Step 1: Parts List and Tools Needed
1x 18 inch of ¾ inch diameter PVC pipe (you may need a little more)
1x 24 inch of ½ inch diameter PVC pipe (you may need a little more)
2x 90-degree slip/slip elbow couplers for ¾ inch diameter PVC pipe
2x 45-degree slip/slip elbow couplers for ¾ inch diameter PVC pipe
2x 3-way slip/slip/slip 'T' couplers for ¾ inch diameter PVC pipe
2x 10 inches long ½ inch diameter riser pipes, threaded at both ends (aka "nipples", shown in black below)
12x 90-degree slip/slip elbow couplers for ½ inch diameter PVC pipe
4x 3-way slip/slip/FIPT 'corner' couplers for ½ inch diameter PVC pipe (FIPT means female threaded)
2x 2 inches long 10-24 thumbscrews
2x 10-24 wing nuts
Pen or pencil that will make a mark on PVC pipe (black Sharpie recommended)
PVC cutter (preferred) or hacksaw
Drill with 5/16 drill bit
1x strip of medium grain sandpaper (approximately 1 inch x 4 inches)
Do not use the PVC cement until you have completed the entire footrest and tested it a bit. You may want to make some minor adjustments or customize this design for the particular chair you are using, and it will be *much* easer to do this if you haven't glued everything together!
Step 2: Assemble a Leg Collar
Design note: The taper from large at the top to small at the bottom didn't require any special design considerations in my case, but notice that the front legs of this chair are straight and at a 90-degree angle with the floor. If the front legs of the chair for which you are building your footrest are curved or at an angle, you may need to modify this design by increasing the size of the leg collars. Cut 4x 1.5 inches sections off the ½ inch diameter PVC pipe for use as "spacers" between the couplers. Use these spacer sections, 3x of the ½ inch elbow couplers and 1x of the 3-way slip/slip/FIPT 'corner' couplers to assemble a "collar" that will go around the bottom of the chair leg. When you squeeze all of the pieces together, the spacer pipes will be completely hidden inside the joints. If the diameter of your chair leg is larger than ~2 inches you may need longer spacers, and parts of them will be visible.
Step 3: Assemble the Uprights
To complete the first upright, screw one of the riser pipes into the 3-way corner coupler of the bottom collar. Then cut 4x more 1.5 inches sections of ½ inches diameter PVC pipe for use as spacers for the top collar and screw the riser pipe into to the 3-way corner coupler of the top collar as well. Now, build the mirror image of this first upright for use on the other front chair leg.
Step 4: Add the Crossbar Mounts
Now it's time to add the mounting points for the crossbar. This is the horizontal piece of pipe on which your child will actually rest their feet. Drill a hole through each of the ¾ inch 'T' couplers, about ½ inch from one end, just big enough for the thumb screws. (see picture for hole placement). Remove the thumbscrews from the 'T' couplers, and remove one collar from each riser. Slide one 'T' coupler onto each riser with the hole you just drilled at the top and screw the collars back on, making sure the upright rests flat on your work surface. One at a time, hold each 'T' coupler at the top of its riser and use the holes you already drilled as a guide for drilling through the riser. Note that the height of the cross bar is adjustable by drilling additional holes closer to the bottom collars, but don't put the holes too close together! I recommend waiting to drill additional holes until you need them. Insert the thumb screws and screw on the wing nuts to hold the 'T' couplers in place. The result should look like the second picture below. Now you are ready to assemble the cross bar on which your child will rest his (or her) feet.
Step 5: Assemble the Crossbar
Design note: Don't cut your crossbar pipe until you have measured! Connect the uprights to the chair legs and partially remove the top collars as shown in the first picture below. Cut 4x 1.5 inches sections off the 3/4 inch diameter PVC pipe for use as spacers in the cross bar assembly, and lay out the remaining parts. DO NOT CUT THE CROSSBAR PIPE YET. Make sure the 'T' couplers are pointing straight forward and measure the distance between the inner edges of the 'T' couplers as shown in the second picture below. Subtract ¼ inch from your measurement to determine the required length of 3/4 inch PVC pipe for the cross bar. Now that you know how long it needs to be, cut the crossbar pipe. Design note: measure between the 'T' couplers instead of after you have the other couplers attached because it can be difficult to keep the crossbar "arms" created by the other couplers straight until they are held in place by the crossbar. Use 2x of the ¾ inch spacers to connect the 'T' couplers on each upright to a 45-degree elbow coupler. Use the remaining 2x ¾ inch spacers to connect each of the 45-degree elbow couplers to a 90-degree elbow coupler. Insert the cross bar between the two 90-degree elbow couplers.
Step 6: Finishing Touches
If you partially removed the top collars, re-assemble them now. The result should look like the first picture below. Time for a test drive! Check that everything fits together snugly and adjust any joints that are out of square. If your top or bottom collars need to be bigger, use longer spacers between the couplers. Ask your child to try out their new footrest and verify that their knees fit comfortably under the edge of the table, etc. My kids were more excited to give it a try because I let them watch and play with the pieces as I put them together. If your chairs are significantly taller than mine, the crossbar may not be high enough. Try using longer risers. If the crossbar is too high for them, drill some holes lower down on the risers and lower the crossbar to use the lower holes. If you want to protect your chair legs from rub marks, consider putting some felt or other non-abrasive material between the top collars and the chair legs. Now that you have all the design kinks worked out, it's time to glue the joints together. Use the strip of sand paper to rough up the spacers and the inside of the couplers, and then glue them together. This is especially important for all of the joints in the crossbar assembly (from 'T' coupler to 'T' coupler). Glue all of the "slip/slip" joints *except* the front and back joints in the two top collars (so you can still take them off easily). Remember that you can always drill new holes lower down the riser, as your child's legs grow longer.