I have just built an exposure lamp setup so I thought I'd share some details for members that may be interested or find details that may be of use for their own projects.
I got the idea for the basic design from eBay where people are selling metal units based on a halogen lamps. I noticed that the design of these units was just a halogen lamp mounted on a simple frame and thought I could fairly easily make a similar frame out of wood and fit my own lamp. I have basic skills in DIY and woodwork but completed the unit in about a day with no major problems. The total cost for the lamp (1000w with 2 bulbs), metalware and wood was less than £30 (about $60) and about a third of the price of the eBay version. For people with their own timber and a few bolts and screws the price could be even cheaper.
The unit has a baseboard large enough to take a screen 25 inches tall and the lamp height can be adjusted with a simple clamp mechanism up to a maximum of about 40 inches. To expose screens you will also need a piece of dark coloured sponge (bought from a furniture upholsterer or eBay) to support the squeegee side of the screen, and a piece of glass to hold the transparency tightly against the print side of the screen.
I will post complete details of the design if people are interested, but for now here is a picture of the prototype unit (apologies for the poor-quality phone-camera picture).
OK here are some more detailed instructions for building the exposure unit.
The most complicated part of the unit is the adjustable clamp and lamp unit but I designed it to be really simple to construct and operate. This part is the cross piece that actually has the lamp mounted on it - it can be raised and lowered by sliding it up and down the vertical side 'rails' and locked into place when in the right position.
The first thing I did was buy a lamp so I could find the best way of mounting it on the clamp bar. I ordered a 1000w halogen security lamp which produces the right sort of light and enough power to expose emulsion on screens. Once it arrived I took it apart by first opening the glass cover 'door'. Inside was the reflector which is held in place by a single screw.
Once the screw is removed the reflector can be lifted out by easing it past the two ceramic bulb mounts. Inside is the bulb mounting bracket held in place by two screws:
These screws are only very short and screw into the inside of the lamp casing. Once removed the lamp bracket can be moved to one side (it is still connected to the lamp by wires):
These screw holes provide an easy point to drill through to the outside of the lamp case and provide a way of mounting the lamp on the clamp bar. The case is only a few mm of aluminium and is easily drilled through with a steel drill.
Now replace the original screws with longer screws (or bolts if you prefer) which are then used to both hold the bulb bracket in place and mount the lamp on the clamp arm. You can see the wood screws I used in the photo - they are visible because I took the picture after I had finished building the unit which was then dismantled so I could get some photos. Attach the lamp to the clamp arm (instructions on how to make this follow), replace the reflector, put a bulb in the lamp and reattach the lamp cover and that's the hardest part done.
Make sure you do not touch the glass of the bulb when you put it in the lamp, if you get dirt or grease on the glass it will blow when it is turned on - use a clean handkerchief or something similar.
This method was chosen to work with the lamp I bought - if your lamp is different you may have to find another way to mount it on the clamp arm. The bracket that came with my lamp was no use because the lamp was designed for wall mounting and the supplied bracket could not be adapted for this project.
Now that you have a way of mounting the lamp you need to build the clamp arm itself. Here's a picture of it:
The design of the clamp arm is fairly self explanatory from the picture. The centre piece of the arm is where the lamp actually screws onto and is much shorter than the overall length of the arm. Crucially the thickness of the centre piece is the same as the thickness of the side rails so the entire arm fits snugly around them.
The two outer pieces of the clamp arm are made of flattened wood which can flex slightly. The flexing movement is used to provide the clamp action of the arm controlled by a bolt and wingnut at each end of the arm. The gap between the bolts is such that the clamp arm can be fitted comfortably around the side rails with only a small amount of movement possible - less than 0.25 inch.
The bolt fits tightly into the back side of the clamp arm but very loosely in the front side (the wingnut side). This makes it much easier to adjust the clamp because the bolt is held in position by the back arm and cannot turn freely, whilst the front arm can move over the bolt with no resistance when the wingnut is adjusted. This clamp action is easy to use and is rock-solid when tightened by hand. Put washers where bolt-heads and nuts meet wood to stop them sinking into and damaging the wood.
The three wooden pieces of the clamp arm are simply bolted together (or screwed if you prefer). Make sure that the bolts used to hold the arm together do not get int the way of the screws that hold the lamp onto the arm. If you look at the photo you'll notice that mine are very close, but I got away with it (by sheer luck).
