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Custom Sanding Blocks From Bondo


Houdini

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I know people have used Bondo before to make cusotm sanding blocks and was wondering how well these hold up. Does any one know if the Bondo is durable or if it will crumble and warp/break with any type of pressure? I'm trying to find something that is comparable to the strength of wood at least. I was also considering using an epoxy resin such as what is used on boats

FYI: If you want to make a sanding block using Bondo: I got this technique from Taunton's Complete Illustrated Guide to Finishing by Jeff Jewitt. Great book on finishing, although I haven't tried this particular techinque yet, it looks pretty good.

Begin with a 3 to 4 inch long section of a moulding or fretboard or whatever shape and apply a thin coat of furniture paste wax to it to act as a mold release. Using scrap wood or cardboard, make a 4 sided rectangular box to act as a form for the bondo. Put the fretboard shape into the form with the fretboard side facing up. Mix up the Bondo and put it into the form making sure you don't leave any air gaps. Overfill the form with the bondo Take a block of wood that is slightly larger than the form and drive 3 screws into it so that the heads project out of it about 1/4 inch. Press the wood with the screws into the bondo. The screws act to hold the wood block to the bondo. When you press the block into the form, make sure that some of the bondo squeezes out. This will ensure that there are no gaps between the fretboard and the bondo. After 5-10 minutes when the bondo becomes rubbery break the form off of the bondo and take the fretboard shape off. Let the bondo cure. If it distorts, put a piece of fine sandpaper on the fretboard shape and run the new bondo sanding block along it a few times. When the bondo is dry, spray some truck bed liner (available in spray cans at hardware stores) on the form to act as a cusion for sandpaper. Now just use Pressure Sensative Adhesive (PSA) sandpaper and attach it to your form and you have a custom sanding block. :D

Edited by Houdini
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You probably could use wax paper as long as you make sure that you don't get any sharp edges or crinkles (is that even a word) in it. I know this doesn't apply to guitars, but I probably wouldn't use wax paper if I was doing something more complex such as a moulding for a doorway or wall. The wax paper won't form to the shape very well. :D

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I would use a two part bondo filler called Awl-Fair, mix the red and the white together and get a wad of bubblegum that cures in about 20 minutes. Has the same properties as wood, ie. can be drilled, sawed etc. but twice as light, should not be dropped onto a concrete floor tho.

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I've probably used this trick a hundred times, no exaggeration. Got it from the same place too. Fine Woodworking is a great publication.

I use Saran Wrap and don't worry about the wax.

As another comment, Klingspore Abrasives (they have a website) makes an adjustable sanding block. Neat gadget.

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I use bondo for a lot of things, but for the use or abuse that a sanding block might take, I rather make it from fiberglass first, just use the same technique you have for bondo, lay a thick coat of fiberglass resin, or gel coat resing, then build up with glass matt, the shreded one not the woven since it is stiffer, thn once dried you can fill it up with bondo if you like or with more resin. I rather use the wax or if I got no wax, I have used WD-40 or silicon spray.

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