Clay, Application to Refinement

 

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 Corvette Scale Model (pt 2)

Armature build (pt 2, page 1) (pt 1) (pt 3)

In the previous section Armature Build Part 1, I covered the method used in producing the outline of the Styrofoam? on the tracing paper and the marking out of the baseboard that will carry the Styrofoam?

This tracing paper will be the template for cutting out the foam but first I have to glue the baseboard together. These two pieces will be the backbone of the armature. The materials for this stage are;

  • 3/4 inch plywood

  • Titebond II waterproof wood glue

Plywood for producing the base board to carry the Styrofoam.

As you can see from the image, the plywood has been cut on the table saw to give two pieces, one at 27" x 8 7/8" x 3/4" or 685.0mm x 225.0mm x 18.0mm. The second piece at 20" x 8 7/8" x 3/4" or 508.0mm x 225.0mm x 18.0mm.

Just to recap on the reason why the two pieces are a different size. The front end of the Corvette at 1/5th scale is very slim and to ensure adequate material i.e. foam and clay, the baseboard has to be staggered. I opted for a double thickness base board to ensure minimal or zero flex in the model.

The wood glue, Titebond II is normally carried by your local hardware store or D.I.Y centers such as Lowes or Home Depot just to name a couple.

This glue acts pretty fast, forming a skin within 20 minutes and hard within 4 to 6 hours. I used a piece of cardboard and cut teeth in with scissors to give a notched effect when I applied the glue. This helped to supply glue to both surfaces when rubbed together.

To stop the plywood from sliding away from each other when glued, a couple of 1 1/2 inch nails were hammered in. This will hold both pieces in position while the clamps are put into place. 

Titebond II a premium waterproof wood glue.

Both base boards glued with Titebond II and clamped.

The six inch C clamps staggered along the length of the plywood applies even pressure so as to assure adequate bonding. This will prevent the plywood from curling and maintains an even thickness.

Clamping of base board showing nail and clamp position.

The close-up photograph to the left shows the nail hammered into position, this helps to keep the boards aligned while the clamps are put into place.

I always do this  purely for my own benefit so that I don't have to worry about the boards sliding on the glue when clamping. This will give a clean aligned baseboard for the model. It is not a necessary procedure but it will make life easier especially if the task is being done alone.

Once again the close-up to the right shows the offset of the boards to allow adequate materials for the front end of the model. The nail set into the two pieces of plywood eliminates slide on the glue while clamping takes place.

 

Offset of the plywood allows sufficient material on the front end of the model.

The next stage once the base is made is to make the towers that will lift the base into the correct position. The material for this can be a simple piece of 2" x  4" studding used in construction. You will find the dimensions to be closer to 1 1/2" x 3 1/2" because it is already planed from its rough state. 

The sizes that are needed for the towers are, 2 3/4" x 1 1/2" x 8 7/8" or 70.0mm x 38.0mm x 225.0mm. The most important dimension is the height, 2 3/4" or 70.0mm, this is the amount of lift needed to bring the baseboard into the correct position. The 1 1/2" or 38.0mm thickness is not critical and the length for each of the towers, 8 7/8" or 225.0mm should correspond to the width of the baseboard.

Tower placed into position on the baseboard.

From a length of studding a twenty inch piece is cut off on the compound miter saw. This will provide enough material to make both the towers required.

The first process is to ensure that the sides are square to each other. For me to achieve this I chose to use the table saw. My first task is to skim the edge to get my first flat plane. I then cut the width to 2 7/8" or 73.0mm, this will allow me enough material to get the precise width after truing the sides.

For the side faces I set the fence of the table saw so that the blade just skimmed off the face allowing any twist to be taken out. This will then be repeated for the other face. Once this was done I could concentrate on skimming both edges to the width required, 2 3/4" or 70.0mm. I decided to trim the edge in two passes instead of one to make sure that the towers would have a flat face that would seat onto the table and the model baseboard. 

Once the overall height is achieved the length can be marked out with a combination square and then cut on the compound miter saw.

With the two towers now cut to height and length, positioning onto the baseboard is the next procedure. The first task is to mark onto the model baseboard the wheelbase so that the towers are positioned centrally. This will put the towers behind the wheels when they are in position. The wheelbase for the Corvette 1/5th scale is 531.0mm or 20.9" and the baseboard is set equally between the wheel envelopes. In this instance I decided to mark 75.0mm or approximately 3" from the front end of the board for the center of the front axle, from that point the wheelbase is then marked on, leaving an overhang of 79.0mm or approximately 3 1/8". These marks were squared across the board with a combination square ready for aligning the towers.

Now that the wheelbase position has been established on the model baseboard, a centerline is scribed through the thickness of the towers so that they can be aligned with the centerline of the front and rear axle. To hold the blocks in the correct position on the baseboard, one inch double sided tape is placed on the underside of each block, then pressure is applied to position, ensuring that the centerline on both sides of each block lines up to the line on the baseboard.

Baseboard with both towers affixed.

With the blocks held in place on the baseboard with double sided tape a register mark needs to be made on the inside of each tower with a pencil. This mark on each tower and baseboard will allow me to place them in the correct position each time, as there will be several removals during the doweling process. It also eliminates the possibility of putting them on the wrong way around.

From the end of each tower a mark was made one inch in from each end. This will be the center spot for each of the dowels.

The size dowel that I chose for this project was 7/16". This is more than adequate to keep the model stationary on the board for this project. If the scale factor was bigger then I would have gone up a size to 1/2". The dowel size is relevant to the amount of weight the model will carry. If the dowel size is too small there may be a small amount of movement during the initial blocking in process because of the weight of clay being pushed onto the model.

To drill the dowel holes I used a 7/16" spade bit, the reason for this is, this particular bit has a central point that will easily pick up the marked center points of the dowel locations on the towers. With the drilling process, the hole needs to be drilled completely through both tower and baseboard so that when the baseboard is placed into position on the model table the holes can be drilled through the baseboard to give a correct location on the model table. This will prevent any miss alignment to the model table.

Drilling the holes requires two settings because of the amount of travel of the drill press quill. First off, set the baseboard on top of a piece of spare plywood for this simple reason, the spade bit is going to travel all the way through the baseboard and it's better to drill in to wood than the the bed of the drill press. I clamped the baseboard down to the drill press bed to allow freedom of my hands, that is, I would not have to use one hand as a clamp. After clamping, the bed was raised until the point of the bit just touched the center mark of the dowel position, the drill press bed is then locked into position.

Boring the hole is a simple procedure but make sure that you back the bit out of the hole regularly to clear the hole of wood chips. This will prevent the hole from clogging and possibly moving the tower off of the double sided tape. With my drill press the quill has a travel of approximately 4" or 100.0mm which means the bit does not travel all the way through on the double thickness of baseboard plus tower as the overall thickness is 108.0mm or 4 1/4". 

To achieve this a second operation is needed, the table has to be unlocked and elevated enough so that the bit will complete the through hole. The setup is, turn off the drill press and elevate the table allowing the bit to travel down the hole. Make sure there is enough elevation for the bit to complete the hole, hand turn the bit to ensure that it is still central to the already drilled hole and relock the table. Double check that the bit still runs freely before powering up the drill press, then complete the boring of the hole. This same procedure can be used to complete the rest of the holes. If there is a question that the double sided tape will move when boring the second hole, secure the first with a length of wooden dowel rod, this will locate the first hole position securely.

With the towers secured to the baseboard the next step is to locate the baseboard to the model table and this I will cover in Armature build (pt 2, page 2)

Copyright © 2006 - 16 Steven Austin

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