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

[Robert ButlerParticipant @robertbutler92161]

OP promoted to Moderator as well now! And after 4 pages of posts we are are back to where we started from as with other Forum Topics posted by OP who also lacks grace.

If this "invention" ever gets beyond prototype stage I pity the poor bugger who draws the short straw to put it into production.

Robert Butler

[Nick WheelerParticipant @nickwheeler]

Posted by Robert Butler on 04/01/2022 18:46:10:

If this "invention" ever gets beyond prototype stage I pity the poor bugger who draws the short straw to put it into production.

I'd love to see the inventor's face when he finds all these lovingly crafted high precision features that have cost him so much time and effort immediately deleted in favour of simple to produce parts, that can be assembled by unskilled labour in a sweatshop somewhere none of us have ever heard of.

[Dave SParticipant @daves59043]

Posted by John Smith 47 on 04/01/2022 18:28:24:

@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.

Implicit maybe, but in the spec – not at all. I can legitimately sell you a long scale that is off by 0.05mm after the same move that a short scale would be out of spec at…

Distance travelled is only one of the variables that a longer scale introduces. A longer scale is of course the most obvious one (thermal expansion). Time to move is another. There are others as well if you think about it.

[rhetorical question] Would a slow move over a short distance be less accurate than a fast move over the same distance? [/rhetorical question]

The main reason I tend to use my traditional Verynears is that, if Im honest, the digital ones nearly always have a flat battery

However I also use them because Im not fooling myself that they are super accurate. 0.5mm is plenty for verynears, even if they do read to 0.1mm. Like most here I will often make one part and then make the mating part 'to fit'. For that as long as the first part is within 0.5mm of its nominal it very rarely matters….

In the interests of this thread I have wounded a Stanley Knife blade:

I just boshed a 45ish degree 'radius' on the back edge with a diamond stone.

This is the (quite poor) photo through an inspecion microscope:

measurment of a radius on an edge is potentially doable in this manner, with the bonus that you can inspect the finish as well.

Inspection microscopes, unlike dissection ones, have an x-y stage under them. This one is imperial – it does 1/10000" on its dials. I also have one with 0.001mm micrometers.

Fixturing is not hard – there is no force. This would be adequate for instance (took it after, when I though a fixture photo would be useful, hence the upside downness of the blade):

As you are planning on subbing out this work once a spec is figured out you need to also think about how you are going to inspect and reject sub standard parts.

If a spec came to me saying 0.25mm radius I would look at it and think about:

A: Quote high enough that the work buggered off, or paid a hansome profit for actually doing the job properly

or

B: just break the edge like we always do and hope no one notices…

If its important enough to spec then its important enough to check.

Dave

 

 

Edited By Dave S on 04/01/2022 20:32:21

Edited By Dave S on 04/01/2022 20:33:10

Edited By Dave S on 04/01/2022 20:33:51

[Andy StopfordParticipant @andystopford50521]

The OP might care to read this article:

https://en.wikipedia.org/wiki/Accuracy_and_precision

[Former MemberParticipant @formermember37818]

[This posting has been removed]

[JasonBModerator @jasonb]

I just remembered that out good friends at ARC sell similar "L" shaped gauge sets. Metric set goes down to 0.5mm but the imperial one may be of more use as that gives 0.010", 0.015" and 0.020 (approx 0.25mm, 0.38mm and 0.5mm) so would cover a few of your smaller radii and not a bad price compered with a Starret set link

[John Smith 47Participant @johnsmith47]

@JasonB – thanks.

Yes I did see that offering at ARC Eurotrade.

It's possibly worth a thought, although the set costs £30.11 PLUS …

[Did you read the "New customs rules and charges for shipments to the EU from 1st January 2021" ?]

"On arrival of the parcel in your country, the postal service or courier will contact you to ask you to pay the import entry charge (usually between £6.00 to £15.00 equivalent in Euros), plus Duty (for goods above a certain value)… "

For these reasons I no longer buy ANYTHING from continental Europe.

I don't want to get into a political discussion, Brexit really is a disaster for certain activities.

J
 

Edited By John Smith 47 on 05/01/2022 09:33:23

[Anonymous]

Posted by John Smith 47 on 05/01/2022 09:33:04:

For these reasons I no longer buy ANYTHING from continental Europe.

Any genuine modeller/engineer would know that ARC is based in the UK. Nuf sed!

