Anyone made their own crosman metal breach ?

[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.

[Shed tuner]

I've got a 16mm bar that'll do nicely.. means I can do it all without repositioning the work in the clamp too, as the travel in the mill is only around 70mm, whereas with your approach I could do the whole lathe bed length... can also fine tune the radius with cutter seating depth.

Just need to build a workpiece clamp on the toolpost, but that's not too big a deal... time to dig out the mig...

[hmangphilly]

I've got a 16mm bar that'll do nicely.. means I can do it all without repositioning the work in the clamp too, as the travel in the mill is only around 70mm, whereas with your approach I could do the whole lathe bed length... can also fine tune the radius with cutter seating depth.

Just need to build a workpiece clamp on the toolpost, but that's not too big a deal... time to dig out the mig...

How were you originally thinking of holding the workpiece jon ?

[--ped--]

you don't need to use a ball nosed endmill you can just mill slot like a falcon uses

[Shed tuner]

you don't need to use a ball nosed endmill you can just mill slot like a falcon uses

was thinking of the need for the transfer port seal to be close.. but then again, easy anough to make a new bespoke transfer port.

I'm actaully rather glad I started this thread - lots of interesting things to think about - thanks all for the ideas and input

[Shed tuner]

How were you originally thinking of holding the workpiece jon ?

I have a right angle milling adapter that sits atop the slide instead of the toolpost (with about 70mm vertical travel via it's own slide), which has a small machine vice mounted on it, facing the chuck.

I can modify an old crude tool holder to clamp the workpiece, so it can approach horizontally rather than longtitudinally...