enlarge hole made in plywood?

[Florin Andrei]

I made an eyepiece rack for a telescope (see picture), it's where I keep the eyepieces when they are not used. The standard barrel sizes for most eyepieces are 2" and 1.25". I used a 2" hole saw and a 1.25" Forstner bit, and the holes are the perfect size, the eyepieces fit just right. The rack is made from 3/4" plywood. So far so good.

233637

But there's an issue. I want to coat the whole thing with epoxy, to protect it against humidity. Then I want to paint it. After epoxy, primer, and paint, I assume the diameter of the holes will shrink quite a bit and the eyepieces probably won't fit anymore.

I looked for slightly bigger hole saws or bits, but they are too big, the gap would be too large.

Is there an easy way to enlarge those holes a little bit, maybe a couple mm added to the diameter, while keeping them round and smooth?

Thanks!

[Jamie Buxton]

One way is with a pattern bit in a router. A pattern bit has a ball bearing above the cutting edges. You can construct a pattern bit from a straight bit plus a bearing of your own choice. Choose a bearing a little smaller than the bit diameter, and you eat a little bit from the inside face of the hole. Then change to a bearing the same size as the bit diameter, flip the panel over, and remove the part the smaller bearing was just bearing on. Or you can use a flush-trim bit.

You can get a variety of straight bits and bearing diameters from most full-service bit retailers, like Eagle America. http://www.eagleamerica.com/

[Chris Padilla]

Unless the fit is really snug, I don't think your finishing would add enough to matter.

[Prashun Patel]

First, I don't think you'll gain that much doing epoxy AND paint in terms of moisture protection if this is not subject to a lot of moisture. If it were me and I wanted it painted, I'd just use a quality enamel paint. I would also not paint the insides of the holes, since they will receive a lot of rubbing and the paint will ultimately chip from here. I would instead seal the rim with shellac. This will provide some moisture protection, and will minimally alter the diameter of the hole.

[Kevin Bourque]

Cut it bigger , or sand it bigger with a drum sander on a drill, and use grommets in the holes. The grommets will cover any irregularities and will protect the lenses.

[Rich Engelhardt]

Spiral wrap some sandpaper on a dowl rod and spin the rod around by hand in the holes.

There's no need to use a power anything here since the amount of material you need to remove is so small.


Is there an easy way to enlarge those holes a little bit, maybe a couple mm added to the diameter, while keeping them round and smooth?
The thickness of the materials you plan to use is going to be a lot closer to the thickness of. maybe 4 or 5 pieces of paper - roughly 20 mills.

A few turns of a dowel rod with some 150 grit sandpaper should be more than enough.

That's assuming you use an epoxy.

A gloss enamel such as Rustoleum - which will offer plenty of protection and resist scuffing pretty well, is going to be about half that thickness - roughly 10 mills or about as thick as a doubled up piece of copy paper.

If you just want to seal and protect the wood, a couple of coats of shellac will work fine.
You can buy a spray can of Zinsser Seal Coat and spray it on.
The shellac will go on roughly 2 mills thick - or - about half the thickness of a piece of copy paper.

I'm using the copy paper as a reference you can use to spot check the amount of sanding you'll have to do.
Since it's so minimal, it's going to be easy to overshoot the mark.

[Jeff Duncan]

I'm with the hand sanding technique if you need to enlarge just a bit. I also question the need for a thick coating? If this is carrying eyepieces I would think it won't be exposed to the elements? As such a thin coat of finish should be good.

good luck,
JeffD

[Joe Angrisani]

First, I don't think you'll gain that much doing epoxy AND paint in terms of moisture protection if this is not subject to a lot of moisture. If it were me....

I can tell you don't have much telescope time under your belt. A telescope and it's mount can often drip water in the course of a night's observing.

[Ryan Hellmer]

In the boat building world, holes in wood are often sleeved with something waterproof prior to final boring. Maybe find some PVC that is the correct diameter, enlarge the holes with a router bit, epoxy the PVC sleeves in and then rebore to final dimension that way the entire exposed area is plastic, not wood. Just a thought. For reboring the holes you could either make plugs to give you a center or clamp and bore on a drill press with forstner bits.