Robert Marshall
03-01-2020, 6:42 PM
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 (http://www.moulthropstudios.com/), and also John Williams of Tampa (http://www.urbanwoodcreations.com/the-work.html), 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."
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.
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.
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.
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.
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!
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."
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.
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.
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.
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.
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!