On Mon, 14 Oct 2013 22:56:21 -0500, Ignoramus30725
wrote:
I am just curious. Are screw machines completely obsolete technology,
meaning that they cannot be used in a cost competitive modern
production process? Would that be a true or untrue statement?
Tomorrow, there is going to be an auction with about 80 of them for
sale. I want to make sure that I see them properly. In my eyes, they
are scrap metal material, not resellable.
i
Screw machines in the proper application are still probably one of the
best types of "automatic lathe" on the market.
They dont work so well in short run job shops..but for say..a company
that does repeated large quantities of the same parts over and over
again..they are the utter tits.
Ill give you and example. Lug nuts.
They are cut from bar stock on screw machines in many cases, which
includes forming any tapers, drilling and tapping and so on. Need a
million lug nuts? Screw machine. Need 1000? CNC lathe
There are 2 main differences in screw machines. One type uses metal
cams cut from 3/8-1/2" steel plates. The notches, rises and whatnot
are put in by special cam cutting machines like a small upside down
mill and just like a kids wind up music box..the various notches,
rises, slopes and whatnot are used to control the actions of the
various tools. These cams are saved and numbered and when the repeat
job comes in again...they are installed with the proper tooling and
dialed in and off you go. Cam machines often have the cams stored in a
large filing cabinet drawer with the tooling for that job along with a
print etc etc.
The other type uses precut cams installed in the machine which are
arrainged by turning them on a shaft to different positions..much like
an "adjustable cam"..which in effect they are. Works much the same
way as cut cams. Set up each time can be a pain in the ass as you
cant simply pull one out of the drawer and install it with the proper
tooling. They dont however need a cam cutter or be sent out for
cutting by a company that does cut cams.
Now there are CNC screw machines since the early 1990s Star, Citizen,
Tornos, etc etc all started figuring ways to operate them via a
computer with no cam. Most are just as fast as a mechanical machine
and setup is far easier. Maintainence is higher of course as they are
not purely mechanical, but they are able to do shorter runs of parts
with much shorter setup times and often use the same tools from job to
job.
A Bechler screw machine..mechanical..can be set up for a fairly
complex job in 4-10 hrs. Tornos can be set up in 3-5 hrs. A Citizen
screw machine, CNC, can be set up in 30minutes to an hour.. All of
which require often special tooling..Screw Machine Tools..often left
handed drills and so forth. Traub is another fine mechanical screw
machine, along with Strohm, BSA, Acme-Gridley (usually very large work
capable..up to 10" diameter) etc etc etc
Modern CNC Screw machines are blazingly fast. And expensive
http://www.youtube.com/watch?v=H0DR7YqLM2o
I think Somma is the last American screw machine tooling company
surviving
http://www.sommatool.com/
Take a look at the tooling, tool holders and other fun stuff. Most
folks here will not have seen em before..and its interesting. Keep in
mind..that America was built on US made screw machines like Brown and
Sharpe and Gisholt and many many many others. along with the Swiss
Traub, Bechler, Davenport, etc etc.
I should mention that many of them..had multiple spindles. So when you
set up a machine..it took one cam..but up to 5 sets of tooling..each
spindle would run the same cam program..and cut multiple parts at the
same time. OR....it would perform seperate operations as the part was
rotated around s circle..still in its spindle ...each position
performing a seperate operation or group of operations.
Really really high effeciency..for a mechanical machine
As you will notice in some of the videos below..they are performing
multiple operations AT THE SAME TIME on a single part, or one after
another etc etc. Screw machines can compete with CNC lathes in many
many operations. But..not all. But if you have one specific job that
is long term..it can kick CNC ass for 1/100 the initial investment.
Ive bought and sold perfectly good screw machines for $250-500
Try to turn out the same parts with a CNC machine sold for less than
$70,000..and the screw machine will likely kick the ass of the CNC
even then.
All gone now or changed over to CNC machines..but their machines
still turn out billions of parts every day in little crowded stinky
NOISEY shops all over America
Many have been converted to mechanical /CNC.
I know a half dozen guys who have mechanical screw machines tucked
away in the back of their shops that they will run one part a year.
They may get an order for 10,000 lugnuts..and can turn em out in a
couple days, then they put em back to sleep for another 11 months.
The machines having long long ago been paid for..and are cheap to run
and need little maintainence while they rest.
Most screw machines make parts from either bar stock..or rolls of
"wire"...up to about 5/16" in material diameter. After that..it was
bar stock in rotory feeders, or one bar at a time. Ive got a few
Tornos shops that use both Omniturns for the secondary ops and the
screw machines for primary ops. They turn complicated parts as small
as .015 in diameter...15/1000s of an inch. Watch movement screws
for example. Little bitty *******s that can take a half day to crank
through a 10' bar of .018 material....bar being the only way to
describe a small tiny wire..shrug
http://en.wikipedia.org/wiki/Automatic_lathe
Some interesting videos on YouTube will show you how they work..and
why many screwmachine guys are deaf.
They will do this, hour after hour after hour, day in and day out
http://www.youtube.com/watch?v=I9UCwntixPg
(making specialty bolts from hex stock)
http://www.youtube.com/watch?v=aU45h7C0FQI
http://www.youtube.com/watch?v=mUpXm3cbMJE
http://www.youtube.com/watch?v=XeAXMWLZW-0
http://www.youtube.com/watch?v=er2RB...Lmw 8p-YFjkl_
This particular machine will turn out a fully machined part..not just
half of one....
http://www.youtube.com/watch?v=edJYI...Lmw 8p-YFjkl_
There are a few other types of screw machines...many of which hold the
material rigidly..and the tools turn..not the material. Those tend to
be feed from coils of wire..as the wire spools cant be spun.
A side note..if you are going into a screw machine shop..wear your
old shoes. Most of them have been running oil, both as coolant and
machine lubrications..and the kitty litter (if any) used to sop up the
spills and splashes will be everywhere. As you may have noticed in
the above videos. They are not generally...clean shops.
Gunner, who has a serious love of screw machines..but wouldnt own one
on a bet...his last 4 going to scrap because he couldnt find a buyer
for very good quality, excellent condition, machines
As a side note...you may enjoy these as well...polygonal turning
http://www.youtube.com/watch?v=tf1A7S3iWIo
http://www.youtube.com/watch?v=1Y0hK53nuLM
Now...lets do that with a single point tool...
http://www.youtube.com/watch?v=2QRZnvtax-E
This is one of the better videos Ive seen
http://www.youtube.com/watch?v=6IEt7pwG3ko
Now..polygonal turning has been around for much longer than CNC..
I maintain (2) Japanese Nikkos polygonal lathes that were built in
1967, All machancal and they will do just about anything the above CNC
machines can do..except cut curves. Tapers..no problem
Gunner
--
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