Andrew

[John Smith 47Participant @johnsmith47]

Posted by Andrew Johnston on 05/01/2022 09:48:12:

Posted by John Smith 47 on 05/01/2022 09:33:04:

For these reasons I no longer buy ANYTHING from continental Europe.

Any genuine modeller/engineer would know that ARC is based in the UK. Nuf sed!

Andrew

OK that IS embarrassing. I am new to this game. Don't shoot me.

[JasonBModerator @jasonb]

And any non genuine one could just read the address at bottom of homepage or get it in larger print by clicking "contact" at the top of the home page.

Even if it's £30 that is not bad as you get 3 usable gauges for the £10 each which is better the £18 for a single Starret

Edited By JasonB on 05/01/2022 10:16:20

[John Smith 47Participant @johnsmith47]

Posted by JasonB on 05/01/2022 10:14:39:

And any non genuine one could just read the address at bottom of homepage or get it in larger print by clicking "contact" at the top of the home page.

Even if it's £30 that is not bad as you get 3 usable gauges for the £10 each which is better the £18 for a single Starret

Edited By JasonB on 05/01/2022 10:16:20

My apologies. You are of course correct. I had just come from a .co.uk website that turned out to be despatching from China(!), and I was also distracted by the Euro part of the ArcEurotrade, but mostly I mis-read their message.

Beyond that, to minimise any further duplication, please see the other thread for my response.

What I will put into this thread is a couple of photos of my new toy.

After zeroing, at full extension it looks like this:

And you will be please to know that after x10 full-scale openings & closings, it has returned to looking like this:

Quite dinky. Nice piece of kit.

JasonB – All reasonable points, however I reserve my right to stick to my budget of £15, in case none of them turn out to be particularly useful to me personally. 

Edited By John Smith 47 on 05/01/2022 11:23:39

[Neil WyattModerator @neilwyatt]

Did anyone suggest taking an impression of the corner using plasticine or blu tack, then selecting a drill that's a good fit in the impression?

Neil

[Neil WyattModerator @neilwyatt]

Posted by Tim Stevens on 30/12/2021 18:31:24:

the link sent by Peter H was caught by an oddity in the software used by ME* – it came out like this:

radius%20gauge%200%20-%2010%20mm%2C%200%2C1%20mm%20%280597305%29

Some typesetting and word processing programs use an extra 'hidden' symbol or two to tell the computer what it intended. Here the extra symbols include %, followed by a number, calling up a letter or symbol not in the 'standard alphabet' used in the days of 8-bit and 16-bit computers. I'm not sure what you or I can do about it, except wait for ME to update – or, * perhaps the fault lies within the computer used by Peter H. I wonder …

Cheers, Tim

Edited By Tim Stevens on 30/12/2021 18:33:09

Hi Tim,

It's not an oddity used by this website, it's a universal convention.

%20 substitutes for ASCII character number 20 hexadecimal (decimal 32), otherwise known as 'space'.

If you include a space in a URL it is treated as the end of the URL, so %20 stops it breaking and is automatically inserted by browsers etc.

Neil.

[Neil WyattModerator @neilwyatt]

Posted by Pete. on 30/12/2021 23:03:18:

I was under the impression commercial projects were a no no on this forum, this project appears to be 100% about making money and 0% about someone learning workshop skills as a hobby.

This is not the case.

The forum can't be used to promote commercial products or services, side-stepping paid advertising.

Discussion of technical aspects of commercial jobs or product development is welcome (as long as it isn't an undercover way of promoting a product), as we can all learn from such issues.

For example, it would be perfectly OK for a car restorer to recount how they dupllcated a broken part or filled creased bodywork with lead.

Obviously, if individuals would rather not offer advice to someone working on a commercial project, that's their prerogative.

Neil

[John Smith 47Participant @johnsmith47]

Posted by Neil Wyatt on 05/01/2022 15:02:37:

Did anyone suggest taking an impression of the corner using plasticine or blu tack, then selecting a drill that's a good fit in the impression?

Neil

No, but nice try.

The trouble is that faces are at 90° to each other. i.e. The arc of the radius on the fillet is also only 90°, so it will be slightly hard to determine where or not the drill is fitting snugly into what is only a 90° corner.

[John Ockleshaw 1Participant @johnockleshaw1]

Hello John,

With regard to your original request for a source of small radius gauges.

Get access to a sink type spark eroder with DRO on the X and Y axes and a lock on the Z axis.

Cut yourself five pieces of 3 mm diameter copper rod; about 25 mm long and turn down 1 .5 mm of the ends to 1.0 mm dia. 0.8 mm dia, 0.6mm dia, 0.4 mm dia and 0.2 mm dia .

