Scale Factor Calibration Blocks for Keel Bulb

thingiverse

I hate trying to guess how much to scale a bulb when you don't have pure lead or want to fill a printed bulb shell with leadshot, etc., and have the same final weight. So here are two files to help out. I have cross-checked them multiple times via Fusion 360 and the results get me to the exact desired weight. The only caveat is that when you do the equation, make sure you copy all the decimal points... otherwise you only get incredibly close :P I have put the relevant weights, equation, etc., into the actual STL box so you can reference them without needing anything other than the box itself :). File#1: BulbCalibrationBox.STL: Basic box for you to fill with the material you are going to use for your bulb. This is more for people wanting to fill a printed shell with something like lead-shot. If the calibration box was filled with a solid block of pure lead, it should weigh 725,888 grams. We can use this to get the correct scale factor to use in your slicer or CAD app to get the designed weight no matter what material you have (obviously use the heaviest stuff you can). Put the box on your scale, set the scale to 0. Fill the box with your chosen medium to the top. Read the weight. Do this equation on your calculator... Cubed Root of (725.888 / The weight of your material) eg. I fill the box and the contents weigh 567.68 grams. 725.888 divided by 567.68 grams = 1,27869222096956 Take the Cubed Root of this = 1,085397143711735 That is the scale factor to use! Just whack it into your app when you use the "Uniform Scale" option. File#2: 64cm^3-725_888g-Lead.STL (You are going to make a plaster mold, etc.) This can be used to check the shrinkage of the mold/material. DISCLAIMER..... Molten lead is both physically and chemically hazardous. Read up and buy Haz-Mat masks, etc. Don't be a dumbass and don't point at me if your plaster mold explodes because you didn't take due diligence. Print the cube and make a small test mold (Make sure you have read up ALL the info on this if you are using plaster. It MUST be completely dry before a pour..... like baked in the oven and left for ages dry. Lead explodes on contact with water!!!) Pour the molten material in. Once cooled, weigh the block. Do the same equation from phase 1. Cubed Root (725.888g / Weight of your material) Now you know how much to scale the plug for your mold & material whilst taking shrinkage into account. Hope it helps people.