Disappointed with my parallel clamps

[Matt Day]

I'm in the process of assembling my bench base and was clamping up this morning. I used dowels (via Jessem jig) for the joinery and planned to use a parallel clamp to tighten the joint flush. The joint is a 5"x1.75" stretcher to a leg which has 8 dowels in it. I began applying glue and things were going okay, but I couldn't pull the joint tight.
I reach for another parallel clamp and tried that, didn't really help much. I start getting antsy and nervous. So I reach for another and still nothing! Now I'm in panic mode. Did I mention my 10 month old was beginning to stir and fuss on the video monitor? So I had three parallel clamps (jet and bessey) and I was turning those pesky handles with all my might and it wasn't going anywhere! Thoughts of having to trash a couple weeks of work and explain it to the LOML are going through my head now. It would have been comical to watch I'm sure, and only my fellow ww'ers would understand what it's like!
Looking for yet more force, I grab one if my Rockler aluminum bar clamps and try that. The joint pulls together right away, and all three of my expensive clamps crash to the bench top. Happiness and relief set in and the rest of the glue up goes smooth.
But how is one cheap bar clamp putting more force on the joint than 3 of my parallel clamps? It's a lot easier to get grip on the handles of the bar clamp and they are longer so I can generate more force I suppose. The negative of the bar clamp is they tend to pull the joint out if square so you have to balance it with another clamp on the other side.
So the lesson here for me is that parallel clamps are not the be all and end all of clamps. Maybe the next time any of you get into a similar situation, try some other types of clamps.

[David Kumm]

Parallel clamps are really more about lighter force and keeping the stock flat and not bowing. Pipe and particularly bar clamps are for exerting lots of force. Parallel for glue ups, bar for big joints. You need some of each. Dave

[glenn bradley]

I'm with David. Parallel clamps are expensive because they clamp parallel. Sounds like you were having a hydraulic problem and overcoming that with pure pressure can blow out the side of a dowel hole. Groove your dowels(?). If you have joints that need to be crushed together during dry-fit, try easing the fit a bit. Things don't have to be sloppy to be easy to assemble (when I'm lucky :)).

In the immortal words of Sam Maloof "leave room for the glue!". M&T and dowels are prone to hydraulic lock if there is no escape path for the fluid.

I find clamp pressure charts always stating different things than what my gut tells me :o:

253833

[Harold Burrell]

253833

Wow...that's pretty interesting.

[johnny means]

It shouldn't take that much effort to close a joint. That last clamp was simply the straw that that broke the camel's back. +1 on grooving your dowels. Also, brush dowels with glue, don't squirt glue in holes.

[glenn bradley]

Just to add credence to my constant state of surprise by clamp pressure ratings. The Fine Woodworking picture in my post above rated the Irwin Quick Grip at well over 400lbs. The latest Wood Magazine rated eleven different quick grip style clamps; none were rated that high. Three were under 100lbs, Six were under 200lbs with the Lee Valley aluminum version at 269lbs and the top-of-the line Irwin at 386lbs. ???

I share the opinion that if you need hundreds of pounds of force to smash your joints together, you may want to fall back and re-group. I do sincerely understand the added pressure of an already stressful glue-up being compounded by the baby stirring. When trouble rears its ugly head in mid assembly and the baby's waking up . . . things can get pretty interesting ;-)

[David Kumm]

Dowels are notoriously fussy. I'm impressed you could close up a joint with eight of them at all. You did well. Dave

[Wade Lippman]

I hate parallel clamps and sold off most of mine when I moved.(I kept 4 6' off brand that no one would give me a decent price for)
I replaced them with the ones labeled aluminum bar clamps in the illustration.
They are much lighter and easier to use than parallel clamps.
Okay, they are not parallel and you have to be careful not to make your wood bow; but that is rarely a problem.

Before I sold them I put bicycle inner tubes over the wood handles; that helped a little, but not much.

[Harry Hagan]

Interesting.

My Jet parallel clamps are touted to, ". . . provide powerful 90-degree clamping capabilities at up to 1,000 pounds of pressure." Certainly not with me cranking on the handle.

It looks like my El Cheapo aluminum bar clamps may have been a better investment than I thought. Time to get them out of the box!

[ian maybury]

Think like with most mainstream market woodworking stuff the marketing claims don't necessarily relate to the technical realities.