I used 75mm long 6mm (M6) bolts both for the clamps and to hold the arm together.
In my unit the distance between the rails and the size of the base board is 25 inches, because this is big enough to hold the screen lengthways in the same orientation as the lamp bulb itself. If you need more space you can easily make a larger unit, though there may be a limit to how well a single 1000w lamp works with larger screens.
More info about the base unit and side rails soon which is much simpler than this part!
Last edited by mrobsessed; October 23rd, 2007 at 09:20 AM.
Here is the final part of the construction details of the lamp - the side rails and the base unit. This is fairly self explanatory but I will provide notes for those that may find them useful.
The Base unit itself is just a piece of board large enough to hold the largest screen you want to expose. I don't need screens larger that 24'' (longest side) so I made the baseboard 25'' long - thats the distance between the side rails - and about 20'' wide.
To give the base some weight and stability I screwed it onto three beams of square cross-section (1.75'') wood from the board side using countersunk flat-headed screws - these will screw down flat into the board surface.
You may notice from the photos that the base beams protrude from under the base board. This was not intended and is purely due to me changing the design after I had the wood cut to length in the timber shop.
I had originally intended to have the 3 beams pointing the other way, ie the same direction as the clamp arm with the side rails attached to the ends of the middle beam. I realised that it would be better to attach the rails to the sides of the two end beams which would give a flatter and squarer position to fix them, so I altered the design slightly. Because the beams are longer than the width of the base board they protrude, and while this looks messy there was no real point cutting them down to the size of the base board as it didn't affect the end result.
Next the side rails have to be fixed to the base section. The side rails are just squre cross-section (0.75'') wood that is long enough to hold the lamp the correct distance from your screen.
The lamp to screen distance has to take into acount the total thickness of the base unit, the thickness of the screens being exposed and the depth of the lamp and clamp arm. I chose two 4 foot pieces of wood which gives me about 34" of distance from screen to lamp.
Using the light distance = diagonal size of screen this is only just big enough for my purposes but adequate. A 20'' x 24'' screen needs 32" of distance using the diagonal rule. You may want to give yourself a little more height to work with, like 4.5 or 5 foot rails if you think you may need this - if you want to expose larger screens you will have to work out a rail length that works for the screen size you want to expose.
The most important thing about the rails is that they are the same width as the centre piece of the clamp arm so they fit snugly inside the clamps at each end.
To fit the rails I used plastic cupboard fixing blocks which are available in any DIY shop. I sandwiched the rail between two of these and taped them into the correct position, then drilled a hole through the rail using the centre hole of the blocks as a guide. Then I removed the tape and bolted the blocks into the same position using a 50mm M4 (4mm) bolt and nut. finally the rails are screwed into the side base beams making sure that they are correctly positioned and vertical.
This gives a strong fixing for the rails and the unit can be dismantled easily if needed to be moved. The picture of the rail mounting above pretty much speaks for itself.
Finally a cross piece joining the top of the rails adds some rigidity to them - I fixed mine with metal corner brackets but as with the rails themselves there are dozens of ways to attach these parts to the rest of the unit and you may have a method that works better for you.
The clamp arm can be fitted by removing the end clamp bolts and rotating it into position, slotting the rails between the clamp jaws and replacing and tightening the bolts.
I wired the lamp up to an electrical flex - make sure this can safely take the wattage of the lamp - and fixed the flex to one of the clamp jaws using a zip tie. You may also want to fix the flex to one of the side rails so that it doesn't cast a shadow on the screen during an exposure.
Needless to say with apparatus made out of wood that uses a lamp that gets very hot - NEVER LEAVE THIS EQUIPMENT UNATTENDED WHILE IT IS BEING USED.
Hope this is of use for some of you - if you need any more help let me know!
I don't know, I have not used it yet. I am new to screen printing and am still getting the equipment I need together to start work. I dont have much of a budget but so I am trying to build whatever equipment I can myself so I can practice on a basic setup before investing in more expensive equipment. The next project will be a basic press, maybe a 2 or 4 colour machine. If it works out I'll post the details for that on the forum as well.
I expect that the exposure time will be about 10 minutes or maybe less.
My exposure set up is just ,like this one except I painted my board black I find it helps me get crisper lines. This setup is for the hobbyist and if you plan to do any amount it may be worth an investment ans exposure up grade. My exposure time is 11 min but that will very.
