In the absence of a surface grinder, we've jigged an '09 receiver onto the mill, and dropped the mill head to 30 degrees.

We intend to use an end mill to cut off the sides of the charger hump.

The job will be finished with files, and then stones.

Is there a better way to do this on a milling machine?

flaco

Yup. A $500 tilting rotary table. Take your time flaco, you'll do fine.

One has to tilt the reciever or the mill head, either way works fine. Its probably more rigid to tilt the head unless one makes a dedicated fixture for this op.

I mill this as well but I've taken a different approach.....I just mill away a lot of the bridge to make the action a bit lighter as weight reduction is something I look for. I then hand file the balance of the ridge.

Mind you this is not normal and most folks don't like this.....but it's what I do and will continue for my own guns.

You can buy a mandrel and jig from brownells for about 75 bucks (080-098-001) ans it's very easy to make a rotating axial jig to hold it, but you can order the madrel, jig, grinding stone and arbor from brownells
http://www.brownells.com/aspx/NS/store/productdetail.aspx?p=985&s=

and spend at 200 to have something that will give you the ability to clean up many many many mausers.

you can also shop build this for about 30 bucks, and get the grinding cup.


but in general, removing the hump is something you can do most of with a normal mlling operation, and then draw file

jeffe

I've been using a bench grinder and files for the last 30 years and am happy enough with the results. I can do the job and do it as well in less time than it would take to set up to mill.
There are times where the use of the mill is warranted but I've never felt this was one of them. My opinion only, of course. Regards, Bill

I tried this many years ago in my highschool shop class. Needless to say the teacher was not too impressed when I showed him the endmill cutter. The charger hump was a little too hard for the highspeed cutter I was trying to use. Ended up grinding it off by hand and finishing on a belt sander.

Vapodog did you make or contour the corners on that base? I like the look very much.

I always used that brownells jig, a mandrel, and a grinding cup in my drill press. Worked like a charm.

Its not cutting the charger hump off thats hard. Whats hard is fitting a scope mount base seemlessly so that it looked like it grew there.

quote:

Originally posted by D Humbarger:
Vapodog did you make or contout the corners on that base? I like the look very much.

Yes, it's merely a series of vertical plunges with a 1/2" carbide endmill.

Takes very little time and removes about an ounce of unneeded steel and makes the hump very easy to remove as there's so little left to remove.

I put the recoil lug of the receiver in the mill vise and screw a bar on the front of the vise. The tang of the receiver is then screwed down onto shims on top of the vise.

I make passes with the mill to get close.
Here is a pic of me cutting on a 1903 Oberndorff [Turkish Mauser with very high hump]







Then I finish with a file, as inspired by J Belk on the this forum. Here is one of Belk's pics

quote:

Originally posted by 22WRF:
Its not cutting the charger hump off thats hard. Whats hard is fitting a scope mount base seemlessly so that it looked like it grew there.

Maybe I should have made my previous post more clear. What I was trying to get at is this.

Why wouldn't a person do the whole thing to a known radius so that one could either modify an existing scope base or make a new scope base that looked professional, e.g. fit without large gaps?

Well, yup, 22WRF, that's how it's done.

After milling the hump down to the 30 degree flats, the radius on the top is carried through from the back of the bridge.

flaco

I'm with Bill Leeper, 15 minutes on a snag wheel and thirty minutes draw filing does a good job.

While I'm sure a good job can be done of removing the charger hump by hand, one advantage to using a precision machine setup is that you make damn certain that the crest of the bridge is on center. Otherwise you are assuming that it is and following that contour. If you have no plans of scoping then it is a moot point. But, if you intend to scope the rifle, it would be nice to know it is on center.

That one of the great things about amateur gunsmithing, figuring out how to use the machines you have and creating something you want. Poleax is right about making sure the angles are centered with the bore line. A reciever is a delicate instrument because you're using the rear bridge to mount optics. When I first started I used a bench grinder to grind the hump off making sure I didn't go below the rear bridge angles and then use a file.

I attended one of Mark's NRA summer classes about 4 years ago. Mark is being very modest here.

Flaco, to answer your original question. If you will set up with an indexable fixture you can not only cut an accurate 30 to 34 degrees (they vary) but you can also cut an accurate radius on the top by blending the cut one or two degrees at a time.

Machining or grinding these dimensions accurately will allow you to duplicate them on your bases, creating an air tight fit.

I highly recomend attending one of Mark's classes or buying his book, you will be glad you did.

Freddy Johle

I kinda liked that thing Jim Dubell does. He cuts the whole damn thing off and welds a new piece on. That way you can make a nice flat top scope base integral with the action.

quote:

Originally posted by 22WRF:
I kinda liked that thing Jim Dubell does. He cuts the whole damn thing off and welds a new piece on. That way you can make a nice flat top scope base integral with the action.

