Tips For Chopping Your Pre War Classic Car

By Curt Iseli   –   Photography By the Author

When customizing originated, the goal was to refine the lines Detroit provided and, in some cases, restyle more common marques to resemble their up-model counterparts. When I bought my 1941 Buick Super I felt like I had a head start. Pre-war Buicks were part of that up-model bracket to begin with, boasting sleek body lines, long wheelbases, powerful overhead valve engines, and some deluxe interior appointments. But there’s always room for improvement, and since I wanted to build a late-’40s/early-’50s–style custom, a chopped top was always part of the plan.

Much of the custom work has been done in my home garage, but lowering the lid was over my head, so to speak, so I turned to Cody Walls at Traditional MetalCraft. Since every car is different, we’ll save the particulars of how my Buick was chopped for the accompanying captions and use this space to share some of the “universal truths” I learned that will apply to most mid-’30s to late-’40s chops.

With the paint stripped, cut lines were marked in pen. We started 3 inches, marking the pillar centerlines to aid alignment during reassembly.

Planning and Research Tips for Successful Car Projects

As with any project of this magnitude, it’s important to start with a plan. There’s plenty of reference material out there, so take the time to research examples of cars like yours to see how they were chopped. When you find a profile you like, try to track down the owner or builder and ask questions. Often, they’re happy to share information and sometimes even construction photos detailing their efforts.

03 Stock profile of Buick car with paint removed and cut lines drawn
Here’s the stock profile with the paint removed and the cut lines mapped out.

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DIY Tips to Save Money on Car Chopping

If you’re paying a shop to chop your car, there are a few things you can do that will save money. First, don’t underestimate the time it takes to remove everything that needs removing. Decades-old rubber window gaskets will fight you every step of the way—and if you intend to save your curved glass backlight you’ll need to work carefully. Make notes on how window regulators and other door internals come apart, and bag and tag fasteners to ease reassembly later. Naturally, the seats, door panels, carpet, and headliner will need to be removed to avoid damage (or fire) once the cutting and welding begin. And don’t forget to number the headliner bows from front to back as you take them out. If you’re on a budget, there’s no sense paying a shop’s hourly rate to handle these tasks you can easily do yourself.

04 Cutting quarter windows of Buick car with metal cutoff wheels
The quarter windows were cut out first. Metal cutoff wheels easily slice through multilayer steel like these B-pillars with more accuracy than a Sawzall.

Sourcing Spare Sheetmetal and Donor Car Tips

Chopping a top has been compared to chopping an egg; when you remove the middle and reunite the top and bottom portions, there’s going to be some extra material needed to make everything fit back together. If you can locate a donor car and harvest some spare sheetmetal from key areas you’ll be ahead of the game. An extra pair of window frames (cut from the sills up) and the corresponding interior moldings will help because the tops of the chopped frames will need to be lengthened. A four-door donor will do just fine since the section that will need to be lengthened is straight. It will also be helpful to have a chunk of the donor’s roof taken from just above the door frames, encompassing the drip rail, inner door jamb, and about 8 inches into the roof itself. If you can’t find these parts locally, call some boneyards around the country that specialize in vintage tin. I sourced what I needed through “Flat-Top Bob” Owens at Owens Salvage in Texas who had a ’41 Buick four-door sedan that he was willing to aerate for me.

05 Removing inner structural steel from Buick car for hammer and dolly work
Inner structural steel was removed to allow access to the back side of the roof for hammer and dolly work. These pieces will be replaced later.

Effective Techniques for Metal Cutting and Welding

The last couple of planning and preparation steps involve bracing the body to keep things square (1-inch square tubing welded in an “X” within the cabin will suffice) and laying out your cut lines. At Traditional MetalCraft, Walls uses strips of thin, flexible plastic in varying widths (1, 2, or 3 inches) to mark off top chops and section jobs. Start with a conservative amount. Once you remove material and see how things look, it’s easier to cut more off than to add it back on.

