What tool do I need? I need to measure the radius of a tiny fillet on a 90° edge.

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Smith 47 on 04/01/2022 11:46:34:

…

Srely at least some of the stated inaccuracy must come be incurred during the 10mm of travel.
Presumably the internal digital measurement tech to be standard, off-the-shelf parts.

I mean if I zero the device and move it just 0.10mm, what do you think the range of readings will be?

It will read in the range 0.04 to 0.16

Probably inappropriate to measure a 0.1mm radius with instruments of this type because their error is a significant proportion of the radius. The instruments are more useful on larger diameters – ±0.06 is an error of 1.2% on a 5mm radius, rising to 60% on a 0.1mm radius.

How accurate does your measurement need to be?

Which of these examples are unacceptable and why? (Comments apply to both inner and outer chamfers)

For comparison, bottom left is a perfect radius. These are nearly impossible to make by hand, and although a machine will do better, cost rises steeply with increasing precision. There would have to be a very good reason for designing an accurately radiused chamfer, and most production engineers would look hard for an alternative.

Next up is a faulty radius; it's offset by 10%. At R0.1mm, the measuring instrument would have to be good for 0.01mm, which industry would normally say requires calibration ten times better, i.e. ±0.001mm. That's beyond any of the caliper instruments so far mentioned in this thread. And, is this faulty radius really a problem? For many purposes, it's near perfect. If so, we've spent a fortune on measuring the wrong thing.

How about the radius with variable error? My example is typical of a machine made radius, hand-made would be worse. It's close, but a suitable instrument would detect radial and axial imperfections. Again, is this curve unacceptable in the real world?

Lastly, is a radius approximated by 10 straight lines. Again, a comparator will detect it's wrong, and by how much, but why does it matter?

I don't measure radii often enough to justify buying a special caliper or gauges. And when I do measure radii, so far there's been no reason for the answer to be particularly accurate. As always with unusual requirements, it's best to question them rigorously. In engineering, the most expensive mistakes are caused by faulty requirements!

Dave

Edited By SillyOldDuffer on 04/01/2022 13:13:05

[JasonBModerator @jasonb]

Simply by the amount of pressure you apply to the sliding head you will get a slightly different reading this is why callipers are not regarded as being as accurate as micrometers and even they will vary depending on your "feel" when using them.

Take a look through the Insize cataloge, I have the paper one that is about 1/2" thick all the standard shape callipers are +-0.03 to 0.04 accuracy, the ones with long reach legs, funny ends ext less accurate. Now look at the micrometers and they show accuracy in microns generally +- 2 or which is 0.002 or 0.003mm. You will see similar figures if looking at Mitutoyo. I'm sure these Insize ones would be ideal for checking weld prep chamfers and the like.

They have some very good optical measuring equipment in the catalogue that would be ideal if a bit out of price range.

Edited By JasonB on 04/01/2022 13:13:18

[John Smith 47Participant @johnsmith47]

Dave S – I'm still not with this.

> I.e. it will be within the range no matter the length moved.
Yes, but in practice the accuracy of readings will entirely depend on where the inaccuracies are coming from.

In my experience, if I zero my current digital calipers, and move them to 10mm and back, I would still expect it to read either +0.01, 0.01 or -0.01. Yes, after a large number of measurements it is more likely to no longer still say 0.00, (albeit in my experience not by more than 0.01 or so).

i.e. In my experience opening and closing the calipers enough times will eventually create new errors that become obvious when the device closed and no longer reads "0.00mm".
And I have been assuming that the manufacturers would make their accuracy claims that assume a reasonable amount of use after each re-zeroing by the user.

But if opening and closing the calipers multiple times since the last re-zeroing does NOT create new errors, I find that surprising.

Either way, in this case are we seriously expecting that if I zero the device and move it by exactly 0.1mm that it will immediately read as much as "0.16mm" or as little as "0.04mm"?

(And by implication if that if I move it to 9.1mm that it would ready as much as 9.16mm or as little as 9.04mm?)

Personally my best guess is that error come from two effects
A) Errors that are proportional to the distance away from zero,
B) Errors that are proportional to the total distance moved up and down, up and down.

If either (or both) of the above are true, then the accuracy of measurement would be much increased by a recent zeroing followed by only a small amount of opening/closing travel.
 

