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Chop that top

It only takes two hours - we show you how - on AMT/Ertl's 1965 Buick Riviera

By Tim Boyd
In-Depth Techniques
Within hours of the opening of Scale Auto's "Roundtable" (August 2005 issue), in poured the questions - and the subject of chopping tops kept coming up: Is there an easy way to reduce the height of roofs for street rods, customs, and '50s/'60s street warriors? Can chopping be done by the less-experienced modeler? How long does it take to chop a top? Are certain types of cars easier to chop than others?

I've done articles on this subject (see References box), and the short word is that chopping anything - aside from a 1920s to early-1930s body, with completely upright roof posts - is a fairly involved procedure.

When windshield pillars (A-pillars) and rear window pillars (C-pillars) began to slant with car designs starting in the mid-1930s, chopping became far more complex. Add in the "tumblehome" that became more popular in car design as the century progressed, and chopping a top became similar to taking a section out of an upside-down ice cream cone: When you put the pieces back together, the top part is too short in length and width to bridge the gap of the lower part of the cone.

This means that after removing the two- to five-scale-inch top section, you typically must cut the remaining roof apart in both directions so that you can extend its length and width to bridge the larger gap.

(When viewed from behind the car, tumblehome is the amount that the "greenhouse" of the car tapers to a narrower form from the top of the fenders to the roof.)

In a desire to show enough of the chopping technique to allow our first-time top-choppers to get their feet wet but not to overwhelm them, I wondered if there was a simpler technique I could demonstrate for this article - one that would definitely reduce time and complexity, but would be a bit restricted in its application. In our own version of "Reality TV" our studio cameras would record just how it all worked out.

This simplified technique is best suited to cars of the late 1950s to early 1970s that have narrow and straight A-pillars, wide C-pillars, and relatively little tumblehome.

The 1964-71 Thunderbirds, Rivieras, Toronados, El Dorados, mid-to-late-1960s Ford Galaxies, and 1969-73 Chevy Impalas are good candidates for this technique; the 1949-51 Mercurys (thick A-pillars and relatively narrow C-pillars) and the 1968-70 Chargers (severe degree of tumblehome) would not work for this top-chopping approach.

This technique works only for mild top chops - less than three-scale-inch reduction in vertical height (less than 1/8 inch in 1/25 scale). This is OK, as when building 1960s cars, car-design experts view radical chops as being outré; a two-scale-inch chop yields a far better result than a four- or five-inch chop.

So although it's a bit narrow in its application, in theory our simpler approach will still apply to many of the bodies that fit the currently popular genres of lowriders, mild street customs, and "real street/g-force style" 1960s-vintage street machines.

Did our theories work? Follow the next 19 steps and decide for yourself.

In less than two hours (including the time to set up the photography and deal with some superglue that wasn't bonding particularly well), I completed an effective 2½-scale-inch top chop on AMT/Ertl's 1965 Buick Riviera.

The finished body will require minimal use of body putty/surfacer, and no molding or reestablishment of character lines will be needed.

I don't want to oversimplify here; if this is your first top chop, you may want to practice on an extra body rather than your in-process contest-winner.

As with any technique of this type, practice makes perfect. But I rate your chances of success as very good if you've followed the guidelines above.

We hope that if you've been considering top-chopping for the first time, you'll accept our challenge, follow along with the photo steps, and add top-chopping to your repertoire of model-building skills. Drop us a line and let us know how it works out!

We're using AMT/Ertl's evergreen 1965 Buick Riviera to demonstrate how to perform a 2½-scale-inch chop to the "greenhouse" area of the body. Begin by removing the vent-window pillar (marked in red).

Instead of chopping the A-pillars, we'll bend them to a more-horizontal position than the relatively upright configuration of the stock body. To help the bending process, "score" a horizontal cut at the bottom of the A-pillars. The trick is to make the cut deep enough so the pillar will bend, but not so deep that the pillar joint breaks during handling.

Turn the car over and "score" along the inside joint where the A-pillar meets the roof. Cut to about 1/3 of the depth of the styrene to preserve strength, while enabling the styrene to bend at the joint later in the chopping process.

