Introduction: Screen Print Shop Part 1: ShopBot Silk Screen Printing Frames

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I'm setting up a screen printing studio and one of the things needed in quantity are screen printing frames. I could cut up wood and assemble them into frames but that would be time consuming and expensive. If you have access to a ShopBot or similar CNC router table you can make a large quantity of frames quickly and cheaply. I will assume in this instructable that you know how to use all of the equipment already.

Tools:
ShopBot with a 4'x8' bed or larger and associated tooling
Cordless drill and wood screws (for hold downs)
Table Saw (with adjustable guard), router (with adjustable guard), or ShopBot end mill that can cut 1/8" groove

Materials:
4'x8' sheet of plywood, preferrably high quality with good dimensional stability, 3/4" to 1.5" thick

If you're wondering why I have a ShopBot and other fun tools but am making my own frames its because I made it at TechShop where I have access to all these tools (techshop.ws).

Step 1: Make Your File

The first step is to lay out your frames in your CNC software of choice. 2" thick frames are a good size of strength. I went with square frames, starting with 24"x24" squares and nesting squares 4" smaller than the previous one.

If you wish, you may download and use my file: https://docs.google.com/open?id=0B6tM1GvaYXt3SUlLTWV4TEI4cjA

In my picture:
The rounds are drill holes to use as hold downs.
The lines highlighted in pink are the spline grooves, these are optional and I recommend only using these if you have a router bit that will cut a perfectly sized groove for your spline. Something between 0.125 - 0.19 " (you can get a variety of splines to fit groves in that range from the local hardware store). 
The black squares are the frames. By nesting frames you can cut a large amount out of a single sheet of plywood. In this case there are 6 20"x20", 6 16"x16", 9 12"x12", 9 8"x8", and 9 4"x4" frames.

If the plywood is warped at all the frames will pop up when they get cut out and can potentially damage the ShopBot. You may want to liberally add screws, or, in my case, use lots of tabs.

Step 2: Cut Out the File on the ShopBot

Throw your plywood onto your router table and get to work!
I assume you know how to operate it.

I used a 1/4" upcut end mill. This has left a messy cut that will require some sanding to clean up.
I also thought that I could pick up .25" spline at the local hardware store (turns out I can't) so I routed 1/4" grooves into the frames as well. If you have a tool that will cut appropriately sized grooves this would be a good time to do it, otherwise, skip that step and just cut out the frames.

Step 3: Clean Up the Frames

Since I used tabs to keep the frames in position while they were being cut out I need to sand the inside and outside edges of the frames to clean them up. A spindle sander happens to be a great tool for this job. You can finish it up by hand or with a hand sander.

Step 4: Cut Out Grooves

You could use a router for this step, or the shopbot. I used a table saw with adjustable guard.

Most circular saws have 1/8" kerf which should make a perfect grove for a 0.125" spline. Turns out that its not actually a perfect groove and is too tight. Now would be a good time to decide the size of the spline you want to use. 0.125" spline is the smallest available spline. Since I thought I would be able to just cut a groove leave it at that I purchased 0.125" spline. In restrospect I should have went with a thicker spline since it would be more forgiving of differences in groove size. 0.170" would have been nice.

Start by setting your guard to 1/2" or whatever your preferred position is.
Adjust the height of the blade to cut a groove deep enough - you want your groove to be deeper than it is wide.

Run each side of the frame down the blade to cut a groove, making sure to press down evenly as it passes the blade so the groove is not cut too shallow.

Once you have done all of the first passes go ahead and cut some grooves in a piece of scrap wood.
Adjust the guard - in my case I tried to move it 1/32" - and run it down a groove in the piece of scrap wood - this will widen the groove. Test your spline to see if it can fit in the groove and is tight. You need to be able to fit the spline in, but you need it to be tight or else the screen will pull the spline out when you try to tighten it. There isn't much room for forgiveness.
Adjust back and forth as necessary until you achieve the optimal groove width.

Run second passes on all the frames.

Step 5: Stretch Some Screens!

You're done, hopefully! If you've cut the grooves right you can now lay some screen on the frames (in the pictures I am using $2/yd organza).

I suggest wetting the fabric first to make it easier to stretch.

Insert spline on one side with a spline tool.
On the opposite side pull the fabric taught (if you pull too tight you'll rip the fabric as you push the spline in), and put the spline in.
Turn 90* and pull tight and spline and repeat for the last side. If the screen is loose in any position pull out the spline slightly and pull it tight and insert the spline again.

If it looks light the frame below and is nice and tight then congrats!