Quote Originally Posted by Wobblybootie View Post
Do any of the learned members have views on the accuracy/repeatability of C5 compared to C7 Ball Screws. Also, is the extra cost of C5 kit worthwhile for the sort of work folks produce? For myself it is something I may consider bearing in mind one of the things I am looking to do is the engraving of custom made Fountain Pens (I already have an interested party in such a project)
For a machine doing fountain pens you wont have leadscrews longer than 300mm. C7 is 104um for error and fluctuation per 300mm length, C5 is 18um error + 23um fluctuation = 41um, these are all worst case figures.

If your leadscrew is a 5mm pitch, direct driven then you are looking at a resolution of .025mm per step, or 25000um. With a C7 screw your worst case error is 208/25000 = 0.8% per step, with C5 its 0.16% per step.

Spending your money on making the machine rigid and look at double preloaded nuts to remove backlash will improve the accuracy far more than going from C7 to C5!

Basically for engraving a fountain pen there is absolutely no point, as your engraving tip is massive compared to this error (and anyway the rigidity of the machine will introduce larger errors).