Coating for mold

[Jim Hilburn]

Last year I made a spur of the moment decision to build an archtop octave mandolin. You may remember the photo's of the finished instrument.
I had to start by making the molds and templates and then hand-carving the first plate with which I could then use on the pantograph to make the remaining plates. I also made a mold for future use.
I didn't want to buy some hardwood that I didn't know how it was seasoned, and all I had was this basswood that I could use. I think it will be quite stable but it's very soft and isn't going to like having the probe on the duplicator running over it so what I need is a good hard coating that will resist wear and also be pretty slick. You know, something space-age.
Any suggestions?

[sunburst]

I made a couple of basswood templates for mandolin plates, years ago when I was using a duplicarver, thinking the same as you, and the templates promptly warped.
I was thinking of a possible coating too, but gave up the idea when I had to scrap the warped pieces, so I can't help you on the coating, and I hope your's doesn't warp, but if it does, I'd say try quartered material next time.

[Antlurz]

My solution would be to make a casting of the top then pour an acrylic master using the mold made of the original. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wink.gif

Hard, smooth, and you still have the pristine original carving.

Ron

[David Newton]

West System Epoxy, or, any thin epoxy, several coats.

[Mandoborg]

Jim, i had great luck with what Dave said..... Mixed up some West Systems, brushed the entire template with it, then put it in the oven on a cookie sheet on wax paper on Broil for about 2-3 minutes or so, keep a close eye on it so it doesn't bubble... the house will stink, but it comes out like Glass ! Mine have been in use for over 6 years and theres not a scratch on them.

Jim Combra

[Jim Hilburn]

Great.
Can't wait to tell the wife what I plan to do in the oven.
But sounds like the way to go.

[Mandoborg]

They get over it quick Jim !!....... remember it doesn't cost anything so it's better than the old ' guess what i bought today ' death glare http://www.mandolincafe.net/iB_html/non-cgi/emoticons/wow.gif)

Might try a heat gun, probably do the same thing, just didn't think of it at the time, you'll be amazed ... dipped in glass !!

I had pictures, just can't find the disc right now.....

[David Newton]

I don't think there is any real advantage to be gained by cooking. The epoxy will cure the same with it's own generated heat. You can add some silica to the mix if you are looking for a harder surface, but it also thickens the mix and makes it harder to spread evenly. Sounds like for your application, just the epoxy will work fine.

[Jim Hilburn]

So this stuff's not cheap, is it.
Do you think I should get fast or slow hardener?

[Darryl Wolfe]

I would use some Dupont Chromaclear 7500. Basic high dollar automotive show car paint system. I used it over plaster of paris and you would think it was solid acrylic. I use is on all of my electric guitar finishes. BTW, I have tried to make clear acrylic templates from a reverse mold and they alway shrank too much to be of any use.

[nelson_luthier]

The west system is like honey and won't penetrate as well as Smiths penetrating epoxy sealer (http://www.smithandcompany.org/). I have used this for years under the trade name of "Restores it". It mixes up as thin as water and has extremely good penetration. That basswood will soak up a bunch of it on the first few passes, but once the first coats cure it will start to just lay on the surface like paint. The surface stuff will be as durable as a lacquer finish, but it will really toughen up that bass wood. Perhaps you could harden the wood with this and then coat the surface with the west system. Best of both products?

Greg N

[Magnus Geijer]

I was looking at setting up for a duplicator, and I was thinking about making the mold out of oak or maple and then just slosh it with polyurethane. I take it that wouldn't hold up well, then, or would the additional hardness of the wood make enough of a difference?

