Thread: Surface Plate Substitutes

I note several members are saying that glass flows and is why old window panes are thicker at the bottom than the top.

This is a complete misconception
From Wikipedia

On the basis that all solids such as granite[29] flow in response to small shear stress, some researchers[30] have contended that substances known as amorphous solids, such as glass and many polymers, may be considered to have viscosity. This has led some to the view that solids are simply "liquids" with a very high viscosity, typically greater than 10^12 Pa·s. This position is often adopted by supporters of the widely held misconception that glass flow can be observed in old buildings. This distortion is the result of the undeveloped glass making process of earlier eras, and not due to the viscosity of glass.[31]

At room temp glass has about the same viscosity as rock. The reasons that really old glass windows have panes of glass that are thicker on the bottom than the top is because early glass makers could not make flat glass and it always came out slightly thicker on one side of a sheet than the other. To make the window look consistent glaziers usually chose the thicker side of the glass sheet to be installed at the bottom of the window pane.

Hi Greg,
Have you tried hand lapping on your granite plate? i.e. was it the glass or the method that was the issue. Maybe if you had scraped the planes to the glass you would have had a better result? "energy of rupture" and all that.
Glass locally is very flat... how flat is a lake? but just like lakes I'm told that glass can have waves, I believe they a pretty long waves but don't know the details.
I think if the parts are being clamped together glass seems to work pretty well. Sliding ways on the other hand are a little different. Though as always it depends where you are starting from and when you are going to say "that's good enough". Starting with a 0.003"+ woof in a cross slide glass should get you started in the right direction, where to stop is up to each of us.
But as others have said, glass beaks and granite is cheap.

Originally Posted by simonl

Hi all. Im not experienced or qualified enough to make comment on suitability of glass but i can say that glass is considered a liquid. A supercooled liquid to be precise. It does slowly flow over many years. In fact if you were to measure the thickness of a glass window in a very old house, it would be thicker at the bottom. However it is so slow that i don't think this property would be a factor in its use in this thread.

Hi Simon,
As I understand it that's not correct, its in fact a Amorphous solid. Hope that clears things up




Rather then me try and explain it I'll give you a couple of links.
http://www.scientificamerican.com/article.cfm?id=fact-fiction-glass-liquid
The picture in the first link is how some early window glass was made, it wasn't the same thickness the day is was put in.
http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

Stuart

Originally Posted by Greg Q

The biggest improvement comes from mating frog to sole, and cap iron to blade, and lever cap to ditto. When you clamp down the lever cap on a perfectly tuned plane the entire assembly becomes monolithic, and feels and acts rigid and true. I recommend it as an experience in knowing the goal of the fitter's art.

Hi Greg,
Just to go a little OT, you mean scrap them to each other? I'm not a woodie(in fact I had to google to be sure I knew what parts you were talking about lol) but I do have a stanley out in the shed I could have a play with. Its a nasty day to do any real work .

Stuart

Actually you can scrape them to each other, or each to the master plate. Either way works since we are talking about relative, not absolute flatness. Most frogs that I have checked have three tiny contact points relative to the sole, and the same relative to the blade. All of that produces chatter.

Even lapping the parts against each other with some valve grinding compound will yield a much more rigid tool. Who doesn't like that?

GQ
Never one to shy from a cheap joke...

Originally Posted by Stustoys

Hi Greg,
Have you tried hand lapping on your granite plate? i.e. was it the glass or the method that was the issue. Maybe if you had scraped the planes to the glass you would have had a better result? "energy of rupture" and all that...

Stuart

yeah, I think the human motion has a lot to do with the end result, which is why I now like scraping. As for lapping on my granite: I am going to succumb to superstition here and eschew introducing any fugitive abrasives to my plate. You know how grit always manages to detach itself from abrasive paper and lodge where you least want it? I'm afraid of that.

I had a friend who had a lap dance in 1988. He's still paying the price after confessing that. Nothing good comes from lapping, I have concluded.

GQ

Originally Posted by Greg Q

As for lapping on my granite: I am going to succumb to superstition here and eschew introducing any fugitive abrasives to my plate.

You could always use the cara-tec approach and just lap straight on the granite!!

"Measuring 300 x 230 x 50mm with 0.0001" accuracy. Perfect for lapping tools or checking setups on small engineering projects. For longer life wet and dry paper can also be used as the grinding agent."

I know they are cheap but are they that cheap?

Stuart

Who's nose doesn't always appreciate the coffee it receives due to Greg's inability to shy from a cheap joke.

Hi,
I got my carbatec granite this morning. Following on from Greg's points about hand planes I might spot my $400 Clifton no 5 just to see what its like. When bought it came with a certificate that stated flatness etc. Clifton bought the Stanley bedrock moulds so they are supposed to have a 100% mating frog. I'm keen to see just what percentage it really is. I'll start a new thread if my findings are worth it. I may be younger but maybe I could do with a more rigid tool too!

Ewan

Originally Posted by Stustoys

Hi Greg,
Have you tried hand lapping on your granite plate? i.e. was it the glass or the method that was the issue. Maybe if you had scraped the planes to the glass you would have had a better result? "energy of rupture" and all that.
Glass locally is very flat... how flat is a lake? but just like lakes I'm told that glass can have waves, I believe they a pretty long waves but don't know the details.
I think if the parts are being clamped together glass seems to work pretty well. Sliding ways on the other hand are a little different. Though as always it depends where you are starting from and when you are going to say "that's good enough". Starting with a 0.003"+ woof in a cross slide glass should get you started in the right direction, where to stop is up to each of us.
But as others have said, glass beaks and granite is cheap.





Hi Simon,
As I understand it that's not correct, its in fact a Amorphous solid. Hope that clears things up




Rather then me try and explain it I'll give you a couple of links.
http://www.scientificamerican.com/article.cfm?id=fact-fiction-glass-liquid
The picture in the first link is how some early window glass was made, it wasn't the same thickness the day is was put in.
http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

Stuart

Hi Stuart,

I did know that glass is amorphous i.e. no crystalline structure but I must be out of touch with the latest thinking! When I studied materials science at Uni, glass was a supercooled liquid. It's embarrassing when you find out that your way of learning is outdated and incorrect!

Anyway, do we really have to strive for super flat surfaces when there are so so many lovely curves in this world?

Simon

In any case, claims that glass panes in old windows have deformed due to glass flow have never been substantiated.

My opinion of my Physics Lecturer has somewhat been diminished!

Thanks for the info Stuart!

Simon

Originally Posted by Stustoys

You could always use the cara-tec approach and just lap straight on the granite!!

"Measuring 300 x 230 x 50mm with 0.0001" accuracy. Perfect for lapping tools or checking setups on small engineering projects. For longer life wet and dry paper can also be used as the grinding agent."

I know they are cheap but are they that cheap?

Stuart

Who's nose doesn't always appreciate the coffee it receives due to Greg's inability to shy from a cheap joke.

I never understood the principle of going out of your way to find a flat reference only to destroy it with abrasives. I discarded two nice pieces of glass that I dished following tips in some magazine. Its amazing how quickly it abrades away with a little bit of lapping. Using paper is better, but you still get unseen, but damaging particles getting loose.

Stu, you need to pop over next week to try a Burundi/Sulawesi blend I just roasted. It should be a monster.

G and also Q

In the pursuit of finding out about this glass. I just went and stole a 370mm square from the shopfitter guys that used to be next door. I shall cast it upon granite, and thus indicate it.

Update at 5.00

Phil.

Originally Posted by Greg Q

I never understood the principle of going out of your way to find a flat reference only to destroy it with abrasives.
Stu, you need to pop over next week to try a Burundi/Sulawesi blend I just roasted. It should be a monster.

Yeah I was a little shocked when I first layed eyes on the caratec add. Also I'm not exactly sure how well it would work. Wouldnt the grit try to bed into the cast iron and lap the granite?

MMMM coffee(though really you do need another name for it, would be a shame for people to confuse it with that brown stuff I normally drink lol). I'm free Monday if that suits(well I'm free most days but I dont like walking that far lol)

Hi Phil,
Why didnt I think of that, I have a few pieces of 10mm glass in the shed(old shelves). look forward to the update.

Hi Simon,
Having a brother in the glass trade helps.

Stuart

I cleaned the plate, and the glass, then laid the glass straight down on the table. Extended the arm out so I could get to the middle of the plate, zeroed one corner, and run the glass under a static clock. Its really only a test of parallelism.

It was fair in one direction 0 – 10 microns along both edges.
The other way it was about zero to 36 microns, over 350mm

Attachment 209665

Attachment 209666

Then I set it up on 3 precision buttons, in an ode to surface plate support. Just to see how flexible it is.

Attachment 209663

Attachment 209662


It sags by it own weight a good 40 microns, when measuring across the end that is only supported at one point. So that’s 0.040 in 175mm That was across what was the better side.

Dropping a certified Dunhill blue pack of Fags, causes it to deflect a further 5 or 6 microns. I weighed the pack, its 30 grams.

Attachment 209664

So when its supported, its better than a couple of thou, and that’s about all. Fine for layout and scribing work. Probably not quite good enough for anything using slip gauges or tenth clocks. And as a lapping plate, it aught to take you to within a few thou.

That’s what I found.

Regards Phil.

Hi Phil,
Would you be able to measure the thickness at the coners when you get a minute?
Thanks
Must run

Stuart