Re: [taigtools] Making a really thin paraboloid?
- On Sun, 31 Aug 2003, Paul Anderson wrote:
> Tom Benedict wrote:Got a funny on that one, too!
> > Apparently some people at ESO pointed a four meter
> > telescope at Venus and the collected light heated up their CCD enough to
> > damage it.
> Piffle! Makes you wonder what would happen if they pointed it at the sun:)
If anyone gets the chance to visit McDonald Observatory in the Davis
Mountains in West Texas, be sure to go on a tour of the summit, but also
try to catch the solar observing.
Frank Cianciolo, who's now director of the Visitor's Center, used to give
the solar observing tour on a little 5" or 8" telescope. At first he did
it with a 3" aperture mask, and used the telescope to project the image
onto a 3x5 card, but without fail someone would ALWAYS try to stick their
head in front of the card and look through the telescope directly. Frank
took to starting his speech by using the telescope to burn holes in one of
the visitor's center pamphlets, and handing it to whoever looked most
likely to stick their head in the beam. Even with that, people still
These days I think they've got some dedicated video setup, so the risk is
a think of the past. Still, one of my fondest memories of the place is of
Frank burning holes in a pamphlet, handing the still smoking paper to some
kid, and saying, "Don't."
- I finished the prototype. It's not all THAT thin, but that's for another
day. I've uploaded pictures to my photo gallery. It's cut out of 2"
diameter Delrin, and was done with my CNC mill converted to a lathe.
Unfortunately I still haven't found all my lathe tools since moving, so I
wound up using a facing tool swung around at an angle. It's got a
miniscule tip radius, so the cut looks a little ragged. It's pretty
smooth to the touch, though. I also wasn't 100% careful about setting up
the tool, so there's a central pip because the tool wasn't completely on
centerline. When cutting the final part, I'll either find the rest of my
tools, or grind a new one to spec. I'll also be a lot more careful when
centering, and use a slower feed to improve surface quality.
After careful consideration, I'm going to urge the guy doing the optical
design to either live with the fiber fed pinholes, or spend the time to
let me learn how to make draw dies. We're in a bit of a rush, so my guess
is we're going with fiber.
My only concern with all this is that I was told to hold the figure to
1/10mm, which I've done, and to make a part about 50mm in diameter, which
I've done. I get the uncomfortable feeling this "prototype" may wind up
being part of the production optics. Hopefully I've still got enough
Delrin to make a better part and slip it in.
While all this was going on, a hurricane passed not too far from here.
There was no real damage where I am, but my shop took on a little water.
Mmmm, gotta love my Shop Vac.
All in all I'm pretty stoked. I got to try my hand at contour milling,
and even though I didn't use it the results were great. I also got to try
cutting a mathematical profile on a lathe. Again, the results were great.
I'm also learning about draw dies, even though I may not wind up making
them for this project. Can't complain. Shop life is good.
- I wound up on a web site for a PCB milling machine that got me thinking
about toolchangers again. At one point someone (ticutter?) was discussing
designing a toolchanger for the Taig CNC mill. Any word on this?
The PCB milling machine I saw had automatic tool changing capability. It
had a rack on the mill table that held around six to eight tools, each in
a toolholder. The pictures weren't large enough to see what the
spindle-end of the toolholders really looked like. To change tools, it
would move to an empty spot in the rack, magically release the tool, move
to a new spot, and magically pick up the new one.
Near as I can tell, at the very least you need:
1 - A way to start and stop the spindle
2 - Some way to know where all the tools are
3 - A way to grab a toolholder
4 - A way to release a toolholder
#1 can be handled with a relay. I'm in the process of adding this to my
mill at the moment. Still waiting on parts.
#2 can be handled with home switches and some way to refer to an absolute
coordinate frame. (I hope.) So long as the tool rack lives in the same
place all the time, this would be a one-time setup.
#3 and #4 are the kickers. I'm sure there are lots of ways to do this,
but the one that keeps coming up in my mind is some sort of power drawbar.
I'd like to think there are better ways to do this. The paper sketch I
have at the moment involves a power drawbar, and a collet/toolholder setup
with a taper and splines. I'm fairly certain it would work, but it's not
pretty and I'd rather not build it.
For PCB milling, you may be able to get away with something as
straightforward as a nice strong magnet to keep the collet seated, and a
coil to force tool release. I don't know. (This might explain the way
the toolholders appeared, small though the pictures were.) I've had
enough tool dig-ins not to want to go this route on my mill. Firm
mechanical attachment is a good thing.
I don't know if I'm ready to take this on as a project yet, but I'm
certainly interested in looking at design ideas. Has anyone tried to
build such a beast for their Taig? I know someone built a full-blown
turret tool changer for a Sherline. I wouldn't be against setting up
something like that, either.
Always looking for new reasons to go, "WHAT?! HIT ESTOP!" in my shop...
- i got home from work tonite to find a package on my doorstep, got all
happy and thought about dancing a jig... then i decided to stop in
here at the forum to say: "my lathe bed is longer than your lathe
- On Tue, 9 Sep 2003, mark allen wrote:
> i got home from work tonite to find a package on my doorstep, got allPictures! I want pictures! Don't worry, I trust you. But if you're
> happy and thought about dancing a jig... then i decided to stop in here
> at the forum to say: "my lathe bed is longer than your lathe bed.
going to make me lust after your lathe bed, do right by me and let me know
exactly what I'm missing.
- At 02:13 09/09/2003 +0000, you wrote:
>i got home from work tonite to find a package on my doorstep, got allMark -
>happy and thought about dancing a jig... then i decided to stop in
>here at the forum to say: "my lathe bed is longer than your lathe
Is this an extruded aluminium lathe bed, or is it steel like the
- the bed in question is a cuesmith bed. four feet long. $250. i'm not
entirely sure of it's composition... i'm pretty new at this. it's
rather light.... lighter than i was expecting. but then i don't have
a little bed to compare to. nevertheless... if it'll work for cue
turning, it'll work for my needs. . . 4" diameter stainless... about
just kidding. i just want to spin slightly longer chunks of wood than
the little bed'd handle.
have a day :-|