep. I even use this method, now, for making scope bases with 15 min. to 1 deg. slope for BATs and Nesikas. Quicker than tilting the head and having to tram it back in.

Keep them cards and letters coming guys, I am being enlightened even as we speak (write?)

I have really been enlightened by all the input, even my own, however I have not reached the end of my quest. Yesterday, I got a Remington model 7400 in the shop that had a leupold one piece base and rings with a 3 x 9 scope. The customer could not get the scope sighted in without putting .045" worth of shim under the rear attach screws. Naturally, he was torquing the scope but was also at the end of his adjustments for elevation. I looked at it for a whie and determined I needed a tapered base with about .060" taken off the forward end tapering to zero at the rear. Now, it is a one piece base and has a radius the full length. What to do? Boring head? Tip the head on the mill? Never worked before for me. Anyway, I got out the Machinery's handbook, dug out the formula for determining the radius of the receiver and then got out the formula for the angle to tip the head. I came up with 36 deg, 24 mins with the cutter I was using (7/8) and tipped the head. Took a piece of scrap aluminum and took a cut. It was not right. After trial and error (four times), I came up with something over 29 deg, checking with some blue on the reciever and spotting it in. In closing, the base came out perfect and I lapped the rings, but why didn't the formula work for me?

Jim

Jim,

In my opinion, part of the problem is tipping the head itself. The scale on the side is a "guide line" only. You need to setup a sine bar and indicate it to be satisfied that the angle is "dead nuts."

The problem you just described? I cheat. I use radius end mill cutters (yes, they can cost a bit if you have to have them made up). I just put the part in the vise shimming the end, and use an indicator to check the height difference, moving the table back and forth. You can do the same thing by tipping the head of course if you don't have the end mills, but I only have a mill/drill right now, not an option.

As I work as a machinist too, I have had to tip the head on a verticle many times for work. I've found that it is necessary to indicate the head using a sine bar to be accurate. You cannot trust the scale on the head.

It does not take much deviation to make a difference of several thousandths on small parts. The formulas work, you just can't measure the differences with dial calipers.

My two cents,

Eric

I would have made the base with two contact pads where the recive has its holes. You could then using a boring head bor the pads to fit the reciver. I would the mess with miling out the taper and the rest of the machining nessisary.
Ray

Hey Jim, Looks like you are getting some excellent info about your question.

But, I've got a curiosity type question for you. Is there a particular reason you did not just go with the Burris Signature Rings and a set of the Eccentric Inserts in your example?

I can understand your desire to know how to make the radius or taper cuts you need. You can use that same information on other projects.

Just seems like it might have been faster, much easier, less stress on the scope, better grip on the scope, better chance of CenterLine alignment and less expensive to use the Signature Rings.

The Burris rings with the inserts would not have helped. It was pointing at the north star and could not get enough elevation down to get it on paper. If you re-read the thread, it states he had .045" shim under the rear two screws. This effectively lifts the back od the scope and makes it point downhill more. I eliminated that by removing material from the front to the back, .060" in front to 0" in back. Get it?

Jim- I may not be addressing your problem completely, but I've been making second recoil lugs and angled scope bases by using a small Hss fly cutter in the mill with the scope bases held by a fixture designed to hold the base vertically in the mill vise( off the end of the vise). I adjust the angle of the work in the vise with a machinists protractor and adjust the radius of the flycutter to match the radius of the barrel or receiver ring. By using a larger fly cutter or boring head you can make very large radius's this way. The head is trammed and you feed down very slowly as this is an interrupted cut ( thats why I use HSS not carbide). It works amazingly well and I usually get it right on the first try. I've tried the tilting the head trick and the results have been variable.-Rob