Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!agate!howland.reston.ans.net!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!ncar!uchinews!cdsmail!timbuk.cray.com!hemlock.cray.com!kilian
From: kilian@cray.com (Alan Kilian)
Subject: Re: Two setscrews: 180 degrees or 90 degrees apart?
Message-ID: <1994Feb17.213850.27431@hemlock.cray.com>
Lines: 53
Nntp-Posting-Host: poplar12
Organization: Cray Research, Inc.
Date: 17 Feb 94 21:38:50 CST

Well, I don't drill the two setscrews at a 90 degree angle for two reasons.

1) I don't have a tap that has threads cut out to the very end of the tap
   and so I need about 1/4 Inch deeper hole than the threads. (The first
   1/4 Inch of the tap has gradually increasing threads) so the bottom
   1/4 Inch of the hole cannot be used. So, I drill straight through and
   tap right through in one go and I have two threaded holes 180 degrees
   apart. If I drill two holes 90 degrees apart and all the way through
   the hub, there's not much left and the wheel wobbles even with 4 screws.

2) I can't ever find the EXACT size drill for a motor shaft. I even use 
   reamers and I just can't get the EXACT size hole in a hub. This means 
   that if I have a single setscrew or two 90 degree apart setscrews that 
   the wheel will not be centered on the shaft. With two 180 degree screws,
   I can tighten them alternately, and adjust them to get the wheel centered.

So there is a method to my madness. What works is kept, what fails gets tossed.

              -Alan Kilian


> From: mboettch@students.wisc (Michael E. Boettcher)
> 
> In article <1994Feb9.133224.4782@hemlock.cray.com>, kilian@cray.com (Alan
> Kilian) wrote:
> 
> > What I finally did was to buy a hobby lathe and vertical mill and I now
> > use the lathe to build small aluminum "mags" that fit the motor shaft
> > and a rubber tire from the model airplane store and have two setscrews on
> > opposite sides of the motor shaft. I file two flat spots on the shaft and
> > bingo only two hours metal work per wheel and I'm all set.
> 
> 
> Just a bit of practical information.  When you drill the two holes for the
> two set screws, try to keep them 90 degrees apart.  If the holes are on
> opposite sides of the shaft, the set screws may allow the wheel to pivot on
> the shaft if the fit isn't tight.  This lets the shaft and wheel to wear.
> 
> This is standard for bearings, pulleys, etc.  The two set screws force the
> shaft to the other side of the hole, and take up the slop in the fit.  
>  
> Then again...  since the shafts are so small this might not be practical,
> and since the system will not be used for extended periods, this probably
> will not matter.
> 
> Just thought that I would point it out. (had to fix a gear the other day
> that someone made with opposite side set screws)
> 
> 
-- 
 -Alan Kilian           kilian@cray.com 612.683.5499 (Work) 612.721.3990 (Home)
 "Seeing is much more than the perception of images. 
  It is the application of knowledge" Some Visual Agnosia expert on NOVA
