This instructable will show how to build a cable exercise machine rated at up to 300lb (420lb-120lb safety margin - see step 11 for rating justification) that allows you to do more than a dozen different exercises. I have been using it for around five months now, and have been very pleased with its performance. And at $100 (compared with $500+ for a simple commercial model that does not do as much), it is well within the home bodybuilder’s budget.

See below for a PDF with multiple drawings of the project, including dimensions. Also, see below for a Youtube video showing the machine in use, along with some of the exercises you can do using it.

Pully Machine Drawings.pdf
Download

Step 1: 2. Parts/Tools List

Below is a list of everything you will need to make this project.

Notes:
Unless otherwise noted, all item numbers are from Lowe's. Just go to www.lowes.com and enter the item number in the search bar to see exactly what I am talking about.

PARTS:
1. 8-foot 10"x2" board, cut by your friendly Lowe's representative into a 6' section and two 1' sections (Item #201521, $9.57)
2. 10-foot 10"x2" board, cut into the following pieces:
     (Item #201523, $12.97)
          a. 12” piece
          b. 12.25” piece (x1)
          c. 33.25” piece (x1)
          d. 62.5” piece (x1)
3. 8-foot long 2"x4" board, cut into the following pieces:
     (Item #46905, $2.47)
          a. 82" piece
          b. 9" piece
4. 10-foot long 2"x4" board, cut into the following pieces:
      (Item #76854, $4.97)
          a. 82” piece
          b. 9” piece
          c. 16.25” piece
          d. 4-5” piece
5. 2 3/8"-16X3-1/2 Grade 8 bolts (Item #136102, $1.46/2 pack)
6. 4 Flat washers 3/8-16 Grade 8 (Item #136056, $1.09/pack)
7. 2 Hex nuts 3/8-16 Grade 8 (Item #136068, $1.21/pack)
8. 3 3" 5/8R Satin brass door hinges (Item #308904, $2.17 each)
9. 3" screws, approx. 40 (Item #112363; buy from local store where you can buy just what you need by weight)
10. 1.25" screws, approx. 85 (Item #227168; same as above)
11. 16' of 3/16" steel cable, 740lb rating (Item #348184, $0.58/foot) cut into the following pieces:
          a. 7' piece
          b. 7.5' piece
          c. 9" piece (x2)
12. 8 3/16" wire rope clips (a.k.a, cable clamps) (Item #348302, $0.88/ each)
13. 3 heavy-duty pulleys, rated at 480lb (Item #348562, $4.58 each)
14. 2 4" T-hinges (Item #315669, $1.78)
15. 4 4"x6" Shelf Brackets (ACE Hardware, Item #5294079, $0.99 each)
16. 2 8-foot 1"x2" boards cut into the following pieces:
       (Item #201999, $1.97 each)
          a. 18” piece (x4)
          b. 12” piece (x1)
          c. 12.5” piece (x4)
18. 4 Carabiners, "Zinc-Galvanized Steel Carabiner Spring Snap Link Hook" from Amazon,
          $2.06 each, 100mm size for 500lb rating.
17. 1 Dumbbell - This one is up to you. Personally, I bought the $6.87 dumbbell handle from Wal-Mart (Item #SDA-GG14TRB), and it has lasted just fine with no signs of wear. If you want to pay $40-$50 for a set of handles that are officially rated to any weight you want to put on them (such as the Troy GOD-20 Olympic Dumbbell Handle), that is your choice.

TOOLS:
1. Drill
2. Measuring tape
4. Various drill bits
5. Small hand saw
6. 2 pairs pliers or lock clamps

SAFETY:
While building this cable machine, you will be using several things that could be potentially dangerous. For the tools (drill, saw), make sure you have read the owners manual for your specific tool and know how to use it, and wear the appropriate protective clothing (safety glasses, gloves). For safety in using the finished cable machine, see last step.

Step 2: The Base

For the base, I found it worked best to assemble it upside down.

Place the 33.25” 2x10 board flat on the floor. Place the end of the 62.5” 2x10 board on top of it, dead center, and then put two 12” 2x10 on either side (refer to photo)

Use 5 2.5” screws per board to fasten down the 12” boards, and 4 screws for the 62.5” board. Make sure to bury the screw heads just a little, so that they will not mess up whatever floor you place the machine on.

