Clamp calculations

[Tony Wilkins]

Trying to see if I have enough clamps for my table top. Read about this 45 degree rule in spacing them out. Will probably cut it down to 8’ (currently 107”). For the three panels, the distance to first glue line is average of 11 to 12”. The width will be about 34”.

[William Fretwell]

Tony, in your favour you only have two glue lines. Also in your favour the boards at 11” or so and fairly thick no doubt are very stiff, the clamp force applied will spread evenly.
What you do need because of the stiff boards is very straight well matched glue line. The clamps are not going to close errors, however many you have.

I see the boards stacked on edge with a lamp behind them and much fine tuning. When you are ready, my table top experience says a clamp 2” from each end and a clamp every foot is plenty. A rope wrap can be added with the clamps if you are short.

[Cameron Wood]

The 45˚ thing is fine, but it depends on the strength of the clamps as well.

Rubber bands spaced a certain distance will produce even pressure, just not very much of it.

[Tony Wilkins]

The 45˚ thing is fine, but it depends on the strength of the clamps as well.

Rubber bands spaced a certain distance will produce even pressure, just not very much of it.
Most of my long clamps are Bessey and Jorgensen parallel clamps.

[Cameron Wood]

If your top is 1" thick, and 8' long, then at 250 psi clamping pressure (quite low in the range of recommendations)
there should be 24,000 lbs pressure. with one clamp every foot- 9 total, each clamp should produce ~2,600 lbs force- about the weight of a car every foot.

[Kevin Jenness]

If your top is 1" thick, and 8' long, then at 250 psi clamping pressure (quite low in the range of recommendations)
there should be 24,000 lbs pressure. with one clamp every foot- 9 total, each clamp should produce ~2,600 lbs force- about the weight of a car every foot.

You can safely ignore those pressure guidelines developed for industry. All you need is enough pressure to pull the joints up tight, and if the joints are accurate it doesn't take that much force. For what you are talking about I would typically use 6-8 aluminum bar clamps but with such wide boards could probably work with 4 or 5. For reference, Jorgensen aluminum bar clamps are spec'd at a maximum force of 1,000#, their heavy I-beam clamps at 7,000# and light duty Pony F clamps at 300#. I've glued up many a door panel with those Pony clamps without issue.

[Richard Hutchings]

I'd argue that you don't need any pressure if the joints are perfect. At least on smaller projects I've gotten good results with rubbed joints. So I wonder where the idea of huge amounts of pressure comes from.

[Kevin Jenness]

I'd argue that you don't need any pressure if the joints are perfect. At least on smaller projects I've gotten good results with rubbed joints. So I wonder where the idea of huge amounts of pressure comes from.
It comes from the glue manufacturers for industrial situations where the mating surfaces are less than perfect and hydraulic presses are used to achieve the specified pressures. The successful use of vacuum presses with maximum pressure of about 11 psi demonstrates that the industrial guidelines are not gospel.

[Edward Weber]

I've been woodworking for a long time, I never heard of the 45 degree rule.
I looked it up, IMO, it's just common sense to spread your clamps out for even pressure.

[Rafael Herrera]

The better the edges are matched to each other, the lesser the need for an inordinate number of clamps or high pressures.

[Cameron Wood]

I put that clamp pressure thing up for shock value, as it runs so counter to most folks' experience,

but for that example, using pipe clamps, which are said to produce about 1,000 lbs force, one would use 24- about one every 4".

[Tony Wilkins]

The better the edges are matched to each other, the lesser the need for an inordinate number of clamps or high pressures.
Which goes back to my skill with a number 7 :rolls eyes: :exasperated look to heaven emoji:

[Jimmy Harris]

I've accidentally glued enough things together in my life to know you don't need any clamping pressure to form an incredibly strong glue joint. Now, I'm not saying I don't use clamps or that they're not necessary. In fact, I use a lot of clamps every time I glue up! But, I don't worry about math or theory when it comes to clamps, and it's never come back to haunt me. I just eyeball it and if it looks fine, it'll be fine. Works every time!

