The top chop and roof filling operation seen here was done at Metal Fab in Minneapolis on a Model A belonging to Craig and Cindy Oldenburg. Craig decided on a 3.5in chop after careful study of some similar cars at shows and events.
Here we have the before picture of the Model A about to have its top hammered. Craig decided on a 3-1/2 inch cut after careful study of Model A Fords seen at shows.
The plan Craig and Jim Petrykowski laid out called for the top chop to be done more like a section job than a conventional top chop. Because the Model A is a pretty square car, the top could be dropped down intact.
If the wood support structure is good, like it is in this Deuce, it’s tempting to just remove it before cutting starts, then trim and reinstall it after the chop is finished. If the wood is gone, new wood kits can be ordered for many popular cars, or metal tubing can be substituted.
Jim wanted to weld either high or low on the top, so the large panels wouldn’t warp and so the welds would be easier to finish. Some of the welds could be hidden by body lines, and even those that couldn’t would be close to a corner or reveal, which would make them easy to finish later.
The layout of the cuts is just as important as the cutting itself. Before the cutting was begun, the window was removed and cuts were made past the body seam.
The body was solidly bolted to the frame and reinforced before the top was cut off. Craig and Jim did the cutting with a Sawzall and a cut-off wheel. After the cut, the sections that were cut out of the posts were held in place with small vise grips in order to keep the top from collapsing at one corner.
Before starting on this Model A, Jim cuts the rear window, with a flange, completely out of the body.
The extra metal at the rear corners was left attached to the top and allowed to slide down inside the body when the top was set back onto the car. At this point, Jim and Craig did some careful measuring, making sure that the top dropped 3-1/2 inch at each corner and each post. This is where knowledge of the original body dimensions pays off.
Jim carefully cuts along the scribed line with a cut-off tool. Because the Model A is a pretty square car, Jim designed the cuts to simply drop the top.
Where the top slid past the body at the rear corners, the line where the top and body meet was marked so the excess metal could be trimmed off. A sanding disc was used to trim the top exactly to the correct dimensions.
Until they’re ready for the big drop, all posts are temporarily clamped together.
Cutting the posts at either the top or bottom eliminates the need to reconstruct the posts after they have been sectioned right in the middle. In order to make the top fit the new location, Jim slanted the front posts back slightly. The rear body corners were trimmed so the top would seamlessly butt to the body.
The Sawzall is used in areas that can’t be reached with the cut-off wheel. Note again that the cut is at the bottom of the post, not in the middle.
Where the front posts meet the body, the base of the post (the part of the post still attached to the body) was slit at the corners so it could be tapered slightly to match the dimensions of the upper portion of the post.
Craig cuts the window posts with another air-powered cut-off tool. Note that all the cuts are made near the top or bottom of the opening — to make welding it all back together much easier.
The rear post (at the front of the rear window) was cut high. When the top was dropped, pushing the top back slightly was enough to create a pretty good fit that wouldn’t require a lot of finish work later.
Liftoff. Now the easy part is done and the real work begins.
Craig started work on the doors by removing 3-1/2 inch from the doors so that they matched the top posts. Rather than welding the cut-down door together and hanging it in the car with the assumption it would fit, Craig hung the bottom of the door and spent considerable time lining up the top part of the door.
With the top off, it’s easy to carefully cut some seam areas that will be butt-welded later.
Burrs along the cut-line must be removed before welding everything back together. By keeping the file at a 90-degree angle to the metal, burrs are removed without chamfering the already thin metal.
Plenty of checking was done to ensure that the door fit the opening correctly before the final welding was done with the heli-arc.
At this point, Jim and Craig have a Model A with two good doors and a chopped top, ready for the next step, filling the roof.
Time to begin putting the Model A back together again. If the layout and cutting were correct, there shouldn’t be a need to take the top off again.
Fill a Roof
Jim Petrykowski says, “A filled roof is like an enormous patch panel — one that’s located where it’s easy to see but hard to install and hard to finish.” The key difference between a roof and a regular patch panel is that you can’t just go out and buy a roof. You’ve got to either have one made or find a suitable roof on an existing car.
At the rear corners, the extra metal was left on the top; it slid down past the outer body panel as the top was set back on.
Having one made can be expensive. Because most roofs need just a little crown, the filled section is often made by an experienced craftsman on an English wheel. Most hot rodders take the easier course and look for a roof that can be transplanted from a junkyard refugee to the coupe or sedan in the garage.
Here’s the corner after the extra metal has been trimmed from the top. All welds will be butt-welds, so everything must fit very nicely before the welding starts.
