Expanding 28mm holes to 30mm holes on plexi

i am changing 28mm buttons for sanwa obsn-30, i have a plexi on top with holes of 28mm in diameter as the title says and i need to make them 30mm, because i don’t have enough money to buy another plexi and i would be a waste not to use the one i already have. is it posible to do that with a dremel? a friend suggested using a file, but i think it will take forever with a finishing tool like that. what do you think i should do? do you have any other ideas? i am all ears.

Some people have talked about expanding 28mm holes to 30mm by sticking a tube of sandpaper in there and rotating it, I don’t know what this would do to the plexi though.

you could sand it like that, although you might end up with slightly irregular edges.

if you have a quality drill bit, my preferred method is to drill a 30mm guide in some scrap wood, clamp it together with the plexi (sandwich it with scrap on the bottom, guide on the top) and re-drill it like that.

Here is the post I read about the sandpaper idea. His holes seemed to come out just fine.


most if not all of the unevenness of the sanding will be covered by the lip on the button anyway. If you get it snapped/screwed in there tight you it’ll be impossible to tell the difference without actually taking the button out.

I agree with ShinjiGohan, you won’t be able to see any imperfections.

As far as HOW to expand it, I don’t recommend the Dremel. I used to work with it a lot making custom cases for things, like computers or 360’s, and as it grinds, the plexi can literally start melting and instead of just grinding it off, it makes it get all clumpy.

2mm is not that much to grind, I personally would go buy 2 different grades of sand paper. One grade around 100, and 1 around 300+. Start with the 100 and get it out enough, and smooth it with the 300. This way you don’t run any risks of slipping with the Dremel and ruining your plexi. Just cover the rest of plexi with something… tape, maybe. so that you don’t scratch it with the sand paper either.

yes, i was thinking the buttons may cover the sanding imperfections. i will try the tube idea and post the result later.

i finally chose to use a round file, i finished the 8 holes in les than a couple hours (they may lokk a bit uneven but the buttons cover the imperfections so it’s ok):