I do have one rule, however. Whenever I start a new project, I buy 2 new clamps for it. You'll always be 2 clamps short of what you think you need, and you can never have enough clamps.

[Rafael Herrera]

Which goes back to my skill with a number 7 :rolls eyes: :exasperated look to heaven emoji:

I don't really know what your skills w a jointer are, so I don't understand why you're exasperated.

An old joining technique uses pinch dogs, which can still be bought, to glue up two boards.

I have to admit I've not used them, but I do have a set for when I decide to use them. I assume that if the joint has no gaps, a dog on each end does the trick.

510115

[Tony Wilkins]

I don't really know what your skills w a jointer are, so I don't understand why you're exasperated.

An old joining technique uses pinch dogs, which can still be bought, to glue up two boards.

I have to admit I've not used them, but I do have a set for when I decide to use them. I assume that if the joint has no gaps, a dog on each end does the trick.

510115
I actually have some pinch dogs somewhere (added to anLV order once upon a time). I could use them on this, especially since I plan on breadboard ends. My exasperation is trying to get perfectly straight over 9 foot of length of each board. I’m getting better as I go along but I’m a perfectionist. I’d like to do rub joints with hot hide hut I don’t trust my ability to get test perfect with the edges.

[mike calabrese]

Just to add another point of view relative to clamp pressure and attachment placement.
When clamping panels using a ton of pressure is a problem.
Ideally when glue is applied to properly milled panels we use whatever pressure needed to bring the panels into full contact and get the desired glue squeeze out.
Once that is accomplished to satisfaction we back off the clamps retaining sufficient pressure to keep the panels together. We kind of gage this by cranking enough pressure into the clamp such that it will not slip off when the panel when we try to take panel weight onto the individual clamp and not have it slip off the panel.
Additionally if you apply clamps such that the lip of the clamp is the gripping point such that the pipe is well above the panel you will induce potential bowing into your panel / top. This is especially true even if you alternate the clamps on both sides of the panel which is highly recommended practice. The vids below show some methods to prevent warping the panels using cauls etc. I like to set my pipes against the panel using a barrier to prevent glue stain from the metal pipe. We use coroplast (plastic cardboard) pieces between the pipe and the work.
There or all kinds of other barriers that can be used as simple as wax paper, packing tape wrapping on clamp pipes parchment paper .
Parallel clamps are nice to have but honestly not needed. Bessy clamps are expensive an example
https://www.homedepot.com/b/Tools-Hand-Tools-Fastening-Tools-Clamps-Vises-Clamps/BESSEY/Parallel/Clamp/N-5yc1vZc266ZdepZ1z0qyuuZ1z116id
Pipe clamps are a darn sight cheaper EXAMPLE
https://www.grizzly.com/products/grizzly-bear-grip-3-4-pipe-clamp/t28947?gad=1&gclid=EAIaIQobChMIw-q81Nm3ggMVRURyCh1JxQnZEAQYAiABEgK5pfD_BwE
Yes you have to add the 3/4 pipe at any length you like but you can buy about 4 pipe clamps including the pipe (length dependent) for the price of a Bessy parallel clamp.
I am bias I have never used anything except pipe clamps for over 50 years. The only truism in woodworking is YOU CAN NEVER HAVE ENOUGH CLAMPS

calabrese55

https://www.youtube.com/watch?v=32RuFcmmVZg there are many more on the topic here on the right panel.

[Richard Hutchings]

I actually have some pinch dogs somewhere (added to anLV order once upon a time). I could use them on this, especially since I plan on breadboard ends. My exasperation is trying to get perfectly straight over 9 foot of length of each board. I’m getting better as I go along but I’m a perfectionist. I’d like to do rub joints with hot hide hut I don’t trust my ability to get test perfect with the edges.
I have never used pinch clamps but I would try to have a convex curve on at least one of the boards. Then they clamp in the mid section first and close up on the ends last.

[Tony Wilkins]

I have never used pinch clamps but I would try to have a convex curve on at least one of the boards. Then they clamp in the mid section first and close up on the ends last.
That’s part of the reason I haven’t tried it. Seems like a bad way to do it after accepting the reasoning behind a spring joint. However, I bet it isn’t necessary.

