crashtestdummy

Btw we need to decide on secondary size as I massively overestimated the necessary size for visual.

Factored just about everything in no and after selling my stuff I should have much if any extra to put to it hopefully but if I have it will be worth it. Im hoping as soon ad I get some more grit I can start hammering down to sagitta on the mirror and catch up so we start the tile tool set at a similar time

So,im getting on with the mirror,currently at 25 hours from start to where I am now,between 2 and 3mm sagittal on the front so I thought I would go through some plans. my friend damian is building the shell for the scope with his woodworking and engineering skills and im helping where I can and having him show me how to do some woodworking so when I come to build my next scope(26" f3.5ish) I can build a bit more of it myself.im hoping to add a few personal touches to the design as everyone likes things a bit different to other people so here is a small list of things that will be mounted onto it. Focuser-http://starlightinstruments.com/store/index.php?route=product/product&path=35&product_id=50 I currently have,and love my moonlite but once I have the paracorr in it and a big 2" 100 degree eyepiece inserted,it sticks out miles and has a little flex which you can adjust but it makes the focusing a bit stiffer than I want.the feathertouch with SIPS is much stiffer and lower profile so that fulfils 2 targets straight away. finderscope-https://www.altairastro.com/product.php?productid=16703 im currently in two minds here between getting this and the straight through focuser as a stand alone focuser as I don't star hop well with a right angled finder.or.........keep it as a right angled finder for close up galaxy hopping and get a smaller secondary 9x50 finder for the initial star hopping or just a RDF or telrad.Im just wondering if having two finders would be too much clutter.The weight wont matter too much with the big heavy 20kg mirror at the bottom. eyepieces-no change needed really as I already have the 20mm,14mm and 9mm Explore Scientific 100 degree ones and a 2" 2x focal extender.realistically it would be nice to have something a bit wider than the 20mm as with my focal length of 2016mm is 100x which to mee is a little narrow for low power.the 25mm ES 100 would give a better 80x but they aren't highly rated and the exit pupil will be getting large.plus the paracorr magnifies things a little.I wanted to keep my 30mm ES 82 but its exit pupil is over 8mm so that wont be a good experience. luckily whatever I get I will have the sale of a 16" modified Lightbridge with dew kit and moonlite duel speed,a paracorr2 and the 30mm Es 82 to contribute.infact it should pretty much cover the price of the bits and coating the mirror and secondary so I wont have much to put to the scope really. hopefully do a mirror update at the end of next week. clear skies

An SCT is much more glass though as it has the primary,secondary and the corrector plate hence the massive weight.mine is a 43mm thick blank,you could always use a 25mm plate glass blank and have it slumped.that would be almost half the weight.John Nichol showed me one and it's probably the way I will go for my 26".

The current 22" weighs 22kg so I would think it would be about 30kg or thereabouts.

It's a slow process,more so the bigger you go but I really wanted to do one and there's no time like the present. John will do a great mirror for you,that's for sure but he will also give you advice about making your own.I'm sure he will run another of his mirror making seminars some time soon

I initially planned an 18" F3.9 but the 22" blank was only about £50 more so I couldn't help myself.obviously the 18" would be much less grinding.are you grinding yours yourself or buying one?

Oh and to add,my next one will be a 26" f3.something :)

I think everyone should have a go at grinding at some point,it a really interesting experience but hard work.I know that when I look through that eyepiece for the first time with a mirror that I've ground will be a great experience.

My current 16" f4.5 is 1829mm focal length,the new 22" is going to be f3.6 and 2016mm focal length.likely one small step at zenith which is quite manageable for my height.Any less than 3.6 to me is just more coma and grinding.for an 1800mm 22" would be about f3.2 which is a bit too much to me.

Enhanced coatings for the primary and secondary are £338 which isn't too bad but I need to include the price of attatching the secondary holder to the secondary.also the price of the secondary too.I'm hoping the whole scope shouldn't cost more than £2500 including a new featherlite focuser with sips coma corrector. With smallers scopes you make them for your own enjoyment/achievement but with big scopes the savings are big too.

