Kitchen Table Workbench
If you're into building or repairing electronic equipment you'll need somewhere to do it. This is a neat solution that takes the form of a non permanent worktop that can be placed over a kitchen or dining table to create a workbench that can be easily stored away after use. A protection sheet placed underneath will stop the table from getting scratched
It consists of a rear module made from white conti board with a couple of mains outlets and a master cut off switch mounted on it. This also functions as a shelf for test equipment or components etc. In front of that is the worktop itself which is a sheet of 1220mm x 606mm x 3.2mm white faced hardboard. The size of the work surface depends on the table it's going to be used on, but I chose these dimensions as they are a standard size available at my local DIY store which also suited the table
The workbench can be stowed away after use
Most of the building time is spent on the construction of the rear module/shelf which is made from two lengths of white 2440mm x 152mm x 15mm conti board cut down in length to match the size of the worktop. I used conti board because of its low cost, but the downside is that it's a pig to cut with a saw without chipping the surface. If you haven't worked with this stuff before then have a practice first. When you buy it the ends are generally rough anyway, so this is a good place to start honing your skills. My tip is to first mark with a pencil where you want to cut and then score it with a Stanley knife. I suggest doing this all the way around the board, in other words, on all four surfaces. Even the knife can cause chips so start lightly and then gradually apply more force until you clear the surface and are through to the chipboard underneath. This should be enough. With this material it is very unlikely that the top and bottom faces will end up with a clean cut. The top face will be the neatest, so take this into account when preparing what is to be visible on the finished unit. To cut out the holes I used a jigsaw fitted with a worktop blade which cuts on the upstroke. This reduces chipping on the top face. Do not saw along the score line but instead go just to the side of it then use a file to finish up to the line later. I found that filing a shallow bevel along the score line also helps combat chipping when filing near it. Finish off with light sandpaper and check the cut for squareness. If all is well you can call yourself an expert and have a cuppa!
A recessed batten is used to ensure the whole thing doesn't fall off the back of the tabletop
The design of the workbench is such that as few ends as possible are visible. In fact the only ends that need to be finished properly are those of the top shelf, although I did do the bottom of the end pieces as well... but that's just me! The visible ends are finished off with iron on edging strip. I actually found this the most easy and satisfying part of the project. Just take your time and make sure a fresh blade is used when trimming away the excess. Standard dry lining back boxes were used to mount the switch and sockets onto the front face. The type and number of sockets is down to personal choice, but I thought 4 outlets was enough. The thickness of the conti board is 15mm which is right on the limit of what the back boxes can be mounted on. Manufacturers may vary but the ones I used (purchased from Screwfix and made by Appleby) just about clipped into place. Other countries may use a different method to the UK. To accurately cut out the holes it's best to first make a paper template and then use this to mark where the boxes are to go, as before, marking with a pencil and then scoring with a knife to reduce chipping when cutting out with the jigsaw. This doesn't have to be so neat because the sockets will cover any rough edges. One thing to be aware of while cutting out the holes is that the conti board becomes quite fragile at those points and the surface can crack if too much downward force on the jigsaw is used, so the board will need to be supported horizontally
6 Amp IEC inline plugs and sockets are used to connect the mains isolation transformer
For assembly I used the easy option of 90 degree PVC angle brackets to secure everything together, though care must be taken to position everything accurately. This method of construction also ensures that there are no metal screws visible or accessable to touch, which is good for electrical safety. Two strips of sticky felt were added at the back to act as a buffer between the unit and wall. And that's it for the woodworking class. All that remains is the electrics. Now of course you know at this point I'm going to say that if you are unsure of electrical wiring you should not attempt this yourself, and that it should only be carried out by a qualified electrician and that there are lethal voltages involved, so there... I did
The ideal workbench should have several barriers of protection for the user:
1) The mains supply to the bench should be fed via an ELCB (Earth Leakage Circuit Breaker)
2) The mains supply to the equipment you are working on should be fed via an isolation transformer
3) The floor should be insulated to separate you from earth (wearing safety shoes also helps here)
4) The work area should not be within easy reach of earthed metal objects
The transformer should negate the need for items 3 & 4, but transformers can fail so it's better to be safe than sorry
The wiring diagram is shown below (the transformer connectors have been omitted for clarity)
The fuse, switch and neon lamp are all part of the switch plate assembly. The red double socket is raw (un-isolated) mains which can be used for running already isolated test equipment (no need to load our isolation transformer unnecessarily), and the blue double socket is isolated mains which should be the only socket ever used to power equipment being worked on. Note: on the actual unit the raw mains is the socket on the right and the isolated mains is the socket on the left, not as shown on the schematic
Isolation transformers can be quite expensive, but you can bag yourself a bargain by searching on eBay. Look for something in the region of 500 to 1000 Watts power handling. It depends on what you are going to be working on of course. To house the transformer (some are encased already) I used a plastic storage box from Homebase, with the cables entering and exiting through strain relief grommets (B&Q) as used by aerial riggers to bring coax into the house through the wall. The transformer was bolted into place by 6mm x 12mm roofing bolts which are cheap and have larger than average heads. As the transformer gets quite warm, even when idle, a plastic louvre vent was fitted in the lid of the enclosure to let heat escape. The whole thing looks neat and is very cost effective
The mains isolation transformer housed in its plastic enclosure
Due to its weight, the transformer would render the workbench difficult to move about if it were built in, so it's mounted externally and connected/disconnected using 6 Amp IEC plugs and sockets which also allow it to be bypassed if not required. I also use a plug adapter type ELCB as well as relying on the house ELCB
In the UK, mains outlets used in service workshops are generally colour coded red for raw (un-isolated) mains and blue for isolated mains, but I just labelled mine with red and blue text accordingly. I'm aware that in the photo there is a central heating radiator nearby at earth potential, which although the isolation transformer should protect against, is not the ideal situation. Earth leakage trips are now fitted by law in new homes, but if you don't have one, the next best thing is to use one of the small plug in types used for garden appliances which are not too expensive to buy... not that you can put a price on safety. Always remember though not to let all these safety measures give you a false sense of security. If you connect yourself across the two mains terminals you can still die!
So there it is... an easy to make workspace where you can build all your electronic goodies!