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 2 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 725,888g. 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 calculater.... Cubed Root of (725.888 / The weight of your material) eg. I fill the box and the contents weigh 567,68g. 725.888 divided by 567,68g = 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 mould etc) This can be used to check the shrinkage of the mould/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 mould explodes because you didn't take due dilligence. Print the cube and make a small test mould (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 mould & material whilst taking shrinkage into account. Hope it helps people.