mapstar

Interesting bit of research and good to see the pupils involved. A thermal camera is a novel idea. I was ronchi testing a 14" mirror yesterday in preperation for a build will you be trying this with the students? This is also a good test for showing how thermals in the light path affect the performance of the optics. I have yet to do a matched test image to see how it compares but the software is easy to use although having a micrometer stage is the hardest part to set up. The mirror thread I did may help explain better. Damian

They hold collimation really well if accurately designed and built to be assembled time and again with just the minimum of tweaks. I probably adjust mine 1-2mm max which is easy to do. Preventing flex can be difficult but not impossible. Rotational forces on the secondary can be an issue, too much tension can distort the U T A so caution should be observed when strumming on the vanes to test the tension.

What is the secondary size Jim? I had 3 attempts at the spider until I was happy with it. I used 1.5mm thick material in the end but my secondary is 130mm MA and weighs .7kg. Damian

Looks great Jim very nice work.

Nice project and well done getting this far. Must say that it's nice round although not the most inefficient way to use ply as there is a lot of waste. A torch can be used to roughly determine the focal length of the scope or a focault/ronchi test.

Thanks for reading through, enjoying it and for the compliment. A 14" is a really good size in terms of aperture size and transportability. The views are a pleasure to share and don't hesitate to ask if we're ever at the same star party. Damian

Mag 15.8 according to the software I use and DSO browser so should be achievable from a dark site with slightly bigger aperture

Nice write up Mark. It is right in the North corner of Virgo next to the border of Bootes/Coma may get a look at it tonight if the weather plays ball up here

The slip rings and new spider detailed on page 10 of the build were recently tested at the Peak Star party. They both worked without fault and I can highly recommend the slip ring mod to any dob owner especially if you don't have the space to fit a battery in the rocker box. Here's a photo at the recent star party courtesy of Wookie1965 as I didn't take any. The cable can be seen plugged into the base board. Good view of the new spider. Here's another view of the scope (Courtesy of Swampthing) and shows the cable plugged in to the base board and also the one from the rocker to the mirror box. Probably the only part I will change for a coiled one. Good comparison with a 10" scope if you needed an Idea of the difference in size. When disassembled the 22" actually forms a smaller stack than the 10" The mirror box weighs 31kg and is the heaviest part to answer the question I get asked quite a lot . Enjoyed the build so onto the next. Damian

Yes 2x M4 button head screws hold the vanes to the upright pillars. I think you can see one on the left ( bottom) and the rear ( through the top disc) vanes in the central boss pic. Works o.k. so the next spider I make will be for a different scope

The next mod I did was due to rotational flex of the spider caused by the weight of tge 5 1/4" minor axis secondary. This alters the collimation slightly. I went through a couple of different versions before settling on whats seen below. The original, then one with an octagonal central boss which had two fixings at the end each Vane. This was stable but I just didn't like the look of it and due to a slight error gave a fifth diffraction spike. Having no turning facility I had three aluminium discs laser cut. 2 x 100mm dia x 5mm and one 131mm dia x 6mm thick for the secondary holder top plate. Next I made the 4 new spider vanes from 1.5mm thick mild steel. The mill playing a huge part in this. I did the drawings for these on CAD software so could've also had them laser cut. Any excuse to make some turnings I would use the two 100mm dia discs as the top and bottom of the spider central boss joining them with 4 uprights that the vanes would attach to. Here is the nearly completed spider 4 tapped collimation holes in the lower disc and some end fixings to allow the four fixing screws at the end of each vane. After spraying black the spider was installed in the UTA. Central boss The secondary dew heater would be connected through the vanes and then via an insulated copper strip across one of the vanes soldered at each end then bonded with epoxy. All finished it was ready for star testing and I was finally happy with the results. Clear skies Damian

Very nice Neil

Not quite as epic as the other thread Chris. Thanks for the recognition, the scope will be hopefully getting some starlight this weekend at the PSP. The milling machine rebuild is here if you missed it as it makes for another Interesting read http://www.model-engineer.co.uk/forums/postings.asp?th=119748

Answers:- 1 No but it keeps my hands soft 2 errrrrr MK3 Hope it's given a few pointers.

Thanks. More to come

Cheers Mike as you know I've been meaning to complete this mod for a while. New spider to document next. Looking at the weather I should be out tonight but packing for the PSP tomorrow.

Managed to get the slip rings finished off today First off I drilled a 10mm hole in each brush holder to accept the copper rod. Here it is with the brush holder still in the milling machine vice. The hole had to be deep enough to accept a decent slug of copper for the brush and also the spring. Here we are with all the parts assembled and also the exploded view. I'd soldered a copper braid to each brush for a reliable connection which wouldn't just rely on the spring and copper to brass. The braid was brought through what would be the brush holder top. A crimped lug then completed the whole assembly. Two square section holes were then cut through the lower board of the rocker box using a 1/4" router and a jig. After these were both cut I gave them a quick coat of paint to seal the ply and inserted the brush holders with a little vaseline to lubricate and stop them tarnishing. Pressing one of the brushes down on the spring It was then a case of refitting the rocker box on the ground board. The only thing left to do is connect the cable to these with crimped lugs once I know the length to the rocker socket. I will probably fit an insulating cover over these but the power tank is double fused so o.k. for now I plugged in the battery and tested at the holders for volts Onto the next Mod which is a new Spider Damian

Bring it along to the PSP sure it will get sorted

You may or may not have seen the complete milling machine rebuild here Neil http://www.model-engineer.co.uk/forums/postings.asp?th=119748

Spent the afternoon creating lots of brass turnings. Heres the machining pics Two nice shiny blocks ready for the next stage. Two mounting plates and the T shaped brush holders Not quite finished as I've got the hole in the bottom to bore which will accept a 9.5mm spring and 10mm diameter copper brush. The copper hasn't been delivered as yet so I will finish them hopefully tomorrow. It is just a case then of drilling two holes through the rocker box bottom and fitting the mounting plates to accept the brush holders. Another photo of the holders as they will be mounted in the rocker box. Two button head M4 screws retaining each brush box in the mounting plate.

Finally with the wiring soldered to the under side I could feed the wiring through to connect the socket. After the socket was soldered on the whole slip ring assembly was screwed in place. And the XLR socket on the outsidd of the ground board. The ground board wiring was now finished. Next job was to make up two brush boxes for fitting to the rocker box. Brass was the best option so I will be on with making them today and post the results later. Damian

The routed slot so I could feed the wiring in beneath each slip ring. After sealing it with paint it was time to connect it all up. The two brass rings had a thorough clean so that the solder would take. I used a blow torch for this as an Iron would not be sufficient to get heat into such a large area.

Here's the XLR socket fitted just above one of the feet on the ground board. I then drilled a hole from this to the larger hole behind to feed the wiring through. Using standard XLR wiring pin 2 pos 3 neg.

Struggling to upload pics at present with the error message There was a problem processing the uploaded file. -200? Not sure why this is maybe admin can help later. Damian