We began with the 3-inch templates, marking the top and bottom cuts using a ballpoint pen. Pen contrasts with bare metal better than scribe lines (unless you’re using Dykem) and, unlike tape, it won’t burn back when you start cutting. Marking the vertical centerline of the pillars with a straightedge will help with realignment when you weld everything back together.

06 Welding square tube bracing in Buick car cabin to maintain body squareness
The bottom radiuses of the quarter windows remain in place for now. One-inch square tube bracing was welded in the cabin to keep the body square.

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 Effective Techniques for Chopping Car Roofs

In many cases, you can leave the backlite surround attached to the car and just lean it forward, but if you are removing it be sure to mark the centerline (on the surround and the roof). Anywhere the cut lines you lay out to make a sharp turn (like going up and around the backlite), radius the corners rather than marking hard right angles to reduce shrinking when welding seams. When it’s time to start slicing, cutoff wheels are faster and more accurate than hacksaws or Sawzalls. Spring for the metal wheels; they’re a little more expensive than composite, but they’ll last longer and won’t explode if the wheel gets stuck in the middle of a cut.

Whenever you encounter multilayer structural steel that inhibits being able to reach the backside of the roofskin (like the inner structure around the quarter windows, for example), don’t be afraid to temporarily remove it. That steel will need to be modified anyway, and having easy access to the back of the skin will help you accomplish better results. You can always replace those inner steel pieces after the hammer-and-dolly work on the roofskin is complete.

07 Making precise cuts around the backlite of Buick car
Here’s the moment of truth. Note the cuts around the backlite; welding a radiused corner won’t shrink the metal as much as welding a right angle.

There are a few things that have been explained in other top chop how-to articles that bear repeating. First, start by cutting the top off at the upper marks, then chop the pillars while they’re still attached to the body. Trying to cut pillars on the roof once it’s separated from the car is a difficult proposition. Also, eyeball your work throughout the process. All the measuring in the world won’t tell you if a chop looks right; you’ve got to use your eyes. And pay close attention to the size and shape of the quarter windows. So many chops go wrong because the quarter windows become too small as the top moves down (and forward).

In many cases, the main sections you’ll need to fabricate from scratch are the sail panels. Poster Board is handy for determining size and shape and it can also serve as templates when you’re cutting the new panels from 18-gauge steel. Since they’re one big compound curve, Walls uses a Pullmax and an English wheel or power hammer to do his shaping. This could also be done with a mallet, a beater bag, and a benchtop English wheel. That said, if you don’t have the tools or skills to form them on your own, consider having a properly equipped sheet metal shop tackle them for you. Having a properly shaped panel as opposed to a conglomeration of pie-cut sheet metal strips will result in a smoother profile—and a lot less filler.

08 Window frames of Buick car waiting for roof height finalization
Window frames will be chopped once the height of the roof is finalized. The backlite will remain anchored to the catwalk and simply lean forward.

Read More: More DIY Tips on How to Sand a Car for Painting

As the roof comes down, it will also slide forward so that the tops and bottoms of the A-pillars meet. In the back, you’ll fill the extra space by leaning or repositioning the backlight and filling the gaps with new steel. Around the sides, you can make up the gaps in the window frames and the sides of the roof using the parts you harvested from the donor car. If you can’t find a donor, these pieces can also be formed from scratch. Just take the time to replicate the inner structure, drip rails, and any feature lines that run through the window frames.

09 Realigning lower rear radius of quarter window after cutting B pillar
After cutting 3 inches from the B-pillar, the quarter window starts taking shape. Aligning the lower rear radius will take additional work.

Effective Welding Techniques

Once everything is tacked back in place, push the car outside or to the middle of your shop and take a good look at it from every angle. If the proportions look right and the lines flow it’s time to weld everything up. TIG or oxyacetylene welding will yield the best results since they can be planished (hammer-welded), whereas MIG welds are harder and can only be ground smooth. Heat is inevitable in any type of welding, so regardless of the welding process you choose, it will be necessary to massage the expanses of steel once everything is stitched back together. Walls use a combination of hand hammers and dollies as well as a portable, pneumatic planishing hammer, working one section at a time to planish the welds and address any high or low spots. Spending extra time at this stage will reduce the amount of filler needed before paint.

