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Home Made Sight Tube: Problem With Pipe Size

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#1 FirstSight

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Posted 19 February 2013 - 12:40 AM

It's been periodically suggested here on CN that a passable sight tube can be easily and cheaply built from PVC pipe, e.g. Don Pensack's post of 10/10/12 here in the CN reflectors forum (scroll down; it's about the 8th post on the page). While I already have a couple of really good commercial sight tubes myself, most of the neophytes bringing reflectors to one of the telescope tune-up clinics our club periodically conducts (including a very recent one) do not. So, when going out on a household mission to Home Depot last Sunday, I thought: "while I'm there, and if the required materials (pipe section, end cap) are cheap enough, why not give this idea a test?" And so, intending to make a 1.25" sight tube, I grabbed the 2"=>1.25" adapter from the Moonlite focuser on my dob so I could test the fit of the pipe, and headed off to Home Depot.

FIRST, it was immediately apparent from eyeball inspection that standard 1.25" gauge PVC pipe was nowhere close to an appropriate fit. The problem is that the outer diameter of standard 1.25" pipe is actually 1.66 inches, including the thickness of the walls. So I tried the 1-inch size PVC pipe, which was tantalyzingly close to fitting, but still too fat to go into the adapter, even by force; the next size down (3/4") was much too small. I went around Home Depot trying virtually every plausible type of pipe in every section of the store (including electrical conduit), and nothing in stock worked. BTW: there were no standard sizes that would have fit in a 2" focuser tube either.

Now obviously, there *must* be an available source of pipe suitably gauged to fit 1.25" focusers; else commercial makers of sight tubes and combo tools would not be able to construct them either. The real problem, however is whether there is an easily, commonly, inexpensively available source available in most cities where ordinary folks could get appropriate pipe and end cap to make a sight tube from. DOES ANYONE know what the appropriate type of pipe would be, and where a common, easily available source for it would be?

OTHERWISE, the idea of a cheap, easy, homemade sight tube constructed out of decently sturdy material is but a wonderful idea that turns out to be just an infeasible pipe dream.

BTW: I'm aware of the potential alternatives to a sight tube e.g. collimation cap, and the arguments pro and con. However, here I'm interested in the feasibility of an inexpensive, homemade sight tube out of sturdy material.

#2 Nils Olof Carlin

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Posted 19 February 2013 - 05:04 AM

hi Chris, this isn't news to you and not the kind of answer you want, but here in metric Sweden I have easily found tubes to fit 1.25" focusers. In the image, the cheshire cum sight tube is from a long piece of electric conduit I convenently found discarded, The whitish ones are 32 mm (=outer dia, here!)plumbing tube (this piece fit directly), for f/5 and f/5.6 respectively (the peephole cap is interchanged). They have shiny insides which helps a lot - I am convinced you can center the primary (and of course secondary) more accurately than with crosshairs. The metal one is from a vacuum cleaner pipe - it is the first tool I designed, for a 6" f/5 without a center spot.
Yes, I would encourage others to try make sight tubes - make them length/inner dia equal to the f/ratio (one for each telescope, if needed). Pull it out a bit to frame the secondary, then in to frame the primary.

Nils Olof

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#3 Mirzam

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Posted 19 February 2013 - 07:28 AM

It used to be that metal sink trap fittings had 1.25" ID on one end and 1.25" OD on the opposite end. You could cut off the 1.25" OD section to use for the sight tube. This may be one of those many things that has gone the way of the Dodo, but I mention it just in case.

JimC

#4 Mirzam

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Posted 19 February 2013 - 07:34 AM

Aluminum tubing is another possibility, but you might have to turn the OD down slightly to fit into a focuser.

Online metals

JimC

#5 Steve OK

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Posted 19 February 2013 - 10:39 AM

The metal sink trap fittings are still around, and are 1.25" OD. I've used them to make sight tubes. One to look for is a 6" extension. It has a section of 1.25" OD that flares to a larger diameter at one end. I think the larger end is bigger than 1.25" ID, however. They are typically chrome plated brass, easy to cut. Last I checked they run about $6.

#6 CatseyeMan

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Posted 19 February 2013 - 10:53 AM

Aluminum tubing is another possibility, but you might have to turn the OD down slightly to fit into a focuser.

Online metals

JimC


A 1' length of T6061 aluminum 1.25" OD (+/-.015") mechanical tubing in 2 different suitable wall thicknesses is available from McMaster-Carr:

.065 Wall

.083 Wall

#7 FirstSight

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Posted 19 February 2013 - 11:18 AM

I appreciate the suggestions so far; I anticipated McMaster-Carr would likely have appropriate tubing.

However, a key objective is to enable anyone shown instructions or an example on a given morning to go right out that very afternoon and quickly, easily, cheaply construct a passably usable sight tube for themselves, from readily available local materials. The sort of neophyte reflector owners who end up sticking with astronomy more ambitiously longer-term will probably end up at some point wanting to upgrade to better-quality, better-machined collimation tools such as the Catseye system, often not very long after they've upgraded their scopes to something more capable.

Of course, once a suitable local pipe source is found, the other key component is some sort of compatible end-cap suitable to accurately drill a 2mm peephole through the center thereof. That's why it's frustrating that PVC pipe didn't (so far) work out as a solution; but-for the lack of proper-gauge sizing, it would have been perfect. Maybe the plumbing drainpipe idea will pan out...