Edited By John Smith 47 on 04/01/2022 13:20:31

Edited By John Smith 47 on 04/01/2022 13:24:03

[John Smith 47Participant @johnsmith47]

@SillyOldDuffer

OK I think we've done this subject to death!

Speaking pragmatically, I currently have no way of ANY sort to measure any of my fillet radiuses. And there don't appear to be any tools that can help much other than a chamfer measuring tool which will of course be making the assumption that the fillet is extremely circular (which it may not be).

And so even if a reading of "0.04mm" might genuinely mean "0.16mm" maybe that is sill better that absolutely nothing.

'CIRCULARITY' of radius
Getting at least SOME sense of the cross-sectional shape of the fillets that I am grinding using a deburring wheel would be also nice… but maybe that is just too difficult.

I mean, it would be very nice to have some sort of device to help me see roughly what shape (i.e. roughly how circular) the hand-made fillets are, because when they are made by machine, presumably they will be made more accurately and certainly more consistently.

For that I was hoping to get some of those Starrett things I mentioned on page 1, and shine a light behind them to broadly see what sort of profiles my deburring wheels are creating.

OK I think I'll just buy that Insize 45 degree chamfer measuring gauge and be damned.
(But although it is only a working hypothesis, I still strongly suspect that in practice, it will be significantly more accurate than "+/- 0.06mm" when used for small chamfers. )

J

PS If at some point I can be bothered, I could use the other blades to measure a fillet at 30 degree and 60 degrees as well as at 45 degrees and run the trigonometry to see roughly how circular my fillets are.

[JasonBModerator @jasonb]

Posted by John Smith 47 on 04/01/2022 13:18:59:

In my experience, if I zero my current digital calipers, and move them to 10mm and back, I would still expect it to read either +0.01, 0.01 or -0.01. Yes, after a large number of measurements it is more likely to no longer still say 0.00, (albeit in my experience not by more than 0.01 or so).

although it may have said 10.00 when you moved it the jaws may have been a 9.94 to 10.06.

Same if you zeroed it and then put the jaws on an exact 5.000mm dia you may get a reading of 4.994 to 5.06

So lets look at your chamfer. zero and then take a measuerment and the screen shows 0.25 however the chamfer could actually be anywhere from 0.019 to 0.031.

Now convert that to a a radius, do you use 3.14, 3.142etc for pi

From the above two lines the actual reading you get could be either of your 0.2 or 0.3 radii increments or anything in between so if you want to be measuring and quoting by small amounts you need an apropriatly accurate tool. It's generally said your tools need to be 10times more accurate than the part.

[OldironParticipant @oldiron]

I have a set of gauges that Peak4 linked to in his answer. They seem to be accurate enough for what I need. At 0.3 the radius is tiny and needs a set of magifiers along with my reading specs to be able to actually check the radius. They seem to be ok unless you are working to atomic standards.

regards

[KWILParticipant @kwil]

To quote John Smith 47

"OK I think we have done this subject to death"

I agree whole heartedly!

[John Smith 47Participant @johnsmith47]

@JasonB – that's all find in theory and is obviously within spec. But what assumptions are you making about where and how the errors creep in?

J

PS Fwiw, I absolutely love my AccuMaster Fractional 6" Calipers. I think they are rated at "0.02mm" accuracy but in practice they seem accurate to +/- 0.01mm, which is easily good enough for me. They are so much quicker to use than analogue/Vernier callipers. The only time I have any problems is when I fail to re-zero them after a lot of opening-closing travel, at which point they don't reliably read "0.00" when closed.

They are exceedingly repeatable and the only time I have measured larger objects (e.g. steel parallels) they have been absolutely spot on (if recently re-zeroed).

Edited By John Smith 47 on 04/01/2022 15:13:43

[John Smith 47Participant @johnsmith47]

PS I have placed an order for the 45° Digital Chamfer Gauge (1180-6) – made by Insize. Should arrive tomorrow.

One thing to be aware of is that Cutwel's website is lying to us. Each tool can ONLY measure one specific angle, whereas the Cultwel website implied that you could insert blades of 3 different angles, but I spoke to Cutwel and you can't!

