Creating a Fiberglass Snowmobile Trailer (aka - Cutter)





Introduction: Creating a Fiberglass Snowmobile Trailer (aka - Cutter)

Here is a snowmobile cutter I built over the last winter. It is a cat chasing a mouse chasing a chunk of cheese. The cheese is the hitch and the cat is the actual trailer. It is sized to carry a banana box and a bit more. The cat's tail is a handle to open the storage area and is held closed with magnetic latches.

As I haven't made anything with foam and fiberglass in some time I wanted a project with many compound curves.

People ask if it will carry passengers. I briefly considered a rumble seat but despite our well maintained roads it seems passengers deserve a suspension. Someone without a snowmobile might consider a smaller dog or person pulled version or toboggan.

Step 1: The Planning and Layout

I started with a general sketch of the cat. The mouse and cheese were ideas that came later and were not originally planned.

The sketches were then turned into various scaled drawings with the layers of foam inserted within. The approximate shape of each layer was freehanded over the various surfaces but a lot of time was not spent trying to match coordinates between views. It was easier to tweak the layers as they were cut and shaped.

The measurements from the drawings were scaled up and drawn onto pink extruded polystyrene foam insulation. I started with a simpler sub assembly, the skis, rather than the main torso. The parts were cut out and glued together to create the appropriate thickness. Each section was then sculpted and shaped. This step was accomplished using a mix of hot wire cutting, saws and sanding.

As the legs were fairly simple, I started with them.

Step 2: Jigging the Basic Shape

Remember that while Styrofoam can be hot wired, you must use epoxy resin as polyester will dissolve it. The floor was made of denser 3/8" urethane that cannot be hot wired.

After the skis were covered with fiberglass the vertical portions of the legs were glued on. The outer legs are set farther out than the front legs, somewhere I think I was picturing the curves of some sports car. The body and head were sculpted of foam and shaped as the skis. Fiberglass was applied once the desired shape was achieved. The leg cores were then added to the skis and the ski /leg sides jigged to the center vertical and horizontal planes of the body.

Additional layers of fiberglass were going onto the lower legs, so rather than trim the excess fiberglass from the first layup foam spacer blocks were glued onto the bottoms to allow the skis to sit parallel to the floor during jigging.

Step 3: Head, Shoulders and Haunches.

The legs, shoulders and haunches were built up with additional layers of foam and fiberglass.

For the head I considered lots of jigging with strips of 3/8" or 1/4" urethane contoured over them but in the end decided there would be enough free handing around the face to stick with layers of precut foam that wouldn't be trying to change shape as material was sanded off.

Step 4: Build the Cargo Lid

The upper portion is sculpted and hollowed out.

Again, I considered 3/8" foam bent over jigging but decided to continue with the hot wired foam arches I used on the more tightly contoured head. Part of this was because I had to deal with the curves of the rear hips rather than have everything come to a taper front and rear.

Two inch increments were marked off front to rear on the horizontal and vertical planes. Measuring along them gave the dimensions to cut the arches. They are not perfect circles, adjustments were built in with multiple radius points on the foam. As with the rest of the cutter, both sides of a section were pinned (or can be screwed or 5 minute epoxied) together, hot wired together, trial fitted, rough sanded and installed as pairs rather than doing one side at a time.

Step 5: "If It Didn't Carry Cargo It Would Just Be Silly" ( Making the Lid Open)

The hinge was put on the left hand (Driver's) side so that when properly parked the lid would open from the sidewalk side of the street. The reality then and now was people park on whatever side of the street doesn't have the "No Parking" signs up for plowing purposes, regardless of the direction they were driving.

Considering the typical building's door hinge pin, I used 3/8" rod to eliminate any worry of it ever bending or breaking. I also used stainless steel rod to eliminate any worry of the hinge rusting. The bearing on the end was capped off with grease in it, to supply grease to the hinge rod over the years. It would have been easier to remember to oil the hinge from time to time. Make sure any surface getting epoxy is properly degreased.

On the side that opens, the tops of the right shoulder and right rear haunch, each have a thick nylon spacer washer embedded in them. A straight edge was run from the axis of the hinge to the shims to align them with the direction the lid would be coming at them. Corresponding pins in the lid drop into them to keep vibration from shifting the lid as it moves down the road. Since it isn't expected to do a lot of bouncing, three pairs of magnets are embedded in the surfaces to hold the lid down rather than trying to fabricate a latch.

