FABRICATING THE FRAME
The perimeter frame is made of 4x4x1/4-inch steelangle on the sides and front. The pieces are cut to make outsidemeasurements of 16 feet by 78 inches. Cut the corners at a 45-degreeangle so they fit together smoothly. A piece of 4-inch channel forms therear-most crossmember. It is installed flanges-out.
The frame will bebuilt upside down so there won't be any overhead welding. Set theframerails flange-down on cinder blocks. This gets them off the floor.Measure corner to corner in an X pattern. Tap the pieces around untilthis measurement is equal both ways. Now the frame is square. Put a goodtack weld in all four corners before welding it solid. Check thecorner-to-corner measurement again. If it is off a little, rap it with ahammer.
Cut seven pieces of 11/2-inch square tubing to 771/2 inches tofit inside the frame. The inside of the 4-inch angle, as with all angleiron, has a radius. The tubing can be cut straight and then radiused ona grinder for a good fit. Willing to take a short cut, I cut the tubingto 77.25 inches and did not grind a radius. The Millermatic sewed up thegap like Betsy Ross putting stars on a flag. Notice the photo showingthe locations of the square-tube crossbars. The center crossbar is onthe centerline between the two axles. This should be 18 inches behindthe center of the trailer bed. The next two are away from the centerunder the mounting points of the spring hangers. One more should beplaced halfway between the front spring mount and the front of theframe. In the rear, 40 inches from the rear would be about right.
The tongue must be securely welded to the frame. Be sure to decide on ahitch before welding parts in the wrong place. The location of thetrailer hitch ball should be a minimum of 36 inches in front of the trailer frame.
Nowthat the basic frame is together, it must be notched for the dovetail.The dovetail is the drooped section at the rear of the trailer. Thisenables the use of shorter ramps. The dovetail line should be 48 inchesfrom the rear end of the trailer. There needs to be a drop of 6 inchesmeasured at the rear. Using the torch, cut the vertical flange of the4-inch angle 48 inches from the rear. Remember, the frame is stillupside down. I placed two jackstands 6 inches higher than the cinderblocks under the rear channel. Standing on each side of the frame at thenotch, my weight bent it down properly.
From scrap, cut a diamond-shapedpiece 4x7x1/4 inches thick. Place it on the outside of the frame overthe notch. Weld it inside and out. The remaining piece of 4-inch channelshould be cut in half. The two resulting pieces will make the tongue. Bythis time, you should have selected a hitch. Some are made at differentangles. The tongue sides should be at the correct angle for your hitch.Consider it a minimum to have 36 inches from the front of the trailer tothe center of the trailer hitch ball. More would be better. Some goodwelds here will give you peace of mind for a long time. With the basicframe done, set the axles on the frame and hook up the spring linkage.Place a 2-inch block between the axle and the frame to set thebump-travel limits.
The frame is almost ready to be turned over. The springbrackets have been welded in. The dovetail has been cut andbent. The crossmembers are in place. The tongue sides have been located and welded. The axles must beremoved before turning the frame right-side up.
Measuring carefully, align the axles parallel toeach other and square to the trailer frame. Weld the spring hangers inplace. Next, the axles must be removed so the frame can be turned overmore easily. Turning the frame over is an operation that requires greatcare. Use an engine hoist to raise one side of the frame to about a70-degree angle. At this point, attach safety chains to heavy objects onboth sides of the frame.
I used the rollcage of our race car for oneattachment point. The other chain ran from the trailer frame to thetrailer hitch on the tow vehicle. Step by step, I let one out andtightened the other. It gets a bit dicey when the frame goes over-centerand the tension goes from one chain to the other. Keep yourself out fromunder the side coming down. Use the engine hoist for the final loweringjust like the initial pickup. If you don't, the frame will skid sidewaysduring the last few feet of lowering. This sort of surprise will makeyou wish you had taken those dancing lessons when you were young. See below for the photos where the frame is flipped over
Save your bravado for the racetrack. Be very careful turning thetrailer frame over. You did remove the axles, didn't you?Photo A shows Sleepy picking up one side with an enginehoist. This is the easy part. | 
In Photo B, you can see the safety chainsin place. One is attached to the race car, the other to the towvehicle. Work these slowly, loosen one, then tighten theother. Don't let the trailer move more than a foot at a time. Using thismethod, one person can do the job safely. | 
Photo C is the last step inthe process. Use the engine hoist to let the trailer all the way down. Failure to use a hoist in the final step willallow the bottom of the frame to slip toward the tightchain. This can be as dangerous as it is exciting. |
Withthe trailer right-side up, weld all those places that will be covered upby the purling before you forget.
