My astronomy project:
3D CAD design of a 3" Rack and Pinion focuser

Content:

Ideas about 3D-print rack and pinion gears:

1. 3D-Printing Rack & Pinion gears
2. How to implement the Rack & Pinion into the focuser
3. Combined Rack & Pinion and worm gear
4. 3D CAD focus shaft holder and focus chassi
5. 3D CAD and print of worm gear
6. To be continued

Related projects:

• Repair and adjusting focus friction
• Tangent arm focuser
• Rack and Pinion focuser
• Push and Pull focuser
• Focus and camera rotator
• Focus and temperature drift

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

3: Combined rack & pinion and worm gear

After a lot of planning I decided to do a first attempt with a 24 teeth helical gear module 0.5 mm, this is too big to fit inside the original holder of the focuser drawer. If I chose this option I have to build a new chassi for the focuser. I also want to have the second gear box implemented on the same shaft as I have the rack & pinion gear. I use my own calculation sheet to find what ratio that external gear box shall have, I got it to 1:60.

Calculation of focuser gear ratios:

• ../../astronomy-calculations/ focus-gearbox-ratio/ focus-gearbox-ratio.html
  (Focus gear ratio)

My attempt to combine a rack & pinion gear with a worm gear. This worm wheel must have a much more advanced geometry later. This one is just to have something to find out how to make the chassi that hold the focuser together. Two extra thin roller bearings will hold the shaft in place, dimension of them is 15x21x4 mm.

This is the chassi that hold the focuser together. I will now do a CAD in an attempt to 3D-print a new one. If I keep the original I must have much smaller rack & pinion gears to get them to fit inside. I also think it's not so wise to destroy this original part.

A 2D CAD of the profile of the focus chassi. Because it's made of plastic instead of aluminum I made it thicker.

Revolving of the 2D sketch make it to a cylinder. I added a clamp to attach it to the telescope, with this I can rotate the focuser freely around the telescope tube. The original design has three lock screws which has some drawbacks, the small edge to the left hold the chassi in correct position relative the telescope where it attach.

This is the old bracket that holds the roller bearing for the focus shaft. I need it to be different to fit my construction.

This is one of the ends that hold the roller bearings. The roller bearing will be inserted in this slit.

A lid and holes to let the shaft go trough.

A split of the drawing show the top hole. In this hole which shall be treaded with M4 a screw will be inserted. With this screw I can move the roller bearing up and down and set the force it press the shaft's helical gear against the rack gear.

I changed the design a bit with a bigger hole. The slit seen from under where the roller bearing is inserted. I need two of these and some sort of frame that hold them together. This unit will then be placed on top of the focus chassi. It will be printed as one unit.

I make a copy of the first roller bearing holder and rotate it 180 degrees.

Make a module that shall connect these two walls.

Fuse them together to act as one part. I could have designed it with a more rounded top, but I think it could be good to have this flat side to attach other equipment on.