Hi all, 
Included herein is a reply from Chris Chapman in relation to this subject.  The reason for
this approach is that Chris uses the AOL email system which can neither send to, or be 
received from PSN.   Meredith Lamb

----- Original Message ----- 
From: Meredith Lamb 
To: psn-l
Sent: 12/6/2003 9:53:24 PM 
Subject: A "new" seismo base plate adjustment screw/s approach


Hi all,

Have tried researching this on the PSN web site search function, but I see no reference. 
It maybe nothing new...(?)...but it sure works great!  Best of all, there is little to no adjustment
screw wobble, with quite solid firm movement.....and no base plate bolt threading (tapping)
to be done.  The normal "fitting" of the nuts to the bolts, alone by themselves is quite loose
and non-exact....but not in this application.

Basically this approach uses a standard bolt and three nuts, but, the seismo base has
only some predetermined chamfer widening of the bolt hole/s that is larger than the bolt
(adjustment screw) diameter, but only wide enough to make contact with the chamfer on
the nuts.

The nuts themselves have 6 planes (hexagonal outer shape), and some chamfering on
the outside top/bottom outside edges.  Non-chamfered nuts are useless.

One nut is above the other two; this is a locking nut only....which may or maynot be
absolutely necessary depending on how much tension the other two nuts are adjusted too.

A crude guide to trying/using this; could be the "base material" I used.  It was actually
a hardened tool steel machinist "parallel", that had two holes through the item.  The actual
hole/s were .5" in diameter but the chamfer was wider and made full contact with the nuts
chamfer (.575").  The actual bolt thread diameter was .311".  Here, the hole drilling and 
chamfer was done with a likely professional grade machine somewhere of course, but it
was likely done straight into the item without a lateral tilt offset.  If your hole and chamfer is
done by hand, the bolt may not be exactly standing upright 180 degrees to the "base plate"
material when installed.   Visually for this "model", I couldn't see any bolt tilt.

One nut is threaded on the bolt, then passed through the base material, and the other
nut is threaded on lightly finger tightened to where....the bolt can be turned (adjusted) but the
nuts don't.   With the two nuts on the bolt thread, increased turning of "a" nut, narrows
the space for the inside bolt thread, and lessens the "normal" bolt freedom to wobble.
Increased finger tightening of "a" nut makes this "bolt wobble" almost nil, and of course
makes it harder to turn the bolt (adjustment screw), but the firmness of the approach
seems to enhance the mechanical stability quite noteably.  One might call this a 
holding/tension/friction adjustment nut.  A wrench isn't needed of course for this or
the locking nut.

One may have a tough time trying to use non-chamfered holes for this approach;
most of my attempts failed with various material.  Various large drills (movement
limited) could be used for creating a chamfer; but their is other tools for this also.

One "could" epoxy the nut/s.  Epoxy one or both after adjusting the nut/s to  your
satisfaction.  Its possible the top nut "could" remain free of any cement, to adjust 
the fitting tension on the nut to their satisfaction, whenever they wish  

For smooth bolt thread movement action,  I'd suggest that the bolt/s be re-die-ed to 
eliminate burrs, or clogging matterial that might be in the threads.  I'd look for a 
straight bolt thread; theres no use buying a bent bolt.

One might also consider that in the base plate hole and between the nuts is a air
space that might serve as a "lubricant reservoir", for any of a variety of such lubricants
or types for various material.   A thicker variety of non-liquifying grease might be a good 
bet (auto grease) for the iron/steel bolts/nuts functioning over time, as well as anti-rust
prevention.

One might try this out on scrap material first before plunging into using it on the planned
for base plate installation.  One doesn't need expensive adjustment bolts/nuts with this
route.

Merry Christmas and happy new year everyone!

Take care, Meredith Lamb

****** Chris Chapmans reply below:

12/19/03

Hi Meredith, 

     Ordinary grease is made from oil and soap. The soap decays with time, but some soaps are better than others. The high temperature Molybdenum disulphide grease used on cars is fairly good and the moving surfaces get coated with the solid MoS2 lubricant. Vaseline also lasts a very long time. Don't use graphite grease; it is inclined to promote corrosion. 

     The critical point is that the expansion coefficients of the adjustment bolt and the nut or threaded baseplate need to be identical. This greatly reduces any tendency for the adjustment to creep as the temperature changes. 

    You can buy large multi flute countersink cutters quite cheaply, but I am not sure that this angle is quite correct for the nuts. Countersinks may have angles of 60, 82, or 90 degrees, 90 being the most common. You can get drills with a cone of 118 degrees, but 135 degrees is more common. The ordinary drills with two flutes do not centre very well over a smaller hole and are inclined to chatter. You can get smoother cutting by using a drill press and opening up the hole first with a standard countersink. The bevel angle cut on nuts may not be very well defined. It seems to vary from 100 to 110 degrees in the ones that I have measured and the depth of the cut may be asymmetrical - check both ends of the nut. 
     Drilling an accurate clearance hole in the baseplate with a drill press and then sticking a nut onto the flat surface is another option and this gives a high strength glue joint. 

