A question for the Dremel afficionados

[Michael GilliganParticipant @michaelgilligan61133]

Sorry, Hopper, but we have different viewpoints

I intentionally made no mention of my “use-case” in the question … because I didn’t want to introduce ‘noise’

My concern is not really about how close 3.2mm is to 1/8” … but rather about Dremel’s target value and implicitly the tolerance [at which we can only guess] to which the shanks are made.

The question has attracted far more attention and heckling than I ever anticipated.

MichaelG.

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Edit: __ predictably enough, I posted ^^^  just before I saw Dave’s contribution

[NealebParticipant @nealeb]

…which just goes to show how noise gets introduced even when you don’t want/expect it!

I would suggest that the answers to the original questions are, in order, “probably not” and “certainly not”.

Accurate but unhelpful?

So, if we look at the context of the data given, then the answer is “none of this matters” because Dremel know quite well that the practical difference between 1/8″ and 3.2mm is zero – in the intended application which involves their own collets and their known capability.

And then we get to the real question – is a tool intended for use with a “domestic-quality” tool likely to be appropriate for use with a high-quality machine? We did, eventually, arrive at a discussion of this one!

However, I would wonder if the uncertainty in shank diameter pales into insignificance beside the question of the accuracy of the business end of the tool – a grinding point intended for use with a hand-held tool might not have the accuracy needed for for a high-quality machine? Or is that just introducing more noise?

All this reminds me so much of the discussions around my ME society’s clubhouse table by a bunch of model engineers justifying sitting there with a mug of coffee in hand. It’s all very entertaining but doesn’t always reach a clear conclusion!

[Nealeb]

On Nealeb Said:

…

All this reminds me so much of the discussions around my ME society’s clubhouse table by a bunch of model engineers justifying sitting there with a mug of coffee in hand. It’s all very entertaining but doesn’t always reach a clear conclusion!

Angels and heads of pins come to mind, yet once again.

[Michael Gilligan]

on Michael Gilligan Said:

I intentionally made no mention of my “use-case” in the question … because I didn’t want to introduce ‘noise’

 

The question has attracted far more attention and heckling than I ever anticipated.

MichaelG.

Is there an element of paradox here?

 

[Clive Brown 1]

On Clive Brown 1 Said:

Is there an element of paradox here?

Quite probably, Clive

… nearly equalled by the futility of those closing words in my ‘Profile’

MichaelG.

 

[Michael Gilligan]

On Michael Gilligan Said:

Quite probably, Clive

… nearly equalled by the futility of those closing words in my ‘Profile’

MichaelG.

 

One difference between the debates/discussions here and the ME clubhouse version (apart from the coffee mugs) is that down at the club, we do know a lot more about each other. I didn’t even realise that I and others have a “profile” here, let alone that it might give context to a post. Maybe “futility” and “forum profile” go together? I say this very tongue-in-cheek – I’ll buy you a coffee should we ever bump into each other, Michael!

– Brian (who started model engineering in student digs in Bangor, North Wales, so many years ago)

[SillyOldDufferModerator @sillyoldduffer]

Michael surely deserves a gold-star for asking this years most difficult to answer simple question.   He asked:

Has Bosch really changed the tool shank diameter from 3.175mm [1/8”] to 3.2mm, or are they just incapable of expressing numbers to 3 decimal places ???

Although the question can be interpreted in a simplistic way,  I suggest Michael’s cracker has hidden depths!    They include:

• Fractions versus decimals
• The accuracy of decimal notation and how to represent it
• The correct way to round decimal numbers, and when not to!
• The difference between decimal numbers as used in day-to-day maths, and specialist applications like engineering, manufacturing, and science.
• Metric versus Imperial and the evil resulting from converting between them

Stuff we take for granted today, but took millennia of painfully slow hard work to understand.

Fractions and decimals take us to the concept of the number line; what are numbers, how accurate are they, and what operations can be performed on them?  (Add, subtract, divide, multiply and many others).   Just dipping into the subject as applied to Michael’s example reveals there’s a lot to it.  This is what I remember being taught aged 11 or so:

After we leave school these rules fade because most ordinary sums are “good enough” without applying them.  Doesn’t mean they don’t matter though!   In Michael’s example Bosch misjudged their audience; I blame their Sales Department!

I won’t go any deeper.   The subject is endless, not many Model Engineers are interested in maths, and my skills are superficial.

Dave

 

[HopperParticipant @hopper]

None of which has anything to do with the nominal size of 3.2mm replacing the nominal size of 1/8″.

If you were in the drawing office at Bosch specifying a manufacturing tolerance to a contractor on a drawing, three decimal places might make some sense. Might. More likely two though.

But to label consumer packaging with a nominal size in three decimal places of a millimetre would be an absurdity.

[Nick WheelerParticipant @nickwheeler]

Perhaps they would have been better using the normal American labelling approach of some random number that has only a tenuous relation to the actual measurement – a #73grinding stone?

[Michael GilliganParticipant @michaelgilligan61133]

@sillyoldduffer

Thank You, Dave

MichaelG.

[duncan webster 1Participant @duncanwebster1]

Pedant alert:

SOD states pi is rounded up to 3.14. That’s actually rounded down. His text should more accurately have said ‘pi is rounded to…..’

