shaft supports and deflection

[dwwright]

Hi,

I'm starting to collect parts for a new cnc gantry router. I'm looking at about a 4' x 6' table. I picked some shaft supports for 3/4" shaft on ebay and was wondering how much (if any) deflection could be expected if I used 3/4" X 48" shaft supported on each end for my X axis on the gantry and closed bearings? The Y axis will be 1" on rails and open bearings. Most of the time it will be milling mdf or plastic.

Thanks,

[ger21]

Depends how much your Z axis weighs. The Y is usually the one on the gantry, btw.

[ViperTX]

Thompson Industries has a "deflection calculator" you can use...you can also search this formum has we have done these calculations before and the numbers will amaze you....if you don't want to do the calculations then use supported shafts.

[jeffs555]

Like Viper said, the numbers would amaze you. Most people grossly underestimate the deflection of unsupported shafting. By my calculations, it would sag nearly 0.02 inches just from its own weight, with an additional 0.05 inches of deflection for each 10 lbs of load.

[smarbaga]

you could lessen the travel and put 2 supports on each end say 3 to 4 inches apart. this will greatly reduce sag.