On Sat, 08 Mar 2008 01:33:04 -0600, F. George McDuffee wrote:

On Sat, 08 Mar 2008 00:15:56 -0600, Tim Wescott
wrote:
snip
Is this just what I can expect to pay for these things? Did I go to the
wrong shop? What are the cost drivers here?
snip
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Looks like an interesting project.

The first cost driver is the low volume.

I would take a walk through WalMart, a kitchen/restaurant supply with
lots of pans, etc. and see what was close enough to modify. Possibly
something plastic, unless you need metal. A plastic box with a snap on
lid is good as you can pack everything inside.

These sites also looked interesting (stand on end?)
http://www.radiodaze.com/catalog-306-page62-63.pdf
http://www.hammondmfg.com/dwg20.htm
http://www.hammondmfg.com/dwg11.htm
(many other types on hammond site)


The brush/anodize finish looks nice but is extra handling and an
avoidable cost. If possible get a prefinished container or chassis

It may be cheaper to drill oversize holes for the bearings and then use
separate bearing pieces with sheet metal screws to allow
adjustment/alignment rather than trying to hold close tolerances on
position and size on a single fabricated/folded part.

I would consider plastic for the bearings also. You should be able to
make quite serviceable bearings yourself from plastic strip, possibly
reaming the bearing hole for a good finish if required.

You can also make a long reamer/alignment tool from a piece of drill-rod
to insure that the holes are inline from side to side. Indeed, you
might be able to use pop rivets here also eliminating the sheet metal
screws and speeding assembly.

If you need it, as a box or pan with closed ends will be considerably
more rigid, you may also be able to use off-the-shelf L brackets and
pop-rivet to the sides.

A little value analysis and you should be able to knock these out at
home with a drill press. For sheet metal a special drill is helpful.
For examples click on
http://www.castlewholesalers.com/GEN...tal-Drill-1-8-
to-7-8-Capacity.html
http://www.use-enco.com/CGI/INSRIT?
PMAKA=302-1109&PMPXNO=947556&PARTPG=INLMK3


Another possibility is a wood base with the "sides" made from commercial
L brackets attached to the base with screws.

Good luck and let the group know how you make out.

Feel free to email if you think I help.


I'm planning on either using Rulon bearing inserts from McMaster, or just
running the shaft against the aluminum.

Dunno about the adjustable bearing idea -- I've considered it, but if I'm
paying to have it assembled it may be worth a bit of time on a milling
machine to avoid having to find someone who's capable of doing the
bearing adjustment right. The whole bearing adjustment issue is being
driven by the sensor, so I'm going to look into that part independently.

It's important that it look reasonably professional, but bare aluminum
may be good enough -- I may ask for another quote without the anodizing.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html