ok, first attempt using sketchup 8

[JAZZCNC]

IMHO the purpose of the theoretical calculations, recognising they can't model every real-world situation (but can get very close if you can identify all the 'gotchas') is to see if you're in the right ballpark...

Yep I agree can be ok for a rough ballpark (Thou yours did seem a bit off base.!!) . . . You only have to look to the BIG BOYS in theoretical design and performance like F1 teams and see that even they can't predict and 100% confidently model every outcome.!

Hey, no offence taken Jazz,

Good now give us a hug.!!. .

[JAZZCNC]

Ok thats good but bring the screw to the front, will be much stronger having the ball-nut close the Z Axis back plate.

Have you got the 20mm steel plate.? If not I think you'll maybe change your mind when you see the price.!! It's not really needed either and I'd use ali for easy working.

[deannos]

Ok thats good but bring the screw to the front, will be much stronger having the ball-nut close the Z Axis back plate.

Ok, thats no problem, i will do that. Is this to prevent racking etc

Have you got the 20mm steel plate.? If not I think you'll maybe change your mind when you see the price.!! It's not really needed either and I'd use ali for easy working.

No i haven't got any steel plate and a quick google has made me change my mind, but if i use ali how would I join this to the steel gantry?

[JAZZCNC]

Also now confused after reading comments on the other post about the "effect of forces on gantry cross sections" and the following was mentioned-

Am i going round in circles

Dean don't worry about it your only cutting wood the box section will easily handle it. The box can resonate but cutting wood it won't really matter or show.
There are also ways around this if it does by filling with sand. So long has the resonance doesn't affect the motors then you won't have problem and because your using belts then this won't happen and why it's good idea to use belts.

[JAZZCNC]

No i haven't got any steel plate and a quick google has made me change my mind, but if i use ali how would I join this to the steel gantry?

Bolt or weld Angle brackets to box then bolt thru Ali plate into brackets.

[deannos]

Bolt or weld Angle brackets to box then bolt thru Ali plate into brackets.

Excellent, an easy solution i didn't even think of.
cheers Dean

[deannos]

I have moved the ballscrew to the front of the gantry and will be using 20mm ali instead of steel plate, too costly. Have added some steel angle to corners to connect gantry to end plates.

[deannos]

Would this design be ok, i thought i would use some 100x60 box section as bearing plates. I would have some left over from the gantry and it saves on the Ali plate. The extra height would help with the bed, bit more room to play with. This box section is only 3mm thick, is that ok. I have used 300mm, 2 x 800mm and 1400 SBR20mm rails. The ball screws are 350mm, 2 x 800mm and a 1450mm length.

[wilfy]

2 questions for me that dont mean much to your build sorry :D firstly is that still an RSJ you got across the Y if so your second picture doesnt make it look like that... petty i know..

EDIT: oh scrap that i just read it's box section... my misunderastanding eek... either way second question applies

secondly how do you plan on fixing the box section to what i think is the RSJ?

[deannos]

secondly how do you plan on fixing the box section to what i think is the RSJ?

The gantry is box section and this will be bolted/welded to the bearing plates. I have put some steel angle holding the Gantry ends to the end plates as well, but the plates will also be bolted to the bearing plates. Rsj is only used on the base "X"

A couple more pics, it might help