Tuesday, February 9, 2010

4.7kg pull Extruder drive using Meccano Worm gear

Four Meccano worm gears arrived, that I dilled out to 4.5mm then 5mm to fit the stepper shaft.
I've removed the furniture screw, one plastic block thus reducing the flexing of the whole extruder assembly.
The 1st stepper I used was 4.6 kg/cm or  0.451  Nm torque it had no difficulty.
I'm now using a stepper with  4 times less torque at 1.1 kilogram centimeter or  0.108 newton meter. 

The geaing is 26:1 so the extruder resolution should be at least 20 times better than the splined shaft extruder. 

The drive has changed from 5mm splined shaft to 7mm gear drive.


Here is a picture of the new extruder.



Testing the New extruder causes my ABS stock hanging frame to start bending, as it goes past 4kg of pull.
I achieve 4.7kg of pull before the gripping pulley slips on the shaft or the gear slips on the shaft or on the ABS rod. I.E. tighten the gear the shaft slips with the pulley tighten the pulley the gear slips or the ABS then slips. The Conrad gear or an AK47 "worm" gear are just about the same as each other in my set up no difference.. my  "worm" may not be as good as it should thou!


I need flats on the shaft and stronger springs to clamp the bearing into a sharper "worm" pulley.


If the splined shaft gave me 1.7 kg pull this must be not far off Adrian's pukka Mendel extruder.
Getting 4.7kg pull with a low cost low torque stepper using an easy to make drive construction.
Is the best I can do so I'm giving up trying to get a better pull than  4.7kg for now.
My next task is to add a feed guide then  marry the extruder to the drive system test then add it to Mendel.


As I need to have two working machines for the show time is short for me to mess around any more trying to get better results that may not be needed. There is still the PID temprature control to get working for both the Ext ruder and Bed yet. I will make drawings once I can prove it works OK if there is time left before the show to do that.


Oh the side effect of the smaller stepper is the whole assembly has weight reduction from 560gms down to 346gms. Just over 200gm weight saving if that will make any difference to performance... ??? I don't know ???
  
I think I have achieved the best pull I can with out using any RepRapped or specially machined parts.
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