I am still in the market for buying two or three simple super-small L-shaped fillet gauges i.e. with a design like the Starrett so that I can check the circularity of the profiles that my deburring wheels (I have 2 different types) are making. (??)

Edited By John Smith 47 on 04/01/2022 15:14:27

[JasonBModerator @jasonb]

Not really a lie, it's a general description of the chamfer type of calliper, if you then click "view full range" it lists the three callipers

Edited By JasonB on 04/01/2022 15:24:56

[Martin King 2Participant @martinking2]

Probably just me but do I discern a possible typo in all this?

Could tool be misspelt when troll was intended?

I’ll get my coat…….

Martin

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Smith 47 on 04/01/2022 13:45:24:

…

Speaking pragmatically, I currently have no way of ANY sort to measure any of my fillet radiuses. And there don't appear to be any tools that can help much other than a chamfer measuring tool which will of course be making the assumption that the fillet is extremely circular (which it may not be).

And so even if a reading of "0.04mm" might genuinely mean "0.16mm" maybe that is sill better that absolutely nothing.

…

In which case the answer is to eyeball it, and seeing R0.1mm would need the aid of a loupe. The human eye is good at spotting malformations, especially when the radius can be compared with a gauge with a bright light behind, and then in front of it. Finger tips are remarkably sensitive to tiny irregularities as well.

Human sensory methods don't measure anything in the sense that a machine can be told to remove 0.05mm or whatever to correct a dimension. But they do allow the workman to progressively refine his work. From what you've said, your chamfer can be made as well as is needed without measuring it at all.

Before science and technology merged everything was made by comparing rather than measuring. Because it takes so long to do well, most early products were crudely made, but craftsmen have been capable of making fine mechanisms like clocks for centuries. Also high-art, decoration, jewellery and other posh stuff. Apart from the cost, other serious problems are training craftsmen, and their inability to make parts identical within tolerances. Whilst craft methods are no good for mass-production, they're often excellent in a home workshop.

Likely none of the disadvantages apply to you unless the radius is part of a delicate bearing. Otherwise, the radius can be formed by several strokes of a fine toothed file angled to produce a reasonable curve. If the result looks OK it probably is.

If the subject has been done to death, why are you still asking the same sort of question? From my side of the internet I can't tell if you need a gauge and eye-glass costing £10 or a Shadowgraph like this one, £4,388.60 on ebay.

Dave

[John Smith 47Participant @johnsmith47]

Posted by JasonB on 04/01/2022 15:24:07:

Not really a lie, it's a general description of the chamfer type of calliper, if you then click "view full range" it lists the three callipers

Edited By JasonB on 04/01/2022 15:24:56

Wrong. If you click on the link to the individual product for Sku:"1180-6"
(https://www.cutwel.co.uk/0-10mm-0-0-39-45-digital-chamfer-gauge-1180-series-insize )

You get this:

==> It says "Product Information" and the very first of the bullet says "Measure 30 degree/45 degree/60 degree chamfers".
Note that it it says "Product Information". It does NOT say "Product Range Information"

If you read all of it carefully this is self-evidently a mistake and if you are moving at speed it is easy to be fooled, as I TBH, I very nearly was.

The Cutwel staff agreed with me, were hugely apologetic and said that they will change the text ASAP.

[John Smith 47Participant @johnsmith47]

> In which case the answer is to eyeball it, and seeing R0.1mm would need the aid of a loupe.
Yes.

> Finger tips are remarkably sensitive to tiny irregularities as well.
Yes, and that's the whole point.
Small deviations that the human eye can't really see unaided can make or break the user-interface of a product.

> From what you've said, your chamfer can be made as well as is needed without measuring it at all.
A prototype yes, absolutely.
But when specifying a product for someone else to manufacture… absolutely NOT.
If even in small scale production which could initially be done by hand, a loose specification could make or break the entire viability of the product.
Worse, the eventual larger-scale production would of course be done by robots, die pressing, tumbler machines and who knows what.

And really, that's the point, I need to specify the required output not the processes.

Re the Shadowgraph, as I have now said more than one, my some of my fillets are quite long and I have assumed that it would be extremely difficult measure the size of a fillet along the length of a longer fillet on a part. Obviously it would also be well beyond the budget of £100 or so, which I have also mentioned more than once.

