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How tight do I need to set my clamps?

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Forum topic by Tom posted 05-18-2016 01:30 PM 829 views 0 times favorited 14 replies Add to Favorites Watch
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Tom

130 posts in 522 days


05-18-2016 01:30 PM

I’ve been doing a bit more woodwork and made a few cutting boards/shelves. I’ve put the clamps on fairly tight and notice once the project is dry they appear bowed sometimes. Is this non-square cuts on the strips or too much clamp pressure? I tend to test fit/clamp to make sure everything is good but keep having this issue.

Basically: How tight do the clamps need to be?


14 replies so far

View a1Jim's profile

a1Jim

115202 posts in 3039 days


#1 posted 05-18-2016 01:47 PM

It may be that it’s a matter of having clamps on both sides to equalize the clamping pressure to avoid bowing.

-- http://artisticwoodstudio.com Custom furniture

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Tom

130 posts in 522 days


#2 posted 05-18-2016 01:57 PM

Maybe that’s the issue. All my clamps were facing the same way on the same side. I’ll have to switch them up next time I make something.

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shipwright

7167 posts in 2260 days


#3 posted 05-18-2016 02:50 PM

I think Jim has your answer but there is another one to the question.
Different glues require different pressures.
Urea formaldehydes require quite high pressures while epoxy joints can be “glue starved” by too much pressure.
PVAs don’t need much pressure if the fit is good and hide glues even less.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

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Betsy

3338 posts in 3358 days


#4 posted 05-19-2016 02:11 AM

You also have to take into account that the smaller the project the easier it is to over clamp and get the bow you mentioned. The photo Jim shows would be almost impossible to bow the boards but you start looking at 3/4 or 4/4 boards and it’s a lot easier to bow the board.

Don’t be a gorilla tightening the clamps – Like Paul said, the clamping pressure can be different depending on the glue you are using.

Just because you can turn the clamp some more, doesn’t mean you should.

In general terms, for me anyway, I try to tighten the clamps as evenly as possible, a little on one, then a little on the next and so on. Once all the clamps are even and feel tight I’ll spin the screw another 1/2 turn or so. If I can bump the clamp and it moves – it’s not tight enough – then adjust as necessary.

Not sure if I explained myself very well.

-- "Our past judges our present." JFK - 1962; American Heritage Magazine

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waho6o9

7172 posts in 2039 days


#5 posted 05-19-2016 02:43 AM

http://www.mikes-woodwork.com/Cauls.htm

http://www.bowclamp.com

HTH

“Basically: How tight do the clamps need to be?”

Just snug em up, not too tight and not too loose.

View jbay's profile

jbay

812 posts in 361 days


#6 posted 05-19-2016 03:03 AM

Yes to Cauls
Yes to Clamps on both sides
I tighten my clamps fairly snug, then after 20 minutes or so I give them an extra turn.
That is, when I think about it. I doubt it really needs the extra turn but if I don’t I notice the clamps aren’t as tight when I take them off as when I put them on.
I’m assuming were talking about using the most common glue, being tightbond.

-- My “MO” involves Judging others, playing God, acting as LJs law enforcement, and never admitting any of my ideas could possibly be wrong or anyone else's idea could possibly be correct -- (A1Jim)

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bonesbr549

1176 posts in 2529 days


#7 posted 05-19-2016 01:12 PM

As others have stated and I’ll 2nd 3rd etc. In my early days I use to slather as much glue as possible and have a test of my manhood to see how tight I could make it. Its just not necessary.

Now I use a reasonable amount of glue (if more than slight squeeze out its just a waste of glue.

I also clamp 1 up 1 down and always use an odd number with one in the center and the other even.

I use calls if waranted, but if I’m to trim the panel down and its long grain to long grain, I don’t worry about it.

Hand tigh and a 1/2 turn more and thats it. Never had one fail on me.

-- Sooner or later Liberals run out of other people's money.

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JackDuren

136 posts in 421 days


#8 posted 05-20-2016 10:34 PM



I think Jim has your answer but there is another one to the question.
Different glues require different pressures.
Urea formaldehydes require quite high pressures while epoxy joints can be “glue starved” by too much pressure.
PVAs don t need much pressure if the fit is good and hide glues even less.

- shipwright

I have yet to see a “glue starved” joint unless on purpose….

View JackDuren's profile

JackDuren

136 posts in 421 days


#9 posted 05-20-2016 10:36 PM



I ve been doing a bit more woodwork and made a few cutting boards/shelves. I ve put the clamps on fairly tight and notice once the project is dry they appear bowed sometimes. Is this non-square cuts on the strips or too much clamp pressure? I tend to test fit/clamp to make sure everything is good but keep having this issue.

Basically: How tight do the clamps need to be?

- Tom

Tight enough that there is no more glue to press out. This comes with experience.

View shipwright's profile

shipwright

7167 posts in 2260 days


#10 posted 05-21-2016 12:44 AM


I have yet to see a “glue starved” joint unless on purpose….

- JackDuren

Do you work with epoxies a lot?

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

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JackDuren

136 posts in 421 days


#11 posted 05-21-2016 12:51 PM

we use all glues at work. We make interior and exterior tables for restaurants….

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shipwright

7167 posts in 2260 days


#12 posted 05-21-2016 02:02 PM

I built wooden boats for many years and used a great deal of epoxy. There are certainly places where you can drive the glue out of an epoxy joint and cause failure. Trust me on that one please.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

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JackDuren

136 posts in 421 days


#13 posted 05-22-2016 03:17 PM



I built wooden boats for many years and used a great deal of epoxy. There are certainly places where you can drive the glue out of an epoxy joint and cause failure. Trust me on that one please.

- shipwright

I can’t agree or disagree with building a boat and its + and – on the use of epoxy. I can only respond to its use in the question at hand.

Building boats your king of the sand box as I don’t, but in furniture that’s another sand box.

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wuddoc

93 posts in 3180 days


#14 posted 05-22-2016 09:01 PM

Check out Dr. Gene Wengert, he is Professor Emeritus in Wood Processing, Department of Forestry, at the University of Wisconsin (Madison) AKA “The Wood Doctor”. I find he is an authoritative voice in the woodworking industry.

He has a white paper on adhesives and clamping pressures. Search on the internet for the PDF sponsored by Franklin Glue. GLUINGWOOD: A STICKY BUSINESS

There are drawings and pictures showing problems in this paper.

-- Wuddoc

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