SkyWatcher 80ED Crayford focuser to electronically controlled Rack and Pinion

I made these models to use with MyFP2ESP32Focuser, a DIY focuser that can be used with NEMA17 motor

Update (30th April 2026):

I ditched the old design which still used the Crayford design and made the whole camera assembly slip under heavy weight. That was because the focuser tube wasn't sanded completely straight. So i opted to go down the Crayford focuser route. First I tried 3d printing a rack and pinion (the pinion being glued to the focuser shaft), but it still slipped. So I went with a metal construction. Use the NEMA17 models only for this build!

I am not responsible for the damage to your telescope!

What you need:

• 4 x M3x10mm

• 6 x M3x16mm

• 4 x M3 spacers (7mm wide)

• 4 x M3 spacers (10mm wide)

• or do 8 x M3 spacers (10mm wide), both will work

• 2 x M3x6x4,2mm threaded insert

• Starpal DIY rack and pinion (https://www.aliexpress.com/item/4000559298333.html)

• Rigid brass coupler 4mm - 5mm (https://www.aliexpress.com/item/1005003878358597.html), they didn't include the m3 screws for the coupler, so be careful with that

• 1,75mm PTFE tube (https://www.aliexpress.com/item/1005008009091649.html) or something to put between the tensioner and the focuser shaft

• Patience

Printing:

The three big parts (focuser assembly, NEMA17 mount and spacer) need to be printed in 0,2mm layer height. The remaining two small parts (tensioners) in 0.12mm layer height, also check the picture for orientation. I used 15% infill, which worked well for me. No supports needed either. For the material I used regular Elegoo PLA (orange color).

One more thing to print is the stopper, which i made in the slicer. Add a primitive cube with measurements of 3x6x2mm and print it with 0,2mm layer height.

Preparations:

1. Dissassembly

Firstly take the scope off your mount and find the focuser assembly. There are 4 bolts on the corners of assembly, unbolt them. The tube and assembly should come off now. Be careful not to lose the 4 o-rings - they will be needed later on. Unbolt both knobs. You should now only use the regular speed knob (grey color), everything else will be replaced.

1. Focuser tube and gluing

You first need to file the ends of the Starpal rack so that it fits on the Crayford focuser. Sand the focuser tube just a bit too to give the glue something to stick to, clean it and then superglue the rack to the tube trying to keep it as straight as you can. Once the glue is dry, glue the stopper to the bottom like it is on mine. It should look something like this.

1. Filing

This is the part you have to be careful in. For the focuser tube to now fit into the telescope, you have to sand or file the part of scope the rack goes through. Precautions i took were to not hold the scope pointing downwards, that way the metal dust doesn't fall on the glass, keeping it clean. During filing go back and forth testing if the tube already fits into the scope, it should move freely and not hit the scope at all. Once you're done, clean everything and make sure there is no dust inside. Then lets move onto the next part.

1. Assembly

Firstly put threadded insert in the two middle holes. Into those holes screw in two M3x16mm bolts.

For the tensioner, cut a small section of PTFE tube that fits in between the model. This makes sure the plastic doesn't melt from the shafts' friction. Make a section for both tensioners. This can be quite finicky!

Now put the spacer on the NEMA17. Make sure the long motor bolts are threaded in from the back. Then attach the NEMA17 mount with 4 x M3x10mm bolts with spacers. After that you need to add the rigid coupler. Larger hole on the coupler is for the motor side, other side is for the shaft. I've made holes on the bottom of the assembly to tighten the coupler on both side, use those. Then put the shaft through the focuser assembly. The longer side goes to the knob, shorter side goes to the motor (take a look at the second picture).

On the other side attach the knob and through the bottom you can bolt through 4 x M3x16mm bolts, attach the o-rings to them. Lastly add the tensioners to the sides of shafts' gear and tighten the bolts under them. These are for the tension. Now you should also make sure that the NEMA17 is correctly adjusted, it should be level with the knob. Once it is leveled out, tighten NEMA17's bolts to the mount. You should now have something like this.

The hardest part is now done, lets put it all together. First insert the tube into the scope, then attach the whole focuser mount and assembly, tighten the four corner bolts (O-rings on the inside). Lastly adjust the tension and you're done!

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Printed in PLA, 0,2mm layer height, 15% infill.

A spacer is needed to use the NEMA14 with the telescope focuser.

Use washers on bolts to mount either focuser mount to the bottom of the Crayford focuser.

Also use longer bolts for the motors, that go through the back of the motor and are tightened with a nut on the front. This is to ensure that the motor doesn't detach itself during focusing.

P.S.: I found that NEMA14 didn't have enough torque to move the focuser tube with a DSLR. NEMA17 moved my DSLR camera easily.