View Full Version : vibratory polishing and protecting 28 tpi threads

12-23-2010, 10:36 PM
So I may be making batches of parts that I want to polish which have 1x28 tpi and 7/8x28 tpi threads. I'm assuming they need to be masked somehow. Any suggestions?

12-23-2010, 10:52 PM

I would polish before threading if possible. But if you must thread and then polish, I would use a softer media like walnut. But most anything you do will round the thread profile.


12-23-2010, 10:55 PM
Just use a non toping insert, then insted of polishing making the thread profile less accurate, Its making it more accurate.. :)

12-24-2010, 12:55 AM
just throwing it out there... never tried it, but maybe dip the threaded sections in wax? Then you could easily remove the wax from any areas still to be polished, but keep the threaded sections safe.

Mike Burdick
12-24-2010, 01:06 AM
I've used Plastidip for protection when sandblasting. It might work for what you are doing.


12-24-2010, 01:23 AM
I would imagine that wax would get worn away long before any polishing happened.

How about making female threaded pieces that you screw the bolts into?

12-24-2010, 02:08 AM
Wrap the threads in electrical tape. Unless the media is really aggressive, it will work. Big question is what media? Walnut is no problem. I run a taped up container in walnut and corn for hours when moly coating bullets.

Liger Zero
12-24-2010, 06:13 AM
There are rubber/rubbery-plastic plugs that you can buy.


When I had to acid-dip/tumble parts at Ssspinco (not a typo!) we used these folks for caps. Look under "vinyl products."

12-24-2010, 04:20 PM
Ooooh I think the caplugs are just what I'm looking for. Thanks!

02-14-2011, 04:21 PM
So I've found that I need to hit the threads with a little scotch brite to smooth out the crests. Could I accomplish the same thing by leaving the threads exposed when polishing with walnut an rouge or would this take down the threads too much? I've never used vibratory polishing but I'm looking for some way to cut down on manual labor.

02-14-2011, 04:46 PM
12" rod with a threaded end to screw the bolt or screw into to protect the threads and hold the bolt for polishing.

02-14-2011, 05:12 PM
I using walnut shell I don't believe you will need to protect the threads. If unsure throw a few in the tumbler and let it rock and roll for a few hours. Might save yourself a lot of extra work..

02-14-2011, 06:05 PM
What do you mean by "polish"?

How rough are the parts to begin with?

I do alot of tumbling of brass castings with good detail, and also brass machined parts. All for eventual plating, which hides absolutely nothing.

You will find that you probably will be using somewhere between 2 and 4 types of media, depending on how rough it is to start and how fine a finish you need. I use a medium plastic media, followed by a fine, and then finally a polish called Shell Sheen, which is kinda like walnut shell. I should burnish after that, but many times don't have the time to do so.

With my parts, I don't worry about the threads at all. I've never had a problem, but I don't start with a real abrasive media.

Plasti-dip would certainly work, but could be a pain getting off, same with wax. Tape might work if you could get it to stick through out the cycle.

If your starting with walnut shell, I wouldn't worry about the threads unless you are tumbling them for a week (literally), which is an indication that you aren't using aggressive enough media.

If you have steel parts with a machine finish, I doubt that walnut shell (by itself) will do much for you. Walnut is really a polish, it's not really a remove material media.

02-14-2011, 08:19 PM
I'm finishing 6061 with a "good" machined finish. I'm looking into those plastic caps to protect the threads from the coarse tumbling. Guessing I'll need three stages of media. I level of "polish" I need on the threads would be equivalent to holding a patch of red scotchbrite on them for a few seconds while on the lathe.

For the coarse I'm looking for the equivalent of a medium sand blast, and for the fine...a high polish. I don't have actual surface finish specs. I'm doing some flashlights and want the bodies to come out matte and the heads to come out polished. Can I do this in 3 stages? I'm thinking the bodies go in the coarse tumbler and the finish on the heads is probably good enough to skip the coarse and just do the last two steps. Thoughts or recommendations on media types grades? Thanks for the suggestions so far!

Forrest Addy
02-15-2011, 12:55 AM
Piece of shrink tube?

02-15-2011, 09:34 AM
Ive never used the scotchbrite, so I'm kinda guessing at the finish.

Depending on the time frame needed, I would try a medium media first. That might well give you the finish you are looking for in the coarse finish you mention.

For the fine high polish, you'll probably need to do a fine and then a polish - walnut shell for example.

With tumbling, it's not an exact science. I think that you'll want to put both the bodies and the heads through the medium, but feel free to try starting with the fine, and if that doesn't give you the finish you desire in the time you want, go to medium.

I use media used for jewelry. It's a plastic media and it's called medium, fine and Shell Shine (which seems to be a walnut with some polishing compound mixed in by the manufacturer). I do it wet with a deburring compound which washes away the sludge. With aluminum, you don't need anything too aggressive, especially if you have a pretty good machine finish to start.

02-15-2011, 10:39 AM
Cheap vinyl tubing from the hardware store. Make sure it takes a little effort to get it on the part, or it will tumble off.

02-16-2011, 06:34 PM
Can you run multiple bowls on one tumbler? I'd like to get a "good" tumbler but if I'm going to need three of them...that's a lot of money. Can I just buy one base and have three different bowls? I know places like HF sell them cheap but I've had less than stellar results with HF in the past.

02-16-2011, 07:34 PM
You mean each media type has it's own bowl?

Why do that? Dump and clean out the bowl and put the new media in. They are easy to clean up. Damp rag will do it.

If your going to do flashlight sized parts (ie 6" long x 1.5" diameter) your gonna need a pretty good sized tumbler.

I have a 20" diameter tumbler that I made and I doubt it would be big enough for your purpose. It might be, I don't have any experience with parts that large.

02-16-2011, 09:17 PM
I'll be processing a fair number of parts so I don't want to clean out a single bowl every time if I don't have to. My largest part is 1"x4" so I was hoping to get away with a 15" (approx) bowl. I'd like to do 10 parts at a time.

Also, what determines if you use water in the bowl or not?

Thanks for all the help! New territory again :) I just polished 10 lights with a buffer and that isn't going to be a lot of fun if I have to keep doing that.

02-16-2011, 09:27 PM
If you want the bodies to be matte finish, why not do it chemically?

Wouldn't take long to etch in lye solution.

02-16-2011, 11:20 PM
The bowls can be changed on many tumblers. Just pick a bowl you like and one base or make a base. The large Harbor Freight bowls look decent. There's not much to that type of tumbler, a base, 4 springs, and a motor. If a spring breaks, replace it. If the motor burns out, replace it with one from a vent hood or some other small fan motor. The motor shaft has a small weight on it that is mounted off center to provide the vibration. Some of the reloading forums have threads about making tumblers or repairing tumblers. It could easily be done by someone capable of machining flashlight parts.

02-17-2011, 12:05 PM
I made a tumbler that the bowl is held on by 1 rod with a nut. It's about 75 lbs loaded with media. I saved about $300 over a commercial tumbler of the same size. I would have saved another $300 if I knew of a better idea for a bowl other than a replacement bowl.

Seems like you could run all the parts through the same media before switching to a finer media. Might want to run a batch through all the steps to prove your process/media selection, before running all the batches through.

02-18-2011, 01:16 AM
Idk about you but running multiples of large objects through a tumbler is bound to create nicks on most parts.