|
[DPRG] Re: Monday Night Chat - machine tools for robot building
(LONG)
Subject: [DPRG] Re: Monday Night Chat - machine tools for robot building
(LONG)
From: David P. Anderson
dpa at io.isem.smu.edu
Date: Tue Mar 6 17:07:40 CST 2001
Re: Monday Night Chat: machine tools for robot builders.
Hi DPRG and SRS, and RoboDave
Here is the aforementioned follow up on last night's mill/lathe discussion:
I've had a lathe for some years before I bought a milling machine. It is
an 8" Emco-Maier (Austrian) Compact 8E that was sold in the before-time by
Sears under the Craftsman label. They are still sold by Blue Ridge Machinery.
http://www.blueridgemachinery.com (pretty pricy, about $2000 last I checked.)
I love this lathe. It was owned by two different professional machinists
before I bought it. I think it was new circa 1975. It is an excellent
and extremely precise piece of equipment. I bought it used for $500 with
only one chuck, a tail stock, and no tooling. I've added over the years
probably another $2000 in tooling, including a four-jaw chuck, face-plate,
and milling attachments.
Grizzly sells a Chinese knockoff of the same lathe for about $800. Check out:
http://www.grizzlyimports.com/fcgi-bin/lookup.fcgi/products/lookup.cfg?q=item&kw=G4000
Jet sells a similar machine, I can't lay my hand on the URL.
Dave, your question is not a simple one for me to answer. I probably use my mill
more often than I do my lathe. Especially for layout work and as a drill press.
That said, if I only had one machine it would be the lathe. With horizontal milling
attachments. I can do all milling operations on the lathe that I can on the mill,
albeit less conveniently. But I can't do all lathe operations on the mill that
I can do on the lathe. The lathe is the classic universal tool of the industrial
revolution, the only machine, as is said, able to reproduce itself.
So I'd suggest that's a good place to start, and then purchase a dedicated milling
machine sometime later when you get tired of breaking down and setting up the lathe
milling attachments all the time :) At least that's what I did.
The Sherline equipment is very excellent hardware also, and the way it can be
reconfigured for various lathe/milling/drilling operations is very clever and
versatile. But it is rather small. You might also look at TAIG and SAKAI, both
in the Sherline size/price range. But the Sherline clearly has the most developed
tooling, after market goodies, and so forth.
The imported "mill drills" available from various sources (Jet, Grizzly, etc)
seem pretty popular. A big disadvantage of these machines over the others is
that the milling head is usually mounted on a cylindrical column, with no
dovetails or keying. This makes it very difficult to move the head (like to
change collets or drill chucks) and get it back to the same place. More useful
than a drill press but less useful than a real vertical mill, or the mini-mills
like the Taig, Grizzly, and Sherline.
My vertical milling machine is a Grizzly G8689. This is a nice little manual mill
design by Atlas as the CH-10M, indifferently manufactured and assembled somewhere
in the Orient. Check out:
http://www.zdnet.com/yil/content/depts/billsbest/thatlas.html
for a nice Atlas/Sherline comparison.
The Chinese-ness of the manufacture is evident from:
1. Plastic rather then metal gears in the mill head (I've
broken two, Grizzly sent a metal replacement for one of them)
2. The X/Y table flatness was off by 6 thousandths from the front to
the back of the table as I received it. I took it to a local machine
shop and had it ground flat within .001 for $50.
3. Both X and Y axes were jammed, and the vertical column and mill head
were incorrectly assembled. I had to dis-assemble and re-assemble
the mill to get the lead screws, nuts, and gibs to work correctly.
3. The lead screws are not the standard 10 threads per inch ACME
threads, but rather 16 threads per inch ACME threads. This means the
table moves 1/16 inch for each full rotation of the handle, or 62.5
thousandths per revolution. Since my calipers and indicators are all
marked off in thousands, this makes measurements and layouts very
confusing, requiring modulo 62.5 math. I need to move .375 inch,
how many handle revolutions+ is that? To make matters worse, the
handle micrometers are divided not into 62.5 divisions, but rather
63 divisions. So rotating the handle twice will move the table 125
thousandths (1/8 inch) but counting divisions with yield 126. Bizarre.
The web page referenced above includes an article on replacing the
lead screws and bronze nuts with standard 10 TPI hardware, which I
may do some day. In the meantime I have mounted cheap dial calipers
to the table X and Y axes as a sort of poor man's Digital Read Out,
and I just ignore the handle micrometers.
With the above modifications I have a pretty nifty machine, which
I use quite frequently. You also really need a lathe to make wheels
and axles and shaft couplings and lots of other things needed by
most robots.
As a final note, the price of any of these machines new will generally also buy
a used Southbend, Rockwell, or other real-live classic American made hi-quality
industrial machine. 50 years old. Watch ebay.
The Southbend 9" lathe is pretty common and exactly the right size for robot
building, IMHO. A real knee-mill can be had for similar $$$, (if you have
somewhere to put a 1500 pound chunk of cast iron and steel). Figure to triple
the outlay for tooling, and that is probably a good ballpark number.
regards,
dpa
More information about the DPRG mailing list
|
