New bearing holder idea

New bearing holder idea

Post by showar » Mon, 08 Mar 2004 13:45:20


I've been preoccupied for the last month or so with the purchase and
installation of a significant piece of equipment in the shop.  It's a
machine called a "water jet".  It will cut virtually anything using high
pressure water (50,000 psi in our case) and abrasive.  We will use it to
cut stainless steel, aluminum and plastic mostly.  I've heard of water
jets being used to cut diapers, insulation, granite, cakes (yes cakes!),
glass ...

Yesterday we finally got it running for the first time - pretty
exciting.  You know that there's some interest when the shop guys will
hang around after hours on a Friday night just to watch it run.

Even though I personally won't be running this machine, I MUST know what
it's all about and there's no better way to learn how to run a machine
than to use it.  For some time I've had an idea for a new bearing holder
design so today I made one using the new water jet.

I've created a gallery with some photos of the 'new bearing holder'
(http://www.unicyclist.com/gallery/wjmuni) .  I'm actually making an
entire frame with the water jet but so far I've just photographed the
bearing holders.

Basically, the bottom of the fork leg is an arc of the same radius as a
40mm bearing.  The width of the fork leg at the bottom is 40mm wide and
the thickness has been machined to 12mm - same as the bearing.  The
bearing is held in a "U" shaped retainer that's been machined to accept
the bearing with lips on both sides.  The "U" retainer is attached to
the bottom of the fork leg with a couple of screws coming in from the
sides.  The nice thing about this design is that it's impossible to
overtighten anything that will put a bind on the bearing.  Also notice
that the bearing is held with lips on both sides and the same lips
extend along side the bottom of the fork leg to keep everything
aligned.

I don't like to blow my own horn but I think it's a pretty cool idea.  I
intend to make a complete 24" MUni frame using the water jet and I'll
post more photos as the project progresses.

SH

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New bearing holder idea

Post by Sofa » Mon, 08 Mar 2004 22:10:02

Quote:

> *run a skewer and quick release (for "no-tool" wheel
> removal)?.......... *

Awesome idea!

Beautiful design as always, Steve

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New bearing holder idea

Post by showar » Tue, 09 Mar 2004 06:20:55

Quote:

> *Looks like a nice design .... How about if you extended the "U"
> section and instead of 2 screws; drill through so that you could run a
> skewer and quick release (for "no-tool" wheel removal)?.......... *

That's a great idea!  I didn't think I could make a quick release with
what I've already got so I did what might be the next best thing:  I
machined a slot from the***hole in the "U" retainer to the edge so
they can be removed without taking the screws clear out.  The skewer
idea is the ultimate though.

The frame is done ... talk about rapid prototyping.  There's quit a bit
of machine work to do after the parts were cut on the water jet but it
went pretty fast.  The water jet part was REALLY fast - the crown blank
took 8 minutes to cut and both legs took 11 minutes!  I've posted some
more photos in gallery.

Now it's time to make a ridable MUni out of it and go for a spin ...

SH

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New bearing holder idea

Post by cyberbellu » Tue, 09 Mar 2004 07:20:57

Quote:

> *  
> I don't like to blow my own horn but I think it's a pretty cool idea.
> I intend to make a complete 24" MUni frame using the water jet and
> I'll post more photos as the project progresses.

> SH *

Go ahead and blow. It IS a cool idea.  Now all you have to do is
convince the foreman that you've made a couple of connecting rods for a
steam locomotive.

It's amazing that the water doesn't wear out.  Tough stuff!

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New bearing holder idea

Post by showar » Tue, 09 Mar 2004 14:06:57

The Water Jet Muni has been assembled and ridden but I wouldn't say it
was a "brilliant" success ...

The water jet machine cuts hard material such as steel or aluminum with
a combination of high pressure water and abrasive (red garnet usually).
The orifice that the water passes through is either ruby or diamond.
We got two spare ruby and one diamond with the machine.  Right now I
don't know what the difference between them is except the diamond is
more expensive.  The "mixing tube" is where the abrasive is injected
into the water stream.  It's made out of tungsten carbide.  Soft stuff
like diapers are cut with water only ... much gentler on the baby.

Back to the MUni ...

I robbed the wheel setup out of my current MUni but had problems right
away.  The "U" retainers are pretty wide and the hub flanges on this
particular wheel are wide too, so the spokes rubbed slightly on the "U"
retainers.  The hub is a Profile copy that I made.  I made new spacers
to widen out the bearings slightly,  then had to spring the fork legs
out a little to match the wider bearing spacing.  The "U" retainers
*just* clear the spokes now.   Not ideal but it works.  The rest of the
assembly went fine.