[Jim Koepke]

Just my 510119

There was no mention of the glue to be used. Each type will have different needs.

Epoxy can cure without clamping and can fill small spaces. This can be handy for quick repairs.

PVA should be clamped tight enough to cause glue squeeze out. This of course requires a thin coat of glue on each piece, but not enough to be dripping before clamping. Over tightening of the clamps may cause glue starvation.
Wide panels may benefit from the use of cauls to prevent bowing at the joints. Some like to have a slight concavity at the center of the joint. Some of my joints do not have this. Over a length of 8' and ~15 years in an uncontrolled environment have not suffered from the joint not being sprung.

Some folks use hide glue without clamps, this is supposedly one advantage of a "rubbed joint." IMO, pinch dogs may have been used with hide glue to speed up gluing multiple boards together.

Again, these are just my thoughts (opinions) on the subject. They cost nothing and that may be all they are worth.

jtk

[Rafael Herrera]

Starting on page 158 of Peter Nicholson's book, there are instructions on how to go about planing a straight edge, joining two boards, etc. These instructions worked for wooden planes and are probably easier to follow with metal planes.

https://archive.org/details/PeterNicholson1812/page/n235/mode/1up

My regular jointer is a Winchester the size of a no. 7. I worked on it until I got it flat to less than 1.5 thousands using a calibrated Starrett straight edge. I didn't use a gigantic granite block, I put the plane in the vise and sanded off the high points using sandpaper glued to a block of wood. In action, this plane cuts a shaving up to the end of the board without the need to press down at the knob. It works pretty well and I've got seamless joints of up to 5 ft long.

Eight feet is more of challenge in your case, let us know how your edges look like. If your no. 7 is not quite flat or the edge straight, maybe you need to address those to see if the joints improve.

Rafael

[David Carroll]

This is peripheral to the point of the thread, I know (my specialty), but there are ways to clamp boards for glue-up without store-bought, expensive clamps. For small panels like panels for doors, or other smallish projects I've made a clamping board, which is a panel (plywood) with a glued and screwed batten along one edge and another batten, parallel to the first fixed firmly with c-clamps, with space enough between the battens to just barely fit the finished panel you are gluing up, you should have to force the panels to fit between the battens. You prepare the edges, apply the glue and put the opposite edge of each piece against one of the battens with the glued edges together and push them down, springing them into position. (don't forget the wax paper beneath. A surprising amount of force is exerted on the panel. You can hold the panel flat against the plywood base with weights, spring clamps, or squeezy-clamps.

I have also made temporary bar clamps using 1 x3 wood with a block glued and screwed to one end and another block fixed in place at the other end about 1-1/4 inches beyond the width of the finished panel then during glue-up, once the glued-up panel is together, a pair of wedges works in the 1-1/4-inch gap to force the boards together. I used clamps like this for years.

Granted, these "clamps" do not exert the kind of pressure that iron clamps do, but as already pointed out, your glue joint should be well fitting in the first place. If you have gaps in the joint and you need to force them together under protest, then clamps like mine won't work very well.

Of course, another technique is a "sprung" joint, where the edge is shot square and straight and then a final pass or two is made with a shorter plane (I use a smooth plane set to cut a fine shaving and I start in about an inch from the end, with very little pressure on the plane and then bear down harder in the middle and then ease back out of the cut stopping about an inch from the far end. This makes a hollow in the middle of the edge, of about a thousandth of an inch, on each board. Then when gluing up only heavy clamping is required in the middle of the panel. The ends hold themselves together.

These days I use match planes on most panels. Not so much for the added gluing area but for alignment. Of course, on fielded and raised panels you would see the tongue and groove, so it doesn't work in that application, unless painted, but for other panels it really does help when working alone. Of course this does require one face of each board to be serviceably flat to run the fence of the match planes against.

