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 Post subject: Custom build Rocker Table
PostPosted: Fri Sep 24, 2010 6:15 pm 
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So after reading a ton of posts, I think I'm nailing my rocker table design.

Since I have CAD software available (purchased and licensed), I'll start by prototyping in CAD and then build it.

I'll do the same for the board, including some CFD studies, before building it.

For the rocker table, I'm going for a width adjustable table, depending on the board I'm aiming at, with 600m top width board. But I'm still deciding on this one, since it only depends on the metal strips on the sides of the table.

Which brings me to the question of stability.

Does any one think that my table can be a bit unstable due to the metal strips that define the table width?!

Attachment:
Rocker_table_V2.jpg
Rocker_table_V2.jpg [ 138.67 KIB | Viewed 2723 times ]


The 3 vertical wood slabs will be trimmed to give the concave and rocker of the board. They're not trimmed on the image because I haven't completed the board yet.

The second question is regarding the table per se. What should I use as the table slab? Wood sheet? Metal sheet (how thick?)?

If I use a metal sheet (stainless steel), can it be used often for different concave/rocker shapes?

I'll be waiting for your inputs!!


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 Post subject: Re: Custom build Rocker Table
PostPosted: Fri Sep 24, 2010 9:02 pm 
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Are you asking about the surface the board will be on? Plexiglas made a nice surface. The 1/8 cheap fiber board rocker table I built worked but wasn't mirror smooth. I was thinking about this yesterday and an substrate should work if you cover it with fiberglass then polish and mold release that surface.


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 Post subject: Re: Custom build Rocker Table
PostPosted: Sat Sep 25, 2010 10:17 am 
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Actually, I was thinking of a rough surface for the board surface. Although a mirror smooth surface looks nice, some roughness is good for speed, as the it creates a thin layer of turbulence that works as lube. But that can be achieved with a layer of something else between the rocker table and the board.

But yes, I'm asking about the surface wthe board will be on.
It has to be deformable, but re-usable, as I plan to make different boards in a near future!


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 Post subject: Re: Custom build Rocker Table
PostPosted: Sat Sep 25, 2010 1:17 pm 
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Location: rhode island
if the 3 stringers dictate rocker and concave,
what is the function of all the threaded fasteners?

CFD= computational fluid dynamics ?
what software do you think will help with your design?

do you intend to vacuum bag with both table and board inside.
just the board inside,
or just 1/2 bag the board to the table top?

that will influence structural requirements and finish of the table.

from what is shown in your model, the 3 lengthwise stringers will provide longitudinal stiffnes.
but the cross -members (metal strips?) are the only source of lateral bending strength.
you may have issues constraining the concave in the table top as well as the board blank.

you could always 'dog' the whole thing down to a stout work bench until the details get sorted.
-bill


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 Post subject: Re: Custom build Rocker Table
PostPosted: Sat Sep 25, 2010 6:13 pm 
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Simpler works well too, here's a 3/8 baltic birch ply table surface supported with wood blocks at ends and a thin batten under the middle of the table for concave, curves controlled by big old deck screws. Uses battens instead of a bag to press the board.
The 2 layer cedar core pictured ended up with a 0.3-.4mm glue layer of epoxy reinforced with fibers. This table would be fine for full bagging (I'd give it more support for 1/2 bagging), but I probably won't bother -it's easy enough to get a 50:50 layup by hand over this wood, and the core...
won't soak up too much resin IF you are careful, but you do need to be careful....
Anyway, I like this table because it is SO simple. Also cheap. 8)


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 Post subject: Re: Custom build Rocker Table
PostPosted: Sun Sep 26, 2010 8:33 pm 
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The function of the threaded fasteners is to hold the table surface in place and maintain the concave and rocker.
Something like this (the length of threaded fasteners are not updated on the image):

Attachment:
Rocker_table_V2_02.jpg
Rocker_table_V2_02.jpg [ 96.02 KIB | Viewed 2574 times ]


The image represents the final table design with a board silhouette on top.

The lateral metal strips will be used to change the table width and hold it together.

I'm planning on vacuum just the board, without resorting to the table top except for support and shape.