     You can buy special nuts which have a large 45 deg chamfer on one end. These should be excellent when used with holes shaped with a 90 deg multi fluted countersink cutter. 

     You can also buy special nuts designed for insertion into sheet metal. They are longer than ordinary nuts and are turned down to a small tube at one end. When used in sheet metal, the turned down end is inserted through a hole in the sheet and the end is splayed with a press or a ball hammer. However, they can also be pushed into a plain hole drilled in say Al plate and secured with epoxy or Loctite. You can use one at both ends of a hole drilled through thick plate. This can provide a very precisely aligned rigid mounting. 
      
     Another method of providing a thread in soft Al plate is to drill out a central clearance hole for the bolt and then use a 'special' counterbore cutter to drill a flat bottomed hole slightly smaller than the outer diameter of the nut, to the length of the nut. You then press in a nut into the hole, maybe adding epoxy or Loctite, using a vice or a press. The six corners of the nut bed into the softer Al quite easily. 

     To get epoxy to perform well, the surfaces need to conform closely and there needs to be an appreciable glue area. It does not hole a sharp edge very well. 
    
    One thing that I have been doing is to drill the end of the vertical adjusting screws with a centre drill. I then stick a Stainless Steel ball bearing into the V cup, with epoxy. The diameter of the bearing is slightly less than the tap drill size for the thread used eg use a 5 mm ball for a 6 mm OD thread. This seems to give a contact which does not change with time. The wide angle points which are sometimes used seem to 'bed into' the mounting plates and may wander a bit. The seismometer is mounted on 2" squares of 1/4" thick stainless steel bonded to a concrete floor. 

    I drill and tap the hole in the steel seismometer baseplate. I put a nut and a wavy washer on the bolt, screw it into position and tension the nut. You can get wavy washers in phosphor bronze and stainless steel. They look like a very thin ordinary washer but are bent to have three S shaped curves which act as a spring. A dab of rubber contact adhesive will keep the nut from rotating as the suspension is levelled and the wavy washer keeps the screw thread under tension. 

     Regards, 





Hi all, 
Included herein is a reply from Chris Chapman in relation to this subject.  The reason for
this approach is that Chris uses the AOL email system which can neither send to, or be 
received from PSN.   Meredith Lamb
 
----- Original Message ----- 

From: Meredith Lamb 
To: psn-l
Sent: 12/6/2003 9:53:24 PM 
Subject: A "new" seismo base plate adjustment screw/s approach



Hi all,
 
Have tried researching this on the PSN web site search function, but I see no reference. 
It maybe nothing new...(?)...but it sure works great!  Best of all, there is little to no adjustment
screw wobble, with quite solid firm movement.....and no base plate bolt threading (tapping)
to be done.  The normal "fitting" of the nuts to the bolts, alone by themselves is quite loose
and non-exact....but not in this application.
 
Basically this approach uses a standard bolt and three nuts, but, the seismo base has
only some predetermined chamfer widening of the bolt hole/s that is larger than the bolt
(adjustment screw) diameter, but only wide enough to make contact with the chamfer on
the nuts.
 
The nuts themselves have 6 planes (hexagonal outer shape), and some chamfering on
the outside top/bottom outside edges.  Non-chamfered nuts are useless.
 
One nut is above the other two; this is a locking nut only....which may or maynot be
absolutely necessary depending on how much tension the other two nuts are adjusted too.
 
A crude guide to trying/using this; could be the "base material" I used.  It was actually
a hardened tool steel machinist "parallel", that had two holes through the item.  The actual
hole/s were .5" in diameter but the chamfer was wider and made full contact with the nuts
chamfer (.575").  The actual bolt thread diameter was .311".  Here, the hole drilling and 
chamfer was done with a likely professional grade machine somewhere of course, but it
was likely done straight into the item without a lateral tilt offset.  If your hole and chamfer is
done by hand, the bolt may not be exactly standing upright 180 degrees to the "base plate"
material when installed.   Visually for this "model", I couldn't see any bolt tilt.
 
One nut is threaded on the bolt, then passed through the base material, and the other
nut is threaded on lightly finger tightened to where....the bolt can be turned (adjusted) but the
nuts don't.   With the two nuts on the bolt thread, increased turning of "a" nut, narrows
the space for the inside bolt thread, and lessens the "normal" bolt freedom to wobble.
Increased finger tightening of "a" nut makes this "bolt wobble" almost nil, and of course
makes it harder to turn the bolt (adjustment screw), but the firmness of the approach
seems to enhance the mechanical stability quite noteably.  One might call this a 
holding/tension/friction adjustment nut.  A wrench isn't needed of course for this or
the locking nut.
 
