[Robotgroup] Sears offering CNC system

[Vern Graner]

Saw this on another list I'm on (the Halloween-L) and thought I'd cross
post it here as I think it relevant to some of the recent conversations
about fab-lab:

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> On 1/10/07, Brett Hays <bretth at htonline.net> wrote:
>> Speaking of routers...did anyone see that Sears Compucarve
>> commercial on tv lately?  A CNC (or at least computer
>> controlled) router for $1899...way too cool.
>>
>> You could DIY your own with far more capabilities
>> for much less.
>>
>> ***waiting for SpookyDad's comments***

Spookydad said:
This Sears Compucarve has caused a bit of a stir on a couple of the CNC
lists I am on. On the surface $1899 seems a little pricey for a small
router. When you first look at the homebrew CNC hobby, it appears that
the you can build your own machine for a lot less. It is less but not a
lot less.

A typical list would be:

-MDF sheets $60
-Acme screws and nuts. $40
-Bearings $45
-Guide rails/bars/rods $40
-HDPE for bearing blocks etc $40
-Wiring, switches, enclosures $100
-Stepper motors, drivers, power supply $450
-Breakout box $45
-Mach 3 software $160
-SheetCAM $150
-Meshcam $150

That is $1280 before you add your router. If you plan to do any serious
carving of text then I would ignore the MeshCAM and SheetCAM and buy
VCarve Pro for $500. SheetCAM is so good at simple 2D carving that it is
worth having SheetCAM and VCarve Pro. VCarve will do what SheetCAM will
do and much more but SheetCAM does the simple stuff SO much faster and
easier.

This doesn't account for your time to build the unit or the time working
out the various timing/wiring/control/tuning issues. Then you have to
spend time learning about what all the stuff does and how it works together.

Now on the other side of the coin, the Compucarve unit has it's share of
downsides. The biggest, IMHO, is that it is a proprietary software
control system that doesn't run standard G-Code. You are stuck with the
one company's offerings for the design library.

The other problem with the sears unit is the limited width. 14 1/2" is
not a very wide board. With careful design you could piece boards
together.  he carving depth is limited to about 1". This means it isn't
true 3D carving. This is probably adequate for most signs/tombstones etc.

The upsides to the Sears unit are many. It is a plug and go unit from a
single vendor. This means there is ONE place to go when you have
problems. This is an advantage because you have one number to call and
they can decide what particular piece isn't doing what it is supposed to do.

Another nice feature of the Sears unit is because it is essentially a
fancy thickness planer with a roller bed, the length of the carving is
limited only by your workspace.

What is unknown about the Sears unit is the speed, accuracy and
repeatability of the unit. Speed may not seem like much of an issue if
you are not doing production work, but if it takes 3 hours to carve the
text on a tombstone, it can get tiresome fast. A major problem with
homebrew routers is electrical noise that causes the router to "loose
steps". In simple terms, that means the router head stops moving while
the computer thinks it is still going. Usually this is only for a second
or two but this is enough to ruin the piece you are working on.

This is not bad on a 10 minute job on a piece of scrap MDF. If it
happens on a $50 piece of maple after 4 hours of carving, then it IS
significant. Repeatability measures how well it can produce the same
cut. This is essential if you are making a production run of the same part.

The cool thing about the Sears unit is that it is really a CarveWright
machine. The company was formed by a bunch of NASA robotics engineers
right here in Houston. Their website is:
http://www.carvewright.com/index.html

I believe you can download a trial version of their software for free. I
have already spent $1500 on my machine so I am committed to the homebrew
path.

SpookyDad
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Vern


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