Guess it's down to geometry and tightening method. The bar in a parallel clamp (which being solid isn't necessarily all that stiff anyway compared to e.g. the much larger/deeper box section used on some) is potentially handling a very large bending moment if the force ends up being applied out near the tip of what are long jaws - compared that is to a short head like that on say a pipe clamp.

The other issue is that (a) the thread is fairly coarse to give a decent closing movement/turn which also reduces the force generated by a particular level of effort at the handle, while the format of handle used gives minimal leverage anyway. i.e. it's not like they are designed to apply maximum force.

My caution about parallel clamps is that the recent examples have so much plastic in them, particularly the handles. Most plastics start to become brittle due to the effects of UV light and the like - by 10 years (or potentially much less depending on the polymer and the amount of UV inhibitor used) the chances are they may not be up to much.

Has anybody seen this happen so far? I've had the handles on cheap F clamps come apart, but not parallels...

ian

[Roy Harding]

I'll jump in on the "leave room for the glue" crowd - although I don't use dowel joinery, I DO use plate (or "flat dowel" also known as Lamello) joinery on occasion - it's interesting to note that the slots are cut somewhat larger than the biscuit. Part of this is to allow for expansion of the biscuit - and part is to allow for glue. I do a LOT of mortise and tenon joints - I undercut the cheeks and faces of the tenons with a 45 degree "channel" to allow for the glue squeeze out. I also bevel the end of the tenon to allow for glue on that end of the joint. Although I don't use dowels - the grooving opinions expressed above make sense to me.

As far as parallel clamps go - I've never had a problem with them, and like others, I suspect that the problem regarding not being able to close up the joints is related to the glue not having anywhere to go.

My kids are all grown and gone now - but I understand (and remember) the urgency imparted to the situation by the baby fussing!! Just think though - in a few years you'll have an excellent helper and apprentice in residence with you! The few times of panic and possibly a ruined project or two are a fair price to pay for the priceless times you've got ahead of you. I envy you the future - none of our boys (in their 30's and late 20's) give any sign of having a serious relationship - so my chances of being able to re-live their childhood with grand children are daily receding.

[Bill Huber]

I really don't think it is the clamps, I have never had a problem closing a joint with my clamps.

I have had a problem when I did not have the holes drilled deep enough on each part for the dowels.
I have taken care of that problem with my drill bit guide I made.
http://www.sawmillcreek.org/showthread.php?153582-Drill-bit-collar-jig-for-Jessem-or-DowelMax-dowel-jigs&highlight=jessem+dowel

I agree you should be using good expansible dowels, I get all of my dowels from Lee Valley.
http://www.leevalley.com/US/wood/page.aspx?p=32732&cat=1,250,43217,43228

If you are using smooth sided dowels and they are tight in the hole then there is no place for the glue to go when you try and clamp it. The dowels from Lee Valley let the glue come out around the dowel so this is not a problem.

I always dry fit all my dowel joints before I do the gluing.

[Michael Peet]

Interesting, Matt. Is it possible the parallel clamps were "maxed" out, meaning no more screw travel? This has happened to me (all of us?) at some point. Now before I begin a glue-up I make sure there is plenty of screw travel on all the clamps I plan to use.

I do know that my parallel clamps can apply much more force than is good for the project. Discovered the hard way, of course.

Glad you got it sorted out!

Mike

[Matt Day]

Interesting, Matt. Is it possible the parallel clamps were "maxed" out,

Mike - I've been there before! I make sure I have enough travel left in the screw too, and I checked.

I used Woodcrafts dowels with the glue channels, and made sure I left room for glue.

I think I did everything right making the joint and gluing, but I think the point is that I couldn't get the clamps I initially choose to exert enough pressure. I was able to pull the joint together with 1 bar clamp by itself - it wasn't in addition to the other three clamps.

The main thing I really struggled with with the parallel clamps was that I couldn't get enough of a grip on the clamps to really generate some force. I had a momentary temptation to grab my drill and pop a hole through the handle, then stick a threaded rod or something through it as a sort of cheater bar. Am I the only one who has gotten sore wrists and hands trying to tighten them up?

Bill - I like that jig you made for setting the stop collar, thanks.

[Roy Harding]

An interesting article regarding clamping force here: Link (http://www.woodmagazine.com/woodworking-tips/techniques/skills/take-it-easy-with-clamping-pressure/) There are others to be found.

