Must pulley and idler sizes match?

mrehorstdmd

@PassiveAggressor Just grab a piece of belt and try it:

Belt pitch is the spacing between teeth when the belt is straight.

PassiveAggressor

@mrehorstdmd ah I see. In the midpoint of the belt there is no stretching. But because the belt has thickness on either side of it, teeth get closer and teeth get further I see now

mrehorstdmd

@PassiveAggressor I had one of the links wrong- I fixed it.

A Former User

It must be pointed out that when using "toothed" idlers if you install genuine High Quality Bearings E.G.

From the likes of F.A.G. or S.K.F then they last very well, but expect to pay a premium for quality bearings.

A Former User

<<@deckingman said in Must pulley and idler sizes match?:
just for info, when the automotive industry changed from chain driven camshafts to belt driven ones it was found that having the tension too high would cause the belts to "whine" or "scream". It would be reasonable to assume the same would be true with our printers. So slackening the belts might make them quieter (although there are other reasons why one might not want to do that).

Its funny you should mention this as one of my students presented his thesis on toothed belt tension (and the harmonics) using a high speed camera, a Belt Tension Meter RTM-400 and a high accuracy acoustic meter from Schmidt Control Instruments.

Watching the belts deflect at differing tensions and the resonant frequencies they produced was quite interesting

mrehorstdmd

@PassiveAggressor If you assume the thickness of the belt is zero you will position pulleys incorrectly. You must include thickness of the belt when you're laying out a belt driven mechanism because the working segments of the belt have to be absolutely parallel to the guide rails (just as you would position lead screws parallel to the guide rails).

See: https://drmrehorst.blogspot.com/2018/08/corexy-mechanism-layout-and-belt.html

PassiveAggressor

@mrehorstdmd yes I have read your blog some bit, useful stuff. I only regarded belt as zero thickness in relation to spacing of the teeth on the idler

PassiveAggressor

@mrehorstdmd sorry one more question, why do toothed idlers and untoothed idlers have the same outer diameter? Shouldn't toothed idlers be slightly bigger in diameter because they have teeth that mesh the teeth?

deckingman

@PassiveAggressor What you are asking is essentially the same question that is in this thread title and which the OP raised back in January 2019. Idlers come in a range of sizes and are available as toothed or un-toothed. As has been explained numerous times in the 4 years since this thread was started, idler sizes and pulley sizes do not have to match as long as the critical parts of the belt paths are parallel to the relevant axes.

Exerqtor

Maybe it's time to lock the thread, feel like the subject has been answered full & well for several years IN this thread by now. But it still keeps getting bumped and pop up on the recent feed lol.