Stell frame cnc 1500X1000. Adjustable table your opinion please

[Jonathan]

Well ounce again I'm going to have to disagree.!! . . . Not on the strength basis has that's true but on the fact it's better to use larger.? It's only better if the application warrants it and in this case it doesn't. The thicker wall thickness will be more beneficial because it will be less resonant, going Larger on the tube size just increases resonance. For this application then 60mm tube will be more than strong enough so strength isn't a problem so any extra efforts to improve would be better focused on reducing resonance and going thicker on the wall would help here.

I don't disagree with you. If you read what I said carefully you'll see that I acknowledged other factors come into it, and was making general comments, not specific assertions for this build.

Oh dear again I'm disagreeing. . Lol . . I don't have any problems with my aluminium bed and differing finish.? I get the same finish regardless of whether I'm working direct on bed or on any other sacrificial surface. If your bed is affecting finish then reckon you've under built it or your clamping methods are poor.!!
If anything I get more trouble when using MDF than I do when working direct on bed because material can slide if cutting deep, direct on the bed I get much better hold down.
Also Poor finish comes mostly from the tool chattering so if your struggling with finish then I'd be looking at the machine strength and resonance, hence why I put more importance on material Thickness than Size when it comes to steel. (obviously size has to be fit for application)

I agree that if my gantry was stronger it would help reduce chatter, but it's the same gantry with or without the MDF bed and the MDF sheet placed on top of the aluminium bed on my machine definitely makes it easier to get a good finish, so it must be having a damping effect. I'll reiterate for clarity, by 'good finish' I mean 'looks good' - the part itself is clearly not going to be as accurate if it's clamped on MDF.

Also, that's not to say the machine wont get a good finish using just the aluminium bed - it's just more difficult to get the right parameters. Here's a recent example: