How bad is a dirt cheap Chinese surface plate?

I paid € 89 for a 12 inch surface plate from China that is reported to be flat within 7.1 microns. Is that true? And how do you measure that without very expensive professional tools?

Maybe you wil get some inspiration from my approach. Anyway, have fun watching.

I see that in this video I forgot to mention an important setting of the laserpointer. I went to great length to ensure that the beam was exactly parallel to the surface of the plate. That is very important to avoid misinterpreting the results of the measurement.

Excellent information about the repeat-o-meter and the auto-collimator in these video's:

[LilMissMurder]

Here's another way of looking at it: For the price of an expensive one and a bit of elbow grease, you could buy three Chinese cheapies and use them to create three perfectly flat plates... and sell two and turn a profit.

[CS-Sir_Twit]

Awesome work once again. I love seeing the practical application of theory with available tools. This is what engineering is all about.

[lnchgj]

As a recovering metrologist (although I specialized in RF) I have to say I am very impressed with your gear. I was always impressed with the PhysD folks, although I kept them at bay telling them there were a million ohms on the O'scope inputs. 🙂

[ghian]

Thank you - I really appreciate this video, and it was so timely despite my finding it by accident. I became a bit obsessed recently whilst exploring the the science of flatness - my interest in this was triggered by wanting to flatten a number of sharpening stones that I inherited, although the degree of flatness required for that, even for lapping the back of an expensive paring chisel, is perhaps not (quite) as critical - I am sure some will disagree! 😂 About the music - Andante Cantabile - at first I thought it an odd combination for your presentation, but what a pleasant surprise! As I listened and watched, the 'fit' became better and better. It's a wonderful thing how music speaks to us sometimes.

[janlolwitz]

I played through the same idea, but with the laserpointer attached to the piece, that is actually the measuring point, reading the results on the wall. But this is of course much more elegant, thank you for that idea, I might give it a try.

[therealspixycat]

I thought about using the same offset laser magnifier setup but never tried it (bought even ultra flat mirrors). I am now going to try this out definitely. Thanks!

[colincreedtattoomachines]

That's a nice find on that Surface Plate.
Even more so now that you've established its "true" flatness, Well done!!

[HM-Projects]

very informative, cheers. it's amazing that you can get this level of accuracy for for less than $100!

[ogaugeclockwork]

Excellent methods and explanations! Thanks!

[wizrom]

Clever.
Didnt have super-accurate optics available, but you did have... DISTANCE! 👍

[DontCallMeGarage]

just buy 2 more of those plates and some lapping compound.... then you can have 3 perfect plates in a matter of 3.5 million or less hours of lapping.

[rossilake]

Robin Renzetti has a series on his auto-collimator on YT. He made most, if not all the parts. My hobby parts rarely go to the moon. 👍

[gyrogearloose]

The Andante Cantabile . . . never so suspenseful! Thank you!! And best wishes with all your projects . .

[Villiavereb]

Dear Friend!
I had calibrated (measured) lots of surface plate. We had measured only 8 lines, 3 lines X and Y direction and 2 diagonals. After measure we calculate "closing error", that is diffent of measured values at same point in two direction. The stepps of the meause was distance of touching point in the equipment.

[pcfred]

Flat enough for anything I'd ever do.

[lpjunction]

At such price, you are supposed to buy 3 plates, and grind against each other.
You get 3 flats, an interesting project and a chance to make a new Youtube video.

[regdor]

Wow, the random dust participles in most shops would make this plate a much better value than a more expensive

[iotaje]

Interesting!

For the optical measurement device I recall another youtuber using the 5*5mm captor chip from a camera, which had a very high pixel count and so a high resolution, along with a jobsite laser level.

[schublade]

Excellent video - really nice measuring contraptions

[bobuk]

Hi folks, I did a simpler version of this on a similarly sized Chinese granite plate. Very similar results, nearly all within tolerance stated with a couple of outlying areas.