Masking Tapped Holes for Painting

[Steve CrowParticipant @stevecrow46066]

 

Hello, I have a slab of aluminium 12″ x 6″ x 3/4″ as the base plate for my watchmakers lathe with over a dozen tapped blind holes in it from M2 to M6.

I intend to paint it with Paragon enamel paint, much like the sensitive drill below.

When I painted this last year, I used sacrificial screws to mask the holes, removing between each coat. I found the screws disturbed the flow of brush and paint and made getting a good finish more difficult.

Would I be better not masking at all and tapping out the paint at the end?

How about filling the holes with melted beeswax and tapping that out later?

I would be grateful for any suggestions or advice.

Cheers, Steve

[Bill PhinnParticipant @billphinn90025]

I’m not sure what type of screw you were using that disturbed paint flow, but socket or slotted set screws that sit just below the surface would be my choice.

[BazyleParticipant @bazyle]

Plasticine, Bluetack ? Not sure if either of those introduce contaminants to the surface though.

[JasonBModerator @jasonb]

I was going to say the same as bill, grub screw just below the surface will allow you to brush over the top which you can’t if the screw is sticking out the hole

[MikeKParticipant @mikek40713]

Foam earplugs work.  Similar could be cut from packaging foam.

Mike

 

[MikeK]

On MikeK Said:

Foam earplugs work.

Most adult human beings will have lugholes that are considerably larger than M6, the size quoted in the original post.

[JasonBModerator @jasonb]

They roll down quite small and should fit into that size hole OK

[DC31k]

On DC31k Said:

On MikeK Said:

Foam earplugs work.

Most adult human beings will have lugholes that are considerably larger than M6, the size quoted in the original post.

I just tried it…An M6 bolt is about the size of this ape’s earholes.  And everybody knows how to use scissors on foam.

Mike

 

[Dave SParticipant @daves59043]

I would not mask and just run a tap down the holes afterwards if required.

If it’s a tapped hole it’s likely that something is bolted over it, and so slight imperfections at the edge where the thread is will be covered anyway.

But then again I don’t do “perfect”, I usually just do functional.

[Alan DonovanParticipant @alandonovan54394]

I would not recommend re-tapping the holes on aluminium as there is a possibility/tendency to remove extra metal from the thread, due to the paint ‘blinding’ the thread start, thus thinning the thread form and making the thread weaker.

I accept that in this instance it most probably doesn’t matter, but those are my thoughts.

Alan

[HopperParticipant @hopper]

I just screw up a ball of paper towel and jam it in the hole. Works for me.

[Pete RimmerParticipant @peterimmer30576]

<p style=”text-align: left;”>Same here blue paper towel rolled up, poke the thin end in and give it a bit of a turn then snip it off.</p>

[Steve CrowParticipant @stevecrow46066]

Thank you for all the replies, I thought I’d clarify a couple of things.

I’ve just checked the tapped holes. There is one M6, 8 x M3 and 14 x M1.6.

I’m going to be (brush) applying a lot of paint. An etch primer, a couple of coats of primer, about 4 of enamel and a couple of coats of lacquer.

I’ve tried the grub screw below the surface but at this diminutive size, the hex socket completely fills with paint making it quite difficult to remove. Might be better with slotted screws but I still don’t fancy it with M1.6.

As for paper or foam, again I think the small sizes involved will make things a bit fiddly.

I am still considering beeswax. Once the painting is complete it would be a matter of breaking throught the skin and tapping out the wax. Beeswax works as a tapping lubricant anyway so this might avoid damaging small threads in soft aluminium.

Another alternative might be to fill the holes with vaseline though this might play havoc with the cleaning process pre-etching.

Can anyone see any pitfalls with this method?

Steve

[Trevor Drabble 1Participant @trevordrabble1]

<p style=”text-align: left;”>My humble offering would be to screw wooden dowelling into each threaded hole ,  and with a knife file , cut a shallow annular ring around the dowel at a point slightly below the surface of the plate in order to allow a small amount of paint to be stored . The advantage of using wood is that it is relatively soft and so will allow the a thread to be formed without damaging the original hole . My original preference would be to use balsa , but that now seems difficult to find in smaller sizes . Lime however is a suitable substitute , and Cornwall Model Boats ( no connection ) have it in stock from 2mm upwards .</p>

[John PurdyParticipant @johnpurdy78347]

How about round tooth pics for the smaller holes? The ones I have, and have used for that purpose, are 2mm in dia. The tapered end just screws into the hole.

John

[Steve CrowParticipant @stevecrow46066]

I think the problem is, not how I mask the holes but how I remove it later.

I’m looking at something that sits flush or just below the surface so I can get a good flow of paint.

[bernard towersParticipant @bernardtowers37738]

Your flow of paint will always be interrupted because of the hole, surely if enough paint is applied it should settle nicely around the holes.

[Author]

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