As a rough guide so far: 22" blank £475 10kg weight disc £20 3kg 60grit £30 3.5kg 80grit £15 1kg 400grit £13 1.75kg 220grit £12 Spirit level £8 Gorrilla bucket £12 Belling stones(6!!) £10-15 12.5kg 80grit £50 Still have 10kg of 80,all the 400 and 1kg of 220 left

Well ive not posted for a few weeks as ive had lots to do work and personal life wise so not had that much time with the mirror but I finally finished getting the back flat which was my main aim so I could finally move onto the front.As I said in an early blog post,my mirror was nowhere near uniform when I got it so I had to take lots of glass out of the middle to get it flat as it was convex.i wasn't 100% sure I had got it right so I travelled up to see mirror maker supremo John Nichol for a second opinion.If it hadn't have been for John I very much doubt I would have had the confidence to even think about a project like this but after attending his mirror making seminar last year and email support in the mean time it really did fill me with confidence to have a bash.Was a great eye opener seeing his mirror making facility,all those machines and all that glass!!!! I had travelled to see John to make sure I was going right and I had explained how my mirror had been and how i had tried to grind it flat and that I though it was slightly turned at the edge so he had actually set his machine up ready to correct this as we had both assumed the worse.Well I put my mirror down on the table and unpacked it for John to check out to see if I had got the mirror flat enough and uniform and out came the straight edges and the mirror makers eye and the first comment was "well Rich I think you have had a wasted journey".Well to mee that had made the journey anything but wasted as It was massive relief for me to know it was bang on and ready to go ontot the front after a quick half an hour blast with some 220.i was left with a really fine casting mark on one edge which I may polish out later but on the back to me it isn't important. after a quick bit of 220.decent bevel too :) finally the mirror is turned over to show the high ridges on the front ready to grind.its not 100% clean so not as shiny as it could be grinding the higher thin casting marks on the front to me is a bit of a nervy experience as you feel as though they are going to snap off and its a noisy experience with much vibration.rather than doing long strokes I shortened mine down to lessen this vibration and after about half an hour they were much lower after another hour I was left with a few higher ridges near the edges which I used a smaller 6" sub diameter tool locally to grind these lower which seemed to work quite well.after about 2 hours the front is almost fully clear of casting marks and has a sagittal although the flipside of having a raised part on the back is that I have a slightly depressed part on the front which John tells me will more than likely grind out as I remove 10mm of glass to get my focal length.one thing I did notice when using the 60grit,its amazing how quick you can grind down a 3mm bevel when the surface is flat!!!I ended up with no bevel at all so have been really luckly not to get lots of shells on the edge.i did get one slight shell but it will bevel out when I next redo it so very very lucky escape!! just a few casting marks left now,one on each side and they will grind down slowly as I keep pounding away with the 80grit. making decent progress and the next few weeks will be spent doing the boring part of hogging out the curve and topping up the bevel from time to time so I wont likely bore you with regular updates other than when the curve becomes apparent. just some notes to add: grinding he back I used 3.5kg of 80grit,2g of 60grit and 250g of 220 grit so far on the front I have used 2kg of 60grit and about 1kg of 80 so far. myself and Damien(master) purchased a 25kg sack of 80grit between us and shared it out so hopefully that will get me somewhere towards my curve before I have to order anymore.80grit grinds much much slower than 60 so expecting it to take me well into the back end of February to get to my curve at the minimum!! in all time wise it took me 14hours to get the back flat!!!! so far ive spent 4 1/2 s on the front with an hour and a half being on the bevel so 18 1/2 hours in total so far. Im not managing to put ion the time I had hoped when I planned the grind but with the weather as it is,observing time hasn't been eating into grinding time!!!! cheers for looking Rich

So first up I bought a new car a month back and I had decided on something a little bigger than my 206 estate so I bought a 307 estate. here is how to fit a meade 16" Lightbridge,an eyepiece case,2 chairs,battery,clothing and boots a tip for people who have bigger mirrors and like to clean them.my 16" mirror wont comfortably fit in the sink like my 12" and 8" did so I originally bought a small kids paddling pool.this proved ok but was too flexible so ive now used the gorilla tub that I use to clean my 22" blank when grinding.works a treat!!! finally-I managed to get hold of a bigger(and heavier) weight dics for grinding the 22" blank grinding the centre down still looks small on the blank despite being 10 1/2" diameter considering stacking the 5kg weight ontop and welding it on for some mega weight when hogging out the curve.the sagittal for f3.6 is about 1cm so the extra downward push will mean I don't have to push down as hard. not done anything else on the blank as im having a second opinion on Saturday to see how ive done so far.even though its my first grind I want it to be right!!! hopefully going to do some observing from a dark site Saturday morning 2am onwards when the moon dips.leo and virgo galaxies on the agenda.hopefully the dew wont be too bad. clear skies

and I have just ordered a 10kg cast iron weight disc which is 11" to replace my 5kg 9" one.this should be much better for hogging out the front :)

