# Long years since High School Math



## ship (Aug 7, 2009)

Ok... re-arranging and painting the living room and the library part of it is like a 4' cubic stack of books, LP-78's and CD's. Backstage handbook is lost within the pile but it's time to replace the broken non-free spin belt for my random orbital sander given it broke.

3/32" dia. belt, 8.5/8" length once broken length of the belt. What is its' OD?


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## n1ist (Aug 7, 2009)

Circ = Pi * Diam, so it looks like 2.75"
/mike


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## jwl868 (Aug 7, 2009)

Unless the material stretches along the outer diameter and compresses along the inner diameter, then the centerline diameter is about 2.75” per the above post, and the outer diameter is about 2.75” + 3/32” = 2.84”.

Joe


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## derekleffew (Aug 7, 2009)

ship said:


> ...the broken non-free spin belt for my random orbital sander given it broke. ...


Trick question. By definition, random orbital sanders do not have belts.


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## ship (Aug 10, 2009)

derekleffew said:


> Trick question. By definition, random orbital sanders do not have belts.



Mine does. Porter Cable model #334 as modified to #333 series = I like the velcro pad better. Belt don't really move persay, it just provides friction to slow down pad spinning especially after shut off, it doesn't drive the pad.

McMaster 8.1/2" OD o-ring worked fine part #3044K656. Will see how long it lasts given the material type is different, price and +/- how much it costs in lasting above or below what a Porter Cable replacement O-Ring would cost. I forget what I paid last time I replaced it.

In fitting well it would seem the old broken measurement was a stretched one that's now invalid.

Thanks for the math above. Part 37 on the Porter Cable #334 website parts list though such a part is not listed for specific detail or part number.


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## derekleffew (Aug 10, 2009)

_Mea culpa._ I confused "sanding belt" with "drive belt."

Porter Cable Part#903373, $7.95. http://www.ereplacementparts.com/po...-orbit-palm-sander-parts-c-129_1997_2006.html.


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## ship (Aug 11, 2009)

derekleffew said:


> _Mea culpa._ I confused "sanding belt" with "drive belt."
> 
> Porter Cable Part#903373, $7.95. Porter Cable 333 Parts List and Diagram - Type 3 : eReplacementParts.com.



Hmm, cool thanks, the urathane belt needs to last six months to pay off it would seem now.

Still though in that 1/8" shorter belt fitting well and working well tonight... perhaps 1/8" oveall stretch of a fairly short belt in overall length should be considered in buying a new belt as concept. This given perhaps the stock dia. of the belt in stretching that proposed 1/8" might have also been thicker. Will see how long the McMaster belt lasts on the other hand at half the price. Amazing the difference for now once I replaced it and also cleaned all the scum off the blower fins.


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