In a message dated 2008/05/31, tchannel1@............ writes:

Hi Ted,

>        1) what top bearing / flexure are you using?    (The top hinge is a 
> SS wire, don't know the dia.  but very thin.)

       That should be OK, so long as the wire is hard drawn and 'very 
springy'. Annealed wire needs to be pulled / drawn to harden it. I usually use nickel 
plated music wire. It is cheap, readily available and it is quite rust 
resistant.

>        2) what bottom bearing / flexure are you using?   (The bottom is a 
> ball bearing on sidebyside drill bit shanks.)(this I think could be my weakest 
> point, this arrangement may not be good enough)  (I may rework this)

       Sorry, I remember now. Ordinary drill shanks are unlikely to last 
long, due to friction corrosion. I use a SS ball on a SS scalpel blade glued to 
the end of an Al alloy arm with acrylic glue. I can set this for 30 seconds 
without any problem. I suspect that a loaded ball rolling on two cylinders may 
have a small amount of rolling friction. It will tend to try to push the drills 
apart. 

       You can also used the crossed shanks of two tungsten carbide drills, 
used commercially and for drilling glass circuit board.

>        3) have you checked both the coil and the damping magnets for 
> whiskers? They tend to grow with time and can cause the beam to stick. I use one of 
> the pen lasers to check that the gaps are clear.   Not sure what whiskers 
> are............but it is a new machine.

       Shine a light into the magnet gaps and view from right angles or the 
far side, preferably with a magnifying glass. Whiskers are literally that - 
tiny hair like strings of magnetic particles sticking up ~at right angles to the 
edges / surfaces of the magnets. They can be quite difficult to see, but they 
grow with time from dust in the air. A laser pen will show them up clearly.

       I use Gaffer Tape / Duct Tape to remove them. It has a rubber adhesive 
on a loose woven backing strip which is particularly good at removing grit, 
dust and swarf. You press it on firmly all over the magnet surfaces / edges and 
then peel it off.

       From bitter experience, if you HAVEN'T cleaned your magnets this way, 
they are VERY LIKELY to have whiskers. I always clean the magnets during 
assembly and check them again after mounting them in place. Do CHECK !!

       Regards,

       Chris Chapman   
In a me=
ssage dated 2008/05/31, tchannel1@............ writes:



Hi Ted,



     &=
nbsp; 1) what top bearing / flexure are you using?    (The to=
p hinge is a SS wire, don't know the dia.  but very thin.)



       That should be OK, so long as the wire=
 is hard drawn and 'very springy'. Annealed wire needs to be pulled / drawn=20=
to harden it. I usually use nickel plated music wire. It is cheap, readily a=
vailable and it is quite rust resistant.



     &=
nbsp; 2) what bottom bearing / flexure are you using?   (The botto=
m is a ball bearing on sidebyside drill bit shanks.)(this I think could be m=
y weakest point, this arrangement may not be good enough)  (I may rewor=
k this)




       Sorry, I remember now. Ordinary drill=20=
shanks are unlikely to last long, due to friction corrosion. I use a SS ball=
 on a SS scalpel blade glued to the end of an Al alloy arm with acrylic glue=
.. I can set this for 30 seconds without any problem. I suspect that a loaded=
 ball rolling on two cylinders may have a small amount of rolling friction.=20=
It will tend to try to push the drills apart. 



       You can also used the crossed shanks of=
 two tungsten carbide drills, used commercially and for drilling glass circu=
it board.



     &=
nbsp; 3) have you checked both the coil and the damping magnets for whiskers=
? They tend to grow with time and can cause the beam to stick. I use one of=20=
the pen lasers to check that the gaps are clear.   Not sure what w=
hiskers are............but it is a new machine.




       Shine a light into the magnet gaps and=20=
view from right angles or the far side, preferably with a magnifying glass.=20=
Whiskers are literally that - tiny hair like strings of magnetic particles s=
ticking up ~at right angles to the edges / surfaces of the magnets. They can=
 be quite difficult to see, but they grow with time from dust in the air. A=20=
laser pen will show them up clearly.



       I use Gaffer Tape / Duct Tape to remove=
 them. It has a rubber adhesive on a loose woven backing strip which is part=
icularly good at removing grit, dust and swarf. You press it on firmly all o=
ver the magnet surfaces / edges and then peel it off.



       From bitter experience, if you HAVEN'T=20=
cleaned your magnets this way, they are VERY LIKELY to have whiskers. I alwa=
ys clean the magnets during assembly and check them again after mounting the=
m in place. Do CHECK !!



       Regards,



       Chris Chapman