Wood Base (v1) for Bowflex 552 Dumbbells

UPDATE: This is version 1 (v1). Version 2 (v2) is easier to build and is recommended. I decided to leave this Instructable here for reference. See the WARNING below if you still are considering going with v1.

This is a simple plywood base for a pair of Bowflex SelectTech 552 dumbbells. The cradles are screwed onto the plywood. The main purpose of this is to keep the cradle from lifting up with the dumbbell when it is set to the 52.5 lb (max) setting. That happens because the empty cradle is quite light, and even with the dial set properly, the notched ring can catch on the hook in the cradle enough to lift it up. This is described and demonstrated in my YouTube video: Why Bowflex Dumbbells Get "Stuck". The added weight of the plywood and the other cradle prevent this problem from occurring. A secondary benefit is that it keeps the two cradles nicely aligned with each other, and they stay in one place on the floor.

There are two versions. One is for carpeted floors. It has shorter screws that are recessed into the bottom of the plywood, and it has no feet. The other is for hard floors. It has longer screws that are not recessed, and it has rubber feet. The carpet version would slide around on a hard floor, and the feet of the hard floor version would make divots in a carpet. It's also possible to make the carpet version and add and remove the feet depending on where the dumbbells are being used. I built the carpet version, so that is what the photos in this Instructable show.

There are many ways that the cradles could be attached to the plywood. You could probably just glue them on. I wanted to do it in a "reversible" way. This is almost true with this design. Each cradle does get two small holes drilled in its bottom. But the cradles can be removed from the base and (other than those two small holes) they will be the same as they were before adding the base. I thought this might be important to some people who would want to keep open the option of selling their dumbbells to someone who doesn't want the plywood base (or wants to sell them individually.)

WARNING: It is possible to damage your dumbbell cradles with this design. And in any case, it requires drilling holes through the bottoms, and that probably invalidates the warranty. The v2 design uses straps to hold the cradles to the base, and no modification to the cradles is needed at all. The scenario where the cradles could be damaged with the v1 design cannot occur with the v2 design. The only advantages of the v1 design are that it is a bit cleaner looking without the straps, and a bit less expensive because you don't need to buy the straps.

Materials

• 3/4" (or 23/32") plywood large enough to cut a 15" x 15-1/2" piece

e.g. :

Home Depot: Handprint 300950

Lowes: Model 199340

•  4 wood or sheet metal screws:

#8, 1-1/4 inch flat head (for carpet version)

Preferably > 20 TPI

e.g.:

Home Depot: Everbilt 807271

Lowes: Hillman 490269

Lowes: Hillman 490014

Lowes: Hillman 35054

Amazon: Hillman 490269

#8, 1-1/2 inch round/pan head (for hard floor version)

Preferably > 20 TPI

e.g.:

Home Depot: Everbilt 802922

Lowes: Hillman 35128

Amazon: Hillman 35128

•  4 washers to fit screws (#8, I.D. 3/16" O.D. 7/16")

e.g.:

Home Depot: Everbilt 802461

Lowes: Hillman 490685

Amazon: Steel Flat Washer, Zinc Plated Finish, ASME B18.22.1, No. 8

•  4 screw-in rubber feet (hard floor version only)

e.g.:

Home Depot: Everbilt 49131

• Spray paint or brush paint (optional)
• Long zip ties or lashing straps (optional?? - see step 12)

Amazon: 48-inch black zip tie

OR

Amazon: 48-inch lashing straps

Tools

• Carpenter's square
• Pencil
• Sharpie
• Saw:
• Table saw (preferred), or
• Circular saw, or
• Hand saw
• Clamps
• Drill
• Drill bits:
• 7/64"
• 3/16"
• 5/8" Forstner or spade bit (for carpet version only)
• #2 Phillips hand screwdriver
• Sandpaper or finishing sander

• Mark a 15" long x 15-1/2" wide rectangle on the plywood using the carpenter's square
• Use a table saw, circular saw, or hand saw to cut the 15" x 15-1/2" piece

NOTE: Once you have decided which plywood end is which and which cradle goes on the left and which goes on the right, you should keep track of that. There may be slight asymmetries, so this assures that everything will be aligned when the cradles are screwed onto the plywood. This step and the next suggest writing on the plywood and cradles with a pencil or Sharpie, but whatever works for you is fine.

