Belt Drives, advice,opinions,experiences.

[OzDragonflyer]

Hi all,

My medium sized router has 5tpi ballscrews on x,y axis and am seriously considering converting it to belt drive for more speed in 3d contouring work.

I've been thinking of the GT2 timing belts/pulleys from sdpsi, but these are only available in 15mm width. Seems very narrow and may not handle the power required?

What is everyone else using? Also, are idlers really necessary?

Any experiences,ideas,tips or even pics/links to your machines would be of great help!

cheers

dave.

[planekrazie]

Check out my build thread http://cnczone.com/forums/showthread.php?t=50855.
All belt driven except the z axis. I love it. No backlash so far.
if you have any questions, ask away.
Steve

[OzDragonflyer]

Thanks PK.. great looking machine,beautifully simple! Looks really easy to keep clean too

Is one main drive pulley adjustable for belt tension?

I was concerned that XL belts at 1" wide have quite a large pitch which may affect power transmission.. but using a 15 tooth pulley like you've done has a min 7 teeth engaged at any one time, which should be enough!

[harryn]

The path I (think I ) am on is the Brecoflex AT5 x 25mm wide. The timing pulleys can be obtained with zero gap between the belt and pulley.

The AT 10 is definitely stronger per tooth, but at least in theory, the smaller pitch allows smaller pulleys dia.

I am still working out the aspect of the jack screw / pulley sizing. 1/2 in / 12mm dia is pretty cheap for components but seems likely to bend. 3/4 in (about 19mm) seems about right, but the cost of bearings and shaft goes up very fast, esp. for ball bearings. I am wondering if a bronze / oilite bushing is adequate for the jack shaft.

[planekrazie]

The stepper mount is adjustable. All I have to do I lower or raise the mount which has slots for the bolts. The main drive pulleys on the x axis are for L Belts. These are 3/4 Inch wide. The y axis is using XL belt which are 3/8" wide.
Thanks for the compliments.
Steve

[blackbeard52]

Steve

Are you coming up for the Mach convention?

Bob

[OzDragonflyer]

I may go with AT10 for the main drive and L for the reduction.

The problem will be that the motors have 1/4" shaft and will have to sleeve the pulleys to fit. Is there a better way?

Where are you guys getting your belts/pulleys from? There seems to be a lack of stock, and some places are really expensive.

[harryn]

Originally Posted by OzDragonflyer I may go with AT10 for the main drive and L for the reduction. The problem will be that the motors have 1/4" shaft and will have to sleeve the pulleys to fit. Is there a better way? Where are you guys getting your belts/pulleys from? There seems to be a lack of stock, and some places are really expensive.

Hi

I was wondering if you could advise me on the AT 10 vs AT 5 question ? I looked closely at using AT10, especially since it is much stronger and the individual tooth strength is very high.

The advantage of the AT5 is its flexibility - it can be used on much smaller timing pulleys, yet still is stronger than any stepper motor I plan to use - even NEMA 34 motors. At least that is what I interpret. I think you can get AT5 pulleys for that shaft diameter.

My thinking is to go for 25mm wide belts for everyting, as this is a common pulley and belt size. There is such a discount for qty on timing pulleys that it makes sense for me to try to design with a common size whenever possible.

As for supplier, in the US I am looking at Brecoflex.com - not a discount supplier, but good response. Pulleys can hit $ 30 / each though, esp. for the zero tooth gap versions. 6 pulleys + jackshaft + bearings + 2 belts + who knows what per axis is starting to add up to real money. This is for a 4 x 8 ft. system (goal size).

[OzDragonflyer]

Hi Harry... yep i can see where you're comong from re the AT5 belts. I read somewhere that the teeth should be rated at min 15x the load they would be expected to carry, so I was thinking the bigger teeth of the AT10 would offer that extra security.

I've yet to work out the loading on my machine, but with a 5:1 reduction it would be quite significant with 470oz steppers driving them.

I'll check out brecoflex, thanks for the link.

[Kipper]

Originally Posted by OzDragonflyer Where are you guys getting your belts/pulleys from? There seems to be a lack of stock, and some places are really expensive.

Just recently I discovered Megadyne who make belts and pulleys and have a distributor local who sells them, Prior to this I've been buying from the states in 50M lengths with 3 drive and 6 idler pulleys...For less than $100 shipped, God bless America because in the UK that would cost me one testicle and an arm! I jest ye not.

[harryn]

Originally Posted by OzDragonflyer I may go with AT10 for the main drive and L for the reduction. The problem will be that the motors have 1/4" shaft and will have to sleeve the pulleys to fit. Is there a better way?

I have done more digging and learned some more - probably obvious to everyone else here.

I found an on-line deflection calculator and was playing with it for shaft diameter. For the main shaft of one axis, I estimated a force of 100 lbs - about 40 Kg and 18 - 36 in length. In order to get reasonably small deflections ( a few thousandths) , it seems I will need something like 25mm / 1 inch shaft. That is pretty heavy duty!

Such a large shaft diameter largely eliminates using AT5 pulleys as most of them are too small in diameter, so I guess I am back to AT10. I am still playing with trying to reduce the shaft diameter by bearing placement, but getting below 16 - 20mm dia looks tough.

With regard to mounting the pulleys on the shafts, I had planned to use set screws, but I now have learned that a better way (technically) is to use a tapered bushing. They come in various sizes, but basically are a collet that goes over the shaft and is tightened to fill the gap between the pulley bore and the shaft. It solves your motor shaft question. Neat concept - price - about the same as a pulley or even more - can easily hit $ 30 - 50 / each.

McMastercarr.com and econobelt sell them - I am sure many others as well - and there are a variety of configurations.

It seems like this is a key component of belt drive based systems that cannot be easily done without. If the axis (say a gantry) is driven by two belts they need to be aligned and pre-tensioned. In order to do this, sometimes one pulley must freely rotate relative to the shaft and the other pulley. In a key based system this is not possible, and trying to do this with a setscrew into hardened shaft (and holding the location during use) seems nearly impossible.

The tapered bushings seem like one of the few options out there for this.

What is your take on the pulley mounting aspect and shaft diameters ?

I found the calculator with a search engine (dogpile in my case) just typing in "deflection calculator" in case anyone is interested.

[harryn]

BTW - I am kind of following the animation from yneb in post 17 of this thread.

http://cnczone.com/forums/showthread...858#post532858