You may
purchase the PVC pipe in 80mm or 90mm dia tubing. I used 80mm dia PVC for
the construction of this VG unit. You may prefer to use the 90mm pipe. If
you choose to use 90mm PVC pipe then be sure that you get the 90mm flanges
an other material to suite the larger diameter pipe. Cut a piece of the 80mm PVC
tube to a length of 600mm. This will be the main centre tube of
the vandegraff unit. The belt will run up the centre of this tube to the
top roller. Cutting and forming the top of the centre tube is as per
figure 8 and 9.
You can use a handsaw, jigsaw or small grinder to cut and shape the top
of the main tube. You may like to make the 35mm cut of figure 8 down to a
length of 50mm if you wish. This 35mm cut allows you to adjust the belt to
the correct tension. The more adjustment you can give the belt the better.
You may find that your belt may need this extra adjustment. The other 30 x
50mm cut down the tube can be done in only one side of the
tube if you prefer. It is not necessary to cut out this 50mm section from
both sides of the tube. The 30 mm wide x 50mm deep cut is where the top
static comb/electrode will come through to interact with the top
roller.(see figure 9,10) You can drill an pop rivet the static comb onto
the bottom bowl when the bottom bowl and curved flange are glued into
position on the centre tube. The curved flange of the bottom bowl should
have already been glued and pop riveted to the bottom bowl. If you have
not done this then do it before you glue the flange and bowl into position
on the centre tube.The bowl/curved flange assembly will be glued 75mm down
from the top of the tube.(see figure 9) You will need to leave the glue
dry on bowl/curved flange/centre tube assembly before you do any more with
it. Once you have this assembly in place you will have an assembly that
looks something like figure 10.The bottom flange and centre tube need to
be moved up or down to find the best position. The bottom flange should
not be glued into position until you have completed the motor
mounting section. The final position of the centre tube and bottom flange
depends on your motor size and mounting location.
You will need to have cut
the hole in the top of the wood frame before you can mount the bottom
flange. Once you have mounted the motor and the bottom roller is aligned
centre most under the centre tube you will be able to slide the centre
tube up an apply the PVC glue then move the tube back down to the final
resting place. So only temporarily place the bottom flange onto the centre
tube at this stage.
Top Electrode/Comb
Once you have glued the bottom bowl/flange
assembly onto the centre tube you can then pop rivet the top electrode
comb into position. The comb can be made from any thin or sharp pointed
metal. You can use a single needle or multiple points as in figure 12. I
use thin (0.1) high tensile shim steel. You can buy shim steel in packs of
various thickness from your local bearing supplies. Use the sharpest edge
shim steel you can get. Cut a piece of shim steel 25mm wide x 25mm long.
Cut one end of the shim steel strip into multiple sharp points with a pair
of tin snips.The more points you can cut into the shim steel the better.
(See figure 12) You can then pop rivet the pointed shim steel onto the end
of a piece of tin 30mm x 120mm long. Bend the tin strip into an
'S' shape so you can pop rivet the end of the tin down onto the bowl. You
will have to manually bend the tin in an out as you adjust the electrode
points optimum distance away from the belt. Important: Try to get the
top comb/electrode points as close to the belt as you possibly can. This
will give you the best voltage potential possible. Be watchful that you do
not allow the points of the comb/electrode to touch the belt at any time.
This will blunt the points and cut into the belt. The belt will flex
outwards from the rollers as the motor runs to full speed. So watch that
the points of comb/electrode do not touch the belt when the motor is
running full speed. You will have to do adjustments to the comb/electrode
to make allowances for full motor speed.
Alternative
Cut a piece of the 80mm PVC
tube to a length of 600mm. This will be the main centre tube of
the vandegraff unit. The belt will run up the centre of this tube to the
top roller. Cutting and forming the top of the centre tube is as per
figure 8 and 9.
done in only one side of the
tube if you prefer. It is not necessary to cut out this 50mm section from
both sides of the tube. The 30 mm wide x 50mm deep cut is where the top
static comb/electrode will come through to interact with the top
roller.(see figure 9,10) You can drill an pop rivet the static comb onto
the bottom bowl when the bottom bowl and curved flange are glued into
position on the centre tube. The curved flange of the bottom bowl should
have already been glued and pop riveted to the bottom bowl. If you have
not done this then do it before you glue the flange and bowl into position
on the centre tube.The bowl/curved flange assembly will be glued 75mm down
from the top of the tube.(see figure 9) You will need to leave the glue
dry on bowl/curved flange/centre tube assembly before you do any more with
it. Once you have this assembly in place you will have an assembly that
looks something like figure 10.The bottom flange and centre tube need to
be moved up or down to find the best position. The bottom flange should
not be glued into position until you have completed the motor
mounting section. The final position of the centre tube and bottom flange
depends on your motor size and mounting location.
You will need to have cut
the hole in the top of the wood frame before you can mount the bottom
flange. Once you have mounted the motor and the bottom roller is aligned
centre most under the centre tube you will be able to slide the centre
tube up an apply the PVC glue then move the tube back down to the final
resting place. So only temporarily place the bottom flange onto the centre
tube at this stage.
the bottom bowl/flange
assembly onto the centre tube you can then pop rivet the top electrode
comb into position. The comb can be made from any thin or sharp pointed
metal. You can use a single needle or multiple points as in figure 12. I
use thin (0.1) high tensile shim steel. You can buy shim steel in packs of
various thickness from your local bearing supplies. Use the sharpest edge
shim steel you can get. Cut a piece of shim steel 25mm wide x 25mm long.
Cut one end of the shim steel strip into multiple sharp points with a pair
of tin snips.The more points you can cut into the shim steel the better.
(See figure 12) You can then pop rivet the pointed shim steel onto the end
of a piece of tin 30mm x 120mm long. 
Bend the tin strip into an
'S' shape so you can pop rivet the end of the tin down onto the bowl. You
will have to manually bend the tin in an out as you adjust the electrode
points optimum distance away from the belt. Important: Try to get the
top comb/electrode points as close to the belt as you possibly can. This
will give you the best voltage potential possible. Be watchful that you do
not allow the points of the comb/electrode to touch the belt at any time.
This will blunt the points and cut into the belt. The belt will flex
outwards from the rollers as the motor runs to full speed. So watch that
the points of comb/electrode do not touch the belt when the motor is
running full speed. You will have to do adjustments to the comb/electrode
to make allowances for full motor speed.