• Set dumbbells to 52.5 and remove from cradles
• Flip cradles over and remove all four feet from each using Phillips screwdriver or a drill with Phillips bit
• Separate two halves of each cradle, keeping track of which top goes with which bottom, and which end is which
• Use a Sharpie to mark the inside: "L" on both the top and bottom halves of the left cradle
• Use a pencil to mark "L" on the label on the bottom of the left cradle
• Use a Sharpie to mark the inside: "R" on both the top and bottom halves of the right cradle
• Use a pencil to mark "R" on the label on the bottom of the right cradle

• The 15" dimension is the length of the cradles and the 15-1/2" dimension is the width of the two, side-by-side (touching)
• Use a pencil to mark "L" on the left side of the top of the plywood
• Place both cradle bottoms on the plywood with the one with the Sharpie "L" mark on the left
• Clamp the cradles to the plywood such that they are aligned with each other and centered on the plywood in both directions
• It is important that they are clamped securely enough that they will not shift during the next step

• Using a 7/64" bit, drill down into each support post through the bottom of the cradle and into the plywood
• You may drill all the way through the plywood if there's nothing to damage behind it. Or you may drill all four holes part way and finish the holes after removing the clamps. (Or you can drill into your workbench like I did - oops!)
• Again, it is very important that the cradles do not shift during this step!

If you are using the 1-1/2" round head screws for the hard floor version, DO NOT DO THIS STEP. This step is only for the 1-1/4" flat head screws. If you use the longer screws with the recess hole, they will be too long!

• Unclamp the cradles from the plywood
• Flip the plywood over so the bottom is up
• Use a 5/8" Forstner bit or spade bit to create a 3/16" deep counterbore around each of the four pilot holes
• The depth doesn't have to be exact, but you can use the 3/16" drill bit diameter to help estimate it

NOTE: this hole needs a flat bottom, so a normal drill bit won't work

• Use the 3/16" bit to increase the 7/64" holes in the plywood to 3/16" (DO NOT REDRILL THE HOLES IN THE CRADLES!)

• Mate the two "L" cradle halves and re-attach them to each other with the four feet
• Mate the two "R" cradle halves and re-attach them to each other with the four feet

• Flip the cradles and the plywood upside down, keeping the left cradle on the left side of the plywood and the right cradle on the right side of the plywood (looking up from the bottom, that is)
• Put one washer in each of the four recess holes (carpet version) or just around each hole (hard floor version)
• Insert the four screws through the washers and through the holes in the plywood
• One screw at a time, move the cradles around slightly while pushing the screw down lightly until the screw tip "finds" its hole in the cradle. Use the Phillips hand screwdriver to start driving the screw into the cradle (only one or two turns)
• When all four screws are started, drive them the rest of the way in with the screwdriver, but just before they are tight, flip the assembly over and adjust the alignment.
• Do not overtighten the screws
• If you can't get the cradles aligned, re-drill the 3/16" holes to 1/4" and try again

If you built the carpet version and don't mind the square corners and unpainted plywood, you can skip to Step 12. If you built the hard floor version, you need to add the rubber feet (Step 11). If you do want the corners cut and/or to paint the plywood, complete one or both of the following two steps.

• Mark the plywood with a pencil to follow the contour of the cradle corners
• Remove the cradles from the plywood
• On each corner, mark a diagonal line tangent to the curved line
• Cut the corners as marked
• Use sandpaper or a finishing sander to sand the cut corners (and the other sides, if necessary)
• If not painting, reassemble as described in Step 8.

• If you skipped Step 9, remove the cradles from the plywood. Remember to keep track of which is left and which is right.
• Mark the bottom of the plywood with an "L" on the left side (the "L" on the top will be painted over).
• Use spray paint or brush paint to paint the top and sides of the plywood. I used flat black. The cut corner pieces can be used to raise the plywood so you can get good coverage on the sides
• Don't paint the bottom. It won't show and could mark up your floor
• Reassemble as described in Step 8

There are no photos of this because I built the carpet version. But if you built the hard floor version, you need to screw on the rubber feet. These will keep it from sliding around on the floor and will provide clearance for the non-recessed screw heads and washers.

NOTE: This step was added after the original v1 Instructable was published. It describes how the cradles can be damaged. Now that the v2 design has been published, it makes no sense to build v1 with straps. Just build v2.

The screws into the plastic support posts are not a strong enough attachment to support much force. It's enough to handle the slight catching of the notched ring on the hook in the case where the dials are properly set to 52.5. BUT, if the dials are not aligned and you try lifting a dumbbell with the other one still in its cradle, you could pull the screws right out of the plastic, or worse, you could pull the support post right through the bottom of the cradle. Personally, I think I have a good enough sense of when the dumbbell is not releasing from the cradle that I will never lift it with enough force for this to happen.

If you are not as sure about this, then you should strap the cradles to the plywood base. The loop length is 40 inches, so the strap needs to be at least 45 inches long. The photos above show one option using zip ties and another option using lashing straps. A single 48-inch zip tie or lashing strap should be enough, but two will provide even more protection and (in my opinion) looks better.

Consider yourself warned. Please do not complain that you damaged your dumbbell cradles if you have not done this step!