Using "Bondo" to make perfect radioused clamping cauls

"Bondo" is a product used in the automotive repair business to repair dents in metal. It starts out as gloopy substance with the consitency of clay and then hardens nearly to the strength of steel.

My previously made wooden clamping caul for my radioused neck and tail blocks was just slightly off so that I couldn't get perfect even clamping pressure on these critical parts. Not ideal.

So I got some Bondo and using my neck block as the positive mold (convex) with wax paper between the block and wax paper underneath the Bondo, pushed the block into the Bondo. After about 15 minutes before the Bondo completely hardened up, I trimmed off the excess that squeezed out around the block. An hour later I removed the block and waxpaper and had a perfect negative (concave) piece way harder than wood.



You can barely see the radius in the picture but it is there. The center line is marked and the arrow for the up or top side.

The piece can then be glued to a block of wood to give perfectly even clamping pressure. When I used it to glue in a neck block and I got perfect glue squeeze-out which was a happy sight to see! Perfect.

So, it wasn't as messy as I thought it would be and only took minutes to do. I can see this method as having many uses such as making perfect sanding blocks to put a consistent radius on back braces for instance.

The biggest downside that I can see is that Bondo is not cheap and set me back $12 for can. Also it stinks and my shop smelled like an Auto Body Repair Shop for the rest of the day, a smell I'm sure we are all familiar with. Just thought I would pass this tip along to UU.

Interesting idea! There's a product called Durham's Water Putty, which one mixes with water, much like plaster of paris. It also works like clay for a short while then sets up really hard. The advantage of this product over Bondo is that it doesn't smell and it's relatively cheap. Obtainable at most hardware stores. Great stuff

Bob

I worked in construction for a while. I wouldn't use durhams it much too soft and in my opinion doesn't hold up very well. After thinking about it. I might try a product like Henry's feather finish. A cement base patch. Dries fast, water resistant and harder than Durham. Available at home depot.

Or try Polymorph...if you google "Polymorph YouTube "you will see some great demo's

I've made most of my bridge cauls from Autobody Plasitc. Once it hardens it's very durable. My brother owns a body shop so I just go there to make them and leave the smell there as well.

Flyfish57 said:

I've made most of my bridge cauls from Autobody Plasitc. Once it hardens it's very durable. My brother owns a body shop so I just go there to make them and leave the smell there as well.

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Thanks. I hate to say that making a Bondo caul for bridge clamping never occurred to me. But of course! I only have the one (expensive) violin clamp for clamping my bridges and have always struggled to get even clamping pressure. Now I don't have to buy two more violin clamps. This time I'm going to make the caul outside so I don't have to deal with the stink. Thanks again.

Or you can use Friendly Plastic from LMI. Reusable too!
http://www.lmii.com/products/tools-services/clamps-vises/friendly-plastic