My desktop cnc router

[fahque99]

I have just finished the first basic design of my cnc machine and made a few parts and I was looking for some feedback on the design.
It will use 5/8 cold rolled rails with bronze bushings and the rest is MDF.
It will be running a 5 amp trim router.

I just want to cut wood, plastic, and PCB's

[lumberjack_jeff]

That looks cool. I would suggest wrapping the gantry underneath the machine as well if it isn't already.

If you do that, I suspect you could get by with one x-axis stepper.

[FandZ]

Why not beef it up to 1/2 rails and bushings? I haven't checked prices but I wouldn't imagine it would be much more. Also, how do you plan to join your corners?

[fahque99]

There is a bottom plate, but I still want to use 2 steppers to stop racking.

5/8 is bigger then 1/2

[fahque99]

Corners will be partical board screws and glue, or brad nails and glue.

[FandZ]

Originally Posted by fahque99 There is a bottom plate, but I still want to use 2 steppers to stop racking. 5/8 is bigger then 1/2

LMFAO.... You got me there. haha I was just drawing up some circles in cad they were 5/16. DOn't know how I transposed those.

[lumberjack_jeff]

Originally Posted by fahque99 There is a bottom plate, but I still want to use 2 steppers to stop racking.

My 4x8 table has two steppers, and it doesn't eliminate a small amount of racking. Have you considered the under-the-table crossed-cable racking prevention setup?

http://www.cnczone.com/forums/showth...racking+cables

[samco]

That doesn't makes sense.. A stepper on each side should stop racking.. Is it backlash?

sam

Originally Posted by lumberjack_jeff My 4x8 table has two steppers, and it doesn't eliminate a small amount of racking. Have you considered the under-the-table crossed-cable racking prevention setup?

[lumberjack_jeff]

Each stepper is driven by an individual driver. In my experience, the dual x-steppers do not always lose steps simultaneously. First one stepper will miss steps, then the gantry will rack slightly and the misalignment will increase the forces seen by the other and it will lose steps. When the program is restarted, the gantry must be realigned.

IMHO, a gantry which is light enough to be driven by one stepper, *should* be driven by one stepper, and not just for cost reasons. I have considered installing a cable system similar to the one linked above to prevent racking and equalize forces, but my gantry design doesn't lend itself to that solution very well.

[FandZ]

Originally Posted by lumberjack_jeff Each stepper is driven by an individual driver. In my experience, the dual x-steppers do not always lose steps simultaneously. First one stepper will miss steps, then the gantry will rack slightly and the misalignment will increase the forces seen by the other and it will lose steps. When the program is restarted, the gantry must be realigned. IMHO, a gantry which is light enough to be driven by one stepper, *should* be driven by one stepper, and not just for cost reasons. I have considered installing a cable system similar to the one linked above to prevent racking and equalize forces, but my gantry design doesn't lend itself to that solution very well.

Jeff, I've read that opinion before but the way I see it, whether it's left or right, If your running your machine past it's capability your going to miss steps. 2 or 1 stepper isn't going to make a difference if you are cutting faster than your machine can go. It's just a lot easier to tell when you hit a performance wall with a 1 stepper driven axis but it's not because you are useing 2 steppers rather than 1.

That said, I'm useing just one stepper on my X axis and can't complain.

[lumberjack_jeff]

Originally Posted by FandZ Jeff, I've read that opinion before but the way I see it, whether it's left or right, If your running your machine past it's capability your going to miss steps. 2 or 1 stepper isn't going to make a difference if you are cutting faster than your machine can go. It's just a lot easier to tell when you hit a performance wall with a 1 stepper driven axis but it's not because you are useing 2 steppers rather than 1. That said, I'm useing just one stepper on my X axis and can't complain.

When I miss steps on my Y axis, I simply need to re-zero and move on. When I miss steps on my X axis, because those missed steps probably caused a crooked gantry, the problem is somewhat worse.

If I had a smaller machine, I'd prefer a single X stepper like yours.

[fahque99]

So it looks like I should be using 2 home switches on the X axis (one for the X motor and one for the W)