Aluminium profile CNC

[BriceO]

I'll go for the top one so, I wasn't thinking that it could have any bending problem, thanks.

Limiting factor is the gauge of the extrusions on the bed sides.

I'm not sure to understand it. Do you mean the extrusion is it too high?

Good idea for the end plat, do you think 5mm aluminium is enough to do it?

I found this documentation about hiwin rails : http://www.hiwin.com/pdf/linear_guideways.pdf
It can be interesting for someone. Is it a good choice to have a HGW (wide flange carriage) could be a good choice for the Y axis for example? And HGH for X and Z axis.

Any advice higly appreciated.

[routercnc]

I'll go for the top one so, I wasn't thinking that it could have any bending problem, thanks.


I'm not sure to understand it. Do you mean the extrusion is it too high?

Good idea for the end plat, do you think 5mm aluminium is enough to do it?

I found this documentation about hiwin rails : http://www.hiwin.com/pdf/linear_guideways.pdf
It can be interesting for someone. Is it a good choice to have a HGW (wide flange carriage) could be a good choice for the Y axis for example? And HGH for X and Z axis.

Any advice higly appreciated.

The extrusion is not too high all I wanted to point out was that using extrusion, especially thin wall (gauge) extrusion, will be the limiting factor for the stiffness. The wall is thin, and it essentially has lots of deep slots cut in it. Imagine pressing sideways where the gantry rail is situated, and imagine how it will want to bend and vibrate.

Lost of people use steel box section instead as it is much stiffer, with a continuous outer section, usually with a high wall thickness (to allow thread tapping), and it is cheaper.

End plates of 5mm will be fine as shear panels don't need to be massively thick to be effective, but it will limit feed in / out access if that is a consideration.

Hiwin carriages - either wide or narrow are both fine. Use wide if that gives a better footprint and mounting for your design.

[BriceO]

Thanks, is it the same problem for the Y axis? Should I place the rails on top and bottom or is it fine?

To be honest, I can't really imagine how it will bend and vibrate. I was thinking that the weight/force is supported by all the length of the extrusion.

[Davek0974]

Thanks, is it the same problem for the Y axis? Should I place the rails on top and bottom or is it fine?

To be honest, I can't really imagine how it will bend and vibrate. I was thinking that the weight/force is supported by all the length of the extrusion.

Yes it is, but, the ends are fixed - the weight/force now tries to act upon the whole beam but cannot move the ends as they are fixed - it will then act upon the point where the force is applied, if say it is applied centrally then the force will try and bend or push the beam in the opposite direction to the force - the beam will bend. The skill in designing beams is to transmit those forces to the ends of the beam without letting it bend - this is done by using heavy enough section material or bracing thinner section material with struts or triangular trusses.

Vibration is the same really, just many more, smaller forces that need dampening out or preventing in the first place - mass is a good way of stopping vibration or at least moving the harmonic point to somewhere outside the range of expected vibrations.

[BriceO]

Thanks for these explanations, I used the Item site to calculate deflection of the profile (http://product.item24.co.uk/en/home/...ral-41665.html) for 1200mm and 400N. If I do it right I have a deflection of ~0.01 mm.
I was thinking that Aluminium was a good compromise between weight/strength and offer a good flatness. I don't have enough experience to determine how bad is it.

Sadly, I already have these "light" profiles. Should I go for steel box section instead for X and Y? Do you have any advice plz?

[routercnc]

Thanks for these explanations, I used the Item site to calculate deflection of the profile (http://product.item24.co.uk/en/home/...ral-41665.html) for 1200mm and 400N. If I do it right I have a deflection of ~0.01 mm.
I was thinking that Aluminium was a good compromise between weight/strength and offer a good flatness. I don't have enough experience to determine how bad is it.

Sadly, I already have these "light" profiles. Should I go for steel box section instead for X and Y? Do you have any advice plz?

The deflection calculation will probably be just simple bending, so either simulates a plunge in Z or simulates the sag caused by the weight of the spindle assembly. This is usually easy to get a low value.
What really tests the machine design is cutting in the X direction (confusingly many US builders call this the Y direction, so be aware if you are reading different forums) because this puts a moment on the gantry and tries to twist it. This is usually the limiting factor and will result in much more deflection at the tool tip than the Z direction loading.

However, based on the fact you have the extrusions already, and you mainly want to cut wood, then stay with them and build it as per the top picture in post #26.

Also be aware that the aluminium profile is not especially flat unless you have it specially machined.

[BriceO]

Ok, I will do the best with this and maybe add steel plate to the back to add weight and strength.

I just received an offer from Chai for these components:

-2 HIWIN HG20 rails + 4 blocks hgh20CA ZA 1800mm
-2 HIWIN HG20 rails + 4 blocks hgh20CA ZA 1380mm
-2 C7 Ball screw RM2010 total length end machined 1760mm with ballnut
-1 C7 Ball screw RM2010 total length end machcined 1360mm with ballnut
-3 2010 Nut Housing
-3 Jaw Flexible Coupling 6.35mm*12mm (Ballscrew to NEMA23)
-3 BK15/BF15 P5 AC

Chai price is 656 usd Total. Air shipping cost is included.
Fred from BST Automation is USD1155.00 for the same items.

Is it normal to have a big difference?