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Pattern tool to adjust Z-Depth

Just came across this video
uneven surface and probe for more accurate Z-depth
While this could be perfect for a gantry cnc machine, depending on the sled diameter of the Maslow, I think this could be interesting for all that have a slightly warped spoil-borad and sheet. Thoughts?

Interesting. Warped plywood is common, and it is why we designed the www.metalmaslow.com with the smallest sled diameter of 12" vs 18". Our sled is 65% smaller than the default and therefore able to handle warped surfaces better. Added bonus of smaller more dense sled is can cut a few inches closer to the edges and is easier to handle.
New sled we are getting read to ship out is less than 15" diameter which is about 30% smaller than default sled.

even with the large sled you can cut very close to the edge, if your chains are
at the right height on the sled, you can get within an inch or two so of the
edge even with a 18" sled

a smaller sled has the problem that it will fall into a smaller pocket/hole in
your workpiece.

David Lang

most people have tabs hold in pieces, so there are no holes for the sled to fall into. on the top edge one can get much closer with a smaller sled vs a larger sled which requires a skirt around the top to prevent tipping and ruined cuts.

Maybe it is my sled balance, but I can cut all the way to the top of the sheet, but it will tip on the bottom. It sounds like a sled center of gravity issue, not a sled footprint issue.

if you are just doing 2d cuts, that is correct, but if you do pockets, you are
more likely to run into problems.

not disparaging your product, just noting the trade-off and disagreeing that you
need a small sled to get close to the edge

David Lang

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correct some people have issues with sled tipping at top, others at bottom, depends on how it is weighted. best to use a skirt regardless of sled size

there are two things

  1. the CG in the x/y plane.
    This is what’s causing you to tip at the bottom (the
    same weight distribution that keeps the sled from rotating has more weight below
    the motor so it will tip when you get close to the bottom, an adjustable skirt
    on the bottom of the machine will solve this)

  2. the CG in the Z axis (aka ring height)
    If this is too low, as you get more tension on the chains (along the top) and
    the chains get shorter (top corners), the chains pull the sled away from the
    workpiece.
    If this is too high, as you get close to the sides, the chain is trying to tip
    it over and you can’t get as close to the edge
    If this is perfect, you can cut very close to the edge.

on the bottom you need 6-8 inches of support below the bottom of your cut, on
the sides, you can get by with just a couple inches of support, unless your
chains/ring are far too high.

David Lang

depends on if it is cutting with a 1/4" bit that is 3" long vs a 2" long 1/8" bit the behavior is different because the hitachi router is much heavier and its location determines the center of gravity. I merely pointed out that the behavior may not be from a smaller vs larger sled, but from how it is balanced and its center of gravity as mentioned.

@Metalmaslow Your approach with a metal sled is the best I’ve seen so far. However it also depends on how flat you can keep your ‘Z-Tower’. I’ve spent days on testing distributing weight with double sided tape. Why is my z-motor down and not on top? Why are my weights flat as possible? Why do I have a ‘pendulum weight’ at the bottom (not because I can’t deal with rotation, my spindle is centred ~`0.2mm’) , because rotation can bring me in the limits of the chain-mount. If you draw a line with your sled at the top of the sheet (between the chain-mounts), it will be close to the centre. At the bottom it will be close to top of your sled. My opinion is that we have a moving centre of gravity, depending on how high we are on the sheet. I could not eliminate the tipping, but with motors adjustable to the thickens of the sheet, distributed weight, and light weight sled with the shortest c-beam possible and the z-motor down, I got close to have little tipping at the top and bottom. If I had your metal sled with my setup, I guess I would have no tipping.


Edit: This is what I started with when we had fixed chain-mounts

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