alistairolsen
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| posted on 22/7/11 at 03:34 PM |
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Specifying an interference fit....
Say I had a wheel bearing and wanted to bore out a tunnel in a casting to take it, like the sierra rear end arrangement, how would I go about it?
I dont own an internal micrometer, but do have a digital caliper which whilst not ideal gives reasonable readings, the issue being what size to aim
for.....
Cheers
My Build Thread
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coyoteboy
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| posted on 22/7/11 at 03:45 PM |
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This page should give you all the info you might require :
http://www.mitcalc.com/doc/tolerances/help/en/tolerancestxt.htm
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Mal
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| posted on 22/7/11 at 04:58 PM |
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SKF have for many years produced a technical handbook telling you everything you ever want to know about bearings.
One section has housing tolerances for difference styles of installation. You may find this information is now on the SKF website.
If the the nominal outside diameter of the bearing is, say 100mm, you can take it that, near as damn it the actual diameter is precisely 100mm and you
only have to find a suitablehousing bore tolerance for your application. Some arrangemants have a close fit for the inner ring onto the shaft and a
slight clearance between the outer ring and the housing.
You have to look at the application in detail.
Mal
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Litemoth
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| posted on 22/7/11 at 05:04 PM |
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Put the bearing make and number up and we'll have a pop at telling you the bore size...(from tables, not pulled from the ether of course)
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A caliper WON'T really be good enough for measuring this job though.
[Edited on 22/7/11 by Litemoth]
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RAYLEE29
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| posted on 22/7/11 at 05:27 PM |
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Hi, a good starting point would be a couple of thou but the finish must be good if you do go too big you can always use loctite bearing fit but aim
for a good mechanical interferance that still allows the bearing to run free.
if you go too tight the race will seize up.
hope this helps Ray
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Project7
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| posted on 22/7/11 at 05:40 PM |
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There is a standard for defining the limits and fits between holes and shafts
This website explains it
http://www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm
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alistairolsen
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| posted on 22/7/11 at 05:45 PM |
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The bearing is:
Audi 80 quattro, 1985, 2.2 litre
Height 37,0 mm, Outer Ø 68,0 mm, Inner Ø 39,0 mm
OE NUMBER 321 498 625 E
Also fitted to Golf Sychro 4x4 models and some others.
It's to go in a modified steering knuckle which is originally to take a nominally 66mm bearing.
If a vernier isnt in any way up to it, what am I looking at? Something like this?:
http://www.workshopping.co.uk/product/draper-expert-50-160mm-bore-gauge-set/02753/
My Build Thread
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flak monkey
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| posted on 22/7/11 at 07:11 PM |
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Push in bearing fit is normally size to size. Anything tighter tends to reduce the running clearance of the bearing which can make them run hot,
unless they are designed to have a tighter housing. Anything tighter than 0.02mm interference on up to a 100mm bore will be an exceedingly tight
fit.
Normally for a bearing of that size you would specify +0/-0.02..
Oh and you need to check the bearing OD with a micrometer, you'll probably find it to be 67.99 OD.
[Edited on 22/7/11 by flak monkey]
Sera
http://www.motosera.com
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Litemoth
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| posted on 22/7/11 at 08:25 PM |
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[Edited on 22/7/11 by Litemoth]
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Litemoth
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| posted on 22/7/11 at 08:25 PM |
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OK, here goes,
Most of the bearing manufacturers recommend an N7 tolerance band for the 'Bearing housing' for this size/type bearing.
I'd prefer to speak to SKF to confirm as this is a bit of a special and also known as BAHB311315BD & IR8052 & 540733.
Looking up N7 - for a 68mm O/D gives -9/-39 microns which = 67.961mm to 67.991mm range.
Due to the bearing width and the associated press force, I'd recommend you go for the M6 tolerance
this = -5/-24 microns which = 67.976mm to 67.995mm range
If the bearing is a class '0' it'll be made to 68 (- 0.013mm) i.e. 67.987 - 68.000mm - difficult to measure with a vernier!!!
LINKY
Hope this helps....
[Edited on 22/7/11 by Litemoth]
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alistairolsen
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| posted on 22/7/11 at 08:59 PM |
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Hmm, some proper measuring equipment required! interesting stuff, thanks gents!
My Build Thread
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Litemoth
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| posted on 22/7/11 at 09:03 PM |
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Some of the chaps on here must have (a lend of) a bore mic/set .....It's the kind of thing you don't get the value from unless
you're standing by a lathe for a living....
Anyone??
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