Replies

1. 
   RickL | Aug 31, 2006 08:01pm | #1

   FWW did this years ago using a hydraulic ram with a gauge on it to measure pressure. You should read the article if you can locate it also there is standardized tests in the indusrty for furniture. Don't know where to find it offhand but it does exist.

2. 
   tms | Aug 31, 2006 10:50pm | #2

   Hey Textacoman,

   The standard industry tool for this kind of work is called an Instron, made by surprisingly enough a company called, ... Instron. They are in essentially every machine shop that does any destructive testing for quality control. They are also in a lot of university and college engineering labs.

   If you live near a university or local college that teaches basic mechanical engineering, I'll bet that you could get someone to test your joints for you. The great thing about the Instron is that it is usually hooked up to a chart recorder, so each student can have a paper chart of the failure point of his/her joint.

   Tom

   ps. Here's a link to Instron. Maybe if you contact them, they will help you locate the nearest instrument.

   http://www.instron.us/wa/home/default_en.aspx?ref=http%3a%2f%2fwww.google.com%2fsearch

   
   

   ---

   Edited 8/31/2006 3:51 pm ET by tms

3. 
   Lataxe | Aug 31, 2006 11:01pm | #3

   Tex,

   One sort of test is the mechanical stress test that I think your'e planning.  But another test for WW joints would be a simulation of dry-damp cycles, to see how joints fared over the many expansions/contractions involved as the climate changes over the year.  This sort of stress it probably what most furniture gets destroyed by, rather than mechanical stress caused by excessive applied forces.

   I suppose it would take time but perhaps it would be possible to set up a chamber with controllable humidity, to accelerate the humidity-change cycles....?

   Lataxe

1. 
   Rich14 | Aug 31, 2006 11:19pm | #4

   Testing joints?

   I've always just lit one end and inhaled deeply . . .

1. 
   dukeone | Sep 01, 2006 05:25am | #5

   Be sure not to light the end with the filter!!Kenneth Duke Masters

   The Bill of Rights December 15 1791 NRA Endowment Member

   LEAA Life Member

   CRPA Member

4. 
   9619 | Sep 01, 2006 05:12pm | #6

   Textacoman,

   That sounds like a great project for an 8th grader. Some people have told you that it was already done, and that the people used big expensive powerful dangerous machinery. I suggest that you read the past reports to see what they found.

   I suggest that you do NOT try to use expensive dangerous powerful machinery. So how can you do your project SAFELY and interestingly???

   Pick a small number of joints to test. Keep them simple. For example, just take two 1"x2" pine boards, about four feet long and glue them together at their midpoints. Then make a "lap joint" with the same size pieces of wood, and glue them together. Then take two more pieces the same size and just nail them together, with no glue. Then take two more pieces and put two screws through them, with no glue. Then take two more, and cross them, and drill two 1/4" holes through them and put dowels through them, using glue. Now you have a bunch of joints to compare.

   Now you have to make some hypotheses as to which joints will win and why they will win. You can get some help with this from any woodworker. You should try to make some hypotheses before you ask someone else.

   Now you have to test them. Make sure you have an adult help you with this part. Get a big cloth bag which can be hung from a rope. Then get some weights, which can be bricks or cinder blocks or weights from a barbell set. then clamp one of the boards to the top of a workbench or a table. Tie the rope with the bag to the board which is not clamped. Now start adding weights, one at a time, until it breaks. Record the number of bricks or cinder blocks or weights that each broke under.

   The idea I suggested will have to be adjusted. You may need to put the weights in something other than a bag. I was just trying to give you an idea of how to do a safe, fun, useful project. You need to do some "pilot tests", as they say in science, to see about how much weight you will need. So glue some boards together and see how many bricks you need to break the joint. If you need to many bricks, use smaller joints. ( for example 1'x1" boards that are 3/4" thick. Sometimes the most important part of a science projects is this part in which you figure out how to "tweak" the method you will use to make your test.

   Be sure you have an adult around for all of this, who will check out your plan, and who will be there every step of the way. Stand back when you add the weights. If you use longer boards, you will get things to break more quickly. Always have an adult in the room when you are doing your testing!!

   I hope you find this useful. PLEASE STAY SAFE. Please let us know what you decide. My three kids did science fair projects every year, and they learned a lot and had a lot of fun. I wish you a lot of luck.

   If you have any more questions, please write to me. If I did not explain myself well, or if I used words that are too complicated, ask me to explain better.

   Enjoy,
   Mel

   PS STAY SAFE!!!!!! This project can be done safely, but it can also be done unsafely. BE SAFE!!!! Never do any testing without an adult present and helping.

   Measure your output in smiles per board foot. 

1. 
   glatt | Sep 01, 2006 05:44pm | #7

   I like the experiment you suggest. I would add that instead of making full sized joints with pine, it would be safer to make model sized joints, and/or to make joints from a wood like balsa. If you make them small, you will be dealing with less weight to break them, and it will be safer.

2. 
   textacoman | Sep 01, 2006 06:14pm | #8

   Thanks for the responses. This is actually an expansion of my sons project last year. We made five different joint out of 1x3 poplar: butt, biscuit, pocket screw, half-lap and mortise and tenon. We secured each test joint onto a steel column in my shop, attached a come-a-long to a 600lb. game scale and cranked until the joint failed and measured the force applied at that point. Crude, but it worked. I had to disassemble the game scale several times to reset the the inner workings. It's not designed to endure the shock of destructive testing. This year, his teacher wants him to test different species of wood using a m&t joint, which we found to be the strongest. I'm afraid my game scale won't survie this round of testing and that is why I'm seeking alternate methods.

   We did keep safety in the forefront and my son had a great time with the project. Thanks again.

1. 
   John_D | Sep 01, 2006 07:48pm | #9

   It might also be fun to explore strengths and weaknesses of different joints.  For example a groove housing a shelf will do great holding up books but won't have the resistance of a sliding dovetail to pulling apart.  Point being different joints are used in different places, because different forces are brought to bear.My goal is for my work to outlast me.  Expect my joinery to get simpler as time goes by.

2. 
   Buster2000 | Sep 01, 2006 08:13pm | #10

   I think 9619 has a good idea.  Sonce you'll be testing MT joints secure the leg and just ensure that the "arms" are all the same length.  The arm will act as a lever, so if you want to go with less weight you can just make it longer.  Maybe one of the engineers lurking around may be able to provide you with a formula to calculate the force required to break the joint.

   Rather than test different woods perhaps different contructions of the MT could be tested (widder tennon, deeper tennon, etc.)

5. 
   GDH2 | Sep 04, 2006 05:21am | #11

   Cool project, interesting issues...

   If I spent 30 minutes I could devise a test using a hydraulic jack, a 10' 2x4 (a lever), and a scale to measure force. A 10:1 ratio from the lever would mean a 400# limit scale could measure a 4,000# force.

   A car floor jack would be my first choice although a bottle jack would be more civilized - but no 8th grader would choose "civilized"! Now if I could only think of a way that flame was necessary...

1. 
   QCInspector | Sep 05, 2006 04:55am | #12

   If your son's school has an Automotive or Metal Shop then they probably have a hydraulic press with a pressure gauge. The test pieces can be mounted and the pressure recorded at the point of failure. You could locate a more sensitive hydraulic gauge if the one on the press doesn't have a fine enough scale.You could also attach the test samples to a wall or post and hang a drum (start with the bottom 6" or 8" off the floor, remember the toes) to an attached lever (your 10 footer for eg.) and slowly fill with water. When it fails you can dip the drum and calculate the weight that was applied. Extra points for volumetric/weight conversion calculations.;-)