Sunday, March 20, 2011

A Spray-Painting Lathe

I'm making a new standpipe for an ornamental lawn sprinkler. When it's done and ready, I'll need to clear-coat it, and that prospect left me a bit apprehensive.

I'm pretty good at spray-painting, but I'm not a talented 'natural' at it, and I wanted to improve the odds of ending up with a flawless outcome. That led me to construct this crude prototype of a spray-painting lathe.[1] Here's the headstock end.

And here's the tailstock end.

The standpipe is not ready for clear-coating yet, but I did have an immediate requirement to repaint three square-tubing side table legs. I made up a suitable mandrel for them and tried it out. I'm very pleased with how it went. Here are photos of a side table leg readied for painting.

I plugged in the rotisserie's motor, painted a leg and found that the equipment and the method work beautifully. That barbeque rotisserie motor/gearbox has an output speed of about 5 1/2 rpm. I got the hang of it very quickly and got flawless results. I wish all of my ideas would turn out as well as this has.

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The woodworking part of constructing this was strictly crude, simple and utilitarian -- I just wanted a framework that would do the job.

Adapting the drive unit called for a bit of machining work on my metal lathe, but nothing difficult. Pictured below are the items I needed to fabricate.

The square drive adapter was made from 8mm square rod salvaged from the tractor-feed assembly of an old dot-matrix printer. It's 4 5/16" long overall, with a pointy end turned at one end, and a 3/4" long round 'land' turned at the other end to take a short length of 5/16" I.D. rubber tubing as a flexible coupling. Needless to say, this is the sort of thing that calls for a four-jaw chuck.

At the upper right is one end of the mandrel for the sprinkler standpipe shown in the first two photos above. It's a 40" length of 10mm diameter steel rod, with one end turned down to fit the flexible coupling. At its tailstock end, it's simply borne directly in a round-bottomed notch in the tailstock upright. At the lower right is one end of the mandrel for the square table legs. It's a 29 1/2" length of 1/4" diameter steel rod. I built up its drive coupling end with brass tubing and CA adhesive. A short length each of 9/32" and 5/16" diameter tubing glued in place did the job there.

Front and centre is a bearing I made up from odds and ends to bear the tailstock end of the 1/4" rod. It just slips into place in the notch in the tailstock.

When I first tried this out with the square table legs, the rotation speed seemed a little fast, but as I said, I got the hang of it very quickly and now I'd say that it runs at about a perfect speed for the application. As a means of spray-painting long skinny objects, this lathe can't be beat. You'd have to be trying to botch a job on it.

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[1] My son and I had a slight disagreement about how loosely/broadly the word 'lathe' can be defined/applied. He maintained that a lathe is for shaping things on. I maintained that any machine that spins things horizontally for any purpose can be called a 'lathe'.

I'm not certain that I'm right, but I'm older so 'spray-painting lathe' it is.

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