Radiused groove in cylinder port face

[OregonBill]

Dumb question of the day: How do you cut the radiused groove in the cylinder port face that accommodates the cylinder, the two being silver-soldered together in constructing a very simple steam engine?
Can it be done on a lathe or do you have to have the milling attachment?

 

[MachineTom]

Two ways to do it Lathe or Mill. If mill a rotab and a ball end mill. On a Lathe the you can use a preground carbide Oring cutter, the ones for ID orings, then mount the tool 90° to boring position and groove the face, you can freehand grind a cutter, but the radius is tough to get right when freehand grinding. Also make sure there is enough relief for the cutter to avoid rubbing the groove.

 

[GWRdriver]

Bill,
You can probably do this in the lathe, by offsetting in the 4-jaw, the thing is you will need some extra stock in order to hold the piece in the chuck. If you don't have enough extra material to for chucking you will need to solder the blank to a chucking piece. If you are using brass or bronze, soft solder has enough strength to do this if you take it easy, and not take too much depth of cut per pass. This job will have what is called an "interrupted cut", where the toolbit makes an impact each time it cuts into the workpiece as it comes around. This puts more stress on the setup than if it was a continuous cut. Lighter feeds and shallower cut depth will reduce the effect of impact during machining.

PS - Tom, I think the "groove" Bill refers to is actually the radiused underside or "saddle" which allows the valve block to nest on the cylinder OD. Bill, correct me if I'm wrong.

 

[OregonBill]

Thanks guys. I'm trying to visualize this operation on a minilathe. Will see if there is something on Youtube. It seems to be a very common step in making simple steam engines.

 

[GWRdriver]

Bill,
What's the swing capacity of the lathe you have, and does it have a "table" surface on the cross-slide? You may be able to make this a boring job, mount the block on the cross-slide and machine the radius using a boring bar between centers. The picture shows boring a hole between centers. You would be boring only part of a hole. This could also be done using a flycutter held in the chuck. (In all cases cautions for Interrupted cut would still apply.)
I hope this isn't getting to be boring.

 

[OregonBill]

Harry, I don't have the lathe in hand yet, but am waiting for the Micromark 7X16 to ship.

 

[R.G.Y.]

Can you drill a hole the size of the cylinder in a block, then cut the block in half.

 

[OregonBill]

R.G.Y., that would work, although it might use up more material. I was also thinking of holding the port face against a turning rod that had emery cloth wrapped around it ...

 

[R.G.Y.]

I should have said bore not drill perhaps. But you do get 2, so you can keep one for another engine.woohoo1I think the emery could take some time, and the ends tend to flare out.