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"...but I don't have a lathe."



 
 
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  #1  
Old August 17th 05, 06:57 PM
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Default "...but I don't have a lathe."

"...but I don't have a lathe."

Sound familiar? The truth is, you probably have any number of things
around your shop that can serve as a lathe.

In a lathe, the work rotates against the cutting tool. ( In a milling
machine, it's the cutting tool that rotates against the work.) The
main purpose of a lathe is to produce a circular part, which is
achieved by pressing the cutting tool against the work-piece as it
rotates. Anything that achieves that goal with sufficient accuracy for
the task at hand will allow you to do the job.

The most common thing used to rotate the work is the ubiquitous
quarter-inch drill-motor. A drill press works even better. And the
cutting tool may be anything from a hand-held file to an angle-head
grinder fitted with a flapper wheel; even a portable belt sander can be
your 'cutting tool.'

"Tried that," they usually say. "Didn't work." Odds are,
they didn't try hard enough :-)

The trick to holding the work-piece in a drill-chuck is to use a
coupling nut. Put the coupling nut into the chuck and tighten it
evenly, taking the slack out of all three jaws. (Just put the chuck
key in each hole in turn, taking out any slack. If you tighten a
Jacob's chuck at only one point there will always be some slack in
the other two positions, usually enough so that whatever is chucked
will not run true.)

The centroid of the work-piece is then drilled to accommodate a bolt
that matches the coupling nut. The standard 1/4-20 will serve for most
work but coupling nuts come in all sizes. To keep the work-piece from
spinning on the bolt you may use a lock washer.

When using a hand-held tool as your cutter, be it a file or even a
belt-sander, the trick to producing a true edge is to use your eye to
align the OPPOSITE edge of the work with a known-true reference, such
as the string of a plumb-bob. Or the blade of a protractor, if
you're creating an angle. Any deviation is instantly apparent and
just as quickly corrected.

In most drill presses the chuck is attached to the quill with a simple
taper. A taper has the advantage of providing a virtually error-free
alignment but has the disadvantage of not being able to withstand much
of a side-load. Even a 3M fiber-wheel (used for dressing aluminum
edges) may cause the chuck to leap off those cheap Chinese drill
presses. To prevent that from happening when using the drill press as
a lathe, the head of the bolt you use to secure the work-piece to the
coupling nut should be drilled in a cone large enough to accept a small
ball bearing. Simply trapping the ball between the drill-table and the
bolt will provide enough axial pressure to prevent the chuck from
coming adrift.

- - - - - - - - - - -

There are endless elaborations to this theme but the basic idea is that
you DO have a lathe, if you put a bit of thought into it. Although
crude in appearance such jury-rigged tools are accurate enough to allow
turning down a piece of 4130 tubing to fit a standard bearing, make
circular flanging dies of any diameter and even create the plug for a
10 x 12 inch spinner for your propeller hub.

-R.S.Hoover

  #2  
Old August 18th 05, 02:09 PM
LCT Paintball
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Default

.. Put the coupling nut into the chuck and tighten it
evenly, taking the slack out of all three jaws. (Just put the chuck
key in each hole in turn, taking out any slack. If you tighten a
Jacob's chuck at only one point there will always be some slack in
the other two positions, usually enough so that whatever is chucked
will not run true.)


The hole you choose to tighten a chuck has no bearing on the centering of
the jaws. They're all on the same screw.


  #3  
Old August 18th 05, 02:34 PM
dodger
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It is indeed the same screw, but the mating surfaces of the chuck are
not perfect and tightening only one hole will cause some off centering.
Tightening all three holes reduces any such tendency. Ask any machinist
they will tell you "tighten at all holes".

  #4  
Old August 18th 05, 07:25 PM
LCT Paintball
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Tightening all three holes reduces any such tendency. Ask any machinist
they will tell you "tighten at all holes".



I've been a Tool and Die maker for over 20 years and I disagree with your
statement. A drill chuck isn't meant to be accurate, nor is it meant to be a
three jaw lathe chuck. I'm not saying you can't do some cheating here and
there, but expect the accuracy of your equipment to take a beating. I do
understand that you can't always have the perfect tool for every job that
needs to be done, but you gotta be careful when you improvise. Remember, a
drill press isn't designed to take side loads, and neither is a drill chuck.
With that being said, I'll admit that before I bought my first CNC lathe, I
used one of my CNC mills as a lathe to make simple plastic parts.

Perhaps the difference is the quality of my equipment. The drill chucks I
use are completely rebuildable, and cost almost as much as some people spend
on their whole drill press. Perhaps that's why I've never had an accuracy
issue when tightening only one hole. Or, maybe it's because if I really need
it to be accurate, I use collets instead.

I think your ideas are very reasonable if the craftsman doesn't get in a
hurry and chooses his cutting tools carefully. Avoid clamping things to the
table, and feeding in with cross slides if you have that capability. As long
as you're using hand held tools, it would be difficult to overload your
bearings, and with your mounting idea, you'll be less likely to have the
part go flying across your shop. Especially if you back up the end of the
part like you suggested.


  #5  
Old August 18th 05, 07:55 PM
abripl
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You can get an import mini lathe for under $400. I got one for building
my home built making many valuable custom precision parts and do not
regret the investment. There is no way you can reach the versitility or
precission with a drill chuck. There is a 7x12 mini lather for sale on
eBay now for $360 with no bids
http://cgi.ebay.com/NEW-METAL-LATHE-...c mdZViewItem

--------------------------------------------------------------
SQ2000 canard: http://www.abri.com/sq2000

  #6  
Old August 19th 05, 04:53 AM
Ernest Christley
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LCT Paintball wrote:
Tightening all three holes reduces any such tendency. Ask any machinist
they will tell you "tighten at all holes".





I think your ideas are very reasonable if the craftsman doesn't get in a
hurry and chooses his cutting tools carefully. Avoid clamping things to the


Mr. Paintball, I think the giveaway was when Veedubber mentioned "cheap
chinese drillpress". In my mind this is one of the $30 Harbor Freight
models. It takes about two of those to complete a Dyke Delta. (the
first one wears out halfway through). Combining precision in the same
sentence with one of these is a great injustice to the english language.

Now not every piece on an airplane requires millionth of an inch
accuracy. Will an airplane crash if the plug used to make lightening
holes is slightly oblong?

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."
  #7  
Old August 19th 05, 05:36 PM
ຮູ້ເທ້າບໍ່ຖຶງການ
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Thanks again veeduber!

  #8  
Old August 19th 05, 05:45 PM
Flyingmonk
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Thanks again veeduber!

 




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