Fancied a change of pace so decided to make one of the finder mounts.
A quick play with the modeler to make something like this.
The two rings are 50mm dia.
Parted the rings then had to work out how to drill and tap them so I marked 6 radii off and used the square to set them vertical. Drilled then replaced the drill with the tap and started it, removed from DP and finished tapping in the vice them moved round to the next hole. The two legs were cut with the angle iron guides and hacksaw and a heap of filing (I still cant believe how handy these are) then the curve for the rings to bolt onto was cut using the home made boring bar with a long bit. I first had to bore out the old tool holder to fit the 14mm qctp post. The finished item all bolted up with the sun finder clamped in the rings. Only two more to make, one for the laser finder and one for the 2" optical finder (2" telescope) I used a short length of stainless 8mm shaft to ensure everything aligned ok. The grub screws will be swapped for brass knurled ones and the black screws will be stainless on my next order.
Managed a bit more. Made a lost foam pattern for the first part of the scope that the lens cell has to bolt to.
Buried in the loose sand and then filled to just under the edge of the tin. The straws are breathers.
Fired up the furnace and soon had a pot of metal.
Lifting it out with my new crucible tongs.
Starting the pour
Heaps of flames from the burning foam.
After a while its shaken out
Gee it looks ugly, still some plaster adhering.
After cutting the sprues off it looks a bit better
Turned the outer dia to size to then took a skim from the tube so I could use the steady to bore the inner dia.
Once bored to size I removed the casting, turned up a mandrel to fit in the end, re-mounted and centred the casting to thin the tube and add some grooves just for show and cut the threads to screw into the joiner. (still to be cast in I hope brass)
Unfortunately there are too many porosity pin holes to be able to polish the casting so I will powder coat it black.
Thanks. This was my first go at lost foam and I think I will second that. The next foam pattern was a disk to make the joiner but was a total failure. It was interesting but I dont think I will do it again.
I've just finished a wooden pattern for the brass joiner and optical stop but have to replace the motor in my muller for a more powerful one which is why I went with the lost foam.
Lens cell joined to the front barrel, undercoated only, I cant make up my mind as to gloss black or matt black, they both look good.
The flange is separated with an "O" ring to allow collimation of the lens via the three screws and three grub screws.
The six screws inside the cell that hold it to the front flange were drilled and tapped from the outside then plugged with aluminium plugs and turned down to size.
They are virtually invisible.
That cast piece looks really good painted! I don't usually paint my castings. I would say the paint has to match the objective lens holder. Are you going to repaint that as well? How about Marks crinkle finish? Gloss would look great but you know it will get marred up.
What is the purpose of the threads on that piece? They look very clean for an un-treated casting. My castings machine poorly in general.
The thread is 1.25mm and the front lens cell will be painted the same colour as that cast section.
There will be a small section in brass (if all goes well) that has a smaller internal dia to act as the joiner to the main tube and as an optical stop.
I had to cast that section because the internal dia of that front part is 83mm dia at the front reducing down to 76 for the first stop, the 80mm tube has an internal dia of 74 which just fits the optical light cone where it will screw into the joiner.
In all, the focal length requires three optical stops to prevent grazing reflections from entering the eyepiece and I decided to machine them as joiners.
Most telescopes just push sheet metal ones down the tube but I thought that as the tube will be over a meter in length it would be nice to be able to dismantle it into shorter sections for traveling.
More complex than I imagined. I will have to read more about this:
"In all, the focal length requires three optical stops to prevent grazing reflections from entering the eyepiece and I decided to machine them as joiners."
The front cell is finished
all the lens edges have been blackened but I still have to blacken the screws inside.
The gloss black doesnt look as glossy in the photos.
You can just see the pusher grub screw that allows the cell to tilt for collimating.
Finished threading and polishing two of the tubes, (only one in the photo) how tedious is polishing. The original surface is the top tube.
Still some ultra fine scratches to remove so its back to 1500 grit then rouge.
I cant cast the brass joiners yet due to the changeable weather, sudden showers that I dont want to have molten metal around.
The first brass lump has been cast as a lost foam project for the joiner.
Man thats ugly, runners and sprue to remove.
Then a bit of machining and a thread cut we get this, its difficult to see but there is a 1.25mm thread there.
I dont know if it was required but decided that discretion being the better part of valor I decided to make a threaded plug to fit the end so there was no chance of distorting the part when I clamped it in the chuck to part, turn and thread the other end.
