View Single Post
Old 04-24-2013, 04:53 AM
cal50 cal50 is offline
Join Date: Mar 2011
Location: Ohio
Posts: 144

In the final stretch now......

Tonight its "Tap the lug" night. After I get a threaded hole in the right spot I can then do the final bedding on my rifle and wrap it up.For those that do not know what a transfer punch is you shall see.... A transfer punch is a precision center punch. Its designed to slide inside a hole and transfer the center point to the surface on the other end. In my case I drilled the hole thru from the bottom of my Mac stock into the rear lug area ( .250 / 1/4" diameter). I wanted to then insert my action into the stock then use the transfer punch to mark where I drill and tap the real lug mounting hole. It worked out pretty good but not perfect. IMHO if I ever do another one I will drill the hole from both ends and meet in the middle.

After measuring the side to side position the transfer punch mark was .030 off center. Since I do not want to purposely drill a hole off center on my receiver I will add clearance to the thru hole in the stock. I had planned to open it up anyway but it bothers me when things are not what I planned.

I will open up both sides and equal amount and blend.

A Transfer punch~

Punch in hole~

Business end~

How you "transfer" the mark~

Once you get the punch mark on the receiver you can then accurately drill the 1/4-28 tapped hole. You set up the receiver as before by indicating it in so its level and square. I use a piece of reamer blank ground to a sharp point. It's this sharp point I use to position it to the punch mark on the receiver I made with the transfer punch. I only have to align it one direction becasue I used my edge finder or wiggler to find the center of the lug off of the receiver. If you have a keen eye you can get it within or under .005. You put the the pointed blank in the spindle and crank the table around to center it. Once I find the center I zero my readout on the mill. I already have the correct drill, tap, center drill and chamfer tool laid out. Always double check your tap drill size BEFORE drilling the hole. Also its good to have only the correct tooling at hand so no mix up. Don't ask me how I know this....

Center Drill~

Hole drilled and chamfered~

Tapping the hole~

I always start my tap's while its in the machine,they are ALWAYS straight this way. I start them by hand then remove and hand tap, less chance to break a tap when done by hand. In the pic I use a spring loaded tool in the spindle to keep pressure on the tap handle and start it by hand for a few full threads. Use a good cutting / tapping fluid. The Springfield receiver machined up nice and I can tell the steel is of a good quality becasue of the cutting chips produced.

If all goes well you get a mounting hole that will last past my lifetime.

Its a Springfield with a tapped lug ?....but Springfield never made any.....

Not show was trimming the 1/4-28 stainless steel screw to the proper length. I just slipped it in the stock with my bushing (under the trigger guard) and let it stick thru into the rear lug bedded pocket. My rear lug measures 3/8" thick so the screw should not stick up more than 3/8" or it could be a problem with your bolt travel. I needed to trim and chamfer about .190 thousandths from the thread length and re-chamfer.

I test fit everything again by putting my action into the stock and tightening down the rear pillar and it works without binding or surprises, need to re-blue the rear lug radius.

Now I can go back and do the final finish bedding of my rifle and re-blue the radius I put on the real lug corners.

Last edited by cal50; 11-10-2017 at 02:13 PM.
Reply With Quote