Making Drive Gears
          for Alt, Az scopes
For some time now I have been contacted by a number of people about how to make large aluminum worm gears for driving their Dobsonion scopes.  Once I mention the use of a lathe that pretty much ended the conversation, leaving me feeling off about my VADS (Visual Assist Drive System) page on the 40 Pounder Project, the thought that the scope was built virtually without a lathe and now needing one to complete the scope with a drive just wasn't right. The funny thing is in the back of my mind I somehow new it could be done in a simpler fashion after all it was so effortless on a lathe. It wasn't until this years planned trip to Mt Kobau that got things rolling, being a guest speaker for the first time meant having to bring something new and exciting to the talks. I took a real hard look at the idea and soon realized there was hope to build a gear cutting machine out of ordinary components using only the basic hand tools (NO lathe work at all).

My procedure with the DIY in mind

1. Blank Disk Cut out appropriate size disk using Plunge Router (1/2" OD. standard bit, NO carbide) either for the under side of the rocker box or with plans to mount it to a ground board, if you plan to use it under the rocker then you can let the existing teflon ride right on the aluminum disk! or cut out it's center making a ring gear out of it. At this point I should answer the most asked question about my gears "does an exact size need to be calculated" for consideration of teeth matching up where they will join during cutting? the answer is No! any size disk will automatically turn into a flawless gear. If things don't come out right off the bat then keep progressing deeper into the disk until the machine runs smooth where the join is. Inspect with a magnifying glass until teeth matching looks perfect. The disk thickness I have worked with has been no thicker then 1/8" so I can't say if something as thick as a 1/4" wood work out, but I have found it totally unnecessary for gears any thicker then 1/8" they are super strong and light weight. Don't forget to cut 2 you need to drive the Altitude bearing.


2. The Machine After only 2 afternoon I cobbled together a simple cutting machine from off the shelf components. By hammering the shank end of a Spiral tap into a piece of 1/2" pipe then jamming that through a couple of 1" OD. roller bearings I had the basic tool made. With a hand drill a hacker U joint  and a tail support for the tap things were coming together. Mounting all this to a pivoting arm that was bolted to a 3/4" plywood sheet I soon got the impression things seemed strong enough to do the job. Now would be a good time to list the parts and mention you can make the cutter a lot more robust then I did this machine was made from stuff I already had lying around after all it was only a test..

1. 1/2" by 13 thread per inch SPIRAL flute tap   (store bought off the shelf)
2. hollow piece of 1/2" pipe   (scrap piece of junk)
3. 2 roller bearings 1/2" ID   (any automotive store)
4. Thick plywood    (3/4" or thicker)
5. Hand drill
6. Aluminum 1" x 3" box material   (aluminum recycling scrap yard)
7. Slotted U joint   (piece of channel slotted with a hand hacksaw)
8. Brass bolt   (1/4" coarse sharpened with a point)
9. bearing supports ( I trapped the roller bearings in some aluminum C channel)
 

3. Beautiful gears
This gear was just for experimentation it ended up with 450 teeth and has a OD. of 11",.would work nicely on a 8" dob rocker box.

4. Spring load worm arm (Azimuth Drive)
To drive the worm wheel I use a piece of stainless steel ready rod  again an off the shelf part that comes in 3 ft. lengths for about $20.00. The ready rod is rolled during fabrication and turns out as close to perfect as you need in fact I don't think my new lathe could do as an accurate a job. Attach a motor (stepper,DC,servo) and your ready to experience VADS or possibly a computerized scope that automatically locates objects.

 Spring load worm arm (Altitude Drive)

Only a drawing  to show here because I used a tangent arm on the 40 Pounder Project but I now see what I could have done to one of my altitude bearing plates.Also you can see I have routed out the center of the gear and then sliced it in half all that's left is to wood screw it to the Altitude bearing.

more on the way!
 The Gary Wolanski Telescope Projects
 40 Pounder Project