Hello Dick:

The formula for deflection uses the square of the cross section. So 0.5 squared = 0.25 and 0.472 squared = 0.222. The difference is 0.027 or about 10% stiffer, for the same material. Others have increased the bar diameter and bored the carriage out. I would suggest turning the ends down to 12mm so you don't have to modify the base.

Deflection = wL3/24AD2

w = load

L = Length ( cubed )

A = Sectional area of beam

D = Depth of beam ( squared )

This formula is for 16Kpsi steel with a Young's Modulus of about 200 GPa, while for carbide is it about 600 GPA.

Now if you went with carbide bars the material stiffness is much higher. At work we did this for the grinding mandrills for 3mm holes. It might take some fancy tricks to mount 12mm carbide bars, but I think it could be done.

McMaster has 10mm x 100mm bars for $42 each, so someone should have 12mm x 300mm available.

Carl.

( Retired tool design engineer )

On 4/15/2020 10:09 AM, OldToolmaker via groups.io wrote:

I am not an engineer so I need to ask a specific question concerning way bar flex. What would be the increase in rigidity (flex) if the way bar diameter was increased from .472” to .500”. ?I understand from past discussions that material hardness has little to do with flexing whereas diameter does. I am considering trying to increase diameter asas it will not require a modification to the base casting. I will however need to modify the cross slide hole size or build a new cross slide to suit and tail stock. Any input would be welcome.
Dick