On 2012-03-03, Karl Townsend wrote:
On Fri, 2 Mar 2012 20:13:56 -0700, "Bob La Londe"
wrote:
The HF mini lathe hasn't been used since I got the slightly bigger much
older, and much better HF lathe. I wanted to use it the other day though
because it has gear selectable forward and reverse carriage feed. The I
remembered I stripped those little nylon gears. I am sure I can get a hold
of HF customer service and get a part number for those gears if its not in
my manual for the machine, but I was wondering if somebody knew of a source
for metal replacements? I know Little Machine Shop was the threading gear
set in metal, but I didn't see the rest of the gears for the machine.
My next thought was maybe to try and make some metal gears, but I have never
done that before. Any suggestions on the approach for that? Best alloy for
reasonable wear?
You'll need a dividing head, and involute gear cutter for the
diametrical pitch and pressure angle and the approximate number of
teeth in your gear. eBay is a good place to shop.
With these two tools, its a piece of cake, cut a tooth to depth,
rotate head, cut next tooth.
Yes -- even easier with a horizontal spindle mill with lever
feed, but not bad with a vertical spindle mill.
However -- the first trick (aside from getting a dividing head)
is finding the proper gear tooth cutter for *your* gear. Given that it
is an HF machine, the gear will probably be metric, which here in the US
makes both the proper gear tooth cutters, *and* the tools for measuring
the gear pitch. IIRC, the pitch is specified in "module" for metric
gears, while in either diametrical or circular pitch for inch gears.
Of course, it is possible to grind special lathe bits to the
shape needed, and mount them in a rotating shaft to take the place of
the gear tooth cutter -- but it will be slower since it has only one
tooth, while the cutters probably have eight or ten teeth.
You might read "Gear and gear cutting" by Ivan Law to get a good grasp
of the subject. You'll need machinery handbook to calculate your
depths and blank and rotation values, etc.
To replace a plastic gear, I'd use AL. Otherwise, I've made gears out
of 4140 and then hardened. I've had one running in my backhoe for ten
years now.
That sounds like a good choice -- with one caveat:
*If* it is going to mesh with another aluminum gear, you will
have galling (transfer of metal from one gear to the other) at the
pressure points. You want unlike metals (e.g. stainless steel meshing
with aluminum, or brass, or whatever. Stainless and Aluminum are
probably the worst for galling.
This is a good basic skill to have. You're sure to be confused at
first, but then it will seem easy. Just like learning to ride a
bicycle.
Right.
So far, I've made one gear (and planned others). It was a brass
gear to replace a broken plastic one, and I've previously posted the URL
documenting that project, but if you are still interested, here it is:
http://www.d-and-d.com/PROJECTS/TEK-Gear/index.html
Enjoy,
DoN.
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