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:
Tom from Oxtoolco: • Repeat O Meter
Robin from Robrenz: • ULTRA PRECISION REPEAT...
NYC CNC: • DIY Rahn Repeat-O-Mete...
Machine Tech Video Blog: • Autocollimators 1: Int...
ADTW learn: • Autocollimator Working...

[@LilMissMurder3409]

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.

[@Michel-Uphoff]

Yes, using the Whitworth method, diamond paste and a lot of patience that's feasible.

[@Bob_Adkins]

@@Michel-Uphoff Use dry diamond powder, paste is only for very small areas.

[@Michel-Uphoff]

@@Bob_Adkins You're right. I didn't pay attention.

[@shanent5793]

The repeat-o-meter and your indicator stand are not measuring deviation, but only repeatability. Suppose the instrument is zeroed on a flat area and then placed over an area where the profile is 0, +4, 0, such that the intermediate feet are over the 4. The instrument would indicate -8, while the actual deviation is +4. Thus the repeat-o-meter is mostly useful for evaluating local flatness after determining the overall flatness by other means. The measurements taken by the laser don't have a reference thus the measured position of the dot will be a combination of several factors, so it isn't as reliable as the autocollimator. Both are really measuring the angle and any profile needs to derived from those measurements. In this case the feet are shown as 25 mm apart while the mirror is moved in increments of 20 mm. If the increment were 25 mm, then we could multiply the measured angle by 25 mm and determine the vertical change between points. Then a line can be fit to the points and the maximum deviation determined. It would also be good practice to measure along a loop and ensure that the readings all sum to zero ie. closure. It should be possible to construct a suitable autocollimator with a long focal length lens, beam splitter and point source. Focusing the image on a CMOS camera sensor and processing it digitally may be easier than trying to replicate the vibrating slit and optics of a conventional device.

[@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. 🙂

[@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.

[@ogaugeclockwork4407]

Excellent methods and explanations! Thanks!

[@colincreedtattoomachines]

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

[@ifanstarr]

Fascinating stuff!, cheers 👍

[@wizrom3046]

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

[@schublade4]

Excellent video - really nice measuring contraptions

[@harlech2]

Very well done!

[@ghian696]

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.

[@janlolwitz951]

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.

[@nunomiguelrodriguessilva3028]

You are a genius! Thank you for sharing!!!

[@gyrogearloose1345]

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

[@HM-Projects]

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

[@darkobul1]

Where? i only see such plates from india.

[@Michel-Uphoff]

I bought it 1.5 years ago. Can't find them either now. Here is a link to (I think) the same product (now with a higher price tag and not available): www.hbm-machines.com/nl/p/hbm-8-micron-300-x-300-mm-vlakplaat

[@Michel-Uphoff]

Now that I look at it a little more closely. No, it is not the same surface plate.

[@1pcfred]

Flat enough for anything I'd ever do.

[@walterretlaw4051]

¡¡Tal cual..! Habría que ver para qué necesita él tanta "planitud".... en mi caso, como yo trabajo hasta la centésima de milímetro (0,01mm) por la precisión de fábrica que traen los instrumentos y previendo que aún yo podría estimar, por la Teoría del Error y por mi experiencia, hasta la mitad de una centésima de milímetro (0,005mm), yo no veo objeto práctico alguno que ese mármol posea tanta "planitud". Vuelvo a repetir, habría que saber para qué este YTber necesita tanta "presición". Saludos.

[@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!

[@Michel-Uphoff]

Great! It would be nice if you could share your experiences.

[@rossilake218]

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. 👍

[@Michel-Uphoff]

As far as I know Robrenz has made an external mirror for the auto-collimator (and an excellent one), but not the auto-collimator itself.

[@KamiCrit]

That was awesome. Would there be any advantage to using a dial test indicator in the DIY repeat-o-meter?

[@trackie1957]

Much appreciated.

[@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.

[@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 KZbin video.

[@hughezzell10000]

Now that would be a lot of work. Trust me, you'd be time and money ahead just buying the reliable expensive flat.

[@normcameron2316]

I was thinking the same thing. I've done scraping and am curious to see how much improvement one could make, or not with some effort.

[@freddupont3597]

@@hughezzell10000 Obviously not - fact is that this plate is exceptional for its price!

[@Posredstvennyye_Proyekty]

impressive

[@RedDogForge]

Brilliant! What a wonderful repeatometer! Thats a fine dial indicator as well, im not familiar with the brand? The large dial is absolutely ideal.

