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I would like to make some solid molds for side bending with a heating blanket. 3/4" MDF is a bit cheaper then the cheapest suitable plywood. Will I have problems with it when it gets hot?
Thanks,
Rob

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Rob: I've used MDF for forms and they have worker out fine for me.The only problem I've seen is that the MDF is less stable then ply in that it takes up and releases moisture easier. This has not resulted in any problems for me. You may want to put three through bolts in your molds to make sure you don't get seperation. Good luck with your project.
Tom

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A person who has never made a mistake has never made anything!!!

Tom,
MDF works fine for me, too.
The only drawbacks are it`s one dusty mess in the fabrication stages (which is only temporary), and the molds or forms are relatively heavy.
There is also a myriad of other uses for it when making the various jigs and fixtures that I`ve made so far.
Go ahead and invest in a sheet, and you`ll more than likely go for another.
For the price, you can`t go wrong.
For your well being, use breathing protection. The stuff will load you up and stick around for a few days.
Coe Franklin

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Give me 50 cents worth of regular.
Check my oil too, if you don`t mind,,,

you can get a few off them , the water will make them spongey after a few uses so be careful

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

You can always seal them to protect form the water damage. A little shellac maybe ?

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the heat makes the shellac bubble

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I really prefer Baltic birch. I used to use particle board and coat it with polyester resin, but like ply better. What's a few bucks compared to the effort to make the mould?

The standard MDF you get from the home depot, etc. is also made with formaldehyde (a known carcinogen) and I believe it releases a bit of it when it's heated. They do make MDF without formaldehyde (this stuff is also a little harder/more homogenous throughout and would probably hold up a little better) but you'd probably have to order it. I'd stick to ply.

I've been using fibercore for most of my molds and jigs. It' MDF with a layer of Baltic Birch on either side. It's been very stable, really flat, and easy to rout and shape.

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Terence, where do you get this Fibercore? Sounds appealing.
The problem with MDF is that, even if it is extremely stable, it will swell and lose shape if water is dropped on the material. And IME warm water will get through any sealer, shellac, oil or urethane.
Formaldehyde is present in the glue used for most plywoods.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Thanks for the answers.

Now that I have these answers, perhaps the better question would have been how do I seal them for better longevity. Titebond 3 has some amazing heat and moisture resistance, not sure if it can handle that much heat though. I can thin that to help seal it, or just be careful.

I really hate being cheap, it is only $12/ sheet difference from the ply, but all those $20 dollar expenses really add up, I will use 2 sheets to make 2 bending and body molds. (The GAL 20's Gibson LO and the Antes parlor plans are under way) I will have material left for other jigs. I have used MDF for jigs in the past and it is easy to work with. My budget is really limited for this project, and if these molds wear out from use, then I am happy I have made that many guitars.

The hardwood supplier I am using has the fiber core product as well, I have some in 1/4" left from some other projects. It is a nice product, I have used it to make the templates to start these molds.

Thanks again, the material will be delivered today and the molds will be underway.
Rob

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Would it be recommended to use an epoxy resin to seal it up? You would never have to worry about moisture, but heat may not be nice to it. I have thought a few times about getting sheets of counter top material and gluing that on, but again wonder about heat resistance.

For mine, I have bent and welded a metal form and cover it with foil to protect the wood from the aging steel. Works great but wasn't the cheapest or easiest to make either.

Matthew

Rob, I've made my molds from MDF and used the HVAC foil tape to seal. Works for me. Tony

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Tony Flippo

Tony,
Perfect, I even have a roll in the shop, I love solutions that involve stuff already on my shelf. Do you overlap the edges? If you do does the tape thickness matter in the flatness of the mold surface? Two layers could certainly cover the seems with no unevenness.

Do you have pictures of your jig with a side in it? I am wondering how the 4 carriage bolts are used in the bending process.

Thanks for the tip.
Rob

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Rob, I do overlap the edges a small amount. The thickness of the foil is only .002” so I don’t bother taking into account the thickness – what’s a few thousandths between friends? (that may cause some churn in the left brain camp).

