crashtestdummy

My test set up is pretty much compete but I'm currently sunning it up in the Algarve so no time to do anything.it's weird not being able to see ursa major at all!!

I am going to keep on polishing as we are pretty sure the problem is that I've not been polishing enough through centre.I'm just going on what John told me after looking at my mirror and asking what strokes I had been doing

I am using a sub diameter lap,it's about 17" :) I'm hoping it's quite spherical when I'm rid of the depressed centre but time will tell

Finally after just over 100hrs work spread over nearly 10 months I've finally had my mirror tested for the first time. There are good and bad bits. Good:nice spherical curve and no turned down edge. Bad:it has astigmatism in the form of a depressed centre. John tells me this is due to not polishing through centre and not turning my mirror enough but says it should polish out hopefully.so I'm going to do a couple of hours polishing through centre then 're test and see if it's better if not I may need to go back to 600 with the tile tool and do some more through centre work.all in all its no big deal and I'm pleased with how well I've done for my first bring.need to get my tester finished now so I can see how I'm altering the shape with my through centre polishing. I'm on holiday in a couple of weeks but hopefully November with be the month I start figuring!!! Wish me luck!!

ive loved almost every single of minute of it too :)

Yes but because of the amount of edge I had to remove(as advised) it will have slightly changed the shape of my tool toa shallower curve so despite the pencil test being perfect it may not have been the perfect result for a sphere.Will soon find out :)

I meant the curve being too shallow not the depth which is ok.I had to grind my edge down quite a lot to get my sagitta right hence why I'm worried about the curve.

My fl is about 2000mm so between f3.5 and f3.6

After the dissapointment of having many scratches in my lovely polished mirror I've been back through 400 and 600 and have now done another 4 hours of polishing with little or no scratching!This weekend I will make the long journey from Portsmouth up the teeside to see John Nichol at his mirror making seminar and will have my mirror tested for the first time. People who know me know that I'm the ultimate pessimist so you won't be too surprised when I say that I'm expecting a turned down edge and the curve to be slightly too shallow and slight zoning on one section.this is just from what I can see and feel through the lap but by Sunday afternoon I will know for sure.I've currently just broke the 100 hour mark so have a lot of time invested in this project with hopefully only a bit more polishing and figuring to go.if my.mirror ends up needing the curve deepening then there will be no annoyances,I will just crack on and get it done!yes I will be dissapointed but disappointment won't get the mirror finished!! On an unrelated note-I went out and did a bit of messier hunting in the garden with the 15x70's.it's nice to get some stargazing done from time to time or I will end up losing my way arround the night sky!!!ticked off a few Inc m31,m11,m27,m13,m92,m29.happy days but can't wait to look at them with a 560mm scope rather than 70mm binos!! Clear skies

That's a small area 5-10mm wide around the edge.have ground through 400 and 30 mins of 600 with a nice smooth grind and no scratches but still not getting the edge.it polished well with the lap so hoping it's just my tile tool that's beyond its best.

One thing to add-as I've done some 400 I've noticed that a small area about 5-10mm wide doesn't seem to be roughing up as well as th centre so I'm thinking I may have a slight turned down edge.it could just be due to my tile tool getting a bit more worn as I had to grind the edge down after hogging to get my sagitta.Going to carry on through 600 and a few hours polishing then will find out when it's tested but I'm expecting a bit of extra work.steep learning curve :)

Well as stated in my last entry I had picked up a few small scratches during polishing,nothing that was visible without really looking and catching them in the right light.I had decided to carry on as they wouldn't affect the final finish but tonight after 15 mins of polishing I had ended up with half a dozen bigger scratches.I think I must have got some grit on the mirror when pressing the lap and not cleaned it off properly so to cut a long story short I didb15 mins with 600 alu oxide that didn't lessen the scratches so got rid of them with half an hour of 400 sic.Will do a bit more 400.tomorrow and get the 600 done again and hopefully be back on to polishing again by the end of Thursday. One thing to ask-does polishing too dry or with too little ceo make scratches easier to get? Gutted how much less shiny the blank is at 400 than after nearly 5 hours polishing. Oh well its lucky I enjoy polishing!!

I am going to go back to my original 2" overhang stroke instead of the 1/3 through centre as I didn't get scratches doing the initial stroke and still had good contact and even polish

Yeah I did the cold press for 15 mins with a cerium wash.when I do my second mirror I will make no mistakes :)

Have polished for 4 1/2 hours now and a few more fine scratches are evident now probably just because it's easier to see them now.I can't get them to show up in photos so obviously they are pretty fine.spoke to John Nichol who saidits hard to get it perfect so going to keep polishing for now then have him look when we test it at the mirror making seminar in two weeks.if they are too big I will go back to 600.I have loads of time so its no buggy I just want to make sure it will coat ok Did a 15min wet press today which went much better so will do that in future if needed :)

The scratch is shallow enough that my finger nail won't pick it up but after doing an hour today I'm not 100% sure it's lessened or not but will have a look in the light tomorrow. The scratches won't effect performance or the coatings but I will know they are there!!

