Hobbing a 180 tooth aluminum worm gear on the 9x lathe
Here's some information
on an experimental set of worm gears I built for one of my telescope
visiting Chris Heapy's web site I decided to give gear hobbing a try! Please note that my "experimental"
worm gears are no where close to the quality Chris has achieved but more of a learning experience for me.
To build a worm gear using this method requires a mill with either a diving head or a rotary table and indexing
plates to index or "notch" the gear blank to the correct number of teeth to be formed. Once this is done the gear
is placed on the cross slide of the lathe using a bearing support. A hobbing cutter ( described below ) is then
centered in the lathe chuck and supported by a tailstock live center. Once it's determined that the cutter and gear
blank mesh properly the lathe is ran at a slow rpm while cutting oil is applied to the cutter. The top slide is slowly
advanced until the teeth are fully formed. Since I plan on building more than one worm gear I did go to some
extra effort and build a heavy duty bearing support just for the 9x lathe. This allows the worm gear blank to be held
securely & in perfect alignment while turning cutter form the gear teeth. I've included pictures along with building
details for anyone interested.
Gear / Bearing support mounted on cross slide of the 9x lathe. The ball handle on the left is "pushed in"
to lock up the shaft for attaching or removing the attaching nut on top. I built the bearing support to fit 1/2"
thick gear blanks. Once the bearing support is attached to the cross slide no height adjustments are
necessary I also built the bearing support with a 1" OD spindle. Boring the gear blanks to a 1" ID
makes alignment easy. ( Building details below )
This was an experiment to see just how well threaded bolt stock could work for worms.
These are 3/4"-10 tpi threaded grade 5 studs 6" long.
For the next project I plan on turning my own 10 tpi worms. ( see below for update )
Finished 180 tooth worm gear.
I just finished a set of 200 tooth aluminum gears
using 10 tpi Acme threaded rod. I purchased the
1/2" od x 10 tpi x 3' threaded rod from MSC industrial supply for $6.00 The Acme thread shown
below makes a very nice worm gear. The Acme threads are very close to a true worm form. Very good
thread depth. I used the exact same procedures for hobbing these gears as described in the info below.
If you plan on hobbing any worm gears I would highly recommend using the Acme threaded rod.
Acme thread on top & a regular bolt thread on bottom.
Here's the hob I made by grinding slots in the 10 tpi Acme threaded rod.
Finished gear & worm shaft
Finished pair of 200 tooth worm gears !!
Click below for more details
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Copyright 2001 / 2003 Steve Bedair