DC

[Lee Schierer]

For a glue up that is 107" long, I would recommend gluing up the first two pieces by themselves. I would use at least 10 clamps spread along the length. More is better rather than fewer. Be sure to use scrap pieces to protect your finished edges from indentations from the clamps. Gluing just two pieces makes aligning the surfaces much easier. You can start from one end with light clamping pressure and align the surfaces where that clamp is applying pressure. Then move to the next clamping position and repeat the alignment process. You still need to move fairly quickly according to the glue set up time. Once all the clamps are set with the face surfaces aligned go back and increase the clamping pressure. Do the same thin with the third board after 24 hours of set up time.

I'm also an advocate of alternating clamps top and bottom of a glue up where possible.

[George Yetka]

Trying to see if I have enough clamps for my table top. Read about this 45 degree rule in spacing them out. Will probably cut it down to 8’ (currently 107”). For the three panels, the distance to first glue line is average of 11 to 12”. The width will be about 34”.

The answer is you never have enough. But 8 should be sufficient for an 8' table not include and used for cauling.

I am covered with 1',2' but once I go above i'm limited to 4-50s and 4-60s and 6 pipe clamps

[Tony Wilkins]

I don't really know what your skills w a jointer are, so I don't understand why you're exasperated.

An old joining technique uses pinch dogs, which can still be bought, to glue up two boards.

I have to admit I've not used them, but I do have a set for when I decide to use them. I assume that if the joint has no gaps, a dog on each end does the trick.

510115

Was really happy with continuous shaving and then discovered I’d been standing too close and made a consistent high edge next to me… d’oh.
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[Rafael Herrera]

Was really happy with continuous shaving and then discovered I’d been standing too close and made a consistent high edge next to me… d’oh.
510168

Just for the heck of it, extend your index finger, rest it on the top of the cutter, and try again. How does it feel?

If you position the plane left or right or right side of the edge, the shavings will be biased on that side. You can do fine adjustments that way.

[Tony Wilkins]

Just for the heck of it, extend your index finger, rest it on the top of the cutter, and try again. How does it feel?

If you position the plane left or right or right side of the edge, the shavings will be biased on that side. You can do fine adjustments that way.

picture is of me using my LV 5.5 afterward to take a thicker cut on the high side. I do extend my finger when I use a Bailey style plane. I’ve tried it with the Norris style LV planes but since there’s really no place for it, it feels strange n

[Rafael Herrera]

I do extend my finger when I use a Bailey style plane.

Just a thought.

I'd suggest you test for square more often that you have been. If you catch yourself before the error is to big, then you can correct it by simply moving the jointer to the required side.

[Tony Wilkins]

Just a thought.

I'd suggest you test for square more often that you have been. If you catch yourself before the error is to big, then you can correct it by simply moving the jointer to the required side.
Definitely should have but got on a roll. Unfortunately, the roll was toward a cliff lol.

[Jim Koepke]

Was really happy with continuous shaving and then discovered I’d been standing too close and made a consistent high edge next to me… d’oh.


Consistency is good. It is easier to correct a consistent error than one that is uneven.


Just a thought.

I'd suggest you test for square more often that you have been. If you catch yourself before the error is to big, then you can correct it by simply moving the jointer to the required side.

Regular checking is my main reason for having a small try square at the bench.

Correcting by moving the jointer to the high side is mostly used with a cambered blade.

One early piece I read on jointing an edge was to skew the plane and start the plane's body on one side and to shift to the other side over the length of the work. This was to even out the wear on the plane's blade, allowing it to stay sharp longer.

Not using a cambered blade in my long planes my method is to set the toe of the plane on the high side and hold it square by feel. Depending on how out of square the edge is and how thick the shaving is, the plane takes a shaving and all following shavings are taken with the plane riding on the surface made by each new shaving until a full width shaving is removed. This takes a little practice to get the feel for it. It has been working for me over many years now with usually only 3 or 4 shavings to bring an errant edge to square.

jtk

[Tony Wilkins]

Consistency is good. It is easier to correct a consistent error than one that is uneven.



Regular checking is my main reason for having a small try square at the bench.

Correcting by moving the jointer to the high side is mostly used with a cambered blade.