[Cody Colston]

I have quite a few of the Bessey K-Body clamps and love them. When I need more clamping force than I can apply with my grip, I use a 12" pipe wrench on the wooden handles. ;)

[phil harold]

I coated all my handles with plasti dip definite improvement

http://www.amazon.com/Plasti-Multipurpose-Rubber-Coating-11601-06/dp/B0006SL0VO/ref=pd_bxgy_hi_text_y

[Jim Neeley]

I went through the clamping pressure quagmire a few years ago after I'd glued up my bench with epoxy and people were telling me I hadn't used nearly enough pressure. My bench was made from laminated 3"x 1.5" x 84" pieces with the 3"x84" faces glued together using 16 Bessey K-body's.

People were talking about Titebond and referenced this link:

http://www.titebond.com/Libraries/LiteraturePDFs/FF683_GlueGuideTB.sflb.ashx

which called for 100-150 psi for softwood, 150-200 psi for medium density wood and 200-300 psi for hardwood.

At 300 psi, for 3" x 84" pieces would require 3 x 84 x 300# = 74,600# of force. Even with the hypothetical 1000# max for a parallel body would require 75 clamps; using the 370# in the table would have required 204 clamps.

How do you call bullsh*t???

My pieces were carefully planed to be flat and to match together and my 16 clamps was probably overkill.

Can you imagine trying to explain to the LOML that I was going to spend $10,000 on clamps (200 x $50) to glue up a workbench top? I finally figured it was the lawyers talking where they tried to allow for gluing pretzel-boards together or as a protection from lawsuits.

Three years later and a lot of hand planing and chisel work and it's solid as can be.

Jim

[phil harold]

which called for 100-150 psi for softwood, 150-200 psi for medium density wood and 200-300 psi for hardwood.

At 300 psi, for 3" x 84" pieces would require 3 x 84 x 300# = 74,600# of force. Even with the hypothetical 1000# max for a parallel body would require 75 clamps; using the 370# in the table would have required 204 clamps.

How do you call bullsh*t???


They define clamp spacing,
So 12 clamps wood be sufficient


Clamps should be positioned a minimum of 1 1/2" - 2" in from the sides and
evenly spaced at 8" - 12" throughout the piece

[ian maybury]

Wonder how correct/on what basis those clamping pressure numbers are offered Jim? My perception was that the aim with a PVA is to bring the surfaces into close contact so that the glue isn't required to do any gap filling, but not necessarily to apply a lot of pressure? I thought I read that the stuff relies heavily on wetting/wicking effects for penetration.

Which if true suggests that accurate joints are the game rather than huge clamping pressures. Which is presumably why parallel clamps work pretty well in most cases.

It seems for example that PU does require a fair amount of clamping pressure - not only to also avoid gaps, but because unlike PVA the pressure is quite important to preventing foaming and driving the glue into the pores to get good penetration.

Whatever the scenario it's hard to see how very high clamping pressures like those can be used in practice - in that (a) clamps don't deliver enough force, and (b) without pretty major steps being taken to distribute the load the result will be crushing of the wood under the foot.

I guess the issue as you say is that when it gets down to gluing up large areas the old pressure = force/area rule kicks in. At the level that since area is measures in e.g. sq inches, and sq. inches are calculated by multiplying length by breadth (e.g. 1 sq ft = 12 x 12 sq in = 144 sq in.) the number of square inches rapidly multiplies.

With the result that regardless of what the adhesive might or might not like it's just not possible to apply significant pressure (in terms of pounds per sq in) over any significant area. So it's OK to think of high(er - probably still not of the order listed) pressures in small area joints like say in the legs of a chair, but they are not very likely if gluing up wide stuff like bench planking. i.e. a blanket recommendation for gluing pressure like that seems pretty suspect, and anyway not representative of how the glue performs in practice - if only because a glue that was highly dependent on high pressures for good bonding would only be usable in certain categories of joint and would fail in everything else. Even less so if the fact that a wide plank will bend under the resulting reactive loads from the glued area so that whatever pressure the clamp works up will really only be applied under the foot is taken into account.

The OP may have a point - many so it seems get to glue up bench tops using PVA and clamps without trouble, but it seems highly unlikely that in practice they use clamping pressures even remotely close to those listed. It seems to suggest too that (since high clamping pressures are not a realistic option) that (a) correct surface preparation (freshly planed with sharp knives, and truly flat surfaces), and (b) no interference with the wetting action of the glue (as a result of say inappropriate cleaners, or the wood being left for too long after planing) are important.

