Thick glass can substitute for granite

george wilson said:
Wait for Enco free shipping. Order a granite plate + whatever else you need to buy to get the minimum cost for free shipping. I've been getting heavy brass bar stock shipped for free. They may have a $100.00 min. by now. I can't blame them!!
Click to expand...

Shipping wasn't the issue, it was the jump in the item price (the granite plate) from $37 to $113.

M
 
so how would one go about testing the "flatness" of a home hobby granite sink cutout reference plate or a tempered glass plate / granite sink pancake layering plate for true flatness?

ideas:

a) tram "flat" then test concentric circles?
1. an lever could be used to amplify the sensitivity of a dial indicator
2. glass is very smooth, if not flat..., tramming might work well with amplified sensitivity

b) ink another "flat" and compare the touch patterns under different orientations. (reverse, iterative
1. would not give clear indication of which direction the test surface is not true
2. cant scrape glass flat
3. hard to see ink on granite
4. relies on flatness of second flat however as a test of uniformity, would be useful.
 
Years ago, I used to use a piece of 1" thick tempered glass as a surface plate. I worked well as I wasn't doing super accurate work at the time. Back then, I didn't even have the instruments to determine how inaccurate it may have been. If that's all you got, it will work.
 
I have a 24"x24" x1 1/4" high end granite counter top. It is flat as I can mesure. As a hobbyest it's only use is for layout witch I use a phase II hight gauge for. It works fine for what I need. When I was younger and messin with 2 cycle motor cycles we used an old temperd oven window for laping the heads and it worked great.
 
Tony Wells said:
One of my early mentors used a tombstone as a surface plate, but I suppose a piece of tempered safety glass would be cheaper and easier to get. I'd stay away from plain window glass. It's wavy and not flat.
Click to expand...

I guess a tombstone could be pretty cheap... unless you get caught!
 
I guess you could buy yourself one,leave it blank and get some use out of it in the shop until it was needed elsewhere. Might be an interesting epitaph on it at that time between the Dykem stains.
 
I lap surfaces by attaching a sheet of very fine grit sand paper to a piece of glass, and moving the workpiece in a figure 8 motion on the sand paper.
 
Tony Wells said:
One of my early mentors used a tombstone as a surface plate, but I suppose a piece of tempered safety glass would be cheaper and easier to get. I'd stay away from plain window glass. It's wavy and not flat.
Click to expand...

Tempered glass is also not flat:
http://en.wikipedia.org/wiki/Toughened_glass#Disadvantages
It also cannot be cut to size.

I have some chunks of float glass that were the surfaces of coffee tables. Not being tempered they can be cut and are far flatter than I can measure (which isn't saying much). They're only 1/4" though, so they are too flexible.
 
You must log in or register to reply here.
Back
Top