Finishing stem and shank faces

[d6monk]

Hi guys,

I was wondering how everyone goes about finishing their stem and shank faces. Recently I saw some pipes where the stem and shank faces (and tenon) were so smooth they look like they had been buffed--mine are much more rough. In fact, all i do on the stem face is cut very slowly on a high spindle speed with a sharp lathe tool. I've been too scared to sand (and especially buff) that area for fear of it messing up the stem/shank junction. I do carefully sand the shank face on a flat piece of glass, but I don't buff it either. The tenon I also hate to sand although I usually do this a little. So, what do you guys do? Am I being too careful?

Thanks!

[JHowell]

Metal lathe or wood lathe? You're not getting a clean cut with the tool, which could be for a few reasons.

Spindle speed -- may be too high. The faster the spindle speed the better the finish, until enough heat is generated that the work melts or galls, then you get a rough finish. Ditto feed for a metal lathe. The slower the feed the more overlap between cutter passes, but longer the tool dwells near one spot, the more heat. There needs to be the optimum balance between speed and feed for the material. Also, light finishing passes are helpful.

Tool -- may not be as sharp as you think, or may not have enough relief or rake. Rubber needs more rake than metal, the shavings need to depart at less of an angle or they fracture away from the surface just ahead of the edge. Also, tools need to be sharpened frequently. A very clean, round radius to the cutting edge helps make smooth finish cuts. Make sure you're right on center with the tool; skewing creates more friction.

Setup -- may not be rigid enough. Rubber is pretty resonant, so unless you have it chucked close to the tenon you'll get chatter. And rubber is pretty soft, so even a high resonance will show in the finish. Shorten tool overhang to minimum, shorten unsupported work to minimum, add a live center if possible, anything to minimize flex. Make sure headstock bearings are in good shape.

All of the above are interrelated, and bad surface finishes are kind of chaotic -- a tiny change can make them appear, and a tiny change can make them disappear. A little different tool geometry, a little slower spindle speed, a little less stem protruding from the chuck, try one thing then another. Unless your lathe is completely clapped out, getting good surface finish is just a matter of time and experimentation.

Good luck,

Jack

[KurtHuhn]

I have found dull tools to be the number one cause of rough finish on everything from ebonite to steel and back again. If I notice that the finish on a workpiece is getting rough, I take my tool over to the belt grinder and give it a couple passes with a 400-grit belt and it's back to razor sharp and cutting smoothly.

I also have found that I get the best results from good quality tools and toolbits made from high speed steel (HSS, typically M2 alloy IIRC) and not so much from the carbide tipped tools - either brazed or inserts. I tend to use the carbide tools for roughing, then use HSS for light finishing cuts as Jack described.

[d6monk]

Thanks both of you, that's very helpful.

I have been using a taig lathe to do this, but I saved up for a couple of months and just bought a jet bd-920w. I just got it set up, but have not used it for any pipe making yet. Anyway, I have been using HSS tools, but maybe without the correct geometry/sharpness. I have the end cutting edge angle 30˚, side cutting edge angle 0˚, end relief angle 10˚, side relief angle 10˚, side rake angle 15˚, back rake angle 5˚, and a nose radius of maybe 1/16". I grind them from blanks and sharpen them on a 120 grit grinding wheel then go at it. Maybe I'll try increasing the side rake angle. Ill also follow as many of your other suggestions as possible to minimize flex etc.

I also guess that this means you don't sand and/or buff the stem and shank faces or tenon?

Thanks again!

[JHowell]

You may find that your problems disappear with the Jet. Bigger, heavier, can turn slower. With a Taig anything that isn't really small gets the SFM way up there. You may be fine with the tool geometry, just keep it sharp and see how it goes with the Jet. You're right about not sanding the stem face, sometimes I'll sand the shank face, depends on the finish left by turning.

Jack

[d6monk]

Thanks again Jack.

[Nick]

One thing I do when working with the stem face is buff it while its on the lathe. i do this by holding a hunk of compund against the stem face and the use a q-tip to polish it. I use both red and white. it really comes out nice.

[ckr]

About the same as Nick. Once it is faced I sand with 400 and 600 and then move to compounds with a piece of cut tee shirt. Always sand a bit heavier in the center and work out a bit lighter, it will be slightly concave although you won't be able to notice it. It is all done before drilling or turning the rod down to size.

[JHowell]

SNIP it will be slightly concave although you won't be able to notice it. SNIP

This is true if the stem stays perfectly round. If the stem winds up being oval . . .

I guess it depends on the degree of concavity; my recommendation would be to keep the mating surfaces flat.

Jack