Hi Guys,
First of all, thank you for being a wel responsive community. My last post had some very helpfull reactions and ideas.
I created a stool. It’s a simple. It has four legs and four rails with a mortise and tenon joint, in which the tenon joins in a miter within the small stool leg.
Now, I would like to test it’s strenght properly. What kind of test do you guys recommend? How do I check what kind of stress it can handle. And as it is a test, I don’t mind if the stool is going to break. I haven’t got any fancy tools for measuring the force. Any idea’s, links or video’s are always welcome.
A big thanks,
Max
Replies
I read that when Sam Malouf (or maybe it was another guy) made his first chair, he wanted to see if it was well made and strong. So he hauled it up on his roof and dropped it on the driveway. It held together. You might try that. :)
Haha love it!
My older brother and I tested each other the same way on the garage roof a looooong time ago!
Don't know if Sam Maloof actually did that, but it was a tradition where I come from. Although its founder, Rick Turner, has moved on and they have moved from their 60 Brady Alley location in San Francisco, CA. and are now in Santa Rosa, CA., Alembic used to test new brands of instrument cases by putting one of their (in 1970's dollars) $1,200.00/$1,800.00 brand new guitars or basses in one, take it up to the roof of the two story building and toss it off. If it survived, they'd use or recommend them. That's part of the reason you see Anvil Case's on airlines traveling between so many concerts. When they moved, the store part of their operation was taken over by Ron Armstrong & two partners and became Stars Guitars. One day a salesman from Choice Cases came in with his old, gold top Gibson Les Paul in one of their fiberglass, foam lined cases and was telling us how great it was. So Ron, smilingly, took the case from him, went up the stairs to the mezzanine and tossed it off to the hardwood floor below. The look on the salesman's face was almost as priceless as his look of relief when the case was opened and his old Les Paul was still intact. (We would've fixed it for him, if not for free, at least for a reduced price, if it had been damaged, but he didn't know that at the time.) Thanks for reminding me. Yes, I was the Guitar Doctor for Stars Guitars and we really did believe in"Industrial Strength" when it came to protecting and building things.
Take your stool to a local machine shop with an arbor press and offer them a couple of bucks to turn your stool into kindling, heck they may do it for free just for the satisfaction of crushing something. Just be sure to take along a piece of plywood big enough to support the stool. The one potential drawback is their gauge may not be sensitive enough to to register hundreds of pounds.
As an alternative you could take it to the local gym and start piling weight plates on it until it gives but the owner may not appreciate his weights crashing to the floor when it does.
Thank you for your answer! I am going to search for a machine shop in my area. I agree, they might like the idea of demolishing it. Who wouldn't?
It's a stool. Sit on it. Often.
You could pile a bunch of weight on it, but so what? A really poorly made stool should be able to take a very large pile of dead weight without breaking. It's hardly a real world test.
A stool in everyday use has to withstand all sorts of racking, twisting, diagonal and other types of loads. There's really no way to realistically test for all that. Just use it. Subject it to the kinds of stress a stool is supposed to take.
Thank you for the response. I've decided to follow up on your advise. I am making an extra stool today in the same way, to use it at home for a full month. I believe you are right that using it everyday for a longer time exposes different stresses and weaknesses than exposure to brute force. But I hadn't thought about it that way. Thank you for the idea!
Testing for strength is fun, but not especially relevant. I particularly like the arbor press idea!
It's a stool, not a structural member in a multi-storey building. It's for sitting on not for dropping.
Chairs and stools are necessarily a compromise. A solid block of wood is also a stool after all, and will be almost indestructible. A bit heavy and chunky-looking but a stool nonetheless. A stool made from drinking straws will be light and airy but delicate to the point of uselessness. Somewhere along the line from eternal wooden chunk to ephemeral pile of straws we find the type of construction that meets our aesthetic needs, uses material efficiently and lasts long enough to justify the effort involved.
When Ikea test their furniture they develop machines that mimic the day to day use that the item will experience - locks are turned, drawers opened and closed. Stools and chairs? - they have hydraulic 'bottoms' applied to them repeatedly.
For me, the most useful test of raw strength is to put a heavy load on the stool whilst it is balanced on 2 legs. The load should be applied perpendicular to the plane on which the legs rest, and directly over the feet of the stool in contact with that plane. This will test the resistance to racking loads, which are the main way chairs and stools fail.
Repeatedly loading and unloading the diagonals of your stool will test resistance to racking forces under more dynamic circumstances
Subjecting the stool to daily use is a very practical test which will tell you more about its overall suitability than any other method.
The trouble with all these tests is that you need some reference point to determine if your stool meets the criteria being assessed. How much weight is enough? How many times must it withstand what diagonal stress? How will you determine failure? Must it be rigid? is a little wobble acceptable? How about a pile of splinters?
In short, before testing, ask what standard you require the stool to meet. Is it to last for all time in daily use, or is it to be an art-piece and used only to demonstrate that such is possible? Probably your aim is somewhere in between, but to which end of the spectrum will determine your needs for strength, criteria for acceptable performance and ultimately your method of testing.
Thank you for your reply. It's exactly the explaination that I needed!
Can you sit on it without it collapsing under your weight? Can you rock back-and-forth? Stand on it? Handstand on it?
Regards from Perth
Derek
When I worked in the Conservation dept of a museum, my boss, the Conservator, had a very simple test for chairs (and stools). With the chair standing on a flat floor, grasp by the top of the back (or seat of a stool) and twist it - firmly - noting how much it moves. If there is much apparent motion, it would be a candidate for rebuilding (or disposal). Furniture in good shape won't wrack noticeably, it will simply slide on the floor.
You could theoretically design a stool (or anything) to carry as much weight as you want. But then, it would look like a tree stump. The key is to meet the projected need with the most elegant and economical use of material.
Sit on it and twist repeatedly. Tilt it back on 2 legs with your weight. A static load won't tell you much, as we constantly twist and turn, and those changing forces are what do the damage to joints.
One caveat: if it fails, it could HURT !
Splinters in the behind can also be embarrassing at the emergency room.
There's also the urban myth about the large person in the hospital emergency room requiring the extraction of such a stool from where it had become "lost". So ..... testing of the stool here should probably avoid the option of having a 400 llb person perching upon it to see if it creaks.
Yes. I mean, no.
Lataxe
Destruction testing will never replace sound workmanship. If your design, joinery and process is sound, you should not need testing. Testing is a means of discarding bad product from a untuned production line, effort placed in process control will yield better quality. Even if the stool fails at a high amount of stress, what guarantees that the next one you build will have the same strength unless your joinery and process are repeatable ?
Gulfstar while I may agree with you in the cases that a stool or chair is of a time proven traditional design and construction, but there are many woodworkers/artists who push the envelope in design and in these cases, especially if it will marketed commercially, testing does have a place. I would feel much better knowing my stool/chair withstood 600 lbs. of dead weight vs watching it shatter at 300 lbs. Can an typical woodworker test every possible stress placed on a chair, absolutely not, but we can test a couple of scenarios that would provide some peace of mind that a design will hold up in the real world.
Thank you all so much for the great answers! I will be looking into them and give them a try!
“[Deleted]”
So many variables - species; moisture content; type of construction and more, so little information - thickness of parts, diameter(s) of tenons/mortises and their fit. Kind(s) of adhesive used - if any, splay angles of parts, & etc.. Where to begin? The best advice given thus far is to give it "Real world" testing. While "Strength" is relative, if you go "Overboard" in your testing, you may well suddenly go there for real, so be careful.
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