It is based on the Everett style mold, but without any springs – I just push carefully by hand and lock down with the carriage bolts. Homemade and cheap enough not worry about messing them up. The blocks are made of pine 2x4s and they also have foil tape on the side facing the wood. All materials from HD.

This side is just for demonstration purposes with no heat blanket. I usually sprits sides with water and wrap in tin foil then place heat blanket on top These sides are for a lacewood dread I got off ebay that I’m going to reshape into a Payne SJ.

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Tony Flippo

One of the local lumbar yards carries it here. I bought some by mistake a few years ago thinking it was birch plywood and really liked it for some jigs mainly because it is so flat and easy to shape with sanders/routers etc. The MDF will split easily if you drive a sheetrock screw into it without predrilling. It's also pretty heavy which can be a good thing sometimes. Here's a circle routing jig made from it.

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Is MDF suitable for side bending molds...well thats a good question...seems others have answered to it so I wonder if MDF is suitable for sides and backs.

Ya can you dig it..a MDF build...finished with duck tape...by god it be beautiful.


Icu
the
Padma

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I am not sure about the duct tape, I think I would dip the whole thing in that liquid rubber tool handle stuff, or perhaps we can do a burst finish with the rubber coating going into some fine silver duct tape. The binding could be a few layers of colored electrical tape. I can dig it, but it may require plenty of Northern Cali's finest to actually make it beautiful.
Rob

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This is true. However MDF contains far more formaldehyde resins (typically 9% by weight) than plywood. To quote the EPA, "...Medium density fiberboard contains a higher resin-to-wood ratio than any other UF pressed wood product and is generally recognized as being the highest formaldehyde-emitting pressed wood product." In addition, it has become fairly easy to find plywood that emmits little to no formaldehyde.

I wonder if you could paint them with engine paint? Its heat resistant to 1,000 degree F

Was talking to a Cabinet customer of mine yesterday I mentioned that I would like some molds made from his cnc router from mdf but i was concerned it would have trouble with the wet application . He said not to worry he keeps MOISTURE PROOF mdf in stock. So , all I have to do is supply cad drawings and he will router my molds for me at a VERY good price

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I am very cheap but I still say plywood if it is only going to be a few dollars difference.

I use mdf on some of my molds. To cut down on weight, you can just use every other layer and space them apart with spacers made from the scrap pieces that are left from cutting out the shape. The 1/2" or 3/4" gap between each layer does not cause any problems with the bend.

I have never had any problems with moisture. Apparently some folks use way more moisture than I do. I simply spritz the side that I am bending, wipe off the excess, wrap the side in aluminum foil, and sandwich the side and the bending blanket between the SS slats. The only thing touching the form is the lower slat in the sandwich. No moisture ever gets to the mold. This heating blanket method with solid forms is much easier for me than the Fox style bender that I built years ago. I like having the support under the full length of the sides, rather than the metal rods going across.

I can't comment about the formaldehyde, but I will do some research for my own benefit. I like the idea of the foil tape, but my forms have suffered no problems resulting from glue failure caused by the heat.

The forms are really easy to make. Cut and finish one layer to the proper shape, and use that piece as a pattern for the other layer to run on the flush cut router bit. Of course you cut each layer on the bandsaw to within about 1/4" of the right shape. Do the routing outside, and have a dumpster rented to haul away the pile of dust you will create.

I will probably use Todd's idea above for my next form. I like the idea, as well as the material choice. I will still leave every other layer out with a spacer in its place.

I say spray that sucker with Rino Tuff Bed Liner , she will never wear out

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The Shallower the depth of the stream , The Louder the Babble !
The Taking Of Offense Is the Life Course Of The Stupid One !
Wanna Leave a Better Planet for our Kids? How about Working on BETTER KIDS for our Planet !
Forgiveness is the ability to accept an apology that you will probably NEVER GET
The truth will set you free , But FIRST, it will probably Piss you Off !
Creativity is allowing yourself to make Mistakes, Art is knowing which ones to Keep !
The Saddest thing anyone can do , is push a Loyal Person to the point that they Dont Care Anymore
Never met a STRONG person who had an EASY past !
http://wiksnwudwerks.blogspot.com/
http://www.facebook.com/groups/GatewayA ... rAssembly/