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gregbrown
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| Posted: February.02.05 at 9:19am | IP Logged
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I'm doing an open-hole repad, and the grommets will not hold the pad in
the cup (grrrr). I made a shrinking die, but the grommet seems to
expand again the minute I press it back into the pad cup. What do other
people do?
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admin
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| Posted: February.02.05 at 11:58am | IP Logged
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Hi Greg,
First make sure the grommets are not split. This is common. If they are, replace them.
Second,
maybe you just aren't shrinking the grommet enough. For a shrinking die
I use the Allied rotor valve bearing shrinker. One of the collets is
just the right size to also shrink flute grommets.
Some people
will use their brass mouthpiece trueing tool to widen the chimney on
the key. I have never tried this because I figure I can replace a
grommet a LOT cheaper than a key section if things don't go as planned.
But it may be an option for you.
You can also usually just order replacement grommets. They usually fit.
Anyone else have any other methods?
Michelle
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marksteenis
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| Posted: February.02.05 at 1:24pm | IP Logged
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at the national napbirt convention last year, i showed a die press for
shrinking grommets. ed kraus is working on this project and may have
something available soon.
mark
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admin
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| Posted: February.02.05 at 1:45pm | IP Logged
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Cool. Can't wait to see it. The big 'ol rotor shrinking tool works but is a little clumsy.
Michelle
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gregbrown
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| Posted: February.02.05 at 1:46pm | IP Logged
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Michelle and Mark,
Thanks for the replies. I did shrink the grommet
down to the point where I needed to gently tap it back into the cup - I
couldn't push it in by hand. But they seem to just then expand right
back to a too-loose state. I wonder if the die I made only shrinks the
very bottom of the grommet chimney, which then doesn't have enough
strength to "hold" when it is put back in the cup.
I keep thinking
there must be a better way of doing this altogether - I mean the
grommet system altogether. That's another discussion though.
thanks again for the help. Sounds like I need to call Allied.
Anyone else?
Greg
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GordonPalmer
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| Posted: February.02.05 at 1:52pm | IP Logged
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I use the Ferree P61 French horn rotor bearing tool. Is that the same as Allied's?
I
have noticed that the result is a slightly triangular cross-section. I
improve this by turning the grommet 60 degrees and squeezing again.
My
thinking is that if it is a little triangular there is more chance of
it leaking. Even so, I use a little 222 Loctite as a sealer after
installation.
Damn those open holes!
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admin
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| Posted: February.06.05 at 5:13pm | IP Logged
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Hi Gordon,
I
thought both the Allied and Ferree's were pretty much the same although
I have never used the Ferree's. However, I do not get the triangular
problem with the Allied one. So there must be some difference.
Michelle
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GordonPalmer
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| Posted: February.06.05 at 5:54pm | IP Logged
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Hi Michelle
With ANY collet-type shrinking device, unless you
shrink to the EXACT inside diameter that was originally drilled when
making the jaws of the tool, there will be some non-cylindrical
distortion.
With the type of tool we are talking about, the
hole through the tool's collet jaw is cylindrical only when the tool is
not compressed. As compression progresses, the hole is increasingly
non-cylindrical as the curvature in each of the jaws becomes less
appropriate.
The more jaws there are, the less is this effect.
With three jaws it is quite pronounced. Furthermore, the triangular
distortion of the grommet does not readily show up by comparing
DIFFERENT diameters with a calliper. (Indeed, the correct
triangularised cylinder shape could successfuly be used for roller
bearings.)
Whether this slight triangulation actually causes
leaks depends on whether there are sufficient forces, when the grommet
is installed, to force the grommet back to a cylindrical shape.
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admin
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| Posted: February.06.05 at 6:42pm | IP Logged
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Ahh. Now I see what you're saying....I just took a loot at the swedging
too. It does indeed start to go into a rounded triangle when closed
almost all the way. I'll have to pay more attention to how much the
collet closes when swedging the different sized grommets.
Now I'm even more interested in making the "draw-plate" type swedger.
Thanks Gordon!
Michelle
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JeffPeterson
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| Posted: March.27.05 at 10:42pm | IP Logged
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One quick and easy way to get them to fit is to stick the tips of a
closed pair of needle-nosed pliers into the open hole(from the pad side
with grommet installed)
press gently and twist a full turn.
A
much better solution is to replace the metal grommets with delrin
bushings by Jim Schmidt. The delrin holds much more securely, seals
better, and because it prys off easier it does not murder the pad after
repeated shimming attempts. He even makes a sleeve for Yamahas to give
the bushing a parallel surface to grab against.
They are available from www.jlsmithco.com or www.jsengineering.net.
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Topic: How do I shrink open hole grommets?
