Moving Knot vs. Shaft

I'm sorry if this has been addressed before, but the forum is waaaaaayyy too deep to search is such a short time!

Basically, I have a 4 ft. gantry, chain driven by two slaved motors, one on each side. I still have some amount of racking with this setup and it is driving me stupid!

I am familiar with the moving knot cable system, but the structure of my machine makes it a bit difficult to implement, but not impossible. Another thought I had was that I could couple the two sides together with a shaft. My motors are single ended, so I couldn't do it there, but if I added a shaft with a sprocket on each end and rode the chain over them, it would force them to move together. And this would be the easier of the two options to implement.

Are there any draw backs to the shaft option where the knot cable would be better?

Thanks.

You shouldn't need to use either, when using slaved motors to move a gantry.
Either your chains have a lot of slack, or one of your motors is stalling.

Even if you physically link the two motors together, whatever is causing the stalling is still going to be there. But instead of racking, you'll just lose position. Either way, the usability of the machine probably won't improve much.

First, make sure you're chains don't have any play or backlash. With the machine still, pushing very hard on either side of the gantry should result in zero movement.

If it's not moving, then the issue is with the motors, drives, power supply, or possibly the gearing.

Can you list all the components you're using, and what kind of machine this is?

Are you direct driving the chain, or are you using a reduction?

Servo's or steppers?
Al.

These are steppers. And when I say the motors are slaved perhaps I should clarify that only one axis driver drives both motors, one through a MOSFET circuit connected to the driver output.

The gantry is made of 3/4" square tubing with steel angle for rails allowing the Z-axis to slide along it. V-groove bearings throughout. Originally the same motors and drivers moved a wooden machines quite easily. But the amount of slop from the wood inspired me to construct it out of steel.

Now I have quite a bit of chatter. It won't accurately cut the same design twice in the same spot. From the looks of the cuts, it is losing position in the Y direction, and I can't pin point why. One of my theories is the greater gantry width is allowing just a tiny bit of racking to drop one side behind the other. If I could mechanically couple the two sides, it may force them into sync, but alas, I'm a novice.

Thanks for any insights you guys have.