Measuring PCD holes

Muzzer

That is interesting, but I have never seen a wheel/tyre balancing machine that did anything other than use a tapered centering plug to pick up with that central bore.

I'd have bet the farm on that being wrong! Now I'm not so sure. At school I was taught that the Ancient Greeks did not have algebra. I was misled. Or not paying attention. Either way it's a good job I'm not a betting man.

Dave

Friend of a friend needs to be extremely careful in how he has spacers made and fitted if he doesn't want sheared wheel bolts/studs and then the wheel parting company at speed.

The wheel should be located on a spigot that forms part of the hub, as it will be as originally fitted on the car by the manufacturer. If you are making spacers, the spacer needs to be bored with a female spigot housing on its inside face that has a tight fit to the hub spigot. In turn the spacer also needs to have a hub centric spigot machined on its outer face to locate snugly in the wheel centre.

Both female and male spigots on the spacer need to be exactly co-centric with each other, or it can set up a centrifugal imbalance which can be impossible to balance out, and be dangerous as it puts a lot of loading force on wheel bearings and ball joints.

ALL of the wheel bolt /stud clamping effort is designed to be only for that, in other words neither the studs/bolts or their cone shaped mating surfaces are designed to take any lateral shear force, the hub to wheel spigot should take care of that.

If you know all this already, my apologies.

I think your farm is safe. Algebra was developed by Arabic mathematicians 1000 years after Euclid. The Greeks and Romans didn't really have the concept of a zero as we know it in their mathematics, which would make solving equations tricky.

Cheers,

Rod

Euclid would have drawn it out. Classical geometry is just drawing and comes from Euclid's work. What ever is said it is quite valid and not accurate (probably an order of magnitude less than the measurements taken from the hub).

JA

Edited By JA on 28/11/2016 12:58:07

Edited By JA on 28/11/2016 13:00:13

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Sorry, JA ... I don't quite get your point ^^^

Could you please clarify ?

MichaelG.

Rod and JA : that's exactly what I thought. Then I read about the "Bloom of Thymaridas" in Wikipaedia's 'History of Algebra'. Although based on geometry and not a fully developed algebra, it does include solving simultaneous linear equations in Euclid's time and place. That's my interpretation anyway. But I admit my maths knowledge is sadly limited.

Dave

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Yes.

TBH I thought their use had been banned years ago back in the late 70's - early 80's due to their use and other modifications causing poor handling and effecting the whole balance of the car. Not to mention stud shearing.

I 'think' this craze all started in the UK of putting flares onto wheel arches, widening the wheel base, lowering the front and jacking up the rear due to the US TV series Starskey and Hutch.

Of course said 'victim' car had to then have the obligatory stripe, stick in sun visor with names on and most importantly a monster size CB antenna.

Nick

Thanks David. I found that very interesting and informative.

Steve

Edited By Steven Vine on 28/11/2016 13:42:32

Nick

I was there, been there done that .

And that's how I know .

Cor, you lot don't 'arf make it complicated!

Use my method and if it doesn't come very close to a 'sensible' dimension, take the average of a few measurements.

Neil

MichaelG

I have been sitting for about an hour trying to think of how to reply to this.

My first draft was on how the Greeks would have solved the problem arithmetically. I had to retreat on that one since it appears that I am, or even we as modern man are, wrong to consider equations as algebra. Wikipedia, as Dave says, suggests that the ancients solved equations. I think that is a tall order. OK they could multiply and divide (and used squares, cubes, square roots, cube roots and pi) but they were hindered by their numbering system (I haven't a clue on how to add and subtract using Roman numerals). Romans used fractions, so I guess the Greeks did, but we are taught that the Arabs (not the French) introduced the decimal system. Given all this drawing the problem out as a piece of geometry makes full sense.

Return to your query, the accuracy of the result is limited by the drawing accuracy. If it was drawn full size the accuracy would be no better than a hundredth of an inch while the measurement accuracy would hopefully be to the nearest thou.

Neil - We can make the simplest question very complicated.

JA

Interesting link, thanks.

It's algebra, Jim...

Rod

I gathered(?) that this was an old vehicle, possibly around the same vintage as various Renaults, Citroens, Fiats etc that had no centre hub in the first place (1970-80s IIRC). Look them up if your memory fails you. So it's possible that the feature wasn't used for location although I agree it's unlikely on a vehicle like this.

Renault 4, 5, 16, 17; Fiat 500, 600, 127, Shitroen 2CV / Ami etc etc....

Edited By Muzzer on 28/11/2016 16:13:55

In the general case I still think you'd want to take an average of the values you obtain from each pair of holes if you're using the perpendicular bisectors method because there'll inevitably be some variation in hole dimension and position as well as in your measurements.

It's especially the case when trying the work out the PCD from blind tapped holes - I recently had that problem when trying to make a backplate for an old 3-jaw chuck where each hole ID measured differently and I didn't have any of the correct BSW threaded rod I could sacrifice.

Jon

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Thanks, JA ... I didn't mean to cause you too much bother.

I do accept your point about drawing accuracy [although, if carefully planned & executed, I believe this exercise could be done to better than a hundredth of an inch], but what particularly interests me is that the method is theoretically perfect, and therefore any inaccuracy is attributable solely to technique.

MichaelG.

Thanks. I realise I have a good item for my Christmas present list - a good comprehensive history of mathematics.

JA

Nick might just be easier to cut the disc out of the wheel rim and have your welder mate put it back in with the new offset

Ah, not so......I have had exactly this problem which took me some time to understand - balancing tyres at the tyre centre produced a clearly out of balance wheel.

Eventually I took the car to a performance focused place and they took one look and got out a 5 way 'sliding spider' affair that they installed in place of the cones. This looks like 5 studs on some form of geared backplate that expand in unison, maintaining their centre distance. Add wheel and then screw up 5 nuts and balance.

Cause of lots of grumbling at the tyre place since it is a non trivial exercise but perfect result.

Wheels are of GKN origin and were originally shod with Avon tyres way back in 1973.

Scroll operated spider, but at a performance focused place. Now we all know where to go. Thank you