Tuesday, 18 October 2011

You've got to admit, it's getting better ...

... A little better all the time!

Well, I owe a HUGE debt of gratitude to Triffid Hunter and David Drew for their comments on my previous post http://julianh72.blogspot.com/2011/10/cheers.html . Triffid Hunter was 100% spot on in diagnosing my main problem as being backlash.

When first assembling my machine, I had no real guidance as to how tight the belts should be, and I was worried that if I over-tightened them, I could stall (or burn out ) my stepper motors, or break my machine. Triffid Hunter said "They should make a tone of 100hz or more when plucked like a guitar string. That's a low G sharp for the musically inclined." Or to put it another way, they should be "as tight as a tourniquet, dry as a funeral drum". (Google it, if you don't get the reference.)

So I set to tightening my belts. My X-axis belt was not too bad, but needed just a little bit of tightening, but my main problem was my Y-axis belt. Having had the root cause pointed out to me, sure enough, you could actually see the backlash on the Y-axis pulley every time it changed direction.

I have seen a number of clever tricks to tighten the belts on your RepRap, including this http://www.thingiverse.com/thing:10082 and this http://www.thingiverse.com/thing:4535 , but I decided to go with a much simpler solution - make a loop of cable ties around the ends of the belt, and then pull it nice and tight, and cut off the loose ends:
Simple (crude, even), but very effective, and easily adjusted without needing to tighten or loosen any clamps. If you over-tighten it, just cut it away, and have another go. So, I tightened both belts, and repeated some of my test prints - and the results are an astounding improvement (to me, anyway!):
Compare the 20 mm Calibration Cube to what I was getting earlier http://julianh72.blogspot.com/2011/10/always-listen-to-people-who-know-what.html and my second attempt at the RepRap Teardrop Shot Glass http://www.thingiverse.com/thing:11944 against my first attempt http://julianh72.blogspot.com/2011/10/cheers.html , and you would have to agree that this is a dramatic improvement.