NOTES:
1. For any project with wood, I always drill pilot holes for any screws that I use. It ensures that the screws go in straight, and prevents the wood from splitting. All steps in this project assume that you are drilling pilot holes for every screw.
2. In case you are confused by some of the dimensions I am throwing out vs. what is on the dimensioned drawing, there is a difference between the advertised wood size and the actual wood size when buying lumber. 2”x10” is the size of board before they compressed it. The actual size is now 9.25”x1.5”. The same concept holds true for the other sizes of boards.

Step 3: Upper Pulley Assembly

I found it easiest to attach the shelf supports to the top board, and then to attach it as a piece to the 6’ board.

Using a hand saw/circular saw/etc. cut 2 45-degree pieces off of the 9.25” 2x4 board. Fasten it dead center to the top board using 2 screws from underneath.
Note: I used a scrap that I had left over, that is why mine is in 2 pieces vs. the one 9.25" piece in the photo.

Screw two of the pulleys to the 45 degree surfaces on top. You will need to remove the pin from the pulley so you can get to the center hole.

Taking the 12.25” board, stand up a 12” board in the center of it to represent the 6’ board.

Put the 4 shelf supports on either side of it, and screw them into the 12.25” board. Now you can remove the 12” board and screw the assembly on to the 6’ board.

Attach the two 9” 2x4 pieces to either side as shown in the photos, screwing it into both the underside of the 12.25” board and into the sides of the 6’ board.

Step 4: Attach Upright Assembly to Base

For this step it helps to have someone to help hold as you screw everything together.

Holding the 6’ board assembly right up against the 33.25” base board, fasten it down with all three hinges side by side, using 1.25” screws.

Step 5: Attach 45 Degree Supports

Take the two hinges and screw them into the 16.25” board at the edges as shown. Then screw the other ends of the hinges into the two 6’-10” 2x4’s. Lay this assembly on the 5’-2.5” base board, and use 5 screws to fasten it 1.75” away from the back edge.

Now raise a 45 degree support up to meet the 9” 2x4 board at the top. Pinching them both together, drill a 3/8” hole through both at the same time. It is important to do it this way to ensure that the holes will line up. Repeat with the other 45 degree support.

Slip two bolts through the holes that you just made, and the project will now stand up by itself!

Step 6: Attach Lower Pulley

This step is very simple - just use 3 2.5” screws to fasten the last pulley to the very center of the 33.25” base board.

Step 7: Make the Stool

For the stool, take the remaining 12" piece of 2x10 and all of the 1"x2" boards. Screw them together as shown in the photos and diagrams; in the colored diagram, the yellow legs are 18”, the red cross pieces are 12.5”, and the green cross piece is 12”. It is very important for this step that you drill pilot holes for all screws, since it is extra easy to split the small wood pieces. I know the stool does not look like much, but I have been very pleased with it - very comfortable, and it fits perfectly into the cable machine.

Step 8: Attach Cable

When fastening cable clamps, I found that I could make the clamps very tight by using a pair of pliers along with a socket wrench. See photos for an example.

Take each 9” piece of cable and, folding it in half, fasten the ends together with a cable clamp. That being done, fasten each loop to the dumbbell handle with a hose clamp.

Now for the main length of cable. Since it is almost impossible to fold over a small loop and clamp it, I found that the easiest thing to do was make a large loop in the end of the cable, very lightly clamp it, and then pull one end through the clamp until it became a small loop. Having done this in one end of the 7.5” cable, run the other end through the two loops created above for the barbell before repeating the process on the other end.

For the cable going to the lower pulley, you will need to thread the cable through the pulley before making the loops on each end, since once completed the ends will be too large to go through the pulley.

After you have finished making all of the loops in the cables, use electrical tape to make sure the cable ends stay tidy and do not poke you as you are changing weights.

Step 9: Extra Features

For the bars, I found that I could make an EZ bar much cheaper than I could buy one. However, for the wide lateral pull down bar, it was much cheaper to buy one off of Amazon.

Take a 1” Tee, and slip a large wing nut into the side. Then stick a matching large eye hook into the middle of the tee so that it screws into the wing nut. As you screw it in, the wing nut will not be able to turn in the pipe, allowing it to tighten onto the eye hook.

Once this is accomplished, it is a simple matter of screwing in the nipples, elbows, and caps as shown in the photos.

For keeping the cable tidy, I found that some nails driven half-way in to the base served as a good way to wind up the lower cable when not in use. A nail into the underneath of the top board gives a place to hook the upper cable while you are changing out attachments. See photos.

Step 10: Use and Safety

The safety of this exercise machine, as with any exercise machine, is dependent on the condition that it is in and in proper use.

