Stuffing box, any ideas?

[Kaleb]

I am working on a double acting piston valve steam engine, and I would like to know how I should go about making stuffing boxes or glands for the piston and valve rods. Can you please give me some pointers here? Here's a rough cross section diagram of the design I'm currently trying to use:

 

[ksouers]

That looks right, Kaleb.
As alternatives you might want to try twisted teflon tape in place of the string, or impregnate the string with heavy grease. Just giving ideas.

What is you are having trouble with?

 

[kvom]

It doesn't look as if the cylinder has a cover in the drawing. The spigot for attaching the gland and nut looks a little short assuming the drawing is to scale. Assuming it's long enough to be threaded then the gland and nut could be a single piece. if you do have a cover then the gland would be machined as part of the cover.

 

[shred]

You could also try a lightly-compressed (5-10%) O-ring in place of the string. Kozo likes those a lot on his live steamers.

 

[Blogwitch]

Here is a C-o-C showing the three most popular types.

Bogs

 

[Kaleb]

The main problem is that the holes I drill in the nut and the entrance to the cylinder, I can't get the right size, 3mm, won't fit, 3.5mm, much too sloppy. Is this as much of a problem as I think?

 

[tel]

Is this as much of a problem as I think?

While there is some latitude here, in needs to be as close as you can reasonably get. Try a 1/8" drill, or a 3.2, 3.3 or 3.4. If you have difficulty sourcing them locally,(engineering shop) get 'em here. Note that these are packs of 10 pcs, so the price is pretty good.

 

[Blogwitch]

Kaleb,

Where you might be going wrong is your machining procedure.

You must have both parts screwed together BEFORE drilling the hole for the piston rod. If you don't do that, the two parts, being made at different times and machine settings will almost be guaranteed to be out of concentricity with each other, especially if they are a threaded pair done with taps and dies. Stuffing glands are usually made as a matched pair, purely for that reason.

In fact to do it correctly, you should have the stuffing gland fitted to the cylinder bottom, then the cylinder fitted onto a trued up mandrel, finally the piston rod hole is drilled. Doing it that way, the bore and gland will be perfectly in line, allowing the piston free movement up and down without being forced onto the sides of the bore by an out of line gland to bore.

Bogs

 

[Tin Falcon]

Kaleb all good advise. There are options go to the John-tom. com sites and download a couple or few of the Elmers engines plan sets there especially the double acting engines . and look at how he did it. the pm research vertical oscillator douse not use a stuffing box and glands just a straight hole . also look at the kn Harris plans an see how he does it. I think there are other da plans there as well.
It seems like you are trying to design on your own young man admirable but IMHO build a few proven designs that are out there . And study as many plans from different people as you can then take what you feel are the best design features from several designers and make an engine you can call your own. Then work from scratch.
Tin

 

[Deanofid]

The main problem is that the holes I drill in the nut and the entrance to the cylinder, I can't get the right size, 3mm, won't fit, 3.5mm, much too sloppy. Is this as much of a problem as I think?

Well, what size is the piston rod? You need those holes to match your rod pretty close, right, and I don't mean 0.5mm close. More like 0.05mm close. If you don't have a reamer that fits, make a D-bit to match your piston rod, and presto!

The way John Bogs says to bore everything in one setup is the way that offers the best chance for good results.
The screw in gland nut he shows in the C-o-C will work fine, mostly. If you use tap and die for that, thread run out will cause the hole in the nut to wander as you screw it in. It may only be happy at certain timed places on the thread.
The one he shows second on his drawing is probably the easiest one to get right, and they work very well.
Depending on the size of your engine, an o-ring may be too tight, and fussy to adjust. Consider using Teflon tape, or yarn moistened with oil, then rolled in dry graphite.

Good luck.

Dean