Centec 2 ballscrews

[jonnydeen]

things have been slow to progress lately due to lifes consistent interuptions but on another note...
I now have ballscrews!
2x 1204 & 1x 1605. 250mm, 450mm and 450mm respectively
also got my hands on a nice 20mm 2mt drill bit to drill the hole in the mills base casting for the z axis screw


now that i have me some screws i need to get them machined. i have arranged for a friend to do this for me as the boxford doesn't have much in the way of change-gears and im afraid id screw it up (pun intended).

but before i can do that i still need to order bearings and pulleys so i can factor them into the design. this leads me to a few questions...

1) pulleys, is there really any difference betweel xl and htd or other types of pulley?

2) bearings, i see alot of people using angular contact bearings, wouldn't ball thrust bearings be a cheaper alternative or is their something im missing?

3) i see that using belleville washers is also quite common for preloading the bearings, would an easily available split washer not do the job?

[Jonathan]

now that i have me some screws i need to get them machined. i have arranged for a friend to do this

Why couldn't you get them machined by the seller? Assuming you bought them from China it should be very cheap. It's not easy to do it yourself due to the hardness of the surface.

1) Different tooth shapes which are more/less accurate (backlash etc). HTD is generally considered the best for this application.
2) Could be, but I think they'd be harder to mount and pre-load accurately? Also possibly lower efficiency, but I'm not sure.
3) No since it wouldn't apply an even force on the bearing ring. Belleville washers may not be nessecary - it depends how you mount the bearings. The BK/BF blocks don't use them, instead they rely on the bearings being ground such that when they are tightened together the correct pre-load is applied, or they use shims. If you do use Belleville washers then you can put the ballscrew in tension, which is good since it increases the stiffness of the system a little (or a lot depending).