Chriske

Just removed this one from my printerbed. Not perfect, but it'll do. The remaining small artefacts are caused by the high printing speed (130mm/s), need to slow down to make a perfect one. Height 230mm nozzle 0.4, time 4.5h. Four perimeters, no infill. Now I'm busy drawing the Trunk now.

Thanks Gina..!

The square hole is there to have access to the bolts, inside the scope part, to fasten the grips and a few other parts.

Very professional looking painting 'room'..🤭 A few Hubble parts

The mirror should be able to move in its holder, just a fraction of a mm. The mirror should, depending on its size, rest on 3, 6, 9,18 or 27 soft pads. Small clips on top will prevent the mirror from tilting. We never use glue or whatever to secure the mirror in it's cell either.

Oops forgot to upload these two pictures ... silly me..🤭

this is how far I got today Due to these two bolts at both ends I can't store HST in my workshop anymore. This is how I store HST from now on, in my van. Two thick wires connected to the roof of my van support our HST. As a matter of fact it's floating for the very first time...😁

Started applying Mylar

Nice one...!! I'd change one thing. The focusing knob should positioned a bit higher. Fingers will get stuck while focusing. Especially in Winter wearing gloves.

That device does what it's suppose to do,very handy..! HST-instrument part completely finished, all grips in place. 20200527_110210.mp4

A M-o-M (Mirror-o-matic) is a very good concept. The mirror rotates and the 75% diameter tool swings back and forth. There's lots of information on the net about the technique 'how-to'. I have two of these machines that can easily handle 20" mirrors. I'm busy right now grinding a 20" f/4. Carbo is fed by a peristaltic pump. To avoid contamination every grid has it's own separate system. These machine's have a autonomy of about 1.5 hours. When the containers, filled with a mix of carbo/water(stir constantly), are nearly empty the machine halts automatically. The courser grit is fed by hand. There was no way to feed carbo 80 through that peristaltic pump. In fact one of these machines is Marc's. Side by side we use to grind our own mirrors in my workshop. We had lots of fun building them and grinding mirrors with it. Almost every year we tried to make a new scope, every time a different scope. Target and goal was open door at our local observatory. Very often a weird scope that has been built only once by an amateur. This time we were busy building a Stevick-Paul. A few month's back Marc past away at age 57, and I never touched our machines again from that day on. Sorry to go of topic...😧 At about the same time we made our MoM's there was that guy Gordon Waite building his mirror mirror grinding machine. He uses a fixed post grinding machine. iow the tool is stationary. He has a set of movies on YouTube. There's even a set of movies on very fast mirrors. If we would do it all over, we probably would build a 'Waite version'. Simple to build. But these MoM's can easily grind in 'fixed post' modus too.

A few planks, some screws, two thick bolts was all I needed to make me a small device in which I can hang HST on top of my workbench. HST will rotate, lying horizontally, around it's axis. Now I can keep on working with this 'contraption'. So I need to mount HST only one time/day. Not yet tested, tomorrow morning first time. Fingers crossed..!

Thank you all, for the nice comments...!!😉

today some light work, testing different surfaces for HST's scope. Think I'll go for the mylar. Aluminium foil : Mylar :

That's a challenge indeed 800mm f/3.3...😳 The largest I've made so far is 20" f5.6.( by hand). Two identical disks to make a bino. Almost polished out. On hold because I've promised... right now there's again a 20" f/4 on it's way(for a friend), but this time it will be made using a M-o-M. Most of the time I use these M-o-M's fixed post. All these mirrors will be supported 27-point (PLOP) My problem is : there are only 24 hours in one day...😬

