In a message dated 2006/10/05, tchannel@.............. writes:

>    I am in the process of building a sensor bases on your prototype, and 
> great drawings. I have most of the parts located, again with your help and 
> others on the mailing list. I will send pictures as I go along, if you like, and 
> if you tell me how to send them.

Hi Ted,

       gif or jpg images would do fine to my EMail address.

> I regards to the angle between the bottom and top hinge, a fraction of a 
> degree, how do you measure for that? Or do you adjust and measure the period, 
> instead?

       I don't measure it, I calculate it. Then I make the structure so that 
there is a small amount of adjustment. The axis is defined by the centre of 
the ball and the edge of the top wire clamp. You vary the slope of the long 
horizontal baseplate to set the period accurately, using the end adjustment screw, 
but you keep the arm parallel to the baseplate. 

> Chris, I see on your drawing you did not need to brace the vertical arm of 
> your device. Looks very strong.  How did you attach that vertical to the 
> cross member?

       In my case the bottom of the vertical was milled flat and then the 
centre sections were milled out ~15 thou so that there were four longitudinal 
narrow strips about 1/16" wide x 3/4" long at the corners. Then two bolts were 
put through the cross bar, the long base and threaded into the vertical at the 
front and back ends. If you don't mill out / file out the centre sections, the 
clamp force will be at the centre, not at the edges where you want it and it 
will rock just enough to give trouble. An alternative is to use a flat end and 
3 or 4 shim strips.
       You can also make three point suspensions, or you can glue the 
vertical to the long base with two part modified acrylic glue. This is strong and 
tough, unlike epoxy which is brittle. However you have to be very quick as it has 
a gel time of about a couple of minutes in a warm room. 
       An alternative construction might be to use a 3" dia tube for the 
vertical? This can be held on either with a central vertical threaded rod and a 
top plate, or by mounting a 3/4" circular rod horizontally through two holes in 
the vertical tube, drilling and tapping this and putting a vertical bolt up 
through the baseplate. You would make three contact strip suspension flats at 
120 deg.
       You can use an SS ball on a carbide flat lower hinge or crossed 
cylinders. You can buy 1/8" solid tungsten carbide drills from www.Smallparts.com or 
www.Digikey.com and cut the shanks to length with a carbide disk. Glue one to 
the head of an SS bolt and the other to the end of the arm with two part 
modified acrylic glue. I usually file a shallow V first to locate the shank 
mechanically. Mount the vertical rod or the ball on vertical support and the 
horizontal rod or the flat on the arm, NOT the other way around! 8 thou Nickel plated 
piano wire is available for mandolin strings at a music shop. See 
www.daddario.com
    Another method of construction which you might wish to consider? In this 
I used Al alloy U channel, 3" wide x 1" high and three triangular 3/16" to 
1/4" thick corner plates at the end T / L joint. The vertical is attached to the 
long horizontal base with two 5" corner plates and four SS bolts per plate. I 
use two plain SS washers and a spring washer per bolt to prevent it digging 
into the softer Al. The open U is on the inside of the 90 deg joint. The cross 
bar is attached to the outside of the vertical with four bolts and a 7" 
triangle. It seems to work OK and makes quite a neat job. I bought it cut / chopped 
to size, from a local metals supermarket. You maybe able to get 2" x 1" U 
channel from building supplies / DIY. I tend to make things more massive than 
absolutely necessary. The secret of the rigidity is mostly in the three large 
triangular joint plates. 
    I tend to use 18" to 24" long tubular arms. 22" gives a 1.5 sec basic 
pendulum which you can extend by x20 to 30 sec. 3 ft is a bit bulky, but it gives 
maybe 40 sec or more? You can get compression fittings for most tube. I use 
1/2" SS water pipe and brass water fittings, 15mm OD, but the tube may not be 
widely available? It is light but rigid and non magnetic. Hard drawn Cu or 
brass are alternatives. You can also buy general purpose brass compression 
'engineering' fittings for a wide range of standard pipe sizes, but these may only be 
available through a few more specialist suppliers and they tend to be more 
expensive than water fittings. Check on the availabilty of thin wall welded SS 
water pipe? 

