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Project: Making Perfect Keyhole Flanges

I know many of those who are into reef keeping have experienced the wish to work with acrylic and build their own skimmer or reactor, or... whatever. Goodness knows, if we could DIY some of the equipment we need, we'd have a lot more money to spend on livestock. But I think that wish often goes unfulfilled because this or that detail of a particular project just seems too difficult for the average hobbyist to manage. I know, for me, it was always the keyhole flanges. You know those cool covers, on top of commercial skimmers and reactors, that are so easy to remove by just loosening a few thumbscrews, .

The trick to achieving a perfect flange (if you don't have a CNC router) is templates

When I first began attempting DIY projects, I often tried my hand at keyhole flanges. It seemed there was always a problem that caused my efforts to be less than successful. Most often, the problem seemed to be one having to do with not being able to locate the holes for the thumbscrews accurately enough. Well, after many disappointing attempts, I finally came up with a simple and surefire way to make perfect keyhole flanges.

The trick turned out to be using templates and, of course, that meant finding a means of making an accurate one. I tried many ways of creating a perfect template. I dug out my old drafting tools from high school - can you believe how long some of us keep things - and tried using compass and straight edge. Most of my attempts were halfway decent, but none were perfect. There was always one or two holes that were just a little bit off, but the little bit was enough to keep the flange from working well.

Creating and printing a pattern of the flange with PostScript

I finally stumbled across a way to create a perfectly symmetrical keyhole flange template. Back in 2003 or 2004, I was reading an old Reef Central thread on DIY skimmers. There on the page was a picture of a schematic of a keyhole flange. The author (I would love to give him/her credit, by name, but I can no longer find the page) described the schematic as having been created using PostScript - Adobe's programming language for printing line graphics, etc. He/she went on to describe the basics of how the .PS file - the file which contains the commands to the printer that cause it to print the schematic for the template - was created.

Well, having a background in computers and data processing, I had some experience with PostScript, but from many years before. The examples the author had given, though, were more than sufficient to allow me to recreate what was necessary. The first thing required was software to read and process the files I adapted. I looked around the internet to see what I could find. I came up with GhostScript and GhostView - software that was originally written by Aladdin Enterprises and released for private use under General Public License (GPL).

Without going into any technical stuff, the pic below, is an example of what a PostScript command file displays, when processed by the correct software. When printed, this particular file will print out a schematic of a keyhole template designed to be used with 4-1/2" OD acrylic tubing. The beauty of PostScript is, and this is the important part, the object depicted on the paper will have the exact dimensions of object to be created:

Notice that the schematic has:

  • Two concentric circles. The outer circle is the circumference of both the flange cover and the lower flange, itself. In this case approximately 7" (4-1/2" for the tube plus 2-1/2" width to accommodate the flange bolts).

  • The inner of the two circles is the inside diameter of the acrylic tube which is to be closed by the flange.

  • Six small equidistant circles - these are where the holes are to be drilled in both the flange cover and the lower flange. They are meant to accommodate 1/4"-20 nylon or stainless steel thumb screws.

  • Six large equidistant circles - these are where the heads of the thumb screws pass through when the flange cover is being placed on the lower flange.

  • A central mark at the exact center of the schematic. This is very important in the construction of the template as will be described later.

Once I had managed to get the first file for 4-1/2" tubing working correctly, it was a simple exercise to replicate the file for use with other tubing sizes. In all, I came up with seven different template files. Tube sizes covered are: 2-1/2" OD, 3-1/2" OD, 4-1/2" OD, 6" OD, 8" OD, 10" OD and 12" OD. After the files were completed I printed out the schematics and proceeded to make templates. I still have, and use, the templates today.

Obtaining the software and data files to create schematics

So, if you wish to try your hand at keyhole flanges, you need to download and install the GhostScript and GhostView software, as well as the PostScript files for the different template sizes:

  1. GhostScript setup file: go here and scroll down towards the bottom of the page. You'll see a large blue header called "Microsoft Windows". There are two files listed for download - you want gs864w32.exe if your Windows version is 32bit or gs864w64.exe if you have 64bit Windows. This is the GhostScript setup file. Download it. When the download dialog window pops up, I would suggest clicking the SAVE button so that you can save the file to your hard drive.

  2. GhostView setup file: go here and look just below the "Obtaining GSview" header. You'll see a number of links. The first one is gsv49w32.exe - click it (gsv49w64.exe if you have 64bit Windows) and download (save) the setup file.

