Parts List:
● 2 meters of natural 2 ply rubber upholstery webbing, non-stretch. ● 1 x small tube of contact cement
● 1 x sanding block an 80 grit sand paper
Rubber Belt Splice
figure 19
T
he vandegraff belt is manufactured from a 1400mm piece of non-stretch type rubber upholstery chair webbing. Note : the rubber must be the natural beige colour an of the correct non-stretch type. Do not use the elastic stretch type or black coloured webbing as this may not build a static charge. Or if the belt stretches to much it may not stay fix to the rollers during operation.The non-stretch webbing used inthis design comes in large length rolls by 50mm wide. Ask at the shop where you purchased the rubber webbing to cut at least 2 meters off the larger roll to ensure you have enough length. Remember, a belt 650mm long will need about 1.4 meters of webbing. This 1.4 meter length includes the two 50mm splice joins at either end of the belt. (see figure 19) Do not be afraid to order too much. The webbing is 50mm wide, once the rubber is trimmed down there will be enough webbing to make two complete vandegraff belts each at 20mm wide.
Trimming The Rubber
We will not be using the entire width of the belt so it needs to be trimmed down its entire length.Using a long metal straight edge, clamp the rubber webbing an straight edge to a firm flat bench top or length for wood. Using a sharp knife or blade, cut a 20mm wide strip down the entire length of the webbing. This will leave you with a belt 20mm wide by 2 meters long. Before you cut the belt to its final 1.4 meter length, it is a good idea to put the belt into the correct position on the vandegraff frame and roller mounts to see that you have the correct length to cover the distance around both the upper and lower rollers. If you are confident the belt is long enough then cut the belt to its final length. Do not forget to allow extra length on the belt for the 50mm splice joins. The rubber webbing is made 2 plies thick, separate 50mm of the ply from each end of the belt (see figure 19 ). It is important that you trim the two unused splice tabs from the correct side of the 50mm splice. Be sure the belt is layed out correctly and that there is no twists in the belt. You must remove one 50mm splice tab from the top of one end of the belt, an the other 50mm splice tab from the bottom of the opposite end of the belt
(see figure 19 ). If you get these cut off tabs wrong the belt will not glue together correctly. Be sure to leave the string fibre layer inside the original ply on at least one of the 50mm tabs. If you don't the belt will stretch at the join and may break. Now using an 80 grit sand paper an a wood sanding block, sandpaper a taper at the end 50mm location of the splice tab cut and the main part of the belt. (see figure 19 ) This taper will allow a stronger lump free join in the belt. Its important to get no lump in the join so the belt will run around the rollers with out vibration to the vandegraff unit. The belt can run at a good speed so you want to get this splice correct.
Splicing The Belt Ends Together
You should be ready to glue the ends of the belt together. Add liberal amounts of contact cement to both ends of the 50mm splice tabs. Wait for a period where the contact cement feels tacky an almost dry to touch on both tabs. Slightly stretch the 50mm tabs of the belt and place the ends together to contact each other at the glue.When placing the ends together allow about 2mm of overlap from each end of the tabs. You will sand this 2mm lump off 24 hours after the glue dries. Make sure you have no twists in the belt when you place the joins of the belt
together. Before the glue dries clamp the glued join between two lumps of wood firmly in a vice or clamp. Important : do not over tighten the vice or clamp else the pressure will squash the glue and rubber permanently out of position. Allow the glued join of the belt at least 24 hours to dry between the clamp before you attempt to do any thing further with it. After the glue has dried, sand paper the 2mm over lap lump off each end of the join until no lump is felt on either side. If your join has moved sideways in the clamp simply trim off any excess rubber sticking out from either side of the belt. Your belt should now be ready for use on your
Vandegraff generator. Take particular note of which way the join splice end overlap travels when you place the belt on the generator. You do not want the sand papered join of the belt hitting the rollers foremost before the rest of the join. You must have the natural section of the belt travel over the rollers first before the sand papered join contacts the rollers. This will prevent the very ends of the join from coming loose at high speed. Be sure of the belts correct orientation and direction of travel around the rollers.