re: thomson shafts was Re: Cnc Project-- combo router- plasma cutter

Doug,

A Few points re: "thomson" shafts and bearings:

1)The name itself is a big part of the cost. There are aother Mfr's
making good "thomson" style stuff. Interchangable even. BUT thomson
RAILS are good!

2)The rails and bearings are fairly priced, IMO. The "highway
robbery" occurs in the shaft SUPPORTS and bearing MOUNTS. Supports
just require holding one dimension(and can be shimmed!) and mount
blocks are "about" precision boring. You can trade time for money
here, if you can machine these parts accurately yourself. Or know a
friend who can... :-)

3) The newer super-duper-ball bushing allows the same loads to be
carried by a 1/2" shaft as used to take a 3/4" shaft. It "looks" weak
to an experienced eye, but the engineering calcs are there to back up
the claim.
Think about the typical 23 size, single stack stepper of a few years
ago(about 50 oz. in.) Now they are 125+ oz. in.! (better magnet
technology and mfg. controls) So don't let what "looks right" keep
you from saving money by trusting the engineering behind the newer
products! Having said that, It CAN BE HARD to DO this!! And if you
are making it to SELL, Ya BETTER take the "looks right" into account,
or people will not buy, and you will NOT be told WHY!

4) The industrial people are moving to the "ground linear rail"
systems (like THK) in DROVES. Check to see if these are close enough
to (or better than) the "thomson" prices to be a viable alternative.
These will look even MORE "too small" for a given load!! One thing to
be careful of here. Many of these systems require an ACCURATE, FLAT,
STABLE mounting surface. Alum. extrusions used "as is" are not
gonna' "cut it"! SOME of these systems have "compliance" built in to
accomodate an inaccurate mounting/structure. Be aware and make good
choices. I have seen more than one person frustrated as to WHY these
D@#$ expensive rails won't work!!!

5) Present yourself as an INDUSTRIAL user! Who will be buying a LOT
of stuff! Not as a home shop guy making "one machine for my garage"!
There are definite price structures which although not always fair,
MUST be taken into consideration.

Hope this helps.

Ballendo

>I just priced out Thompson shafts and linear bearings
>for a 5'X10' router today. We have to find a more cost effective
>method.
>Doug