Speaking of bearings…
I have been looking at weight reduction, both on my own (human) chassis as well as for any future printer designs (calls of ‘you fat bastid’ will be treated with the disdain only us cuddly types can muster!).
I had a very interesting chat today with a technical specialist in the polymer bearing industry who assures me he has a linear bearing capable of working on carbon fibre tube, at only slightly less than double the friction of a ball-bearing. That is significant.
They are selling them into robotics, space and aerospace engineering and have been getting great results. As far as wear goes, it is better than with un-anodised aluminium, worse than with chromed steel. With a wear rate of .0.00053 millimeter/km, that is also significant - compare that to a roller bearing on a hardened steel shaft of 0.00002 mm/km.
At 82c each for a flanged bearing of 81012mm, they represent good value, if I can get a carriage’s weight significantly down. My 300mm carbon shafts weigh just 3g each. Compare that with the same in steel of 120g each. Each!
So, while there isn’t ‘no’ wear, the wear is certainly very low (being 25 times that of a ball-bearing on a hardened steel shaft).
The other advantage is in the reduction in overall size and weight of the carriage and supports. Because the Y-axis mass is reduced, the central (hotend) mount can be made lighter and because the X-axis doesn’t have to locate 240gm of wildly oscillating steel shafts, it can also be made lighter.
Considering the cost of the bearing and the cost of the carbon shaft over the potential speed gains through reduced inertia and overall reduction in wear and tear, I think it is certainly worth progressing.
While we were discussing carbon, he mentioned aluminium shafts as another option - I was initially dismissive, being that aluminium has the strength of an udon noodle in similar dimensions, but he assures me they are selling lots in comparable situations to carbon fibre. A hard-anodised 8mm aluminium shaft weighs around 40gm in a 300mm length at around $13/metre. The wear with their matched polymer bearing is comparable to chromed steel.
40gm vs 120gm and $4 each vs $3, but with significantly higher (for me) shipping costs is a no-brainer.
I also just bought a bench power supply that can show (in mA) the current draw - so that will be useful in determining which method is the most efficient, from a stepper/driver/controller perspective.
I will be trying out both CF and aluminium shafts as soon as I have cut out my new printer chassis. I am looking forward to seeing the results.
#FlatSli3DR #Sli3DR #Bearing