Another aspect of high quality body and paint work is the gap sizes being perfectly consistent. This means several things:
•Each gap is ‘straight’ when sighting down it.
•Each gap is exactly the same size from beginning to end, with no variation in width.
•Every gap around the entire panel is the same exact size.
•Every gap on the entire vehicle is the same exact size, at least for similar panels. A typical example is the doors, hood and deckled gaps should all be the same size.
There are several stages of making the gaps perfectly precise. The absolute most important stage is during metal work, and making them as close as possible in metal. There will be opportunity to get the gaps dialed in during the body work stages, but that is absolutely not a crutch for doing subpar metal work.
The first step is to figure how how big the gaps need to be. There is no set rule to what size to make the gaps. Nearly every project is going to be different. Some European cars, such as earlier Porsches might be around .090” door gaps, while a 1955 Chevy Bel Air might be .155” gaps.
The size of the gap is almost always determined by how much clearance is needed. This means that the hinge side of the doors is what normal determines how big of a gap is needed for the doors to open and clear the fender while opening. A lot of times, the inside of the fender may need to be cut up to make more clearance for the door. Often times, that inside flange of the fender is at a pretty big angle, not giving much room for the door to open. The same is sometimes true for the door edge, the thinner it can be, the better.
The gap doesn’t really need to be set to a certain width, it should just be as tight as it can be made, and then measure what size it is. Using a digital calipers works very good for this. Digital calipers are fast and accurate, and is very easy to go around and check the other gaps. Using a caliper and knowing the actual size will also be helpful in the later steps.
The width of the gaps is typically done in conjunction with checking and adjusting the panel flushness with the aluminum straight edges. If the panel edges need to move out, which they almost always do, the gap will open up. So, spending the time to get the gap widths dialed in before working on the panel flushness is just a waste of time. The gaps will change when the edges need to be moved around. This is a mistake many fabrication departments make. It’s nice to have the gaps appear as though they are correct and nice, but it’s really just a waste of time if the edges aren’t in the right spot for body work.
The first and most obvious step is to make sure all the panels are adjusted as close as possible. All panels also need to be on the vehicle first. It might seem like the doors and fenders are in the correct spot, but the hood or header panel or front valance might effect how it all fits together, and you need to know this before doing anything. Do the work ahead of time, and assemble everything to avoid surprises and even more work down the road.
It’s best to adjust the panels so no material has to be taken off of the door edge, but sometimes that still needs to happen. This is purely a judgement call. It might be possible that part of the edge needs to be trimmed down, and some of it needs to be added onto. Or, you could adjust the panels so it only has to be added onto and not cut into, but that might effect sometime else. The point is, there’s going to be a lot of times where it just comes down to a judgement call, and try to think through as many options as possible, and then choose one and go with it.
Trimming & Weldning
Normally, first will be trimming down the tight areas. Most times this is down by trimming the edge of the door down using something like a 90 degree grinder, otherwise known as a 3” roll disc. A good method is to use layout dye on the edge, and scribe where the panel needs to be trimmed back to.
After trimming is done, it’s time to weld. TIG welding the edges is much preferred over MIG welding. This is for several reasons. TIG welding allows you to control the amount of heat compared to fill rod going into the panel. There are usually 3 pieces of metal when welding a door edge back together, the door skin, the door shell, and the hemmed edge on the back side. Being able to control the heat better allows you to melt further into these three pieces before adding the fill rod into the edge. Once you’re adding the fill rod, you’re then able to add more, ensuring the weld will have penetrated deep enough into the edge, and there will be plenty of material on the edge to grind and file. A TIG weld can also be hammer and dollied and moved around with a much lower chance of cracking.
Grinding & Filing
As for grinding and finishing the welds on the edges of panels, its best to begin by grinding the weld facing the outside of the door first. This will give you a flat and smooth surface to apply layout dye again and scribe a line where the weld needs to be ground back to. When grinding the edge back, it works well to do the majority of the grinding with the 3” roll disc. When the weld is close to where it needs to be, then switch to a hand file and finish it. This is a little bit slower, but it ensures the edge being as straight and crisp as possible.
Sometimes there’s some voids in the face of the weld. It’s a good idea to go back and weld up the voids, and grind and finish that smooth. If those aren’t welded, or if there’s any voids remaining, they must be sand blasted prior to body work or epoxy. There can be absolutely no weld coloring in the metal under anything, it must be completely gone. So, every weld pit must be absolutely clean and white metal.
To mark the scribe line on the door edge, there are a couple ways to do it. One way is to use the calipers, set to the correct size, and place one side against the other panel, like the quarter panel edge, and drag it down the door, leaving a small scribe line where the door needs to be filed back to. Another method is to measure off of the adjacent panel, and place a small mark, doing this every several inches all the way down the panel. Then, make a nice tape line using the small scribes, and file up to the tape.
Keep in mind, the edges of the panels also need to be ‘straight’. So, going off the quarter flange might not be a straight enough line, and you might need to straighten it out some. The same is true of the door and fender edges. It’s best to start with getting one of the edges straight, probably the door edge, and then make the fender edge match it.
While in the metal work stages of making the gaps correct, all gaps need to be made as close as possible to being correct. However, the door to quarter edge, or any other panel that has a flange like a quarter panel, has a little more leniency because that edge can be dialed in more in the body work process. Where there are two hemmed edges, like a typical door and fender, that gap needs to be metal finished, both the flushness and the width of the gap. This is a time consuming and often challenging process, but it needs to be right.
When using a caliper, or anything else, to measure the gaps, it’s important to make sure it is in the gap squarely at 90 degrees. This is mostly true with the door to quarter panel gaps. It’s easy to make the two edges the correct size, but the quarter panel flange is probably at an angle, making the gap tighter further in the gap. The entire gap needs to be large enough, not just the edges. Sometimes, more cutting is required. The best option might be to cut the edge of the quarter panel and move it around in order to achieve the correct gap.
Making the gaps actually correct and ready for body work can be a big task and time consuming. This step is also very important to not only end up with a much better end result, but also to avoid problems in the coming steps. It is always worth spending the time and effort to make everything correct before moving on.