Curved Corner Frame Construction and Background Installation

By Kevin N. O'Brien  Peoria, IL

Introduction

The surfaces for this background installation were finished basement walls. As a result, one of the project goals was to minimize the number of holes that needed to be drilled into the walls themselves. To meet this goal necessitated the creation of a freestanding frame with the background mounted prior to hanging. The shape of the O scale layout is a L shape with a single curved corner. One wall is 10' and the other 12'. This mounting technique draws on some of the ideas presented in articles by Ken Spelke entitled "Frame Construction and Mounting" and also by Hal Estill entitled "How to Install a Curved Corner Background".

Selecting the Proper Backdrop Size

Clearly, the dimensions called for in this installation were not going to be accommodated by a single backdrop. The question was how many images would be required and at what length. The fact that it was an O Scale Layout dictated that the 36' backdrop height would be appropriate. The first step of determining the number of backdrops is to calculate the continuous length required by the backdrop. This was accomplished using a spreadsheet and the product information contained in the Backdrop Warehouse site. A sample of the spreadsheet follows. Note the deductions necessary to remove the labels and overlap.

Layout in Inches

Length 12 144.00

Width 10 120.00
Total Length Required 264.00
Remove corner replaced by curve 2 x 30" 60.00
Total without Corner 204.00
radius of curve corner 30 47.12

(2 x Pi x r) / 4

Add curve length 251.12
10ft backdrop length x 2 130 260.00 length from web site
Backdrop Material Left Over 8.88
label deduction x 2 (1 per backdrop)1.25 2.50
Remaining Material 6.38
Deduct Overlap 5.5 0.88 As long as this number is > 0 you have enough material

Frame Construction

Due to the length of the two frames that will be joined by the curved corner, the ability to find straight lumber was going to be a challenge. The final lumber purchase list follows:

o 2 1" x 3" x 12' for the frame top and frame bottom for the 12" wall

o 2 1" x 3" x 10' for the frame top and frame bottom for the 10" wall

o 13 1" x 2" x 28 " for the vertical frame supports

The overall vertical dimension of the frame is 34 ". The reason for the odd number is that the printed surface on a 36" x 10' backdrop is in fact only 34 ". The intention of this construction was to only have the printed surface showing; therefore, the frame was constructed to accommodate only the printed area. The lumberyard does not actually carry lumber in the 1" x 3" dimension for the lengths of 10' and 12'. To accomplish this some 1" x 6" boards were cut in half at the lumberyard for a nominal fee. This was done in an effort to maintain the straightest resulting board possible. Interestingly, the board did warp slightly the moment the saw blade finished the cut and so steps were required throughout the construction to get the frame square.

 

Wall Frame Assembly

The frames were assembled using corner brackets that can be found in aluminum or steel at most home improvement stores. In addition, some steel plates with screw holes (see picture Backdrop Mounting Bracket Installation) were used to anchor the outside of the vertical supports to the top and bottom frame boards to ensure that the frame was rigid and resisted warping. The most successful and fastest method to create the frame was to use a long clamp to hold the vertical frame board to the two horizontal boards before attaching the corner brackets. This can be seen in Fig. 1. All corner bracket holes were predrilled to avoid splitting the wood. This step is repeated until the entire single framing element is complete. For added strength wood glue was used at each contact area. Once complete the frame should resemble the picture in Fig. 2. Note you can see the mounting brackets used to attach the outside vertical supports to the top and bottom plates. This same construction technique was used to create the second wall frame.

Frame Attachment at the Corner

Once the two frames are complete it is time to join them together at the corner. This was accomplished using larger corner brackets. These steel brackets were 3" long on each axis to provide strength to the joint. Corner bracket installation is illustrated in figure 3

Creating Curved Framing Elements

Now that the frames are joined into an L Shape, it is time to begin creating the curved corner. The curved corner radius was chosen to be 30". This radius was selected to ensure that there was enough room for the train to clear the background on its 21" radius curves. 5/8" Plywood scrap pieces were used to create the curve. A 30" square was drawn on the board. A nail was lightly driven into a corner of the square. A small thin wire and pencil were attached to the nail. The pencil should start at one of the other corners. Trace the circle on the board by moving the pencil from one corner to the other. Cut the board along the traced line and you will end up with the curved corner support for the backdrop. Two other curves were created the same way. These will be placed into the corner were the frames are joined together. They are attached at the top, middle, and bottom of the frame. Screw supports blocks into the vertical framing structure at the two edges and the corner. This will create a platform for the plywood to rest on. Place the curved corner piece on the supports. A single screw down into each support block held the curved board in place. The finished product can be seen in Fig. 4. The frame is now complete and should resemble Fig. 5.

