-------- Forwarded Message --------
Subject: Re: [Emc-users] Something to think about re the hack-a-day
tool changer
Date: Thu, 18 Apr 2019 23:22:19 +0700
From: TJoseph Powderly <[email protected]>
To: Gene Heskett <[email protected]>
Hi Gene
On 04/18/2019 10:57 PM, Gene Heskett wrote:
On Thursday 18 April 2019 11:50:00 Ken Strauss wrote:
Google is your friend! ft-lb =Nm * 0.73756 So 75Nm = 55.3 ft lbs
55 ft/lbs? Here the tool will walk out and break, very quickly at that
tension. Doubtfull I have used less than 75 ft-pounds on the TTS
adapters I use fairly universally on the G0704.
on the web you can find suggested max torque for er collets
https://www.techniksusa.com/metal/torque_chart.htm
that url has torque wrench adapters as well ( $$$ )
( i have eoc8a collets tho, and have found no numeric values, only
descriptions of hand tightening )
you can find mfctrs saying use 75-80% of the max torque value.
you can find the caveats that the tool shank has to fully contact the
collet, not larger or smaller allowed.
you can find that the release is going to have stiction and release
requires more initial force.
other caveats about cleaning and air blasts are used in industry
( even collets covering the air blast holes and checking back pressure
in attempts to check good seating )
Andy's pragmatic checking of needed torque with a proper torque wrench
is very good ( what works is a good place to start)
also note the xatc ver 0.3 is already old and the google group on xatc
is cold since 2016.
you're kinda the lead developer now
-----Original Message----- From: Gene Heskett
[mailto:[email protected]] Sent: Thursday, April 18, 2019 11:45
AM To: [email protected] Subject: Re: [Emc-users]
Something to think about re the hack-a-day tool changer On Thursday
18 April 2019 07:47:51 andy pugh wrote:
On Thu, 18 Apr 2019 at 10:22, Roland Jollivet
<[email protected]> 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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Cheers, Gene Heskett
tomp
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