Well last night I managed to do some observing for the first time since 4th December!!Really started to worry that I wasn't going to get any done before the next moonrising but was lucky.It cleared about 10pm and I managed to stay out until 1am when the clouds rolled in.They were due to clear again in half an hour but I like my sleep so went in.managed to tick off some more ngc's,herschels and caldwells and add a few galaxies as detailed below: ngc 1973 ngc1975 ngc1977 these are listed together in my guide and just look like patches of nebulosity that I couldn't distinguish in my light polluted skies. ngc1662 ngc2264 cluster easy but could make out the gap of the cone with uhc but not the exact shape ngc 2261 hubbles variable nebula-looked almost like a comet in the 20mm ngc2251 almost looks like an asterism rather than a cluster ngc1817 faint but looks excellent ngc1807 ngc2355 ngc2395 ngc2304 ngc 2419 intergalactic wanderer-was small and faint but I think from a dark site this will be mega!! ngc2683 ufo galaxy,bright and easy find ngc2859 small and faint galaxy ngc3675 faint round galaxy ngc 3184 very faint galaxy,had to use averted so will recheck when im at a dark site. was great to be out but I had left my illuminated finder on so that didn't work and my mirror needs cleaning again as it is a bit foggy on the lower edge after dewing a while back.new batteries on order and try and find the time to clean the mirror in the next 2 weeks :) on to the mirror. a few problems.i seem to have a slight turned down edge at the top and bottom of the mirror(12 and 6 oclock as I call it).when I got the blank it was raised in the middle and I think its just whats left from this so I think I will probably have to do some chordal strokes and get the centre lower then the edges will come back but have asked for some more professional advice to make sure.have got a new straight edge and some more 60 grit and some 400 on the way so hoping to gte the back done the coming week and get on with starting the front!! also thing that at 9" my sub diameter tool is a little on the small side(5kg weight disc) so im going to order a bigger 10kg weight which will be about 11.5". the turned down edges,not massive but I want it perfect you can never have too much grit a staright edge that's actually flat!! a new dust mask,this one I can actually breath in!! hopefully another update midweek. clear skies

Well my sky time has been pathetically poor recently and it doesn't show much sign of getting better in the next couple of weeks.My last observing session was the 4th of December,a quick hour in the garden and one new ngc object and as usual Rubbish seeing conditions.i keep telling myself I wont bother with the garden again but you have to get time when you can :( well the weather has been very bad recently with high winds and rain.i doubt most people have had much luck the last month.there were a few clear night a bit back but ive been having car trouble so have not been able to get out anywhere but hopefully I get the car back Saturday so will be able to take advantage of any clear dark skies. Have now done just under 12 hours of grinding on my 22" blank and im much closer to having the back grinded flat but still have a little bit of a raised section but hopefully I can get this out by grinding the back into a slight concave then bringing it back a little.Im also not 100% confident in my straight edge(I know,how paranoid) so im going to buy another just to be on the safe side as a few quid is worth it in the scheme of things.Have been doing a combination of half diameter tool and a smaller 5" tool which looks comedy on the big mirror. upto now just doing the back flat ive gone through just under 3.5kg of 80 grit so I definitely need to get some 60 for the front or im going to need a 25kg sack of 80!!!!hoping by the end of next week to have the back flat and smoother through 220 to 400 grit and the casting marks ground off the front and a start to the curve but what matters more is getting it right so I don't have to redo anything!! weather for the next week isn't looking too good so looks as though that's another couple of weeks with no observing until the moon goes back down but may sneak an hour early hours of tomorrow and same Friday into Saturday if im lucky,which I aren't. on another note-the girlfriend got tickets to sgl in Portsmouth and I said I wasn't interested!!!!!am I mad?well you are lucky to see stars from Portsmouth so observing is out and im not a big fan of groups so I gave my ticket up for my girlfriends 8yo niece who will have a juch better time than me :) hopefully have a big mirror update in a week or two

You could probably have just switched to a full w-stroke with the full sized tool to get the casting ripples on the edge sorted.a smaller sub diameter tool is definately useful too

ive always said from the beginning that I have plenty of time to get it finished and getting the back flat is reallt important to getting a good overall finished mirror. hope you will eventually get the motivation back to finish that 12" mirror as it will be good practice at rescuing a blank.

