Bending the Sideframe

Now that your bender is assembled, and you have decided on the back height and frame length for this chair, you are ready to start bending. This chapter describes how to bend the main sideframe tubes, drill the holes that will be used to attach the seatback, and drill the brake mounting hole.

Once the first two bends are made in the sideframe pieces, they will be set aside. Only after the x-brace is made and slid onto the sideframe can the third bend be made in the frame.

We have chosen 7/8" O.D. tubing for the sideframe because it is the smallest (and therefore lightest) size that can withstand heavy use. In Paraguay, 7/8" tubing has not been available. They have made a particularly heavy-duty chair out of 1" tubing and have found that it works quite well. The larger tubing only adds about a pound to the chair.

MATERIALS

ITEM QUANTITY PART OF CHAIR
* 7/8" O.D. Tubing 2 pieces, 5' (152 cm) long sideframe
Bicycle handgrips or tubing 2 pieces, 3" (7.6 cm) long handgrips
* 1" O.D. Tubing or 3/4" Thin Wall Conduit can also be used.

Note: In our design the sideframe tubing must fit snugly inside the pieces of tubing which form the bottom of the x-brace and the top of the footrest. Before selecting sideframe tubing, be sure that you can buy or make tubing in a size that will fit snugly over it. See Chapter 5 for tables on available sizes of tubing, and combinations of tubing sizes that will work.

 

JIGS AND BENDERS

(Hossfeld dies and a Hossfeld-style bender frame can be purchased as a part of the Basic Tool Kit. If you wish to make your own, instructions for making the bending frame can be found in Appendix A.)

(Instructions for making these jigs can be found in Appendix B. They can also be purchased as part of the Basic Tool Kit.)

DIRECTIONS

1) If you have not done so already, measure the customer and determine the height of the seat back and the length of the frame. (See Chapter 4 for information on how to design the chair to fit the customer.)

The following directions will be for a standard-size frame with a back height of 24" (61 cm) and a frame length of 17-1/2" (44.5 cm). Alter these measurements to make a larger or smaller chair.

2) Measure 3-1/2" (8.8 cm) and mark where to make the first bend in each 5' (152 cm) length of 7/8" tubing.

3) Set up the Hossfeld style bender to bend tubing using the die set for 7/8" O.D. tubing with a 2" bend radius. See Chapter 6 for a detailed description of how to bend tubing and how to set up the bender. Put some wax or grease on the draw block. Do not get any on the back block! If you are using one of the alternative sizes of tubing, check the chart in Chapter 5 for the appropriate die sizes.

4) Align the mark on the tubing with the positioning mark on the form die. Clamp a pair of vise grips onto the tubing right next to the back block.

5) Bend the tubing 90°, forming a right angle. Use the plywood square to be sure the angle is exactly 90°. A description of how to make the plywood square is found in Appendix B.

6) Remove the sideframe tube from the bender. Holding a straightedge along the top of the bend, measure 24" (61 cm) down the tube and mark the beginning of the next bend.

7) Align this mark with the positioning mark on the form die and bend the tubing 90° in the opposite direction from the handle. Use the plywood square to be sure the bend is exactly 90°.

When making this second bend be sure that the top of the tubing in the first bend is level with the top of the form die. If the tubing is tilting even slightly, the second bend will point off at an odd angle. Laying a straight edge along the top of the form die can help you to accurately judge if the tubing is correctly aligned in the bender.

8) Place the seat back tube drilling jig onto the sideframe piece as shown.

9) Clamp it in place with the drill press vise. Sight along the long piece of frame tubing to be sure that the tubing is aligned correctly in the vise. The long piece of tubing should be parallel to the column of the drill press.

10) Drill the seat back holes. The hole size should be about 3/16" (5mm) in diameter. Use the smallest size of hole that will accept a #12 sheet metal screw. When drilling the holes, only drill through one side of the tubing. Do not drill completely through to the other side. These holes will be used to attach the seat fabric to the frame.

11) Place a straightedge behind the second bend. Measure 12-3/4" (32.4 cm) down the tube and mark where the brake mounting hole will be drilled.

12) Place the brake hole drilling jig on the workbench. Make a level surface by adding pieces of 3/4" (20mm) plywood on either side of the jig. Position the sideframe in the jig so that it lies flat on the table. At the mark for the brake, use the jig to drill a 5/16" (8mm) hole all the way through the sideframe tube. Make sure that the drill is vertical. If the jig keeps the drill bit from pointing straight up and down, see Appendix B for instructions on how to adjust the jig to drill vertical holes.

13) Set these frame pieces aside until the x-brace has been made and slid onto the sideframe pieces. The third bend can only be made and the brake mounting welded in place after the x-brace pieces have been put onto the frame (Chapter 8).

IT IS IMPOSSIBLE TO PUT THE X-BRACE PIECES ON AFTER THE THIRD BEND HAS BEEN MADE.

 

 

 

 

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