How to have surface table really 'flat'?

[Sentinel]

I have a CNC machine that looks like this:




I have tried placing different types of surface (wooden plates) on the top, but it seems impossible to get perfectly flat piece of wood. I'd end up having 0.2m - 0.8mm differences in height, across the board, which resulted in deeper cuts and cutouts through the table itself.

I also have aluminium plates for that machine, which look like this:



However, when I place piece of MDF (for example) on top and try to clamp it, I still end up with 0.2mm differences at places.

Now, I am thinking of using double-sided tape across the whole length of MDF piece, hoping that will tie it to the aluminium plates properly.

But before I do that, I wanted to check what other people are doing, and how are they solving the problem of having 'perfectly flat surface table'.

Any ideas, comments and suggestion are more than welcome

Thanks.

[TSJ]

Level the machine, use the aluminium base as shown with a sheet of MDF attached to it. Put an edge on the mdf and add the epoxy from this web suite:

http://www.precisionepoxy.com/

It will form a flat surface well within your tollerances.

[ger21]

Shim your machine level, then hold down a sacrificial base, then machine it flat.

[dfurlano]

Sure its the table and not something else?

[stevespo]

Like Gerry suggested, firmly attach your MDF board to the aluminum t-slot table, chuck a decent size bit in your spindle, and then flatten your whole tabletop. You will lose your t-slots, unless you then go ahead and cut new ones in the MDF.

I have a 3/4" thick MDF "spoil board" which I trued this way with a 1.25" flat bottom router bit (in a 2 HP router). I have not measured the accuracy, but I can cut through parts fastened to the MDF with double sized tape (.005" thick), and not even touch the tabletop.

I guess another option would be to carefully shim your aluminum t-slot table, but that would be very time consuming.

Steve

[wcarrothers1]

I have 2 slabs of MFD.

The bottom one is trued then another is placed on top of that. Seems to end up with a pretty true top piece and still retains that shiny skin on the piece that gets the punishment.

I've also coated it with some thined urathane from time to time..

Course my table isn't a solid sheet of aluminum either..

Trued with a 2" "Plaining" wood bit from woodline

b.

[rlrhett]

Very nice looking machine. Compact, which I appreciate very much, while still having a reasonable work size. Did you build it yourself? If so, you should share your plans. If not, where did you get it?

Thanks,

[Sentinel]

Originally Posted by rlrhett Very nice looking machine. Compact, which I appreciate very much, while still having a reasonable work size. Did you build it yourself? If so, you should share your plans. If not, where did you get it? Thanks,

I didn't build it, I've bought it from German company.

English version of their site is here:

http://www.cnc-router-routers.com/

[jalessi]

Several questions?

What is supporting the aluminum or wooden plates?

It looks as if they free span your machine.

There will be more the .2mm (.007) deflection in your table if is not supported correctly.

The link below explains more about these issues.

http://www.8020.net/Design-Tools-27.asp

After supporting the bed correctly you will have to mill it flat to get close to holding the tight tolerances you are looking for, even then without a vacuum table gravity might not be enough. Some other members are sure to have a simple solution to these issues.

Jeff Alessi
jalessi@aol.com