Step 6: Ears and Tail

While we wanted swept back ears, we did not want the lid to hang up on them when it opened. Eventually the top and back surface of the ear foam was covered with fiberglass, the foam then completely removed from underneath, ear canal dimples were cut into the sphere of the head and more glass applied to the underside of each ear.

The tail was made of 3" thick foam, made by layering 2" and 1" foam together. Curves were in each section, with new sections at different angles to give a 3-D curve. To get a more or less round tail cross section, rasp file the 3" X 3" cross section into an octagon, then rasp that into a 3" diameter tail.

Care was taken that the tail was far enough out from the rear right haunch that it would not hang up when the lid opened. I then touches the torso between the rear haunch and front shoulder to prevent too much stress traveling along the tail to the back. In reality, three layers of fiberglass later the tail and lid are so stiff that this contact point could have been eliminated and the tail left completely free of the torso.

Step 7: The Hitch

The 1" hitch shaft is welded to a 7/8" solid steel cross shaft, turned down on each end to fit into bronze bearings. The cross shaft came polished and would have fit directly into larger bearings with some sort of thrust surfaces on the ends but instead was turned down on each end to use the smaller bearings side-to-side thrust surfaces.

The hitch was made removable to ease storage or stuffing it into the car if it had to travel. Bearings were encased in flocked epoxy and glass with steel spacers providing the holes for the bolts. As it is important to have a hitch that doesn't come off on the road, it was overbuilt with eight grade eight 5/16" bolts and lock nuts through steel plates holding it on. Keep in mind a single 5/16" pin holds it to the snowmobile. Shorter bolts shown in the bearing block picture were keeping things aligned. The bolts holding them on go up through the bottom steel plate, through the steel spacers embedded in the bearing block and into a coupler nut (a.k.a. tall nut) embedded in the body. Shorter bolts inside the body go through identical steel plates inside the body into the same coupler nuts, assuring the bearing block cannot be pulled or sheared from the body.

The bearing blocks were slid onto the ends of the cross shaft of the hitch, the hitch was put in place with the bearing blocks mounted with connector nuts through holes in the body and the voids then filled with fiberglass and flocked epoxy filler. (Don't forget to use mylar tape or other release agent between the epoxy bearing blocks and epoxy applied to the body.) After setting, the hitch shaft was removed to allow clean up around the bearing blocks and to curve and add the mouse to the hitch shaft.

The center layer of foam in the mouse was cut off along the bottom, when reunited to the sides of the mouse this created a tunnel for the hitch shaft to pass through. Two nuts embedded in the body allow the mouse to be bolted to the shaft but also make it removable. Mouse ears were made out of foam, covered with fiberglass, the foam dug out, the ears were trimmed and glued to the head and shoulders. Additional fiberglass through the front of the ears tied them to the head.

The cheese was made by wrapping fiberglass around foam cores. The front of the wedge was then carved as needed, a hex shaped hole was cut in back and the shaft slid through the hole. The nose of the cheese was then glassed over and the various sized holes molded into the cheese with doming punches.

Step 8: Finishing Touches

The eyes are magnifying glasses with the irises painted on the inside / backside. I made the eye openings before I bought the magnifying glasses and had a bit of trouble finding the right diameter.

I was going to take it down state for painting and airbrushing but wanted to get it on the road, so I settled for spray cans. I suspect it will be repainted into different breeds from time to time.

Whiskers are 1/8" carbon fiber rod put through pre-drilled holes and anchored under the nose with silicon. In the event it comes home with a broken whisker it should be fairly easy to pluck and replace it.

Step 9: Road Test

Road Test



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    28 Discussions


    2 years ago

    When I googled "DIY snowmobile cargo box" I didn't expect to find this. So awesome.


    2 years ago

    Love it

    this is one of the best Instructables i have seen. im 13 and have been learning to use fiberglass so ive been searching for some tips, by the way how much resin and cloth did you use i want to build one and go 40 mph down the road on it :-)

