spinning problems

Jane Strouse (strousej@chem.ucla.edu)
Thu, 06 Nov 1997 16:09:16 -0800

With a very high volume usage I learned years ago that if you can't
solve spinning problems in under 5 minutes, clean the spinner housing. We
do it rather frequently with no problem whatsoever. The first point made
by Ken Fishbein is very important (see below). But, it is not necessary to
remove the upper stack to clean the spinner housing. We simply keep a
piece of tape with a mark on the shim assembly (directly above the probe)
and one on the magnet to be assured that the orientation is the same when
you put it back. With these shimming afterwards to write a new shim file
is fairly straightforward. One could do all those things on the upper
stack but I have rarely had to remove the upper stack at all.

Jane

>Date: Thu, 6 Nov 1997 13:41:24 -0800
>From: fishbein@vax.grc.nia.nih.gov
>Apparently-To: <mjs@chem.ucla.edu>
>
> Glenn,
>
> Here are some pointers on removing the upper shim stack and/or shim
>assembly:
>
> 1. Check to see whether the shims are bolted to the underside (OVC
>plate) of the magnet before pulling out anything. On our magnet, there is a
>clamp which holds the shims in place below the magnet, but this may not be
>the standard configuration. If there is nothing holding the shims to the
>underside of the magnet, put a box under the magnet to prevent the shims
>from falling down when you release the upper stack.
>
> 2. Before pulling out the upper stack, scratch some alignment marks
>into it and the top magnet flange so the stack can be re-inserted with the
>same height and radial orientation. This is critical because the height and
>radial position of the upper stack sets the height and radial position of
>the shims.
>
> 3. Loosen the long screws at the top of the stack, then gently pull
>the stack upwards. Inspect the two O-rings at the bottom of the stack to
>see if they are damaged or unseated. If necessary replace them, using a
>thin film of epoxy cement or grease to hold them in place as you re-insert
>the stack.
>
> 4. Check the fiber optic spin rate sensor at the end of the stack.
>Make sure there isn't any dirt on the surface of the transducer.
>
> 5. If all is well with the upper stack, remove the shims, being
>very careful not to stress the cable carrying the shim current leads.
>Inspect the spin turbine at the top of the shims. If the pin holes in the
>turbine are blocked, you can remove a screw and pull out the turbine for
>sonication. Note that all air connections for spinning and lift pass
>through the upper stack; no air connections are made through the shims.
>
> 6. To reassemble everything, first re-insert the upper stack and
>set it to the correct height and radial orientation. When the upper stack
>is locked down, crawl under the magnet and push the shims into the bottom
>of the magnet, rotating the shims until they engage the spin rate
>transducer on the bottom of the upper stack. Push the shims up as far as
>they will go, then have a second person tighten the screws on the top of
>the upper stack while you hold the shims firmly in place.
>
> Good luck, and let me know if I can provide any further information.
>
> Best regards,
>
> Ken Fishbein
> Facility Manager,
>NMR Unit
> NIH/NIA/GRC
>
>Ph. (410) 558-8512
>FAX (410) 558-8323 or 8173
>E-mail: fishbein@vax.grc.nia.nih.gov
>Address: Ken Fishbein
>NIH/NIA/GRC
>4940 Eastern Avenue
>Baltimore, MD 21224 USA
>
>
>
>
Dr. Jane Strouse
Dept. of Chemistry and Biochemistry
UCLA
Los Angeles, CA 90095-1569
(310)-825-9841 - voice
(310)-825-0393 - FAX
strousej@chem.ucla.edu