Yep, thats a small inclusion hole you can see there, dang! but I'm not re-casting that (yet)
Its back in the 4 jaw and I've now parted it to length and hope to start on the thread today. (no pics of this bit yet)
And now its machined and threaded to size and successfully holds the two parts together as well as looking great (or so I think)
Only another two to cast and machine. At least I've finished polishing the tubes.
Looking great! , you're fooling yourself. That is magnificent work but I may be a little biased as I am an itinerant banana bender. Did you grind youy own lenses as I knew a painter friend in Rockhampton who ground his own but it was a PITA just watching him slave for hours over one facet.
Thanks for the kind words.
The lens's came from surplus shed and were old Jaegers.
I forgot to mention I parted off a 3/4" section first before I turned the inner dia. It went very smoothly for such a large lump.
Had an awesome couple of days, so much done.
Cast the three joiners in brass in green sand.
Machined them to size, bored the baffle dia.
Then bored half way through to leave a thin section for the actual baffle and threaded the inside.
I then screwed a mandrel into the joiner, skimmed the bit thats protruding in the hope it would be more concentric when reversed to bore and thread the other side. This turned out to be the case but lets be honest, its not sub micron accuracy here.
Once the other side was finished it was impossible to remove it without marking the brass so I wrapped it in plastic tape and jury rigged a strap wrench from some steel banding
ID-10-T alert! The design was for 15mm of thread on the ends of the tubes and in the joiners.
Unfortunately after machining all the defects off the brass there was only sufficient material left for 10mm of thread so I had to either recast or shorten the tube threads. Yep, easier to shorten the threads.
I removed the bearings from my fixed steady and replaced them with oil soaked hard-wood shoes to keep the marring of the tubes to a minimum as I shortened the threaded ends
This worked really well and they all screwed up to make this. There is an "O" ring on each end of each joiner to seal the joints.
Tomorrow I'm off to get the 50mm tube for the focusser draw tube and then very little for the next 4-5 days as I have to go for an operation on my jaw. (Shameless plug for some sympathy)
Making the draw tube for the focusing unit was a bit of a pain.
The closest size tube I could obtain was a threads thickness too small so I had to bore and thread the inside of the tube then make an insert that was just that much thicker.
Just so the diagonal could screw on.
Still, it works and it all looks good.
Now I need a block of ally 70mm x 70mm x 50mm thick for the focusser body that will bolt to the brass end plate.
I've found a source for an 80x80x80 block for $26 but with postage I expect that will end up closer to $50.
Thats a lot of spondulics for what will be a lot of swarf. Maybe I will have to cast one.
Time to get some grain refiner and de-gassing tablets.
Still waiting for the block of ally so I started on the finder scope.
I'm using a doublet from an knackered binocular.
The right hand joiner was already made, one end of the tube was threaded, so today I cut it to length and threaded it, also there is approx 30mm of taper on the inside with a fine thread for anti reflection once its painted matt black.
The centre joiner has three different dia threads, one for the tube, one for the lens cell and one for the lens hood.
I cut a fine thread inside the hood and have sprayed it matt black.
All assembled it looks like this
More polish needed on the hood and tube but the joiners will be gloss black.
You can just see the gaps left for the "O" ring sealing glands so moisture doesnt wick into the tube.
Finder scope finished and looking very nice.
However, I now have a cemented 50mm japanese doublet that may be a better objective but it needs the central tube to be another 15mm longer and a different lens cell. Maybe after its all finished.
At last I can start on the focusser unit.
I couldnt find any 60mm plate but did find some 100mm round.
Now came the hard part, I dont have a mill but need to convert this cylinder to a block.
It wont fit securely in the chuck.
I scribed the block size on the top of the cylinder, drilled the centre and mounted it on the compound in place of the tool post.
I used a rule to align the scribed line with the face of the chuck.
The only tool I could use that had sufficient off set happened to be the Eccentric Engineering diamond tool holder and this proved to be just right held at an angle in the 4 jaw.
about half way through here. as I got closer to the scribed line I just had to make a tiny re-alignment to bring it back to spot on.
Instead of doing the same thing to the other side I mounted it against the chuck jaws as there was just enough room and have started milling the other side. I'm hoping they will be parallel by doing it this way.
The first cuts seem to point this way.