Hi, Why does a difference of 0.025 mm matter ?

Maurice

Have you measured one of the 3.2mm ones Michael? it would confirm if they are telling the truth or rounding it up then you may be able to sleep easy tonight.

At least they are consistent as the collets are also given as 3.2mm so you should not need to worry about fit and if anything like mine they will close down quite happily onto 1/8″ and 3.175mm shanks as well as any 3.2mm ones.

If the 3.2mm ones are made to similar tolerences then they should be closer to 3.175 than the old 1/8″ ones as they would be that little bit bigger!

Anyone who worries about a dremel shank size varying by that microscopic amount needs to chill out, IMO.  Most normal people are likely to not notice, or bother about, a one thousandth of an inch.  Only precision fits, like shrink fitting, or similar, actually need to measure to better than that.  Poster will just have to lap the shanks by that odd thou (if necessary) and also should check the collets are actually to that same precision (which I very much doubt).

Only if the shanks will not fit the collets is there any worry whatsoever.  Even ER-8 collets (precision items) accommodate shanks with a 0.5mm range – and nobody moans about that.  They understand that the stated precision will only be at the specified collet size and not the whole usable range).

Further, expressing the dimension to two significant figures means that the actual third significant figure value could be anything between 3.15mm and 3.24mm? (simple maths convention for rounding numbers🙂).  That might/should indicate the collet would accommodate any shank size in that range.

As an aside, I wonder what exactly was the tolerance for the value 1/8”?  Plus or minus 1/16th, 1/32nd, 1/64th, 1/128th, or ….?

Truth or inexactitude?  More what the packaging doesn’t say than a deliberate fib or cock-up I feel.  We aren’t told he all important tolerances, and without them the dimensions we’re given are just guidelines.  Both the hole in the collet and the diameter of the shaft were made within manufacturing tolerances,

I suggest there’s no particular need for the collet in a hand-held tool to be high-spec.    For example, 3.175mm is within tolerance for an H9 shaft in a 3.2mm H8 hole.   As a user convenience this is a ‘Free Running Fit’ allowing tools to be inserted and removed easily.

Grip is achieved later by tightening the collet, and it is how well the collet and collet holder are made that determines alignment and run-out.   I don’t recall the collet system being fully specified in my Dremel manual; only the basics.

The simple message in this diagram from Michael’s packaging tells me the collet is a notional 3.2mm, therefore don’t  shove a 3.3mm twist drill into it and expect the Dremel to still be good!  The shaft on the tool should be 3.2mm or a little under.  3.175mm should be fine,

Collets are easily damaged by pushing even slightly oversized rod into them.

Rod smaller than nominal collet size is less of a problem, unless of course a Gorilla deforms a collet by forcibly squeezing one below it’s minimum diameter.  Anyone measured the minimum diameter a Dremel collet can grip?

Dave

Sort of off-topic, but Jason – thanks for the mental exercise as I sit here with my morning coffee.

It has been maybe 30-35 years since I used an imperial micrometer; I got “converted” in the mid ’90s when living in Europe, and don’t own any inch micrometers.

Thanks for the flash-back to my youth!

JohnS.

On 19 September 2024 at 23:14 Michael Gilligan Said:

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 ???

 

Neither. Bosch is not stupid. Both 1/8″ and 3.2mm are the nominal shank size. To specify a mass produced non-critical shank size to 3 decimal places of a millimetre would be plain stupid.

On 20 September 2024 at 12:01 Bazyle Said:

Given that it was originally a German company why would they have made the parts 1/8″. Probably not going to change for the American connection. Or maybe it is some round figure in 64ths.

Dremel was originally an American company. Hence the nominal 1/8″ shanks. Bosch bought the Dremel company out in recent years. 3.2mm is the internationally accepted and used equivalent nominal size to 1/8″.

All sorts of things from pop rivets to metal plate are sold as nominal 3.2mm rather than change machinery and rolling mills etc to make them a round 3mm and then have a problem where new pop rivets or plating would not fit together with old mating components etc.

Not “convenient metric presentation” at all. Just a nominal size, as per standard practice worldwide.

What next? Measure the hole up the middle of a piece of half-inch water pipe and wonder why it does not measure 0.5000 inches?

Interestingly, the metric equivalent to 1/2″ water pipe is 15mm water pipe, because that is closer to what the hole in a nominal 1/2″ pipe actually measures.