  3. PostScript flange definition files: These files are located on my website, so all you have to do is click here. Note that they are zipped into a compressed folder.

Once you have downloaded the three files, you need to install the two programs (GhostScript and GhostView) and unzip the PostScript template files. To install the programs, just double-click on the files and follow the instructions.

Unzip the PostScript (flange definition) files and place them in a folder of your choice.

You should now be able to view and print the template schematics. To do so, start the Ghostview program. You will be greeted by a screen similar to the one shown above, where the template schematic is displayed.

Note: whenever you start Ghostview you will see the following popup window:

GSView is free for personal use, although there is a fee if you register it, so just click "OK". Do not click on "Register Now".

Using GhostView is very simple and exactly like any other document based program when opening and closing files. Just click on FILE>OPEN, then find the flange file you want to use (they're where you placed them during unzipping).

Once you have a schematic displayed on screen you can print it. And once printed, it is in the form we need to build a template for a keyhole flange - if only life was so simple. The problem arises when we want to make a flange for a tube size larger than 4-1/2" OD. Any larger that that and the schematic will not fit on a normal piece of paper (8-1/2" X 11").

What to do? Well, actually the solution is very simple. If you look at the picture of the schematic, above, you'll notice that the whole thing is symmetrical. If you took two copies of the schematic and laid one on top of the other so that the two concentric circles on the top copy are over the circles on the bottom copy and then rotate the top copy, as one of the equidistant circles (the thumbscrew holes) on the top copy overlays one one of the circles on the bottom copy, all other thumbscrew circles will also match up.

This means that in order to create a template schematic where the diameter of the template is larger than the size of the printer paper, all you have to do is print enough copies of the schematic to allow the piecing together of a complete schematic using a number of prints. Once you have all the lines and circles perfectly aligned, use Scotch Tape to hold the pieces together.

One final note on this very simple but, difficult to describe, procedure: At times, when having to piece together copies of a schematic, it may be better to use a landscape printer orientation than a portrait orientation. I won't even try to explain why - just change orientation and note the difference in what can be printed on one page and you will immediately see what I am alluding to. BTW - you can change the printing (and display) orientation by using the "ORIENTATION" menu item at the top of the GhostView program window.

Tools you'll need

First, let's talk about the tools needed to proceed. Admittedly a fair assortment of tools are required to be successful at template building. BTW - I'm not listing things like hammer and screw drivers, etc. So, taking that into consideration, here's what's required:

  1. Some means of cutting wood.

  2. A drill press - doesn't really matter if large or small. Quality is also not really important, but without a drill press, it would be a no go.

  3. Either a full fledged router table or a router that you can mounted beneath some kind of fairly sturdy table. As for motor size, a router with 1-3/4hp or more will do fine.
  4. Plunge router

  5. Router bits - 5/16" straight bit and  1/4" spiral flush trim bit like these:

  6. Circle cutting jig that can be attached to the router. I would recommend a Jasper 200 jig like this one:

    It makes circles from 2-1/4" to 18-3/16" in 1/16 inch increments and really makes the job easy and enjoyable - and the price is reasonable.

  7. Drill bits - 1/8" normal, 5/8" forstner
  8. 1/4"-20 thread tap and matching drill bit (13/64 or no. 7) and tap wrench. This is only necessary if you want threaded holes in order to be able to screw in the thumbscrews. If not, you can use a 9/32 drill bit and thumbscrews with wing nuts.

Making flanges, templates and the materials needed

My preferred material for making templates is 1/2" MDF (medium density fiberboard). It is very easy to work with and inexpensive. MDF is usually obtainable at big box stores such as Lowes and Home Depot. If you can't find it there, check out the nearest lumber yard or plywood specialty store. The following lists materials for both templates and flanges

  1. Cast acrylic for the flanges. I normally use 3/8" stock, although some hobbyists prefer 1/2". The decision, of course, is yours. Color makes no difference as far as functionality is concerned - I like the way black looks.

  2. 1/4" silicone o-ring stock. I've found that silicone makes the best o-rings. Here is one of the better sources: McMaster-Carr. Search for "silicone o-rings" then choose (click on) "cord stock". Then choose (click on)1/4". Then choose (click on) red-orange color.

