Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

Time to fix the bed down. I want to finalise the work holding at the same time. I have a few choices,

1. Drill and tap a grid of holes in the plate and bring these holes up through the spoil board,
2. Just drill and tap the spoil board (pvc foam) creating blind holes.
3. Cut t-slots into the plate and create narrow planks of spoil board between them (I would need to get a special bit to cut the t-slot),
4. Create t-slots from planks of spoil board, not sure how strong they will be.

T-slots are probably more work but less tapping, what do people think?

[JAZZCNC]

I'd go with a mixture of T-Slot Track in the Spoil board around the outer edges and a matrix of Tapped holes.
The T-slot allows quick and easy clamping of large pieces.
The Matrix of holes allows you to clamp small parts easily and just about any where on the bed and nearly always means you can find a place on your part to clamp.

The pain of tapping all those holes is worth the effort IME.!! . . .

[devmonkey]

Cool, any suggestion on the pitch of the matrix? I was thinking 150mm to limit the tapping...

Also would you tap the bed or the spoil board?

[JAZZCNC]

Cool, any suggestion on the pitch of the matrix? I was thinking 150mm to limit the tapping...

Also would you tap the bed or the spoil board?

No 150mm is way too big, 75mm would be max I'd go with, 50mm better. Don't be put off by the tapping, the thought of it is worse than the doing. Plus you don't have to tap every hole straight away, could even just tap every other hole and use the others for dowel pins for fixture guides etc. This is where a matrix really comes into it's own because it's very flexible.

Tap the Bed not the spoil board. You'll be cutting into the spoil board and slowly surfacing it away.

[Kitwn]

I have M8 tee nuts in the underside of my plywood baseboard with a drilled MDF spoilboard on top but I doubt you will allow anything so porous or flexible onto your machine. My spacing is 100mm and it's definitely too large.

One thing to consider is making the effort to get the holes on exact multiples of 50 or 75mm from your zero reference in both X and Y. You probably will drill them here anyway but this makes it easier to plan the layout of a job if you want to drill fixing holes in the workpiece, dedicated spoilboard or a jig. I say this because I made the mistake of drilling the holes, fitting the tee-nuts and then turning the board over to screw it down which means the grid is not as perfectly aligned as I would wish. We live and learn, it'll get fixed one day.

[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 have M8 tee nuts in the underside of my plywood baseboard with a drilled MDF spoilboard on top but I doubt you will allow anything so porous or flexible onto your machine. My spacing is 100mm and it's definitely too large.

One thing to consider is making the effort to get the holes on exact multiples of 50 or 75mm from your zero reference in both X and Y. You probably will drill them here anyway but this makes it easier to plan the layout of a job if you want to drill fixing holes in the workpiece, dedicated spoilboard or a jig. I say this because I made the mistake of drilling the holes, fitting the tee-nuts and then turning the board over to screw it down which means the grid is not as perfectly aligned as I would wish. We live and learn, it'll get fixed one day.

I was going to drill the fixture holes before finally fitting the bed, but I agree it is better to do it afterwards once the machine is properly aligned. I haven't squared the gantry yet, nor properly defined zero. Will get the bed fixed to the frame in its final location, clamp on a sheet of MDF on top to square the gantry, define zero then finally drill the fixture holes.

I'm also toying with the idea of redefining my long axis as Y and the gantry axis as X so it lines up with the natural way of looking at it from the front and the axis orientations match the DDCS buttons, otherwise I'm going to make a mistake. I would define zero as front left.

I have drilled and tapped the bed and frame, and bolted to the locations where I had fixed and milled the aluminium strip. Reads within +/- 0.01mm everywhere in this region and there is a 0.02mm droop towards the as yet unsupported rear end. I think rather than try and shim the unsupported bits with shim material I'm just going to squirt some structural 2 component polyester resin in there, it is close enough and I will just make it worse trying to shim normally.

[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 ;-)

[JAZZCNC]

I have drilled and tapped the bed and frame, and bolted to the locations where I had fixed and milled the aluminium strip. Reads within +/- 0.01mm everywhere in this region and there is a 0.02mm droop towards the as yet unsupported rear end. I think rather than try and shim the unsupported bits with shim material I'm just going to squirt some structural 2 component polyester resin in there, it is close enough and I will just make it worse trying to shim normally.

In the picture you still have the protective coating on the plate so you can't trust those measurements if you did it with that still on.?

Regards the Epoxy and bridge etc then I've probably done more pours than anyone here, I've lost count of how many but it ranges from Medium and V-large, my experience is between both you and Clive. I agree the moats are better outside the frame but you need them both ends of the machine. Also, make the moats lower than rail surface as this seems to help the flow. However the most important I find is the temperature, keep the temp on the low side of what's recommended as it slows the curing process and gives it more time to level. The only tricky bit is it's a fine line between just right and too cold and it not setting correctly.

[devmonkey]

In the picture you still have the protective coating on the plate so you can't trust those measurements if you did it with that still on.?

The covering is tight and uniform so I think I can trust them enough, I DTI'd the milled shims first which was zero everywhere, happy that my +/- 0.01mm on the top is a mixture of error from the covering and the plate itself. Anyway doesn't need to be perfect as the spoil board will take up any error, if I need a very flat part for bolting a vice to I will skim the aluminium bed, I left the bolt heads low enough to do this.