Anyone made their own crosman metal breach ?

[Shed tuner]

I've just finished setting up the milling bracket and vice etc on my old lathe, to do some light milling. And I've got some suitable brass bar.

Currently my plan is as follows, but I'd appreciate input from anyone who's done this before.
The designis to be the same as std crosman, for parts interchangeablity - so same bolt/barrel/mounting height etc

cut bar to length, face, centre drill both ends, drill one end for the barrel dia (maybe 1/2 way though), drill the other for the bolt dia (up to the correct distance, just ahead of the small securing screw. this depth will form my reference point
mill top flat for dovetail
cut dovetail (or leave flat to bolt a bit of picatinny rail onto)
cut flat on opposite side around 10mm wide
use round nose (19mm) milling cutter to create the groove that mounts on the cylinder. Critical dimension is the barrel mounting height, dictating depth
mill out the loading area
install the barrel and bolt and determine correct bolt travel
drill from the side the start, end and a couple of mid positions for the bolt slot (horizontal and vertical) and mill out
drill out the TP
drill and tap the barrel grub screw
drill the small mouting screw hole
drill the rear mounting screw hole

I'm expecting a fair bit of trial fitting and fiddling, but I think I can probably manage.

Input welcome,
JB

[evert]

As said in another thread, I'm following this with great interest as there is a bar of aluminium in one of my scrap bins waiting to become a breech.
I dont have a proper mill, and my previous experiences with my milling attachment are not that great, so I expect to do a lot of dremel and file work on the loading port and bolt handle track.

I dont know how relevant this is to your process, but this guy made his own breech:

http://anotherairgunblog.blogspot.co...ch-part-1.html
http://anotherairgunblog.blogspot.co...ch-part-2.html
http://anotherairgunblog.blogspot.co...ch-part-3.html
http://anotherairgunblog.blogspot.co...an-part-4.html

[Captain Bongo]

Make a few JB if you have the materials. You may make mistakes or work out a better way of doing something half way through an operation, usually one of the last operations. When I was making parts like sizers, bolt handles and piston extensions it usually took a few trial runs before I worked out the most effective method.

Document your process so that you can make one again in the future. I lost count of how many times I have stood there trying to remember how I previously made something.....

[--ped--]

this will help you if you're making one

if it's for yourself possible make it so a larger od barrel can be fitted

[Shed tuner]

thanks guys, and that diag will be handy Ped...

First one will be bog std, next variation I want to do exactly that - make it a little higher for a larger OD barrel, and maybe a Rapid mag system.. but one (baby) step at a time...

[Shed tuner]

just read that blog.. pretty much the same order I was thinking, so that's good. Also an interesting idea of having the barrel setscrews underneath, but I don't think I have enough meat there with std heigh clearance, so will leave that for v2

[--ped--]

you can put set screws radially 120* apart so you have a pair at the top then two either side

[Shed tuner]

you can put set screws radially 120* apart so you have a pair at the top then two either side

that's a good idea.. got more meat at the sides too...

[TonyL]

Very best of luck with these, JB.

[evert]

This thread inspired me, so I started drilling the alu rod today. (the drilling of the center holes is the fun part, the rest of the machining will happen when it happens)
Metric tools limit me somewhat, reamed the bolt hole to 7mm, but I have to hone the barrel hole out a bit to get good barrel fit, as the barrels seem to be a fraction larger than 11mm.

I'm thinking to make a long rod that can be fitted with a HSS bit to machine the bottom radius with the breech mounte on the lathe top slide.
It will probably flex a bit, but should be possible if I go slow.

[Shed tuner]

evert, a round nose milling cutter is the way to go for the underside - I got mine for less than a tenner from e6ag

[dulux]

I've just finished setting up the milling bracket and vice etc on my old lathe, to do some light milling. And I've got some suitable brass bar.

Currently my plan is as follows, but I'd appreciate input from anyone who's done this before.
The designis to be the same as std crosman, for parts interchangeablity - so same bolt/barrel/mounting height etc

cut bar to length, face, centre drill both ends, drill one end for the barrel dia (maybe 1/2 way though), drill the other for the bolt dia (up to the correct distance, just ahead of the small securing screw. this depth will form my reference point
mill top flat for dovetail
cut dovetail (or leave flat to bolt a bit of picatinny rail onto)
cut flat on opposite side around 10mm wide
use round nose (19mm) milling cutter to create the groove that mounts on the cylinder. Critical dimension is the barrel mounting height, dictating depth
mill out the loading area
install the barrel and bolt and determine correct bolt travel
drill from the side the start, end and a couple of mid positions for the bolt slot (horizontal and vertical) and mill out
drill out the TP
drill and tap the barrel grub screw
drill the small mouting screw hole
drill the rear mounting screw hole

I'm expecting a fair bit of trial fitting and fiddling, but I think I can probably manage.

Input welcome,
JB

Hi, one decent way to get a good radius on the bottom of the block if stuck with only a lathe is to use a boring bar between centres and a lathe dog with a flycutting tool at the correct radius and to clamp the work in a fixture in the tool post so you cut the radius as the work traverses. Accurate and less chatter than trying an endmill in the chuck.

[evert]

Hi, one decent way to get a good radius on the bottom of the block if stuck with only a lathe is to use a boring bar between centres and a lathe dog with a flycutting tool at the correct radius and to clamp the work in a fixture in the tool post so you cut the radius as the work traverses. Accurate and less chatter than trying an endmill in the chuck.

I was thinking along those lines, but dont have any round stock long enough to make that boring bar.
A boring bar without a center in the far end will probably give deflection, but I'll give it ago and se how it goes.

[Shed tuner]

interesting idea, thanks....

[dulux]

I was thinking along those lines, but dont have any round stock long enough to make that boring bar.
A boring bar without a center in the far end will probably give deflection, but I'll give it ago and se how it goes.

I'd say it's well worth starting with a length of silver steel, centre it both ends to be driven between centres with a lathe dog and drill for a piece of 1/4 hss and a set screw to hold it.
It's a tool you'll use time and again, not just for this job. Light passes won't mess things like a mill in a lathe chuck if you're tool limited, I've tried both.