New build - Core not level

Mostly Printed CNC - MPCNC Troubleshooting
1

Hi all,

I’m new here, having just finished my Primo build after starting it 12 months ago. Also have a bunch of DIY 3D printers and a 3018CNC that I’m trying to make a bit more rigid, but that’s out of this scope, just for background that I have some mechanical aptitude.

Issue: The Core currently leans towards the front, such that a 16mm mill requires about 0.8mm from first contact with the work surface to contacting its other edge.

With NO Core clamps in place, and the core held against the X-Y junction (where it would be clamped) it doesn’t quite sit right. Whilst the rail-groove will site nicely against the left-right gantry tube, the front-back tube isn’t quite aligned, so when the clamps are added, it pulls the core down to the front.

To test this out, I used a ‘saw drill bit’ saw_bit (see photos) to carve the front core clamp holes a little further down and this managed to get the core pretty much plumb, but installing the rear clamp then pulled it out again. It looks to me like either the two gantry rails are too close together vertically or one side of the core sides has the rail and/or clamp holes too high.

I know a few users have reported their core not fitting well and I’ve read through a bunch but not found a solution that works on my setup. All axes are level otherwise.

Other measurements (25.4mm OD tube):
Top of top tube to bottom of bottom tube: 52.4mm
Gap between tubes: 1.6mm
Distance between tube centres: 27mm
X&Y rails are ~540mm of exposed tube, between mounts.

Parts were all printed by me and seem to be to spec (the core height measures within 0.2mm of what I measured in the STL, once imported into FreeCAD). Printed using J build downloaded in August last year, VER1 editions of Core and clamps - same files as currently on Thingiverse.
Tube is 25.4mm galvanised, measured close-enough to round to not make this difference and tested at different rotations.
Bolts bought from a local supplier through eBay - straight section of shank measures 7.8mm
Bearings as above - measurement of exterior and internal bore are to the published spec for 2RS bearings.

For now I’m just going to drill-out the other holes to try to level it.

Thanks for any suggestions,

Simon

IMG_9063
IMG_90633024×4032 2.45 MB

IMG_9064
IMG_90643024×4032 2.14 MB

IMG_9065
IMG_90653024×4032 2 MB

IMG_9066
IMG_90663024×4032 2.37 MB

IMG_9067
IMG_90673024×4032 2.16 MB

2

Right off the bat I can point out that on the z-axis, the lower bearing mount is way too low:

IMG_9063~2
IMG_9063~22038×2833 1.01 MB

That part should be all the way up against the motor coupler, and that coupler should not be stretched out like that.
I’d fix that first.

2 Likes
3

Thanks Cobalt - I was planning to build higher, so left it sitting low for what I thought would be more rigidity. Will move it after I fix a couple of other things that came up. Looks like at least a couple of the frame rails have been damaged, either pre-purchase, or maybe during cutting to length, so just got some new tube to see if I can smooth travel out.

And need to add my thanks to Ryan for the design - so much flexibility for use.

4

Also, since posting I’ve shimmed the X gantry rail (the higher of the two movable rails) with about 1mm of folded paper. This has now brought the Core to level. Still working on the Z axis too.

5

What part exactly did you shim? Where did you put the folded paper? It shouldn’t need that at all. If your core is leaning, something is either broken, loose, or an incorrect size.

6

The shims are under the tube as it goes through the X-axis trucks. The tube just doesn’t seem to be high enough above the y-axis tube to get the core to sit level. I’ve checked height of both X frame rails and they’re even.

7

That sounds like the feet and/or the tubes connecting the feet to the corners aren’t right.
I would check:

  1. Flatness of the table or surface the feet are screwed down to
  2. Height of each foot to make sure they are equal
  3. Height of each corner

The parts can very well be uneven. Its always best to measure each foot just to make sure and eliminate it as a problem.
The tubes that connect the feet to the corner pieces can slide up and down when installing to make the whole unit level. If you don’t press the feet and corners on all the way (in order to level the base), they can slip down if not tightened enough. Even when tightened, a good hard hit to the top of a corner can shift the tube. Again, that’s assuming the tube isn’t bottomed out on both ends into the feet/corners.
Also check to see if any of the tubes are bent. Lay them on a flat surface and roll them to see if they wobble.
Ultimately, you want to make sure the four corners are exactly the same height. You can also move the router around the milling area and see if the distance from your endmill / bit to the table is consistent all around. That may give you an idea for which corner is higher/lower.

8

The corners have all been set and measured at the same height. The issues doesn’t seem to be a lack of uniform height, it’s the difference in height between X & Y which leg height doesn’t alter. I’m trying to tidy some other bits, so hopefully all will come together with some finesse.