If you see something is getting worn or cracked, replace it immediately. I have been using this machine in almost every workout for the last six months, and I have replaced the cables only once in that time because they were getting frayed.

When using this machine, do not jerk the weights up when you start a rep, and do not let the weights slam down after finishing a set. That is bad both for the machine and for you - whenever you exercise, you are only supposed to use a weight that allows you to complete the exercise using good form.

Step 11: Weight Rating Justification.

Below are the conservative ratings of each part of the project. Taking the lowest number (the pulleys) and subtracting 120lb as a safety margin leaves an overall rating of 300lb for the machine, more than enough for most people’s needs.

1. Pulleys: 420 lbs
2. Carabiner: 500lbs
2. Cable: 760 lbs
3. Main 6’ board: 1987 lbs
4. Screws holing lower pulley in place: 1620 lbs

The pulleys, carabiners, and cable were the easy part - they have ratings already on them. The main 6’ board, which supports all the weight during use, was a bit more involved.

Main Support:
The formula for determining max weight on a vertical board (Ref 1) is:

P/A = (0.30*E) / ((l/d)^2)

Where:
P = Max lbs (answer)
A = cross sectional surface area of board (9.25”x1.5” = 13.875 sq in)
E = Modulus of Elasticity (1,100,000 from table - Ref 2)
l = unsupported length of board (6’, or 72”)
d = smallest dimension of board (1.5”)

The boards I got form Lowes were Southern Yellow Pine (SYP printed on board), however I did not know the species that everyone will be able to get, so for the value of E (and later on Fc and G) I chose the most conservative value given for any type of pine in the table referenced.

Results:
P/13.875 = (0.30*1,100,000) / ((72/1.5)^2)

=

P/13.875 = 143.23psi

=

P = 1987lbs

However, the max pressure cannot exceed the value of max compression parallel to grain (Fc), or the tendency for wood to shear apart at the grain under pressure. The most conservative value for pine is 2,440psi (Ref 4), however this value need to be multiplied by a number of corrective factors taken from tables (ref 7)
:
Fc’ = Fc*Cd*Cp*Cm*Cf

Where:
Cd = Load duration factor (1.6 because this is going to be a temporary load - not applied to the board 24-7 as if it were part of a house; ref 3, figure 6)
Cp = Column Stability Factor (0.0853)
See photo for calculation to get Cp
Cm = Wet service factor (1.0, since not in a wet environment; ref 7)
Cf = Form Factor (1.0 for a square board vs. round post; ref 7)

This gives:
Fc’ = 2440*1.6*0.0853*1*1
=
333psi

Times that by the dimensions of the board gives:

Max pressure = 333psi*1.5*9.25
=
4620 lbs

Which is far more than needed for this application. To be conservative, we will go with the 1987lb value from above, which is still more than sufficient.

Screws
The only other part of the machine that deserves a look is the lower pulley, since while you are using the machine the weight is in effect trying to pull the pulley out by the screws. How many pounds does it take to pull a screw out of wood? The answer is given by this formula (ref 4):

P = 15,700(G^2)DL
Where:
P = Max lbs (answer)
G = Specific gravity of wood (0.35 per Ref 4)
D = diameter of screw (0.1248 per Ref 5)
L = Length of screw (2.25” to be conservative)

Results:
P = 15,700(0.35^2)(0.1248)(2.25)
=
540 lbs

Considering that there are 3 screws holding the pulley in place gives a total pressure of 1620 lbs to rip the pulley out, assuming the pulley does not give way first.

Note:
The above calculations are to show the reasoning for my opinion that this machine is capable of handling 300lbs. While I am in engineering, my background is in electrical - I am not a structural engineer. Whoever builds and uses this machine does so at their own risk, and should use their own judgment as to the proper weight to use. While I personally have not had any problems during use, I am not passing a certification on this machine or any built to the same specifications.

References:

1. http://www.irssg.com/civil/files/library/share/timber.pdf (pg 7)

2. http://www.woodbin.com/ref/wood/strength_table.htm

3. http://www.awc.org/pdf/WSDD/wsdd.pdf (pg 18)

4. http://www.woodweb.com/Resources/wood_eng_handbook/wood_handbook_fpl_2010.pdf (pg 111-112 & 198)

5. http://www.engineersedge.com/screw_threads_chart.htm

6. http://www.mcvicker.com/vwall/page009.htm

7. http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge-design-specifications/page/section13.pdf