Epoxy coating using a slow rotation rig

[Robert Marshall]

I'm working on developing the equipment and techniques to apply epoxy coatings to bowls and hollow forms. I would like to get some ideas and suggestions from those of you who have tried this. I am inspired in pursuing this by the work done by the Moulthrop family of turners from the Atlanta area, and also John Williams of Tampa, both of whom produce amazingly perfect-looking hollow-forms and bowls, coated with what looks like perfect epoxy. I don't pretend to be in their class, but I'm trying to work my way in that direction.

First, a brief account of what I've done so far.

I have built a rotary rig consisting of a rotisserie motor, a removable PVC spindle, a box to contain the motor and spindle, and a flat PVC plug fitting that screws onto the spindle and acts like a chuck, as the point of attachment between the spindle and the item being coated. The motor spins at about 3 rpm.

I have used this to apply epoxy to 2 items: an 8-inch shallow spalted maple bowl, and a 12-inch diameter, 14-inch high hickory hollow-form. Both are what I would call somewhat successful, in that they are smoothly-coated, after 2 applications of epoxy to each. Both have a few air bubbles, but generally okay.

So here are the areas in which I'm looking for "guidance" in the form of "here's what I do and what works for me."

1. Spin rate -- 3 rpm seems okay to me. There have been times when it appears a bit slow, and drips start to form, but I have always been able to catch those before they become a problem. This obviously ties into another question, epoxy viscosity. The less viscous, the higher the RPM needed to keep it from dripping, or so it seems to me.
2. Viscosity -- I want it to go on smoothly and spread-out so as to be cover without high or low spots. Viscosity is can be lowered by either or both (a) thinning the epoxy with a solvent (alcohol or acetone), or (b) warming the epoxy mix to a higher temperature. Warming has some risks, in terms of decreasing the "pot life" of the epoxy mix.
3. Application method -- I've worked with sponge brushes, and I'm planning to try out chip brushes. Both of these are cheap applicators, which is desirable for epoxy, since cleanup is pretty much a wasted effort. Use-once is about the only approach for applicators that I can see.
4. Number of coats, and procedure between coats -- I'm convinced one coat is not enough, and it seems you either re-coat while the underlying coat is still 'tacky,' or you wait until full cure of the underlying coat, then sand, and re-apply after cleaning off any sanding dust.
5. Manner of attachment between the spindle and the work -- I've used hot-glue, mostly, to join a PVC fitting (flat-faced PVC plug screwed to the PVC spindle) to the work. Hasn't been perfect, but the only 'drop' I've experienced could probably have been avoided with more dots of hot-glue. And that drop happened after the epoxy had cured, so no harm done.

I would appreciate any insights or suggestions those of you who have tried this approach might offer. Thanks!

[Perry Hilbert Jr]

Interested in this. A couple years ago, I saw wooden bowls at a department store that appears to have a melamine type liner fused to the inside. I couldn't figure out how they may have accomplished the fusing of the liner to the wood. Unless it was some sort of paint/spray on material. The liner was thin, although it seemed to be thicker than a painted surface, perhaps a 1/16th of an inch.

[Tom Wilson66]

Haven't tried this with bowls, but have put an epoxy coating on pen turnings to cover thread wrappings. My fixture uses a microwave turntable motor, which runs about 6 rpm. This is fast enough to prevent the dripping of the coating unless I thin it too much. Did that once, never again. To apply the epoxy I used small disposable brushes, cost about $0.03 apiece. They would not be big enough to coat a bowl before the epoxy started setting, though.

Using this setup I put on a fairly thick coat of epoxy, so I did not need a second coat. The only real problems I had were if I didn't thin the epoxy a little bit, I could not get it on quickly enough to finish before the epoxy started to thicken up. Once it gets even the slightest bit tacky you are out of luck as far as getting a smooth finish.

If you want more information for using epoxy this way, go to one of the fishing rod building sites. They do this all the time for wrapping guides and finishing their fishing rods, and have some very definite thoughts on how to proceed. That is where I got a lot of my ideas.

Tom

[richard shelby]

I've done this a few times when the piece needs to be "waterproof" My lathe (Nova 1624 with DVR motor) has a minimum 100 rpm. This works OK, just be sure to cover the bed with newspaper to collect drips. I apply the epoxy with a gloved hand using my fingers. Smooth it out and watch for drips until it starts to "kick". With a DVR retrofit the rpm range is considerably extended. You still have the step pulleys which can increase or decrease the rpm range beyond the digital readout of the controller. It might be possibel to go down to 10 rpm, but 100 works just fine.

