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There is a form of deep throat clamp used in a certain style of boat building known as a 'lapstrake' clamp. This kind of clamp is used in building old-style lapstrake boats (where the upper plank laps over the lower). Also known as 'clinker' boat building. A large number of clamps are needed to get a good fit down the length of the planks. Builders of lapstrake boats will commonly make themselves sets of these clamps numbering in the dozens. There are several flavors of these clamps, always home or local shop made to my knowledge. An online search for images of lapstrake clamps will produce many varieties. Since they are specialty clamps used for clamping together the bottom edges of two relatively thin planks, the jaw opening need not be great, but the throat depth must be quite deep.

I have always preferred the kind that can be engaged with one hand. The sort I make have a lever which produces a cam action by turning in a circular socket made to match the heel of the lever. The accompanying pictures should give a good idea of how this works.

A strong, relatively straight-grained material is needed, usually oak, ash or something of the sort. Clamps are usually made from 1" - 1-1/4" stock, although thinner or thicker ones may be made for specific types of work. The hinge can be simple, or no hinge at all since the clamp is held together by the straps, and the pressure of the cam when in use forces the heel ends together. However, I like to have a hinge to fix the clamp in alignment. In this example, the hinge is a simple piece of webbing nailed to the arms with weather stripping nails. The straps are metal, 1/8" x 1/2"+, and drilled near the ends to accept a bolt to connect them to one arm of the clamp and to the cam lever.

The location of the bolt in the cam lever should be over or slightly beyond (towards the jaw) of the bolt in the lower arm in the 'engaged' position in order to 'lock' the clamp in place, meaning the range of thickness the clamp can handle is limited. Sometimes a little rosin applied to the cam area makes thing stick, or even a thick rubber band placed on the upper arm before use, can be used to hold the cam lever in place in the case of thicker stock.

Patterns are used to lay out the stock, and decide on the jaw width opening. Since the clamps will be used on something with a set thickness range, it is not necessary the clamp jaws close completely. In fact, I always put a small spacer between the jaws to decide how long to make the straps and where to drill the holes for the bolts. Depending on the radius of the cam and socket, the clamp will provide a jaw opening range of around 2" - 3". I suppose if you needed more jaw range you might make straps with a number of holes at different spacing, and simply move the bolt to the next hole on one end or the other.

Even if you don't build lapstrake boats, having one or two of these around comes in handy when you need to clamp something deep into the work. I am surprised at how often I use mine, and always grateful to have one or two around.

As a lover of most things wooden, I am a believer in spending a little extra time to make things attractive and elegant looking. It really doesn't take much time, and the results are always good for your soul. I hope you like these!

  • At the request of a fellow Lumberjocker I have added a blog entry on how to build these clamps.

(Helpful Hint: Buy some pick-up bed liner material at Lowes or Home Depot to use as jaw protection. It is cheap,, comes in rolls and can be cut to shape and glued on using contact cement)

Gallery

Comments

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5,820 Posts
Ultra-cool-another great clamp. Thanks for posting.
 

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429 Posts
Nice thank you for the post I thank I will make some and like you sad make more holes
 

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475 Posts
Very interesting. I did not know this type of clamp. Thank you for posting
 

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369 Posts
I've added some jaw protection to prevent marring of the work. Truck bed liner which comes in rolls and can be contact glued to jaws works great. When it wears out, just replace.

 

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1,256 Posts
Nice, do you make boats? if yes, post some pics!!!
 

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2,109 Posts
Sweet clamp !
 

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Yes, hi Jap. I've made many boats in my time - so many I've lost count. My true and most basic love is small, custom wooden boats, and I've built a number of lapstrake models, mostly to my own design. I've also built a number of larger boats - with much help - in my career, but somehow those, while gratifying, don't provide the satisfaction of a boat I've built strictly by myself. Usually, I have had a small boat project going in the corner of the shop which I worked on in my off time - sort of a busman's holiday if you will. I'll look around to find some pictures to post.

In the meantime, here's a link to a 'cradle boat' I recently built for my newest grand child:

http://lumberjocks.com/projects/69035
 

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118,619 Posts
Very cool Clamp Erik
 

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3,573 Posts
I like your clamps.
Do you think instead of a metal or rubber hinge that cutting a vertical slot in the ends of the arms and inserting a wood plate in the slot that is cross pinned to the two arms with a dowel (or bolt) would work? I may give it a try when I get a free moment.
 

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Yes, LesB, that will work. I've also used a metal strip. Since the ends force together tightly and would press on the fastenings, you should leave a bit of 'slop' in the pin or holes for the fasteners.
 

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Nice clamps Eric.
It's nice to find another retired boat builder here at last.
My boats were almost all of the larger variety but custom wooden boats of all sizes have been my life.
The only clinker I ever built was an 8' dinghy and these clamps would have come in very handy.
Thanks for posting.

Please post some of your past work. There are lots of folks here who love to see wooden boats.
 

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Thanks for the post Eric, I can already think of several uses for this type of clamp in my shop.
 

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Great idea!
I was thinking that if the cam handle closed towards the back hinge it woul allow you to reach the clamp into tight areas. I just repaired a dollhouse for a client and clamping parts inside it was challenging.
 

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You are absolutely right Wdwerket. That should work fine too, just maybe not as 'one handed'. Thanks for your comment!
 

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interesting clamps, I always like seeing home made clamps.
 

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thank you for reminding me of this project bushmaster :)
now I finely can add it to my favoritlist since they are some off the clamps
I will make a few of

thanks for sharing it with us Eric

Dennis
 
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