On many engineering detail drawings there would be a statement linking tolerance to the number of decimal points. In this case 3.2 would be +- 0.05. Bit much to expect Joe Public to understand this, if you ask for a 1/8″ drill in my local hardware shop they offer you 3mm as it’s “the same”

[duncan webster 1]

On duncan webster 1 Said:

[…] if you ask for a 1/8″ drill in my local hardware shop they offer you 3mm as it’s “the same”

Thus demonstrating that the rot has set-in

… even grocery purchases are better-toleranced than that.

MichaelG.

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Half a pound of Coffee, anyone ?

[Michael GilliganParticipant @michaelgilligan61133]

… let me just chuck this document in, for broader reference and possible amusement:

http://bwma.org.uk/wp-content/uploads/2019/04/A-Fair-Measure.pdf

It was published a while back

Read it, or don’t, according to your preference.

MichaelG.

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Here’s a sample:

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[JasonBModerator @jasonb]

So is that why all my Dremel bits were under nominal 1/8″? have they reduced the amount of material being used but are still charging full whack?

Interestingly the Dremel shanks are plated so I would expect they have to have a bit more flexibility in size than a ground shank.

[Michael GilliganParticipant @michaelgilligan61133]

🙂

just out of interest … are the carbide ones plated ??

< shock/horror if they are >

MichaelG.

[JasonBModerator @jasonb]

Will double check in the morning but I don’t think so. I also did not measure the Dremel ones so will do that too.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Jason

MichaelG.

[duncan webster 1]

On duncan webster 1 Said:

Pedant alert:

SOD states pi is rounded up to 3.14. That’s actually rounded down. His text should more accurately have said ‘pi is rounded to…..’

Hopper is right!

On many engineering detail drawings there would be a statement linking tolerance to the number of decimal points. In this case 3.2 would be +- 0.05. Bit much to expect Joe Public to understand this,…

Yes, but who is Joe Public?   I’d expect a Dremel user to have some technical nous.  Maybe not though – quite a lot of excellent work is done by practical men who don’t understand how their tools work.  Most car drivers don’t know or care how the engine works, and those that do often have limited understanding  – more to IC engines than Suck, Squeeze, Bang, and Blow.   I’ve grasped adiabatic expansion, but entropy is beyond me.

Might have to forgive Bosch because they sell to artisans and engineers, and many of their customers must mix both skills to some degree or other!

Dave

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, with reference to Dave (SOD) post, very interesting, but we weren’t all taught the same way, however I think fractions often get a raw deal, and many only associate them with feet and inches, and consider then to be too complicated, but they are quite universal, e.g. 25% of 1M is 250mm and a 1/4M, 25% / 1/4 0f 1 Tonne is 250 Kg. / 1/4 Tonne, 25% of 1 Ton is 5 CWT / 1/4 Ton. The thing is they work with both imperial and metric, but they can get you head scratching when the units themselves are fractions or decimals. They also work with volumes, as many fuel driven vehicles, fuel gauges are marked out in 1/4’s (25%). How many people have said they’ve only got about a quarter of a tank of petrol, but profess they can’t understand fractions.

Regards Nick.

[JasonB]

On JasonB Said:

So is that why all my Dremel bits were under nominal 1/8″? have they reduced the amount of material being used but are still charging full whack?

 

<p style=”text-align: left;”>LOL. Shrinkflation! That would also explain why the grinding tip diameter in the pic posted way back above is specified as 19.8mm and not the full 20mm!</p>
So really we should be measuring the lengths of Dremel shanks to see if those dastardly production engineers have been making them shorter. That is where the real cost savings lie. On say a 40mm long shank, a shortening by 2mm, unnoticed by the consumer, would result in one “free” shank for every 20 made.

[not done it yetParticipant @notdoneityet]

Nick,

I think you may have overlooked that the length metre, in SI Units, is lower case (not upper as you have used).🙂  I note you have used ‘mm’.

Same with kilograms, where the kilogram is lower case.

Another possible ’can of worms’?  Well, not really if we all stick to the modern adopted scientific notation of SI units which has been in use for nearly the last 65 years (although Imperial, and cgs metric systems were used, in education, for some decades afterwards).

I was taught in BTUs, Calories and Joules for units of energy.  I now try to stick to SI units (apart from UK road distances which have been retained, despite ‘metrication’ in most other areas).  But the USA is only slowly changing from their BTUs, gallons, and inches to the otherwise almost universally adopted SI system.  In the US, the public mostly use the old imperial units while the scientific world has adopted the SI system in recent years.

It was reported that one US Mars space mission missed the planet because someone used the wrong metric conversion factor when changing from feet and inches to metric!

[JasonBModerator @jasonb]

The Dremel branded carbide burrs all seem unplated and are close to 1/8″ all falling between 0.124″ and 0.125″, none oversize.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi NDIY, you are correct, I should have used lower case letters, thanks for pointing that out, however, I think most people will understand what I was saying. I’ll try to do better next time.

Regards Nick.

[JasonB]

On JasonB Said:

The Dremel branded carbide burrs all seem unplated and are close to 1/8″ all falling between 0.124″ and 0.125″, none oversize.

 

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Many thanks for continuing to take my question seriously, Jason

… I do appreciate it.

MichaelG.

[duncan webster 1Participant @duncanwebster1]

……I’ve grasped adiabatic expansion, but entropy is beyond me……

Dave

Don’t worry, it’s beyond most engineers. It’s one of those concepts one just accepts. In any real process it increases, but the smaller the increase the better. If you come up with a process idea where entropy decreases you’ve probably got it wrong somewhere

[Author]

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