Black Beauty Arises!
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@gtj0 thanks for the answers! Great, I'll go twisted in my core to be too. So thanks for sharing, you helped me a lot!
Thinking about the idlers... Yes toothed could be better actually that way
. I go toothed too, but saw some discussions bearings would be better. Nah, I like the toothed stuff!Cheers!
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@QuintBrand said in Black Beauty Arises!:
@gtj0 thanks for the answers! Great, I'll go twisted in my core to be too. So thanks for sharing, you helped me a lot!
Thinking about the idlers... Yes toothed could be better actually that way
. I go toothed too, but saw some discussions bearings would be better. Nah, I like the toothed stuff!Cheers!
Ah toothed idlers as opposed to bearings not smooth idlers. The bearing sandwich, such as that used by @mrehorstdmd, has a large enough diameter that there's much more surface area to spread the load so having the belt teeth ride over that smooth surface is not an issue. I went with the idlers just because of space constraints.
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@QuintBrand The problem with the toothed pulleys is that the bearings in them are very tiny and wear out quickly. They typically have 3 or 5 mm bore which means the balls have to be very small which puts a lot of force on the races.
The 3D printer pulleys, smooth, but with 3 mm bore, I originally used in my sand table lasted for about a year of sporadic use before they started squeaking and binding.
A Gates manual about timing belts recommended a minimum of 9 teeth in contact with the pulley surface if using smooth pulleys. The belts bend over about 90 degrees of each pulley in a corexy machine. So if you're going to have 9 teeth over 90 degrees, that suggests 36 teeth going around the pulley. With 2 mm pitch, the circumference should be approximately 72 mm (a little less, actually), which leads to about 23 mm diameter. 608 bearings are 22 mm in diameter, are made in huge quantities for skates, motors, and machines, so are very cheap and readily available. They will last long time under the loads presented by a 3D printer.
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Thanks for the nice additions a remarks! Wear and tear is not something I was think of to be honest ;-). I've also studied some of the Gates documentation, which is really nice till you want to do the math yourself: have you ever found the Specific Stiffness of GT2? I didn't unfortunately and once you start searching for the specifics I got lost in the fast amount of info ;-).
I thought driven pulleys require a lot of teeth, but was not away non-driven should be too. Makes sense when it comes to compression of the belt on the idlers though.
Most pulleys are 21 tooth on Ali, bit strange in view of your comments. These bearings are tiny indeed ;-0!!!
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Someone asked for a link to the pics...
https://imgur.com/gallery/H9qKVcL