[@regdor8187]

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

[@AAAAAAA35]

A very good point. Any particle can be micrometers, if the measuring is not in the cleanroom. LOL.

[@johnkelly7264]

Really interesting... Subbed here.

[@Bob_Adkins]

You can *sort of* use a precision 3-point spirit level in place of an autocollimator.

[@Michel-Uphoff]

see: kzbin.info/www/bejne/bneZpaGFfsxjfKM

[@jimspencer3072]

I can live with that for the hobby shop...

[@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.

[@Bob_Adkins]

Huge exaggeration man, I it took me less than 2 million.

[@lpjunction]

That will be stone age plate making. In this era we use Arduino with some motor and gears. That will cut down orders of magnitude.

[@OscarzProductions]

Loved the video. What is the music used?

[@HeinrichVonPhoezenstein]

Mozart Piano Sonata No. 13 Andante Cantabile

[@teegee2556]

Very cool project, enjoyed watching it and learned a lot! I am looking to buy such a plate, could you give us the link to the plate you bought? Seems to be a good value for money equipment :)

[@Michel-Uphoff]

Here (at a higher price now, and not available): www.hbm-machines.com/nl/p/hbm-8-micron-300-x-300-mm-vlakplaat

[@fletcha7777]

@Michel Uphoff I don't know if you ever put it in but I can't find the link to buy the plate?

[@Michel-Uphoff]

www.hbm-machines.com/nl/p/hbm-8-micron-300-x-300-mm-vlakplaat It isn't exactly the same plate, but i comes close. Not available at this moment I see. www.ebay.com/itm/304437672481 Not the same plate, and I suspect of a lesser quality. Still costs more than twice I've paid. www.manutan.co.uk/en/key/surface-calibration-plate-cast-iron-ribbed-surface-mat-manutan This plate looks more like mine, but costs way more (£279.00 excl. VAT) and has an flatness of only 40 µm. So I'm afraid that at this moment the market for cheap and reasonably good cast iron surface/inspection plates is very thin..

[@fletcha7777]

@@Michel-Uphoff thanks for your help yeah I've been looking and I haven't found any available around the price that you were talking about.. thanks again

[@Michel-Uphoff]

@@fletcha7777 You could try to get a quote here: www.exportersindia.com/product-detail/cast-iron-surface-plates-4223722.htm

[@fordguy8613]

Genius

[@iotaje1]

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.

[@Michel-Uphoff]

That could work very well. A disadvantage could be that those laser levels are often too long for such a small surface plate as mine.

[@iotaje1]

@@Michel-Uphoff what do you mean by too long? I was referring to the little boxy devices that project flat lines onto walls

[@Michel-Uphoff]

Ok. That could work!

[@iotaje1]

@@Michel-Uphoff The laser line itself is pretty thick, 3-5mm, but it is flat and consistent and the very high resolution of the chip allows to detect very small changes.

[@Michel-Uphoff]

I understand that, but there will still be some challenges that need to be overcome. One of them seems to me to be the amount of light, which will have to be dimmed if you don't want to completely saturate and overradiate such a chip. Cutting off the current through the laser diode seems desirable to me, that usually also makes the line thinner. Sometimes, like with my laser, you can also adjust the focus. Then follows the interpretation of the results, which could simply be done by eye via a screen, or special software must be available or written. But all in all, this seems to me to be a very suitable method. Fun to experiment with when I have time. Here I have a projection eyepiece with a 640*480 chip that is 6 mm wide, so about 0.01 mm per pixel. At a distance of 4 meters, for example, this amounts to about half an arc second of angle difference per pixel. And for that, the front of my laser's 40mm base should, in theory, have to drop or rise a fraction of a micrometer. It won't be all that easy in practice (noise, vibrations, temperature changes, moving air, changing refraction index and so on) , but it's certainly worth a serious effort. If I find the time, I will come back to it in a video.

[@CrazyTony65]

Stone it off good and random, even pattern with a surface ground stone and some thin oil, then check it again.

[@jacquelinesears1770]

These videos are every where we in the mold trade NEVER worry about such things Grind that thing Not only have i ground my cast iron plate flat as f#$k i ground the legs to make it parallel just like the molds i built

[@charlesspringer4709]

I would guess that the height of the block your gauge is attached to changes by about 2u per deg C and every time you touch it the temperature goes up. I would expect it to be taller in the right than on the left.