The same principle works in reverse when vacuum bagging. Even though full vacuum is maybe only 14psi the forces can be pretty enormous because 14psi x say 12in x 12in (our 1 sq ft again) = 2,016lbs (heading for a ton)

:) There's a classic parlour trick that demonstrates this beautifully. Place a decent stack of encyclopaedias or similar heavy books on a table. Insert a polythene bag of about the same area flat under them, pull the free end into an inlet and blow into it. The books will with almost no effort lift and fall over - despite the lungs being capable of raising only about 2psi +/- max. The explanation is in the maths as above...

ian

[ian maybury]

PS Looks like you were through this issue last year Jim - this is a good thread on the topic from way back that came up when i Googled the topic: http://www.sawmillcreek.org/showthread.php?166480-Reality-Check-Requested-Glue-Clamping-Pressure-Gone-Wild

It seems from it that correct control of the glue line thickness may be the key issue....

ian

[Thomas Hotchkin]

I have quite a few of the Bessey K-Body clamps and love them. When I need more clamping force than I can apply with my grip, I use a 12" pipe wrench on the wooden handles. ;)
I find that I can almost double the clamping pressure with my Bessey K-body clamps using cotton latex gloves on Bessey slippery red handles. Tom
http://d3s23h5t9xs8e6.cloudfront.net/images/photos/50481/50481_4278-1760-cotton-latex-coated-gloves_detail.jpg?1314392948

[glenn bradley]

I coated all my handles with plasti dip definite improvement

http://www.amazon.com/Plasti-Multipurpose-Rubber-Coating-11601-06/dp/B0006SL0VO/ref=pd_bxgy_hi_text_y

I do what Phil does. I think the subject is wandering a bit. Parallel clamps are made to clamp parallel. Different brands do this to differing degrees. Various clamps are made to do various jobs. A cross-peen hammer is just the thing . . . but not for framing a house. right tool for the job and all that ;-)

[Chris Fournier]

In my opinion, if you need gloves, wrenches or whatever to really crank down on your parallel clamps to close up a joint one of two things is true:

One, your joint is poor and you are feeding in excess pressure to deal with less than marvelous workmanship. Just because your joint closed up doesn't mean that it is now a good joint - it is infact under a lot of tension and the glue is gonna be in trouble.

Two, you are using the wrong kind of clamp. For a bench top I'll use Besseys to fill in the glue up but I have proper I-beams that can apply over 4000 PSI to do the heavy lifting. I use the example of a bench top because I am expecting 3" plus wide multiple gluing surfaces mated up in a single action. Lots of pressure required.

The engineers who designed your parallel clamps but round handles on the screws for a reason, with this round handle you cannot over strees the clamp beam. Cheat the handle and you can damage the beam. Look at I-beam clamps, they give you a t-handle because the beam can take all that you can give it.

As a general rule, if you have to ply on gross amounts pressure or persuasion while putting something together it is most likely that something is wrong with the assembly or with your choice of tools.

[Harvey Melvin Richards]

In my opinion, if you need gloves, wrenches or whatever to really crank down on your parallel clamps to close up a joint one of two things is true:


In my opinion, you are dead wrong. I have very large hands and I have a difficult time gripping the Bessey handles to get them tight. The Jorgenson handles are larger and easier for me to grip. I also do what Thomas Hotchkin does and I uses rubberized grippy gloves.

[Chris Fournier]

In my opinion, you are dead wrong. I have very large hands and I have a difficult time gripping the Bessey handles to get them tight. The Jorgenson handles are larger and easier for me to grip. I also do what Thomas Hotchkin does and I uses rubberized grippy gloves.

...I have very small yet powerful hands and my palms have the coefficient of friction equal to 80 grit sandpaper! I was designed for clamping I guess.

[Matt Day]

I like the tip on the rubber/nitrile gloves, I'll have to use that. The handles get even more slippery when you're hands get clammy from a stressful glue up!

[Cody Colston]

Chris, you are certainly entitled to your opinion.

[Curt Harms]

Not an original idea but it seems like it should work:

Golf Club Grip Tape
http://www.worldwidegolfshops.com/prod/golf-course-accessories/golf-grip-tape.html?gclid=CMbUurrrsLUCFYdT4AodGX8A6g

[Charles Wiggins]

I have two thoughts: Dry fit test run and a mallet.