    1 reply

    I recall the Q2 aircraft I helped build had two layers of glass on the outside and one layer inside except for a second layer where people or cargo would be pressing on it. A test lay up was a layer of bid (typical woven cloth), 2 layers of uni (strands all one direction) and another layer of bid. These four layers were then joined with four more layers over 1/2 inch foam and were quite strong. Since we aren't trying to build something that has to fly, I recommend three layers of glass on outside surfaces, several more on the skis or anywhere you think it could get beat up with extra layers on the surfaces bracing them, and a layer or two on inside surfaces. It is better to use too much than not enough, but I doubt you will need more than six or eight layers for smooth snow at any speed. You may also consider putting a layer of wood, metal strip, plastic snow sled, pick up truck bed mat or some other material on the ski if you expect to go over rough stuff. I didn't keep careful track, but probably used a gallon and a half of resin. If you are already working with fiberglass, try to keep track of how much you use with a certain amount of cloth, then calculate approximately how far you get with a batch of resin. I made several drawings and calculations, but then went by the seat of my pants, deciding a detail had enough glass on it when it "looked right." In hindsight, the four layers on the ears should have been six or eight as they have no core. Calculate the surface area of your project and multiply it times the number of layers inside and out. If you end up buying too much glass or resin, hopefully you or someone else will be able to use it on a later project. ******** Remember, it was rather simple to cut out flat foam side and top profiles, glue them together and add filler to get a complex looking shape. I don't think I mentioned it, but I cut notches into foam parts to align them, much as a tailor does with fabric. You might start with something boxier than a cat-- If you look closely at most cars, trucks or snowmobile hoods, they are mostly curved flat surfaces and softened corners but impress the devil out of people. Ask yourself what balloons or Tupperware would look like if covered with glass and paint.

    This is an amazing project and Instructables. Thanks so much for taking the time to document all this. I am curious, where did you learn to do this? What other projects have you made in the past? Also, what kind of foams can you use without he resin damaging it or dissolving it or something?? And let's say you were making somekind of sculptures for the lawn.. like a fiberglass santa or something like that.. and you wanted to make it more detailed, on the face for example, do you know of any material you could put over the fiberglass and sculpt in fine detail that would be durable? Can you sculpt bondo very well?

    3 replies

    I did the typical polyester resin repairs to rust outs on a car and small scraps on a beat up boat, then helped build a composite airplane in the 1980's. I patched a couple of rusty floors on our winter driving Corvairs, for the thickness graphite is probably as stiff as steel for patching tight spots like under a windshield. Since then it was pretty much odds and ends around the house, fixing broken handles, a simple box for the radon venting before we poured the basement and an equipment pedestal for our ambulance. Start small and simple, work with others to study techniques and ideas and share ideas on Instructables. You might also talk to theater people who make sets for plays, they go the other direction, using acetone and other chemicals to make styrofoam look like aged stone for MacBeth's big finale. Those, of course, will not last long out doors and are flammable indoors.

    Styrofoam and polystyrene foams are available locally in sheets up to 4' X 8' in thicknesses up to 2". They can be cut with a hot wire that can be made as long as you want (although four foot is my practical limit) so you can easily cut curves or textures out of the long axis of a sheet (or airfoils for an airplane out of blocks, as we home builders have have). On the other hand, if it is going to be around gasoline or other solvents, order urethane or other fuel resistant foam. These foams CANNOT be hot wired but the urethane sands and sculpts VERY well. Automotives and hardware stores have polyester resins and glass, keep in mind wax is put in the polyester. It absorbs humidity and cures tacky for the next layer to stick all the better, the wax shields it for a glossy finish but can cause adhesion problems on the next layer. Polyester resin will dissolve styrofoam, polystyrene and other readily available foams, on the plus side it is much more UV resistant and costs less than epoxy. Epoxies won't dissolve foams, stick to just about anything but cost more and you can develop allergies similar to poison ivy, especially if you are casual handling it. Epoxy takes longer to cure, generally a good quality.

    If you want fine detail, use urethane and coat it with epoxy or polyester resin without the glass, it will be fragile without the glass. I'm not a big fan of Bondo but did use it for filling some parts of the cat cutter. It is polyester based and will absorb water, if you wet sand the finish you may see your paint fall off later. Composite airplanes are filled with a mixture of epoxy and micro balloons, the balloons are tiny glass spheres that are so light they behave like dust. They are inert but play havoc on your lungs if you inhale them. Mixing more balloons with less epoxy will give a softer, lighter material that can be sculpted into very fine detail. The epoxy base needs a day or two to set but you could probably make a 30 minute polyester concoction. Keep your mix ratios consistent so you don't have hard and soft streaks in your carving. While the catalogues say it has no structural strength, it will take a fair amount of compression, it is my understanding it provides the buoyancy to the remotes that go into places like the Titanic.

