The Gashco

When I started out in Astronomy in January 2003, I never believed I would be making my own telescopes before the years end.

Really it's the Internet that is to blame, I joined a discussion group (Astronomydaily.com) on the first of April 2003, after a short while here somebody posted a link to a website (surplusshed.com) that was selling Meade 114mm mirror sets including Primary, secondary and cheap finder. Inspired by others on the site I went ahead and purchased a set. At $29.95 they were a good deal .

Just under 3 weeks later the parts arrived at home, at which point I had to let on and tell my wife I had ordered them.

This was when the design dilemma started, I knew I had a cardboard tube big enough for the optics in the attic, but having spent out on the mirror, it was not prudent to outlay a fortune on parts for the base. I decided it would have to be a Dobsonian base, but using materials I had in abundance. Being a Manager of a Drawing Office, the first thing that caught my eye was the end stoppers for the Cardboard rolls that the paper our large printers used. These were a sturdy plastic , and smooth, my immediate thought then was for the Altitude bearings.

The optics were all measured out from the calculations provided by a piece of software called Newt2.5 and the big mailing tube was marked out

This was about the time I decided that I could use the cardboard tubes to mount the bearings in. I was playing with the design in CAD and realised that a 45 cut across a tube would, when glued together again give a right angled joint, this inspired me to the design of the base.

The Azimuth mount is an old gramaphone record (originally there were two) and 3 felt pads as used for the base of furniture.

The focuser has evolved in several stages, I heard you could use plumbing fittings , but could not find the ones I wanted at first to make a helical focuser.

I settled in the end for a simple push pull focuser made from a 40mm to 32mm reducer inside a 40mm push fit tank connector. After several months I obtained the right sink drain connection and replaced this with a helical focuser, using PTFE tape to both tighten the screw thread and make a nice smooth operation.

After some trials I found that getting the scope pointed where I wanted was a bit of a trial with the original cheap finder, so decided to make a new finder. As it happened I had just dug out an old pair of 10x50 binoculars and found them broken at the focuser. The same weekend I picked up a broken pair of 16x50's for 1 at the local boot fair, so with plenty of optics available I set about making a finder. Using some more cardboard tubes in several sizes I fashioned a holder for the finder, with 6 adjustment screws for accurate alignment, I used one of the prisms from the binoculars as a diagonal, using black felt behind the surface to ensure good reflection. Then mounted the binocular eyepiece in a sliding cradle to allow focusing. A nice coat of matt black paint inside and out and a couple of hairs glued in the eyepiece finished this piece off.

Mounted above the bearings to avoid unbalancing the scope, this gave me the finder I had been looking for.

I picked up a very small CMOS webcam at about this time , which was taken out of its case, had the corners of its single circuit board shaved off, and was then mounted to a film canister.

I was now in business for astro-imaging.

Through all this time many others throughout the world on the Astronomydaily site were also constructing their own 114mm Dobs (or babydobs as they had come to be known). The most prolific of these was in Croatia. Beri as he is known to us had made about a dozen scopes in a marathon scope building event with members of his club. He has since gone on with assistance of members of the Rochester (NY) Astronomy club to make more scopes for the schools and youngsters in that country, so much so their government has got involved with the project.

The Gashco EQ

My next project started when we were looking at some small 2.5" spherical mirrors of 24" focal length, once again being sold by Surplusshed, this time for only $6 each..

Two of these and some 17mm diameter FS mirrors at 10 for $6 were purchased as an experimental set, so that I could play around with different mirror arrangements. I started out making a classic newt, using the 17mm secondary mounted on a piece of dowel, which in turn was glued to the centre of a piece of hacksaw blade. This was positioned in the tube, collimated and fixed with some epoxy resin.

The mirror cell was made using one of the plastic end caps from the paper tubes, with some 60mm coach bolts expoxied to a base that the mirror was fixed to using silicon sealant. These bolts each passed through a spring that had been originally destined for the rear brake shoes of a car, with a couple of wingnuts on the back, the mirror cell was complete.

The focuser was constructed using a 22mm tank connector for push fit plumbing, this has about 30mm of threaded section, the main nut is epoxied to a side tube coming off the OT. The helical focuser is simply threaded into this, fortunately one of the 16x binocular eyepieces fitted the other end nicely.

