On Thursday 18 April 2019 07:47:51 andy pugh wrote:

> On Thu, 18 Apr 2019 at 10:22, Roland Jollivet 
<roland.jolli...@gmail.com> wrote:
> > To recap; small steppers 'drive' the carousel around to tighten the
> > motor.
> No, the motor drives round the carousel to tighten the collet.
> It is really rather clever. Assuming that it can't work based purely
> on guess-work seems silly.

No, not silly, experience Andy, experience reaching into the bank account 
to replace tooling that broke by walking out of the holder when I 
thought it was tight enough.  

> I suggested a very simple test using the same torque wrench as Gene
> presumably uses now to tighten his collets to the correct torque to
> test the hypothesis.

All 4 of my 5 torque wrenches are in foot/pounds. The smallest is in inch 
pounds.  How much is 75Nm, in inch pounds.                                      
> But, assuming a 5mm pitch screw and 5:1 motor reduction:
> (0.5 Nm stepper * (2 * pi) / 5mm ) * 5:1 = 3kN. On the end of a 75mm
> arm that is 235Nm.
> Correct torque for an ER20 is 75Nm.

That is no where near tight enough to keep it from walking out of the 
collet and breaking the tool because its digging 3/8" on a cut that 
should be 20 thou if it hadn't walked out.  Here I use an end wrench 
about 15" long, ground thin enough to fit the flats on the TTS holder, 
and a 10 or 12" crescent wrench and a pull on the wrenches that is 
likely in excess of 100 lb-ft. I don't have a newtom-meters to 
pound-foot conversion handy but that certainly is tighter than 75Nm.

Ditto if using an R8 directly, the R8 gets tightened with a 20 volt 
electric impact wrench driving an 8 point 10mm socket a lot tighter than 
I can draw it by hand with the supplied toy 10mm endwrench.  If not, the 
TTS in the R8 may slip and walk out. The life of that socket before it 
splits might be 50 times, its hell on good quality sockets.                     
> (Though I am not convinced that an ER17 can really lift a 300kg mass,
> so suspect I messed something up. )

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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