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 had 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 a 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.
Below 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