One may have a tough time trying to use non-chamfered holes for this approach;
most of my attempts failed with various material.  Various large drills (movement
limited) could be used for creating a chamfer; but their is other tools for this also.
 
One "could" epoxy the nut/s.  Epoxy one or both after adjusting the nut/s to  your
satisfaction.  Its possible the top nut "could" remain free of any cement, to adjust 
the fitting tension on the nut to their satisfaction, whenever they wish  
 
For smooth bolt thread movement action,  I'd suggest that the bolt/s be re-die-ed to 
eliminate burrs, or clogging matterial that might be in the threads.  I'd look for a 
straight bolt thread; theres no use buying a bent bolt.
 
One might also consider that in the base plate hole and between the nuts is a air
space that might serve as a "lubricant reservoir", for any of a variety of such lubricants
or types for various material.   A thicker variety of non-liquifying grease might be a good 
bet (auto grease) for the iron/steel bolts/nuts functioning over time, as well as anti-rust
prevention.
 
One might try this out on scrap material first before plunging into using it on the planned
for base plate installation.  One doesn't need expensive adjustment bolts/nuts with this
route.
 
Merry Christmas and happy new year everyone!
 
Take care, Meredith Lamb
 
****** Chris Chapmans reply below:
 
12/19/03
 
Hi Meredith, 

     Ordinary grease is made from oil and soap. The soap decays with time, but some soaps are better than others. The high temperature Molybdenum disulphide grease used on cars is fairly good and the moving surfaces get coated with the solid MoS2 lubricant. Vaseline also lasts a very long time. Don't use graphite grease; it is inclined to promote corrosion. 

     The critical point is that the expansion coefficients of the adjustment bolt and the nut or threaded baseplate need to be identical. This greatly reduces any tendency for the adjustment to creep as the temperature changes. 

    You can buy large multi flute countersink cutters quite cheaply, but I am not sure that this angle is quite correct for the nuts. Countersinks may have angles of 60, 82, or 90 degrees, 90 being the most common. You can get drills with a cone of 118 degrees, but 135 degrees is more common. The ordinary
 drills with two flutes do not centre very well over a smaller hole and are inclined to chatter. You can get smoother cutting by using a drill press and opening up the hole first with a standard countersink. The bevel angle cut on nuts may not be very well defined. It seems to vary from 100 to 110 degrees in the ones that I have measured and the depth of the cut may be asymmetrical - check both ends of the nut. 
     Drilling an accurate clearance hole in the baseplate with a drill press and then sticking a nut onto the flat surface is another option and this gives a high strength glue joint. 

     You can buy special nuts which have a large 45 deg chamfer on one end. These should be excellent when used with holes shaped with a 90 deg multi fluted countersink cutter. 

     You can also buy special nuts designed for insertion into sheet metal. They are longer than ordinary nuts and are turned down to a small tube at on
e end. When used in sheet metal, the turned down end is inserted through a hole in the sheet and the end is splayed with a press or a ball hammer. However, they can also be pushed into a plain hole drilled in say Al plate and secured with epoxy or Loctite. You can use one at both ends of a hole drilled through thick plate. This can provide a very precisely aligned rigid mounting. 
      
     Another method of providing a thread in soft Al plate is to drill out a central clearance hole for the bolt and then use a 'special' counterbore cutter to drill a flat bottomed hole slightly smaller than the outer diameter of the nut, to the length of the nut. You then press in a nut into the hole, maybe adding epoxy or Loctite, using a vice or a press. The six corners of the nut bed into the softer Al quite easily. 

     To get epoxy to perform well, the surfaces need to conform closely and there needs to be an appreciable gl
ue area. It does not hole a sharp edge very well. 
    
    One thing that I have been doing is to drill the end of the vertical adjusting screws with a centre drill. I then stick a Stainless Steel ball bearing into the V cup, with epoxy. The diameter of the bearing is slightly less than the tap drill size for the thread used eg use a 5 mm ball for a 6 mm OD thread. This seems to give a contact which does not change with time. The wide angle points which are sometimes used seem to 'bed into' the mounting plates and may wander a bit. The seismometer is mounted on 2" squares of 1/4" thick stainless steel bonded to a concrete floor. 

    I drill and tap the hole in the steel seismometer baseplate. I put a nut and a wavy washer on the bolt, screw it into position and tension the nut. You can get wavy washers in phosphor bronze and stainless steel. They look like a very thin ordinary washer but are bent to have three S shaped curves which act as