SLED RX: METAL RUNNERS: PART 2

This is the second of a series of articles about the use of metal runners in sled construction. In this issue I will talk a bit about choices for connecting your stanchions to the runners and the types of materials used to construct them.This is the second of a series of articles about the use of metal runners in sled construction. In this issue I will talk a bit about choices for connecting your stanchions to the runners and the types of materials used to construct them. One note here on last issue’s article. According to Jim Miller of Prairie Bilt Sleds, the Rex runners that they sell are matched at manufacturing and each pair is stamped with an individual serial number and has the height of the runner arc recorded. If you have any trouble matching the height on your pair of runners, check the numbers on each runner to make sure they are the same. Basically you have two choices for attaching stanchions to your metal runners, traditional tying or bolting. For tying you can either purchase or make UHMW blocks that slide into the upper track of your runners. Like tying any sled, you would like to have the holes in your blocks used for tying 2 ½” to 3” from the base edge of the stanchion to give you good angles for proper flexing of the joint. When using this method it is also important to have the tying blocks long enough that they are able to be butted up against the base of your stanchion to keep it from sliding forward or back. You will need to have a tenon on the base of your stanchions to keep it firmly in the top track of the runner. Secure your tying blocks with bolts that travel through the blocks and into a toggle nut. It is very important to tighten these bolts securely and if you live in an especially cold climate make a point of letting your sled cool and then retighten all your bolts as the plastic shrinks enough to affect tension. At several points, the front hole of your footboards, your brake attachment and your driving bow, drill a hole through the runner for your bolt end to go through so that, when secured, these parts cannot shift. The toggle nuts used generally come in two sizes, ¼” and 5/16”. When using tying blocks I recommend the ¼” size for its smaller profile and I use the 5/16” when I bolt brackets on the runners. Another important tip is to make sure and soften the edges of the plastic around the hole where your tie will run. UHMW plastic has very sharp edges and can cut your line during use.Personally I like to bolt my stanchions to the runners using an aluminum L- bracket with a UHMW plastic gusset. Another way is an aluminum U-bracket with your stanchion bolted inside. I like the way Jeff King uses aluminum pipe for his stanchions, with several inches of a UHMW filler strip extending beyond the end that then connects into the runner bracket. This gives you a nice amount of flexibility while maintaining a solid connection between the stanchion and runner. You can reference Jeff’s sled in Mushing #124 (Sep/Oct 08) page 37. Note the uncomplicated design.So far I haven’t seen any real advantages for tying your stanchions into metal runners over bolting them. Your final goal is to secure the stanchions in one place and both methods accomplish this. But because of the possibility of the ties being cut or abraded badly I prefer the usually hassle free bolting method.If you are using wooden stanchions I would think twice about using the metal U-brackets. These long stanchions have an enormous amount of pressure on them and you may want to add a short extra lamination of wood to the lower end of the stanchion to reinforce it. It is also a good idea to use at least 1/8” thick pieces of plastic to sandwich the bottom of the stanchion. When all these are added together the U-brackets can be too narrow. Try to use an L-bracket instead.Of course you should be laminating all the wood you use on your metal runners. Three layers of at least ¼” thick are recommended but you can certainly go a bit thicker. For my crosspieces I prefer the traditional mortise and tenon joint used on most sleds. It is still the best joint to give you the flexibility you need to drive the sled and the security needed in holding the sled together. Use a blind mortise in your stanchions to maintain the maximum amount of strength in the outer edge where all the hitting occurs.Metal stanchions give you the peace of mind that comes with knowing that your stanchions won’t break but come with their own downside. They bend into shapes when struck sharply that you more than likely will not be able to straighten, especially out on the trail. This, in turn, can make your sled drive in a rather poor matter and you may have to adjust your towline to compensate for the twist in the sled.A Schedule 40 pipe of 6000 series aluminum is a relatively easy material to come by at most pipe and metal distributers. Use either the ¾”id or 1”id for distance sleds and ½” for sprint or light duty sleds. For crosspieces you can use either the pipe or 1” by ¼” aluminum flatbar. If you use pipe make sure you put plastic inserts into the ends of the pipe and flatten them out so that when they connect onto the stanchions the flat sides meet. I like to put a small, thin nylon washer between my metal surfaces to give them a smoother movement.As metal runners are on the market longer and their advantages and limits are better understood, there has been a number of new ways to prevent the rear of the runner sliding off when it breaks. There has been a series of fixes that have entailed putting as much unbroken UHMW as possible between the rear sled supports and the footboards. In the beginning we tried to just fill the upper track of the runner, but by the time we drilled holes through these strips of plastic there was hardly any connective plastic left. The latest way is a slotted strip of UHMW that runs both in the upper track and on top the runner itself. Available commercially or makeable with a good tablesaw, these strips then become part of the mounting platform for your aluminum brackets and runs back through the footboards. Again it is very important when using this system that you retighten your bolts here after the sled has been in the cold temperatures because the shrinkage in this strip of plastic can be significant. I want to finish off this segment on metal runners with a note on design. Again I would like to reference Jeff King’s sled used in the Iditarod. While the exact design isn’t for you, the overall simplicity should be. I see a lot of home-built sleds and I cannot emphasize how important it is to keep things simple. Try to use the same size hardware whenever possible and think in terms that someday you may have to fix this sled on the trail. Just because the runners are metal doesn’t mean that the rest of the sled needs to be ultra-high tech. Simple will make your life easier.Next issue I will wrap up this series of articles on metal runners with some information on cooler holders and other pieces to finish your sleds. Until then, enjoy your time on the runners.

Share:

More Posts