When boxing a typical steel c channel frame, are steps required to prevent it from warping? Or do you just make up your boxing plates and weld them in ? If steps are needed to keep it from warping, what do you do? Thanks, Joel
The way I have always welded boxing plates is I slightly grind the frame and plates at a angle then tack them in place, to prevent warping you need to spread out your welds and keep jumping around, it' slow but effective. HRP
If you want your frame to remain square, you need to have the rails clamped into a jig before doing major welding on it. Boxing it is major welding. Any welding will cause shrinking, which is what makes things warp. Even doing skips in your welding will make small bits of shrinkage.
Boxing is overrated. It's kind of a Me Too thing. There are reasons for it but no so much for most builds. And yes, you can do more damage than you can repair.
When we used to box rails in my shop we would mark out the rails in 4 inch increments on both sides then start at one end and work our way from one end to the other skipping every 4 inches and going back and forth side to side. Then repeated the process filling in the blanks. My welder always went slow pausing between welds. We also had them clamped in a fixture to hold them.
does it need to be fully welded? Or can you just weld it for an inch every four inches, or something similar? The purpose of boxing is to keep the frame rails from being able to twist. That might, or might not, be required on the car you're building.
I’d like to hear from the engineer folks. Does it need to be solid? Do we do it just for looks? Even in a jig, the frame will move. Physics is physics. I’ve watched frames we boxed jump out of jigs after welding. This debate was funny on American Hot Rod years ago.
That would help keep it from moving around. The taking your time when welding is probably more important as far as far as keeping from actually warping. The guy who welded up my rear coil spring suspension when I had it in the 48 welded these long pretty beads that ended up getting the frame too hot and causing it to twist. We didn't have it set in any sort of setup to hold the frame in place and it ended up with a twist that I now wish I had had a frame shop straighten out.
As far as boxing goes, the old riveted frames were designed to flex and work as part of the total suspension package. That was to get over the roads that people had to drive on at the time and in the case of my 48 when new, to take off across the pasture and handle the ups and downs of the terrain in the process. You only hang on to the front of the bed with your fingers between the bed and the cab once on less than smooth terrain to find out how much those trucks flex. The way we set up the suspension on a lot of our rigs now we don't need that flex plus most of us aren't going off roading our hot rods. We do run a lot more power that by it's self can twist a frame to the point it won't return to straight plus welding in crossmembers and other pieces moves the flex to the rails rather than the riveted points.
So...if we know that welding naturally causes shrinkage and possible warpage, what real value is a fixture or jig if it’s still going to shrink and move. I’m planning on boxing my Model A frame and do not have a jig.
I have no way to quantify the difference with or without a jig. I have c-notched and boxed the rear section with and without using a jig. Both times the rails moved down.
Back to your question. Boxing requires that you start off with your chassis or frame square and flat level. It needs to be restrained to keep it that way during the boxing process. Boxing can be dont several ways and can depend somewhat on what year chassis you have and what existing components exist with it such as cross members and X members etc. Boxing is a bit like painting there are several steps of prepartion to do before getting the plates welded in/on. I always clean my frame by sand blasting so I can see what I have to work with and if any other chassis rail repairs maybe required. Probably the next step is to determine what bolt holes you will require and what hole you choose to weld closed. Required bolt holes will either need hidden nuts welded into place or insert nuts which ever you prefer. For the actual boxing process, you will chose a plate thickness. A lot of folks are happy with 1/8" but the tide seems to be turning to a 3/16" preference these days. I used to bevel my boxing plates as mentioned by Hotrodprimer. I now get my plates laser cut with the plate width equal to the opening size of the frame rail channel . About every 9" I ask the laser guys to leave little tags equal roughly to the outside dimension of the channel rails along the top and bottom edges.. These tags prevent the plate from falling inside of the channel while the main cut line of the plate helps form a small open area suitable to run a fillet weld and connect the plate to the original chassis rail. As mentioned by Krylon32 once tacked in place, you will perform a stepped welding process and move around/along to different locations to reduce heat focus and tendencies to warp. If using several shorter pieces of plate to do one rail, it is wise to create a intwined connection or join where the boxing plates touch/meet. I always liked the chassis boxing jig that was used by Squeek Bell over in Bakersfield CA. A very clever setup that consumed much less floor space than the regular chassis tables you see. Sadly, I dont have a pic to post, but somebody out there may have one to share.