[Dave Mount]

Epoxy comes in different viscosity resins and different hardener speeds. There shouldn't be any problem finding a combination that works well. Ambient temp is a co-factor, of course. Check out www.raka.com, or better yet, call them and tell them what you're trying to do and they can recommend a combination of resin and hardener. I keep resin in two viscosities and three hardener speeds on hand all the time so I can deal with the vagaries of projects and seasons (I only heat the shop to low 50's in the winter).

For bowls, the centrifugal force at the rim increases with increasing diameter, and I think you want the rotation to be slow enough that the primary force is gravity pulling down, not centrifugal force pushing toward the rim. I would think 3 rpm would be good. I used to use a 2 rpm motor to rotate fishing rods while the epoxy on the guide wrappings cured. 2 rpm was because that's what I had, not because it was specifically recommended, but it worked.

No affiliation with Raka, just a satisfied customer.

Dave

[Richard Coers]

Have you seen a Moulthrop piece in person? I've seen them at SOFA in Chicago. They are not as perfect as I had imagined by the photos. In pieces that are black resin, you can see fine sanding lines and even evidence of a couple bubbles. They certainly don't look like glass. Natural wood helps mask those issues.

[Pete Staehling]

Have you seen a Moulthrop piece in person? I've seen them at SOFA in Chicago. They are not as perfect as I had imagined by the photos. In pieces that are black resin, you can see fine sanding lines and even evidence of a couple bubbles. They certainly don't look like glass. Natural wood helps mask those issues.

I talked to a friend of a friend whose wife does epoxy coated drinking travel mugs that look perfect. I have not actually seen the rig or the process, but the finished product looks perfect. He said he used microwave turntable motors that turned 1 rpm when he set up her rotary rigs.

She applies the epoxy over her art work. Sorry, but I don't have any details about what epoxy or the process she uses, but I do know that the rpm was only one for large travel mugs (tumblers?) in her case and the results I saw were absolutely perfect.

Edit:
While I am pretty sure I remember correctly that he said 1 rpm, I checked and all the motors i see for microwave turntables are either 2.5-3 or 5-6 rpm. So maybe either my memory is faulty, he was wrong, or he had some weird motors. In any case the tumbler folks often use microwave turntable motors which are available fairly cheaply.

[Olaf Vogel]

I'm working on developing the equipment and techniques to apply epoxy coatings to bowls and hollow forms. I would like to get some ideas and suggestions from those of you who have tried this. I am inspired in pursuing this by the work done by the Moulthrop family of turners from the Atlanta area, and also John Williams of Tampa, both of whom produce amazingly perfect-looking hollow-forms and bowls, coated with what looks like perfect epoxy. I don't pretend to be in their class, but I'm trying to work my way in that direction.

I assume you have seen this video
https://www.facebook.com/CraftinAmer...type=2&theater

its the only Moultrop video (i know) that shows the finishing process.

Matt applies the epoxy that seems pretty thick. Now I'm sure you can acheive that thickness with various mixtures.
Or...you can mix it and let is sit for a while. Time it and you can get right, as it cures, for the desired viscosity,
(I've had to fill large gaps before, on round bowls, and needed it super thick. So I just let it set up for a while before applying)

The best applicator I've found is silicone bushes from a kitchen store. Or silcone scrapers. The epoxy peals right off silicone.

I'me pretty sure that Matt applies a very tick coat, then sands down and polishes.

#4 - I do one coat, thinned down, so it soaks in deep. Especially on end-grain bowls. Then one thick coat. Sand, polish, buff.

I have thought about a jig that spins while drying. But that also requires a dust free workspace - which I dont have.
Varaible speed via VFD would be nice. Getting down to 1-5 rpm would mean a major gear reduction.
And most of my recent work was large diameter platters, where figuring out the rpm was difficult.
So I gave up on this idea.

However, if you consistently do similar sizes / shapes, like Moultrops, then this totally makes sense.

[Dave Fritz]

This from another site, might be helpful: https://www.youtube.com/watch?v=GI1o...ature=emb_logo