If you were to replace your 1000w halogen light with a 1000w Metal-Halide lamp (you'll need to add a shutter which can be as simple as a piece of wood that slides out of the way), your exposure times will drop drastically. Metal-Halide lamp units can often be had from the garbage cans of lighting/electrical contractors. Many large open-bay buildings are replacing them with more energy efficient units. Halogen lights do work, just very slowly. The reason is; it is the UV light that exposes the emulsion on the screens and halogen lights are one of the poorest sources of UV light. In fact, halogen lights give off more energy in the form of HEAT then they do as LIGHT. I have a metal-halide unit with a 1000w bulb and I get properly exposed screens in the 18-20 second range.
I use a very similar setup with a 500W halogen, about 18" height and expose QTX in 5 minutes. However, I had a problem tonight, so maybe thats a little low in some cases...
Edit: Can you explain a little more about the shutter needed for the metal halide, ftemb?
Most metal-halide bulbs are NOT a "hot-restrike" type bulb. There are very new commercial exposure units that have hot-restrike bulbs, but not many. Most exposure units using a metal-halide bulb incorporate a shutter, because the bulb must be allowed to burn for quite a while before it reaches maximum intensity. In the home built unit at the top of this thread picture in your mind a slot somewhere between the bulb and the glass on which the screen is placed. Into that slot all you need to do is slide something (a piece of plywood, sheet metal, etc.) that COMPLETELY blocks the light from reaching the screen. That is your shutter. Slide it open to expose your screen and slide it shut to stop exposing.
I don't know, I have not used it yet. I am new to screen printing and am still getting the equipment I need together to start work ..... I expect that the exposure time will be about 10 minutes or maybe less.
Noel, I'm also in the UK. My exposure unit I think is one of the ones you saw on eBay, I got it as part of a kit. I'm also just setting up, so I haven't used it yet. It didn't arrive with any usage instructions (times and distances) but I have emailed them for some. When they arrive I will post them. Dave
Noel, I'm also in the UK. My exposure unit I think is one of the ones you saw on eBay, I got it as part of a kit. I'm also just setting up, so I haven't used it yet. It didn't arrive with any usage instructions (times and distances) but I have emailed them for some. When they arrive I will post them. Dave
Noel, I got some instructions, and have quoted them below. However, I had read somewhere about removing the glass on the lamp, as they are usually have some UV filtering in them. Did this and did a test strip. On a 24" x 19" screen from 23" above the screen it took 6 mins!
Original instructions were: "Distance from screen to lamp should be no less than the screen internal diaganol.
Screen with a 33" internal diagonal, set distance from the lamp to the glass 33", exposure time is approx 35 mins. 20" x 24" screen as same distance would also be 35 mins, or, at 23" distance would expose in approx 20 minutes. There are many variables that could affect exposure time, so you should always do a test exposure strip."
If you were to replace your 1000w halogen light with a 1000w Metal-Halide lamp (you'll need to add a shutter which can be as simple as a piece of wood that slides out of the way), your exposure times will drop drastically. Metal-Halide lamp units can often be had from the garbage cans of lighting/electrical contractors. Many large open-bay buildings are replacing them with more energy efficient units. Halogen lights do work, just very slowly. The reason is; it is the UV light that exposes the emulsion on the screens and halogen lights are one of the poorest sources of UV light. In fact, halogen lights give off more energy in the form of HEAT then they do as LIGHT. I have a metal-halide unit with a 1000w bulb and I get properly exposed screens in the 18-20 second range.
Ftembroidery, did you find that 1000Watts was a tad bit overkill? couldnt we get by with a 400watt metal halide? my exposier times would still be under a minute right?......no? 1000watts MH is going to be hard to find like you said, but im finding 400watt MH all over the place for $40-50 (not including bulb)
I know of a fellow printer that uses a 400W M-H light for exposure and does just fine. It hangs over his compression lid unit and has a home-built shutter of wood that slides in & out to block or allow the light to expose the screen. My 1000W M-H unit is a commercially made unit for printers (OLEC is the company) with an automated shutter that I got off eBay for a very good price along with the integrator that operates it by the same company (OLEC or OLITE).
Here's my high-tech exposure unit (over my top of the line drying unit). Piece of glass laid over the screen, 20" exposure height. 500W halogen light with glass removed.
5 minutes even with QTX. I exposed some pretty fine lines today, but some of the edges curled during washout. Working on a DIY vacuum unit I saw somewhere else on the net.
Plans for Homemade Exposure Lamp 
