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Washer or no washer, that is the question

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Forum topic by MrRon posted 11-24-2011 07:05 PM 813 views 0 times favorited 10 replies Add to Favorites Watch
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MrRon

4064 posts in 2850 days


11-24-2011 07:05 PM

I am assembling 3/4” MDO plywood panels, surface to edge. One panel will be drilled for cross barrel nuts. The other panel will be attached with 1/4-20 machine screws. The latter panel will be counterbored so the screw head will be flush with the surface. My question is: Do I need a flat washer under the head? The answer will determine the diameter of the counterbore. I don’t want to risk crushing the wood fibers, although MDO is pretty tough stuff.


10 replies so far

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crank49

4001 posts in 2578 days


#1 posted 11-24-2011 08:03 PM

I would use washers to prevent the crushing that would occur from the rotation of the bold head against the wood in the counterbore.

Having said that, if you want to keep the counterbore size to a minimum, use SAE washers. They are smaller, thiner and tighter tolerence than US standard.

I don’t know what you are building and therefore don’t know what structural strength you need, but an alternate to barrel nuts that I have used is a hardwood cross dowel and a lag bolt. I normally use a size larger lag bolt than I would a machine threaded bolt. Makes a very strong joint.

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MrRon

4064 posts in 2850 days


#2 posted 11-24-2011 08:14 PM

I am constructing a CNC router. The joints must be rigid.

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tenontim

2131 posts in 3351 days


#3 posted 11-24-2011 08:17 PM

+1 what crank49 said.

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MrRon

4064 posts in 2850 days


#4 posted 11-24-2011 09:45 PM

Thanks all. Would that also be needed on the wood surface without the counterbore? If I were bolting together two pieces of wood with a bolt and nut, would I need a flat washer under the bolt head and the nut, or just on one of them? I think in such a case, a standard flat washer would be better due to it’s larger surface area for distributing the load. I’ve gone the 2 washer route in the past, but don’t know if it was overkill.

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tenontim

2131 posts in 3351 days


#5 posted 11-24-2011 11:51 PM

I always use washers on both ends of a bolt. Maybe that’s the mechanic in me.

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a1Jim

115690 posts in 3184 days


#6 posted 11-25-2011 12:03 AM

another vote for washers.

-- http://artisticwoodstudio.com Custom furniture

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crank49

4001 posts in 2578 days


#7 posted 11-25-2011 05:20 PM

I always use washers when ever I can on wood joints.
I used fender washers on the draw bolts for my workbench legs.

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ajosephg

1880 posts in 3168 days


#8 posted 11-25-2011 05:44 PM

Another vote for using washers on both ends of a bolt. Also should use a lock washer on one end or the other.

-- Joe

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muleskinner

888 posts in 2043 days


#9 posted 11-25-2011 05:51 PM

I’d always use washers where it doesn’t interfere with the aesthetics. Not only to give a larger load area but to prevent galling the wood fiber.

-- Visualize whirled peas

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MrRon

4064 posts in 2850 days


#10 posted 11-25-2011 06:45 PM

Thanks for the great information. I’m also using lock nuts.

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