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Floe Aluminum Dock Lead Screw Replacement

Floe docks have ACME screws for height adjustment, but they can rust up and aren't designed to be user-replaceable. Hmmm...

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I bought an old but still sturdy Floe roll-in aluminum dock last summer. The dock sat unused for some time prior to the purchase, and a few of the handy lead screws that adjust the height of the wheels had seized up. Upon further investigation (and a consultation of the manual), I realized that the ACME nuts had been welded into the support posts during assembly, making the rusted screw impossible to replace even if I could get it out of the nut. I think you're supposed to replace the entire wheel dolly if this happens, which seems wasteful and expensive. A quick search suggests new dollies are still available from the factory if I screw this one up, but I figure it's worth a shot. Not really a typical Hackaday.io project, but I didn't find an online record anywhere of someone trying this so maybe someone with the same problem will learn from my attempt.

Floe has a wheel kit assembly and installation guide that shows the location of the part ("wheel kit assembly", p/n 110-00146-02) I am refurbishing: https://floeintl.com/wp-content/uploads/2018/03/610-17300-00_Medium_Wheel_Kit_DISC.pdf

  • Disassembly

    zakqwy08/03/2018 at 17:22 0 comments

    Last fall, I removed one of the stuck wheel assemblies and brought it home. The wheels are single piece plastic that fit tightly on an aluminum rod, secured by a cotter pin:

    I unscrewed the three aluminum posts, revealing the Acme screw:

    Notable in the picture above: the nut on the left is aluminum and is roll-pinned to the Acme screw. This nut bore the load of the dock itself via the largest square tube (also on the left); an identical pinned nut that broke during use was attached to the left end of the screw and was used for adjustment from above.

    Removing the Acme screw from the welded aluminum mount required fighting a small amount of rust:

    I tried a good soaking with penetrating oil but couldn't get the screw loose. I used a cut-off wheel to slice into the brass nut a bit, and then tried to split the nut using a punch. This did not work:

    Then I cut an access hole in the side wall of the square aluminum tube, which allowed me to slice the nut the rest of the way:

    I continued to use the punch to pry apart the brass nut (bronze? Might be bronze) and eventually got the far side to fracture. The nut was still frozen to the screw and didn't have much room to move, so I tried hitting the nut with a bunch of penetrating oil. Then I cut the Acme screw right above the nut using a cutoff wheel, and ground a slot into the remaining stub so I could loosen it with a screwdriver:

    Somehow, probably due to a combination of penetrating oil and extra clearance from the split (and using a box wrench to assist the hex-shafted screwdriver), this worked. I was so excited that I took another picture showing the screw at a different angle:

    I drove the remaining screw through the nut and pulled the nut out of the square aluminum tube. This allowed me to extend the Acme screw through the top of the housing, cut it, and remove it from below. Doing so revealed another pinned fastener that prevented me from pulling the lead screw out through the top:

    The blackened area above is where the brass nut used to live. As expected, the rust really just built up around it and didn't actually stick to the nut, which allowed me to remove it fairly easily once I'd increased the clearance by splitting the nut.

    Removing the Acme screw left me with a slightly modified but still hopefully serviceable leg post. My hope is that the hole won't cause any issues; once the new Acme screw is threaded into the new Acme nut, the screw itself should retain the nut side-to-side:

    More to come!

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Discussions

e-randy wrote 05/18/2021 at 17:31 point

Looking at it all again I think your idea of cutting the side of the leg to release the CN may be better. The hole can easily be patched with a brazing rod and the load will be held by the original welds. Of course that only works if you can get the rod separated from the nut. Maybe a good soak with penetrating oil and some heat- since the failure seems to be at the top and not at the CN. Just rambling now. :)\

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e-randy wrote 05/18/2021 at 17:24 point

More notes: 

Loctite Red is waterproof and requires heat to remove so it should be good for securing the nuts on the threaded rod without having to use the drilled pins. Alternative would be to jam two nuts together but that will cause the nuts to protrude above the dock surface unless you can find a thin nut. The rod breaks at the drilled spot so it is just a bad design as done by Floe and I will not go that route if I can avoid it.

I am using 3/4" x 10 stainless threaded rod and stainless nuts. The nuts are a bit smaller than the captive nut used by Floe so you will need at least one washer to put on the top side of the captive nut. I don't think a lower washer is needed because there will almost always be no load other than gravity.

The washers I bought at Grainger were too wide for the captive nut (CN) opening so I had to grind two flats to square off the outside of the washer. 

Floe has a tapered "nut" on the bottom of the rod, I guess to guide it along the inside of the tube. You could get a threaded connector (~2" nut for joining 2 pieces of threaded rod) and cut it on the diagonal to make a replacement. I just ground a chamfer on the nut that will be at the bottom. 

For welding- I used brazing rod and MAP torch. The original welds are just on the short edges. Since the brazing is probably less sturdy I also brazed the long edge. I bet you could use some sort of marine epoxy to accomplish it too.  Follow the brazing rod instructions precisely, especially the surface cleaning. 

I don't have the spacing for the top two nuts. They have to be fixed in position with Loctite so you want to get them in the right spot. No big deal if you mess up because they are easily accessible compared to the CN.

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e-randy wrote 04/30/2021 at 19:22 point

Before I forget- One of the other companies manufacturing something like this uses a nylon/plastic nut to avoid the Al/Fe metals issue. 

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e-randy wrote 04/30/2021 at 19:19 point

I just started in on mine. The captive nut is held in place by the two aluminum plates welded inside the square tube. The welds are very easy to cut using a hacksaw if you have a handle that holds the blade at one end. I will try brazing them back in place or just find someone to weld them back- should be pretty inexpensive bit of work. 

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