Countersink vs. Counterbore

[J Tiers]

Loose fit or Plastic spacers are nice on winter tyres. Goddamn road salt makes close fitting rims stuck really badly. Normal procedure on friends Saab is to back off wheel bolts 3 turns and go for really rough ride. Couple of very thight cornerings with brakings usually loosen the wheels.

Must be on a newer one. Don't recall any troubles with my model 96, nor the 95 wagons we had, and they use salt here like they get paid to take it away.

[MattiJ]

JT,

I think Dian is referring to these: https://www.ebay.co.uk/itm/82-0-70-1...8AAOSwImRYGzH5

They let you use a wheel with a larger centre hole on a smaller spigot - they centre the wheel. Personally, I wouldn't touch them - aluminium ones are also available. Or just use the right size wheel rim...

Ian

Loose fit or Plastic spacers are nice on winter tyres. Goddamn road salt makes close fitting rims stuck really badly. Normal procedure on friends Saab is to back off wheel bolts 3 turns and go for really rough ride. Couple of very thight cornerings with brakings usually loosen the wheels.

[754]

Check these out... bad idea to some on this forum, but widely used it looks like to me.

[J Tiers]

yes, thats it. a lot (most?) aftermarket wheels come with these spacers.

From china?

No plastic spacers on any of my vehicles........I'd make a metal one if I had to. But first, I'd use the correct wheel....

[dian]

yes, thats it. a lot (most?) aftermarket wheels come with these spacers.

[Ian B]

JT,

I think Dian is referring to these: https://www.ebay.co.uk/itm/82-0-70-1...8AAOSwImRYGzH5

They let you use a wheel with a larger centre hole on a smaller spigot - they centre the wheel. Personally, I wouldn't touch them - aluminium ones are also available. Or just use the right size wheel rim...

Ian

[J Tiers]

well, a lot of wheel have plastic spacers. do you "think" these will fight the screws?

Of course they would (if I had ever seen anything with such a thing)

But generally, the plastic will lose the fight.

However, a spacer may not be the same thing as what the subject of discussion here was. Does the spacer go under the screw head?

[projectnut]

One thing bears mentioning here if you are counterboring SHCS for motorcycles , boats or hot rods... beware standard counterbores, way to big a hole.. never looks right .. we use custom ground counterbores or regrind endmills to get a tighter hole.
be careful if chroming..but remember that chrome fasteners available from places like GardnerWescott maybe a bit under size if needed. Like knurl ground off types in chrome.

Keep in mind Imperial size counterbores come in 2 sizes. "Close Fit" counterbores are .031" oversize of the bolt head, and "Standard Fit" are .062" oversize.

[Georgineer]

Back to the original question and an aspect that I don't think anybody has mentioned. I largely went over to counterbores when I started producing things by CNC. It's much easier to design a screw head recess to be cut with an endmill than to try and produce a conical depression, particularly when constrained by time and price.

George B.

[dian]

Your "think" is not the only "think".

well, a lot of wheels have plastic spacers. do you "think" these will fight the screws?

[thaiguzzi]

Assuming you want a flush finished surface (which you almost always do), for a given size fastener, counter sinks will work with thinner material. However when the material is thick enough for a cap screw, it has a smaller head than the large dia of the countersunk so fits in more places. Countersunk screws also positively locate which is less desirable for a fastener, where cap heads with a flat bottom hole allow for some adjustment

This.
I'll add also, that something we look at to be aesthetically pleasing, aka motorcycle side covers, cam covers etc, look much better with a counterbored screw than a 'orrible countersink screw.

[J Tiers]

i think hub centering is so loose it will not interferre with the screws and is mainly for mounting purposes.

Your "think" is not the only "think".

[dian]

i think hub centering is so loose it will not interferre with the screws and is mainly for mounting purposes.

[754]

Those are not the only considerations on wheels , but they are at the factory.
no and many others have modified a lot of wheels, different bolt spacing, bigger hole in the middle , spacers to make smaller holes in the middle, wheels that use tapered nuts , some not, some for Unilugs, all kinds of weird stuff... my point of view is keep a close fit between rim and hub nub. Some of the bigger off road style wide 5 wheels are using aluminium nut.. double tapered.

[J Tiers]

This interesting, half of you guys say you can't use countersunk head on thin stuff. , . how thin is too thin? I have probably used #10 in1/4 thick more times than I can remember.
and now wheels many OEM manufacturers have the wrong idea on wheel mounting, according to you guys.. that is amazing..
I am off to get popcorn..

Thin material is fine. What would be wrong with it? That is THE application for countersunk heads. We used tons of it, literally, in 16 ga material, countersunk, with the proper screws, as did most every company in our industry, it is fine, I don't understand what would be wrong. With thin material like 16 ga steel, you use an "undercut flat head" screw.

As for the wheels, that's a whatever. The reason for the countersunk heads or spherical head is to positively tighten so that the wheel is held on, AND is held against torque positively. If you centered on a boss, and used standard bolts, then braking would cause the wheel to slide and take up the clearance one way, acceleration would do the same the other way.

So they put up with the kinematically redundant setup. My claim is that there is no need for the center boss then, but if the holes are precisely and correctly located there is no particular harm in it. If some holes were "out" , not in position, then the two alignments would fight.