Place some masking tape on a hard surface (glass or a mirror works fine), then cut a strip to uniform width. In 1/25 scale, a 1/8-inch width equates to a three-scale-inch chop. For this 21/2-scale-inch chop, I cut the tape to a width of 7/64 inch - "sectioning tape" in the following steps.

Apply the sectioning tape to the C-pillar area, with the top of the tape serving as an extension of the top of the side window opening (also known as "DLO" for "daylight opening"). I've added red marks at the top and bottom of the sectioning tape as a visual guide for the razor-saw cuts to come.

Apply some tape across the top of the roof, just forward of the joint of the roof top with the backlight. We'll only cut along the back edge of the tape (signified by the small arrows), so the width of this tape is not important.

Begin by cutting across the top. Note that the razor-saw blade is angled to be parallel with the backlight. I cut deeply enough to reach the bottom of the sectioning tape on each side, but as you'll see, I later extended this cut all the way to the bottom of the C-pillar.

Turn the body on its side and complete one cut along the top of the sectioning tape, then make a parallel cut along the lower edge of the sectioning tape. Cut all the way through to the angular cut made in the previous step, so the piece of the body attached to the sectioning tape is cut free. Repeat these steps for the other side.

After the cuts are complete, the project should look like this. The roof section is standing free at the C-pillar area, held in place only by the forward A-pillars. The amount removed doesn't look like much here, but trust me: the end result will be striking.

Carefully push the roof section to the rear, enabling the A-pillars to bend at the intersection with the roof and the beltline of the body. This is best done as a series of bending maneuvers so the styrene will accept the new rearward and downward position of the roof panel. This approach probably will not work with more-brittle resin aftermarket bodies.

After matching the roof section to the C-pillars, it became obvious that I would have to bend the C-pillars inward where they intersected the roof. I extended the cut shown in Step 7, again cutting parallel with the angle of the rear window. I cut all the way to the bottoms of the C-pillars.

Bend the C-pillars inward with your thumbs, again using a series of bending maneuvers. To help the styrene bend, run hot (but not boiling) tap water over the intersection of the C-pillar and the fender for 20-30 seconds, then repeat the bending maneuvers. The tops of the C-pillars should mate with the slightly narrower roof panel without having to be held in place.

Continue to test-fit the roof in its new location by pushing it rearward and slightly downward. As shown here, you are striving for an alignment where the top of the DLO is parallel to the bottom of the DLO/beltline. When all is set, use super glue to attach the roof at the rear C-pillars.

With the roof in place, the rear window is now too tall. Apply some sectioning tape just below the top of the rear window opening. Remove the styrene beneath the tape by cutting along the top and bottom surfaces of the sectioning tape.

After the last step is completed, you'll have a separate piece of styrene representing the top of the rear window. Test-fit it back in place, filing down the mating surfaces if necessary to be sure that the top of this piece mates with the top of the remaining roof panel.

Here's the new rear-window treatment. In addition to gluing the top of the rear window frame in place, apply gap-filling super glue along the remaining cuts from Step 11. Reinforce earlier joints if necessary, so the body will stand up to the filing steps to come.

Before additional bodywork, I reinforced the A-pillar joints from the inside of the body with narrow strips of K&S sheet brass, glued into place with five-minute epoxy.

Use a flat file to "work" the mating surfaces of the roof, C-pillar, and backlight. If you did the previous steps correctly, it shouldn't take too much work to file achieve a consistent surface, requiring only minor filling along the seams to make the body ready for paint.

Clean up the A-pillar surfaces with the file too, in case there is any irregularity from the earlier bending maneuvers. Use the bodywork techniques in the upcoming "Body Building Basics" article (August issue) to prepare the body for the color paint coats. During final assembly, you'll need to cut the windshield apart from the rest of the clear styrene casting in this kit, but after this step it appears to fit perfectly. In some cases, you may need to cut a new windshield from clear sheet styrene to fit the new angle of the windshield pillars.


References

"Building a Late Model Custom," Scale Auto Enthusiast #13, May/June 1981 (Chopping a 1970 Impala)

"Chopping the Mercury Top - Getting it Right the First Time," Scale Auto Enthusiast #14, March/April 1983 (Two methods for chopping a 1949-50 Mercury)

"Retro Rod," Car Modeler 1999 (Chopping a 1932-34 Ford pickup)



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