I thought about holding the 3 stringers to a wooden plank, but there is also a space restriction when I'm not using the table. So I came up with this design for transportation and packaging, besides the adjustable width. :)

All this is being modeled with SolidWorks, and for CFD (yes, computational fluid dynamics) I'll use Flow Simulation (an add-in of SolidWorks).

Here's a small sample of on of the studies.


So do you think that the threaded fasteners make the lateral stringers unnecessary?

Thank you for inputs. Keep them coming! :thumb:


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 Post subject: Re: Custom build Rocker Table
PostPosted: Sun Sep 26, 2010 10:00 pm 
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OK as a devil's advocate, I have more comments.

A great design principle is, build from the fewest, strongest possible components.
This principle may or may not be very well aligned with your renderings. I am not sure it is. ;)
But it is a useful principle, if coupled with the other most important things for your project,
for example, "lightest" or "cheapest" or "more impact resistant" or "easiest to assemble."
Of course, common sense plays a role too....

With 20-30 bolts, you could float the surface on bolts and not need the stringers. With stringers, you could dispense with all those bolts.

With a solid base made of thick plywood, you wouldn't need to worry about knocking a corner of the table and throwing it out of line, and the base would be about the same size as the top, so not much more storage space needed.

60cm is a good width.

Finally, a devilish comment: it's more fun to copy and paste in CAD than to drill and align 20 or 30 bolts. :evil:


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 Post subject: Re: Custom build Rocker Table
PostPosted: Mon Sep 27, 2010 3:02 pm 
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You have a very unusual bottom shape.

But if the computer says it will work....


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 Post subject: Re: Custom build Rocker Table
PostPosted: Tue Sep 28, 2010 11:57 am 
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BWD wrote:
OK as a devil's advocate, I have more comments.

A great design principle is, build from the fewest, strongest possible components.
This principle may or may not be very well aligned with your renderings. I am not sure it is. ;)
But it is a useful principle, if coupled with the other most important things for your project,
for example, "lightest" or "cheapest" or "more impact resistant" or "easiest to assemble."
Of course, common sense plays a role too....

With 20-30 bolts, you could float the surface on bolts and not need the stringers. With stringers, you could dispense with all those bolts.

With a solid base made of thick plywood, you wouldn't need to worry about knocking a corner of the table and throwing it out of line, and the base would be about the same size as the top, so not much more storage space needed.

60cm is a good width.

Finally, a devilish comment: it's more fun to copy and paste in CAD than to drill and align 20 or 30 bolts. :evil:


Yes, you're right on many aspects... I'll have to do some redesign. I'm kinda new at this, and this is just my second "virtual" table design.

But I see that I'm over complicating... From what I've been seeing in other posts (and I've seen a lot of them...), I can easily lose every other bolt (total of 6 on each side) and still maintain design intent. But I'll still make the holes, just in case I want to give a board an un-progressive rocker line.

As for the central stringer, I saw a good solution that will prevent me from making a new rocker template each time I want to make a new board. And adjustable height stringer just a few cm long. Just enough to deform the rocker table top. It's not hard to accomplish and saves some money in the long term (can't find the link right now, but have the image in my head).

From what I've been investigating on shops nearby, I'll spend something like 20€ on wood for the table, max! The most expensive stuff will be the fasteners... :-? But ok... it's a one time cost.

not annonymous wrote:
You have a very unusual bottom shape.

But if the computer says it will work....


It's just a preliminary design also. Some channels conjugated with rocker and concave. If I take out the channels, it's jut a regular board with simple concave and rocker, so there's not much science there. I just want to make it more stable without fins.
My main issues, since I'm new to this stuff, will be flex control. But as said above, still investigating. I'll have to try out a first board attempt, simple, low cost, to check how it works, and then re-design it structurally, regarding wood thickness, fiber laminating, etc.

Once again, I may be over complicating it. But so what... it's a hobby! I like to complicate it! :D


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 Post subject: Re: Custom build Rocker Table
PostPosted: Thu Sep 30, 2010 5:45 pm 
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New table design based on your inputs and some other posts on the internet.

Attachment:
Mesa_V3.JPG
Mesa_V3.JPG [ 79.79 KIB | Viewed 2323 times ]


The central piece will define the concave while the lateral fasteners will old everything in place


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