Gantry with two different size motors on X-axis

Here is a video of the cutter in action.

The frame it self is nice and rock solid, the problem occurs with the free end of the X-axis. And now we are talking about some minor wobbling back and forth during the axis movement.

Single-sided should be OK for a Plasma, I would have thought.

I assume your bearing span is as wide as possible on the driven end?

If things are wobbling it must be due to inertia forces, you might be able to use lower acceleration to reduce this, though the trade-off might not be worth it.

Maybe you misunderstood my drawing, the cables move with the gantry keeping it square. The red and green cables are in tension with each other, with their ends attached to opposite corners of the gantry, then looped over pulleys rigidly mounted to the frame (the red and green circles) . When the gantry moves to the right, the red cable pulls the undriven end of the gantry to the right, when the gantry moves to the left, the green pulls the undriven end to the left. The only real trick is mounting the mess under the table so it's out of the way.

Todd Zuercher wrote: Maybe you misunderstood my drawing, the cables move with the gantry keeping it square. The red and green cables are in tension with each other, with their ends attached to opposite corners of the gantry, then looped over pulleys rigidly mounted to the frame (the red and green circles) . When the gantry moves to the right, the red cable pulls the undriven end of the gantry to the right, when the gantry moves to the left, the green pulls the undriven end to the left. The only real trick is mounting the mess under the table so it's out of the way.

It was one system used with old-school drawing boards.

There were other systems used that might be worth considering too.

That's it, I knew I'd seen that before somewhere, just couldn't remember on what.

Have a look after the 40 second mark, you can see the steel cable move in the background. That machine was used for 5 months every day all day for cutting the pattern on the video. It had one big motor driving the X axis through a ball screw and wired to the other side of X axis with still wire and ball bearings. It did have a bit of wobble when pushing it over 5 m/minute but otherwise was usable.
Regards,
Tom

As used in parallel straightedge ...

www.rexart.com/media/alvin_1101_2201_instructions.pdf

Rick G

Thank you for the suggestions and tips!

After all I have decided to replace the inlineskate wheel with a belt and pulley. This way I'll get an identical gear ratio and I'll be able to run the secondary motor with the same settings as the primary one. I'll use only one home switch for the axis.

I'll update some photos and video here when I get the machine running again.

kemes wrote: After all I have decided to replace the inlineskate wheel with a belt and pulley. This way I'll get an identical gear ratio and I'll be able to run the secondary motor with the same settings as the primary one.

There is no need for it to be 100% identical as long as it is a positvely-engaged drive. The problem with the skate wheel is not the different ratio but the indeterminate gear ratio and tendency to creep over time.

andypugh, I did understand your point about the creep issue. I'm aiming for a simple configuration and to my understanding a similar gear ratio across the axis is a good thing Thank you for your comments!