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 Set screw tips

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rjw
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PostSubject: Set screw tips   Tue Jan 12, 2010 9:56 pm

Here's a set screw tip. Use 2 shorter ones. Install the first then grind the tip of the second flat and install on top of the first. the reason for grinding it flat is so as to not mess up the head of the first with the cup point of the second.

We've been doing this for years and never had ANY come loose and no loctite. We have some setups with 2 1/8" set screws on top of each other rather than 1 1/4" long one with loctite.

Just snug up the first one and tighten the second one a bit more than the first.

This is a standard practice in assembling Bridgeport mills from the factory...not my invention, but it sure works.

You should also have set screws at 2 locations on the pulley...traditionally 90 degrees from each other..but that is open to debate...some like 60 and I often drill thru for 180 locations....keeps things balanced at higher r's.

As an alternative, hollow set screws can be also used as a lock over another regular set screw.

Please feel free to add, comment or ask questions as you see fit.

Richard

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rdubard
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PostSubject: Re: Set screw tips   Wed Jan 13, 2010 12:34 am

Thanks for the tip.

I'm just wonderin' WHY does this work better?

I'm gonna make a guess, and maybe you can tell me if it's right--

With a single set screw, the screw is held in by the forces created against the threads when the end hits the shaft. As the shaft flexes, these forces vary, add in any vibration and the screw works its way loose.

With two, the screws are both held in by the forces created against the threads when they contact each other-- but now all that's enclosed in the continuous metal 'thread tube', so there is little variation in those forces and everything stays tight.

Maybe??
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rjw
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PostSubject: Re: Set screw tips   Wed Jan 13, 2010 9:28 am

I think that part of the problem is related to fittting things.

A nice snug pulley to shaft fit takes a lot of stress off of the set screw...plus set screws are considered a light duty fastening method.

Constant forward /reverse or vibration casues the set screw to walk and eventually come loose. By adding the second one, the 2 screws push against the threads in opposite directions, taking up the thread slop as well.

Advice:

1) don't use set screws if they can be avoided
2) if used, try for tighter fits
3) double set screw to preload the whole system in both directions
4) keyways will obviously take the load off of the set screw

note: no amount of loctite is going to stop a single set screw in a pulley on a sloppy fit shaft from walking

jmo

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Josh Raichel
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PostSubject: Re: Set screw tips   Wed Jan 13, 2010 12:06 pm

For Redemption we had a VERY loose fit pulley go onto the Scorpion motor. We had a setup of 4 set screw holes. And we doubled them up like Richard suggests. We had two holes at 0 degrees, then another 2 at 90degrees. These set screws held up EVEN on a non flat shaft (such as in century III) it was just 4 set screws holding the pulley to the shaft with another on top to hold it in. They never came out. Slipped occasionally (from the huge eggbeater forces) but a re-tighten after every match and it was fine.
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rjw
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PostSubject: Re: Set screw tips   Wed Jan 13, 2010 12:12 pm

and there you have it

vapor bots ho!

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SenaiERI
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PostSubject: Re: Set screw tips   Thu Jan 14, 2010 12:04 am

Thanks for the tip rjw.
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rjw
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PostSubject: Re: Set screw tips   Thu Jan 14, 2010 8:38 am

SenaiERI wrote:
Thanks for the tip rjw.

you're welcome

just remember that there is no substitute for good fits between shafts and bores of componente, use key ways or clamping collars for better results.

but double set screw when using them at all....loctite as well is your choice, but we don't use it...mostly cause we check things between battles and once you break the dried bond, you need to apply more...and it's messy and not really needed except in extreme cases

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