fitting a round rod in a round hole

[vivek16]

A good rule of thumb for reasonably sized bearings (say .75-2") is a .005" interference. You can get more specific as others have said but it will work.

-Vivek

[Cory]

Originally Posted by vivek16

A good rule of thumb for reasonably sized bearings (say .75-2") is a .005" interference. You can get more specific as others have said but it will work.

-Vivek

I wouldn't generalize that much. 0.0005" is good enough for a 3/4" bearing. I had to make a part for a large bearing (about 1.5-1.75" or so) and the reccomended max interference was 0.0002"-0.0003". The extra 2 tenths can make a HUGE difference in how freely the bearing can turn.

[GMKlenklen]

oh god, this is getting complicated...
if i say .7500" hole for a .75" OD bearing, that will work, right? I should be able to put that in there with my bare hands right? i think i'm gonna use hotglue to keep this stuff togeather if i have any problems

btw, so u can sorta see what i'm workin on:
http://www.facebook.com/album.php?ai...&id=1310160279
i have what seems to be the final render up
the motor will be driving the shaft and the rotor at about 300-700 rpm...

[Andy A.]

Press fits are a surprisingly complex subject. You are straying into an area where a lot of numbers come into play and assembly technique matters if you want to do things 'right'. If you want to fudge it, I suggest 'skipping' the problem by drilling a .750 hole and using a layer of locktite on the OD of the bearing. As long as you are careful to keep the bearing aligned and the adhesive out of the bearing it works pretty well.

I'm sure some folks here will cringe while reading that, but it does work. Consider it as an option if you don't have access to a shop with a method of cutting a hole of the size you need (jig boring and/or reaming are great ways to do it).

.745 is a good value for pressing this size bearing into aluminum. Different materials and bearing sizes will change that, so don't use it as the cure all. I prefer to stray on the looser side of press fits in FIRST, so I would recommend that you try to keep the tolerance on the hole size positive so the hole will tend to be closer to .750 then not.

As a general practice I don't model press fits in CAD- bearings and their holes are just line to line fits. I'll save press fit instructions as a call out on the drawing and in FIRST I'll also include a table showing the maximum and minimum material conditions for a given tolerance. Opinions on that will very from designer to designer and shop to shop.

Good luck.

-Drew

[Daniel_LaFleur]

Holy thread revival, Batman.

[vivek16]

Actually, I have since ruined bearings trying to press fit them. If you don't have access to reamers, I would recommend using flanged bearings and some button head screws on the outer edge of the bearing. You can drill and tap the screw holes by hand if you want and it will run very nice. Bearings are finicky.

-vivek