  3. 1/4"-20 nylon or stainless steel thumb screws. Nylon is much cheaper than SS and has always worked fine for me. If you're not going to thread your holes, you'll need wing nuts. Again, either nylon or stainless steel.

  4. 1/2" MDF for the templates.

  5.  3/4" MDF for misc. steps during the template building process.

So let's build a keyhole flange template

We'll be making a template for a 3-1/2" dia. acrylic tube, so let's go through the process step by step:

  1. Print three copies of the 3-1/2" template pattern using the GhostView profram.
  2. The first thing we need is a piece of correctly dimensioned stock. The flange is 2-1/2" larger than the 3-1/2" tube. We need a little extra to work with, so a 7" square piece of 1/2" MDF would be about right. After you have cut out the square, make an octagon out of it by cutting off the four corners. Cut just enough off so that all eight sides are equidistant from the center.

  3. While being worked on, the template stock will need to be mounted on a base of scrap 3/4" plywood or MDF - about 12" square would be good.

  4. Using a 1/8" drill, drill a hole approx. 3/8" deep in the center of the 12" square base you just cut. When finished mount a 1/8" dia. pin in the hole.

  5. Again, using a 1/8" drill, drill a hole, dead center, completely through the template stock. When finished, mount the template stock on the base by placing it over the pin.  This allows us to rotate the template on the base. It should look like this:

  6. Take a copy of the template pattern and cut it out of the page with about 3/8" overlap. Drill or cut a 1/8" hole directly over the center mark. Lay the pattern on the template stock by placing it over the pin. Using tape, Scotch brand works fine, fasten the pattern to the template stock:

  7. We are now ready to start drilling the template. The first thing to drill are the holes representing the threaded holes in the flange base - the part permanently attached to the acrylic tube. The holes need to be dimensioned so that 1/4-20 threads can be cut in the acrylic. This requires a 13/64" drill bit. The drill bit and tap can be purchased as a set:

  8. Mount the base and the template on your drill press so that when the 13/64" bit is lowered to the work piece, the drill is exactly centered over the smaller set of holes on the pattern. Like this:

    The best way to mount the base on the drill table is to use a fence. So, we're ready to drill the first holes. This video clip illustrates exactly how to go about drilling the 5 required holes:

  9. Once the holes are completed, remove the pattern from the base, cut a new pattern from its page in the same way as you did the first. Drill the 1/8" center hole in the pattern and place it over the pin. Now we have to position the pattern on the template stock correctly. Rotate the pattern around the pin until one of the small holes, on the pattern, is 5/8" to the right of one of the holes we just drilled in the template stock. Again, tape the pattern to the template so it cannot move.

  10. Mount a 5/8" forstner bit in your drill press and mount the work base and template, in the same position it was before, against the fence. If the base is in the exact same position as when the thread holes were drilled the holes for the thumb screw heads will also be positioned correctly.

    MDF is a very dense material. Applying excessive pressure when drilling with a large drill, like a forstner bit will cause heat from friction. So much heat that you can actually ruin your bit. So avoid using too much pressure, and back the bit out of the hole every three or four seconds to allow the heat to dissipate. If material accumulates in the bit, stop every so often and clean it out.

    When completed, remove the template from the base and the pattern from the template. Your template stock should now look like this:

  11. Grab an unused template pattern - that's why we printed three of them. Measure the distance from the left edge of a thumb screw hole to the left edge of the adjacent thread (small) hole. Using a ruler, mark the distance, just measured, on the template stock, and mark it with a pencil. Do the same for each thumb screw hole. When your finished, the template should look like this:

  12. Notice that the work base has been scored by the forstner bit where it emerged from the back of the template stock. Before you remove the forstner bit from the drill press, drill a hole completely through the base, right where the bit's score mark is.

  13. Insert a 5/16" straight bit in the router mounted on your router table. Assuming the work base you have been using is 3/4" stock and the template is 1/2" stock, the bit should protrude between 7/8" and 1" above the router table work surface. Place the work base on the router table and adjust the fence so that when the hole you just drilled in the base is placed over the bit, the bit is centered exactly in the hole. Place a stop, of some kind to the right of the work base so that it cannot move laterally, along the fence.

