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post #1 of 17 (permalink) Old 02-01-2013, 01:40 PM Thread Starter
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Question Specialized Tabletop Help Requested...

Howdy Fellow Members,

In my shop I have found myself in need of a specialized tabletop. It will need to be 52" in length and 30" in width. Height is insignificant because it will be positioned between sawhorses - at least to begin with - so there is no concern for legs or their attachment. I picture moving this around my shop with a hand truck, or a couple of healthy men.

I have the materials and a basic design. It will be 1-3/4" thick and made-up of red oak boards averaging 2" wide. There will be (3) 1/2" diameter threaded rods penetrating into counterbored holes and I plan to glue the joints and simply tighten progressively added nuts with heavy flat washers to serve as clamps. The nuts will stay-in-place for the life of this tabletop. The main function of this tabletop will be to clamp objects (workpieces) down vertically via relatively heavy-duty F-Clamps. Currently all of my F-Clamps are "as-new" in that they do not come apart when fully extended, but this is something that I can quickly remedy via grinding the speedbumps off of the ends of the bars. I figure that after said modification, a short bolt with a nut will provide an easily removed replacement speedbump. I also plan to provide 12- 3/4" diameter "dog holes" at strategic locations for the upcoming project it is to be used for. The 12- rectangular holes for F-Clamps (and/or C-Clamps) will each measure 2" x 6" and be aligned in 6 pairs to fit my needs. In no way does the finished product need to look pretty as function is my goal.

I've seen gigantic tables similar in purpose to this in heavy metal-working shops - with frequently spaced openings for their very heavy clamps to be used for securing objects for welding, grinding, etc.

Here's my question: Have any of you attempted to make such a tabletop as I have described - with holes for F-Clamps to penetrate through? I'm not in a huge hurry as this is for an upcoming project and I am a "Plan Ahead" kinda guy. If any of you have any thoughts, cautions, recommendations, etc., please reply. I'll keep my eyes open to this thread.

Thanks so much for any helpful information!
Otis Guillebeau from Auburn, Georgia

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post #2 of 17 (permalink) Old 02-01-2013, 03:57 PM
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Hi Otis,
It might also be helpful to say what type of clamping jobs you need to do. I am curious why your holes through the top need to be 2X6 if you plan on grinding off the rivet that keeps the movable jaw from coming off. Wouldn't a hole just a bit bigger than the clamp bar be big enough? That is something that could be routered out off the edges of the boards before you glue them. I would also remind you that you will probably be down on your knees to get the bottom jaw tightened up if mounted on sawhorses. Just out of curiosity would a clamp system like this work? Veritas® Hold-Down - Lee Valley Tools These are a bit pricey but a homemade version could be done.

I would be a bit concerned about the stability of a 1 3/4" top if you are going to put a lot of pressure on it unless it is attached to a frame. I would also be a bit concerned when tightening down the 1/2" rods. It isn't that hard to draw the top into a curve doing that. My own bench tops are made from 2x4 and 2x6 bolted that way. Although I couldn't put a bow in when tightening, they weren't perfectly flat so I built a big sled and used a router to flatten them.
Hope this helps.

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post #3 of 17 (permalink) Old 02-01-2013, 05:44 PM
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Hi Otis.

This may give you some ideas?

"The ultimate portable work bench"

PAULK WORK BENCH (The ultimate portable work bench) - YouTube

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post #4 of 17 (permalink) Old 02-01-2013, 05:47 PM Thread Starter
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Chuck-meister, Thanks for your comments!
The designed-for clamping projects will involve several assembly sizes being worked-on. Some of the sizes will cover the entirety of the tabletop. Actually, there will be a pair of 4x6's running the length (52") and further extending about 10" beyond that point - for a "runner" length of 6'-0". The "runners" will be parallel and 24" c/c and there will be penetrating horizontal 1" ID steel pipes (1 @ each end). It will be kinda like an old-fashioned medical "stretcher" for one "toter" person on each end. The sawhorse support is just one of the several positions it will be used in. I am actually trying to make this thing quite heavy, hence 1-3/4" thick oak deck. In some other times this "tabletop" will actually be positioned vertically - and this is where the extra weight will be helpful. Rather than being subjected to heavy workloads, this contraption will serve mainly as a support for assembling parts that are sourced and made in-house.
Deflection, I do not expect to be a problem. The greatest point-loads will be mid-span but only maximize when drilling operations (really not much pressure) are taking place. Your point about the F-Clamp attachments is quite good, though; but those larger holes are also designed to double as drilling positions from overhead.
The items we will be clamping to this tabletop are fairly lightweight, but there will also be some through-drilling via a homemade (scissor-mounted router motor) gantry drill.
Bowing and/or cambering would be a problem, but the through-holes will be centered and the glue setting will take place working outward from the centroid. I also expect the 4x6's to serve the "frame" function that you so wisely suggested. Assembly of this tabletop will begin with the 4x6's positioned 24" c/c parallel. Next the 1" ID steel pipes will be passed through and flange-fitted on each end. Then one oak board (with 3- oversized holes) will be positioned atop the runners and glued-down with one face aligned with mid-points of runners. All 3- threaded rods will then be threaded through this first "deck board" to their points of mid-length. Each side of the board will receive washers and nuts (into their respective counterbores). After this board is securely glued, a lag bolt will be threaded upwardly vertical from the underside of each runner and about 1" into the deck board. Then there will be deck boards added with glue, washers and nuts. Further lag bolts upwardly fastened will come-in about 10-12" o.c.
Soon here, I will attach a sketch; but I first need to remove all references to the proprietary products being assembled on said contraption.
Thanks again for your comments!