Thanks,

Magnus

[Ivan Kelsall]

Ron's got it dead on !. What you have Jim,is what is refered to as a 'Master Model'. That's your starting point. It needs sealing & rubbing down to smooth the finish,then having applied a coat of 'Gel coat' to it as a release agent,lay up several layers of
glasscloth impregnated with a 'cold set' resin & allow it to cure. You then have a 'Master Splash'. Make a board to support this on it's 'back' face to ensure that it doesn't flex at all & then into this you can pour an acrylic resin into this to make your
mold.This way you still have your 'Master Splash' into which you will be able to cast many future molds. The 'Master Model'can be kept,but due to the moisture content & the thinness of the wood,it may eventually warp & so would need checking before using it again. It might seem a bit long winded Jim,but you'll have a strong,stable mould,
Saska

[Jim Hilburn]

Thanks to all who recommended West Systems epoxy. It worked great for this application. Once it hardened I level sanded it and just put it to use for the first time. Seems impervious to wear.

[mandroid]

yea the oven thing, {drifting OT}
hot press fit oil seal replacement in the rear end of my old '68 BMW R60 motorcycle took a bit of negotiation with my mother to use the oven, Dad a machinist was the key to it being the right thing to do.

[David Newton]

Your welcome.
Where's the chips? Oh, I see 'em.

[Jim Hilburn]

The router blows the chips off into the corners and all over me.

[ehb86]

I just saw this thread, and realize you already had success with the epoxy coating. However I thought I would add that if you do another, you may want to buy a little powdered graphite from West System and add it to your epoxy. You end up with a super hard and extremely slippery surface.

[thistle3585]

How is that being held down Jim? Vacuum?

[Jim Hilburn]

Carpet tape.

[Jim Hilburn]

If anyone is interested I can give an overview of my duplicator set-up.
First for those who aren't familiar with an pantograph carver, this is a digitally controlled device with dual optical sensors. The digits are my fingers and optical sensors are my eyes.
On the archtop octave that I'm making the top and back are symmetric. So you only need one mold for both. On a mandolin the tops and backs are different with the back having the higher ridge that finishes at the neck.
On my first octave I made one carving cradle to hold the plates while working them. It can also be used with the carver. But since I made the inside and outside mold from the same piece of wood I have to use the holder for the mold. I should have another to hold the plates but in this case Old Standard supplied wood wedges that were extra thick. Once I had them joined and run through the drum sander to a thickness of 7/8" I had a large enough flat surface to carpet tape it to the table and do the inside first. That's what's happening in the earlier photo. Then when it was flipped I still had the full flat rim to attach to the table for doing the outside.
But when I set up for mandolins about 7 years ago I made separate templates for both the ins and outs of both the top and the back. That's 4 separate molds. They are for F style mandolins but I can still use them fo an A without making another full set.
This photo is of the top outside mold. You can see the depth adjustable guide and the plywood around the outside is to keep the guide from falling over the edge and rounding the edges of the blank thats being carved.

[Jim Hilburn]

Here's what's going on on the router side. I do about 4 to 5 sets of passes so I'm not hogging out too much wood at once. The depth is controlled by raising the probe on the mold side. At this point there are a couple of passes to go and I end up with the only the crosshairs showing on top.
At that point I use a safety planer to get the rim thickness and the plate can then go back in the holder to do the inside.

[PaulO]

First off I want to say that I have no business offering any advice on this section of the forum so please be kind.

I got interested in wood preservation with my old house and want to stabilize some rot on an exterior sill. I began hunting and found CPES. I think this is most likely similar to the West Systems product but thought I'd throw it out for you well informed builders. I got the following
from Jamestown Builders and Supply.

"Clear Penetrating Epoxy Sealer (CPES) consists of a tough, flexible resin system in a solvent blend which aids in the restoration of rotted or deteriorated wood. The Epoxy Resin system chemically adheres to the wood fibers and significantly strengthens them while allowing for normal expansion and contraction.
CPES is effective because of the special blend of solvents that allow it to migrate into the wood fibers and into the cellulose of the wood. Impregnation of the wood with the Clear Penetrating Epoxy Sealer changes the cellulose of the wood (which the bacteria and fungi find easily digestible) into epoxy impregnated cellulose which resists the fungi, while reinforcing the wood, and accomplishing restoration."

Now I'll go back to reading the interesting information you all exchange here.

Thanks,

Paul O'Mara