So,ive not actually had as much time to give to my mirror grind as I had hoped,mainly due to my cataclysmic luck with cars.I'd had a Peugeot 206sw hdi for about 3 years and it had been pretty reliable save for the last few months where it had been plagued with a few vacuum leaks and then a niggling fault that I couldn't track down.Anyway I decided enough was enough and money was drawn out of the bank and I went out and bought a 307sw 2.0 hdi as I had wanted something a bit bigger and comfier and something with a bit more poke as 68bhp in an 1100kg car is never going to shift a 22" scope well so went for the 136bhp 2.0.anyway this has turned out to have more faults than the car I got rid of so its been back twice,had a part and now needs a few more and will probably want a new clutch and dual mass flywheel in the new years which the seller is going to be paying for(bought from a dealer).anyway ive been back and forth taking the car back and bumming lifts off my dad so had little time but did order a few bits in the meantime more bevelling stones £2.99 posted from ebay a gorrilla tub for cleaning the mirror off after wets.this is a real life saver unless you can hose the mirror straight down which i cant spent 10-15 minutes topping up my bevels on the back side and then did another 45 mins grinding the back flat.this is a slow progress.infact after 2 hours it doesnt seem to be any flatter yet so im anticipating its going to be a 10h+ job before i can get on to the front.luckily the front is concaved the same amount so what i lose timewise on the back i will gain on the front.just hoping its a bit more uniform on the front :) more to follow over the holidays :)

cheers for the comments guys.should have a little update over the next few days but not had time due to buy a new car to replace my broken down one and then having more problems with the new one!!grrrrr

aperture fever hits us all at sometime.it has now hit me 3 times.8" was big enough for 6 months.12" was big enough for 6 months and now 16" was big enough for 6 months.where next?there's no commercially available scopes bigger than 16" in the uk and to buy one from the usa or a custom uk builder would have cost £7000-10000 for the size I was after so a plan was hatched to build something. myself and damian(master) attended a mirror making seminar with john Nichol who took away some of the myths of mirror making and made it seem much less of a dark art.we came away from the seminar with a real hunger to make one ourselves.originally I had planned to make a 16" to fit in my current scope but when I got the prices and found out it was only about £100 more expensive to get a 22" over a 16" I couldn't resist. im sure a few of you will think im totally mental to just dive into a project this big and I would be inclined to agree with you as the only grinding ive done is to hog out a 12" blank to f5 so im still very much a novice but im prepared to take it steady and take my time and ask for help when needed. about 2 weeks ago I took delivery of a 22" low expansion blank :) :) :) actually I lie,i bought two but one is for my friend damian.we are both building a 22" scope so will be able to help each other on the way. a 70kg pallet applies(2x22" mirrors) a 22" low expansion blank!!(22kg!!!!!) compared to a 12" blank!! damian admiring one of the tables he made for our builds!!! set up in the greenhouse out of the way so I started with the blank just over a week ago and have just been taking it steady.i did make mistakes during the bevelling stage by using the least abrasive side so it took me about 6 hours to bevel both sides and I snapped on stone through stupidity(I tried banging dust off it) and the second ended up like this safety first yesterday I started grinding the back of the mirror flat but its not uniform and has a raised section across the centre which ive highlighted in this photo currently grinding this out with short chordal strokes and will then use w strokes to get it back uniform after I have got the centre back towards the same level.im using up some old 60 grit I had left over from a 12" trial grind then be moving onto 80 grit which will take longer but theres no rush. heres the back of the mirror after just over an hour of grinding.some of the edge waves are still visible but the centre is smooth so im definitely grinding the centre out more than the edge big thanks to john as he has supplied lots of information and help to get me to this point and im sure I will require much more. more updates as and when :)