Snapped my Z-axis belt

(Rick Miller) #1

I was having issues with the z-axis losing registration while milling a part. Finally tracked it down to a spot on the belt that was worn. When that part of the belt reached the drive gear it would slip. I removed the z-axis plate and moved the belt around to get that worn part away from the drive wheel. When I re-assembled it I over tightened the belt and it snapped almost immediately right at that worn point as soon as I moved the z-axis. Unfortunately Carbide does not sell the belts separately. I found them on Amazon. I could have gotten 2 for $15 plus shipping or 10 for $25 with Prime free shipping so going for the set of 10. I guess I’ll have a ton of spares. If you’re looking for spares, the z-axis belt appears to be a 520-2GT-6. At least that’s what is marked on the belt. I hope these fit.

I suspect the issue started with the z-axis being driven to the top physical limits but the stepper continued to run. That was occurring after setting the z origin with a probe. The g-code switches the units from mm to inches and when I raised the bit I absently hit up 3 or 4 times which is fine if the units is mm but way too much when it’s moving an inch at a time. What would fix this is if the firmware would notice that the axis is already against the limit and stop the stepper from any further upward movement. Maybe even back it off a couple of mm. The same could be done for the x and y axis. A step further would be to add limit switches to the other ends of the x and y axis to stop movement in those directions as well if you hit the physical limits. Not much that you can do about the down side of the z-axis since your bit would likely hit something before the plate got the bottom of the z axis. They would probably need something like a closed loop servo to handle that.

(ray) #2

My 10 belts from amazon will be here tomorrow :grin:
My belt broke last thurs.

(Winston) #3

You could probably get close by a combination of setting the correct soft limits, and enabling hard limits.

(Rick Miller) #4

I take it that the hard limits are the limit switches and the soft limits are the other end without switches?

(Winston) #5

Hard limits kill power when a physical switch is triggered (i.e. when you basically crash the machine). Soft limits stop the machine when it calculates that it’s about to reach the end of its travel. Hard limits cause you to lose homing, soft limits usually allow you to back off and reassess. Generally safer, especially since hard limits won’t automatically turn off your router.

(Carl Hilinski) #6

If you have an S03, I think you want the 9mm belts. I believe Carbide upgraded from sixes to nines.

(Rick Miller) #7

The x and y belts are 9mm but the z belt is a 6mm belt.

(Carl Hilinski) #8

Thank you. I didn’t know that they were different. I bought a roll of 9mm to have on hand in case of a crisis, but I didn’t get any z belts. It’s off to the e-store now.

(Rick Miller) #9

The x and y are open belts but the z-axis is a closed loop.

(Rick Miller) #10

The belts I ordered from Amazon are working fine. Just installed one and was able to complete a piece that has been clamped to my table since Sunday when the original belt snapped. Too early to say how durable these are but for now I’m back in action.

(Mel Clench) #11

Found this online for $0.90

(William Adams) #12

The wiki lists some sources:

(Nick) #13

Is there any way to buy just a z axis belt strait from you guys without buying the whole maintenance kit?

(William Adams) #14

Not ordinarily. We’re a small shop and are trying to keep costs down by reducing our number of SKUs. If your machine is still under warranty let us know and we’ll gladly send you one.

The community has notes on parts availability at:

I had good luck ordering from SDP/SI:

If you can’t find a suitable source, let us know at and we’ll see what we can work out.

(Nick) #15

I got the ten pack from amazon and it works well