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Homemade Crayford

iturner2

By iturner2
in DIY Astronomer

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iturner2

iturner2

Posted
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I decided to make a crayford after the teeth got stripped off the rack of the focuser on my Celestron 130eq astromaster. Mixing a plastic rack and a metal pinion is poor design.

I looked at buying a crayford but even the cheapest is out of my budget. So I decided to make one using stuff from the garage, there was no point saving money not buying one and then spending lots on raw materials.

After a week or so designing in my head and looking at other designs on the internet. I decided that some bearings were essential, fortunately I had two broken scrap scooters that I hadn't had chance to take to the scrap dealer.

I extracted the bearings from the scooter wheels. I then cut and filed the scooter base plate to hold the bearings.

One of the scooter had quite nice tube that held the steering bearings, one nice feature was that it had a flat on one side. All I needed to do was cut of some flanges.

Next I need a winder so I went to the local surplus store and bought a cheap screwdriver for a pound, I had to grind the sides of screwdriver blade so I can fit it through a hole.

I then needed a way to mount the whole assembly onto the telescope tube. I found an old ikea plate rack shelf. It is ideal as it has a U-shaped profile, basically a plank with lip at the front and back. This fitted nicely onto the tube, I left the shelf long so it would and more rigidity to the telescope tube.

I have made a few adjustments so I can get enough back focus so I can use a DSLR, and I can use an extension tube for normal eyepieces.

The tension on the crayford can be adjusted by tightening and loosening screws, it easily takes the weight of the camera.

Overall it works quite well and is better than the original rack and pinion. It shows you can make a crayford without high accuracy machining or tight tolerances.

The next stage will be to paint inner surfaces black.

Photos below

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fwm891

fwm891

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Hi

here is a pic of a homemade crayford focusser ...

But it was made for my 16 inch project for me by john wall !!

Bet he would love your design.

He has an all wood design that can be made with drill saw and screwdriver.

Thanks for the photo its just solved a nagging little problem I had on my next project...

Francis

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iturner2

iturner2

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I have made a slight improvement and the screwdriver passes through bearings, making it smoother. I was worried that if the screwdriver was free to turn it wouldn't hold any weight. It is now a lot smoother and still holds it position with a weight.

I think the next job is to add 10:1 reduction or maybe an electric motor?

Mercury - the book is 'Every Photon Counts' see Steppenwolf sig for details.

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