Gallery, Projects and General > How do I??
Quartz Surface Plate?
PekkaNF:
--- Quote from: sparky961 on September 13, 2015, 11:12:06 PM ---So, I had a chance to take a closer look at my haul tonight. Spoiler alert: Don't get too excited.
Good news is that I was able to measure flatness deviation. Bad news is that it wasn't difficult to measure....
--- End quote ---
I know :bang: I had the same feeling. Now, after few measurements/samples I have concluded: Generally glass (compared to a rock) seems (locally) more smooth and flat, but has greater error over a long distance + flexes like there is no tomorrow.
Have you measured diagonally and on each side how much there is error from level, like I did on Reply #28 top picture on this thread page? There is hope, if the plate is relatively true, even though it has hills and walleys....if it is inclined or twisted - ahem.
Pekka
Manxmodder:
--- Quote from: Pete. on September 14, 2015, 01:58:21 AM ---
--- Quote from: krv3000 on September 13, 2015, 05:25:58 PM ---well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat
--- End quote ---
The only problem with that is if you put a piece of glass on a surface plate it might well be flat but if you put it on anything else - especially with a chunk of iron on it - it will bend and not be as flat as it was when you checked it.
--- End quote ---
Bedding the piece of float glass evenly down onto a piece of granite counter top with something like thin consistency tile adhesive or Plaster of Paris may work.
That way the glass is sufficiently supported to prevent bending/twisting distortion.....OZ.
PekkaNF:
plaster of paris is not stable...shrinks forever
Thermal expansion of materials is different and on this scale it ads up. One material/piece if pretty sure.
I haven't found a relatively big piece of glass that is flat. We have a guy working here who used to make machines for a float glass mill and from discussion we concluded that this kind of accuracy is hard to obtain from a standard glass. You might get lucky and find a piece that is cut from the middle of glass (web?) and on the middle of the cycle. Edges are "crabbed" and restrained....you don't want from too close to edge, there is a little tilt. Not much but enough to ruin it for our purposes. When molten glass is cooled it's run over rollers - that produces waviness...you might see that when you run the TDI over the glass and see regular swing.
So, it might be enough to lap a lot of small objects and on many purposes, but I find it too hard to accept as a surface plate - unless ground and for a lightweight objects.
Pekka
BaronJ:
--- Quote from: sparky961 on September 13, 2015, 03:22:29 PM ---
I did try some off-hand "lapping" of just two pieces; a smaller one on a larger one. I did this mostly to test the"feel" of the operation, which was interesting to say the least. When I was using water with toothpaste (yes, you read that correctly) it was smooth in some spots and then just sort of "stopped" as though a corner dug in, or the friction or suction became strong very quickly. It didn't slide smoothly as I expected, rather in a bit of a "jerky" motion.
--- End quote ---
While toothpaste is fine for lapping, maybe too fine for what you are trying to achieve, it needs to be kept wet otherwise as you have discovered dries out and grabs. Fine grinding paste in oil works well but it still needs to be kept wet.
--- Quote ---I did notice that the formerly shiny surface has begun to take on more of a matte finish. I hope this indicates something beneficial, and not just some residual toothpaste haze...
--- End quote ---
Yes the toothpaste is starting to abrade the polished surface and take down high spots but bear in mind that the high spots on each surface will rub each other so you need a third plate to work against the other two. Eventually you will get one surface that is matt all over.
krv3000:
I see I will have to take sum pics at work we have a very very large bit of glass for testing bed plates on press tools to see if they are flat the plates are normally 10ft long by 4ft wide by 4 inch thick yes granted the glass its 12 inches thick and gets recalibrated every year but the principal is the same blue on the plate put the glass on and see watts watt as for the type of glass to use at home go to the scrap yard and get ether a side window out of a panel van as they are tuff end the bit I use at home is a old oven doer in sum old car books to check if your cylinder head is flat they just say any peace of glass big enough to do the job
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version