A frame must have some sort of allowances . A vehicle has a lot of adjustment in it's suspension to compensate and most bodies are shimed as well .
I don’t have a jig but I do have a flat metal table that I set my frame up on. the rails are leveled side to side end to end and squared with uprights welded to the table so I can add crossmembers and box. And whoever says you don’t have to box a frame has never worked with a model T chassis. This is the second chassis I’ve built on this table.
Interesting old article https://www.hotrodhotline.com/content/boxing-frame-article-jim-clark I guess this is one method. I’ve used this method definitely make sure any necessary weld nuts have been handled before boxing
Early frames twist surprisingly easily. Boxing is good. Cross members help. X member is very strong. Cage is strongest. There's a reason. It's not just for looks. Heat warpage is a big problem. If a frame jumps out of a jig after being unclamped, that frame is no good. Even in a jig, the welding needs to be spread out and even. A jig or welding table not only secures the frame, but provides a point of reference to measure from. Height, length, width, and centerline.
A frame table should also be strong enough to chain a frame to and use to pull the frame straight again if bent
How about you tell us what year and make of frame you are asking about boxing? Is it going under a open car, closed, or pickup? What HP is the engine? There's a bunch of variables when building a chassis.
Alot of the older frames allowed around 1/4" variation on things like diamond, side set, twist etc. Fords were the worst up into the late 80's. Ford even had the worst tracking problems (dog walking) on their trucks into the early 90's. Slotted alot of rear housing spring perches back in the day to correct it. .
When I mentioned “jumping” I meant when released from the jig, movement occurred. It’s impossible to keep from happening only minimized. But early frames are inconsistent anyway with large tolerances. Aftermarket rails had to be “persuaded” at times to fit a jig made from an OE frame. Another OE frame didn’t line up perfectly in a jig made from an OE frame. A well placed jack or porta-power with a properly placed hammer blow can work wonders getting them back into sloppy OE specs It’s one reason I “hit cars with hammers”
Yes. Movement when released. I've been considering the feasibility of having a rectangular tube x-member fabricated by the local professionals with short rails at the ends of the X that would fit nicely inside the straight portion of the existing frame rails. And then hot rivet that sucker into my frame.
This is basic backstepping for a weld. Warpage is reduced by welding short sections in the opposite direction of the overall weld. In boxing a frame, each edge of the frame should be welded first one edge then a similar weld on the opposite edge. Then move to the other side of the frame and repeat the process. If the overall weld is from left to right, the stepped welds should be from right to left. The picture shows a stepped weld joining two plates but the process is the same when joining two edges to build a box. On thin material, sometimes it is better to make your first welds, top and bottom of the box on both sides of the frame then skip the second welds and go to the third set, skip the fourth and go to the fifth, etc. This allows the metal to cool. After getting to the end of your box section, go back and start where you finished the weld at three and finish that weld where you started on the first.
Seems to me that 'back in the day' lots of frames were modified or even built from scratch with little more than a buzz box, grinder and a level concrete floor.
and this method. Easy to weld, no edge to radius with a grinder. My structural friend says this method is more rigid.
Your right Anthony strength wise and of course the channel inside a channel method also. This probably completes the list of boxing choice versions.
I went to a shop where there was a '34 Ford frame that the owner had boxed and it was twisted really bad. Later when I returned, Bill had managed to straighten the mess out. He did incredible work.
A guy in town had another fella (amateur) box his 32 frame for him. Did it on the concrete floor with no jig whatsoever. When he was done you could fit the body down in between the rails. A perfect example of the weld shrinking. The inside edge shrunk and made the rails bow outward.
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