Pretty cheap ball screw. 50gbp for the nut. 37gbp for500mm ball screw. C7 straightness what is that. @Tim_Rastall you think the rod straightening process you shared could work if this isn’t straight enough ? Apply the force from the lever and fulcrum to the nut?
http://www.zappautomation.co.uk/en/miniature-ballscrews-6-12mm-diameter/36-r1002-ballscrew.html
Not sure, those things are pretty hard and any damage to the thread would kill the bearings in the nut. Anyhow, check Aliexpress.com you’ll get much cheaper there.
EBay also has a lot of fairly cheap options. Most in Imperial. Cool for me being is based but terrible for current firmware lol 
These look good: Free shipping Ball screw 1pc SFU1204-L500mm ballscrew+1pcs SFU1204 single ballnut CNC Support
Why you looking, new project?
@Tim_Rastall I am considering the virtues of maintenance free x, y, and z unaffected by a heated chamber. pulleys on outside. the current build I have could use 6. 4 for outside on x and y 2 for z also acting as the guide rods. Price goes up but maintenance goes down. I also believe it could improve footprint to print volume ratio as well. Of course I would maintain the ulti style gantry.
@Tim_Rastall I’ll have many machines before I’m through lol. With every problem I solve I find other areas I could make more efficient in future builds. I love the journey and r and d and prototyping is what I do for a living now and my home is my office. Work meets play. I love it
@Tim_Rastall 16mm seems kinda overkill though huh? I was thinking 10 is plenty
C7 is the tolerance class. These classes go from C7 to C1 (or even C0 but I’m not sure). C1 is the best and then it goes down to C7. But ball screws are alway a good choice.
@D_Rob take it from me, they do not work nicely as linear guides, there is always some run out even a few 10 microns and it will show up in your print quality. I went through this a year or so ago with my Z axis and gave up because it was too easy to knock them out of alignment .
Those ones I linked to were 12mm btw.
@Tim_Rastall true. So a linear guide is necessary
@Tim_Rastall odd I went to the data sheet and the smallest was 16. But I’ve seen this before. Bearings with improper data on eBay. Which are probably ali sourced.
Tbh, if you are going to start spending the kind of money that 6 ballscrews will require, I’d go all-in and build something with a milling capability. Of course you’d compromise on speed unless you used steep pitch screws, which aren’t ideal for milling. You should also consider synchromesh as a step up from belts without the expense of ball screws if you just want a more reliable FDM machine. .
Really I’m just thinking out loud, Lol, but enough is enough and this build is nearing it’s end.
I’m the same mate. Have about 3 projects lined up once Ingentis is done. Firstly I’m going to build a cnc mill for aluminium - That way I can build my own extruders and not have to rely on overengineered plastic parts when I want to produce a custom part. After that, an SLS bot, then a concrete printer but they with both cost about $10k I think 
Sound like me.
Just wondering has anyone used twin pitch screws as they are more accurate.