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Sunday, March 03, 2013

Dinette Table Lift Mechanism

This is what being cooped up in the garage during long winter nights yields...

I think I mentioned the design for this sometime ago in the blog. Over the last few months I had an experimental mockup setup in the garage, to determine feasibility. In particular, would the mechanics be enough to bear the load of the (expected) dinette table weight? Results were positive such that I took it into the boat. Though still experimental, here is what I have so far.
One of the lift assemblies

There are two lift assemblies (left and right) that slide in and thru bolt to the boat's glassed in framing structure under the side deck, giving a quite sturdy and stiff attachment. The assemblies are lifting arms on rollers held captive in a section of slotted aluminum. Attached to the lifting arms are lead screws coupled to a drive motor mounted on a bracket at the base. The lead screws and motors provide the up/down movement. The assemblies are designed to be installed/removed with one-person-one-tool without removing finish work (well, maybe a bit of trim). When finished, the lift mechanisms will be completely concealed behind the cabinet.
60 pounds of weight

With two assemblies installed, and motors synchronized  a load test is done, with a heavy piece of MDF and some dive weights placed at a 3/4 table width lever point. Total weight about 60 pounds. The motors had no problem lifting/lowering the load.

Of course the intended feature of this mechanism is to provide adjustable height for normal dinette use, but also

  • lower the surface to convert the dinette into a bunk
  • raise the surface to provide easy access to the boat's electronics underneath
  • all without tearing things apart.

Here are the sample height levels
Normal table height
Lower height for bunk conversion (17 inches up from floor)
Upper height for electronics access (note cabinet extended on slides)
By no means complete, there are still some refinements to be made. I am surprised how well this has worked so far. As I ain't no mechanical engineer, there is still a chance it will fail... completely.

More on this later.

3 comments:

Rhys said...

Very nice, but is it such a great idea to put a motor close to the bilges?

I've thought along similar lines, to have the table lower to make a big bed by trimming it right to the sides of the surrounding benches, but I thought I would either spring (no pun intended) for a robust gas cylinder pedestal, or rig a sort of bottle jack mechanism. Maybe even a scissors lift clad in wood...

Can't argue with its sturdiness, however...that looks good.

Robert Sutton said...

Some sort of protection of the motors is a concern. But they are above the tanks and dinette riser by nearly two feet. Even in extreme heel not an issue. But locating them in a well ventilated area is ideal. Maybe I can invert the motors somehow. Have to think on that one.

Your mention of "gas cylinder" gives me an idea for providing some lift assist, should it be necessary. Thanks!

Rhys said...

No problem. We have to solve similar access and movement issues on our otherwise quite different boats, and would tend to arrive at similar conclusions from different start points.

Recently,I've had to research every type of "gas spring", which is the name of the category, by the way, for every sort of hatch that is heavier than something a simple bronze strut would hold open with confidence, which is why it's top of mind.

While the pedestal ones for helm seats are quite spendy, you could get everything from a bus driver's seat mount to a salvaged barbershop chair base to accomplish the same action in a compact manner.

I need to investigate gas springs for my engine bay hatch and my steel forepeak deck hatch, both of which will be "unlight". Another dinette-weight project will be the new saloon companionway steps I am planning to frame up, which will cover eight Trojan L16s in a welded, stepped box, which will contain battery boxes for each pair. One of the very few things I like about current showroom queens is the gas springs that allow a companionway hinged at the top to rise with a kid's grade of arm strength and stay put under pulled down like a well-fitted sash window. The point is to take all the half-ton of batteries I intend to carry right to the CE of the entire boat, meaning I can dispose of the lead pigs acting as trim ballast forward...and replace it with tools.

The gas springs used for truck engine hoods should be about the right size. You could use gas springs in combination with a locking strut in a number of applications around the boat in a similar fashion.

Lastly, today's hot tip is that Lee Valley seems to be selling moddable warm white and coloured LED strips for a price I find reasonable, and will do so in bulk. I recall you've already installed a few in selected spots, but I saw the RGB ones and thought "hey, go from white to pure red in the pilothouse with the turn of a pot dial? I can get behind that!"

You might want to check it out. I think LEDs are the absolute bomb in any boat place that requires small amounts of light (like inside lockers soldered to a 9V battery and a contact switch)or for "mood lighting" under the lips of cabinets aimed up or down.

We are pretty much at the break point between me wiring up strips off a spool and the price of retail. I thought I'd have to make and measure my lighting, but it's going "prêt-à-porter": just buy what you need and screw it down.