[@Michel-Uphoff]

Yes, I agree. There must be a tiny difference due to heat transfer from my fingertips to the gauge. The question is how much that could be. Assuming this causes an error of 1 micron, the entire gauge (except the spindle..) should heat up about one degree. I only touch the gauge with my fingertips for a few seconds. In that short time, it is not possible to transfer enough energy from my fingertips (about 50 gram of fingertips 33.5C) to the kilogram (27C, it was a hot day here in Nederland) of material of the gauge. If I (roughly) assume that the heat capacity of steel and aluminum is equal to that of my fingertips, then my fingertips would have to cool down roughly 20 degrees C in those few seconds to realize this kind of heat transfer in one pass, so that seems impossible. But there are many passes so the temperature could build up gradually one could argue. But then we also have to keep in mind that the gauge continuously loses heat due to the close and continuous contact with the 25 kg or so cast iron from the surface plate. And of course there is also heat transfer from the metal of the base to the spindle, making it longer and so compensating some of the height differences. And, most importantly, I measured from left to right and vice versa. I looked up the measurement results, and see no discernible difference between left to right and vice versa. But in theory you are right. I could make a non-conductive handle on the meter, but don't think that's really necessary for measurements like this.

[@charlesspringer4709]

@@Michel-Uphoff I agree it is probably insignificant but I did a thumbnail calculation. The number I gave is closer to aluminum than for steel. Steel is about half. And I neglected the cast iron surface plane! I was thinking about figuring telescope mirrors and how touching one raises a fingerprint shaped island. And of course if it was a hot day, the heat transfer becomes insignificant. I suppose a person could buy three of these and lap them against each other to get an "optical flat" 🙂

[@txm100]

Where can I buy it?

[@pauldevey8628]

Where did you find this surface plate? I could use one.

[@Michel-Uphoff]

Here (at a higher price now, and not available): www.hbm-machines.com/nl/p/hbm-8-micron-300-x-300-mm-vlakplaat

[@l.smechoj7918]

Calculate the best fit plane from the measurements taken. The deviations from that plane is what you are looking for. Nice measurement though!

[@stewartfrye]

My friend built an auto collimator using a ccd to accept return light

[@Michel-Uphoff]

Interesting! Is there a video available?

[@hughezzell10000]

Easy reads on these methods can be found in any book on telescope mirror making.

[@Michel-Uphoff]

And in the many KZbin videos

[@NRDavis-wl8vn]

Another source of relatively Flat Granite is a Granite Counter Top Company. One I went to had a Dumpster of Sink Cutouts they paid to haul away. A little donation to the "Coffee and Donut Fund" and I could have all I wanted.

[@ExploringCabinsandMines]

How flat is polished granite from a countertop ? I can find no information on that.

[@tomlutman2041]

It will depend on what you consider flat. They are smooth, but not a dependable surface for machining inspection. They were never made for that

[@paradiselost9946]

@@ExploringCabinsandMines its woeful. stand in a kitchen. look at the reflection of window frames etc. if they arent straight, it aint flat. but! never fear! just grab THREE pieces, some abrasive grit... and start grinding them. a drill press and an "orbital sander" type attachment makes it a breeze to do. you have three dead flat surfaces by dinner time. well, whilst we're in the kitchen...

[@gyrogearloose1345]

. . . relatively flat ! Something like ±0.1mm I expect. Not much use for machine shop. Better look at heavy plate glass I think.

[@NicksStuff]

Could you flatten that plate even more at home? Like with another plate (or two) and diamond compound?

[@Michel-Uphoff]

Yes, that's possible. The 3 plate method should suffice, but there are also other methods. See the KZbin video's about this theme.

[@azimzulfa]

@@Michel-Uphoff hello Michel, can you make a video

[@janlolwitz951]

Why did you add 2× in your formula? If you extend the beam to ten meters you get a P of 400, or do I miss out something here?

[@janlolwitz951]

And 7u was the specification of that certain surface plate anyway, not 3.6u.

[@Michel-Uphoff]

Your missing the law of reflection: The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal. That's why I draw the two blue lines in the sketch. That is the normal mentioned in that law, a imaginary line perpendicular to the mirror surface. According to that optics law tilting the mirror in my setup one arc second leads to a two arc seconds tilting of the beam. A well known example: What angle must a mirror have to let me look around the 90 degrees corner of a house? That mirror has to be rotated only 45 degrees. Hence the 2x.

