DIY gym bench
A while back I cancelled my gym contract because the gym was getting too crowded and I decided to exercise at home. This prompted me to build a gym bench with various inclinations.
By Roelof Strydom
3 000mm x 66mm square pine pole
25mm x 25mm square tubing
12mm threaded bar
Six 12mm nylon nuts
Six 6mm nylon nuts
Two 10mm nylon nuts
Six 6mm bolts
Two 10mm bolts
Six 6mm washers
Two 12mm washers
Two 10mm washers
Four 10mm coach screws
Three 4mm x 40mm wood screws
Drill and drill bits
Time: 1 day
Step 1: The main structure of the bench is constructed from the 66mm square pine pole. It consists of five pieces: Two feet, two legs and the back support beam. For the feet, cut two pieces measuring 300mm long; for the legs, cut two pieces measuring 390mm; and the back support beam is 1 290mm long.
Step 2: Pine shelving was used for the seat and the backrest. If you prefer, you can also use MDF board as this might be stronger.
The pine shelving used here was a bit warped and because it is made up of smaller pieces stuck together to form a big piece, the MDF might be better. From the material you choose, cut the seat measuring 300mm x 280mm. The backrest should be 970mm x 280mm.
Step 3: Originally I was going to use wood to support the bench when it is in the inclined position, but I quickly discarded that idea. The mere thought of that wood breaking while I’m lifting a bar with 60kg of weights prompted me to reconsider.
I then decided on 25mm x 25mm square tubing. You’ll require four pieces of square tubing; two pieces that are attached onto the underside of the backrest and two pieces that will hold the bench in the inclined position. Therefore, cut two pieces measuring 900mm each and two pieces measuring 550mm.
Step 4: Now that everything is cut, you can start assembling the main structure of the bench. On the back support beam, decide which side will face downwards and on this side measure 50mm inwards from both ends.
On the 50mm mark, place a leg piece so that you can measure out the width of the leg, which is 66mm. It’s better to transfer the width by drawing lines on either side of the legs than measuring out the 66mm. Do this on both ends.
Next turn the beam onto its sides and measure out 25mm and draw a rectangle. To join the legs to the back support beam, you’ll need to make use of dado joints. Do the same with the two feet by measuring out the part that needs to be cut out.
You need to cut out a section 66mm wide by 25mm deep of the back support beam and the two feet.
Step 5: Use a table saw to cut multiple slots into the sections you determined in the previous step. Don’t rush this process as the slots have to be accurate.
Rather remove too little wood the first time round as you can always go back and remove that extra millimetre, but if you rush the cutting process and remove 1mm too many, the joints will be loose.
Step 6: With a wood chisel remove the small strips of wood that remain in the joints. The easiest way is to press down into the strips and then twist the chisel to break off the strips.
When all the strips have been removed, use the chisel to clean the joint thoroughly.
Step 7: Dry fit all the joints to see if they fit.
Step 8: Place one side of each leg into the top of the feet and the other side into the bottom of the back support beam.
Start with the back support beam and drill a pilot hole through the beam and into the leg as well. Next take a 22mm spade drill bit and drill a countersinking hole into the beam so that the head of the coach screw sits below the edge of the beam.
The countersinking hole should be bigger than that of the screw head because you need to get a socket into the hole to completely tighten the screw.
Fasten the two feet to the legs in the same way.
Step 9: At one end of the two 550mm pieces of square tubing, drill 10mm holes 25mm from the end. At the other end measure 30mm inwards and drill a 12mm hole in each.
Step 10: Measure 55mm from one end of each of the 900mm pieces of square tubing and drill 12mm holes in each. We made the mistake of drilling these holes at 75mm first, but once we assembled the backrest, it could not adjust as the backrest was pushing against the back support beam.
From this same end, measure out 525mm and drill a 10mm off centre hole in each of the two pieces. An off centre hole is needed so that the corner of the square tubing can move beyond the back support.
Step 11: Measure 330mm from the front of the back support beam and drill a 12mm hole 25mm downwards through the entire width of the beam. Be careful not to drill the hole skew or to cause the wood to break out.
Step 12: Place the two 900mm pieces of square tubing on either side of the back support beam. Temporarily secure them to the back support beam by pushing the threaded rod through the holes in the square tubing and the wooden beam.
Remember to place 12mm washers between each square tubing piece and the beam. Bring the square tubing piece flush with the top of the wooden beam at the back.
Once again place washers between the square tubing and the wooden beam. Fasten the square tubing at the back with a G-clamp.
Step 13: Place the backrest on top of the back support beam and the two pieces of square tubing and centre it.
Now draw lines on the underside of the wood to indicate where the square tubing should be fastened to the backrest.
Step 14: Remove the square tubing from the beam. Turn the backrest upside down and place the square tubing inside the lines drawn on the wood.
Drill three holes in each piece of square tubing at the top, middle and bottom. Drill the holes through the backrest as well.
Step 15: Flip the backrest right side up and countersink each of the drill holes. This is to enable the heads of the 6mm bolts to be flush so they don’t hurt your back when using the bench.
Step 16: Fasten the 900mm pieces of square tubing to the backrest. Remember to add the 6mm washer before screwing on the 6mm nylon nuts.
Step 17: Cut a piece of threaded bar to the required length and fasten the backrest to the back support beam. Place the 12mm washers over the threaded bar before you screw on the 12mm nylon nuts. This will aid with movement.
Step 18: Fasten the seat to the back support beam. The gap between the seat and front of the backrest is 45mm. Make sure the seat is in line with the backrest and screw the seat to the backrest.
Step 19: Fasten the 550mm pieces of square tubing to the square tubing on the backrest. Use the 10mm bolts for this. The head of the bolts should be on the inside.
Step 20: Take another piece of threaded bar and screw two 12mm nylon nuts onto it, but start with the nuts’ wrong side.
Next place the threaded bar through the remaining holes in the square tubing. Screw the two remaining 12mm nylon nuts onto the threaded bar.
There is no need for washers here as no movement will take place. This is the part that will slot into the slots in the back support beam to give the bench its various positions.
Step 21: Determine the 90, 45 and 30 degree mark on the back support beam and make slots at these positions. We used a circular saw to cut out the slots.
Step 22: Test the bench and see if everything works correctly. You will have to remove some wood where the 10mm bolt head pushes against the back support beam.
The finished gym bench
Transfer the width of the legs onto the back support beam, 50mm from the ends.
Flip the beam on its side and measure 25mm.
The part you need to cut out is 66mm x 25mm.
Determine the centre of the feet.
Transfer the width of the legs into the feet as well.
The top part of the feet must be cut out 25mm deep.
Cut slots with a table saw in the back support beam...
...as well as in the two feet.
Use a wood chisel to remove wooden strips from the dado joints.
Dry fit the feet to the legs.
Use coach screws to fasten the legs to the back support beams and the feet to the legs.
The size of the seat is 300mm x 280mm.
The backrest measures 970mm x 280mm.
Drill 12mm holes 55mm from the ends of the 900mm pieces of square tubing.
The square tubing that will support the backrest when in the inclined position.
Temporarily secure the 900mm square tubing to the back support beam. Remember the washers.
Determine the positions of the square tubing on the backrest and fasten it with the 6mm bolts.
Fasten the backrest to the structure.
Use the 10mm bolts and nuts to secure the 550mm square tubing to the 900mm pieces on the backrest.
Determine the 90, 45 and 30 degree positions on the beam.
Cut out the slots with a circular saw.
Check whether the threaded bar fits into the slots.