Buy, or make, five "L" shaped small radius gauges.

Remachine the inside corner radii by "draw filing" with the spark eroder using the five electrodes .

[Tony Pratt 1Participant @tonypratt1]

Posted by John Ockleshaw 1 on 06/01/2022 03:01:32:

Hello John,

With regard to your original request for a source of small radius gauges.

Get access to a sink type spark eroder with DRO on the X and Y axes and a lock on the Z axis.

Cut yourself five pieces of 3 mm diameter copper rod; about 25 mm long and turn down 1 .5 mm of the ends to 1.0 mm dia. 0.8 mm dia, 0.6mm dia, 0.4 mm dia and 0.2 mm dia .

Buy, or make, five "L" shaped small radius gauges.

Remachine the inside corner radii by "draw filing" with the spark eroder using the five electrodes .

Budget is I believe £15?

Tony

[Neil WyattModerator @neilwyatt]

Posted by John Smith 47 on 05/01/2022 19:09:49:

Posted by Neil Wyatt on 05/01/2022 15:02:37:

Did anyone suggest taking an impression of the corner using plasticine or blu tack, then selecting a drill that's a good fit in the impression?

Neil

No, but nice try.

The trouble is that faces are at 90° to each other. i.e. The arc of the radius on the fillet is also only 90°, so it will be slightly hard to determine where or not the drill is fitting snugly into what is only a 90° corner.

I'd be looking for the biggest that doesn't let light through a gap.

Nei

l

[SillyOldDufferModerator @sillyoldduffer]

Posted by John Smith 47 on 05/01/2022 19:09:49:

Posted by Neil Wyatt on 05/01/2022 15:02:37:

Did anyone suggest taking an impression of the corner using plasticine or blu tack, then selecting a drill that's a good fit in the impression?

Neil

No, but nice try.

The trouble is that faces are at 90° to each other. i.e. The arc of the radius on the fillet is also only 90°, so it will be slightly hard to determine where or not the drill is fitting snugly into what is only a 90° corner.

Being 'hard to determine where or not' is a problem common to all measuring techniques, and the cost of getting better answers shoots up scary fast. As space and money are always constrained, it's important to focus.

Only you can answer the question 'how accurate does the measurement need to be?' and 'how much time and money am I prepared to spend'. Until this is clear, you are wasting your time because most of the candidates are off the table. The most accurate methods involve expensive bulky equipment requiring a skilled operator who takes many careful measurements and then analyses the results.

If simple methods like eye-balling and the plasticine trick aren't good enough, then the answer is going to cost money. If money is short, think carefully. You certainly mustn't waste £15 on a Starratt Gauge, or £60 on a Digital Radius Caliper that won't do the job either!

From what you've said of your prototype, it seems unlikely that this radius needs to be measured at all!

Have you thought of dodging all these confusing measuring and practical problems by developing your prototype in 3D-CAD? Being drawn by mathematical formula, CAD Radii and other parts are perfect, with no tool-marks or other inaccuracies, and the dimensions are absolutely trustworthy. No need to measure them.

At the initial design stage, it's advantageous not to bog down in practical details that might not matter. Changing manual 2D drawings is so expensive, old-school Draughtsmen were encouraged to design with production in mind. You don't have to do that. These days, more likely the CAD model will be amended in a separate design review by a Production Engineer. They specialise in making things economically, and are brutal pragmatists. Be warned, they often shoot all the inventor's sacred cows!

Dave

[John Ockleshaw 1Participant @johnockleshaw1]

Hello Tony,

Rod Renshaw, in the other thread on this subject, tells us a 4mm Starrett radius gauge sells for about 8 pounds add to this 50p for 25 mm of 3mm dia copper bar leaving 6 pounds fifty times 5 gauges to buy some beer for the owner of the spark,eroder !!!!

[JasonBModerator @jasonb]

Posted by John Ockleshaw 1 on 06/01/2022 12:55:57:

Hello Tony,

Rod Renshaw, in the other thread on this subject, tells us a 4mm Starrett radius gauge sells for about 8 pounds add to this 50p for 25 mm of 3mm dia copper bar leaving 6 pounds fifty times 5 gauges to buy some beer for the owner of the spark,eroder !!!!