Otis

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post #5 of 17 (permalink) Old 02-01-2013, 06:07 PM
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I'm looking forward to seeing more of this. Pipe clamps would be a cheaper alternative to F clamps and it's easy to drill holes as opposed to making slots. I sometimes use sawhorses and I find the biggest problem is an uneven floor. I would think about a leveling method for the sawhorses to ensure you have a stable work surface.
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post #6 of 17 (permalink) Old 02-01-2013, 06:11 PM Thread Starter
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James, Thank you for posting that! He has some great ideas for making his portable workbench very lightweight! My tabletop differs in that it is designed to be heavy. The products that are to be assembled on mine are less than 30 lbs (14 kg) each, but will require precise positioning, alignment, drilling and access.

That gives me some very good ideas for something else that I am working on!

Otis

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post #7 of 17 (permalink) Old 02-01-2013, 06:19 PM Thread Starter
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Dennis, I see where you're coming from and that is a good point. The F-Clamps are something I have in abundance in many sizes. I have in the past used pipe clamps, but now tend to use "Cabinet Claw" rail clamps much more often. Most of the pipe clamps that I am familiar with have a quite limited reach as compared to the F-Clamps that I have on-hand.
Thanks for your thought-provoking comments!
Otis

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post #8 of 17 (permalink) Old 02-01-2013, 06:53 PM
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Otis if I understand you correctly, the runners and the deck boards will be at 90 degrees to each other. Fastening each deckboard to the runners could result is joints being pulled apart if you get moisture induced movement in the boards. I am assuming that you probably considered mdf instead of oak so why would you not use it? It is more stable, also heavy, and would not require all the hardware to attach it. You could laminate 2 or even 3 sheets together.

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post #9 of 17 (permalink) Old 02-01-2013, 07:57 PM Thread Starter
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Cool Here are two sketches...

Chuck,

I drew some sketches in 2d, because my 3d models become 2d when made into .pdf format.

Moisture won't be a problem, it is in a controlled environment. The oak is already on-hand, as my supply is very close to unlimited. This thing quite likely will get dropped or edges abused over time. Often when stack-drilling I have need to clamp tightly on MDF and it dents too easily for this project.

I do, however; appreciate your point about the F-Clamps not needing the speedbumps removed because of the large opening sizes. I had originally thought of making holes only slightly larger than the clamp bars, but when I was designing it earlier this week it was realized that enlarged holes could double as places holes would be drilled and the increased hole sizes will give a wider range of motion for the clamps. Occasionally, there will be need for some really serious clamp pressures and this will be able to be accomplished using some large C-Clamps that we also have in quantity.

My current built-in workbenches are framed with 2x4's, 2x6's & 2x8's with 3/4" plywood (replaceable) surfaces. We drill-into these quite often, and on occasion we just replace those tops with new 3/4" plywood. I use (no surprise to those who know me well) square-drive flathead screws because they are so easy to remove and reuse. They countersink very nicely without any predrilling - making for a very nice smooth work surface. My current workbenches will not work for this particular soon-to-start project.

I think the attached sketches will clear-up some of my poor articulations!

One other thing, though Chuck; this conversation has reminded me that I am going to need to route a "lip" around the 2x6 holes to support sacrificial covers - your info about MDF reminded me of this need (which would have been easier if 3-5 courses of MDF were to be chosen.

Thanks everyone!
Otis
Attached Files
File Type: pdf TABLETOP_PLAN.pdf (30.0 KB, 91 views)
File Type: pdf TABLETOP SECTION.pdf (23.2 KB, 63 views)

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post #10 of 17 (permalink) Old 02-01-2013, 09:37 PM
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Otis,

I have a picture in my head of what you are talking about. Just a "thin" traditional style European woodworker's (cabinetmaker's or patternmaker's) workbench without the legs. I say thin, as I usually see those 3-1/2" to 4" thick. Like a Holtzapffel, a Roubo and about a half dozen others that came from different regions...

Funny that your father-in-law probably had some along those lines around somewhere....

Here. Free plan designed by Frank Klausz:
http://www.gorillaglue.com/Portals/0...ch%20FINAL.pdf

Note of that plan's "pieces" on the ends of the table. Those add strength to the table laterally across the table.

I got that your holes where 3/4" square and that you were using the f-clamps, but the larger holes- 2"x6"? Festool f-clamps are made exactly for that application (3/4" round holes). I use my welder's f-clamps (a lot beefier).

What works great for doing those square holes is if you cut the length of the square holes as 3/4" deep x 3/4" wide crosscut dados in the glueedge of one of your timbers as you are building and assembling the table. That way one edge of the holes is the gluedge.

Question- Why square holes? Square is traditional... Square dogs in square holes. But not really "required," unless the clamps fit through a square hole easier by twisting them as they go through.

3/4" round holes also work good for those clamps. Many modern designs of those workbenches use round holes, as I think it's because you can just bore a hole and poof. You just then use round dowels as dogs. If you are using take-apart f-clamps to go through that way, you don't need the twist to go through the hole. A holdfast will also work in a round hole (actually better than using in the original square holes), except in your application most holdfasts seem to want to hold better if you have about 2"-4" of thickness in your table.

Edit-- Saw your drawings "after" this post. Hmmm...

Call me tomorrow when you get the time... Besides, I haven't heard your voice in a few weeks!

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Last edited by MAFoElffen; 02-01-2013 at 09:55 PM.
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