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Hi Derek, I use an 80 tooth blade (cant remember but I think it's DeWalt?) and don't have too many problems. I think its getting ready for sharpening though as it's done a lot of work. The sliding table is good although the Nylon running bearings seem poor quality, as they develop flat spots on them making the table bump along. I have replaced both of mine once but the same problem has returned. I keep saying I'm going to get something better for them. I picked up a spare beam a long time ago and extension table which are both still in their packaging unused and I doubt they ever will be? Like you say the table saw with side extension and sliding carriage takes up a lot of space. I also have a kity 1637 planer tucked away under the spotted blanket at the rear of the garage in the shot above. It doesn't get much use nowadays

Anyway moving on from the workshop tools to continue the build. After I had cut the top I then had to work out where the threaded rod needed to come through so I could put in the bushed hole. Here's the box with in final stages of gluing with the two collimation screws sticking out and the cell top mount clearly visible So it was then onto sanding and finishing off with a cover

Hiya Astronymonkey I used Baltic Birch Ply from here as I have used them several times. They aren't the cheapest but with delivery included it makes life easy for me. There are other sources close by me. Quite a few on ebay too http://www.cutplywood.co.uk/products/baltic-birch-plywood-bb-bb-standard-grade?variant=9658998917 It can be difficult to cut without splintering. I find scoring along the waste side with a stanley knife before cutting stops chipping out of the surface, but I also try to cut with the unseen side face down as it's always the bottom side that tends to be problematic. A good table saw has it's benefits and I use a Kity 1619 that I've had for about 15 years now. Here's a few pic's of the kit I use starting with the saw 2.5Hp induction motor very smooth The old Pacera pillar drill which I think has been around longer than I have. High/low speed Home made router table And the trusty routers

Thanks Guys. It's been a long time coming but glad you're all enjoying the read. Amazing what you learn along the way

So to the mirror box construction. Because I intended to attach the lower trusses to the box with a corner piece I designed the box as an octagon which gave me a little more edge clearance for the way I was going to construct the rocker box. This meant a more complex construction than just a square. All the wood was baltic birch ply 18mm thick Here are all the parts laid up with the cell inside before gluing. The ample use of the biscuit jointer provides a lot of strength. The box is roughly 200mm deep and 680mm square Strengthening gussets were added to improve the torsional rigidity of the completed assembly. Large holes were just there for aesthetics really, but provide a way of picking the box up. I had yet to cut a rear hole in the box to mount fans if required. It is essential that at least the left and right panels are parallel and square as the bearings when attached would run out if they were even the slightest bit out. In the four corners I cut a slot out to accept the lower truss mounting points. The trusses would be joined together as in my last build. Having made all the mountings at the same time I used them but in future I have a different design to try. Here's a pic after gluing up with the lower truss mounts loosely fitted, and the top mount for the cell with 8mm countersunk stainless allen cap bolts which were fitted from the rear of the box Once I knew where the cell was going to be I then went about fitting the two bottom collimation points. Packers were made and the two adjusters bolted in using 8mm stainless countersunk allen cap bolts fromm the outside of the box . All the calculations have to come together so that the cell is centralised in the box The collimation is done by only adjusting the two lower points with a 10mm stainless thread from the front of the mirror box. Again I'd made everything to do this way back in the past when I made the other scope on SGL I then made two top pieces (from 12mm ply) to complete the mirror box construction More on the next instalment

The four points or Whiffle tree as it is known is the best support for a large thin mirror. A sling if set wrong can apparently pinch the optics. Here is Mike Lockwood's site with testing details http://www.loptics.com/articles/mirrorsupport/mirrorsupport.html

Just the points Derek no sling First point on either side is 22.5° from vertical then the next two are 45° from that. The points rest (or should do) at the mirrors centre of gravity or just over 16mm from the rear. Hope that explains it referring to the pics

Me too

I'm sure there will be another gathering down that way or somewhere close in the future Paul so you will get a look

Yes, but it's a lot more work which you wouldn't really see any benefit from.

Depends on the error Calv. There's a graph I saw once up to 30" for 18 point's

Cell from the front with the spherical bearings fitted

Cheers Steve I'll try my best

Thanks guys, it takes quite a bit of writing Mike as you point out. Whilst it's cloudy there's not much chance of doing much else!

Cheers Calvin

I had the triangle's (trefoil shaped) cut from 6mm ally at a laser cutter. These were then machined (19mm end mill) to accept a spherical bearing in the middle for flexibility which was glued in using Loctite bearing fit All the dimension's were spewed out by the PLoP (PLate oPtimisation program) I also drilled and tapped the 3 contact points on each triangle ready for fitting the 18 nylon pads that the mirror would rest on. A screw through from the other side would then hold the triangles onto the wobble bars. I also had the edge support brackets laser cut from 1/2" thick Aerospace ally which were then machined to accept the 4 nylon edge support contact points. 2 posts to hold these completed the main parts of the cell 18 nylon pads for the contact points (cnc'd by a friend) and four nylon edge support points finish off the cell which is fully constructed below, a polypropylene ring was used to hold the triangles in the correct orientation. There was a fair while until the next piece of the scope was constructed as the mirror took up quite a bit of my time!

Cheers Paul

Hi all, As a few are aware I had quite a long running mirror thread which came to completion late last year. A lot has happened since with the construction of the scope which is now nearing completion so I thought it about time I added this to the forum for you all to read. The first thing was the mirror cell and I made this quite a time before the actual mirror was finished. It was constructed from 1 1/4" (31.75mm) square section 1.6mm wall aluminium and designed in PLoP for the optimum configuration. The tapped triangle point were made from 1"x 1 1/4" solid bar. The calculation for my mirror thickness showed an error of 1.9 nanometres and calculating in the edge support error this worked out at 2.8nM. All well and good so onto the actual cell which was to be 18 points. Some of these pic's were in my other thread but seeing as I made the cell at the same time it is no different. Here is the cell cut to form the basic triangle with the two edge support mounts at the bottom before machining and welding. The cell would be fixed at the top using a rose joint spherical bearing and then adjust at the two bottom points for collimation. So next I machined the slots out for the wobble bars, drilled the pivot holes for the wiffle tree mounting points, and the threaded holes for the rose joints. And so onto welding it all together which I entrusted to a local welding company in sheffield. Moving on the design and construction of the wobble bars, triangles and wiffle tree edge support's.

Lovely bit of kit Stu

Hiya Derek, I should cancel the red carpet as it's still not sorted!!!!!!!!!!

Very nice

Very nice looking bit of kit there fella. Damian

When it's complete and working Mike please post pics as it will be very helpful for others. Thanks Damian

Hi Mike Not really sure on this one as I tried to get Foucault Images of my mirror whilst testing and found it difficult. I did find it could be done if the camera was set quite far back from the Knife edge (I was using a cheap Samsung L100 camera) Have you had a look at this website it may provide some answers? http://bobmay.astronomy.net/camera/cameratop.htm Regards Damian

Thanks I couldn't quote the strehl ratio as it hasn't been measured, the views should tell the tale and with John having his hand in the final stages I'm certain they'll be excellent. At present the limiting factor seems to be a night without gale force wind and lashing rain! The glass started at 22.5kg and ended up at 17.5kg Allowing for a bit of future proofing and due to the design it will probably mean a couple of steps at zenith as I will probably motorise it. Damian