Hey Mark, I'm not saying this online calculator is no good. Maybe for a less-experienced amateur it will set his alt-pads at a good spot, don't know. There's always that rather important question, what type of formica did you use..? You did some tests already I suppose(?) That is the way to go, test with the materials you have at hand(or can buy in a local shop). There's no way a online-calculator can replace this way of working. Lets say you don't have the correct formica or even do not have formica at all, then you could use another slippery sheet of wood(varnish)/plastic in combination with teflon spray. Anyway, I'd always use teflon blocks. The only disadvantage using teflon-spray is that after a few months/year of usage you need to clean the surfaces because it catches dust. Yet again Teflon-spray does miracles. A very sticky surface will transform in a smooth one after a spray of teflon. And again, as I mentioned higher up, there are some alternatives, like that felt I mentioned higher up. Believe it or not it is a very good solution I'm using right now. The scope hanging in that fork weigh about 12kg. I don't even bother to glue the felt in the rocker. The roughness of the wood catches the felt and hold it in place. The bearing sitting in the rocker is nothing more then a 120mm diameter printed disk(PLA). To be clear on the matter I do not use felt pads, but rather long strips of felt. The felt covers almost 1/2 the diameter of the disk. The last bino I made is hanging in a printed fork and a printed disk. In between is a strip of felt. in the fork I added two very small pieces of double sided adhesive. A cloth or even a blanket/carpet might do the job as well. There are tons of possibilities. I didn't test these last ones yet, but I probably will do for my next scope. A few year back I made a 10' Printsonian. Well for the AZ bearing I did use 3 ball bearings at 120°. To have the correct friction I added a very simple friction device. That device was nothing more the a flat adjustable spring. Adjusting was done with a small bolt pushing against the flat spring. That spring is in contact with the rocker. The ALT bearing of that scope is teflon/PLA (150mm printed disk). My point is : I like to try different methods. It's easy indeed to copy what your 'neighbour' did or what you found on the net, but I myself like to explore other possibilities that works as well(at least) as the classic methods. Chris

In real these grips are painted yellow, don't know why.

Due to a dumb 'accident' I ended up with a few cracked ribs. Silly story, don't ask. So I can't lift HST for the moment and after 'half a pound' of painkillers I can do some light work. Today I cut a few grips painted end started installing these grips.

I opened the link and closed it immediately, sorry.. There's nothing to calculate at all. During course(started 1981) we always use the procedure described higher up, there's nothing more to it. Indeed the inner pads takes all the weight of the rocker and scope. The outer are only to very gently support and at the same time very delicately avoid tilting of the rocker on these central pads. What I forgot to mention is, the central pads need to be positioned as close as possible to the central bolt..! Sometimes we even use a small ring around that central axis/bolt. Using large Alt bearing is not really necessary. Using the correct materials is. But there's a problem with the alt-bearings. Well, not really with the bearings itself. A real problem to overcome is the balancing issue during eyepiece switch. In the early days we all used the familiar 1 1/4 eyepieces. Not only did they have about the same weight, but removing it to replace it with another eyepiece, it did not disturbed the balance of the scope at all. These days it's almost impossible to do that, without the scope falling or lifting rather quick, loosing the object you were observing. I myself have a few Nagler eyepieces. One 20mm --> 1051gr..!! If I'm not mistaken that is about 2lbs..!...😳 I also have 4.7mm --> 180gr. My old Erfle eyepieces(very good quality btw.!) --> 136gr. Well that is a problem, 1kg versus 136gr..! There are many ways to tackle this balancing problem. Just do a search on balancing a Dob and you'll find a handful solutions. Some use a thick steel chains, others use very long springs, and there's also a solution to use a very long rubber band to keep your scope in balance during eyepiece switch. There's also the old counterweight trick, or clamping the scope against the rocker. And there are more possibilities, I'm sure. My solution is simple, I do not use these heavy eyepieces anymore. I do have a large set eyepieces and they're all lightweight. I know, silly, but it works. So these (few) heavy eyepieces I own are 'out of a job' permanently. There's still a difference between all my lightweight eyepieces, but during switch my scope(s) all stay put. And I know, that tilting problem could be solved by applying more tension to the alt-bearing. But that is something I do not want to do. The movement of alt-bearing should 'feel' the same as my az-bearing.

The best way to control the AZ friction to perfection is to add 3 extra teflon pads in the very centre of the rocker, between rocker and groundboard. These 'central pads' are there to support the complete weight of the scope. The three pads at the outer rim do no more then balancing the rocker on the groundboard. To start with, these central teflon pads need to be just a little bit thinner then the outer teflon pads. No more then a fraction of a millimetre or so. Next I test whether the scope does run smooth. And I mean very smooth and no backlash at all. If the AZ runs to heavy I take the rocker and scope away from the groundboard and add a very thin layer of plastic under the central pads and test again. I do not(never) add something under the outer pads of course. If the scope still runs to heavy I'll again add a thin layer of plastic under all 3 central pads and repeat if necessary . I keep on doing this until the scope really floats above the outer teflon pads. Doing this, for larger scope it might be necessary to repeat this the next day, when the RA 'bearing' is 'set'. After that the scope will stay on floating for the rest of it's day. Needles to say for that you need a piece of formica around the central pin of the rocker as well.

these textured formicas have fewer contact points, resulting in a very smooth 'ride'. The 'rougher' the formica, the smoother it will go. Think of ball bearings. Ball bearings have just point-contacts, That's the reason why they work so smooth. + of course, formica is a very 'slippery' material.