Tuesday, March 19, 2013

Simple Things: Glue Blocks

Making Glue Blocks

One of the constant pleasures of restoring period furniture on a daily basis is learning from the "old guys" how they were trained to do things by hand.  I find it difficult to imagine how a young aspiring woodworker today can learn as much from school and books as I have over my career just working on antique furniture, day in and day out.  Sometimes at night too.

As I work to repair and recreate period furniture, I try to put myself in the shoes of the maker, standing at his bench, working a typical pre industrial work week, 11 hours a day, 6 days a week.  Thank goodness that the employer had to supply candles!  My habit is to work 12 hours a day, 7 days a week, but I am slightly obsessive about my craft, and have no other hobbies to distract me.

I have noticed simple tricks over the years, which are so obvious to me that I don't place a high degree of importance on them.  However, sometimes when I mention them to other woodworkers, I see the interest in their eyes, and that reminds me not to take anything for granted.

So here is one of those "obvious" tricks: Glue Blocks.  Need I say more?

Glue blocks are everywhere on antiques.  Wherever you need a support or added strength in cabinetmaking, you find a glue block.  They are simple blocks of wood, generally soft wood, which are placed inside the cabinet, under the base, behind the crest, under the drawer runners, as drawer stops, etc.  Everywhere.  They are in places where it is impossible to use clamps.  They rarely, if ever, have nails and never screws, as it is a waste of hardware, and not necessary to hold them in place.

They are attached using the "rubbed joint" process with hot animal hide glue.  Essentially, the fast tack feature of the glue allows the worker to just apply the glue to the block and press it into place.  Sliding it back and forth slightly a few times removes the air and pushes out the glue, and then it sticks.  Takes about 10 seconds to install.  Ends up stuck as much as if you had applied a clamp.  Neat and efficient.

I got to thinking about these glue blocks.  Making a single block is a bit of work.  Making a lot of blocks is much more efficient.  You need a stick of soft wood, usually about 1" square, but the dimensions depend on the final project.  Using a jointer plane, you shoot it in length on all sides to make it true.  Make sure that at least two adjacent faces are square, and these faces are toothed the length of the stick, using the toothing plane.

Check The Corner For Square

To finish the job, you take the plane and chamfer the opposite corner from the toothed sides.  This chamfer is the clue that led me to understand exactly how this process worked "back then" in a typical three man shop.  I saw this chamfer on all the glue blocks I looked at in early furniture.  At first I thought it was just the worker being neat or showing off, not leaving a rough edge to the blocks.  Then I realized that time and effort was precious when you are working for a dollar a day, and there is no reason to "finish" off a simple glue block which will never be seen by the client.

Tooth Two Adjacent Sides

That made me think that it was the job of the young apprentice boy, working in the shop, helping out.  It would be a good learning experience for the apprentice to prepare these blocks in advance.  He would gain practical experience with the jointer, toothing plane, square, and bench.  He would make long sticks with toothed sides, planed sides and a chamfer, then saw them into short pieces and place them in a box, ready for use.

When the journeyman needed a block, he just reached into the box and grabbed a few, ready to use.  The chamfer was a tactile and direct way for him to determine which two sides needed the glue and were toothed.  He didn't need to waste time looking at each block every time he needed to use it.  Just feel the chamfer and add the glue, press it in place and continue working.  Fast and efficient.

All the clues are there on antique furniture, if you know where to look and how to interpret what you see.  Instead of reading books, I recommend you start reading the original object.


Zach Dillinger said...

A great post! Glue blocks are used frequently in my work. I almost never chamfered them off, but I will from this point on! Thanks!

Tico Vogt said...

There are times when the chamfer makes that corner less likely to be visible.

W. Patrick Edwards said...

I don't really think that the purpose of the chamfer is to hide the glue block or make it attractive. I am convinced that the function of the chamfer is to let the worker feel which side is toothed and glued.

The reason I say this is that the typical antique cabinet is not really well finished inside. The wood is often left rough or with imperfections, which do not show at all to the normal user of the furniture. Most people who own a chest of drawers do not take out the drawers and spend time looking at the workmanship inside.

Also, I have found chamfered glue blocks inside clock cases and other areas of cabinets which are inaccessible unless it is taken apart physically by the repairman. There is no reason to chamfer these blocks when they are completely hidden, unless they were chamfered as a result of the process of making them in advance.

Sam Powers said...

Our home is filled with antiques, usually purchased or found in ill repair. As a woodworker, my wife felt there were no limits to my ability to repair these pieces. I've repaired chairs, old rockers, case furniture, and lamps!

I must say the one thing that always puzzled me were the glue blocks. Sometimes a straight forward corner block, and sometimes a seemingly free floating block in the middle of a case side with no discernible reason for it to be there. Why did the craftsman put it there.

Recently I was repairing a 1800's chest of drawers, the glue blocks were obviously used as part of the drawer runners, but how were they attached... No clamp would reach them.

Hide Glue, and the rubbed joint.

Since my recent switch to hide glue, it all becomes clear.

Thanks for the ah-hah! moment Pat!


W. Patrick Edwards said...

A good furniture detective will be able to distinguish the later repairs from the original work. As furniture has lived for several generations, there have always been repairs made by later workers, some more competent than others.

Many of the repairs made before 1900 were done by wood workers who were trained in traditional methods, and their repairs are often exactly like the original process. However, you can look at the dirt and patina, as well as the tool marks and hardware to determine when things were done.

It is rare indeed to have a piece of furniture which is two centuries old and has never had anything done to it.

You can even look at the original screws and see if they have been removed at some point, since the screws made before 1850 had a slot which was not square bottom. It was essentially a "V" slot, so a modern square bottom screwdriver will slip out of the slot and nick the patina of the screw.

Rare is the screw left untouched! Perhaps the best clue of all that the piece is old.

JC said...

I really love to use glue blocks, especially on cabinet bases, which tend to suffer more abuse when the furniture is moved, or bumped with feet/vacuum cleaners, etc.

1x1 could be much too large depending on what you're building. I mainly work on clocks, so the ones I tend to need are closer to 3/8" or 1/2" square. Then again, I have seen huge ones as well, such as the monster ones in a longcase clock that I'm repairing. These are probably 1 1/2 cut with a full 45 degree face, and they are about 6" long.

I sometimes find them in the full 45 degree triangle format, but most often they are like the ones in your post.

But one of the most interesting applications I've ever seen regarding glue blocks was a video demonstration I had seen online a few years ago. They were adding glue blocks to the back of a bracket foot, and they used stacked blocks probably around 1x1x1 and alternating the direction of the grain 90 degrees (end grain on one side as opposed to the top), to get maximum glue surfaces touching, which seemed brilliant.

W. Patrick Edwards said...

The process you describe is typical of several major regional centers of production in America during the 18th century. The grain direction of the glue blocks is a very interesting topic. In the chairs from that period the glue blocks are vertical inside the seat frame. Later efforts to secure loose chairs usually have horizontal braces in the same corners. Obviously the vertical direction allows long grain surfaces for the glue blocks, where the typical horizontal grain blocks have mostly end grain surfaces.

I like the horizontal direction of the stacked blocks inside the bracket feet. It makes sense. Not only is the glue surface long grain, but by changing the direction of each block, you effectively create a "plywood" strength.

Note that in good construction, the blocks carry the weight and the bracket feet remain slightly off the floor. Over time the blocks wear down and the bracket feet then are sometimes pushed out of place.