diy dob

[ponytale]

Hi all diy /dob modders and stargazers,

i Have now settled in my new home in australia "OZ" i am near wanneroo in the northern suburbs of perth,the skies are pretty good compared to the UK, it is now end of spring coming into summer, today was 33 c tonight will be a low of 20c currently the skies are clear most nights ,

jupiter is to the NE and Mecury and venus are just setting in the west at 8pm. I have been busy putting my dob together after making my mirror in England with much help and advice from Glasspusher,i recieved my mirror back from vacuum coatings the day before i left for OZ, I carried it as hand baggage which got me a few worried looks and a few questions at heathrow, after a second xray and a few queries i was cleared to go,

I managed to buy some 25mm x3mm alloy tube 6mts for $40australian, and some black pvc reticulation tube that sides over the alloy tube like a glove , bargain i thought ? this was cut by me into 4 sections and 4 tube inserts tapped into one end of each they were then fed in to the holes i had cut with a forstener bit in the ply mirror box and the secondary /focuser cage see pics attached the whole ota then fits into the bearing box ,

the trunnions are quite large, as i wanted to use springs to control the balance of the scope.

there are 2 bearings at one end of the bearing box and teflon pad at the other at 70 degrees spacing there is teflon sheet between the side panels and the trunnions and the side panels are fixed with control knobs and springs which allows variable friction against the trunnions,

one of the knobs has a friction brake so i can lock the ota in any position or simply vary the resistance as required , the scope has a good balance and feel, it is nice and consistant at all angles and i can move it up and down with one finger,the azimuth bearing is 2 full size sheets of teflon baking sheet around an 8mm bolt/ pivot, the sheets are both free to rotate so i have 3 friction /slip surfaces ply to teflon, -teflon to teflon and teflon to ply again, this seems very smooth and consistant for full 360 degrees, there is no play/wobble to speak of as the sheets are only 1 mm thick , there is a slight amount of play in the pivot bolt but this will be fixed with a captive bolt and nut with a bush.so first light very soon i hope , probably too warm tonight the stars are very twinkly !! maybe early am ? there is cooler weather due on the weekend , in the mean time i will work on the alt /az scale

markings which will fit on the edge of the turntable and trunnions .

[gooseholla]

Looks nice.

I hope to make my own scope one day -- when I have my own place, and money, and tools, etc. lol

[dobbie]

Nice scope ponytail have you had first light yet? Let us all know how you get on , and don't forget about us in freezing Britain , clear skies dobbie.

[perrin6]

Omega Centauri should look good plus the tarantula neb in one of the magellenic clouds, I forget which one. The milky way is fab in Oz as the richest part is high in the sky plus and the Omega & Tarantula nebulae are higher. Look out for the rabbit in the moon (looks different as it's 'upside down').

[asteria]

Hi Ponytale - nice scope. Thanks for sharing the pics. I'm interested in your teflon baking sheet idea. Is this the non-stick paper that is used in cooking? It doesn't seem that it would be strong enough to carry the weight of the scope. Good idea though and it sounds like it works well. Ed

[gooseholla]

Teflon used in baking stuff is hugely strong and flexible. It is the plasticy baking sheets, not the paper sheets.

[ponytale]

the teflon sheet is the black plastic type for putting in ovens to line them and make them easy to clean it is under a 1mm thick and flexible ,

I had 1st light last night ,it was still 20c at 8pm here but my scope was equalised as it had been outside for days, my 1st veiw was venus just before setting ,very bright so i used it to fine tune my collimation and do inside and outside of focus to get an idea of mirror quality, the results were very good showing no pinching or astigmatism of the mirror, next was the king Jupiter wow my first sight of the bands, awesome the cheap 10mm volcano top plossl perfomed best out of my meagre collection of eyepieces the worst being my SWA 58 6mm tmb planetry plossl , my H20 mm tasco eyepiece was better !!! so a bit dissapointed there, perhaps it will better for lunar use.

next target my 1st sight of M43 in Orion what can i say given the low quality of my eyepieces i was astounded at what i could see a sharp group of 4 stars which i think must be NGC 1977? Group and the veils and clouds of M43 , I cant wait until i get a good eyepiece for my F5.4 set up, any feed back welcome in this area, i guess a good televue 10-15mm and a good barlow ?or a 2" please feel free to advise /guide me .

Summary

overall I am really pleased i went down the path of making a mirror and a scope of my own , the learning curve is steep but rewarding and could reccomend it to anyone,

but of course much easier than it could have been had i not had all SGL advice and guidance , I think i will probably improve on the quality of my scope with 12mm alloy plate and bushes for the secondary / focuser cage and mirror cell money and tools permitting, clear skies !!!

[perrin6]

Good report. I'd like to hear the results of a star test and v. close double viewing.

BTW can't see a finder on your scope, are you making your own ? I recommend getting an old pair of reasonable quality 8 x 40 binos and taking out the lenses to make one. I found a pair on ebay, 8 x 40 makes a very good finder as it has a wide field of view and shows magnitude 7 stars clearly which I find just right for locating objects when star hopping. My 8.7 F7.3 dob shows very good detail on Jupiter with a william optics SPL 6mm eyepiece at X 270 - very contrasty, good eye relief and natural colour (ie. no obvious tint like some eyepieces).

[Glasspusher]

PT, good to hear that you have settled into your new home and that the optics are performing well. Love the Carl Sagan quote.

Best wishes,

John

[asteria]

Hi - thanks for clarifying the baking sheet idea - I'll look into this. I'd never thought of using one (or two) of those plastic oven liners. Glad you've had first light - sounds like a very promising scope. Ed

[jbk44]

Brilliant, love your scope.

