Bob

If you decide to go with this I will make one and give it to you, providing you will then make one as proof that it is cheap and simple enough to make for your intended purpose.

Please advise one way or the other.

Focuser made from chrome plated brass pipe:

Materials Required:

1 1/4" Tube $3.99

1 1/2" Tube $3.79

Poly washers (seals) qty (2)  @ $0.09 ea. $0.18

Polyurethane glue  $6.99  (unused portion has many other uses)

2' x 4' piece of un-tempered Masonite $2.00  (unused portion has many other uses)

Sandpaper approx. $2.00  (unused portion has many other uses)

Tools Required:

Hack saw and min. of 32 teeth per inch -- un-priced -- cost depends on quality.

Hole 1 1/5" hole saw (if used will require hand enlargement) or adjustable hole saw -- prices not determined.

Adhesive backed tape - any type will do.

Large wooden dowel or rod not lager in diameter for cutting tubes, required to prevent damage or distortion of tubes.

Vise or clamps to hold dowel/rod while cutting tubes.

Don R.

To Danco

Many years ago I made a telescope under the instruction of John Dobson who believed everyone should build a telescope and discover the universe first hand.  Mr. Dobson's design became world known as the Dobsonian telescope.

John's design used cardboard tubes to make the focuser, the outer tube had a 1 1/2 inch I.D. tube for a housing and a second cardboard tube that fit inside to hold the eyepiece, sliding the inner tube provided the focusing.  By now you are most likely wondering what this has to do with plumbing parts and DANCO, so I will explain the relationship between the two.

Being a mechanical engineer I realized that cardboard tubes were not a good choice for a precision instrument so I designed one using chrome plated brass drain pipe, 1 1/2 inch for the housing and 1 1/4 inch extension tube with expanded end used to except a standard 1.25 inch eyepiece for the inner or adjusting tube, for bearing I machined Teflon bearings one attached to the 1 1/2 inch tube and one attached to the 1 1/4 adjusting tube.  This design has worked extremely well.

I recently had my primary re-coated (re-aluminized) by Bob Fies in San Carlos, Ca.    Bob also makes telescopes and has an Internet site containing information on how to grind mirrors.  When picking up my mirror I mentioned the focuser that I made for my scope, he expressed an interest in making one for his scope so I explained how I did it, but he wanted me to design something that most anyone could make without machining the bearings. What he really wanted was a design to include in his website.

Now to DANCO's roll in this project.  In looking for off the shelf parts that would work I found at Orchard Supply Hardware (OSH) (owned by Sears) that DANCO 1 1/2 inch x 6 inch drain repair kit (P/N 94932) contained a Polyurethane washer that when installed on the tube fit inside of DANCO 1 1/2 inch Flanged Tailpiece (re: 6 inch length P/N 94929) with a few thousands of an inch clearance, and that DANCO 1 1/4 inch slip joint washer (STK NO. 36660B or P/N 89136) installed on the 1 1/4 inch tube was 1 1/2 inches O.D. I have successfully made a focuser using these parts that works quite well. My concern in releasing this design is that it is entirely dependent on the Polyurethane washer contained in the extension tube replacement part. Can you provide me with some insight into matter as I well recognize that manufacturers substitute different parts that perform the same fit and function.

Your assistance in this matter will be greatly appreciated.

Don R.

 


 Hi Bob

I am pleased with the progress on the focuser; things are going much better than expected. Still getting familiar with the digital camera so have not done any cutting of component parts. Did a temporary assembly to test the functionality of the adjusting feature of the focuser, it works smoothly and will remain in focus without a locking device.  I think you will be pleased with the results. For the first test on your scope plan on applying a wrapping of electricians tape to the eyepiece. Will try applying aluminum tape to the inside of the eye piece holder and if this approach works without being too difficult will include it as an alternative method. Attached a picture of the component parts as purchased, the slip nut will not be used.  

Don R.

TOLERANCES: 

As with commercial focusers the "drain tube focuser" requires very close tolerance between the tube and polyurethane washers in order to produce both the correct friction and retain axial alignment. The drain tubes are not all exact diameters. This is also true of the Polyurethane gaskets. Of the two sets of parts that I purchased, using one set the 1 1/4" drain kit washer included in the kit fit within the 1 1/5" drain tube with acceptable tolerances after applying one layer of Scotch Magic Mend tape while the other set of parts required two layers. In order to provide instructions to whom ever may decide to make a drain tube focuser I decided to find if it was practical to sand the O.D. down to the correct diameter and determined that it is.  Then I encountered still another problem, one of the 1 1/4" I.D.  X 1 1/2" O.D. was far too tight to slide with reasonable resistance, meaning that the I.D. would also require sanding which was found to be more difficult. 

 

Worked out an easy way to sand the a 1 1/4" I.D. x  1 1/5" O.D. polyurethane washer down to fit inside the 1 1/4" tube.

At right is a picture of the Polyurethane glue carried by OSH, It's located in the paint section where the other glues are located. If you get this glue on your skin it will wear off eventually.  If you get it on your clothing or shoes you will be wearing it forever. I have yet to find any chemical that will remove it. Use sparingly -- a little goes a long way.

Don

 

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