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Thread: Pocket Hole vs Dowel Joint
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30th June 2014, 05:26 PM #1Intermediate Member
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Pocket Hole vs Dowel Joint
Hi
Was looking at buying a pocket hole jig to make some bar stools, found a few plans on the net using pocket holes to join the timbers.
Anyway, rang a woodworking shop and was told that a pocket hole joint is not a structural joint and that I should use 10mm dowels.
Asking a loaded question, is this true?
Cheers
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30th June 2014, 06:15 PM #2GOLD MEMBER
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Others opines may vary, however for a bar stool, I would use dowels.
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30th June 2014, 07:19 PM #3Taking a break
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Unless you can get a pocket hole jig big enough to handle coach bolts, I'd stay away from it. I also reckon pocket holes look cheap/tacky, but that's another issue.
Do it properly and use dowels, it's a good skill to have anyway.
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30th June 2014, 07:40 PM #4
Pocket hole screw jointing is for those that have no idea and no skills, too lazy to learn how to do real joints
The person who never made a mistake never made anything
Cheers
Ray
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30th June 2014, 08:24 PM #5
Pocket holes can be just fine if you lack the skills/patience/equipment/time for doing dowels on compound angles. Maybe they are not the sort of joinery I'd use on an ebony and burr walnut stool, but you'll get your pine or Australian hardwood stool knocked up in a weekend or two. If you can afford the time to do dowels, you can afford the time to do proper mortice and tenon joints!
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1st July 2014, 09:22 AM #6GOLD MEMBER
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1st July 2014, 11:39 AM #7Intermediate Member
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Thanks for that, my dowelling skills do need improving
Cheers
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1st July 2014, 09:03 PM #8
and now for the "science"
The June 2014 issue of Furniture & cabinetmaking (a UK mag) tested a bunch of different 90° rail and style joints to destruction using a hydraulic ram
the wood used was 90 x 19 mm sapele.
the results:
3 pocket screws -- failed at 280 psi
(the author noted that "by their nature pocket-hole screws struggle to join components squarely as the force they generate is typically diagonal to the mating faces of the joint)
two 8 x 40mm dominos -- failed at 400 psi
five 10 x 50 mm dowels -- failed at 660 psi (the joint was constructed using a Dowelmax jig -- currently USD$249 plus shipping)
(my note: the "one dowel per inch of width" rule of thumb gives 4 dowels for the 90mm material width, the author used one more)
mortise and tenon -- failed at 420 psi
(the M&T was 45mm deep and used the "thirds rule" )
Comment
I suspect that the apparent superiority of the dowel joint would decrease somewhat if only 4 dowels had been used, or if the M&T was 60-70mm deep
full article here: http://www.webstorm.ca/furniture_and...ength_test.pdfregards from Alberta, Canada
ian
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2nd July 2014, 12:04 PM #9Intermediate Member
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Thanks, I was going to ask that question about strength, from what I have read they said the pocket hole joint was a very strong joint, the test results would beg to differ.
Interesting thought, if I was to screw the timber together wouldn't that be stronger joint than a dowel joint, yes you would see the screws but if they where like a feature. So you would think that a pocket hole joint would be just as strong. However, it seems that length of the screw is less in the hole part of the timber than the mating part (hope that made sense, without pictures), hence the lack of strength.
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2nd July 2014, 04:33 PM #10
It's very rare that you find furniture that has broken in service due to people loading it with steel rams. It's hard to translate to normal use scenarios.
Over time, I'd expect the lack of face grain to face grain contact in a glued dowel to cause the glue line to break as the wood went through seasonal movement, eventually leading to the dowels becoming loose.
In the case of a bar stool, if you assume that we are talking about the foot rail, then loading it to 280psi without a steel ram would require (assuming 3 inch [foot width] by 3/4 inch [rail width] contact area) someone weighing over 600 pounds, or over 1,200 pounds if you want to factor in the join at the other end of the rail.
As even hospital grade equipment fails under that sort of weight, I don't see it as much of an issue.
Of course, that's assuming either bare feet or sneaker-type footwear, but my imagination fails me at the concept of someone weighing 300 kilos in stiletto heels sitting on a bar stool, as that sort of point loading makes even concrete and granite cry.
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2nd July 2014, 06:18 PM #11
I have seen some dinning chairs constructed with pocket holes. From the very cheap set of dinning chairs to the very expensive ones.
Now with dinning chairs you get people sitting in them for a reasonable period of time. So what's the difference between the two chairs. As far as I can tell one is sold for XX amount and the other is sold for XXXX amount.
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2nd July 2014, 06:47 PM #12
Pocket holes
You can tailor statistics and tests to create any result you desire. Why only three pocket hole screws but five dowels? My experience with pocket holes joinery properly created using a good jig is that they are strong, accurate and quick. Like any method you use them to suit what you are creating and you can make them invisible by planning your work correctly. I have used dowels, mortise and tenon, biscuit and pocket hole joinery. Each in appropriate circumstances and each has been successful in its use. Please don't denigrate a system based on personal prejudices. Simply use common sense, each appropriately and enjoy the results.
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2nd July 2014, 08:57 PM #13
Graeme
in fairness, the author of the article I sourced the above results from, did concede that "... it doesn't take an expert to see the inherent problems with [testing the comparison joints presented] ... even the most inexperienced woodworker should be able to predict some of the results."
also in fairness to the testing regime -- nowhere was it stated that the pocket screw joint's failure at 280 psi represented a weak or poorly performing joint
The author noted that components assembled with pocket screws are typically fastened to another flat surface, such as a face frame fixed to a carcass, so in service the issue of the clamping force being diagonal across the joint essentially becomes a non issue.
there's lots of ways the test could be modified or adjusted, each of which could be expected to produce a different result.
But for me the more interesting and pertinent question is: how strong does a rail to style joint need to be?
I've seen articles where the author raves about the speed and convenience of using biscuits for this type of joint -- the Furniture and Cabinetmaking test had joint failing at 180 psi, but if in service the max force will only be 120 psi, then biscuits would be fine.regards from Alberta, Canada
ian
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2nd July 2014, 10:53 PM #14Retired
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I was asked to fix 4 stools this week. They were 20+ years old. Basic as. On one the screws holding the seat to the frame were loose.... No glue, short nasty screws and that was it. The other joints were tolerance fit round tenons. The glue could have been school-grade "Clag" (knackers glue) from what I could tell.
Banged them all open, took out the screws (drilled out, glued and fill-dowelled them) and put in a few long Kreg screws, reglued it all with Titebond 2 and they would hold up a landing British Harrier Jump-Jet.
Much, much much much better....and these were commercially supplied stools originally. The owner was absolutely thrilled.
I don't question Kreg pocket joinery. A simple test will show a single screw is VERY hard to pull out.
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3rd July 2014, 11:53 AM #15
I own both kreg pocket hole jig and a dowelmax. I just use them where they are applicable.
Although that being said since i have had the dowelmax i have been thinking of a lot of methos that i could use it and avoid using the kreg. i personally just find pocket hole joinery ugly. nothing to do with their strength, im sure they very strong for most applications. I only use the kreg now if i were making something that i knew it would be completely covered.
I just prefer using the dowelmax now days, especially the finish and strength i can get with dowels inside a mitre joint is easy to do and looks gread with a book matched grain.