Humble Beginnings - For Alu

[Jonathan]

You've set it to display stress, which is useful when determining if the material will fail, but that's clearly not the case here as the maximum stress is small. Also, you need to be careful at corners or near bolts as the stress outputted by the simulation at these boundaries can be a lot higher than reality, due to some of the assumptions in the calculation. We're interested in the deflection so set the display to displacement and find the maximum points. The results you get will depend greatly on the boundary conditions, so how you attach the bed to the frame in the simulation is important. The mesh quality on the simulation is very poor too, but there's not much you can do about that. If you're going to try and use FEA, then at least start with applying forces to the gantry as the gantry is going to be far less stiff than the machine bed even without additional supports. For the current simulation you needn't include the gantry and X-rails, so you might as well remove them as a significant number of the nodes in the mesh are consumed in these parts.

The extra two rails wont make much difference because the vast majority of the force will be apparent on the other rail, with two blocks, since the structure in between is not particularly stiff. Just use one rail on each side and space the blocks out as far as you can, since the stiffness is proportional to the block spacing which means the deflection is inversely proportional to the bearing spacing squared, so increasing the spacing a little can make a big difference. That's assuming the structure they're mounted to is very stiff, which currently it isn't.

[dsc]

Just a quick stupid question, what software do you use to analyze stress? is that part of the AutoCad package?

Regards,
dsc.

[Husky]

I'm using Autodesk Inventor Professional 2012 :)

[Husky]

Ok, had a play with some more CAD :)

Deleted the side rails & related
Got rid of the aluminium bed
Added more bars for a new bed
changed the rails for slightly longer ones
Added bolted section to allow fine tuning of angles


Some pics:

[Husky]

I'm guessing this is the Spindle I want to go for :)

WATER-COOLED SPINDLE MOTOR 2.2KW AND INVERTER VFD DRIVE FOUR BEARING | eBay

[D.C.]

Yup that is the one.

If you are mounting a metal frame on top of two bits of what looks like wood... Don't.

Wood swells and expands depending on moisture content, the arrangement you have will warp the frame and throw your rails out of alignment. You also have your linear rails going over a joint. Don't do that either, unless you are going to take your frame to a big engineering shop and have the whole thing surface ground you will have zero chance of fitting the rails properly with that arrangement.

[Husky]

Ok, wood is out

Ah ok, good point about the rails! I'll shorten them back down.