Joe's 1000x600x200 steel and aluminium router started

[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?

[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.

[Clive S]

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.

I actually don't agree with the above. I used two moats about a third from each end. But what is a must, the epoxy must be wide enough to all for the mucus (or whatever you call it) on each side and use the very slow epoxy.

[devmonkey]

I actually don't agree with the above. I used two moats about a third from each end. But what is a must, the epoxy must be wide enough to all for the mucus (or whatever you call it) on each side and use the very slow epoxy.

I guess whatever works for you.

I did some tests under the microscope before I did the actual pour, the epoxy shrinkage phase occurs after it has setup too much to freely flow and find level, this (as Boyan determined) is what causes dips around dam ends and bridge joins. I used West's 105/209 and the shrinkage phase starts after about 1 hour by which time it is getting too viscous to re-level itself. The way I saw it is the bridge is only effective before the shrinkage starts and after it starts you want the area x-section of the epoxy you want to keep to be as consistent as possible meaning you have to extend it past the ends of the machine and you want the bridge to be connected to a part you don't want to keep as it either it will pull from the sides or the sides will pull from it. Either way it doesn't matter as you are going to cut this bit off.

The microscope method was stolen from the "Dam Busters" use of angled lights on the wing tips to determine they were the correct height above the water to drop their bombs. You point a laser pointer at an angle to the surface, focus the microscope directly down onto the point where the laser hits the surface and as the surface height changes the dot will move, magic ;-)