Keeping tumbler media out of blind threaded holes?

For years I have used short steel set screws with the top thread either staked over or a tiny TIG tack to stop the set screw at the chamfer in my parts. This keeps any small pieces of media out of the holes.

If I don't plug them it's a PITA ordeal to fish out and break up anything that gets in there and clean it out.

The problem is sometimes the parts get forgotten about overnight and we get rust stains in the holes.

Most all the blind holes I have are M6, M8 and M10. The M6 seems fine. We get any media that small out of the tumbler so primarily it's the M8's and M10's I need a better solution for.

I was looking to buy plastic set screws, but I can't find M10's online anywhere. I figured before I called around tomorrow I'd ask here if anybody uses something else to plug the holes or if you know where to get M10 plastic set screws by the hundreds.

Whatever I plug the holes with needs to be about flush so the finish is even right up to the chamfer. If I just shove a bolt in the hole there is a ring around each hole. That doesn't work.

I know I can make my own, but I don't want to. I have enough shit to do and these are kind of a consumable as they get lost and eaten away over time. Staking/tacking steel set screws is tedious enough.

buy some 2part urethane or silicone rubber and make cylinder plugs that are just barely larger than the minor diameter of the thread, so it is easy to push in and pull out with tweezers? making a mould to make them would be easy enough with couple pieces of aluminum bar tightened in a vice and drilled a bunch of holes in the parting line

thinking about it while writing the previous sentence gave me an idea of making not a larger round plug, but a smaller one and with "wings" milled in the mould, wing width slightly larger than the minor diameter of the hole, here's a picture of the idea, such plugs would be easier to pull out with tweezers, if all the blind holes are same depth, make them long enough so they bottom out



I know screwing in screws to mask holes is quite tedious, something that can be pushed in without tools and removed with little effort might be worth the hassle of making moulds for IMO, rather than screwing in screws, I'm currently half way through 600 parts that need 8pcs M4 screws in them 15mm deep to fill as much of the cavity as possible to minimize bleed out so it doesn't ruin anodizing of the parts, it's just a PIA to do that...

edit: I buy 2 part silicone rubber from medical supplies store, it is used to make dental impressions (I think), comes in different shore hardness, sets in 5-10 minutes, so don't take too much time when mixing it up, quite durable and doesn't stick to anything, so moulds don't need any release coatings, price wise it was about 50 EUR for 2x1l bottles, its 50:50 mix ratio, with 2 liters you could make quite a lot of those plugs

Definitely good ideas, I appreciate the thoughts, but I'd really like to just buy something that does it.

Seems like silicone masking plugs are made in a million varieties, but they're all "pull" style for through holes.

Garwood said:

Definitely good ideas, I appreciate the thoughts, but I'd really like to just buy something that does it.

Seems like silicone masking plugs are made in a million varieties, but they're all "pull" style for through holes.

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Shirley these people have what you need.
Home | Caplugs

FWIW capplugs bought out "Niagra Plastics" that make most of these, they are local.

digger doug said:

Shirley these people have what you need.
Home | Caplugs

FWIW capplugs bought out "Niagra Plastics" that make most of these, they are local.

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Nothing in their catalog looks like it would work. They have some stuff that looks like it has potential, but is too big for the M8 holes. I will call them tomorrow. I'm sure they have an application engineer to help.

I was just thinking about ordering up some short 3/8-16 plastic set screws to see if they'll force in an M10 hole. Sounds terrible, but all it has to do is keep chunks out and stay in the hole.

Why can't you use media that is too big to get in the holes? That is what I have always done.

Buy a roll of round rubber from McMaster or some o'ring cord. Cut to length with enough sticking up to pull out.
I have used cap plugs but they are a pain to pull out if you have a lot to do. You may also be able to buy or make your own threaded nylon rod. You could hot press a hex key into the all thread nylon and make your own set screws. That could be quick with a simple guide.