Not using a cambered blade in my long planes my method is to set the toe of the plane on the high side and hold it square by feel. Depending on how out of square the edge is and how thick the shaving is, the plane takes a shaving and all following shavings are taken with the plane riding on the surface made by each new shaving until a full width shaving is removed. This takes a little practice to get the feel for it. It has been working for me over many years now with usually only 3 or 4 shavings to bring an errant edge to square.

jtk
Sad thing is that I had a small square there the whole time. I just never stopped to check. I keep a camber on all my bevel down bench planes so moving them to the high edge works for me. I think I need slightly more camber on the 7 though.

[Rafael Herrera]

Sad thing is that I had a small square there the whole time. I just never stopped to check. I keep a camber on all my bevel down bench planes so moving them to the high edge works for me. I think I need slightly more camber on the 7 though.

Jointers don't need a significant camber, just the slight one you get by biasing the pressure when you sharpen.

[Tony Wilkins]

Jointers don't need a significant camber, just the slight one you get by biasing the pressure when you sharpen.
That’s how I do it (more strokes on eclipse style guide). Felt as I tried to correct maybe I hadn’t kept enough with the last sharpening as I watched the shavings emerge.

[Mel Fulks]

On short stuff it was common in old shops to put on hot animal glue and just rub them together and stand them against a wall . Ive
done it .

[Mel Fulks]

I made some pinch dogs out of a piece of hardware store mild steel about 1/8th inch thick. Used them in employments, and everybody
wanted to borrow them . Made a wooden box with a slide top for them. Got my Son to make a drawing of a bulldog’s face with teeth
that looked like pinch dogs. I’ve looked for them …numerous times, with no luck . DANG !

[Mel Fulks]

For work more than 2 or 3 feet long many of us used “sprung joints” , some say “spring joints” . They assure the ends won’t pop open. We jointed the pieces with straight cut , then moved out-feed table up just a hair ,and cut again That put a slight arc that kept the ends from ever
popping open. The ends need that since that is where the the moisture is lost.

[Tony Wilkins]

For work more than 2 or 3 feet long many of us used “sprung joints” , some say “spring joints” . They assure the ends won’t pop open. We jointed the pieces with straight cut , then moved out-feed table up just a hair ,and cut again That put a slight arc that kept the ends from ever
popping open. The ends need that since that is where the the moisture is lost.

The ends is why I didn’t use the opposite of the spring joint to utilize the pinch dogs. On the three joints I’ve done so far on this table I’ve done one intentional spring joint and two where I’ve aimed for straight joints on both sides. Of those two, one I did well and the other I tried match planing straight and ended up with a slight spring when I decided to glue it up that way. For the last two joints, I’m going for as flat as possible since the boards/panels I’m glueing up are wider.

I also think I’m going to glue the two joints separately as suggested earlier.

[Tony Wilkins]

Somewhere, someone recommended putting the boards on top of one another regularly to track the high spots. Did that and it did the trick. Final check with iPhone light behind it saw no light anywhere along the length.

https://youtube.com/shorts/ChyC0Lbibsk?si=lbCHxgn5ZQKWdXyU

[Doug Trembath]

Which goes back to my skill with a number 7 :rolls eyes: :exasperated look to heaven emoji:0

Thus your need to fully tune both the Number 7, and your jointing techniques, because after many tables, whenever I match planed my edges, I never have had a failure. Not trying to denigrate anyone, but a sharp, well tuned 7 will leave a perfectly straight joint matched such that even a rubbed glue joint will not fail, clamps not withstanding...

[Tony Wilkins]

0

Thus your need to fully tune both the Number 7, and your jointing techniques, because after many tables, whenever I match planed my edges, I never have had a failure. Not trying to denigrate anyone, but a sharp, well tuned 7 will leave a perfectly straight joint matched such that even a rubbed glue joint will not fail, clamps not withstanding...

it’s an LN #7; I think it’s pretty well tuned

[Tony Wilkins]

One more to go but I’m somewhat happy with how it went. Just put a clamp anywhere that it looked like there could conceivably be a problem.
510577

[Tony Wilkins]

So far so good…
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