Thread: Centec 2 ballscrews
fair points, i will certainly be changing the ballnut mount but the screw mount is, although debatable in need of more thought (access to y axis gib screws has been somewhat compromised)
cost also needs to be taken into account so i may well use standoffs just to get the machine running and then cnc a new mount
got some more feutering done on the x axis design this evening
firstly i modified the stepper/ballscrew mount by lowering the motor giving space for gib screw access holes and then added a rib on the back for some extra rigidity
then i drew a 1204 ballscrew and crude representations of thrust bearings for the ballscrew mount
a 450mm long screw leaves just over 38mm overhanging the table travel extremities
still have to decide on a pulley ratio so i can incorporate it into my design, any thoughts?
could the moderator please change the title of this thread to 'centec 2 ballscrews' as its getting far of the original topic and it would be a shame to have to start again
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?
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).
The Following User Says Thank You to Jonathan For This Useful Post:
thanks for the reply jonathan
firstly, im getting the screws machined free of charge, why pay if i dont need to?
as for pulleys, i will take your word for htd and give them preference so long as i can find a set to fit the cramped x axis
now, the bearing selection is an interesting predicament...
the largest id magneto bearing i could comfortably implement would be E5 (16mm od)
i can easily get 8x16x5 ball thrust bearings
so, do i turn 12mm ballscrews down to 5mm to use magnetos or 8mm and just use ball thrust bearings. or in other words is 5mm sufficient if i ever hope for this machine to cut steel?
and as for bellville washers, point taken
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