Attaching Hardboard to Frame

1/8" Hardboard (wallboard, or Masonite) was used to cover the frame to provide a smooth surface to attach the backdrop. This material is fairly flexible and had no trouble curving to the 30" radius of this corner. If this material is moistened on both sides, curves of even a 12" radius are possible. Hardboard is purchased in 4'x 8' sheets like plywood. It had to be cut to the required 34 " height of the frame.The hardboard was attached to the frame using small screws. It is vital that the hardboard starts straight (true) or by the time you get to the corner, the board will want to dip or rise above the frame. Once the three pieces are attached the frame will look like Fig. 6. To finish the surface, the screw holes and seams were covered with packing tape.

Backdrop Mounting to Finished Frame

The two backdrop prints are now ready to be mounted on the framed surface. To ensure that the print was applied correctly, a thin pencil line was drawn on the back of the print were the top of the printed material started (the bottom of the border). This should line up with the top edge of the hardboard throughout the installation. In addition, a vertical line was drawn on the backside were the backdrop was to begin. This eliminated the product code from showing on the finished surface. The backdrop was attached to the hardboard using Elmer's Spray adhesive. Three people were involved in the installation. One person stood behind the frame to ensure that the frame top lined up with the line on the back of the backdrop. One person applied the spray adhesive and rolled the surface with a clean paint roller. The third person held the remaining backdrop in a roll. The backdrop was installed in two-foot sections at a time. A thorough coat of the adhesive was applied to the two-foot section. The backdrop was placed against the hardboard and rolled into place. The spray adhesive was easy to apply but the residual spray coats the floor and gets very sticky, be sure to use drop clothes in any finished area. This process continues until one of the prints is completely installed. It should look like Fig. 7.  It is now time to overlap the first image with the second to create the transition. The first step is to cut off the border of the second image on the side that will transition with the first image. This is done using a very sharp razor blade and a straight edge. If the blade cuts from the front of the backdrop there is the possibility that you will be able to see a thin white strip from the underlying media. A successful fix to this problem is to cut the backdrop from the back ensuring that the blade is angled away from cut edge (angled into the image, away from the border). This will cut the white backing material slightly inside the cut of the printed material and will ensure that it is not seen from the front. As with the first, the second image is marked on the back using a pencil where the bottom of the border should be on the topside of the print. To ensure a tight bond of the second image over the first, a cardboard screen was placed over the first image to protect it while the adhesive was sprayed onto the overlap area and first two feet of the hardboard. Position the second image to ensure a smooth transition and roll it into place. The same mounting procedure was followed until the second image was completed. Once the two images are attached to the hardboard, the borders can be folded over and stapled to the top, sides, and bottom of the frame. Details of how to handle corner folds can be seen in Fig. 8. It was necessary to cut slits in the border around the corner to get the border to lay flat against the frame. Once all of the borders are folded over and stapled, a final application of packing tape to the folded edge ensures that it will be smooth and that no ripples will be visible from the front. The final product can be seen prior to hanging in Fig. 9.

Hanging the Frame

Prior to hanging the frame, mounting brackets need to be attached to the back of the frame. This was done using the same four holed steel plates used to secure the outside of the frame. The mounting bracket will look like Fig. 10. Hold the frame up to the designated area and mark the bracket holes with a pencil. Make sure that the frame is flush with both walls in the corner. Remove the frame and drill holes to accommodate dry wall mollies. Sink the mollies into the holes at all locations. Bring the frame back into the installation position and install screws into all bracket locations. The installation is now complete and an immediate impact to the layout should be seen. Illustrations of the early stages of layout construction with the backdrop in place can be see in the before Fig. 11 and after pictures.