Look, I know that all this is rapidly becoming TEDIOUS for most of the community here, but through all this endless questioning of my motives, you are compelling me to explain details that I had no intention of going into. These are details that are of no interest to the majority of this community, for which I get flamed if I ignore any contributor's questionings.

So back to my original question, I was just asking if anyone knew of any tools that would help me measure the radius of very small fillets, at a half-sensible (ideally sub £100) cost.

If you think that the answer is "no", then let's move on.

[Robert ButlerParticipant @robertbutler92161]

NO

Robert Butler

[Dave SParticipant @daves59043]

John wrote:

Yes, but in practice the accuracy of readings will entirely depend on where the inaccuracies are coming from.

Whilst that may (or may not) be true without detailed knowledge of exactly how the thing works it is impossible to say where any inaccuracies start.

John wrote:

In my experience, if I zero my current digital calipers, and move them to 10mm and back, I would still expect it to read either +0.01, 0.01 or -0.01. Yes, after a large number of measurements it is more likely to no longer still say 0.00, (albeit in my experience not by more than 0.01 or so).

i.e. In my experience opening and closing the calipers enough times will eventually create new errors that become obvious when the device closed and no longer reads "0.00mm".
And I have been assuming that the manufacturers would make their accuracy claims that assume a reasonable amount of use after each re-zeroing by the user.

Assumptions are dangerous things in metrology.

John wrote:

But if opening and closing the calipers multiple times since the last re-zeroing does NOT create new errors, I find that surprising.

Either way, in this case are we seriously expecting that if I zero the device and move it by exactly 0.1mm that it will immediately read as much as "0.16mm" or as little as "0.04mm"?

Not exactly. I am saying that the range of possible readings it could give and be within the spec is 0.04mm to 0.16mm.

Decent calipers almost never need their zero resetting. It more likely to be reset because you are using it for some other purpose than absolute measurement – for instance I have a target sized shaft so I zero on that and now my digital caliper means I dont have to think about how much to take off (apart from the should I divide it by 2 for this lathe cross slide )

John wrote:

Personally my best guess is that error come from two effects
A) Errors that are proportional to the distance away from zero,
B) Errors that are proportional to the total distance moved up and down, up and down.

 

Guessing is a sure way to be wrong on average 50% of the time… It is very unlikely that total travel distance makes any difference to the accuracy.

 

Split post because apparently I typed to much…

 

Edited By Dave S on 04/01/2022 17:46:56

[Dave SParticipant @daves59043]

Second part to my excessivle long post;

The way *most* of these sort of devices work is based on a pair of printed circuit boards and some sensing electronics. The PCBs form a variable capacior, which is 'driven' to give an output that is proportional to the distance moved. There are many sources of errors in that system. Firstly if there is a clock used to drive things then it is probably a quartz crystal, and temperature senstive. There may be step and repeat errors in the PCB manufacture, as the battery discharges there may be an effect in the sensitivity.
All of these things (and many more I haven't thought of) matter if you are truely wanting to measure an very small thing.

usually for an electronic linear measurement device (which the scale in a caliper is) there is a spec like accuracy 100 to 3000 mm -(5+5L/1000) µm
so for a 100mm scale that would be 5um + 5*100/1000um -> overall accuracy 5.5um, and a 1000mm scale it would be 5um + 5*1000/1000 -> 10um.
Because the calipers are short this is not usually listed – it applies more when you are looking at several different lengths of the same thing.
If you look at mitutoyos calipers as they get bigger their accuracy gets less. They use the same technology, so (for instance) the 200mm caliper is 0.01mm resolution, +-0.02mm accuracy, their 300mm caliper is 0.01mm resolution, +-0.03mm accuracy, and their 1000mm caliper is 0.01mm and +-0.07mm.

