On Sunday, 7 August 2016 21:33:43 UTC+1, newshound wrote:
On 8/7/2016 12:59 PM, tabbypurr wrote:
On Sunday, 7 August 2016 12:51:50 UTC+1, Fredxxx wrote:
On 07/08/2016 12:46, Cursitor Doom wrote:
On Sun, 07 Aug 2016 11:53:28 +0100, Fredxxx wrote:

One of the secrets of any calculation is to have a feel for the result..
I thought the result was too high hence my concern.

The circumferential stress on the drum must be significant, as must be
the bearing and outer case that has to deal with any imbalance.

No wonder they don't last long! Perhaps best to stick to a slower spin
speed!

The forces on those bearings are huge. What I was always more wary of though were the large top loaders. With far more weight & diameter, and lots of rust etc, being near those when they got upto a roaring spin was a reminder of one's nonrobustness in this life.

Rolling element bearings will take amazingly high loads. Part of the
skill in designing washing machines is in the suspension (stiffness,
range, damping). Obviously, you can never get perfect balance so the
drum axis moves in small circles around the centre of mass, this means
the loads on the bearings are much lower than you might expect from the
calc which you have done.

The calcs were someone else's, but of course suspension reduces it some. Memory not clear enough re the top loaders, but I don't recall any suspension on them, just a lot of rust. I presume they were ex-commercial things.


NT

On Sun, 07 Aug 2016 12:56:06 +0100, TimW wrote:

On 07/08/16 12:30, Fredxxx wrote:
On 07/08/2016 11:55, Chris Hogg wrote:
On Sun, 7 Aug 2016 03:21:20 -0700 (PDT), therustyone

[...]

Of course, as it points out in that link, centrifugal force is
fictitious. There is no such force. What you calculate is actually the
centripetal force, i.e. the force required to accelerate the object
towards, in your case, the centre of the drum.

Yes there is: In Newtonian mechanics, the term centrifugal force is
used to refer to an inertial force (also called a 'fictitious' force)
directed away from the axis of rotation that appears to act on all
objects when viewed in a rotating reference frame. Where the name has
also been used to refer to the reaction force to the centripetal force.

If it's not in any dictionary then I might agree the word was
fictitious.


Yes, the technically minded often have a woeful understanding of
language. There is nothing fictitious about centrifugal force, it is
knackering the main bearing of my washing machine even as I type
(terrible noise coming from back corridor). It is just a misnomer.


I never did bother to calculate the centripetal/centrifugal forces for
our first automatic washing machine drum (The very first Hotpoint Quartz
model which did away with the rather klunky electro-mechanically driven
"programmer switch" by using a micro-processor controller board).

Strangely enough, this modern doff of the hat to "reliable state of the
art electronic control" was the very first failure after just a week or
so (possibly straight from the off - the details are now shrouded by the
mists of time) requiring a visit by a service engineer (covered by the
warranty) who changed the controller board out.

After that, we never suffered any further controller board faults in the
remaining 20 odd years that I was able to keep it going, not even after I
modded the board with additional ttl chips mounted "dead bug" stylee to
adapt an ex-Bendix washing machine motor used as a free alternative to
the disgustingly expensive Hotpoint spare.

The Bendix motor was retrieved from a washing machine that had landed up
in our works skip as a "Just might come in handy item to possess". How
little did I realise that my 'foresight' would be put to the test! :-)

Anyway, I digress from the point I'm about to make but I think this
anecdote about being able to fit *any* washing machine motor that you can
get your hands upon, providing it's the same basic design with a tacho
sensor (as they all are - apart from differences in mating plug, grooved
shaft diameter and the number of pulses per rev from the tacho sensor),
is worth reading.

When I first considered using my "Bendix Spare", the very first thing I
noticed was the rather convenient feature of the drum/motor mounting
bracket(s) which suggested that Hotpoint wanted to be able to change
motor suppliers at the drop of a hat. Presumably a practice in
manufacture that's not confined to Hotpoint alone.

Physically attaching the 'foreign motor' was the least of my problems.
All I had to then do was identify the 6 wires (armature, field and tacho
wire pairs) on both motor connector blocks so I could swap the connector
block over to the Bendix motor, work out the number of poles used by the
tacho rotor magnet (6 and 8 poles, afaicr but don't ask me which way
round it was) and compare the belt pulley diameters (basically,
identically grooved motor shafts - afaicr 1 inch and 1 1/4 inch shafts).

Unfortunately, the difference in tacho pulse rates didn't compensate for
the larger diameter Bendix motor shaft come grooved pulley so I had to
'invent' a 'clever circuit' to divide down the incoming pulses before
they hit the i/o pin on the controller so as to maintain the original
1200rpm spin speed (I didn't want to compromise the spin dry performance
but neither did I want to overstress the bearings - I was acutely of the
square law relationship regarding rpm versus stress on the shaft
bearings).

Now, speaking of "shaft bearings", this brings me to the point I wanted
to make and it is this. About a year or so after owning this machine, I
found myself having to buy and fit a drum bearing kit. This bearings kit
consists not only of the two *taper* roller bearings themselves and
replacement shaft seals but also a replacement "Crush Spacer" and preload
tightening up shim".

According to the instructions, the shim (about 4 or 5 thou thick) is
only used when sogging down the end nut onto a shoulder so as to get the
desired amount of crush on the aluminium pre-load spacer before undoing
the nut to retrieve and discard said shim and then finally tightening the
nut onto the shoulder of the shaft thus correctly pre-loading the *taper*
bearings.

