On 2009-07-02, Michael Koblic wrote:
DoN. Nichols wrote:
[...]
OK, I understand the procedure. Clearly this could have been done
neither as per the factory instruction nor using the kit provided.
Well ... it would have been possible to put the washer in there
behind the soft jaws and in contact with the master jaws.
I did not think I could get it in there - too big.
The washer was larger in diameter than the minor diameter of the
threaded hole in the chuck back? Then mount it on a bolt and turn it
down a bit until it does fit. If it will fit the bore through the
chuck, that is small enough.
[ ... ]
Remember -- the parts of the soft jaws are expendable. :-)
Yes. Just as well. I have already started expending them! With the 4-jaw I
just shimmed the workpiece.
Shimming the workpiece has two disadvantages, depending on how
you do it all.
1) If they are kept behind the workpiece while turning, they are
likely to fling out at high speed.
2) If they are tapped out after the jaws are tightened, the
workpiece is likely to work its way in towards the chuck body as
you turn.
You *could* make the shims in the form of turned rings which go
around the last jaw step so there is nowhere for them to go even if the
workpiece is no longer firmly gripping them.
Not to mention doing it at 575 rpm...
I would swear that mine will go slower than that. How many belt
steps are on your pulleys?
6. The biggest ratio is about 3, the motor runs at 1725. The figure is also
quoted by the Taig manufacturer.
O.K. I went down and checked (it was early enough this evening
for me to find the mechanical tach and dig out the Taig to where I could
run it.)
Here are the speeds which I get - run by a 1/10 HP motor whose
"nameplate" (a sticky label) claims 1550 RPM.
The speeds which I measured a
1) 580 RPM
2) 905 RPM
3) 1430 RPM
4) 3260 RPM
5) 5150 RPM
Total of five belt steps with that little tiny belt. :-)
So -- it does run faster than I thought, and my impression that
it runs slower is probably because I seldom use it for anything large.
I've got other lathes more suited for that, and use these for really
small workpieces.
And you could replace the motor with a three phase or a DC motor
and connect an appropriate controller to it to get speeds perhaps
1/6th your current speed. That would take you down to 100 RPM or a
bit slower.
A DC motor, a Variac, and a rectifier would do a nice job there.
If you really care about spindle speed precision, a servo motor and
servo amplifier would be guilding the lilly. :-)
My 12" Clausing will go down to 210 RPM in direct drive,
and if I engage the back gear, it will go down to 35 RPM. The
corresponding highest speeds are 1600 RPM and 270 RPM. Having a
variable speed motor would be somewhat the equivalent of having a
back gear -- except that it would not boost the torque the way a back
gear does.
Or I could make a counter-shaft. Or spend $588 on a 7x8 and tweak the
controller - apparently one can get it from minimum 200 rpm down to 75. Or
(drum roll!!) I could use my RedNeck lathe which goes down to 80 (once I got
it on a stand and sorted out the tooling arrangement - no more than 3 years
from now...).
:-)
The countershaft might be a good idea. Two pulley steps (made
on the Taig) -- one for about 1:1 ratio, and the other for about 6:1
ratio. Or -- if you could pick up a slower motor, make the pulleys
identical, so they step up as much as they step down. A ratio of 2.45:1
(5:2 would be close enough) and a motor whose speed is about 600 RPM
would be nice (though 900 RPM is going to be easier to find, I think.
And bear in mind that the speeds I give above are with no slip. It will
be slower with normal slip. Fore example, the 1650 RPM motor would be
1800 RPM with no slip. (900 with no slip becomes something like 825
RPM with slip, and 600 with no slip becomes 550 RPM with slip.) That
550 RPM would get you down to 316 RPM with your existing gearing.
But a DC motor a Variac, and a rectifier would be more flexible,
giving you a much wider range of speeds, and the ability to change the
speed in mid cut without having to stop the motor and change the belts.
[...]
I started up on that. Inadvertently. The first parting tool I made
just did not cut it. It spun the toolpost and shaved the jaws before
I realized what was going on.
Clamp some heavy paper between the toolpost and the table or
compound and it will increase the holding power by fitting into
OK. Presumably there is a trade-off between the paper thickness and the need
to adjust the tool height. But with my little post that should not be an
issue.
Not much -- you can take out one shim about half the thickness
of the paper (it will compress that much when you tighten the bolt
holding the toolpost in place.)
But the advice on turning the OD jaws is noted. I also found some
good stuff he
http://www.ctemag.com/pdf/2002/0203-topchoices.pdf
related to what the shape of the jaws should be etc.
Of course, this is written from the perspective of someone who
is after 0.0001" runout -- and is working with a machine capable of
that. :-)
Isn't everybody?
:-)
[...]
OTOH the second (re-worked) parting tool works just fine. Once you
get past the squealing and screeching of the bigger OD down to about
3/8" :-)
Keeping the amount or projection down to a minimum helps a lot.
Making sure that the sides of the parting tool are parallel and
perpendicular to the axis of the workpiece helps. Having the parting
happening as close to the chuck's jaws as possible helps. Getting
lubricant to the bottom of the groove helps. And ideally, not having
a compound as part of the stackup will help minimize the flex of the
system.
Done all of the above. Still squeals like a banshee.
Interesting. I get rather quiet parting even with 3" diameter
stock -- but I'll probably be running at about 210 RPM.
But it is better than
it was with the original grind. Still have to keep backing out and clearing
out the chips before the tool digs in and stops the spindle - even when it
reaches the small diameter.
That is another reason to consider the rear-mounted parting
tool. Instead of digging in, it disengages a little when things flex.
Enjoy,
DoN.
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