When the school I teach at finished a new campus and moved into it, I saved as many of the large cardboard tubes from flooring that I could. I'm an art teacher and I always try to save good junk, even if I don't know what I'll use it for. The last time our school moved, more than ten years ago, I saved some of the carpet tubes and made a jungle in one of the hallways. I had similar plans for these tubes, but my wife intervened. She is the principal of our Early Childhood Center (age 3 through kindergarten) and wanted a set of giant Lincoln Logs for the kids to build with. After spending some time searching online for a free plan or tutorial on how to make them and not finding one, I sat down and figured it out myself, first with paper towel tubes and then with the flooring tubes. The tubes I used mostly came from a linoleum-type flooring, but any large tubes would work, I think, probably even PVC pipes. PVC pipes would be good for an outdoor fort, whereas carpet tubes would obviously last longer indoors than out. Fortunately, this project was designed to be used in an indoor playroom.
I am a teacher, and my job is to share knowledge and teach skills to others. I get annoyed when others won't freely do that also, and so I am now going to freely share with you what I have learned the long way. I hope it will save you some time and that you'll have fun with this project.
Step 1: Make a Model to Get the Idea
Before cutting up any of my limited number of large tubes, I first sat down with some paper towel tubes and figured out how to go about it. I would recommend doing this step if you're the type of person that needs to try something with your own hands in order to get your head around it. I am. I will explain in the following steps how to do it but my pictures will be mixed because I've had to go back and recreate some of the steps that I didn't originally take photos of; some will be of paper towel tubes, some will be of the full-size tubes, so just do the same thing with the paper towel tubes if you want to make the model for practice. Measurements don't matter, the process is the same no matter what size tubes you use.
Step 2: Making a Template for the Cutouts
The first thing to do is trace the end of one of the tubes onto a sheet of paper, then cut it out.
Next, fold the circle in half vertically and horizontally so that you divide the circle into equal quarters. Then fold one of the edge points you created to the middle point of the circle. You now have the diameter divided into fourths. The cutouts in the tubes need to be one fourth the diameter of the tube on each side (see picture 2 in step 1 for a visual).
Now take the circle and lay it over the end of the tube and mark the 1/4 depth points. Then use your trusty square and draw lines down the tube a bit at both the points you marked. Decide how much you want left at the end of your "logs" and wrap a piece of paper around the log that distance from the end and trace the edge of the paper around the tube.
Step 3: Finishing the Template for the Cutouts
Now place the circle (you didn't throw it away, did you?) on the tube and mark the other end. Create a line here in the same way as the first one. Use an X-Acto or utility knife to cut the section out that you outlined. Take the cutout and trace it onto another tube in the same place and then cut that one out. Check the fit of the two cutouts, adjust if necessary (you can see in one of the pictures that mine are kind of loose), then do a third one, but do cutouts on both sides of it so that you can sandwich it between the first two logs. Just be sure to get the cutouts directly across from each other.
Now repeat the process, more or less, on a carpet tube and then use a piece of poster board or some other durable sheeting to make a template to trace on each end of every log you make (visible in the last picture of this step). Make it long enough that the ends of the template will overlap when you wrap it around the tube so that you can even the edges up to get everything squared. Also, be sure to make the edges of the template the same width as the distance from the end of the tube to the edge of the cutout. This will save time by eliminating some measuring on each cutout and will ensure that your cutouts will all be the same distance from the ends of the logs if you wrap it around right at the edge of the tube.
Step 4: Lining Up the Cutouts on Opposite Ends of the Tubes and Marking Them
To line up the cutouts on opposite ends of the tubes, I stacked up a few straight boards, put the tube right against the top edge, and traced a line on both ends in approximately the areas where the cutouts would go (picture 1). There's no need to trace a line the full length of the tube unless you're going to cut it into smaller logs, then you might as well trace the whole length of the tube.
Next, take your cutout template and wrap it squarely around the tube where you want to make the cutouts and then trace them both. In picture 2 my wife is marking a tube that we're going to cut into more than one log, which is why she's not at the end of the tube. Otherwise, she would have the end of the template even with the end of the log.
Step 5: Cut the Holes
I used a chop saw to cut the lines that were parallel to the ends of the tubes (picture 1), and a jigsaw to cut the perpendicular lines. Making it a family project, my daughter and son even helped (pictures 2 & 3). We found that placing one end of the tube against an immovable object, like the school (picture 3), made cutting with the jigsaw easier and safer. If you're making the logs for a school, you may even have an enthralled audience (picture 4).
I saved all of the cutouts to use in art classes. I don't know what I'll use them for, but I'm sure I'll eventually do something with them.
Step 6: The Finished Product
When the logs are finished they should fit together nicely, not sloppy but not too tight, either. As you can see in the pictures, I made three lengths of logs with the shortest ones mainly just serving to hold the ends of longer logs together when you can't make a longer wall (see the section closest to my right hand in picture 1). Otherwise, the ends will just be loose and unruly.
As with real Lincoln Logs, the stacking/building possibilities are nearly limitless, providing your little pioneers with countless hours of building fun. You can even make windows (picture 2) and add on to your house if you get more tubes. I didn't attempt the cool green roof like Lincoln Logs have, so it's really more of a fort than a log cabin, but if you make a roof kit for yours, let me know. I'd be interested in seeing how you do it.