The Hobbing Process
Here are some pics of the hobbing process ( this is the fun part ) You
just have to be careful and
go slowly. Let the gear make quite a few revolutions before advancing
the topslide slowly. As I
progressed with the hobbing I increased the rpm's of the lathe. You
also need to use a lot of cutting
fluid to keep the hobbing cutter clear of the cuttings.
Indexed gear set up and ready to start hobbing
I started out with a slow rpm on the lathe and increased as
the teeth were formed. You have to take your time here
and very slowly advance the topslide.
I also used lots of cutting fluid.
It's working
About 3/4 through the process
Once I finished the hobbing I removed the cutter and installed the
worm shaft to
be used. I then coated the gear with metal polish and ran the worm
against
the gear to lap the gear to the new worm. ( very messy )
Completed worm gear!! If you look closely you can see the
index marks at the top to the teeth.
This was because I originally gashed this gear blank for a left hand
worm. Rather than indexing
a new blank for this experimental gear I just used this one. If not
for this the marks would not
have been visible.
Conclusion
I am very pleased with how the gears turned out. The hobbing cutter
worked well but on the next
cutter I will make a wider gash to help make the cutter more aggressive.
I also plan to use a stalk
of Acme 10 tpi stock for the next set of gears. The Acme thread
is a lot closer to a true worm
profile. The Acme thread also has more thread depth which means more
tooth to gear contact.
The threads on the 10 tpi I used are not very deep , the Acme will
do better.
For the telescope mounts I build the worm gears have a very small tangential
load ( 5 lbs or less )
placed on the gears so the regular pitched bolt threads would work
fine. If you need a more
precise gear I would highly recommend purchasing regular pitched worms
and making a hobbing
cutter from this.
Check back for part 2 coming soon
Thanks & Good Luck,
Steve
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