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flip top table: torsion box or plywood?

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Forum topic by Holbs posted 05-28-2013 11:16 PM 1983 views 0 times favorited 6 replies Add to Favorites Watch
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Holbs

1378 posts in 1495 days


05-28-2013 11:16 PM

Finally getting things into place in my garage: finished the electrical, painting, and insulation batts in rafters.
My next step: work tables for machinery. To save space, dual-purpose flip top platforms for each machine is what I had in mind for: 13” planer, 10” drill press, grinder/diamond stone station, mitre saw, Bosch router in my Bosch router table. When not in use, the machine will be flipped over upside down to allow a flat platform up top for infeed/outfeed table duties for other machines as all beds & platforms will be level.

1st option: I took a look at other flip top stands that use 5/8” to 1” thick steel rod down the center sandwiched between an upper and lower 3/4” plywood for platforms. But something does not “click” right. Would this design over a year’s time, bow the platform from 30lb-70lb machinery 1/8” or even 1/2” at the front and back edges? I’ve never dabbled with hardwood plywood or even baltic birch plywood as of yet to know just how sturdy and strong this design could last.

2nd option: 3” height, 16” wide, 20” length torsion box. I know I will have to jump into the torsion box design eventually for my 3’x5’ work surface so have read alot about them and understand the mechanical advantages and am really eager to get started (I felt like I am 43years behind other LumberJocks here, as I have only this year really found my wood “calling”). The torsion box design would be fantastic, as it gives superior strength for the material used (1/2” MDF for example) over a wider expanse. But I can not figure out how you bolt or lag screw something like a planer to the torsion box when the material used is MDF and also, how 30lb-70lb machinery will physically impact the MDF where the steel rods penetrate thru.

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"


6 replies so far

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RogerInColorado

321 posts in 1420 days


#1 posted 05-29-2013 01:49 AM

Something blew up on my reply so this is a delete. Full reply follows.

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RogerInColorado

321 posts in 1420 days


#2 posted 05-29-2013 01:51 AM

I built two flip top tables with torsion box designs, one for my planer and one for my Ridgid oscillating belt/drum sander. I used 3/4 inch plywood for the “bread” in the sandwich and 1/2 thick poplar strips (I think probably 1-1/2 inch wide) for the “meat” in the sandwich. I used 1/2 inch steel rod as the pivot. The sides of the stand were two pieces of 3/4 inch plywood laminated together. I used a gusset between the sides for the planer and I included a drawer between the sides for the sander. In both cases, the initial intent (of the gusset and the drawer) was to strengthen the sides and prevent racking. I planned ahead for placement of the mounting bolts and used T-nuts on the INSIDE of the top underside. If they ever blow out I’ll have to use lag bolts, but they have both been performing flawlessly for almost 5 years flawlessly. I’m pretty well convinced that the glued lamination torsion box approach won’t bow under my loads. The Makita planer is, I think, less than 80 pounds and I think the Ridgid sander is way less than that, maybe 40 or 50 pounds at the most. I banded the edges with 2 inch hardwood strips.

I wouldn’t have the same confidence with MDF as the bread and the meat. Plywood and poplar are not that much more expensive for a project this size.

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Holbs

1378 posts in 1495 days


#3 posted 05-29-2013 03:33 AM

Roger… no pictures or project/blog entries for this torsion box design?

i was thinking along the lines as this from fellow LJ’s and see how it turns out.
http://lumberjocks.com/projects/53637
I bought two 4’x8’ 1/2 MDF for this project. looks like I better get some 3/4” plywood instead. Oh well, I’m sure I’ll use the 1/2” MDF for something in the coming years.

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"

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crank49

3981 posts in 2437 days


#4 posted 05-29-2013 05:00 PM

You could use the MDF as the spacer(meat) between the plywood. Leave a 1/2” gap across the center and your pivot shaft will lay right in there.

I would not see the point in actually making a lattice spacer, like a true torsion box, for something so small. Two or three layers of 3/4” sandply are very strong in a component less than 2 or 3 ft across.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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Holbs

1378 posts in 1495 days


#5 posted 05-30-2013 12:05 AM

i priced out russian baltic birch ‘b’. one place had 5’x5’ for $57. other place had both 4’x8’ and 5’x5’ at around $45 for 3/4”. following yesterday’s downtime of not working on fliptops, 2 things happened: fixed my air compressor so now it’s all ready for brad nailing, and found out i have a broken front guide block (half moon cut out in a guide block at front of my bosch 4100 table saw… has something to do with the tilt mechanism) so table saw is out of commission til i find the replacement part. i could hand saw or circular saw but i really need precision cuts.

-- Yes, my profile picture is of a Carpenter Bee! The name is derived from the Ancient Greek "wood-cutter"

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RogerInColorado

321 posts in 1420 days


#6 posted 05-30-2013 05:12 AM

Sorry, I did the project about 5 years or so ago. I based it on an article in Fine Woodworking that talked about a new “from the ground up” shop he was building and part of it was these flip top tool holders. He designed them to fit under bench tops. The torsion box concept was his and fulfilled two requirements. The top needed to never twist and he needed a quick to assemble channel for his pivot point (the half inch steel rod). He didn’t provide much detail beyond the half inch hardwood between two pieces of 3/4 inch plywood. I had to figure out the dimensions, gussets, epoxying the rod to the sides and capping afterwards on my own. There are lots of people on LJ building flip tops with lots of approaches being implemented. I have found that the torsion box approach I used with poplar and plywood has worked for me. No twisting, no sagging, and the sides are still parallel and provide complete support to the flip top. The half inch rod is completely adequate. It swings smoothly and shows no signs of failure.

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