ID burnishing tools?

Another question. I make my own paintball gun barrels but finishing the ID to a nice high polish evenly is a pain (lots of lapping) anyhow i have been looking into id burnishing tools it looks like the finish they produce is pretty nice but they always say there for finishing hard materials. I would be using it in 6061. so my question is 2 part would a burnishing tool produce a good finish in aluminum and no 2 where can i buy them. my typical suppliers (mc master and enco) dont seam to carry them.

I'd go to Cogsdill as a first port of call as well,. be prepared for severe sticker shock.

i just sent them a request for pricing on an R-656 with MT-3 taper. sami what kind of price should i be expecting (ball park)? I would assume several hunderd (200-300) as a guess.

I'd say you're nearly an order of magnitude shy on your guess. My guess is over $1k but not $2k. Update us when you find out!

tjd10684 said:

i just sent them a request for pricing on an R-656 with MT-3 taper. sami what kind of price should i be expecting (ball park)? I would assume several hunderd (200-300) as a guess.

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I would multiply by four.

eKretz said:

I'd say you're nearly an order of magnitude shy on your guess. My guess is over $1k but not $2k. Update us when you find out!

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Mark McGrath said:

I would multiply by four.

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well if thats the case i guess im going to have to get a bigger jar

either way ill let you guys know

I'm not into paintball. What's the inside diameter of the barrel? I'd be making my own expandable burnisher. Probably similar to the trombone slide burnisher dent remover tool I made. Use tool steel, slightly barrel shaped, od slightly (.001" smaller) than the bore, tap the end 1/8 or 1/16 pipe, split, harden but not temper. polish and buff to highest finish you can. Make it long enough to reach or ad a shank. Peter

You might consider ballizing the barrels. Just google "ballizing" for info. This will get you started:

Burnishing Balls

theoretically they should be 68 cal, but its typical for the sizes to range from .670 on the really small bore side to .700 in a step bore barrel. this is to account for the changing conditions (since the ball is gelatin biased humidity and temp change the ball dia quite readily) and variations in paint manufactures.

Yes, you can burnish 6061. Not only will it give you a very smooth finish, but it will also be a harder surface than if it is just machined.

wagoneer1 said:

You might consider ballizing the barrels. Just google "ballizing" for info. This will get you started:

Burnishing Balls

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Balls work great and are way cheaper then a roller burnishing tool.

Im interested in what the tool will cost now days.
Last roller burnishing tool I bought was over a $1,000 and olny did a 9/16" +/- a few thou. OD. That was 15 years ago.

BKGUY said:

Yes, you can burnish 6061. Not only will it give you a very smooth finish, but it will also be a harder surface than if it is just machined.

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Good i was concerned about galling the surface since 6061 is much softer compared to what they were showing on their site.

IME When ball burnishing Aluminium, it needs lube - MoS2 grease (CV joint) works for me.

I only ball sized alu once, went from a nice accurate bored hole. Worked pretty darn easily. Unlike when i tried in the middle of a hard bit of stainless. That could have done with a slightly larger hole than i tried! Thats the key part to the problem, getting a suitable + repeatable Finnish - starting hole size. IMHO for what your doing gun drilled or reamed is the kinda approaches that would give you what you need.

Several years ago, I had a job which had a 4 inch long hole through 6061 Aluminum. The tolerance and finish was critical. The diameter was .625 but a reamed finish wasn't good enough and the holes varied by as much as +.0003to +.0005. The tolerance was +/-.0002 so several parts were scrapped. So what did I do? I bought a .624 reamer and reamed all the parts, then I tapped a .625 ball bearing into the top of the hole. Using a fixture to keep the part straight, I pressed the ball through using an arbor press fitted with a .500 diameter bar with a .625 spherical concave radius on the end. I used a light oil in the hole and added a small chamfer to each end. This worked great. I finished over 100 pieces with the same ball and all parts were identical in finish and size. This may not work as well for long holes such as yours and of course finding the exact size ball bearing may be a problem. Good luck.
Scotty.

Have you considered honing the bore of yur barrels? Are they a throu bore? No deliberate taper?

A Sunnen cylindrical hone can give you a 2 microinch finish and true cylindricity of less than 0.0002" error. I've used many bore finishing methods over the years, reaming, boring, swaging (some call it "ballizing"), honing, etc. None beats reaming for quick stock removal and to an extent bore straightening. None beats honing for generating atraight round bore provided the hining unit used is of suitable length.

Swaging (ballizing) requires a certain minimum strock, a minimum wall to support endwise swaging force, a maximum of wall allowing for expansion (the metal has to go someplace), and a smooth enough bore that the swage can displace metal to fill the discrepancies. The Cogsdrill rotary swage displaces metal laterally into bore defects but while it will extend displacable metal endwise a trifle you have to have a near net size bore to start with. If sufficient metal isn't there it cannot be displaced to fill voids with neighboring high metal. All have limitations although when properly implemented, swaging does provide near perfecly finished and sized bores.

Reaming when properly implemented can produce superb bore sizes and finishes if the proper stock allowance, reamer prep, coolant, bore prep, feed speed etc are selected. Straight round sized bores? Certainly. Mirror smooth bores? Probably not. But all the variables have to be controlled and implemented. Screw up one and the quality of the work suffers.

Honing a paint ball gun barrel bore to very close tolerances to a mirror finish is very possible but the cost of implementation may be pricey - several hundred dollars and you have to start with a fairly good bore. A multiple length Sunnen honing unit, a feed unit you can mount on a spindle (no sense spending thousands on Sunnen honing machine), stones, a bucket, oil, and aquarium pump, etc. are all (whew!!) you need. Not really a recommendation but something to think about.

http://www.sunnen.com/graphics/assets/documents/ee16b4ec3e7f.pdf

Have you though about using hydraulic chrome-wall tubing for paint ball barrels?

Actually before I chose lapping as my finishing technique honing was my first choice but i was not able to find a hone that was in the size range i needed. Of course i was not looking at manufacturers such as Sunnen just the McMaster catalog. I think im going to give ball sizing a shot their is another factor I forgot to tell you (slips my mind that some people dont know everything about paintball) the bore that im trying to finish is 9" long (and this is a short barrel they can be up to 16) and it looks like most of the reamer burnisher type solutions are limited by the depth of the bore but with ball sizing it looks like the rod can be adjusted to fit almost any length.

I have not considered chrome wall tubing but weight is a factor (some barrel manufacturers are going complete carbon fiber because of this) so I tend to exclude steel as an option, but thanks for the suggestion.

Dumb me, I hadn't considered weight. How about this 4140 aircraft tubing. I looked up the bore for paintball cuns and .689 to .693 seems to be common. Wick's Aircraft sell 4140 tube in any diameter in even 1/16ths, sidewall, and length ypou can imagine.

Wicks Aircraft Supply

For example, there's 3/4 x 0.035 wall tube @ about 4 oz per ft caught my eye. It's seamless, cold drawn to size, and very smooth. It's not much heavier per unit of length than 1/16 wall aluminum and 2 x stronger It's also easier to work with (silver braze to breech block for example). The sidewall leaves a little stock in the bore so you can stuff a swage through it. Just suggesting alternatives. .

Im still interested in what the roller burnishing tool will cost, my guess is $1,500+ they dont give them away but a good one will do thousands of parts, we put them in screw machines with 100 PSI oil blasting on it and the part would have a mirror Finnish, you could see yourself in the part, no need to use a surface gauge. We were making cam shaft fulcrums, for Crane cams.