    Regards,

    Chris Chapman    
In a me=
ssage dated 2006/10/05, tchannel@.............. writes:



   I am in the proces=
s of building a sensor bases on your prototype, and great drawings. I have m=
ost of the parts located, again with your help and others on the mailing lis=
t. I will send pictures as I go along, if you like, and if you tell me how t=
o send them.




Hi Ted,



       gif or jpg images would do fine to my E=
Mail address.



I regards to the angle between=
 the bottom and top hinge, a fraction of a degree, how do you measure for th=
at? Or do you adjust and measure the period, instead?




       I don't measure it, I calculate it. Th=
en I make the structure so that there is a small amount of adjustment. The a=
xis is defined by the centre of the ball and the edge of the top wire clamp.=
 You vary the slope of the long horizontal baseplate to set the period accur=
ately, using the end adjustment screw, but you keep the arm parallel to the=20=
baseplate. 



Chris, I see on your drawing y=
ou did not need to brace the vertical arm of your device. Looks very strong.=
  How did you attach that vertical to the cross member?



       In my case the bottom of the vertical=20=
was milled flat and then the centre sections were milled out ~15 thou so tha=
t there were four longitudinal narrow strips about 1/16" wide x 3/4" long at=
 the corners. Then two bolts were put through the cross bar, the long base a=
nd threaded into the vertical at the front and back ends. If you don't mill=20=
out / file out the centre sections, the clamp force will be at the centre, n=
ot at the edges where you want it and it will rock just enough to give troub=
le. An alternative is to use a flat end and 3 or 4 shim strips.

       You can also make three point suspensio=
ns, or you can glue the vertical to the long base with two part modified acr=
ylic glue. This is strong and tough, unlike epoxy which is brittle. However=20=
you have to be very quick as it has a gel time of about a couple of minutes=20=
in a warm room. 

       An alternative construction might be to=
 use a 3" dia tube for the vertical? This can be held on either with a centr=
al vertical threaded rod and a top plate, or by mounting a 3/4" circular rod=
 horizontally through two holes in the vertical tube, drilling and tapping t=
his and putting a vertical bolt up through the baseplate. You would make thr=
ee contact strip suspension flats at 120 deg.

       You can use an SS ball on a carbide fla=
t lower hinge or crossed cylinders. You can buy 1/8" solid tungsten carbide=20=
drills from www.Smallparts.com or www.Digikey.com and cut the shanks to leng=
th with a carbide disk. Glue one to the head of an SS bolt and the other to=20=
the end of the arm with two part modified acrylic glue. I usually file a sha=
llow V first to locate the shank mechanically. Mount the vertical rod or the=
 ball on vertical support and the horizontal rod or the flat on the arm, NOT=
 the other way around! 8 thou Nickel plated piano wire is available for mand=
olin strings at a music shop. See www.daddario.com

    Another method of construction which you might wish t=
o consider? In this I used Al alloy U channel, 3" wide x 1" high and three t=
riangular 3/16" to 1/4" thick corner plates at the end T / L joint. The vert=
ical is attached to the long horizontal base with two 5" corner plates and f=
our SS bolts per plate. I use two plain SS washers and a spring washer per b=
olt to prevent it digging into the softer Al. The open U is on the inside of=
 the 90 deg joint. The cross bar is attached to the outside of the vertical=20=
with four bolts and a 7" triangle. It seems to work OK and makes quite a nea=
t job. I bought it cut / chopped to size, from a local metals supermarket. Y=
ou maybe able to get 2" x 1" U channel from building supplies / DIY. I tend=20=
to make things more massive than absolutely necessary. The secret of the rig=
idity is mostly in the three large triangular joint plates. 

    I tend to use 18" to 24" long tubular arms. 22" gives a 1=
..5 sec basic pendulum which you can extend by x20 to 30 sec. 3 ft is a bit b=
ulky, but it gives maybe 40 sec or more? You can get compression fittings fo=
r most tube. I use 1/2" SS water pipe and brass water fittings, 15mm OD, but=
 the tube may not be widely available? It is light but rigid and non magneti=
c. Hard drawn Cu or brass are alternatives. You can also buy general purpose=
 brass compression 'engineering' fittings for a wide range of standard pipe=20=
sizes, but these may only be available through a few more specialist supplie=
rs and they tend to be more expensive than water fittings. Check on the avai=
labilty of thin wall welded SS water pipe? 



    Regards,



    Chris Chapman