Before running out to the junkyard, you need to spend some time planning. The new roof needs to be in good condition, the right size, and have the right amount of crown before it will work. The first step is measuring, how big does the new panel need to be? If possible, the existing car’s roof edges should be left intact. Most tops of old cars have more crown near the edge — if you cut the top way out near the edge, it makes it hard to match that crown to the crown of the transplanted roof.
This tack-weld at the window post shows how well everything fits. After final welding, there won’t be much finish work to do — and that's the whole idea.
Finding an appropriate roof section for a sedan is more difficult just because the area is so much bigger. Station wagons and vans are the likely donor cars, but you’ve got to find one with the style that you like (with or without ribs) and with the right amount of crown. Jim Petrykowski suggests that you look for a roof that’s, “on a car the junk yard has pretty well stripped - so it won’t cost as much. Don’t buy one that has any kind of obvious damage from people sitting on the roof, for example. Damage to a roof is hard to repair, time-consuming, and expensive. Avoid wagon roofs with holes for luggage racks, and don’t take one with any rust.”
When you tell the junkyard owner that you want the roof from that Mustang (good for coupes) or station wagon, be sure to take the entire roof, posts and all. Make sure it’s cut off with a saw, so the headliner doesn’t catch fire (and warp the roof). Also, be sure to take home the entire frame of the roof, rather than just the center skin, so that you don’t damage your prize on the trip home.
Once you’ve got the whole roof home, clean it and sand it before cutting it free of its framework. Strip it of paint like you would any piece of metal and then get ready for plenty of planning and measuring before the cutting and welding starts. When you do cut the new donor roof free of its supports, cut it with a zinger or shears so the top won’t warp, and cut the piece as large as possible.
Here, the front post sits on the body. The new post is a little small for the base of the post, due to the taper, but it’s not too bad. It’s hard to see, but the base of the post has been slit at the corners and will be shrunk slightly to match the upper post.
Before Craig went shopping for a roof, he and Jim made templates of the roof edges and the proposed roof center on the Model A so they would know what kind of crown the new roof should have (note the photo on page 59). The crown of the roof is vitally important to your car for at least two reasons. First, the crown of the donor roof must be such that it matches up with the shoulders of the existing roof. Second, how much crown the roof has through the center has a major impact on the overall look of the car.
Craig brought home the roof from a mid-1960s Mercury wagon. Once home, he stripped it of paint and then carefully cut it free of its framework.
The after picture. By planning carefully and then tilting the front posts back slightly, everything lines up without any major metal work.
The new roof was way too large for the Model A, and Jim spent considerable time moving it back and forth, trying to decide on the best natural fit.
When looking for the best natural fit, it helps to step back from the car, so you can actually see it. If the shop is small, it helps to tape the roof in what seems like the best position and then roll the car outside so you can stand back and better assess the fit, the crown, and the effect of the new top on the total look of the car.
Craig spends a lot of time test-fitting the upper and lower portions of the door, adjusting the hinges, and then fitting again before the two halves are welded together. Jim and Craig take their time; it’s easier to make sure the door fits correctly now than it is later. The cuts are made at the bottom of the window opening.
Once Jim and Craig decided on the best fit, Jim trimmed overlapping metal at both ends of the top. Next, they carefully marked the center of the body and the center of the new roof so it wouldn’t be installed with an offset to one side.
After the initial welds, Jim does a bit of adjusting with a hammer and dolly.
During this trial-fit period, Jim and Craig also determined the best angle and fit for the visor. Like the crown of the roof, the angle of the visor has a major impact on the overall look of the car. Some people put a header in across the top of the windshield before the roof is set on, but Jim and Craig decided the visor/roof assembly would provide so much strength that an extra header wasn’t needed.
Inner welds are made last — after the upper and lower portions of the door fit correctly.
It’s important that the crown at the edge of the roof match the crown at the edge of the opening. In some cases, a builder might have to cut the opening larger - though it’s usually easier to do the welding and finishing on the flatter part of the roof, when possible.
Jim Petrykowski on Filling a Roof
After twelve years of chopping tops and filling roofs, and a number of years building racecars before that, Jim Petrykowski has a few guidelines for filling a roof. “Over the years we’ve probably had to redo at least forty roofs where the guy got it so screwed up he almost ruined the whole car. On most cars, it’s the single biggest metal repair done to the car. If you measure the seam on the roof, it’s a lot of welding and a lot of heat. I’ve seen cars where the welding caused the body to shrink so much that there were big gaps in the top of the doors - the top of the car actually shrank by an inch on either side.
A close-up of the finished weld. The door gap is even and the welds are neat and small. Note that the upper and lower parts of the front post have been blended together very nicely.
“Usually, it’s easier to lay the new roof over the opening in the car (after deciding where the roof fits best), scribe it from inside where the two edges meet, and then butt-weld the seam. If a guy overlaps the seam, welds it, and then finishes it later with filler, the seam will usually become visible on a hot summer day. Remember that the roof gets a lot of sunlight and that makes it real hot, especially on a dark car.”