#8 CatseyeMan

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Posted 19 February 2013 - 12:11 PM

I appreciate the suggestions so far; I anticipated McMaster-Carr would likely have appropriate tubing.

However, a key objective is to enable anyone shown instructions or an example on a given morning to go right out that very afternoon and quickly, easily, cheaply construct a passably usable sight tube for themselves, from readily available local materials. The sort of neophyte reflector owners who end up sticking with astronomy more ambitiously longer-term will probably end up at some point wanting to upgrade to better-quality, better-machined collimation tools such as the Catseye system, often not very long after they've upgraded their scopes to something more capable.

Of course, once a suitable local pipe source is found, the other key component is some sort of compatible end-cap suitable to accurately drill a 2mm peephole through the center thereof. That's why it's frustrating that PVC pipe didn't (so far) work out as a solution; but-for the lack of proper-gauge sizing, it would have been perfect. Maybe the plumbing drainpipe idea will pan out...


Well I certainly understand the desireability of immediate-local-sourcing satisfaction in the spirit of innovative excitment (I made mutiple trips in 1-day to Lowes during construction of my scope), but in the absence of such, the next best option is mail order. M-C's order fullfillment is second to none - it's typically a 1-day delivery for anything I order via UPS from McMaster to my area in Madison, AL from their Atlanta DC.

BTW, a quick Google found this brass option at Lowes:

1.25" brass sink tailpiece

#9 precaud

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Posted 19 February 2013 - 01:04 PM

Steve OK has it right, they're in the under-sink section. A few weeks ago I took a 1.25" adapter and micrometer to HD, sat on the floor and went through all of their 1.25" pipes to find one that would fit. Nearly all (PVC or stainless) were 1.25" or a little more and wouldn't slip in. But one of these did: http://www.homedepot...ngId=-1&locS...

I had to go through 20 or so to find one that was just under 1.25" - most were that or larger. So I bought two of them - the one that fit the drawtube, and a regular one to extend it for longer F/ratio scopes. It works fine. A collimating cap fits nicely into the flared end to sight through.

#10 dan_h

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Posted 19 February 2013 - 01:13 PM

As others have suggested, the 1.25" sink trap extension is readily available at any hardware store. Home Depot also carries a 1.25" aluminum tube in the metals section but I think it is only in 3 or 4 foot lengths and the deep hole is expensive for this kind of stuff. MC is the better option.

For an end cap, you can use very heavy tin foil like is used to vacuum seal the larger coffee cans (or hot chocolate, etc). This stuff can be cut with household scissors, smoothed out and simply folded over the end of the tube and a centre hole punched with any available pointy thing. Another option is brass shim stock available at auto supply outlets. Once a top piece is fitted, wrap a strip of decorator tape (duct tape)around the sides to make it permanent and pretty. You would probably be able to make 4 or 5 end caps out of one coffee can seal.

dan

#11 dan_h

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Posted 19 February 2013 - 01:14 PM

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#12 precaud

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Posted 19 February 2013 - 06:15 PM

What about 2" O.D. tube? I've had no luck finding anything that works.

#13 Starman1

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Posted 19 February 2013 - 06:59 PM

What about 2" O.D. tube? I've had no luck finding anything that works.

My local OSH has 4 different "schedules" of PVC pipe, each with a different outside diameter. I forget which schedule was the 1.25" O.D. size, but I believe it was 1" I.D. and 1.25" O.D. (Schedule 40?)
When i did it, I was only looking at 1.25". 2" might be a little more difficult, as it would be 1.75" I.D. probably.

#14 Jon Isaacs

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Posted 19 February 2013 - 07:52 PM

1.25" OD (+/-.015")



That +/- 0.015" would scare me off.

Jon

#15 dan_h

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Posted 19 February 2013 - 10:38 PM

What about 2" O.D. tube? I've had no luck finding anything that works.


I have butchered some really inexpensive 50mm scopes for exactly this purpose. There has to be a better way.

dan

#16 Tom Andrews

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Posted 20 February 2013 - 12:03 AM

I'm a little late to this picnic but I've used the chrome-plated brass sink trap for the 17 years I've been observing. I've used it on the 3 dobs that I've had and on numerous friends' dobs as well. They work well with a very snug fit. I use the cap of a 35mm film cannister on the end with tiny hole in the center.

Here's a picture:

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#17 FirstSight

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Posted 20 February 2013 - 05:54 AM

Hmmm...Tom, that sink trap pipe + 35mm film cannister top does look promising. The possible catch is that 35mm film cannisters, which only a few short years ago were ubiquitous, are rapidly going extinct as a commonly available item.

#18 Nils Olof Carlin

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Posted 20 February 2013 - 07:36 AM

One easy way is to use a flat sheet of any suitable material that can be cleanly drilled, and glued. Drill the hole first, then mark the periphery and glue the tube (epoxy?), last trim if needed.

Nils Olof

#19 Tom Andrews

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Posted 20 February 2013 - 01:46 PM

The possible catch is that 35mm film cannisters, which only a few short years ago were ubiquitous, are rapidly going extinct as a commonly available item.


Funny, I was thinking the same thing as I was posting this.

By the way, I get the pipe at Home Depot, they're 7" long and about $6.00 or $7.00.

Here's another picture.

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#20 CatseyeMan

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Posted 20 February 2013 - 03:22 PM

... The possible catch is that 35mm film cannisters, which only a few short years ago were ubiquitous, are rapidly going extinct as a commonly available item.


Go to Ebay and put "film canisters" in their search engine - "tons" of them readily available and cheap.






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