Re: CNC Router How-To's

In a message dated 99-05-09 14:06:02 EDT, you write:

<< From: garfield@... (Gar Willis)

Pardon e'moi, I tweaked the subject to help follow-on's.

On Sun, 9 May 1999 13:25:41 EDT, Jonty50@... wrote:


>> Hee hee, yeah, unlike the hobby itself, eh? :)

Umm.. I have more hobbies than time or money unfortunately. It's kind of
strange how they all seem to be coming together synergistically lately. I'm
into (in no particular order) astronomy, computers, heavy duty machinery,
electronics, R/C planes, hard SF (the kind with rivets) and amateur science
pursuits ranging from meteor trail observation by reflected radio waves to
building my own seismograph many years ago.

>The V bearings run around $20 each, it basically takes 4 per axis. I've
found
>that the B-W track is not necessary, the wheels do very nicely riding on
1/4"
>diameter hardened steel rod ( I use music wire) that can be just pressed
into
>a 1/8" deep slot milled in an aluminum bar or rectangular tube. Very smooth
>motion, even smoother than the B-W track.

[ Huh, neat trick! This is actually wunnerful news on the pricing front,
[too, specially for guys that wanna route stuff where they're not
[ necessarily looking for Bridgeport resolution.

Thank you.. I got the idea from playing around with sliding glass door
rollers for a really low cost/precision router table (let's face it; for
routing wood 1/64" is more than adequate). The sliding glass door roller run
just fine on 1/4" rod. If you polish the rollers and the rod a bit they are
surprisingly smooth too.. I was gonna use birch ply for the whole thing,
table, gantry and so forth and just rout some grooves for the rod to lie in.
Another promising project that has not yet come to much beyond a few
preliminary experiments.

[ Jonathan (do you go by that, or is Jon OK?), lets peel the next layer
[ off the onion if yer willin? What are you using for axis translation:
[ rackNpinion, lead-screws, what? And WHERE on earth did you source the 8'
[ dimension on the Y axis trans. from?

Jon is fine.. I saw there was already another Jon here so used the
untruncated moniker to try and avoid confusion. BTW, you're one of the few to
spell Jonathan correctly.

I've been mulling several different translation options. There are linear
driver steppers that have a built in lead nut and ride on a lead screw. I had
thought to place a lead screw on either side of the table for the 96" axis
and just allow a linear stepper on either end of the gantry to carry it. This
plan avoids the whipping problem associated with turning long lead screws at
high RPM.

Another option would be a belt drive using a toothed belt and gearwheels. I
have all the parts for this option and am currently designing the gearboxes
required to allow a 0.0005"/step cog belt system. Belt drive is nice because
it has inherent dampening and cushioning properties and also doesn't mind a
some dirt and grit much. Use the larger size belts (I'm using 1" wide "L"
belting) and they are remarkably strong.

Another idea which I'm getting from my Astronomical interests is a form of
friction drive. Before you think I'm completely whacked out, let me tell you
that large telescopes around the world are gradually moving from a worm and
gear style drive to friction drive to track the stars (rotation of the earth
actually) in order to perform long duration astrophotography. Friction drive
is both more accurate and more easily machined than a worm and gear. Yeah, it
surprised me too...

Anyway, I envision an aircraft type cable stretched the length of the axis
with a friction type drive working its way back and forth down the length of
the cable. The cable will describe a path in much the shape of the greek
letter omega as it wraps around two passive pulleys at the left and right
bottom of the omega and a somewhat larger driven pulley that will form the
upper loop of the omega. I've done a couple of quick and dirty experiments
that have made me fairly confident that I could produce such a system that
would work to my requirements.

] Also, given your structure and your axis hardware, roughly what
] resolution are you hoping for?

For my purposes,. I'll be delerious if I get 0.002" repeatability, 0.010"
wouldn't be unusable.


[One of the other nice attributes about this type of guide is that it
[ doesn't require surface friction lube'ing like shafting or ways, eh?
[ That can be a problem when routing things like wood and especially foam
[ or plaster. This fact was brought to my attention somewhat "late" in my
[ own project plans, by a fellow who sent me some in-progress plans for a
[ big router table he had built outta "rollers on tubing". I'll get his
[ reference out if anyone's interested (actually be surprised if he wasn't
[ in the group already, but I've forgotten his name, and his plans are in
[ storage, sigh). He mentioned his design goals were to avoid having to
[ continually worry about cleaning linear bearings and keep the
[shafts/ways wet with lube. I thot that was a pretty important point I
[ had missed when planning me own, so I mention it to "the wise". B)

I've tried the "rollers on tubing". It works fine until you get dust under
the rollers and then the dust cakes under the intense pressure. The nice
thing about the BW wheels riding on hardened rod is that the contact area is
so small and hard that it just cuts right through most crap that gets on the
rods.. BW touts the "wiping action" of their wheels on their V track and it
does seem to work reasonably well that way too...

Well, I've run on at the fingertips for long enough.. Have fun folks...

Jon Croad...