For a mount I was determined to have an equatorial mount, once again construction was to be from cardboard tubes. I had quite a few hours of thinking and doodling before I came up with an elegant solution, once again it was using end caps as bearings that cracked the case for me, though used in a different manner to before.

This time I decided to put two end caps together, with a pipe through the centre which contains a 16mm bolt with 20mm washers to stop the two parts separating, A thin section of milk bottle was used to limit the friction in the core.

With the pivot points sorted, all that was needed was to construct the cardboard mount. I decided on a triple tube pillar for rigidity, I jointed this into the base, and made a slotted joint to hold the tops of the tubes together, which also formed the support for the first pivot. The top part of the pillar was cut and jointed to approximate the correct angle for polar alignment, adjustment for this was planned to be on the front foot to tilt the whole mount to achieve alignment.

A short T piece was made to make the next section, one end having the scope mounted on a pivot, the other having a counterweight. The counterweight is a threaded rod with some heavy 'bushes' that were found in my scrap box, held in position at each end with a wingnut for easy adjustment.

The Gashco Drive

Next I needed to be able to track with the Eq mount, to this end I first thought of a stepper motor, not being able to locate one amongst my scrap parts, I started looking around. This was when I spotted an old cordless screwdriver, that had been sitting around for a while - ever since I had broken the socket and lost the charger.

I took this to pieces and found a nice compact gearbox, a quick disassembly and count showed that it was a concentric gearbox, with two stages of 7:1. I reasoned that if this was extended to 7 sections I would be within ballpark figures of a drive that would turn at 1 rev per day, once connected to the mount.

I decided I would have to keep my eyes open and acquire a few more screwdrivers at Boot fairs. About this time I went Into my local Homebase store, where I naturally looked to see how much the screwdrivers were new - to my surprise and delight I found that brand new they only cost 1.79 - a remarkably cheap price. Of course I bought 5 on the spot.

By cutting the front section off of the gearbox casings I was left with a short section of gearbox body with the teeth inside. Three of these (one cut shorter than the rest) and 5 more of the rear stages from the gearbox, some electrical tape and a piece of 40mm pvc pipe and the gearbox was finished.

As a drive I obtained a lawnmower toothed belt that looked about the right size, and drove it using a 9mm socket that came on a screwdriver hex shaft, to increase the grip I added a sanding cylinder from a Dremel modellers drill, which gripped the belt nicely.

I mounted the whole lot with tape onto a test rig ( two lengths of cardboard tube joined by a tube stopper pivot) and started testing. After a 10 minute run with fresh charge in the batteries I had got a 2mm rotation of the drive, this calculated out to 1.06 revolutions per day, within realms of a simple speed control to get to the right setting for tracking.

I am planning to put in a rotary selector switch to choose between each of the 6 sets of batteries that I now have. These should provide a reasonable length of tracking time for a nights observing session, and with the charging sockets, they can then be connected up and re-charged all at the same time once observing has finished.

In fact all I have left to do is to find a selector switch and to mount the whole lot on the telescope mount.

The only ironical thing about it all was the 4 stepper motors that I subsequently found, squirreled away in a drawer after I had completed the gearbox.

The Gashco Solar

With the coming transit of Venus and the demise of an old pair of binoculars, I decided that a small pocket sized scope for Astrophotography with my Kodak Dc3200 Digicam was in order. Using my now standard 22mm tank connector focuser, mounted in a 40mm pipe stopper, and the whole mounted in a short piece of 2" ID cardboard tube. I proceeded to use one of the binocular 50mm objectives mounted at the other end using electrical tape as a packer. For this I purchased a sheet of Baader film, and following the manufacturers instructions, which came with the film, made up a selection of filters for my telescopes, these mount in the filter / mask holders that each of my telescopes is equipped with. These filter holders are like a cap that fits over the end of the scope and has an internal rim that holds a circular mask or filter tightly between the rim and the end of the telescope.

This scope has a camera steady handle mounted to it using jubilee clips, and the whole can be mounted on a standard photographic tripod.

This setup normally travels around in the car with me and is used for grabbing the odd solar and lunar shot, as and when I get 5 seconds to set up or a good photo opportunity arises.

I have found that for solar work a large backboard made of lightweight foam board helps whilst working behind the scope, so that you are not blinded by trying to look near the sun whilst setting up etc.

 

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