Crosman Steel Breech

[airriflenut]

 fasteddy  you cannot simply re-tap a 4-48 hole to a 4-40.  The tap hole for a 4-48 uses a #40 tap drill, a tap hole for 4-40 uses a #41 tap drill.  The higher the drill # the smaller the diameter it is.  If you try to re-tap the 4-48 hole to 4-40 you will only get 25% or less thread engagement...not nearly enough meat on the threads to hold down a breech.  I know from personal experience on this one, it simply will not work....sorry.

If you have a means to accurately re-drill the holes and tap (breech and tube) you could step-up to  5-40.

[airriflenut]

http://www.engineershandbook.com/Tables/taphole.htm

This is the guide I have always used for any drill and tap application I have, be it Delrin, aluminum, brass, stainless or mild steel.  It gives all drills needed for each tap size plus the drills required for close and lose clearance holes.  I have many copies of this chart that I keep all around my shop...in note books, on clip boards, etc.

On the left it give the major and minor thread diameter for each thread.  If you notice, any tap that is used for very fine threads uses a drill size very close to the minor thread dimension.  Fine threads are VERY shallow.  Course threads are, of course, deeper so a smaller drill would be used to allow for the cutting of the deeper threads. 

Believe it or not, on my Crosmods breeched 1377 (my very first mod) I kept stripping holes from over-torque because I was trying to get too much of a compression fit on the long transfer tube.  I ended up at 8-32 and it has held tight for a very long time...I just don't torque as much now!! 

[rws_53]

If I tap it, I will use probably use a 4-40 and get a new screw.  It just seems like the tube wall is so thin that there isn't much room to draw threads on it.

When I looked at the front hole I drilled, it lined up, but there didn't look like there was enough headroom between the front of the hole and the top of the breech to fit any kind of countersink bit (and I'd have to buy one for steel anyways).

use a drill bit slightly larger than the screw head to countersink the hole

[fasteddy]

fasteddy  you cannot simply re-tap a 4-48 hole to a 4-40.  The tap hole for a 4-48 uses a #40 tap drill, a tap hole for 4-40 uses a #41 tap drill.  The higher the drill # the smaller the diameter it is.  If you try to re-tap the 4-48 hole to 4-40 you will only get 25% or less thread engagement...not nearly enough meat on the threads to hold down a breech.  I know from personal experience on this one, it simply will not work....sorry.

If you have a means to accurately re-drill the holes and tap (breech and tube) you could step-up to  5-40.

There is no hole... that is the problem.  I'm having to drill a hole in the tube to match the rear screw location on the breech, hence I am starting my own hole.  The diameter of the breech hole is 4, so I can use 4-40 on the tube, but what I was concerned with is that upon drilling a hole in the tube, I wasn't sure whether I could successfully draw threads on the wall as they are so thin... but Crosman did it... and I'm sure you guys have... so I will give it a shot!

[fasteddy]

use a drill bit slightly larger than the screw head to countersink the hole

I could try that.  I did find, however, that the bits I already owned were not making much of a dent in the steel breech.  I had to go out and buy a tungsten bit to make the front hole.

[rws_53]

There is no hole... that is the problem.  I'm having to drill a hole in the tube to match the rear screw location on the breech, hence I am starting my own hole.  The diameter of the breech hole is 4, so I can use 4-40 on the tube, but what I was concerned with is that upon drilling a hole in the tube, I wasn't sure whether I could successfully draw threads on the wall as they are so thin... but Crosman did it... and I'm sure you guys have... so I will give it a shot!

If you go with a rear hole screw your hammer would have to be modified to clear the screw.

[fasteddy]

If you go with a rear hole screw your hammer would have to be modified to clear the screw.

The plot thickens!  I'm glad you guys are around to warn me about these things!  Now I'm back to thinking I should work on the countersink! 

I'll have to buy a larger tungsten bit for it... maybe I can return the single bit I bought and buy a kit...

Can I first run another idea by... so you can tell me it is silly and prevent me from trying... is there any way I could try to 'freestyle' a countersink by using a dremel bit?  I have a couple pointed cutters that carve steel up no problem... it wouldn't be a perfect circle, but it could at least get the job done.  Probably a bad idea, right? 

[rws_53]

The plot thickens!  I'm glad you guys are around to warn me about these things!  Now I'm back to thinking I should work on the countersink! 

I'll have to buy a larger tungsten bit for it... maybe I can return the single bit I bought and buy a kit...

Can I first run another idea by... so you can tell me it is silly and prevent me from trying... is there any way I could try to 'freestyle' a countersink by using a dremel bit?  I have a couple pointed cutters that carve steel up no problem... it wouldn't be a perfect circle, but it could at least get the job done.  Probably a bad idea, right?

I did mine on a small Sherline vertical mill using a drill bit to do the hole then an end mill to countersink it.  Do you have a drill press and a way to clamp the work to the table for your Dremel?  Likewise using a drill bit...you'd want to use a drill press and clamp the work down.  Freehand could get pretty sloppy. 

[airriflenut]

If you have a drill press, even a bench top press, you can get an inexpensive cross slide vise to bolt on the press table.  I've got an old Sear bench top my dad gave me a few years back, don't remember any h.p. or such but it's built like a tank.

I got a cheap cross slide (I do mean cheap, about $49) and I use it frequently.  The main thing I don't like about it is that one side of the vise jaws has a slot under the jaw face, I cannot use any parallels due to that.  Something to check for if you go that route.

When I buit my bulk feed Beast I made many of my own parts using only the bench drill press with cross slide, a bench top band saw and a Jet 1014VSI wood lathe.

Good luck and keep if posted.

[fasteddy]

Jees guys... I'm way more of a luddite than all of that.  All I'm working with is a dremel and and a cordless drill.  That is all... 



I drilled the hole in the breech from above with the breech lying on the work bench.  I can clamp it down, if that helps, but that is about it.  I feel like it will be fine, though, as the hole doesn't have to be perfect... it just needs enough room for the screw head to clear.  Hell, if it is more shallow than stock, it will probably function better (won't give enough depth for the pellet to fall face-down into!).

[Tater]

Jees guys... I'm way more of a luddite than all of that.  All I'm working with is a dremel and and a cordless drill.  That is all... 



I drilled the hole in the breech from above with the breech lying on the work bench.  I can clamp it down, if that helps, but that is about it.  I feel like it will be fine, though, as the hole doesn't have to be perfect... it just needs enough room for the screw head to clear.  Hell, if it is more shallow than stock, it will probably function better (won't give enough depth for the pellet to fall face-down into!).

You are not alone there. And mine isn't even a real Dremel, it's a bottom of the line Harbor Freight cheapy with one speed. 

[airriflenut]

If you guys need a rotary tool and don't want to pay the Dremel price or settle for the HF cheapo check out northern Tool.  The have a single tool package, I got one, that comes with a lot of attachments, even a clamp hangar for the tool if you want to use the INCLUDED flexible shaft.  I think i gave around $39 a couple of years ago.  Awesome tool for the price.

They also have a two tool package, the regular variable speed 120v and a small palm size 12v single speed.  The small one is excellent for polishing the barrel leade, bolt race, etc.  It come with even more attachments AND the flex shaft with clamp on hangar.  Around $69 if memory serves me.  Both a much better deal than Dremel offers.

Just an FYI...sorry for the hijack.