THE RUNNERS
Once the frame is right-side up, weld all the places that willbe covered by the purling runners. A few good-sized C clampswill make it easier to hold the purling in place forwelding. Install the outside one first, then the inside.
Two 8-inch purlings need to be cut to fit on each side. Thismakes a 16-inch-wide runner. Purling is commonly available from metalbuilding suppliers. It is roll-formed from sheetmetal in the shape of a"C." Measure inside the frame from front to rear and add 1/4 inch to thetotal. You will have to cut a V notch for the dovetail to take up thedifference. This V notch should be 5/16 inch wide at the flange side andnear zero at the top face. When bent, it will fit right down in theframe. Weld the first purling in next to the outside of the angleflange. Weld it to the angle flange and also to the 11/2-inch squarecrossmembers. Then add the next purling, welding it to the first purlingand to the crossmembers. Depending on your purling supplier, it mightstick up slightly over the angle. Mine did, so I got some 3/4-inch angleto cap it off at the front.
The purling can be slippery at times. Mycure for this is to rake it with the welder. Medium amperage and amedium wire feed works well. This leaves small weld beads similar tovery coarse sanding paper stuck to the surface. Foot traction is muchbetter than it is with diamond plate, and it's a lot cheaper.
The purling has been notched for the bend. My partner Jim fits it downinto the dovetailed part of the frame. Purlings should be welded to each other and to the frame in skip weldsof 2 inches about 10 inches apart.
At thispoint, your trailer should look like a trailer. Next month I will showyou how to build a pair of $12 fenders, a slide-in Superwinch mount, anda tire rack with a deck. We will also be mounting the M&R tie-downs. AndI won't forget to show you the lightweight, swing-away ramps that stayattached to the trailer. Have fun building. Contact Sleepy at:sleepy.gomez@ primedia.com.
RIGHT WELDERLet's take a moment to talk about the welder. I have built several racecars with a 110-volt, 130-amp wire-feed welder. This unit is notrecommended here because the duty cycle is too short in the range youneed. You'll spend too much time waiting for the welder to reset. An arcwelder can handle parts of this project, but some of it will still be aproblem.
The solution turned out to be a Millermatic 185 welder. It is awire-feed, or MIG-type welder. It can be turned up high enough to weldthe axles back together and low enough for the 0.065-inch-thick runners.You can use 0.023-, 0.030-, or 0.035-inch wire and control it properly.Don't let the 220-volt current bother you. An extension cord can be madeeasily from hardware store parts. It can be plugged into the dryerconnection at your home if necessary. The Millermatic 185 will performall the welding chores necessary on this trailer. It will do just aboutevery welding chore in your shop, too. With the optional spool gun, youcan weld aluminum for race car seats and other parts. Since it is builtfor industrial use, this welder will last forever. If you fabricatemetal in your shop, the Millermatic 185 could be the best investment youever made.
The Millermatic needs to have a shielding gas for the bestwelds, as do all similar welders. Flux-core wire is available and isused outside in the wind, but it is more expensive than plain weldingwire. I'm told a flux-core wire weld has less impact resistance thanshielded gas welds. For a shielding gas, carbon dioxide or carbondioxide plus argon can be used. For the best welds, always use thecarbon dioxide/argon mix. Selecting a wire speed and weld heat is a bitsubjective. The video and print instructions that Miller went to greatlengths to produce are invaluable tools for getting started. Afterreading the book and watching the accompanying video, I removed thewelder from its box and ran the first weld 23 minutes later.
MATERIALS LIST
*4x 2 1/2-inch channel; one 20-foot piece; tongue, rear crossframe
*4x4x1/4-inch angle; two 20-foot pieces; main frame, sides and front
*11/2x11/2x1/8-inch angle; one 20-foot piece; ramps, battery box, etc.
*8-inch purling; five 20-foot pieces; runners, ramps, fenders
*11/2x11/2-inch, 11-gauge square tubing; five 20-foot pieces;crossmembers, tire rack sides
*1x1-inch, 11-gauge; two 20-foot pieces;fender mounts, tire-rack crossbars square tubing
*Cost of materials other than wheels, tires, and axles was $306 atEagle National Steel, Hutchins, Texas. This price may have increasedsince publication.
For Parts 2 & 3 of "Building A Race Car Trailer" click links below:
Building A Race Car Trailer Part 2
Building A Race Car Trailer Part 3