I know you knew Ron Lampert...he tigged a piece on and machined a square bridge...what an artist!!!

I cut the mounts in V blocks ala Steve Acker article in The Home Shop Machinist and Machinist's Workshop.
I can get the mounts to be the right thickness and radius, but the fit is still not perfect.
I bore sight the rifle to a scope [in the middle of it's adjustment range] with the mounts loose, but the rings tight to the mounts and scope.
The gap between mount and reciever is filled with epoxy. When it sets up, I tighten the screws. This has a few advantages:
1) No lapping
2) scope and rings can move from rifle to rifle
3) You can center 20 moa high, but I like it right on.

quote:

Originally posted by 22WRF:
I kinda liked that thing Jim Dubell does. He cuts the whole damn thing off and welds a new piece on. That way you can make a nice flat top scope base integral with the action.

What an excellent, and elegant solution

jeffe

tnekkcc,

Filling the gap between the receiver and the mount with epoxy? Why didn't I think of that?

quote:

Originally posted by Mark_Stratton:
tnekkcc,

Filling the gap between the receiver and the mount with epoxy? Why didn't I think of that?

Becasue you are a Craftsman of the highest order, thats why.

Don’t mean to poke fun at tnekkee, I’m sure that in some gunsmithing circles using epoxy in this manner is acceptable. Brownells trys to sell their glass bedding compound as a cure-all. The worst thing that could happen is the epoxy cracks and falls out. Not a safety issue.

I remember when I was back in gunsmithing school, one of our classmates had a problem cutting threads on a lathe. He was completing an action barreling class and was having problems. His solution was to add acraglas to his barrel threads and screw it into the action. I guess he didn’t attend the class where the instructor talked about headspace and chamber pressures. I wasn’t present when he test fired the barrel action, but needless to say, he didn’t pass the class.

Mark,

I've seen a similar stunt on barrel threads....only duct tape was used.

quote:

Originally posted by Mark_Stratton:
tnekkcc,

Filling the gap between the receiver and the mount with epoxy? Why didn't I think of that?

Because you are a gunsmith?
Because you are not an engineer?
Because you are stuck?

I see an excellent application for epoxy and go for it.

All the machinists that see my glassing mounts to receiver say, "That's how Boeing does it."

I know Boeing does not make scope mounts, but they do make a great many precision fixtures.
Much more precision than any gunsmithing will ever be.

Here is a gun that I was present during the design, and it has quite a bit of epoxy in it to keep the most precise things lined up.

It was designed in Renton WA many years ago by a much better engineer than myself.


--

Sorry to ruffle your feathers, I'm sure you're a great engineer. However, we represent different areas of gunsmithing, and that's not bad. You look at firearms as a tool, an ax that shoots. In your world it doesn't matter how it looks as long as it shots straight. Your area uses epoxy, in my area that's a sin.

In my world firearms need to be almost a work of art. A rifle needs to have an octagon barrel, english walnut with a fine checkering pattern with great wood to metal fit, a quarter rib is not out of the question. The metal work needs to be correctly machined so it goes together like a Swiss watch. However the rifles in my area shoot very good as well. We just are in different areas of the trade.

I think the firearms trade has room for us both, don't you?

I understand the dichotomy, the fancy butt cap on a French dueling pistol was not put there by an engineer.

I don't want to be womanly by putting bluing on my barrel, but I tell myself it is to help camouflage it from the eyes of game.

We used the endmill to remove the charger humps on three '09s.

It left such nice clean flats that I didn't much look forward to filing. And, like Jack Belk's surface grinder, it showed all too well where the corners of the flats had been worn down, or in at least one case buffed.

I've filed one of the receivers. I cheated a little to re-establish the corner, and managed to remove the remaining hump in short order. I pretty much expected to cause a little collateral damage with my inexperienced filing, and so I did.

I have the utmost respect for guys who are expert at filing. It always seems to wobble, at least a little, for me.

Anyway, I've stoned down about 3/4 the surface, so there are just a few tiny spots below the surface. Including one tiny pit that was there before I started.

I tried a Warne rear mount, and it seems to fit pretty well.

I wish I had more patience with stoning. Not to mention the receiver's at an awkward height in my vice.

Still, I just leave it and go on to something else when I get bored or tired.

Seems like only a matter of a few more minutes stoning, and this bridge will be done.

And not looking too bad, if I do say so myself.

flaco

quote:

Still, I just leave it and go on to something else when I get bored or tired.

Seems like only a matter of a few more minutes stoning, and this bridge will be done.

I do the same thing, except that what seems like it would take a few more minutes usually ends up taking the better part of a day or two