I am getting ready to D&T my second receiver. For the first one I used a jig and drill press. The jig doesn't fit the small ring Swede I want to do next, but I now have a mini-mill.

The question is how to find top dead center of the receiver ring. I bought the mill used and it came with a "wiggler" and some other edge finding paraphenalia, but I am not versed in their use.

My thought was to chuck up a drill bit of X diameter, lower the spindle and crank it sideways until the edge of the bit just touches the side of the ring, remove the drill bit and crank an additional 1/2 the receiver diameter plus 1/2 the drill bit diameter to get the chuck centered over TDC. That should get me within a few thousands, right? Any other simple or more accurate solutions?

That will work if you trust the receiver ring. Be sure to allow for any run out in the chuck, then flip and use the butt end of the drill bit for your contact point. But be warned, it won't be worth a shit if you can't get it to within .0001 of the mark.

...

Hang a test indicator in the quill.
Run it along the side of the receiver to get it straight.
Then set the indicator so you can pick up both sides of the receiver ring.

Adjust the position of the receiver until you can turn the indicator to either side of the receiver and get the same reading.

One view is that top dead center is not as important in actual shooting use as many seem to think.

Assuming the holes for the scope ARE top dead center after you drilled them, let me ask a related question.... Are the action bolt holes bottom dead center? The reason I ask is because if they are not, or even if they are but the holes in the stock are not, mounting the barrreled action in the stock may well leave you with sight holes which are no longer right on top....Yes? No?

And, even if the sight is not top dead center, it is sometimes not particularly important at the distance for which the rifle is sighted-in.

What is important is that the sight is canted exactly the same for each shot. I know a number of world class competitive riflemen who always "cant" their rifles when shooting...they just do it consistently.

Where it does become important to have things level is when a person is shooting at varying ranges for which he doesn't have "dope book" zeros. then it is important because as he adjusts his sight mechanism up or down he will also get windage changes if the sight isn't dead on TDC.

But, if he isn't adjusting his sight for the farther or closer distance shots, it again becomes relatively unimportant. When using "hold-over", "hold-under", or "Kentucky windage" a person is really using an educated (or uneducated) guess to make his shot anyway, depending on his amount of shooting experience....

I am not trying to discourage you from getting as close to TDC as you can...I think you should do that. But don't feel discouraged if it doesn't come out perfect. As you and your rifle get to know each other, you will still likely do just fine together.

Westpac, I just got that, ha ha ha. I read that post the other day.

Quick asnd dirty (Taken from Maynard Buehler) Level your base with the bottom of the receiver..use parallels or a coouple squares.

If you can clamp the base to the receiver, do so..otherwise use some crazy glue.

You now have a perfect drilling and tapping fixture.

Buy one of those battery operated centering devices...measure the OD at the place where you want the holes and divide it in half...be certain the receiver is parallel to the travel...run the light device down to touch one side or the other at the half way point until it just lights...do it a couple of times, then adjust the measuring barrel on the twisty wheel to zero...run up the quill to clear, and then run in the other axis the amount you divided...you should be right at TDC...or actually dead center on 1/2 the diameter of the receiver or ANY round metalic object.

It takes less time to do it than to read this tome...just don't bend the stem on the tool while your at it.

You also need to be sure the quill is running parallel and perpendicular to the bed...otherwise when you travel to the other end of the receiver, assuming it is traveling parallel, you will drill the hole in the wrong place...it's easy to get one or the other totally out of whack.

If you're gonna mess with this stuff, you HAVE to think square, parallel and perpendicular in all 3 geometric planes...and keep your machinery doing the same.

Luck

Thanks for all the tips! The wiggler is kind of small, and comes to a tapered point so I don't think I can get a good reading all the way on the outside edge. The indicator I have runs in an out, it doesn't bend side to side (non-machinist terms...) like I picture it needing to do for SR4759's advice. Don't want to buy anything else unless I see an ongoing need. Think I will stick to my original plan. Thanks for the tip about reversing the drill bit. That should get me close enough, then I'll just make sure I drill them in a straight line...

quote:

Originally posted by montea6b:
then I'll just make sure I drill them in a straight line...

Get yourself a center drill to spot the holes before drilling then drill and tap one hole before moving to the next, that way your quill will be centered over the hole in case something goes wrong and you need to launch plan "B".

Like DUane says! Only thing is I use a dial caliper and clamp it against the bottom of the receiver and over the top of the scope base making sure it is tight against bpth parts. Super glue it down and use it as a drill jig. I did it all the time befor I has a mill. Measure the holes in the mount and use a drill the same size to just spot the receiver then use the correct size bit.

Well, I would have gotten to it today, but I can't find a tap handle that is small enough. Last time I just used the big handle... the bushings that came with the jig helped keep it perpendicular as I started, and I just kept my hand in the center for feel, and to keep from over-torqueing.

