Designing a better bed

[Robin Hewitt]

To counter sympathetic vibration think stub and unequal helix tooling.
Obviously nobody can talk you out of this so I say go for it, build this monster and be sure to tell us all about it

[Sven]

There are a few concepts and definitions in this thread that in my mind make the discussion a bit clouded, as it often does when it comes up.

Hope I can point all of it out, here it goes.

First and foremost, a cnc machine needs to be stiff (rigid). Everything else comes second.

It can be good if things are strong but it is very hard to build a machine that is stiff but not strong enough.

Then people often say it needs "dampening" and/or "weight" and then go on using either in the wrong way, in real life and in conversations.

If you add bitumen within the construction you will add "dampening" to the structure. It will make any vibrations die out quicker.
But there is a big risk if you add bitumen or similar within the construction.
Chances are you will reduce stiffness.
I am unsure if adding bitumen to a cnc construction is totally useless but I am sure it is extremely hard to do it so that it does dampen vibration without compromising stiffness.

If you add sand to a gantry you will also add dampening but as described above would be missing a great opportunity.

Pouring loose sand in a construction will indeed reduce vibration, in that it helps vibrations to die out.

However, if you add sand with epoxy mixed in, it will become part of the structure, adding stiffness and at the same time adding dynamic stability to the construction, making the amplitude (size) of the vibrations smaller, giving a better finish to the product.

[D.C.]

Obviously nobody can talk you out of this so I say go for it, build this monster and be sure to tell us all about it

Actually your comment about screwing up and still having a sheet of aluminium to sell for scrap did alter my thinking somewhat, don't give up on the subtle prods informing me that I'm an idiot, I might eventually get the message.

I've finished, clearing, cleaning, painting, realising that brushes don't work well on crapcrete blocks, spraying, spraying again, cleaning, etc ordering steel for a worktable and testing.

I'll post back when I've gotten round to ordering the other bits and testing some beams as best I can and then mull things over.

[Robin Hewitt]

don't give up on the subtle prods informing me that I'm an idiot

I'm good at that, maybe there is hope for me yet