Hmmm I suspect you're going to eat this screw up.
Drill + tap failure. Backwoods Outdoors Corbeil Ontario.
- Thread starter Jimbobob08
- Start date
Hmmm I suspect you're going to eat this screw up.
Jonnyofalltrades
Regular
- Location
- North-central Saskatchewan
I have measured factory drilled holes(6-48) with only .050" of material left. I think I would consider that a bare minimum, and usually shoot to have at least .060" left.
Anyone else feel like epoxy is NOT normal to hold the rail in place?
- Location
- Western Manitoba
Before I owned a Forster jig, I had done some Mauser 98 by epoxy the long rail to the receiver - set with calliper jaws to be square. Then drilled and tapped through the scope rail holes. Then removed that scope base (usually by giving it a good smack) and put release agent on receiver(?) scope base (?) and bedded in that epoxy by snugging up the screws. I have never removed them - using the release agent says I could - but the epoxy was never relied on to "hold the rail in place" - except for that first step to get the four holes lined up to be straight.
As I recall - first touch was with a bit just barely small enough to go through the through hole in the rail - - enough to make a divot - then switched to proper sized tap drill and drilled hole in that centre - once I got the Forster jig, discovered is better idea to use too small drill for the through hole, then to finish the hole with a correct tap size bit - saves on wear on the tap bit, and Forster seems to claim the hole is "more accurate" - was almost aways done with the barrel unscrewed - so was four through holes - only needed the starting tap to do all the way through.
As I recall - first touch was with a bit just barely small enough to go through the through hole in the rail - - enough to make a divot - then switched to proper sized tap drill and drilled hole in that centre - once I got the Forster jig, discovered is better idea to use too small drill for the through hole, then to finish the hole with a correct tap size bit - saves on wear on the tap bit, and Forster seems to claim the hole is "more accurate" - was almost aways done with the barrel unscrewed - so was four through holes - only needed the starting tap to do all the way through.
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Well I have been following and felt I couldn’t anything that hadn’t already been said but my first thought was WTF and it really hasn’t changed. I have drilled and tapped enough holes to see a crap job when it’s done. OP I feel bad for you and your probably disgusted with the screw up.
Prior to guntech's post, I thought .060 would be about minimum. The post caused me to question what I thought I knew.
- Location
- Western Manitoba
Go here: https://www.practicalmachinist.com/forum/threads/scope-block-hole-depth-what-is-safe.260558/
Post #7 gives short table to show it varies what is amount to leave - whether on chamber or other place on barrel - what is size of hole. Is likely other dimensions given elsewhere on Internet.
It's because pressure is per sq inch..so the more area the more pressure working on it. If you had 40,000 psi over an area of say 1/16 of an inches area you would only have 2500 pounds pushing on that area
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The thing with jobs like this, is the "Fiddly" bit, is what the customer pays for, not getting it done wrong, but really fast turn around!
Expectations, anyways.
Slow(ish), careful, and RIGHT! And nobody ends up talking poo about you forever after!
Jonnyofalltrades
Regular
- Location
- North-central Saskatchewan
Just in case anyone is wondering about those oversized screws from Brownell's. Most of the kits were out of stock, but I put a taper($29) and bottoming taps($27.) in my cart, along with a dozen weaver head screws($9).
By the time it calculated shipping, it was up to $128.95USD, or about $175CAD.
Ouch.
By the time it calculated shipping, it was up to $128.95USD, or about $175CAD.
Ouch.
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I don’t believe it works that way. Pressure is pressure and it doesn’t decrease because the hole might be smaller.
I agree. The floor or the bottom of the larger area would be weaker. Same with a bridge over a stream compared to a bridge over a lake.
- Location
- Western Manitoba
You might be both correct and in error - the pressure is listed as PSI - POUNDS PER SQUARE INCH - so the FORCE applied is going to be more with more square inches, and less with less square inches - even though the pressure stayed the same. If you apply 40 PSI to two square inches, that area has to withstand 80 pounds of FORCE. If you apply that same 40 PSI to 0.5 square inches, that smaller area has to withstand 20 pounds FORCE. Wall thickness can be thinner, to withstand the same PSI, as the container gets smaller.
I suspect in a round cylinder, like a rifle barrel, is also a "hoop" effect going on, but I do not know how to calculate that - something like the circular arrangement helps to withstand the inside applied FORCE - to resist bursting - drilling a small hole into that has less effect than drilling a large hole.
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Jonnyofalltrades
Regular
- Location
- North-central Saskatchewan
- Location
- Western Manitoba
Scary prices, for sure - but helps put in context for people who have never done it - so REALLY opens eyes to hear advice to use a new, sharp tap and fresh sharpened drill bit "for each hole". To boot, like chintzing out on case lube when sizing - everyone has to do that once - to rip the rim off a case and have body stuck in the die - or to break off a tap in a hole - so your threaded hole "for $15" now becomes some hours of fussing to get that broken thing out of there, and "fix" that hole, and then come up with a replacement tap.
A cgn member pm’ed me contact info to an older smith who’s local to me. I gave him a call a few days ago, and yesterday I brought him my rifle to look at. He deemed it safe to shoot. Pulled open an old box with some 3 decades old rails machined to match 92 barrel contour that attaches via the rear sight dovetail. Mounted my red dot, and sighted it in. Old fella took a tumble last week and I was thankful he took the time to get me up and running for deer season, it was a chore for him.
