Excel spreadsheet to determine workable T-O-M feed rates

thingiverse

This is a spreadsheet to get feed rates for your TOM into the ballpark for nice printing, based on a W/T and a layer height you choose. Flow rate is fixed at 255 PWM due to the extruder firmware and the spreadsheet also helps determine what your flowrate is. This is a work in progress, I cannot be responsible for you totalling your TOM as some basic assumptions I have may be wrong, and my math might be crap. Thanks to Dave Durant who steered my thinking in a different direction, and gave me some impetus to think of an easier way to calibrate my 'bot. Instructions This is meant for a stock TOM, which mine is apart from a fan duct and a relay for the dodgy DC motor. Green fields are values you need to come up with, orange are values the spreadsheet generates First, measure the speed at which the filament is pulled INTO the extruder. I simply measured 20mm intervals along the filament, marked and then started the extruder and timed it. After 6 intervals I averaged and divided by 20. This is your feed rate going in. Then measure your filament diameter (Mine was 2.92mm), extruded filament diameter (Mine was 0.6) and plug these values in. This will then give you a calculated extrusion rate (flow rate). Now this is where some funky stuff is going on. It seems based on my observations that ~13% of the volume is lost during extrusion. There are posts I've read on the MBI forums about it, and people seem to feel it's moisture absorbed by the ABS being cooked off, either that or some nasty volatiles. Regardless, this is why I repeated step one, and marked out intervals on the ingoing filament, then started extrusion and chopped a length off every time I reached a mark. 6 or so lengths of filament, average their length and then put that value in the appropriate field (Mine was 221.7mm coming out for 10mm of filament going in) This then gave me my actual, observed flow rate. Using actual and predicted flow rates I came up with the ratio (0.8716). This ratio needs refinement, as it's based on one observation at one speed and one temperature. So, subject to change. It's there for those that want to skip determining actual flow rate and just use predicted. *EDIT: 0.85 seems to be the current best ratio for determining input volume vs output volume, in my own testing 0.87 produced values for feedrate that were a little too high, I will be doing more testing to determine, but for now if you don't wish to directly measure the extrusion rate of plastic coming out of your toolhead, use 0.85 (on the unmodified spreadsheet, look for the orange field with 0.8716 and replace) Now, plug in your desired Layer height and W/T values, plus your (hopefully) approximate flow rate and the last box will be, in theory, the Feed rate you need to set to get a nice print. I threw away my current SF profile and started with a fresh one (TOM, HBP). The only modifications were the spreadsheet values, and Raft BASE and INTERFACE integers were set to 0. Outline was enabled, and First Object layer infill feed rate was set to 0.8 (bit too fast) and First object Perimeter feed rate was set to 0.55 (bit too slow). Temperature was 225C. From the look of the object, I need to fix my Z starting height ever so slightly, and probably reduce my feed rate a fraction. But it's real close! Please be nice if I've screwed up something good and proper here :P