I went to a trail that's down on the valley floor - there's still lots
of snow everywhere else.  I took off and right away could feel a little
"clunk" when I pedaled.  I rode for a mile or so then stopped to see
what was happening.  The bearings were slightly loose in the holders.
Evidently I didn't get the holes for the screws positioned well enough
and the "U" retainer wasn't holding the bearing snug against the bottom
of the fork leg.  I took the "U" retainers off so I could shim the
bearings with some paper or something but I didn't have anything with me
to use as a shim.  I was out in the lava rock and sage brush so I peeled
a little sage brush bark off and used that as a shim.  Worked good!  The
rest of the ride was fine with no clunking or looseness.  I guess I just
miss-drilled the holes.

From this prototype I've learned that even though the water jet does an
amazing job of cutting aluminum the finish isn't something you really
want to end up with.  It would be better to rough cut the stuff on the
water jet but still take a clean-up cut on a CNC mill so all the
surfaces are smooth and true.  I've also learned that for this style
bearing holder to work well it should be narrower and made with
precision.

SH

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New bearing holder idea

Post by U-Tur » Wed, 10 Mar 2004 05:32:31

Very exciting, Steve!  That's truly an innovation.  No matter what tools
one has available, it's always a pain to take off the wheel.  You appear
to have seriously improved things.  Just one bolt per side (soon)!

Note also that crank grabbers have:

a) protected bearings,

b) an easily replaced bottom piece,

c) a bottom piece that could easily be made from a tougher material,
and

d) a bottom piece that could easily be widened in various ways to
provide better protection for those parts of a uni that are vulnerable.

Nice!

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New bearing holder idea

Post by johnfos » Wed, 10 Mar 2004 05:45:06

Quote:

> *Won't these bearing holders have the same problem as the lollypops?
> The schrew/U-retainer interface will take some of the force when you
> use it, and eventually it will fail. *

I don't know what this design has in common with Taiwan***pops.
Assuming the fit on the bearing is completely snug, with no room for the
bearing to move around (as Steve already discovered), I think the***
area should not be an issue.

Taiwan***pops go against, or ignore, two basic engineering
principles:
1. Don't***bolts into a non-flat surface, unless you have something
for the bolts to seat against.
2. Don't just run threads in and***into one side, when it will be
stronger to run the bolt all the way through.

I think quick-release skewers would be a bit overkill for wheel
bearings. One little allen key is all you need to remove the wheels in
the current design, and this would be lighter and less obtrusive than
quick-releases and the levers that would have to go with them.

Something in between could be a single long bolt, that threads all the
way through the fork, protruding slightly on the other side (so as not
to violate #2 above). Then you only have to unscrew one side, and still
only about as much as the current design, to release the wheel.

The area around the bearing screws does look like a potential weak spot.
Testing would probably have to be required to find out if the***
method would be robust under long-term use.

Thanks for experiementing with your new toy, and sharing the results
with us!

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New bearing holder idea

Post by Carl Ols » Sat, 13 Mar 2004 12:02:49

I've inserted some comments into your original email below...

Quote:
> The orifice that the water passes through is either ruby or diamond.
> We got two spare ruby and one diamond with the machine.  Right now I
> don't know what the difference between them is except the diamond is
> more expensive.

The difference between ruby and diamond is that the diamond will be
much less succeptable to chipping, and in theory will therefore last a
lot longer than the ruby.

Sapphire jewels are also popular.  They are essentially the same as
rubies in terms of performance, but are a different color.

Quote:
> From this prototype I've learned that even though the water jet does an
> amazing job of cutting aluminum the finish isn't something you really
> want to end up with.  It would be better to rough cut the stuff on the
> water jet but still take a clean-up cut on a CNC mill so all the
> surfaces are smooth and true.  I've also learned that for this style
> bearing holder to work well it should be narrower and made with
> precision.

Waterjets are available with articulated tilting heads to compensate
for the taper produced by the jet, and therefore give you taper-free
"true" part.  In addition, you can improve the surface finish by
slowing the cutting down, and using finer abrasive.

Whether this is enough to meet your needs depends on what those needs
are.

There are also some tricks to significantly reduce the amount of the
taper in your part, even if you don't use a tilting cutting head.  For
example, cut with the stand-off as low as you possibly can (but pierce
at a higher stand-off to avoid plugging the nozzle).  Also, slow the
cutting down.  Typically in metals, when you cut, you get a "V" shaped
cut.  If you slow the cutting down a bit, the "V" turns into a
parallel "||" shaped cut, and if you slow it down even more, it might
turn into a upside down "V" shape.  The trick is finding the right
speed, and the right speed is typically a lot slower than what you
need for just cutting.  You can read more about this in the FAQ
section of my web site at: http://www.waterjets.org/waterjet_faq.html

- Carl
http://www.waterjets.org