How do you spray coating on small, light pieces?

Question

Background

When I got into woodworking I was making mostly large pieces (bookshelves, desks, etc). This isn't always easy as I get older, and I'm not always having good days with my back, not to mention the cold winter months. This past year I purchased a laser engraver and it's opened a whole new world for me when I can't pull out the big tools.

The things I create with the engraver tend to be quite small and very light compared to my traditional stuff, as I usually cut from 3mm basswood plywood. I still want to finish these pieces with a nice, high-gloss coating, using a sprayer with water-based polyurethane in the summer and a spraycan of Rustoleum 2x in the winter.

Problem

The problem is that while I could just set a large slab of wood down on some sawhorses and go at it, I need to set these small pieces on a sheet of plywood or some other base. When I spray, the force of the spray tends to lift my small pieces and blow them around, or at least shift their position. Even a small shift can move them onto a part of the plywood that has wet coating on it, causing an obvious problem as it dries.

What do others do to address the problem of movement when spraying small, light pieces?

Some ideas I've come up with that might work, but have obvious issues:

• Laser cut myself an open grid to use as a base so the air can escape under the objects and be less likely to lift them. Not sure if this will leave a grid pattern on the side facing down though.
• Use some sort of sticky substance to hold them down. Not sure what I could use that wouldn't leave residue though.

Answer 1

For a temporary firm hold the first thought is obviously a double-sided tape of some kind but A, they can be very prone to leaving a residue and B, the hold could easily be too strong for your liking. Either or both of these I think may rule it out, unless you want to research and test out some contenders to find one that's in the Goldilocks zone.

Temporary light hold screams Blu Tack to me, and the real stuff (Bostik) is now reputed to leave minimal or zero residue, unlike years ago. But, again by reputation only, White Tak (UHU) is supposed to be even better. With either product any finish that gets onto the tack can just be blending in up to a certain point. If your need is ongoing do expect diminishing returns over a long period, but you should get a very long lifespan from each blob. ¹

Since you have a laser you can come at this from another direction entirely, you could cut yourself the perforated top² for a homemade vacuum table.

In addition to holding the pieces in place you'll get some level of overspray extraction which might prove very beneficial and reduce or eliminate the need for a respirator.

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¹ Based on experience blending in paint overspray into a clone of Blu Tack which I've used both to hold small parts and as a crude masking material.

² Although many similar tables, used for sanding, seem to use pegboard successfully, as in one of the two pictured.

Answer 2

Double sided tape is quite commonly used to hold parts together for milling operations. For example, tape two pieces of wood together then run them through the bands saw and sand to final profile to ensure that they're identical; or hold a template to a piece of wood to run the router around it. Once the work is done, a stiff putty knife will lift the edge so the pieces can be separated.

I'm pretty sure that a little piece of double sided tape would be more than enough to hold your little pieces down to a larger sheet of plywood for spraying. Once they're dry, the putty knife will lift them right off.

You shouldn't need to push down too hard to get them to stick, so that will make removing the tape from the work piece easier. If a little residue does remain, some lighter fluid (or a commercial "goo" remover like GooGone™) will work to get the residue off. Or, you could just give it a light sanding.

If you find that you don't like the results of the tape, there are other temporary adhesives like Blu-Tack ^{just one example, no affiliation or recommendation of this particular brand or retailer} that should hold the piece down, allow for easy removal and this stuff is even reusable (for a while). I don't know what spraying finish on it would do to its reusability, so you may want to test that.

Another option would be to put down a piece of painter's tape on your work surface, put another one on the back of the work piece, then a drop of CA glue on one piece of tape & accelerator on the other piece of tape. The CA will hold tape to tape, while the painter's tape should come off quite cleanly from both surfaces. This one is a kind of "make your own" double sided tape.