So from what I learn sprockets are not precise. So I made a plan. On the Lathe I drilled a hole that is slightly smaller than the diameter of the gear into a peace of aluminum. Turned the shoulder down till it was centered. After that I put the sprockets into the chuck and made the pilot hole bigger. Now they are within 0.1 mm I think that is acceptable.
Creative25 wrote: I just had a rude surprise. The sprockets non precision surprises me. Both the shoulder and pilot hole of the sprocket are at least 1mm off center, compared to the teeth.
I think that you should expect better than that. In fact you should send the parts back for a refund.
Sprockets should be perfectly concentric, they can't work properly otherwise.
If I was making a plasma machine it would be a core-xy bicycle chain machine. Probably.
Yes you actually have to send them
Back. I bought them locally and they had to order them so I decided to rather fix them.
I also have some cam pulleys I got from AliExpress these are also one mm off. Have to fix them as well and make a bigger shaft. If I knew I would have ordered with a smaller bore.
Just saying what does it help to use linear bearings if your pulleys are off center.
With todays engineering capability even cheap sprockets should be pretty close to having their bores concentric with the teeth. 1mm is hugely out of tolerance.
I made my table with chain (on the cheap) but wouldn't do it again. Next time I'll be going with heavy duty non-stretch synchronous belt. My chains are horizontally suspended and with a table size of 2500 x 1500, even with tight chains, you get lots of chain bouncing and that transfers to the cut. It would be better if the chains can be laid along a flat surface and they wrap around a drive sprocket on the gantry. That would eliminate chain bounce.
One other issue though may be chain wear (stretch as many call it). If you cut more in one section of the table than others the chain wear will be more in that area and you won't get linear travel any more. It's a bit like a toothed rack "stretching" in length at a certain section. I'm a mechanical fitter and it's quite surprising how much length change you get when a chain starts wearing. Not a massive issue for transmission purposes but may be for accuracy on a long CNC table.
Another issue is keeping the chains lubricated. You oil chains and oil helps plasma dust stick to it. Belts are dry and if you install a belt with the teeth facing down, resting on a flat surface, and wrapping around a sprocket on the gantry, I think you've got the best of all worlds. The main thing will be to get a belt/pulley type that has zero or very little backlash, as the drive pulley reverses direction.
I agree with you with today’s technology. It Needs a lot of stupidity for making pulleys and sprockets 1 mm out of center.
But still half of my sprockets were out by 1mm.
Maybe for some people the definition of a cam pulleys is A pulley where the pilot hole is not in the center.
As far as chain goes I m planning to do exactly what you suggested. Will post some pictures when I get there.
Just wonder about chain wear if it is the same as on a dirt bike. Worst case I got driving in dirt roads with lots of dust.
I got 3000km day with plasma you want to change it earlier so say 1000km
That is 10000000 meters how long does it take for the Gantry to travel this far?
