[Dongle]

I've just been having a look at the Solsylva site, and quite like the overtable design in terms of its structural advantages for the gantry movement, but then I was thinking, what about the table fixing? surely rather prone to not being completely flat to the table if you see what I mean?

So, firstly, looking for thoughts on if this method is any better or worse than any other design.

Also, would like thoughts on what sort of tube diameter you would use for an unsupported rail of about 3ft which will have a medium sized router as the cutting source - tube will be hard stainless 1.5mm wall thickness.

Thanks!

[ger21]

Also, would like thoughts on what sort of tube diameter you would use for an unsupported rail of about 3ft which will have a medium sized router as the cutting source - tube will be hard stainless 1.5mm wall thickness.

Thanks!

You're always going to get some flex with unsupported rails. The question becomes how much flex is acceptable to you?

[andy_ck87028]

I used 1.5mm stainless tube (35mm diameter) with span of 4 foot.

Tube flexing is exceptionally high and therefore useless unless it is fully supported along its complete length

....... see picture below

The tube is bolted from underneath through holes drilled into the tube every 300mm and pulled down using an inserted plate with corresponding threaded holes. I placed the seam of the tube on the underside as the seam slightly distorts the shape of the tube.

I am delighted with the arrangement which I have used on both x axis and y axis.

It is now rigid.

Andy

[Dongle]

Many Thanks, will alter design to provide support!

Any thoughts as to overtable-style compared to the more traditional gantry?

[High Seas]

One major advantage to "over table gantry style" - If you want to run thicker stock - you can "lower the table" or raise the side rails to accomodate.
You'd need to build in taller Z axis for that and a means to keep it from torquing the Y.
:cheers: Jim

[andy_ck87028]

I've used over table gantry style and as per High Seas comments, I can raise or lower the table as required.

I have raised the X which means there are no 'legs' required on either side of the Y. The main advantage is increased rigidity / reduced complexity.

Happy CNCing

Andy

[One of Many]

I've just been having a look at the Solsylva site, and quite like the overtable design in terms of its structural advantages for the gantry movement, but then I was thinking, what about the table fixing? surely rather prone to not being completely flat to the table if you see what I mean?
Thanks!

If you had spindle control and a fly cutter. You could use a sacrificial board(MDF?) on the table top. Just deck it for a full cleanup and it should be as flat as your router rails are capable of producing. It would be best if a precision level was placed across the rails to verify the structure is held on a flat plane prior to decking the new reference surface.

DC

[Dongle]

cheers guys - I think I'll go for that then as I can make the structure the size I want from Ally easier.