[@Michel-Uphoff]

@@janlolwitz951 It could be that if I were to perform this laser measurement over the entire surface of the plate, I would encounter that 7µ somewhere. This test was limited to only one path, and the measured deviation amounts to that 3.6µ, proving that the plate is not convex or concave, at least along the measured line.

[@janlolwitz951]

@@Michel-Uphoff It took me a while to figure that out. I had trouble to even measure 0,1mm feeler gauges correctly, while sometimes it worked, most of the time not. I drew a few lines in CAD, applied your schematics and it showed me where my error was. This is brilliant. Thank you.

[@kalpetkoff]

Is this plate from HBM Machines? I'm from Bulgarian and I love HBM Machines. My whole workshop is equipped and furnished from HBM Machines.

[@Michel-Uphoff]

HBM is an importer of Chinese tools and machines. Because they order in larger quantities, they can have their name put on the products. So it may well be that HBM occasionally purchases a series of surface plates with their name on it from a Chinese company. This one of mine was purchased through Aliexpress, but HBM also had ones for sale that were very similar to this one.

[@kalpetkoff]

@@Michel-Uphoff yes, I know but the quality is very good.

[@1358sob]

Subbed here ,.. Thanks

[@sto2779]

9:37 - Incredible, how accurate is this setup of your DIY autocollimator?

[@Michel-Uphoff]

See the table at 10:50. Worst case, less than 20%

[@sto2779]

@@Michel-Uphoff Also is it possible to use optical flats to check the granite surface plate's flatness?

[@Michel-Uphoff]

@@sto2779 I have never checked a surface plate with an optical flat. It certainly won't work with cast iron plates that have been scraped, the pits are much too deep for that. But it could also be very difficult on a granite plate, because that black layer reflects little light. Perhaps too little to see the thin film interference needed. Also, if it does work, there's of course the problem I outlined in this video, that two really flat planes don't have to be at the same angle, so something like an auto collimator is still needed.

[@sto2779]

@@Michel-Uphoff Thanks for the clarification.

[@daynosdr]

Im not sure that autocollimator flatness can be better than repeat flatness. Something seems wrong in that.

[@bobuk5722]

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.

[@scruffy3121]

I saw a autocollimator substitute made of a line laser and a webcam that didn't look to bad.

[@Michel-Uphoff]

Do you have a link to a video?

[@scruffy3121]

@@Michel-Uphoff sure. There are pros and cons to it of course. And there are multiple Videos by the same guy. kzbin.info/www/bejne/np-rm6WwlM6hh7c

[@paradiselost9946]

@@scruffy3121 he didnt seem to understand how an auto collimator works, that its the length of the base and the tilt thats being measured, not the actual height as such, which is what he was doing with his sensor and setup. it was a great idea, if sadly flawed... but seriously, you can do better with just mirror on a flat base and a laser pointer, bouncing off to a wall some distance away. the further, the better. would have to go do some reading to brush up on the maths, but it was something like a 130.5mm base shows a 0.03mm deviation with one arc minute of tilt. if an actual value is required. generally its set the line parallel to the ends then graph out the deviation across the length.. no actual figure required.

[@scruffy3121]

@@paradiselost9946 yes, there are many flaws in his approach. But in my opinion it could easily be altered to be a really good diy measurement system. (ignoring the units he is using, one could even use the software).

[@paradiselost9946]

@@scruffy3121 i agree. it was his video that made me go and brush up on how auto collimators work... lol. simply stick the sensor back at the light source, make a base of known length, shorter being more accurate but requiring more measurements, and bam... auto collimator on the sly...

[@freddupont3597]

What you proved is that this Chinese made precision surface plate is extremely good and quite inexpensive. The price is actually unbeatable for the level of quality provided. You also exposed your bias and prejudice with your negative and clickbaity title.

[@Michel-Uphoff]

I have no problems to prove myself wrong.

[@freddupont3597]

@@Michel-Uphoff I have no qualms with that - other that it highlights your prejudice going into the test, and that you did not prove yourself wrong. You knew posting the video that the plate was exceptionally good for the price, but still chose to taint it as "bad", "dirt", "cheap"... That would be entirely different should you have chosen to title the video "This surface plate made in China is exceptional for its price point"...

[@Michel-Uphoff]

It in fact is what I thought when I ordered it.

[@JohnDoe-qg6hm]

Why is there a hole in the surface ?