The finished work. Jim and Craig decided early on that two hinges were plenty, and that it made the most sense to use the upper and lower ones, even though some builders use the lower and middle.
“I tell guys that if they aren’t real good at welding, just tack-weld the roof in place and then get someone real good to hammer-weld the seam, either with a heli-arc or a gas-welding outfit. Wire feed welders often make a hard seam that’s hard to finish; it’s brittle and sometimes cracks later.
The top chop is finished, the doors are done, and the top is ready to be filled. How far out you trim the top opening depends on how good the metal is, and what you have to do to get a good match between the crown of the opening and that of the top.
“Whoever welds the top should move around, so they don’t create a lot of heat in one area. Weld in one part of the roof and then move across the top and work in another area. Too much heat can shrink the whole car or it can shrink one corner so nothing ever fits right again. I try to avoid any seams in the center of the roof; they’re real hard to finish later because the panel moves while you’re working on it and you have to reach way out in the middle of the roof. Always plan ahead to minimize the amount of finish work needed. I try to make the body man’s job as easy as it can be.
Before he went looking for a roof insert, Craig had a template like this one to take along, so he could find a roof with the right shape at the shoulder and the right amount of the crown.
“Shrinking is a hard thing to do, especially for people who don’t do it all the time. Guys at home should try to avoid situations where there’s too much metal. If there gets to be a bulge at one part of the seam, I usually cut a little slit and try to flatten that area out as I go along so I don’t have to go back and shrink it later. Anytime things start to go bad, maybe because the body isn’t square or there’s some old damage to the body that you didn’t see before, stop and fix the damage. The problems are always harder to fix later.
This is the new roof for Craig’s Model A, donated by a mid-1960s Mercury station wagon.
“The top and body should be cut so the corners are rounded, because they’re easier to weld that way. And the body should be well supported before you start filling the roof, so the heat from welding won’t be so likely to pull it out of shape or shrink the top.
“Like I said, filling the roof is like doing a giant patch panel. There’s a lot of welding and a lot of heat, all on an area that’s hard to finish and easy to see when the car is done.”
The wagon roof is way too big; Jim and Craig trim it after deciding which part of the roof has the shape they want. It’s easy to put a roof section on a little to one side — Jim and Craig will carefully mark the center of the roof and line it up with the center of the car before determining the final position of the roof.
Jim decided this time to cut and weld the roof as he went along. Before the welding started, Jim carefully cleaned the two edges, removing any burrs or raised metal. Burrs and nicks make it hard to do a neat weld and should always be cleaned off before the welding begins. The welding itself was done in a simple pattern. First, a three-inch-long section of the seam is tack-welded. Each tack-weld is hammered and dollied. After tack-welding, Jim carefully checks the area to see if the welding has created a bulge or concave area. If no corrective action is needed, then he welds the seam between two of the tack-welds, hammers and dollies that section, and then goes on to the next. All the work is done with a heli-arc welder.
A long seam like the roof is a time-consuming project. After working along one part of the seam for a while, Jim either takes a break or moves to the other side of the car in order to avoid the concentration of too much heat in one part of the roof.
As the roof is trimmed, there shouldn’t be any big kinks or bows in it. The new roof should lay nice and flat on the car. From the inside, you shouldn’t be able to see any big light leaks.
By working the seam with a hammer and dolly, Jim is able to arrange the steel and filler molecules into a strong, forged pattern for a very strong weld. The hammer and dolly work also flattens and neatens the weld and minimizes the amount of warping at the welded seam.
Working in this slow, methodical fashion over the course of three days, Jim is able to finish welding the seam, and Craig now has a Model A with a filled roof. Jim decided not to grind or metal finish the roof for at least two reasons. First, large body grinders take too much metal, cause too much damage to the remaining metal, and often grind impurities from the pad into the metal. Jim explains that if he were going to grind the metal, he would either use the zinger (a die-cut grinder) and a cut-off wheel to carefully take the tops off the welds, or just take a grinder with a foam pad and an 80-grit pad and run that across the seam to remove the worst of the lumps and bumps.
Here’s the new roof, partly installed. Welding in a panel this big leaves plenty of room for error that can ruin the car. Novice welders might want to tack-weld the panel in place and let an experienced veteran weld up the seams.
In this case, Jim chose to do nothing, because, “Whatever kind of finishing you do should be done in concert with the person who’s doing the body work. If I grind off the welds, the body man is probably going to grind it anyway and then we’re taking off too much metal. Most of the time I leave the seam after I weld it and hammer and dolly it. That way the body man knows exactly what the seam or repair looks like and he can deal with the whole thing from start to finish.”