[Quark]

Excellent job PT, your dob is a beauty.

[ponytale]

Thanks everyone for your kind words, did a little bit of window dressing today !!

took off some rough edges , pics soon

[asteria]

Hi Ponytale - I've got one of this non-stick sheets now. Will let you know how I get on with the azimuth bearing. Thanks for the idea! Ed

[ponytale]

Hi asteria, to trim my teflon sheet i fitted over the spindle/pivot pin and held a stanley knife tip over the spot where i wanted to cut the circle and turned the sheet throught the blade with just enough pressure on the blade point to cut the sheet but not the base, you could put a piece of scrap wood or card under the sheet ,make sure there are no scags/ or high spots on the boards to catch the sheet as it is quite thin, here are a few more pics of my scope after i cut out the side panels to take away exccess side friction and cut a shape into the trunnion/bearings to give it a bit of a Lunar look,

i have some brass strip to edge the cut with ,the other pic shows my friction adjustment for my alt bearing the nylon wheel presses against the inner face of the trunnion /bearing panel and pushes it aginst the teflon sheet sandwiched betwen the 2 side panel , hope this make sense?. tony

[asteria]

Thanks Tony - I'm just putting a bit more work in on my project now. Just going to put the az. plate on etc. Thanks for the tips. Ed

[asteria]

The work went well - I now have a smoothly functioning azimuth turntable. I'd really appreciate any more information you have on your altitude bearings. I've read your account above but I think I'm missing something as I can't quite follow how you've managed the bearing surfaces. As I understand it, this is usually done through glueing 'ebony star' formica onto the altitude riser surface, and running this over PTFE blocks on the bearings, but I think you've come up with something different. Any feedback would be welcome.

All the best. Ed

[ponytale]

Hi Ed, you are right i have something slightly different , the 2trunnion /bearing boards that are half moon shaped have a iron on timber edge strip along the curved edge which i intend to replace with alloy T section or L shaped angle curved to fit,

the bearing box has a small mushroom shaped teflon pad which i made by putting a piece of teflon rod in my electric drill and using a file i reduced the size down to 6mm leaving a cap of 10mm at one end like a fat nail ! which is tapped into a 6mm hole in the bearng face,

you can see one in the previous picture, a small white pad .

opposite at 70 degrees is a 20mm bearing mounted on the outer guide panel using a 8mm bolt next to the white knob you can see this is a fixed bearing i set the height the same as the teflon pad using washers as shims,then drilled the hole through the side panel , this gives me a free running bearing on the one side and friction on the other i found this makes it really smooth start stop "no stiction" alt movement i will put up a picture ,as said before there is also teflon between the 2 faces of the trunnion to reduce drag, the adjuster allows me to hold the scope anywhere in the 90 degrees of movement the other white knobs adjust the pressure on the side panels, i will take it apart and put up pics along with this post. Tony

[asteria]

Hi Tony - thanks - I'll study this in more detail. It's an interesting system you've devised. The pics are a great help. Thanks for taking the time to do this. All the best. Ed

[ponytale]

update , I have replaced the iron on edge with 10 x 3 mm alloy this is fixed on with counter sunk screws spaced so they will rarely contact the bearing or teflon pad they will be filled with liquid metal filler and flushed anyway, this will be a lot more durable, and is very smooth running. I am also trying the teflon nail/pad on the inside of the bearing guide panels instead of the teflon sheet which worked really well but was a bit untidy, i may get some etched or a self stick version to try.

ponytale

[ponytale]

used the scope on the moon and jupiter last night conditions were very good here,

the moon was in first quater and had a some earthshine on it, also i took some video with my spc900 webcam , the quality is not as good as hoped i have in advertantly left the led inside the camera working and has caused some degrading of the images as light leaks past the lens ,

i will fix it asap. Jupiter was a little fuzzy but 2 bands could be seen, a barlow is required i think to get a better image. ota movement was pretty good in the alt but a tad sticky in the az , the teflon sheets are very slippery on each other but they are so thin i think a backing may be needed to space the boards apart a bit more, perhaps some felt or card or even laminex on the base side may help i think possibly the stiction /suction of the ultra slippery surfaces may be the cause and two rings /circles of laminex at the outer edges may reduce the contact area without introducing any rocking between the 2 boards .

my home made teflon nail shaped pads are working out really well , i simply put a 25 mm length of 10 teflon rod in my drill and spin it up, i put a coarse file aginst the side of the protrudind rod a take off a bit until it is about 6mm I then taper the end to match a 6mm drill point so when i tap it into the hole drilled in the ply it stops firmly at the bottom , then when in situ i place a washer or two over Nail Head and slice off the excess , i guess this could be done with any size rod in a lathe or drill press etc .see atached scetch

along the way i have also devised an adjustable pad where the rod is pushed back through the ply with a blunt screw or threaded screw in a tee nut , one could even thread some teflon with a tap and make teflon cap nuts .

teflon padnail.doc

[asteria]

Hi Tony - good to hear about the developments. My teflon sheets seem to be working OK, but I did wonder about placing them between a couple of thin aluminium discs to see if it smoothed the motion out. I think I'll see how I get on first before making any changes. I'm working on my alt. system now. Keep us up to date. Ed

[moflaher]

Have look at the Jewel Box, my favourite sight in the southern skies!

[ponytale]

Hi all diy,s found just the thing for protecting my secondary in my truss dob, a soft foam type drink can holder just slipped nicely over the mirror, cost me 99cents at ikea !!!

[asteria]

The simplest things work best! I've been thinking about how to protect my secondary mirror because in the design I am working on it is quite exposed - dew is also going to be a problem!