[@lukeamato423]

For the tip of the indicator to sit in

[@Michel-Uphoff]

After all this time, you're the first to ask👍! I expected that curiosity much earlier. I use the surface plate not only for standard measurements, but also for measurements under vacuum. That small hole leads to the bottom of the surface plate to a connection for the vacuum pump. Then a large bell jar goes on top of the surface plate and so I create a vacuum chamber.

[@JohnDoe-qg6hm]

Ahh that makes sense. I should have thought of that by myself as i used to use vacuume fixtures ! Doh !@@Michel-Uphoff

[@ghian696]

​@@Michel-Uphoff Interesting - I would have thought the vacuum could cause some elastic deformation in the plate? For example, if you had a bell jar with radius 3½ inches - at vacuum, the air pressure on the plate would be around 171 lbs/sq in or almost 78kg. Perhaps I have misunderstood.. and overthinking etc.

[@Michel-Uphoff]

@@ghian696 Yes, that's correct. Although the surface plate is very rigid, there will always be a slight curvature when I vacuum the bell jar above it. The flatness in the vacuum setup is not of great importance, but I have calculated it in the past and arrived at values that are clearly below 1 micron.

[@richardw3294]

Over the top of my head

[@gerardoliveras430]

Would be nice to know where you bought it.

[@Michel-Uphoff]

Here (at a higher price now, and not available): www.hbm-machines.com/nl/p/hbm-8-micron-300-x-300-mm-vlakplaat

[@nychillboy8724]

did you play this piece?

[@Michel-Uphoff]

Ahh... The Andante Cantabile. No, I do play piano, but this piece is played by Brendan Kinsella.

[@Tome4kkkk]

I've just received a Chinese-made surface plate from fine-tools. It's... not shiny, nor even semi shiny. I'm afraid to even check it.

[@Michel-Uphoff]

Shiny or not doesn't matter, just check the flatness.

[@Tome4kkkk]

@@Michel-Uphoff My worry is also that if any die gets on it, it stays there forever. There's no way I get it off from such a porous surface. Or at least it seems to me that way. I've never handled a not-polished granite :)

[@Michel-Uphoff]

@@Tome4kkkk Ahh.. you didn't mention it was a granite plate. Thought it was cast iron. Granite shouldn't be porous. I, in your place, would return it.

[@johnlambo135]

PRACHTIG !!!

[@EugenBadau]

desigur ai "precizat" placa ieftina .Incearca una mai scumpa - chinezi fac dupa cum ai bugetul.

[@hdl4259]

If you buy a cheap surface plate from China, you cannot expect to have a quality of a high precision device from Europe or US. This video is nice to watch. For home use surface plates, you can take polished granit tiles from the hardware store, those are good for home use.

[@Michel-Uphoff]

I got what I expected. A quite nice cast iron surface plate flat within 7µm, that's well within Din 876 grade 1. I have seen "real" brands with looser specs for way more money, so I am happy with it 🙂

[@Webendowed]

I know you will all find this stupid but for me and my small tinkering shop I use one of those granite microwaveable food tray stones. It mics out within my needed tolerances (.001) It had some very small holes and cracks that I filled with a hard wax and buffed. it's new smooth as glass. It sure wouldn't fly in the aerospace industry but for the parts I make at home for projects it works great. Price was good too. I scored 4 of them for 2.00$ at a goodwill store. They are 12"x12" Ok, now everyone can make fun of me. Fire away!

[@Michel-Uphoff]

There's no reason to make fun of you. If this solution suffices for you, then it's ok, right? 0.001 is not high accuracy, but apparently sufficient for your purposes. I also have some granite here, and that is very flat on a small scale, but if I look at the flatness with my laser pointer over a somewhat greater distance, then the plate turns out to be convex, like the example of the cylinder shown in the video.

[@Webendowed]

@@Michel-Uphoff Yeah, I just make parts for repair and a few parts for jigs and accessories in my wood shop. I have an Incra router table which is .001 repeatable which is well within the realm of acceptable tolerances for wood working. I liked your video and learned a few things as well. Never knew there was a tool for measuring surface imperfections and deviations in surface variations with the precise hinge mechanism thingy. I'm not a master machinist but rather a well edumacated hillbilly and farmer. I subscribed and look forward to learning more.

[@NRDavis-wl8vn]

If it works don't fix it. 👍

[@paradiselost9946]

ha ha ha ha. why four? you only need three! lol, all seriousness. three, ground to each other, you got yourself el-cheapo, precise as you want, surface plates. whose laughing now?