[3Dsigns]

As much a possible, I am trying to use stuff I already have to build a CNC milling machine. I have a substantial supply of used 80/20 aluminum including a 50" piece of 3060 for a gantry. I also have a bunch of #40 chain.
How accurate could a chain drive be for a milling machine?

[RICHARD ZASTROW]

80/20 router maybe. Pretty light duty for a real milling machine. What do you want to drive with the chain?

Dick Z

[whateg01]

I don't think I would expect great accuracy with a chain. I'm using a belt on my CNC plasma table, and had thought of using a chain. For something that you don't need a great deal of accuracy on, I think it would be fine. In fact, there appear to be quite a few tables built with it. But for a router or mill, I think it would be difficult to get rid of all the backlash.

Just my 1.9¢.

Dave

[3Dsigns]

Thanks guys!

[Trotline]

Not sure what accuracy you want, but chain drives are out there, and do work. Just like most mechanisms, they need to be properly adjusted to perform up to their potential. Took this pic today, on a machine with a chain driven X axis.


Luke

[3Dsigns]

nice!

[PaulRowntree]

I have chains on X and Y. I think that the accuracy is OK, backlash under control. But the surface finish can show ridges which I believe is due to the cogging effect.

If you do go for chains with a common axle driving both sides of the gantry, I would recommend using a stout shaft (0.5") and support it well at several points between the two drive gears. A reduction (2:1, 3:1) stage would probably be in order as well, especially if you have to go to larger drive gears with the larger shaft. Making sure the two sides of the gantry were 'in-phase' was an issue for my build, so being able to translate the chains relative to the table was important.

Cheers!

[3Dsigns]

Thanks!

[louieatienza]

For routing wood, fine but not ideal. For milling, I assume soft metals, probably not so great.

[harryn]

3D, just MHO, but perhaps it makes sense to start a build thread under the cnc wood router thread and put your questions in the thread ? That way, they are all in one place and easy for people to follow along as you develop the ideas and start building.

Don't worry about asking questions in a build thread - everyone does it, and we are happy to give opinions.

[rbraeking]

Roller chain drive is the least expensive way to transfer the rotary power of the motor to linear motion. Some considerations are sag and manufacturing variations in the individual links of the chain. Chain can also be stretched which would ruin its accuracy. The smaller the pitch of the chain the more accuracy you can achieve. Also the drive sprocket should be large as practical to maximize contact area between the sprocket and chain rollers. My machine is chain drive in both the x and y axis with acceptable accuracy for wood routing.

[PaulRowntree]

Also the drive sprocket should be large as practical to maximize contact area between the sprocket and chain rollers.

Do you use a gear reduction? What ratio?

[rbraeking]

I am using #25 chain which is 0.250 from roller to roller. I drive a 10 tooth sprocket directly from the stepper motor. That gives me 10/4 inches movement per revolution. (2.5 inches) Since steppers prefer to run slowly the system is well suited to the motors. I did have to do some gear reduction on the y axis as I have not yet changed to a more powerful motor. The reduction is a simple jack shaft arrangement with small sprocket on motor driving a larger sprocket on jack shaft which is keyed to a small sprocket that moves the machine. I'm guessing but I believe the reduction is in the order of 3:1. The chains must be tensioned well to minimize backlash.

One caveat with a roller chain system is that chain is not manufactured to as tight of tolerances as rack/pinions or ball screws but it is close enough for a wood router. For a metal mill it would not be strong enough or accurate enough.

The advantage of chain is that it does not whip like a screw. My x axis is 120 inches and my y axis is 52 inches. Any screw or rack/pinion drive that large is way out of my league price wise.