Today I bought a small tap handle that was advertised for 0-1/4" taps. It has a small "slide through" handle and a chuck-like part to hold the tap. The plan was to use a socket-like part in the chuck that would accept the top part of the tap wrench, (keeping it centered over the hole and perpendicular) with a spring to exert some downward pressure. I would then rotate the tap wrench manually and adjust the quill down a little at a time to keep the spring pressure on.

Anyhow, the hardware store tap handle was still too big. Do I have to find a machinist specialty place for a smaller tap handle?

Why not just put the tap in the drill press chuck? It will keep it aligned with the axis of the hole, take the belt off the pulley and turn the chuck by hand.

Use Duane's method for best results. It's an even surer method if you can figure a way to check the boresight of the mount with a bore collimator.

My main smithing mentor made a bushing to allow the holes in the glued-in-place base(s) to act as drill guides. He sized the bushing's OD to match the ID of the 6-48 clearance holes and the bushing's ID to match the OD of a small center drill. The center drill acted to spot the holes for the #31.

He later made another bushing to use a #31 directly instead of the extra step of the center drill. Worked well, FWIW.
Regards, Joe

A couple questions/concerns: Gluing or clamping sounds great for a one piece base, but I plan to use two piece bases. Using this technique with two piece bases would introduce another variable that I would have to control. (In terms of aligning the front and rear bases) Also, I would have to machine bushings to a pretty tight tolerance as well. (Another opportunity for variation to creep in...) Seems to me that this would be a great technique for a guy with a drill press and no jig, but I have a mill. Wouldn’t a mill provide the best opportunity to precisely locate and drill holes along the same axis?

Jim, I like your suggestion to put the tap in the chuck, but I had planned (as Westpac suggested) to center drill, drill, and then tap each hole one at a time without moving anything until I am ready to go to the next hole. I will have to see if I can disconnect and turn the mill chuck by hand. Even if I can, it seems that it would be difficult to control the downward pressure using this technique. I would have to turn the chuck with one hand, and apply downward force with the other.

The spring idea came from an instructional DVD that came with the mill and it looked like a nifty idea to me. I have a shaft extension for my grinder that should work just fine for this.

P.S. The tap holder I have works. I neglected to notice that further inside there is a step which narrows the grip. I was trying to grasp the square shank of the tap down at the tip of the chuck-like holder.

Drill bushings, guides and gluing bases are fine for folks who don't have access to a Mill. But a milling machine is THE perfect platform for precisely locating, drilling and taping a hole in the receiver period!

I prefer to hand feed the tap, but here is a little spring loaded device that might help in keeping tension on the tap while tapping.

http://www.brownells.com/.aspx...duct/Micro-Tap-Guide

montea6b
Your method of touching off the drill to the side and moving over is ok, but a standard practice in the machine industry to cut keyways is to get a thin piece of paper, when everyone smoked we used cigerette paper, then touch the mill to the side of the part holding the paper to the side as well. When the mill cutter took the paper out of your hand you came up and you were 1/2 the mill and half the part away from center.
Always wanted to buy one of those lighted things.
Never bothered to take into account the thickness of the paper. I'm more blacksmith than machinist.

quote:

The jig doesn't fit the small ring Swede I want to do next

What drill and tap jig do you have that doesn't fit the swede?

Westpac, thanks for your concurrence on using the mill vs gluing bases. The spring loaded gizmo looks neat, but I think what I have will work just fine. I might try to post a picture of the set-up later.

Brad, thanks, this tip was also in the DVD. I don't smoke, so regular paper will have to do. I think they recommended a thou for the thickness of standard copier paper.

Mad Jack, the jig is for Mauser 98s and Springfield 1903s. I think I got it from Midway. I thought I might be able to loosen and slide it fore and aft to adjust for the shorter receiver, but the mounting bolt locations will not allow for both bolts to engage. (i.e. if I slide the jig far enough forward for the rear holes to be located properly, the front receiver ring will prevent the forward mounting bolt from going through so only the aft bolt holds.) I can still use the bottom part of it to clamp down the receiver for use in the mill so all is not lost.

I have one of the house brand that midway sells/or sold and can do large rings and small ring Mauser's, as well as Springfields, and jap Arisaka's. It came with two top plates if i remember right have to dig it out and read the paper work. Just wondering are you trying to use the jig with the barrel on the action?

I actually dug out the second top plate last night and I think that one would have worked... Oh well, I have it all fixtured in the mill now so I am going to remain on that path. BTW, The barrel is off.

Got those holes drilled yet

LOL cool

quote:

Originally posted by ted thorn:
Got those holes drilled yet

Nope. Job and family jump ahead of my hobbies... I will report back when I do. Probably this coming weekend.

Hey, this is my 400th post! (add another 1000+ for all the times I wanted to say "nice rifle" but held back.)