"Stealth Pilot" wrote in message
...
On Fri, 2 Nov 2007 09:54:31 -0400, "Ed Huntress"
wrote:


"Stealth Pilot" wrote in message
. ..

I'm restoring an ancient Myford ML7 for use in model engine
building.(K5973)


If I surrender I can still buy replacement gears from myford but
cutting my replacement gears would be quite cool.

What is your capability for cutting gears? Are you using gear cutters on a
mill?

I am about to buy a mill.
I've been looking for ages for an australian supplier of involute
cutters. I'm fairly certain that Suttons, Patience and Nicholson and
Frost all make them but havent been able to find a distributor.
the local engineering suppliers (Blackwoods) seem to have dropped them
as an item in their catalogue.
There is an online model suppliers in Sydney selling involute cutters
at $105 each. I'll try them.

Having done that, commercially and with good equipment, I'd say you're in
for more work that it's worth -- in money, at least. If you enjoy the
work...well, you enjoy the work. Then it doesn't matter.

cant say that I am discouraged here. I set myself two targets for my
workshop upgrade. I want to master screw cutting and gear cutting.
My frustrations with screw cutting are due to the properties of the
alloy I'm trying to use and not having sufficient back rake.

gear cutting in a non commercial environment should not be a torture.
I could use the hercus cross slide as a shaper and plane the inter
tooth gap out.
I could do similar in the shaper.
looking at the wear patterns on the ML7 it is apparent that one gear
was machined with the cutter slightly above or below centre. this
slight misalignment seems to be the root cause of all the wear in the
headstock gear train so it is motivating me to get sorted out with a
proper involute gear cutter instead of just approximating the shape as
is so often done.

You've set quite a task for yourself. d8-) The only comment I'll make here
is that using a lathe cross slide for a shaper will get awfully old after
your second or third tooth cut, and it's hell on the leadscrew and nut. They
aren't made to handle that much load.


As for materials, I'll leave that to others with more experience. My
experience with highly-loaded bronze gears starts and stops with a '57
Alfa
Romeo engine that had a bronze distributor-drive gear. My '58 had a steel
gear. The bronze wore out in a hurry; the steel never wore out when I had
it, and that was a high-rpm race engine. But there are many different
grades
of bronze, and their performance in high-load-bearing applications also
varies widely. I wouldn't attempt to generalize.

Last night I replaced the nut on my hercus cross slide with a new one
supplied by Hercus. The original was bronze. the new one is cast iron.
(might I add that I had a very close look at the machining of the nut.
I have to say that Hercus do immaculate! machining. The guys running
the factory now are superb machinists....but I digress)
The thing that I found interesting is that the cross slide screw is a
slop free fit in the new cast iron nut which indicates to me that all
of the noticeable wear was in the bronze nut.
I can only put all this down to cast iron being a better oil film
retainer than bronze. For cast iron components to display so little
wear they must be better at retaining an oil film. They arent any
harder.

Many cross slides have bronze nuts, and it's generally a better material for
the job than cast iron. If it's a proper bearing grade of bronze and if it's
properly lubricated, it will last a long time. Bronze on steel can run at
about half the clearance of cast iron on steel and it will exhibit less
friction. But if it's allowed to run dry, cast iron will take it a lot
better than bronze will.

It sounds like someone made a lot of parts for your lathe out of some kind
of copper alloy. Whether it's a bearing-brade bronze is a question.

Anyway, have fun with your projects. It sounds like you have the ambition
for it, so more power to you.

--
Ed Huntress