Hi,
I’m working on a small wooden box project. See attached pics.
The box is built. Everything fits together nicely. Very snug fit where the lid meets the inner rails. That’s how I want it to fit. But…
I know I need to allow for the finish. Having never made something that fits like this, I don’t know how much I should allow for the finish, yet it’ll still fit snug once complete.
The inner rails hold the lid square and in place so it’s important that they fit just snug.
At the same time, I don’t want it rubbing off the finish or marring it badly taking it on and off.
Right now my thought is to go with 3 coats plus sealer of oil poly for the interior section including the exposed edging.
Though that may change as I’m also considering going with lacquer for both exterior and interior or visa versa.
Everyone talks about how to finish but I’m finding nothing on how much space should be allowed for two mating finished surfaces using lacquer or poly.
Obviously, now is the time to sand that allowance into the rail. I’m also thinking of adding a slight chamfer to the rails to ease it when putting the lid on.
So how much space is needed? I can’t remove anything from the plywood sides so it all has to come off the rails.
Replies
No one on this? On Fine Woodworking...?
Wow!
Okay well.. thanks anyway.
Cheers...
Finishes are often spec'd in "mils" (0.001") of dry film thickness. The product data sheets I have seen this generally is in the 0.003" to 0.005" range.
But I would strongly recommend against oil-based poly on the inside. it will retain a smell for a long, long time. I'd go with shellac that has a smell that is both not objectionable and will dissipate quickly. Then I'd buff the bearing surface with furniture wax for a lubricant.
@ user-4622261
I'm aware of the mil specs given on finishes but that really doesn't help figure out how much leaway or space I need to give between like finished fitted boards. At least not to me. Figuring a 0.009" to 0.015" doubled at 0.018" to 0.030" for the coats IF one could be that accurate on applying the finish per coat in the first place not really the answer I believe will truly apply.
I thought there might be some rule of thumb by now as far as allowances for finish on wood between two fitted finished pieces.
Shellac is a fine finish. A finish I hadn't considered for this box. For a few reasons.
One being the use of the box. It's to house a tool. Storage for the tool and stand. Which the tool itself will have oil on it. And lingering cutting oil from use.
It's probably be stored in a garage or work area, tool chest... on a shelf in those areas. Which will be prone to heat, humidity and other elements. It's going to have to stand up to some abuse I would imagine.
Poly is very durable. And chemical resistant to a degree. More so from what I understand than shellac.
Even if I wanted to use it, all the places one use to be able to get quality shellac flake are long gone locally.
I have oil based poly on both amber and clear on hand.
I've never heard of this lingering smell you mentioned or any smell coming from oil based finishes let alone oil based polys. Except in application.. all finishes have a smell that may or may not be objectionable when applied or mixed. Once cured, they're all pretty much oder free.
If that were the case with oil based poly or varnish people would have stopped using it long ago.
I refinished just about the entire interior of a 41' ketch with this same oil based poly, floor, walls and ceiling fore to aft. If there was going to be a lingering smell for a long, long time, that would have been proof positive either way.
I'd say within 24 - 36 hrs one is left with only a fresh clean smell. Or zero smell. Nothing from the finish. Full cure is within a week, maybe sooner depending on temps etc. It stops all the major gassing off rather quickly. Within a few days all gassing off ceases.
I think that's a myth someone started about oil based products years back...
Hard wood floors in houses, yacht and boat interiors all done with oil based finishes. I don't hear any complaints about the smell of the finish on their floors in their houses or on their yachts or boats...
Shellac is a fine finish though. One many have forgotten about. Has a ton of uses depending on how it's mixed.
It doesn't last long once mixed though... As long as you mix only what's needed at the time, it's a finish to consider keeping on hand for the right project.
Thanks for responding btw.
I thought this was deserted of all the fine woodworkers.
Cheers...
Short answer? You're overthinking this. Just hit it with a coat of finish.
Long answer? Unless you're putting on a whole ungodly whack of finish just fire a quick coat of shellac or whatever choice of finish you're going with. I'd go with something with a quick cure time given the nature of how the box fits together which is why i'd suggest shellac. You could always also hit it with a thin waxing afterwards to minimize the friction. Your finish is going to be so thin - like mentioned above - that those kinds of tolerances are more for engineers at NASA not woodworkers.
Im also in the you are over thinking it camp. The wood is going to shrink and swell over the seasons and years, no matter how perfect your starting tolerances are. That will have much more of an impact than the finish thickness.
Lots of finishes can emit an odor for several years if inside a confined space, like a drawer or small box. It's common.
If tolerance are really tight, some finishes are more apt to "stick" than others in hot or humid weather.
If I was building a box for a tool, I might not finish it at all. I certainly would not finish the inside.
Ever drill a quarter inch hole for a quarter inch bolt then paint or finish the inside edge or through way? If you have, you know the quarter inch bolt won't fit after finishing.
You have to allow for the finish. Including in wood working.
Anyway, thanks for the responses. I appreciate the thought.
I'll get with a seasoned shipwright, or finisher locally.
Cheers...
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