While at this point it may feel like the lion’s share of the work is complete, there’s still work to be done before the chop is truly finished. Interior garnish moldings will need to be chopped and reshaped, glass will need to be templated and cut, and then there’s the whole reassembly process. (You did bag and tag all those fasteners, didn’t you?) But all of that will have to wait for our next installment. Now is the time to stand back and take in your car’s newly restyled, full-custom profile. MR

10 Reshaping quarter window radius on Buick car using a shrinker
Walls reshaped the quarter window radius by shrinking the pinched seam on a ’40s-era shrinker. Though more time-consuming, this could also be accomplished with pie cuts and welding.
11 Moving the rear corner of the window forward for alignment with new window shape
The rear corner of the window was moved forward about an inch to align with the new window shape. Take care not to make this window too short.
12 Checking the profile of Buick car with the roof in place
With the quarter window dialed in, we set the roof in place to check the profile and make any final adjustments before welding up the A-pillars.
13 Preparing to cut out and replace sail panels after leaning forward the backlite
Once the backlite is leaned forward, the sail panels will be cut out and replaced. The gap above the door will also need to be filled.
14 Lengthening roof and door tops by cutting sections from a donor car
When the top is lowered, the roof and door tops essentially must be lengthened. We cut corresponding sections from a donor car to fill those gaps.
15 Trimming fitting and welding pieces from a donor car into the Buick
Those pieces are trimmed, fitted, and welded in. This provides the driprail and inner structure, while single-layer sections of roofskin are formed from 18-gauge sheetmetal.
16 Mapping out replacement sail panels on poster board
Replacement sail panels are mapped out on poster board. The markings indicate where we’ll need to shrink or stretch the metal to form the compound curves.
17 Transferring basic shape of panels to 18 gauge steel and roughing contours
The basic shape of the panels is transferred to 18-gauge steel, then the contours are roughed in on the Pullmax.
18 Fine tuning panels on the Trick Tools MetalAce English Wheel
Once the curves are established, the panels are fine-tuned on the Trick Tools MetalAce English Wheel.
19 Holding new sail panel in place with Clecos and marking trimming areas
Clecos hold the new sail panel in place while Walls marks where the original roof will be trimmed away.
20 Trimming around the new panel for a neat and clean welded seam
Taking care while accurately trimming around the new panel will help facilitate a neat and clean welded seam.
21 Forming new sheet metal to fill small gaps above backlite and side windows
New sheetmetal is formed to fill the small gaps above the backlit and side windows as the piece is clamped in place here.
22 Patchwork of sheet metal needed to stitch a chopped top back together
This shows the patchwork of sheet metal required to stitch a chopped top back together. The more drastic the chop, the more extensive the metalwork.
23 Gap in the middle showing the need to lengthen window frames
You can see by the gap in the middle that as the window frames are chopped, they need to be lengthened to fit with the lower roof profile.
24 Using straight sections from donor car window frames to fill the gap
Straight sections from the tops of the donor car window frames will fill the gap.
25 Completing the window frame with a 3 inch section from the donor car
A 3-inch section from the donor car completed the window frame. Later, we’ll check the hinge adjustment and add metal to the door edges to tighten the gaps.
26 Fine tuning all welded seams with a hammer and dolly
All welded seams are fine-tuned with a hammer and dolly or pneumatic planishing hammer.
27 Using a portable planishing hammer to address high or low spots in new steel
In addition to planishing the welded seams, Walls uses a portable planishing hammer to address any high or low spots in the new steel.
28 Replacing chopped inner structural pieces after planishing the roof
Inner structural pieces were cut out to allow access to the roofskin for planishing. Once the roof was dialed in, those inner pieces were chopped and replaced.
29 Finished profile of Buick car with chopped vent windows and garnish moldings
Here’s the finished profile. We’ll still need to chop the vent windows and garnish moldings and make templates for the new glass, but this is a pretty good start.


Traditional MetalCraft
(302) 747-6140

Click on this issue’s cover to see the enhanced digital version of Turret Top march 2024

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