    Place the template on the pin in the work base. This is what it should look like:

  14. Ensure that, when the work base is positioned correctly against the fence and the bit is centered in the thumb screw hole. Ensure the bit is set high enough that it will cut completely through the template stock. Turn on the router and rotate the template clockwise until the left side of the bit just contacts the pencil mark. When you have finished the cut, while carefully holding the stock still, turn off the router. Continue to hold the stock until the bit stops completely - DO NOT try to remove the template stock before the bit has stopped. When the bit has stopped, pull the template off the base and move to the next hole. Turn the router on and make the next cut. Repeat the process for each hole. Here is a video clip to clarify:

    The template now looks like this:

    All that's left is to make the template round.
  15. You'll need a base for the template while it is being cut into a circle. You can utilize the work base you have been using, although I prefer to have one at lease 4" larger than the template, on all sides.

    Get a couple pieces of double sides tape and place it on one side of the template. Then stick the template to the middle of the base. This will hold the template while you cut it with your router.

    Mount your Jasper Circle Jig (or whatever jig you will be using) on a plunge router. You will be using a 1/4" straight bit.  When the bit is at the bottom of its travel, it should cut through the template stock + 1/16".

    Set your jig so that the circle it cuts will result in a template that is 3/4" to 1" larger in circumference than the the outer edges of the thumb screw holes. In other words, the outer edge of the template is 3/8" to 1/2" from the outer edge of the thumb screw holes.

    Note: whichever circle jig you decide to use the center pin should be 1/8" in diameter so that it fits in the hole in the center of the template.

    This video clip illustrates the procedure:

    And here's what all the hard work accomplished:

    The extra hole, in the middle, is used to hang up the template on the wall. I have 1/2" dowels on which all my template are stored.

Putting the template to good use

To use the template to make a flange is very easy, compared to making the template itself. I normally use 3/8" cast acrylic sheet when making flanges.

 Then, to complete a flange  I follow these steps:

  1. Rough cut two circles out of the stock acrylic. I make them about 1/8" larger than the flange itself.

  2. Mount the template on the first piece of acrylic with double sided tape.

  3. Using the "threaded bolt" holes (the small isolated holes) in the template, as a guide, drill the holes in the acrylic with a 13/64" bit.

  4. Mount a 1/4" flush trim bit in your router table. Trim around the template to create a circle. Remove the template from the acrylic.

  5. Use a 1/4-20 tap to cut the threads in the holes you just drilled.

  6.  Set up the Jasper (or any other circle cutting jig) to cut a circle with a diameter equal to the OD of the acrylic tube the flange will be used with. Using the center hole in the acrylic flange as the center of the circle to be cut, proceed to cut the center out of the flange blank.  The bottom half of the flange is finished.

  7. Mount the template on the second piece of acrylic with double sided tape.

  8. Drill a 3/8" hole in the middle of each "thumb screw head" hole in the template.

  9. Place the template/acrylic work piece on the router table, acrylic piece down, with the bit centered in one of the holes you just drilled. Make sure the bit is high enough so that the rollers fully contact the template and that the blades make full contact with the acrylic.

  10. Cut out the inside of each template opening. Make sure to move the work piece in a counter-clockwise direction. Otherwise you would be making a climb cut - not a good idea. When finished with all the holes, remove the template from the flange.

That's it! Very easy once you have the template. Have fun.

Oh, before we close up shop, here's an example of what you can produce using one of these templates - just like downtown...



1 2 > [last]
Ryan H says...
glad i came across this, kudos to the author for the detail...bookmarking this site for sure
17th February 2015 4:40pm
Charles says...
Thanks, that was the problem.
4th June 2012 2:13pm
Brynell says...
Boy that rlaley helps me the heck out.
13th January 2012 12:01am
Charles says...
Trying to change some numbers for the 4" tube flange and keep getting an error (don't know what I'm doing). I opened up ghostscript and put in the numbers, 13 .25 6 4 6.125 5 .252 .52 flange, made #6 6.125 and #7 5 to make it a little smaller. Pls help. Thank you for a sharing and your time. Great informative site.
GlassReef: Hi Charles, I took a look at your problem. I show the 7th parameter in the file (the bolt diameter) to be .252 (a little over 1/4"). If you change that to 5 (5 inches), you will get your flange covered with six 5" circles. The boly hole diameter should be left at the given size, as it is intended to accept 1/4"-20 thumb screws. Does this explain your error? If not, please advise exactly what kind of error you are getting.
21st November 2011 1:14pm
Dana Draeger says...
Thanks I figured it out!
GlassReef: Great! Glad it worked out for you.
25th September 2011 8:11pm
1 2 > [last]
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