# Plain bearings (plastic) in backlash free joints

I need to design some backlash free rotational joints for slow and intermittent movements (device for human-computer interaction) for my uni project. Possibly loaded in any direction; the loads won't exceed ~100 N (fyi just to get the sense of scale) and I'd like to use plain bearings, as they should take less space and possibly have less stick-slip and smoother motion than rolling bearings. There's, for instance, that company based in Cologne, Germany that's got a really big variety of bearings - but then again, their off-the shelf preloaded bearings are really hard to move on the shaft (checked it personally), which is definitely not what I'm wanting. I was told by a salesman, that basically, as the bearings are press-fit, you can slightly alter the clearance by changing the hole tolerance. (As an example - with recommended tolerances, a joint with 5 mm shaft would have between 0,02 mm and 0,10 mm of radial play, so choosing a more strict tolerance one can get eg. 0,01 to 0,05 mm play. Side note, perhaps can be useful for others - I was told that changing the hole tolerance generally relates 1-to-1 to the change in fitted bearing inside diameter tolerance, but I haven't checked it for myself and it's word-of-mouth, not in the catalogues).

EDIT: Below is a half-cross-section of a proposed play-free rotational joint: part 3 (with a fixed axis) is connected with axial bearing 5. Part 1, together with two press-fitted flange bearings 4, revolves around horizontal axis. It is all pressed against each other to eliminate backlash by nut 2. I think I can estimate friction caused by axial bearings, simply by defining the torque for screwing the nut.

My question is then:

are there any examples of design or scientific articles regarding play-free (preloaded) plain bearing (rotational) joints? Do you perhaps know from experience, how would such bearings (esp. plastic ones, esp. - I know I'm wanting too much - on carbon shaft) behave when given no or very little radial clearance? (by 'behave' I mean friction and 'feel' in the first place). I assume it should increase, but to what extent?

EDIT: Are such designs used at all, with this intent in mind?

I guess it is rather a matter of experience than pure calculation - but I'm lacking information on both - I'd really appreciate any hint.

• Can you clarify what you are referring to by the term 'backlash?' Typically it applies in leadscrew situations, but you seem to be referring to a smooth shaft. – Ethan48 Jun 11 '15 at 1:22
• yeah, sure - excuse me, I was using interchangeably 'play' and 'backlash' (and sometimes 'clearance' too). Perhaps it's my auto-suggestion because it's almost impossible to g*gle anything when typing 'plain bearing play' - it assumes that 'play' is bounded with game... Yes, I am referring to smooth shaft. I'll edit the question accordingly very soon. Thank you for pointing that out. – Antek Jun 11 '15 at 4:45
• Great edit! Just one more question that may help someone answer. Is part 1 rotating in and out of the page at the top and bottom of your sketch, or at the left and right? ie Are we looking at the edge of a wheel-shaped piece, or the end of a dowel-shaped piece? – Ethan48 Jun 11 '15 at 12:56
• the axis is horizontal, if that helps (I'm not getting the 'top and bottom' or 'right-left' descriptions, I'm guessing it's top-bottom). There's axis line, I'm just afraid it's almost invisible in this hand-drawn sketch. Btw, as I said, it's just half cross-section (for readability). – Antek Jun 11 '15 at 13:00
• alright mates, as i dig into the matter: - it looks i've found one counterexample in "A New Cable-Actuated Haptic Interface Design" by Ferlay and Gosselin (they used plain bearings and complained, later replaced them with rolling bearings) - apart from increased and hard to estimate friction, machining tolerances need to be much tighter (much more precise) than when using rolling bearing to obtain zero clearance, so the only way seems to be preloading, which... increases friction really badly. So now i'm still searching for some more papers. – Antek Jun 11 '15 at 15:50