Aluminium profile CNC

[routercnc]

Z axis bearing arrangement
Arrangement A: With rails on the moving plate (Z axis) the lower bearing is always as close as possible to end of the tool.

Arrangement B: With rails on the stationary plate (Y axis) the lower bearing is much further away from the end of the tool (vs arrangement A) when cutting close to the home position / tall parts. This is less stiff an arrangement Vs arrangement A. However, when cutting at full stretch near the table than they are the same.

So sometimes they are the same, and sometimes A wins in terms of stiffness, depending on the height of the part you are machining.

I've seen arguments made that arrangement B is OK, probably on small Z travel machines, and that it could be said to be a bit easier to build. Jazzcnc put forward an argument for B, can't remember what it was now. My personal preference is A.

Ballscrew 'preload'

"Ballscrews with preload torque" ? You put this right after the sentence over rails and bearings so assume you mean preload on the bearing carriage- the part which slides on the rail? If so ZA is better than Z0 if you have the choice:
http://www.mycncuk.com/threads/9373-...r-a-diy-router

If you mean preload on the ballscrew - the part which rotates and drives the axis then for general DIY machine the ball nuts as supplied from China are fine. They typically have 30 - 50 um (0.03 - 0.05 mm) backlash. C7 grade is fine for DIY machine, but if you really want there is a C5 grade:
http://www.mycncuk.com/threads/1558-...curacy-V-Price

[Nr1madman]

The reason to mount the rails on the Z axis plate is part that the rails actually strengthens the plate. And if you have the bearings on the plate you always have the same distans (leverage) from bearing to the tool tip. If you have the rails on the plate you can raise the part that you are machining closer to the spindle and shorten the distance from bearing to tool tip for higher rigidity.

Most people seem to buy standard ballnuts without preload. What I've seen some people do is use 2 ballnuts and preloaded these against each other for backlash free operation. Or are you talking about ballscrew mounting with 2 fixed bearings instead of a floating bearing in one end?

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[Nr1madman]

Oh!
Don't think you need 2010 screw for Z axis.. 1605 should be fine. Might even be okey with 1204 for Z if you have a smart mounting strategy :)

Have you calculated the length of the ballscrews from desired ballnut travel + ballnut distance + end machining or from what is easy to mount in your design?

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[Nr1madman]

@routercnc
I should just shut up, you explain so much better :D

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[BriceO]

Thanks guys for the explanations ! :) I'll probably use arrangement A and 1605 for the Z axis.
I have 6082 T651 aluminium plate, do you think is it flat enough to use it?

[Chaz]

Thanks guys for the explanations ! :) I'll probably use arrangement A and 1605 for the Z axis.
I have 6082 T651 aluminium plate, do you think is it flat enough to use it?

Nope, try get tooling plate. www.clickmetal.co.uk

[BriceO]

Sadly, I live in Switzerland. Is "tooling plate" a specific type of aluminium as T6 ?

[Chaz]

Sadly, I live in Switzerland. Is "tooling plate" a specific type of aluminium as T6 ?

No, its a milled / ground flat version. Its made in Europe and must be commonly sold. I did see the manufacturer name at a point. Something like Gecia or similar, dont remember.

[Nr1madman]

It's also possible to use "eco cast" and similar flat stock. I looked at this from aluminiumwarehouse as they send over Europe. Im in Sweden so similar problem.

I think toolingplate is called mic6 sometimes to but I might be wrong on this one..

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[BriceO]

Thanks, I just find another site just in case it can help someone: zappautomation but I will try to find it locally.
I understand why the mic-6 would definitely be beneficial in the carriage, where the rails bolt directly, so you only need to worry about alignment. I was just asking me if it is as important as that concerning only the side plates? I ask that because I have a plate that I could use.