Tbh the contact on my lap is good enough that I don't need to press.I'm using a sub diameter lap and all the squares aredull so won't bother pressing anymore. Daniel no I didn't think of that tbh :( Had a look today and have two scratches.will polish tomorrow and check to see if the scratches are lessening and then decide if I need to go back to 600.or not. You live you learn :)

Started polishing at the start of the week and got a good polish up then decided to do some pressing of the lap for good contact.dried everything off and pressed it with about 30kg and left for a few hours.long story short, the lap stuck solid and had to be banged off resulting in a few pieces staying stuck to the mirror.could have been a lot worse and the only bad part was a scratch that was left.the bits cleaned off the mirror ok and after redoing the channels again(the pressing tightened then up) I polished again for a bit.Going to do another hour of polishing to see if the scratch lessens.if not then will do some 600 Ali oxide for a bit to get rid of it then polish again.it's a steep learning curve but I've been lucky with the mistakes I've made. Hopefully an update mid week

Yeah I didn't fancy pushing a 10kg+ plaster tool. I think the scratch was from not cleaning the lap off properly.bit of a rookie mistake really :( Have some more grit so will do an hour with 400 this arvo :)

The scratch was just a little too much to polishing out so used some of my old 600 which put a bigger scratch hence the back to 400.lessons learned :)

Its been a long time since my last update,partly due to hectic schedules with the new job and a week away on the isle of wight for a training course but mainly due to my inability to make a pitch lap first time!! After finishing off with the 600 and having a nice scratch free surface that shows up reflections much better, it was time to get on with the bit I had been dreading-casting a pitch lap. I gathered all the bits I needed for this-a 17" wooden disc for the lap(to save weight over a plaster disc),2kg of the softest guggoltz pitch,baking foil(largest size I could find,the camping stove and a cheap £3.50 pan from asda :) melting the pitch is a job to take your time with but even at 30 minutes to melt it down is way too quick according to others but about the slowest I could do it with my stove.Getting the pitch out of the card containers is a good challenge in avoiding contamination.i used a brick softly to crack the pitch inside the card and then emptied it out into the pan.this takes a good 10 minutes with 2kg. making sure your blank is clean and warm(I dunked mine for 20 mins in warm water),dry it fully and cover fully in baking foil(reflective side up). the first mistake I made was to pour the pitch too runny which meant it went slightly under the join of the foil but it was still useable as sson as it started to thicken slightly I put my wooden disc on top and pressed down to get the air bubbles out and to keep the shape.i then added a 10kg weight to pres it down and left it to set. to cut a very long story short,i didn't wait long enough to remove the lap from the blank and as soon as I started cutting the channels the lap splintered a lot and I ended up breaking the pitch off and starting again.and I repeated this process again another two times until I got to the lap I have now. my current lap still isn't perfect,it has some splintered bits and a few imperfections and the channels need deepening but it does polish ok if a little sluggish unfortunately after 30 mins of polishing I picked up a slight scratch so ive ended up going back to 400 and 600 grit to get rid of this scratch before I start polishing again.even with 30 mins polishing its amazing how much more reflective the blank is!!! hoipefully be back to polishing next week and can see about testing if my blank is a decent sphere or not :) getting there slowly but surely!!

From what I be been told,machine polishing is slower than hand polishing but I've got plenty of time so if it takes longer then it's no big deal.I have 2kg of gugolz pitch winging it's way to me :)

yeah I definitely think those W strokes have probably been causing the scratches as ive only had that one sleek in 4hours of 600.We keep forgetting that we are still grinding novices and we are still learning all the time.Im glad im making my mistakes on this small mirror so when I do a big one it will be right :D :D :D

well after just over 80 hours im ready to pour a pitch lap and start polishing!!! here is a picture to show some shine on the blank after grinding with 600. hopefully on Wednesday I should be pouring the pitch lap and Thursday all being well I should be starting the polishing phase. After enquiring with John he says if im lucky it should take 10-12 hours so im allowing for about 15 and hoping I don't get any scratches as I will have to order more 600 grit and use the tile tool again.Its exciting getting towards the final stages but for me a mirrors quality is down to its figure so that stage is going to be the most nerve-racking for me. Wish me luck!!! clear skies Rich

The plan is to take it to john for final checking before it goes to be coated plus im in email contact with john if I get to a point im not sure about.I wouldnt have got anywhere near where I am now without John and also damian who is doing the other 22" grind.its been great to swap ideas and techniques.the figuring is the bit im not confidnt about. Tbh anyone with patience could get to where I am now. Yeah would have been nice to see the tour winding through the dales :)