Skim bedding methods

S

SEHunter

New member
Although I recently created a thread on bedding an aluminum block stock, I decided to make this one separate to specifically discuss skim bedding. I got some good insight from Scorch and Bart B. in regards to bedding (or not) the chamber portion of the barrel. After doing more research, I found testimonies of good grouping with no bedding in an aluminum block stock but many report that from shooting session to shooting session, although grouping stayed tight, POI tended to land differently which is something I want to avoid in my hunting rifle. I ran upon this skin bedding method. Excluding bedding any of the barrel including the chamber, does anyone have experience with results from skimming the action like this?...

http://www.700rifle.com/forum/22-how-s-modifications/1204-skim-glass-bedding.html
 
I can't remember how to get the link but, Bart Bobbitt wrote a method on bedding that is so simple, it's how I do my bedding.
I'm probably not near as good as he is, but it's fun and easy..
Maybe somebody will get the link to that article posted for you.
 
I'd be interested in reading it even though I made the decision to move forward with bedding my HS Precision stock. I had decided against it until I went to torque my action screws. Out of curiosity I torqued both the front and rear alone without the other one tight. When I did that with the rear action screw, it literally lifted the action away from the front mounting surface of the aluminum bedding block what appeared to be maybe 1/16" to 1/8". This was all the proof I needed to know my action would be stressed if I left it be.

This was just finger snug with a standard L shaped Allen wrench. Couldn't have been more than 20 inch pounds although I didn't check it. When I was curing the Devcon, I removed the line up bolts then applied release agent to the action screws. I barely snugged the front action screw and just allowed the rear screw to seat in place with no torque.
 
In the the thread linked above, the OP basically did a typical bedding job, but instead of removing material as you'd do with wood or composites he drilled out a bunch of divots in the aluminum to get some depth and a better mechanical bond with the epoxy; it won't crack out as easily in a thin "skim" layer.

With an aluminum block that has issues I would use a contact dye to try to find the source of the issue first (may be a small area) rather than basically gutting the aluminum block as he did.

For all intents and purposes he could have pulled out the aluminum block and just filled the void with epoxy. The block serves no purpose now.
 
I'm not sure I'd go that far. The aluminum adds some rigidity at lower weight, which may be desirable in some applications.

However, it is a fact that most people are not familiar with scraping a precision fit between metal parts any more. When I was doing machine too repair part time, I scraped right angles onto three annealed 2" iron blocks one time, referencing them off each other by the rule of threes. I subsequently had them measured in an optics metrology lab, and they proved to be flat and true right angles to within about 20 millionths of an inch across their widths. If I set one face of one of these blocks on a granite surface plate and lifted the far edge slightly, then dropped and pushdd simultaneously, it would glide clear across the surface plate like an air hockey puck on the cushion of air trapped when I dropped it.

We used to weld up and fit 1911 barrel link lugs by scraping to fit the assembly pin on the slide release.

I know a tool maker who worked on aerospace machine tools thirty years ago who said they scraped and then stoned using bi-color dye (blue on one surface and yellow on the other, making green at contact locations) to get to 5 millionths across a super precision surface grinder's ways. 20 days scraping and 20 days stoning, IIRC. The bi-color dye is used because the parts get so close together you can't tell from just one color where it is thinner and where it is thicker. You need the color mix to see where to stone next.

At any rate, with a little practice, some Hi-spot Blue and the right shaped tool, you can scrape a very, very, exact fit of the receiver against the aluminum bedding block.
 
Your last statement was my exact thought as well. I did a partial version of what he did because I wanted to still take advantage of having the solid foundation of the bedding block (at least in the front) but attempt to relieve as much stress from the action as I could. I removed stock material around the sides for clearance as usual in a typical bedding job with the exception of the aluminum bedding block. I drilled small dimples in the aluminum all over except for where the action rested. Then I scuffed up the whole surface with an engraving bit in a dremmel. I stayed away from the markings that the action left on the bedding block. I drilled the dimples else where in the attempt to help the Devcon have more to grab on to. I guess it could be called partial skimming. Or whatever. It was experimental. If it doesn't produce good results, I'll just know to not do it that way again.
 
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