Stick with Ali profile or venture into plate?

[ecat]

Minimum order £100, easy :) I just looked at the cost of the Y cross beam, say 40x200x700, sobering at about £70. Still, in this CNC game everything appears to work out at about £50 to £100 per part :confused:

Time to do the pros and cons calcs..

Cost:
Plate: 700x200x20, something like Steve's, £50
Profile: as above £70.

Weight:
Plate: 7.6kg
Profile: 4.8kg

N.B.
While not total mince, my inability to read all the instructions on botlanta web page resulted in deflection calcs that do not compare like for like, see post 15 for corrections.

Deflection due to 200N vertical force:
Plate: 0.02mm (http://www.botlanta.org/converters/d...c/bending.html, got to love imperial measurements, hope my conversions were correct)
Profile: less than 0.00mm for 40x160 (Bosh profile deflection calc)

Deflection due to 70N horizontal force:
Plate: 0.82mm
Profile: 0.01mm, again for Bosch 40x160

Disclaimer: the above values are from my calcs and sources I've found, they may be total pants!

In this case I think profile wins. k, back to the calcs...

[FatFreddie]

In this case I think profile wins. k, back to the calcs...

Just to throw another spanner in the works, I'm planning on using square tube for best stiffness / cost ratio...

http://www.aluminiumwarehouse.co.uk/...duct_info.html

Not as convenient as profile but it should be possible to join quite accurately with a bit of drilling and tapping and a lot cheaper.

[blackburn mark]

Deflection due to 70N horizontal force:
Plate: 0.82mm
Profile: 0.01mm, again for Bosch 40x160

nice one ecat... your calcs seem to good to be true... fingers crossed
the valuframe 200x40 is much more dense than the Bosch so should perform better

square tube for best stiffness / cost ratio...

great price... would need some special fitting cosideratons to get the most out of its stiffness... internal spacers etc... making good stiff corners would take a bit of head scratching

[ecat]

Just to throw another spanner in the works, I'm planning on using square tube for best stiffness / cost ratio...

http://www.aluminiumwarehouse.co.uk/Aluminium-Square_Tube/c120_129/p29830/Aluminium_Square_Tube_(6082T6)_3_in_x_3_in_x_1/4_in/product_info.html

Not as convenient as profile but it should be possible to join quite accurately with a bit of drilling and tapping and a lot cheaper.

Oo, nice link. I collect them

nice one ecat... your calcs seem to good to be true... fingers crossed
the valuframe 200x40 is much more dense than the Bosch so should perform better

Too good indeed... I should check them again. Meanwhile, A quick sanity check...

The formula is: Deflection =W*L^ 3/ 3*E*I
Where W is force, L is length, E is Modulas of Elasticity in psi, and I is Second Moment of Inertia.
Moment of inertia is calculated by (width * thickness^3) / 12

So I varies with the cube of thickness.
Looking at the horizontal force the plate is 20mm thick, the profile is 40mm thick. 40^3 / 20^3 = 8. Whoops, my calcs are 10 times that...

A-ha, the Beam calc web page is for beams supported at only 1 end, the profile figure is for a beam supported at both ends. Note to self, just because the link comes from a CNC site it doesn't mean the linked page is what you think it is!

There is a spread sheet around here somewhere, I'll get back to you...

[routercnc]

There is a spread sheet around here somewhere, I'll get back to you...

There are two here, one from Ross (#1) and one from me (#3). Mine includes the torsion calc (due to the cutting force being offset in Z from the gantry, trying to twist the gantry). You might want to consider that on top of the vertical and horizontal forces mentioned above.
http://www.mycncuk.com/forums/showth...ail-Calculator

As for cutting ali with simple tools, you can cut profile with a mitre saw with a metal cutting blade, so should be able to cut plate. Mine was a Rexon ~£100, but there are cheaper ones. Blade was a branded part at £44 - you can get cheaper but I didn't want it to let go and do me some damage.