Joe's 1000x600x200 steel and aluminium router started

[Nealieboyee]

I would either bolt down some thinnish alu plate on each member and then skim them all level, or pour more epoxy on the members so they self level. But that means making a framework for the epoxy to travel between members.

[Kitwn]

Epoxy sounds a bit too complicated for something so simple and you'd have to confirm the frame was adjusted to make the plane of the rails orthogonal to local gravity or it becomes pointless.
I'd go with the shim and skim. That cannot fail to put the plane of the base parallel in all directions to the plane which the spindle moves which is what you really want and will minimise the thickness of material you need to skim off the final, sacrificial surface.

[Clive S]

I took the a rough height map with a DTI clamped to the Z. As expected from bringing the rails into plane with laser and epoxy I have around 1-1.5mm total error (this was the frame error before pouring epoxy). The cross members of the frame are also not perfectly in plane and would require a little shimming under the bed.

I'd rather have the bed closer to planar that this, although the eventual spoil board skimming will fix it, so I'm contemplating attaching some shimming material to the cross members and surfacing this then bolting the bed plate down on top.

Out of interest did you put a moat across the two rails when you poured it?

[JAZZCNC]

I would use epoxy metal paste. Use levelling grub screws in the bed and adjust until planer, then remove and skim all the surfaces with a lite coating of epoxy putty then put plate back on and tweak it out any error from lifting etc.
Tape the bed where it meets the epoxy and when dry you will be able to remove bed.

[JAZZCNC]

I'd go with the shim and skim. That cannot fail to put the plane of the base parallel in all directions to the plane which the spindle moves which is what you really want and will minimise the thickness of material you need to skim off the final, sacrificial surface.

It's not possible to skim the whole surface using the machine because plate is the full size of the base so cannot skim the portion under the gantry.!! Only way this could work is if the plate was the actual cutting size.

[Kitwn]

It's not possible to skim the whole surface using the machine because plate is the full size of the base so cannot skim the portion under the gantry.!! Only way this could work is if the plate was the actual cutting size.

Obvious when you point it out!

I like the grub screws and epoxy putty idea, but might it be better to use ordinary bolts instead? It would mean a slightly thicker layer of putty but it would allow you to adjust each bolt with an open spanner while the gauge is on it's head rather than have to measure, move the gantry away to adjust, move it back to measure, move it away to adjust again etc.

[JAZZCNC]

I like the grub screws and epoxy putty idea, but might it be better to use ordinary bolts instead? It would mean a slightly thicker layer of putty but it would allow you to adjust each bolt with an open spanner while the gauge is on it's head rather than have to measure, move the gantry away to adjust, move it back to measure, move it away to adjust again etc.

No point really and you want to be measuring off the bed not the bolt head. A M3 or M4 socket cap grub screw is easily adjusted thru the hole and is small enough not affect the bed too much.

There are several ways to do the same thing and it depends on how your planning on using the bed regards fixtures etc. The main point was Epoxy putty works good for this application, it could easily be car body filler(Bondo to you upside downers) if your on a budget...Lol

[Kitwn]

I was thinking the grub screws would be in the frame, not holes drilled in the base board. Slowly but surely the lights come on.

[devmonkey]

Thanks for the ideas guys. I went ahead and epoxied some 2" x 1/8th aluminium strip to the 3 cross members that are machinable from the gantry. There is around 60mm outside each of these which will be shimmed manually. The rear cross member cannot be machined as it is under/behind the gantry as Jazz says, so this will get manually shimmed as well. Quite easy to do with a DTI n the Z as 90% of the bed plate is supported by the milled strips,



So the exciting bit was getting the machine to machine itself, first time it has cut anything:


Finish was superb for chewing gum grade aluminium, thickness of thinnest final shim is ~1mm.



I used an 8mm 2 flute carbide bit, there is no scalloping which means the head is in pretty good tram (I can't tram it until the bed is on). I ran the tool path twice, initially to bring all 3 strips down to height then dropped the Z 0.1mm for a finish pass.

[devmonkey]

Out of interest did you put a moat across the two rails when you poured it?

Hi Clive, yes there was a moat, I put it outside of the frame at one end. The rails are planar within 10um, I checked them with my laser software. Or at least they were when I fitted them, they have probably drifted a bit as I've hoisted the machine around the shop a couple of times since then. I will recheck them at some point.

I didn't post anything about how I did the pour but there are two important points I'd like to pass on to get the best result,

1. As per Boyan's findings the moat should be outside the frame, close to the same cross section as the rail support epoxy and the pour should extend beyond both ends.
2. You must use non-absorbent material for the moat and dams, anything else and non-linear capillary action into the material will mess things up. I used 10mm pvc angle for the dams and pvc trunking for the moat. The dams were stuck to the frame with thin toffee tape which worked well (didn't leak) but was a pain to get off.