Still does not leave the OP much in pocket as he will need to buy a lathe to turn down that bit of copper

[Tony Pratt 1Participant @tonypratt1]

Posted by JasonB on 06/01/2022 13:03:50:

Posted by John Ockleshaw 1 on 06/01/2022 12:55:57:

Hello Tony,

Rod Renshaw, in the other thread on this subject, tells us a 4mm Starrett radius gauge sells for about 8 pounds add to this 50p for 25 mm of 3mm dia copper bar leaving 6 pounds fifty times 5 gauges to buy some beer for the owner of the spark,eroder !!!!

Still does not leave the OP much in pocket as he will need to buy a lathe to turn down that bit of copper

Oh please no more!!

Tony

[John Smith 47Participant @johnsmith47]

Posted by SillyOldDuffer on 06/01/2022 11:28:37:

Posted by John Smith 47 on 05/01/2022 19:09:49:

Posted by Neil Wyatt on 05/01/2022 15:02:37:

Did anyone suggest taking an impression of the corner using plasticine or blu tack, then selecting a drill that's a good fit in the impression?

Neil

No, but nice try.

The trouble is that faces are at 90° to each other. i.e. The arc of the radius on the fillet is also only 90°, so it will be slightly hard to determine where or not the drill is fitting snugly into what is only a 90° corner.

Being 'hard to determine where or not' is a problem common to all measuring techniques, and the cost of getting better answers shoots up scary fast. As space and money are always constrained, it's important to focus.

Only you can answer the question 'how accurate does the measurement need to be?' and 'how much time and money am I prepared to spend'. Until this is clear, you are wasting your time because most of the candidates are off the table. The most accurate methods involve expensive bulky equipment requiring a skilled operator who takes many careful measurements and then analyses the results.

If simple methods like eye-balling and the plasticine trick aren't good enough, then the answer is going to cost money. If money is short, think carefully. You certainly mustn't waste £15 on a Starratt Gauge, or £60 on a Digital Radius Caliper that won't do the job either!

From what you've said of your prototype, it seems unlikely that this radius needs to be measured at all!

Have you thought of dodging all these confusing measuring and practical problems by developing your prototype in 3D-CAD? Being drawn by mathematical formula, CAD Radii and other parts are perfect, with no tool-marks or other inaccuracies, and the dimensions are absolutely trustworthy. No need to measure them.

At the initial design stage, it's advantageous not to bog down in practical details that might not matter. Changing manual 2D drawings is so expensive, old-school Draughtsmen were encouraged to design with production in mind. You don't have to do that. These days, more likely the CAD model will be amended in a separate design review by a Production Engineer. They specialise in making things economically, and are brutal pragmatists. Be warned, they often shoot all the inventor's sacred cows!

Dave

 

Dave in the nicest possible way… I have not told you every single detail about what I am doing.

> From what you've said of your prototype, it seems unlikely that this radius needs to be measured at all!

You don't KNOW that. And even if true, it is arguably none of your business. I know you meant to be helpful but I am struggling not find that comment both invasive and quite offensive.

Look, I am not building a space rocket, but what I am doing is quite complex, and involves a balanced judgement between competing issues. Even if it were IP appropriate, all of this would take too long to go into, and would be a waste of your time and mine.

Where I have a specific question, I ask it. And yes, almost all of the advice given the framing of the question that I have provide HAS been excellent.. and yet, even whilst it engages, interests /amuses some users, the mere existence of the whole damned conversation seems to irritate various users.

Maybe they are jealous of the attention, I don't know. And if so, sorry but that's simply not my problem.

And to be completely honest, talk about wasting of resources, I see this persistent pestering for me for the absolute full details of exactly what I am trying to do, not just a deep waste of my time but also as an attempted to violation of my privacy.

YES, there will always be a bit of banter and a few interesting deviations and weird facts that people bring to the party – all good fun – but the persistent stream of critical patronising advice and endless critical sniping & bitching about my budget, my level of technical experience… my strategic decisions, my motives, my tone, whether & when I do or don't buy some specific product and then taking umbrage if they are ignored… Although I have been pretty self-restrained in my replies… it's EXHAUSTING.

….Is it too much to ask for the nice folks in this forum to just answer the specific questions that I am asking about tools for model-making?

I know that us 'innovators' necessarily are required to develop thick skins not least because you can't please everybody, not ever. We ask 'naive' questions, make endless mistakes, but we learn and more importantly with fresh eyes we see things that others have failed to. It's what we do.

And, please for the love of God, just let me make my own mistakes.

PS Back to tools, yes, of course I am using CAD. Both 2D & 3D software (Xara & OnShape).

Edited By John Smith 47 on 06/01/2022 14:45:39

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