16 replies to this topic

[AnthonyP]

I'm looking to build a simple focuser out of pvc or abs. I think the easiest way of doing so is to build a helical focuser.

Any suggestions would help.

Anthony

[nighty]

Hi
1 1/2 pvc inside 2" pvc with some fuzzy velcro makes a good slip focuser.

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[ken scharf]

Photo of my homebrew PVC focuser based on this design
http://www.atmsite.o...user/index.html

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[mark cowan]

Here's a well-used one on a 8" made from electrical conduit parts many years ago. If you wrap the threads in Teflon pipe thread tape (you can fix the end with a spot of super glue) the helical action is much smoother. I also have this mounted into a flange on the tube for coarse adjustments, but frankly the collimation isn't all the reliable. BTW that's for 1-1/4" only unless you pull the tube out.

Best,
Mark

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[Mr Magoo]

Is this for a reflector or refractor? Here is a link to one I like out of PVC for a reflector. PVC Crayford Focuser

[Art Bianconi]

The most "out-of-the-box ready" homemade focuser. IMO, are the ones I make from a toilet flush valve.

You'll find them at Loew's and Home Depot in the plumbing section.

I believe that those sold in cardboard boxes at Home Depot are the best as they allow you to open the box and pre-inspect the two parts for close tolerances. The fit does vary from box to box. Obviously, you want the combination of the two parts that has the least play.

If used as is, the focuser is ready for two inch eye pieces. If you wish to use 1.25" EP's you'll need to make or purchase an adaptor.

A helical focuser from a flush valve will cost you about $5.oo

Art

You need to cut away everything to the left of the red spacer and throw away the black rubber seal. What's left is the large "nut" and the threaded body.

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[Art Bianconi]

This is what is left. I machined a 2" to 1.25" EP adapter from plastic and fitted it to the top.

The current generation of flush valves are better than the one shown here as the threads travel all the way up to the lip.

Lots of travel.

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[Art Bianconi]

You'll still have to make a base for it but you'd be faced with that task regardless.

The EP adapter is rendered in black in this image.

Art

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[fxxm747]

Is there any kind of paint or dye that will "take" to the plastic. This looks like a perfect solution for a 3.5" newt project I have using one the surplus shed red tubes they have. I'd like the focuser to be red or black.

[AnthonyP]

You need to cut away everything to the left of the red spacer and throw away the black rubber seal. What's left is the large "nut" and the threaded body.

What the best item to use to cut this?

[ken scharf]

You need to cut away everything to the left of the red spacer and throw away the black rubber seal. What's left is the large "nut" and the threaded body.

What the best item to use to cut this?

Several tools come to mind. One of those fine tooth razor saws used in model making would make a nice clean cut (check out your hobby shop). A band saw with a fine tooth blade would make a very neat cut. If nothing else is available, just use a hack saw. A dremel with a cut off disk will work too, but these sometimes MELT plastic rather than cut it.

[darklyte]

Is there any kind of paint or dye that will "take" to the plastic. This looks like a perfect solution for a 3.5" newt project I have using one the surplus shed red tubes they have. I'd like the focuser to be red or black.

Generally for a nice spray finish use acrylic paint as used on model car plastic bodies. For something that will last a bit longer enamel paints are the way to go as used for old airfix kits. Enamel is also good for coating aluminium too.

You could always buy pvc pressure pipe. It comes in black and with lots of adaptors and stuff with screw fittings. Way better than your run of the mill plumbing fittings. Mostly used for garden pond filtration, ie koi carp.

How about the valve in the attached pic as a focuser body? that inside pipe diameter is 2 inch so there's a heckuva chunky body for running your focus adjuster bar through the side of it...

Toe.

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[Art Bianconi]

"I'd like the focuser to be red or black. "

Any paint applied to the threads will interfere with the smooth movement. I tried it.

I did paint the top surface flat black so as to minimize any chance of reflections.

I am not aware of any dye.

Art

[Art Bianconi]

"What the best item to use to cut this? "

I did mine on my band saw, leaving a short stem. Then I used a 12 inch disk sander to grind it flush.

Bear in mind that the geometry of the valve and stem design differs from one manufacturer to another. That's of no consequence.

Most of the plastic will be cut off and thrown away.

Here you see the Flush Valve focuser fitted with an EP adaptor and an EP.

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[jcjr]

Krylon sells a line of colorful spray paint for plastic. It sticks to PVC fine in my experience.

I'm not expert on anything, but have got in the habit of overcoating "pretty" paint jobs with a few coats of Rustoleum crystal-clear enamel. It dries very quickly, is nice'n'shiny, and seems to protect a finish.

Non-scope-related experience re durability of the clear enamel-- Out old house has ancient glass-knob doorknobs, but the metal parts were not brass, just some kind of plated alloy that had got very grungy over a half-century. We wire-brushed em down to the metal, hit em with metallic-brass Rustoleum, and overcoated with clear enamel. They have been in use a few years, and still look good, and even close inspection looks like brass.

[mark cowan]

Sure, you can just dye PVC (or nylon, for that matter) in sub-boiling water with fabric dye. Be careful you don't overheat it.

Best,
Mark

[fxxm747]

Hey, no harm in trying that...well unless I melt something. Thanks Mark!