O-ring groove machining

[aldea6]

Hi , I would like to put a hexagonal Lothar Walther barrel on one of my guns ; the problem is : how to machine the tiny groove inside the chamber of the barrel for the O-ring? What kind of tool is needed to do this operation on a lathe , or on a milling machine , as the bore is only .25" in diameter? Sketch below.



Thanks

N.B. I'm not sure this is the right forum for this kind of question

 

[mtnGhost]

Yeah, that part sucks lol. A lathe and a small internal boring bar is up to the task. Finding one small enough can be a challenge, so it is quicker to make one from high speed steel. I just went through this exercise for the first time myself, and this took ~6 tries on my grinder before I finally got it cutting perfect grooves:

It might not be the prettiest tool, but the grooves made up for it.

P.S. - you can (and should) practice on softer materials first like acetyl or brass. It will take trial and error to form the right shape. Make sure you test with hardened steel before taking it to your barrel! 

 

[aldea6]

Thanks mtnGhost, I've some 1/4" steel tool round bar in my shop. Just start my grinder and have a try. I first thought to use a very little cutting disc in my Dremel , but that doesn't seem very professional to me .

 

[airgunfans]

You will need a mini grooving tool of this kind. It can work in holes as small as 4 mm in diameter. In China, they are being sold at 85 Chinese Yuan or about 12 USD. You will need a holder before mounting it on the lathe tool post. The holder costs just about six bucks. I am pretty sure that you can find them on Aliexpress , Banggood or other popular sites selling Chinese products. 

Tool holder : 

 

[aldea6]

That's great , airgunfans . Thanks

 

[airgunfans]

You can get it here : 

https://www.aliexpress.com/item/33052825989.html?spm=a2g0o.productlist.0.0.4d484ecfVb7ktO&algo_pvid=61447869-1bd5-44d7-9883-be897f663a54&algo_expid=61447869-1bd5-44d7-9883-be897f663a54-1&btsid=5aa2636d-e099-44fc-85d4-e6c099b1e9c0&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_52

 

[bucketboy]

Or bore out the barrel to tho o/d of the o ring then turn up a bush to fit, hold in place with loctite. 



Bb

 

[mtnGhost]

Or bore out the barrel to tho o/d of the o ring then turn up a bush to fit, hold in place with loctite. 



Bb

 

[Tvanpool]

This is a tool I ground from HS steel to do the job. The tool shown above would not work for me. It might work for the larger calibers but not for .177. The o'ring used for the breach seal in Air Arms .177 guns is 1.5mm cross section x 4.5mm ID, so the groove needs to be about .050" deep and the tool above is limited to 1mm or .040". If you have a piece of 1/4" HS steel it is not difficult to grind the tool, rough it out on the bench grinder and do the finish work with a Dremel. 

 

[bucketboy]

Or bore out the barrel to tho o/d of the o ring then turn up a bush to fit, hold in place with loctite. 



Bb

Why? No different to the impact barrel liner system, I have done this a few times in valves that have a stem Dia of .125, 



bb

 

[mtnGhost]

Or bore out the barrel to tho o/d of the o ring then turn up a bush to fit, hold in place with loctite. 



Bb

Why? No different to the impact barrel liner system, I have done this a few times in valves that have a stem Dia of .125, 



bb

The shot pressure and/or the pellet pin would knock the bushing loose eventually (or right away). Putting a groove in the barrel or in the pellet pin itself would be a lot less risky.

 

[aldea6]

Yes that seems an easy way to solve the problem.My idea would be to bore out the barrel , turn up the bushing , adjusting the O-ring / bushing / barrel with the barrel probe, then blocking the bushing with a clamp , removing the bushing and soldering it to the barrel ( tin or siver brazing).

I'll first try to a old barrel to see how it works

Mike

 

[aldea6]

Putting a groove in the pellet pin is the easiest way to do the job , but I think that the O-ring is going to worn out quickly ; moreover , in the cricket, the pellet probe is totally retracted in the breech block to install the magazine , ant the O-ring will jam with the breech block. Of course this one could be open up , but……...

Mike

 

[bucketboy]

Or bore out the barrel to tho o/d of the o ring then turn up a bush to fit, hold in place with loctite. 



Bb

Why? No different to the impact barrel liner system, I have done this a few times in valves that have a stem Dia of .125, 



bb

The shot pressure and/or the pellet pin would knock the bushing loose eventually (or right away). Putting a groove in the barrel or in the pellet pin itself would be a lot less risky.

Less risky?, with the correct adhesive, there is no chance of the probe or pressure can knock it out.. more difficult definitely particularly in smaller bores.

I have used the bush method before, no issues.

To the OP, if the o ring needs to be in very close proximity to the muzzle then why not just turn down the o/d of the barrel make the sleeve and fit the o ring in that. The sleeve can either be fixed to the barrel permanently or removable for easy o ring replacement.



Something like this

Bb

 

[vmaxpro]

For the future, invest in micro 100 id groovers. 

 

[Long_Gun_Dallas]

Less risky?, with the correct adhesive, there is no chance of the probe or pressure can knock it out.. more difficult definitely particularly in smaller bores.

I have used the bush method before, no issues.

To the OP, if the o ring needs to be in very close proximity to the muzzle then why not just turn down the o/d of the barrel make the sleeve and fit the o ring in that. The sleeve can either be fixed to the barrel permanently or removable for easy o ring replacement.



Something like this

Bb

Thats close to how the fx barrels are assembled. Except the end pice threads on. But, in the end... Whatever works