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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 796 views 0 times favorited 10 replies Add to Favorites Watch
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MrRon

3926 posts in 2706 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

3981 posts in 2434 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.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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MrRon

3926 posts in 2706 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 3207 days


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

+1 what crank49 said.

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MrRon

3926 posts in 2706 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 3207 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

115202 posts in 3040 days


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

another vote for washers.

-- http://artisticwoodstudio.com Custom furniture

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crank49

3981 posts in 2434 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.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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ajosephg

1878 posts in 3024 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

880 posts in 1900 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

3926 posts in 2706 days


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

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

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