Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_30_second_exp_2.thumb.jpg.7719b6f2fbecda044d407d8aba503777.jpg

  • entries
    34
  • comments
    170
  • views
    35,641

totally pitched off with lap making

crashtestdummy

1,050 views

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 :)

IMAG0022_zpsae38bb8e.jpg

IMAG0025_zps560c2028.jpg

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).

IMAG0028_zpsf7125125.jpg

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

IMAG0052_zps8fccc297.jpg

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.

IMAG0037_zpsd328b09d.jpg

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

DSC00117_zps2d54c199.jpg

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!!



4 Comments


Recommended Comments

thats a nice looking lap Rich,gotta hate when scratches happen but

might the scratch polish out well you polish or is it too deep for that.

nice to hear your back at it again.

 

Rick M

Share this comment


Link to comment

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 :)

Share this comment


Link to comment

Hi Crash,

Looking really good, despite the scratches it must be much easier with a wooden base rather than the plaster one.

Keep going, not far to go now !

cheers

Share this comment


Link to comment

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 :)

Share this comment


Link to comment
Guest
Add a comment...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.