Barrel threading, how to do it?

[DCL_dave]

If you take it steady and slow then the out of balance forces won't be too serious. Anyway, it wouldn't be too difficult to mount a balance weight opposing the breech block, much as one might add a balance weight if turning a component fixed to the faceplate.

Slow and steady is fine for screwcutting, but what about turning down to size and crowning, etc,? Btw, slow and steady is all my treadle lathe does!

How would you calculate the weight needed to counterbalance? (it's a bit like a pound of flesh type calculation, surely?)

3 jaw chuck and shims or 4 jaw chuck (which I don't have) is easiest, surely?...it holds the breechblock securely so that the offset mass of breechblock makes very little difference.

[Solvo]

For a rough job yes you can just use a 3 jaw, but most 3 jaw chucks are the self centring type and would make it damn near impossible to machine true to bore as you cant clock in. Not too bad for screw cutting but bad if you want to re-crown.

Weight of the breech block would depend on how you have the work set up, if you have the barrel clamped in chuck near the muzzle the offset would be a problem at any real speed.

Edit - for the balance i wouldn't use any fancy calculation. Last time i did something similar i used a grinding wheel balance to roll the round shaft on, then tied metal to the opposite side of the offset block block to balance it, when happy secured with some stout zip ties. Not perfect and i'm sure there are better ways but it removed the vibration.

[Rich]

A lump of steel the same size as the breech block, and lash it on.

Whatever machining you want to do at a fast speed on a lathe, you can normally do just as well at a lower speed, it just takes longer. My dad always taught me, and this was sixty years ago, when in doubt, slow down.

[johnbaz]

Could the barrel not be held between two centres and a faceplate with a dog to hold it- Weights can be added to the faceplate to make the balance right?


Like this but the centre in the dead end would be better if it was a ground type to allow access for the cutting tool..



One of these but with less material removed so that it fits the bore squarely..






John

[DCL_dave]

For a rough job yes you can just use a 3 jaw, but most 3 jaw chucks are the self centring type and would make it damn near impossible to machine true to bore as you cant clock in. Not too bad for screw cutting but bad if you want to re-crown.

Weight of the breech block would depend on how you have the work set up, if you have the barrel clamped in chuck near the muzzle the offset would be a problem at any real speed.

Edit - for the balance i wouldn't use any fancy calculation. Last time i did something similar i used a grinding wheel balance to roll the round shaft on, then tied metal to the opposite side of the offset block block to balance it, when happy secured with some stout zip ties. Not perfect and i'm sure there are better ways but it removed the vibration.

Sound advice, thanks Solvo. Re. barrel clamped near muzzle, I did say if it was poked up inside the spindle then a bush of some sort would be needed to hold it tight and stop it flapping around.

A lump of steel the same size as the breech block, and lash it on.

Whatever machining you want to do at a fast speed on a lathe, you can normally do just as well at a lower speed, it just takes longer. My dad always taught me, and this was sixty years ago, when in doubt, slow down.

Sage advice, thanks Rich.

Could the barrel not be held between two centres and a faceplate with a dog to hold it- Weights can be added to the faceplate to make the balance right?


Like this but the centre in the dead end would be better if it was a ground type to allow access for the cutting tool..



One of these but with less material removed so that it fits the bore squarely..






John

More sound advice, thanks John ...but you're still hindered when it comes to crowning the muzzle

...and is that half centre from dividing head/ tailstock?

[Solvo]

Not sure id want to stick a centre into the crown on my precious barrel. Can't see it doing any favours for the rifling.

[NickG]

I did one a long time back for an smk xs 19 I was messing with, as I remember I pressed two delrin bushes over the barrel one either end then between centres machined said bushes , clamped the breech end in a 4 jaw clocking the rear bush to keep it true , and used the bush at the front of the barrel to run the steady on clocking the bore to maintain concentricity, a bit of a faff, but it worked .

[don1971]

I had the same problem, although my spindle will take 38mm, it wouldn’t take the breech block.
In the end I did a workaround using a rotary table on the mill.

https://www./community/index.php?thr...-block.256026/

[DCL_dave]

I had the same problem, although my spindle will take 38mm, it wouldn’t take the breech block.
In the end I did a workaround using a rotary table on the mill.

https://www./community/index.php?thr...-block.256026/

Sounds interesting but the link isn't working for me?...and my ancient mill has developed a dodgy knocking sound that I have yet to investigate...