    I have also made molds out of combinations of wood, cardboard, foam and modelling clay. The oils in the clay keep it from dispersing into the clay. Interestingly, epoxy doesn't stick to duct tape or packing tape, so you can wrap an object or make a parting line with tape as a release agent, the strapping tape leaves a glossy finish. Every wiggle, scratch, thumb print in clay as well as dust caught under the tape will appear in the fiberglass. I haven't tried it yet but you could sculpt something in plaster, coat it with a parting material and make a mold.

    Again, go on line to Wick's Aircraft Aircraft Spruce and supply West Marine or other such places and search for Composite Materials. Keep an open mind for projects, the cat's whiskers are made of 1/8' diameter graphite rod similar to what's used in fishing rods and golf clubs, they also have it in rectangular bars that would make killer kite sticks.

    Sorry it took so long to respond on this. Thank you SO much for taking the time to give such a detailed response. I am an aspiring sculptor and can't thank you enough for this information.

    I've seen at least one book on making forms for concrete sculpture from foam, could be a more familiar medium. The last of the hotels will be closing for the season next week, expect to be trading in the bicycles for snowmobiles in about six weeks.

    I love the whimsy of this -- all you need is a snowmobile parade to drive it in. Is it usually still snowing on July 4 where you live? =)

    1 reply

    Snow usually disappears about this time of year, I bicycled to work today. My co-workers have been getting their snowmobiles to the various storage areas today. The ice bridge to the mainland broke up March 30 and the ferry boat began only five days later, this weekend. Snow usually returns early December but comes and goes until mid January. Summers aren't bad here, the lake keeps keeps it mellow, I've never had an air conditioner. There are also no mosquitos, which is rather pleasant.

    That is incredible! For better or worse I live in Florida. It's for better as the low is around 50F, and the high is 75F. Wish I had an environment to use this sort of trailer in. I might try your bicycle trailer idea. It could make for a supercool (but not practical) touring trailer. Or it could be part of a grocery getter. +1

    1 reply

    The ferries have quit running due to ice in the straits, the weather grounded the planes, four of us spent time on bar stools in St. Ignace. One of my fellow travelers grew up in Florida. As I said, this could be adapted to an automobile trailer. I have thought about putting something together with left over Corvair parts, the first trick would be getting the car to the shop without being arrested for having it.

    That is awesome. I have a few questions: (A) how much did this project cost? (B) where do you buy your FG supplies (resin, glass, ect.) (C) How did you learn to 'glass' like that? (D) how many layers this is the body? Keep up the great work, I look foward to trying to apply some of the things you did here to a FG bicycle trailer.

    2 replies

    (A) I didn't keep track of cost. With odds and ends I am I am going to guess $300. I bicycle trailer should use much less material.

    (B) I mail ordered most of the materials, including the metal hitch shaft and bearings, from Wicks Aircraft Supply in Illinois. The whiskers are their 1/8" diameter graphite rod. Type "Composite Materials" in the search box. In years past I have also purchased materials from Aircraft Spruce & Specialty Co. You may also check on line or at boat dealers for West Marine or other products.

    (C) I helped build a home built airplane (Quickie Q2) in the 1980's, maybe you can find someone in your area building or modifying a plane, boat, car, etc. Wicks has a "Composite Practice Kit & Book" for $95 that looks promising. If you can split the cost with others you will also have people to bounce ideas off as you go. I wanted to build something with a lot of compound curves. However, JoAnn's fabrics has smaller diameter solid foam balls that would save time sculpting a head. Also consider the urethane foams, they sand very easily, but cannot be hot wired as the heat gives off toxic gasses. Start simple with just a figure head for a boat, truck grill or something more boxy like a mail box.

    (D) I used a couple of different weaves, both about seven ounce per square yard. Weight and the cost of extra fiberglass were not a consideration so I put three layers on the outside and something like eight on the bottoms of the skis. The tail got three layers while the lid has two layers outside and one layer inside, and ended up so stiff the contact point where the tail touches the right side of the body was unnecessary. You can make simple sample lay ups to test and break, but as a bike trailer should be light weight I think one layer inside and out will work, with a second layer where you want durability. You can always repair collision damage

    Thanks for the quick reply. I don't think I'm ready for anything nearly this complex yet but I am very interested in trying my hand at fiberglassing over foam.

    Wow! thats awesome! Too bad I don't live in MN anymore or I would have made one. Great instructable!

    1 reply

    Sorry you don't live in a snow belt. I'm sure the construction could be adapted to a car trailer, roof top carrier or pick up cap, with the builder choosing his or her favorite critter, character or object.