tolerance for holes used with metric standard bolts

[Shubham]

Hey guys, we are currently facing a problem with the tolerence to be used on holes while using metric standard bolts.
for example the M8x1.25 bolt that we get has variation on the shank diameter of-0.080 to -0.120
whereas the spherical bearing bore has a tolerance of H7 bore(+0.015/0.000) which is resulting in free play.

if i use a conical spacer the lead chamfer of 0.3mm on the bearing bore allows lateral play.

[poe21]

Are these shoulder bolts or standard bolts. Shoulder bolts should be much more accurate than that.

Edit: just realized you are probably saying +/- x amount in mm. Still the shoulder bolts we have are 1/4 inch, and they all have a diameter of .246 inches +/-.001 inches.

[Shubham]

we use standard bolts, thanks for your help.

[Drew Price]

Fasteners are specifically made so that a 0.25" fastener will always be slightly undersized, so that if you mount it in a 1/4" hole, it will fit. Holes should be slightly over-sized, fasteners slightly undersized, unless the fit needs to be zero- or interference fit for some reason.

About the bearings, a few thousandths of play in the bearing bore is fine, you're clamping them down anyway, right? If you're really concerned about it, you may need to use 'shoulder screws' which have a ground shouldered portion and undersized threaded portion to be mounted proud of the surface, or for precision fits, but that might be a little overkill.

Best,
Drew

[sbrenaman]

It all depends on where the holes are. There are some 'right' answers, but the only way to tell for sure is with some trial fits.

[Ben Beacock]

My solution is to use one size larger rod end/spherical and make spacers with a nice slip fit. The other option is to go one size smaller for the bolt. I found that even if you get it nice and tight and hold it with the clamping force, it would eventually loosen up after long sessions. As long as the bolt is in double shear, it will usually be strong enough to cope with the force requirements of the 'next size' rod end.

[ben]

Originally posted by Drew Price:
Fasteners are specifically made so that a 0.25" fastener will always be slightly undersized, so that if you mount it in a 1/4" hole, it will fit. Holes should be slightly over-sized, fasteners slightly undersized, unless the fit needs to be zero- or interference fit for some reason.

About the bearings, a few thousandths of play in the bearing bore is fine, you're clamping them down anyway, right? If you're really concerned about it, you may need to use 'shoulder screws' which have a ground shouldered portion and undersized threaded portion to be mounted proud of the surface, or for precision fits, but that might be a little overkill.

Best,
Drew

we took the shoulder bolt approach. It is overkill - but it is also very elegant. Particularly when you use high misalignment sphericals and dispense with conical spacers too.

Ben

[Drew Price]

That is exactly how I will do it my next time around. I don't want to be messing with making and keeping track of all those little teeny spacers.

Best,
Drew

[woodsy96]

+1. We went to high misalignment bearings last year. They are kinda heavy and bulky, and requrie 5/8" tube for the 3/8" UNF threads, but are SOOOOO much easier to work with. Spacers = mega gay.

We did ask Aurora if they did smaller ones, but they required a minimum batch size.