What are the 2 radii on the rear ring of a large ring 98?
Butch

Butch --

From Mark Stratton's book, the radius on top is 0.547", which ends on a 34* angle on either side. Kuhnhausen might have some different measurements but I'll have to take a look and get back to you later.

-- ale

Brian,
I guess that I better get Mark's book out. That sounds about right. A .500 radius guage was close. I need to make some scope bases for my Banner Mauser in 9.3x62 while waiting on Lilja for a barrel for my 6.5x47Lupua.
Butch

Set the action up in the mill to facilitate measuring. With a dial indicator from the middle (highest) portion of the rear bridge, measure an equal distance from the center toward the sides of the action and move your table up until you get the zero again. This gives you the chord length and the height and is all you need.

Next, to get the radius, use this formula:

R=chord(squared)+ 4times the Height(squared) divided by 8 times the height

I just did this the other day on an FN.

The formula is in the Machinery's Handbook

Thanks for that formula, Jim. I can't wait to use it for my Mauser projects. Here's a numeric expression of the same formula you described:

R = [C^2 + h^2(4)] / h(8)

Good stuff!!

Butch

In Stratton's class I used a simple approach. I inserted a mandrel that was a slip fit in the action. Then measured from the top of the rear bridge to that mandrel with a dial indicator. Adding that measurement to the known radius of the mandrel gave me the total radius. Of course it works on the front ring as well.

Once I'm done surface grinding the action I measure the distance from the top of the bridge to my mandrel then add half the diameter of the mandrel. That gives me my radius.

I'm gonna make chips in the morning. Freddie, if you are close, stop by. Unless something comes up, I will give a report tomorrow evening. Mike, what you and Craftsman said is so easy and why didn't I think of it. Jim, you think I got that far in college math?
Butch

Butch, The sides of the bridge are really flats. The angle depends on what you grind them at. In original form most are about 30 degrees.

Mike,
I think that is pretty close to what I have. I will double check before cutting chips. I had to do the ones on my Pierce receiver 3 times before they were right. I sure hope the first time is a charm on this. I got my Pierce receiver and forgot this project. I am back on it as I have a long wait for the barrel on the Pierce.
Thanks Mike
Butch

By the way, if you keep the width of the base at about .700' you won't need the flats. I havee also found the flats on some Mauser receivers to be different angles from one side to the other.

quote:

Originally posted by Jim Kobe:
I havee also found the flats on some Mauser receivers to be different angles from one side to the other.

That's why you surface grind them.