Something like this?

https://www.amazon.com/Phillips-Screws-Socket-Non-Head-Plastic/dp/B07Z3CTPY4?th=1

https://www.amazon.com/uxcell-M8x10mm-Slotted-Threaded-100Pcs/dp/B01BHQ7HS8

Kinda pricey, might call Portland Fastener and see if they can find them cheaper.

DavidScott said:

Why can't you use media that is too big to get in the holes? That is what I have always done.

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Sounds easy enough. I have two 3 ft long tub tumblers and when we're busy they run non-stop. Hard to take the time, dump the media and screen it.

I guess my answer is laziness? Or I have better things to do than sort ceramic media lol? Tub looks low, I add a few scoops of new.

I havent checked if they have it, but when i have a difficult to find metric component, more often than not Misumi has it.

Misumi is nearly the metric version of Mcmaster

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Garwood said:

Sounds easy enough. I have two 3 ft long tub tumblers and when we're busy they run non-stop. Hard to take the time, dump the media and screen it.

I guess my answer is laziness? Or I have better things to do than sort ceramic media lol? Tub looks low, I add a few scoops of new.

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Plugging holes takes time too. And certainly digging media out takes a lot of time.

I use cap screws on blind holes, but the parts get powder coated so I can get away with a little ring. I have a couple jobs where I tumble the parts before I machine them because they just get holes, or maybe a few holes and one other feature. It's easier on those parts to tumble the material first, and just don't scratch them up at the machine.

I also do small parts with through holes; for those I bought a couple spools of bare copper wire from Platt. I string the parts together on a piece of the wire 25 or 50 at a time, and just toss the bundle into the tumbler. The wire keeps most of the rocks out of the holes, and makes it easy to retrieve the parts. The copper wire won't rust if I leave them in the machine overnite.

Stainless steel grub screws aren't very expensive, they're also an option.

DavidScott said:

Plugging holes takes time too. And certainly digging media out takes a lot of time.

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I can plug holes while the tumblers run. I can't dump and screen while they run.

I guess I'd say I tried it that way and I always got small media stuck in the holes so I went to plugging and it just works.

I'm open to whatever, but screening the media is a PITA.

I use roll up ear plugs.

How about really long m10 nylon screws? You can bottom them in the hole and spin them out with your fingers. The head wont' leave a clean spot because it is not in contact with the surface

gustafson said:

How about really long m10 nylon screws? You can bottom them in the hole and spin them out with your fingers. The head wont' leave a clean spot because it is not in contact with the surface

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True, but wouldn't the media avoid "tumbling" against the part in the same way when it bumps into the screw? That will make a more gradual difference in finish around the hole, which the OP has already stated he wants to avoid.

I'd +1 a little piece of rubber, maybe something that looks a bit like a rowboat mushroom anchor. stuff it in the hole and then pull it back out with needle nose when you're done. Could tool them up and if they work well we could sell them to everyone else

BoxcarPete said:

True, but wouldn't the media avoid "tumbling" against the part in the same way when it bumps into the screw? That will make a more gradual difference in finish around the hole, which the OP has already stated he wants to avoid.

I'd +1 a little piece of rubber, maybe something that looks a bit like a rowboat mushroom anchor. stuff it in the hole and then pull it back out with needle nose when you're done. Could tool them up and if they work well we could sell them to everyone else

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I think it depends what media he uses. Tetrahedron for instance finishes right up to corners pretty well.

Cheap and easy to try tho

OOH OOH automotive panel fasteners

Buy long ones, clip the heads off if they get in the way

wicked cheap

wicked fast

McMaster-Carr

My suggestion is extremely lo-tek but might work perfectly.

Melt some candle-wax aka parafin and wire-basket the screws through it.
They will never rust and are easily removed later.
And very low cost.
No toxicity.

Secondary --
Unless You are using proper Hitachi industrial lion drivers to remove the screws, You are likely doing it very very wrong.
Imo, ime, You get 3-10x the effective productivity with the right tools.
And the industrial Hitachi stuff is absolutely outstanding.

I have 11 of the Hitachi stuff.
Plus a Festool 105 belt sander - best - cost 1200€.

McMaster has off the shelf Nylon screws: McMaster-Carr