Now, having helped my brother re-assemble the engine on his Velocette
Venom with all the palaver involved by the use of *taper* roller bearings
on the crankshaft, some years earlier, I knew full well the importance of
the need to use pre-loading with this type of bearing (*taper* roller
bearings), so when, a few months later, I noticed that the washing
machine drum had lost its initial 'stiffness' I became a little concerned.

Within a year of replacing the bearings, I found myself once more faced
with fitting a second bearing kit. However, *this* time I did *not* make
the mistake of 'discarding' the pre-load setting shim as per the
malicious instructions but held onto it ready to refit it as soon as the
first hint of any slackness would appear.

A few months later, I decided it was time to add the shim back and the
machine never needed another set of bearings for the remaining 16 years
or so before we were offered a hardly used replacement washing machine
which the missus was only too happy to accept from her daughter.

The important lesson to take from this anecdote is that it is far better
to slightly overdo the pre-loading than under-do it when it comes to
*taper* roller bearings even if it means editing the final instruction
given by the "helpful" instruction leaflet so that you *don't* discard
the shim and keep hold of it to refit after a few months of service has
further crushed the crushable pre-load spacer. IOW, don't always assume
that 'helpful' instructions are always in your best interest. :-)

Normal roller and ball bearings have the optimum 'pre-load' built in "by
design and accurate manufacture" so this problem doesn't arise. Possibly
not every brand and model of washing machine uses taper roller bearings
for the drum but the problem I had with that Hotpoint highlights the
problems of shortened service life due to high rpms whenever there is a
significant and unavoidable imbalance to contend with such as residual
imbalance of the load in a washing machine drum or the balance factor of
a single or parallel twin motorcycle engine where these forces on a high
revving engine can far exceed the static torque thrust forces due to a
chain sprocket drive.

Note to anyone rebuilding a Triumph motorcycle twin cylinder engine;
replace *both* shaft bearings with SKF ball race types, the flexure in
the crankshaft ensures that a roller bearing on the drive side *will*
disintegrate in short order if ridden enthusiastically (every 14000 miles
in my case) whilst the timing side ballrace remains in perfectly
serviceable condition notwithstanding that logic dictates you replace it
anyway.

The additional sidethrust is a trifling additional force exceeded by
several orders of magnitude just by revving the engine when in neutral!
Don't be kidded by BSA's faulty un-thought out logic in cursing the
Triumph T120V with a roller bearing on the drive side of the crankshaft.

This is yet another example of the falsity of that stupid saying, "If it
ain't broke, don't fix it!" Luckily, when it finally dawns on the owner
that it was broke to begin with, the solution is very simple! Keep the
replacement parts order simple. Just order a *pair* of SKF *ball*
bearings, no need to make the order any more complicated than that. :-)

--
Johnny B Good

On Sunday, 7 August 2016 21:00:45 UTC+1, polygonum wrote:
On 07/08/2016 20:42, Brian Gaff wrote:
The point is though it is really the effect that occurs when things moving
in a single direction are forced to deviate from that path in a circle.
Brian


One of the issues with the term centrifugal is the apparent, albeit
simplistic, inference that things would literally fly out from the
centre - rather than continue on their tangential path - if released.

--
Rod

Example here.
https://www.youtube.com/watch?v=pR26RMI9T8c

In article ,
writes:
High spin speed seems to be more a selling point than anything else. It isn't necessary and shortens bearing life greatly.

It's a matter of convenience. The faster the spin (at a given drum
diameter), the drier the clothes come out. At 1600 RPM spin, I have
used towels directly taken out of the machine (they aren't bone dry,
but they are dry enough to dry you).

I've also taken the view it's much more efficient than a tumble
drier, so when I've chosen machines, I've gone for fastest spin
speed but no tuble drier feature..

I don't remember what early front loaders did, if 600 or 800 it would have been more significant then.

It was much more common to have a separate spin drier, because that
was pretty useless. Those are now pretty much unheard of.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 08/08/2016 08:33, Andrew Gabriel wrote:
In article ,
writes:
High spin speed seems to be more a selling point than anything else. It isn't necessary and shortens bearing life greatly.

It's a matter of convenience. The faster the spin (at a given drum
diameter), the drier the clothes come out. At 1600 RPM spin, I have
used towels directly taken out of the machine (they aren't bone dry,
but they are dry enough to dry you).

I've also taken the view it's much more efficient than a tumble
drier, so when I've chosen machines, I've gone for fastest spin
speed but no tuble drier feature..

I don't remember what early front loaders did, if 600 or 800 it would have been more significant then.

It was much more common to have a separate spin drier, because that
was pretty useless. Those are now pretty much unheard of.

We've had our Zanussi 1600rpm spin WM for over 12 years and it is still
going strong. We use the 1600 spin twice on every wash.
I agree with the previous poster that the clothes come out virtually dry.
Net curtains are dry enough to hang back up without any further drying.

On 07/08/2016 16:10, harry wrote:


Before spinning, washing machine run at an intermediate speed that is supposed to distribute the washing around the drum.


And if it cannot distribute the washing it modifies the spin to a lower
speed or just stops the spin cycle if too much out of balance.

--
mailto: news {at} admac {dot] myzen {dot} co {dot} uk