JVL machining question

Ok John, I have a legitimate question for you.

How do you (general form) know how much tighter to machine a surface for a press fit bearing? Like for example, a wheel hub, strut top, etc.

Is there a standard amount by material? Or just a "make it .XXXX" smaller per .YYYY" of diameter?"

I figure you'd know... I'm not sure what to google for. I don't know what that would be called.

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Welcome to the cult of JVL drink the koolaid or be banned.

I think somewhere around .0005 per inch seems to ring a bell. My memories foggy though and I'm not a machinest. Most all bearing manufactures have specs available for interference. I'd try and go off whatever they recommend if at all possible.

Machinist's Handbook is full of fits and tolerances.

Many bearing catalogs also list suggested fits.

Gotta get the class of fit right tho.

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John Vanlandingham
Sleezattle, WA, USA

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Well I'm not JVL, but.....
Interference fits can get really complicated. Temperature ranges, loads, and the thermal expansion of different materials needs to be known, as well as the modulus (stiffness of the material). Then you have to think about how it's going to be machined, different processes leave different finish roughness and these will effect how much clamping force is in the interference fits after it's all assembled.

As bearings get smaller or thinner in OD-ID terms, they will compress easier. So care must be taken that they do not end up so tight that the bearings will not rotate or be "notchy" when assembled.

Though, through years of being on this round rock we can observe things and take note of how things are done by people much smarter than us. For lightly loaded things 0.0005-0.002in interference seems to be normal. When things get really serious, I have done up to 0.010in which require a freezer and an oven to assemble the parts properly.

I think SKF has a cool tool on their website somewhere that helps with these calculations.

Hope this helps!

This tool lets you play with different sizes and materials.
http://www.tribology-abc.com/calculators/e3_8.htm

Found by googling "press fit calculator"

I've wondered about this also. One companies struts we dissasembled were so loose on the bushing you could put in and remove by hand.

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Grant Hughes

Good job asking a question without laying in any extras Timm! I R proud.

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-Tom
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What does class of fit mean? Like the material its going into? Or what kind of part it is?

I was just looking around at some spare stuff I had laying around and sort of wondered. Figured you'd know, as I don't know the proper terms to even search for.

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Welcome to the cult of JVL drink the koolaid or be banned.

Class of fit is related to what you're using the sucker for; a fit with more interference is harder to put together and deforms shit more, but has more friction between the two things. http://www.me.rochester.edu/courses/ME104Q.dque/PDF/Fits.pdf is googled; has the basic classes of fit with description; goes from having clearance so things can move relative to one another, to enough interference where you have to torch heat (one of) the suckers. As said, lotta rolling element bearing makers will tell you what class of fit to use; too much and you deform the bearing race, but not enough and the bearing shell may spin in the housing.

As they said:

1) if it's a bearing or similar manufactured component, look through the tech info for it or ask the manufacturer. When you ask, sometimes it's different if the bearing is pressed into steel or aluminum, so know your material first.

1 if it's an OEM part that you're making a new housing for, just measure what it normally comes out of and copy it or compare the fit to the interference fit tables to see about what fit they intended and adjust for your use.

2) If 1 doesn't work, look at machinist handbook interference fits. Anyone doing any machining should have a machinist handbook. old used ones are fine, they don't change much.

As an engineer, you can geek over this stuff all day, but in the end if it's close it usually works. If it breaks in the future, pay close attention to the design and fix it..

Perry

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Perry

FE570s course bike
KTM 950 ADV
74 Beetle turbo-efi etc..
72 Beetle stage rally project WRX powered
Attended about 15 rallies, usually a volunteer in a course car.

Gallant worries about the press fit specifications.
Goofus hones away most of the press fit to make assembly/disassembly easier.

I'll admit to have been a Goofus when putting rearends together. After the fourth time of swapping pinion shims you'd want to as well. I haven't had an issue yet, so either I'm lucky or there's a lot of excess press fit with cheaply mass produced items so that someone doesn't put a high end of spec framus over a low end of spec thingy and end up with a rattle fit.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

Just makea set of assembly races for the pinion that have a go in and out easy, the final assemble with press fit..