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I Need A Finished Product With 3/8" Mounting Hole?


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Looking into making my own climbing holds for an indoor climbing wall at home. From what I understand they have been made. I just need to figure out the shrinkage of my clay so that the mounting hole is a standard 3/8" like commercially made resin holds. I vaguely understand the concept of shrinkage calculation. Roll a slab the same thickness as your finished product, mark with a ruler 10cm, fire at temp and then check against the original ruler for % shrinkage. Do I just increase the desired hole size by the % and voila? Or is there something else to it? Thanks for any advice.

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I think making a shrinkage ruler for each of the different clays you use would be ideal but, instead of 10cm which is only about 4", I would go with 10 inches (25cm). It would be easier to read and calculate the shrinkage. As far as the hole size...there are a couple of ways to go about that but all of them are just starting points until you know exactly how your particular clay body is going to shrink. Your primary consideration would be your boring tool and when you bore the holes. Will the clay be leather hard or bone dry? Leather hard would be easier to work with because bone dry clay is very fragile. What is your drill bit repertoire? What sizes do you have over 3/8"? Try 7/16", 1/2" and 9/16" and see what the holes shrink down to when fired. If one of them works, you have your working tool. Another option would be a 3/8" diamond boring bit to drill the hole AFTER the firing. With that, you'll have the exact size hole you want. You would want to drill those holes using a drill press and jigs to hold your work piece.

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Generally homemade climbing holds are made from cast resin with sand aggregate. If you do them in clay, the best way to ensure a proper hole is to drill post fire using diamond core bits as mentioned above, this requires a lot of patience, time, water, and expense for the bits and water hose attachments for the press, and drainage basin set up. if you're comfortable making molds of any type, cast resin is a really nice option, with not much fear of chipping or breakage. With resin, you can use cheap acrylic paint as a colorant, and end up with some really nice holds. There's a lot of DIY guides available online for the resin holds too. Good luck with either material. 

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For something that is going to be holding my body off the ground I wouldnt worry about trying to make my hole's diameter precise in the beginning. Drill your hole oversive and use a super strong epoxy to glue in a metal threaded insert which you will use to attach to your climbing wall. In the cavity create intential undercuts so that the epoxy will not only bond to the surface of the clay but it will also have a physical joint increasing its strength. Unless you plan on making these "holds" super thick (at least 3/4") walled I wouldnt think clay would be the best option for something which will be holding ones' body during a jarring experience. Use a product that has more shear strength. There are plenty of products out there (resins, etc) which have extremely high PSI strenghts; I personally have used Forton (http://www.reynoldsam.com/product/forton-vf-812/) for casting large scale figures. This material has compressive, tensile, and shear strenghts of NUMEROUS thousands of PSI. Increase its strength by adding chopping fiber strands.

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