Re: CNC Robotics by Geoff Williams

I waited anxiously for this book to become available, and even paid
$15 for overnight delivery when Amazon finally had it in stock.

The pre-pub blurbs say it shows you how to build the equivelent of a
$7500 workshop bot (an intentional play on the name ShopBot I guess)
for $1500, and the cover front and rear are full of promises not
delivered inside...

"Great for use... on the industrial floor" NOT!

"Provides step-by-step instructions for building your own CNC
machine"... "Scaling and customizing instructions for building just
the robot you want"... "Sources for easily obtained parts"

There is no discussion of design rationale, bearing loads, etc. He
just jumps in and, in a 12 page Chapter 1 (three of which are used
for showing the explosion views of the $3000? NuArc copy camera he
scrounged the entire Y-axis carriage and rails from and telling you
he made the Z axis from a TV shelf slide), tells you what he used.
Nothing about the pros and cons and accuracy implications of
different linear motion components, ballscrews vs acme, etc. Less
text in the chapter than someone would use in a post here breifly
describing their homebuilt CNC machine.

Chapter 2 uses 51 of its 62 pages to reprint the manufacturer's
documentation (probably available online) for the L297 and L298 chips
he uses in his stepper motor driver... Chapter 3 is 20 pages showing
how to photo etch his printed cicuit board... Chapter 4 is 13 pages
showing how to drill the board and solder the components on. This
information may be of use to some, but with proven 3-axis stepper
driver boards readily available for $100-150, I think I'd skip the
electronic components gathing, and the gloves, eye protection,
respirator, and the carefully monitored heated baking dish full of of
ferric chloride solution giving off "nasty and dangerous fumes."

Chapter 5 shows you how to install KellyWare KCam software and test
your drives... he barely mentions that he used three PC power
supplies to power the three axii (he left them out on the "Materials
Needed" list that starts the chapter); no discussion at all about
power supply selection issues if you happen to have stepper motors
different from the surplus ones he found.

The next few chapters show how he drilled and bolted the frame and
gantry, and made pillow blocks... how he crudely supported the 3/4"
linear shafting on free-standing bolts (he doesn't say, but I guess
he bought the shafting pre-tapped, which nearly triples the price). I
just love this... "In order to assemble the Y-axis, you will need the
following tools and materials: Guide rails... Slide from NuArc copy
camera...". The shaft support bolts are used to "straighten" the
precision rails to a constant height from the square tubing that
supports them (??).

After a decent chapter on motor and leadscrew mounting (no comment on
the very long skinny X-axis leadscrew), more about KCam, some crude
router mounting, and some examples of some things he's routed, the
book ends with a list of addresses and phone numbers of corporate
headquarters of linear motion components manufacturers, etc.

This book isn't real impressive with its lack of technical info.
Most of it is like the web pages individuals put up showing pictures
of the CNC router they built, often with scrounged/E-bayed parts that
the next guy may or may not be able to find. Like those websites,
it's always interesting to "see how someone else did it", but don't
burn your $35 on this book expecting much more. If nothing else, you
can vicariously "build" your first machine in your mind by reading
this book, then build your first real machine better after more web
research and questions to others online who seem to be more informed
on design issues than this author.



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "MDS1878" <mds1878@c...>
wrote:

> Build your own workshop Bot
>
> Router table project!
>
> I have been waiting several weeks for Amazon to get this book in.

As

> a newbie too this group in many ways I found this book helpful.

With

> that said it does have a number of failings. That reading this

news

> group, makes me quick to realize.
> Using a computer power supply to power three type 34 step motors is
> different. Wonder why he has 15 to 20 ipm travel speed? As a
> machinist Geoff is a great carpenter. Though the section on

building

> drivers I found quite good, also the software section. Using a TV
> tray slide from Home Depot for the Y-axis was creative!
>
>
> On another note I purchased an X-Axis table! See if you can figure
> out what machine this came out of?
> http://cgi.ebay.com/ws/eBayISAPI.dll?
> ViewItem&item=2530755722&category=11805
>
>
> Ken