Belt drive vs direct coupling pro's and cons, Poll

[Boyan Silyavski]

It was done long ago to eliminate vibration when drives were crappy. Now drives are digital so that will not matter so much. Now is done for the sake of hiding the motor, gearing it and so on. And yeah, for the sake of alignment and simplicity, as 2 things bolted to the same plate/plane is easier to align than 2 thing bolted on a same axis.

Anyway i don't like spring couplings and having in mind the cheap price of ball screw mounts, i would always use both sides angular contact bearings. The so called rigid mounting, or scenario D.

At the end of the day machines look more tidy and all is more rigid when you don't see the motors. Protruding motors will need a good mount, not just 4 bolts and spacers, so its up to you.

[routercnc]

I agree with the above. My current machine uses
1:1 belt drive on Z (to hide the motor)
Direct drive on Y through spring coupler (although I had plans for belt drive to hide the motor, but never implemented them)
Direct drive on X and A through spring couplers

My comments:
Choice of which to use on DIY machines is mainly to hide motors, mounting simplicity, and if you want options to gear the drive train up/down
Not noticed errors due to belt play or stretch so don't think that is a factor on DIY machines (commercial machines I've seen are all direct drive though)
Have had those spring couplers break (I don't think they are a good idea on a cnc machine), and next machine will use 'oldham style' couplers which look more robust (although cost a little more)

[Zeeflyboy]

It was done long ago to eliminate vibration when drives were crappy. Now drives are digital so that will not matter so much. Now is done for the sake of hiding the motor, gearing it and so on. And yeah, for the sake of alignment and simplicity, as 2 things bolted to the same plate/plane is easier to align than 2 thing bolted on a same axis.

Anyway i don't like spring couplings and having in mind the cheap price of ball screw mounts, i would always use both sides angular contact bearings. The so called rigid mounting, or scenario D.

At the end of the day machines look more tidy and all is more rigid when you don't see the motors. Protruding motors will need a good mount, not just 4 bolts and spacers, so its up to you.

Angular bearings on both sides!? Am I misunderstanding what you said here and you actually mean one set of back to back angular bearings on one end and a floating bearing on the other or are you actually suggesting angular contacts on both ends (fixed/fixed)?

I don't personally think fixed/fixed is a good idea in general unless you really need that increase in critical speed, but especially so on machines built from aluminium extrusion like Desert's due to the difference in thermal expansion between steel and aluminium.

Re the topic, If you use proper high torque belts (bearing boys is a good source of HTD belts) then slip is a non issue. Theoretically you might have a bit less accuracy due to belt flex and a teeny tiny extra backlash but in reality I don't think it's an issue on a hobby level machine... they are pretty much backlash free and the re-inforcement strands mean that flex is very minimal.

Personally for me I prefer direct with decent couplings, but it's really just a question of what better suits your machine design I think.

[Boyan Silyavski]

My machine has fixed to fixed on all axis and generally having in mind the low price of the bearings i am even doing my foam cutter like that. The only problem with that arrangement that you will ever encounter is if something is not well aligned. I am milling up to steel with my router, so excuse me if i do not trust a fixed/floating arrangement. Plus FYI Chinese sell the many times the BK and other mounts with deep groove bearings, not angular. Sometimes you will have to specifically specify that you like to have angular bearings. Its in the small letters usually if you pay attention. Hence that's why i don't change providers if i can help it.

Buy HTD pulleys from reputable sellers only or you will have a box of faulty pulleys, like the one i have.