There should also be a repeatibility spec – how well the scale shows the same number when moved away from and back to the same place (in this discussion the same place means *exactly the same place*,not I moved it there and back by hand). For Mitutoyo calipers this is typically 0.01mm. so with a 200mm caliper you could be out by 0.02mm, but also get a different number by 0.01mm on measuring the exact same thing multiple times.
Quantifying this is part of when it matters it matters. For most things in hobby land it actually never matters

Your anacdotal assertion that your calipers, which are spec'd as +-0.02mm accurate 'seem accurate to +/- 0.01mm' is just that – a seems – unless you have actually checked it properly.
With a set of calipers it is easy to be 0.1mm out just by holding them "wrong". You might always hold them "wrong", and so repeat to 0.01mm (that is likely the repeatibility spec based on the technology used).
Without a traceable calibration and a temp controlled lab and a whole load of other minor but actually matters things you are probably not making measurements to better than 0.05mm with a set of calipers.

I use my traditional Verynear calipers mostly – when it matters I use a micrometer or other method (gage blocks and slip joints are a good one here).

People get fooled by digital – its not any more accurate just becase the computer shows you a certain number of digits…

Dave

Who used to work in the field of very high precision metrology, and occasionally makes things in is garage

[Dave SParticipant @daves59043]

A high powered inspection microscope has a very thin field of focus.

Mine is 40x IIRC, and you can 'zoom' up and down an edge and examine it in great detail by ignoring the out of focus parts.

I got mine very cheap, mostly because the guy was moving to the USA and clearing out, but a similar one on ebay would probably not be that much.

Ill grab soem pics later when I head out to the garage.

Dave

[Speedy Builder5Participant @speedybuilder5]

for 20 euro, I am tempted to buy this set radius gauge , drill the rivet out, send John the 'leaf' he wants.

All those in favour, send me an un franked UK 1st class stamp.

Bob

[Robert ButlerParticipant @robertbutler92161]

I would repeat in response to the last question by John NO

Robert Butler

[Jeff DaymanParticipant @jeffdayman43397]

+1 on NO

My added bit – Hope this thread goes away and people stop wasting their time with this troll OP.

[JasonBModerator @jasonb]

Posted by Speedy Builder5 on 04/01/2022 18:08:54:

for 20 euro, I am tempted to buy this set radius gauge , drill the rivet out, send John the 'leaf' he wants.

All those in favour, send me an un franked UK 1st class stamp.

Bob

Save yourself 19euro and just drill a 1mm hole in a square of scrap, saw and file away one corner and you have an L shaped gauge with 0.5mm internal radius to send to john. I won't suggest he makes one as that could lead to another long thread

[John Smith 47Participant @johnsmith47]

@Dave 2

> They use the same technology, so (for instance) the 200mm caliper is 0.01mm resolution,
> +-0.02mm accuracy, their 300mm caliper is 0.01mm resolution, +-0.03mm accuracy, and
> their 1000mm caliper is 0.01mm and +-0.07mm.

Yes, interesting stuff… however to my point, is that not exactly what you would expect if errors are proportional to the distance travelled by the sensor, no?

And if that is the case, then surely a smaller movement would imply smaller errors.

I know that my digital callipers have their theoretical limitations and are not doubt loathed by purists, BUT what I have been finding in practise (which for me is what counts!) is that reading my Vernier calipers, particularly when in read in sub-optimal lighting conditions, was either:
A) seriously slowing me up or
B) introducing serious reading errors or
C) sometimes both !

Yes you are absolutely correct about there being quite a lot of skill required in order to make accurate measurements. And my digital calipers are quick to scream at me in this regard! But readings are so quick that I generally measure each measurement at least 3 times to 'sanity check' each of my measurements.

Fwiw, yes I have an old x10 to x20 binocular dissection microscope which I sometimes use to see what's really going on! And occasionally this is extremely useful. The downside is that it can be rather difficult to get it into position.

[John Smith 47Participant @johnsmith47]

Posted by Speedy Builder5 on 04/01/2022 18:08:54:

for 20 euro, I am tempted to buy this set radius gauge , drill the rivet out, send John the 'leaf' he wants.

All those in favour, send me an un franked UK 1st class stamp.

Bob

No. As I said on Page #1, that style of radius gauge is of no use to me because it does not have these features:

[John Smith 47Participant @johnsmith47]

Posted by Jeff Dayman on 04/01/2022 18:26:29:

+1 on NO

My added bit – Hope this thread goes away and people stop wasting their time with this troll OP.

Nobody is compelling you to visit this thread.
If you have nothing constructive to add, please leave.

[Author]

Posts