Brainstorming big machine with the option to make it smaller and more rigid

Mostly Printed CNC - MPCNC Advice
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Thank you all for the help so far. Now that my mpcnc is up and running I understand a lot of the nuances better.

I am seriously considering raising up my mpcnc and doing a most of my work on a 4 inch spoil board. When I make new knife handles I cut a tang hole in the top of a 6 inch handle. It would be great to use the mpcnc. It could save time!

Next I was thinking about bigger CNCs and how I would love a second one for big stock. And a smaller one for roughing out metal parts.

What if you could have a second -adjustable X max and y max axis on some sort of quick release for readjustment. I can’t yet tell if this is a great idea or the product of sleep deprivation (I can blame toddlers…

  1. rollers mounts without motors would attach to the outer XY rails. Quick release clamps can ge added.

  2. a second XYZ gantry can be used at this rigidifying adjustabile intersection. The Z can be an adjustable foot down to the spoilboard.

After I get through my 3 month workshop backlog, I may implement this.

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I can see how that would provide support in the Z direction, but it wouldn’t stop the X and Y rails (fixed and moving) from bending horizontally - and that’s (possibly) the bigger problem.

Also, you’ve pretty much built a second machine. At that point you might as well build a small, rigid MPCNC and a low-rider for the big stuff, which a lot of people seem to have done.

The law of diminishing returns is a harsh mistress.

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I think we have all seen that there is a magic efficiency to the mpcnc. It fits in a pocket of not too much, but more than enough. Which makes it hard to easily get more bang for your plastic.

However. It is also a base for some awesome modifications. There are a bunch of huge changes people have made that have worked. Even if they weren’t the most efficient, they are enjoyable.

Here’s what I think. You could put two more pipes across. You make a new foot where they crossed, that attached to the spoil board. You make two new feet that are part of the “rollers” under the close ends, and also attach to the spoil board. Say the full size is 48"x48". If the smaller area was 12"x12", you would have a lot less error in Z, because the pipes would be supported nearby. I am not sure about the XY flex. The far motor is still 36"+ away. The pipe connecting it has to be able to move, so it can still flex. I think this is what Robin is saying. That will be your biggest trouble.

I have also thought about an mpcnc where the pipes just stick out the ends of the feet and rollers. If you imagine a 12" mpcnc, eith 36" of extra pipe sticking out, it would work a lot like a 12" MPCNC. IIRC, Aaryn did something like this. The downside is, it would take a lot of screws, and readjusting the belts to move it. After doing it once or twice, I would day dream about a low rider.

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Have you considered just putting a hole in your table to accommodate cutting the tang hole? Rather than raise the machine, lower the workpiece?

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As far as the vertical, I still have to clamp a 6 inch knife handle.

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I think the idea would work. But I agree with Jeff. Don’t bother with rollers and another z axis. Just use normal corners and feet. It will be more rigid that way. You may want to consider a modded version of the corner pieces that are easier to tighten and remove without risk of cracking. I would love to see test results. I had the same idea but haven’t implemented it yet.

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Sounds like a drop table is what you need, honestly. Something like this Drop Table Plywood Construction with a series of holes in the center cutout section that supports attach so so you can lower the middle when needed.