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Since when did plywood go metric?

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Forum topic by MrRon posted 03-15-2016 03:51 PM 969 views 0 times favorited 16 replies Add to Favorites Watch
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MrRon

4120 posts in 2905 days


03-15-2016 03:51 PM

I was building a closet organizer and measured the thickness of 3/4” (top choice from Lowes) plywood with a micrometer. It measured .710”. 18 mm =.7087”. This is totally unacceptable for 3/4” plywood. If you use an undersize router bit to cut dados, the dado is still too large as the bit is only 1/32” (.032) undersize. The thickness of the plywood is .040” less. This has caused problems when designing projects. When you assume the plywood is 3/4” (.750) thick and you make your cut, you end up with a dimension that is not what you wanted. I am fortunate that I can layout my work using Autocad. I can draw everything taking into account the actual thickness of the material.


16 replies so far

View Pezking7p's profile

Pezking7p

3181 posts in 1313 days


#1 posted 03-15-2016 04:02 PM

Just the way of plywood I guess. I’ve gotten used to it. It’s one of the reasons I cut plywood dados with a dado stack instead of a router. An exact size dado jig would be even better.

-- -Dan

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jmartel

7135 posts in 1812 days


#2 posted 03-15-2016 04:06 PM

It hasn’t been a full 3/4” for many years now. Use an exact width dado jig as was said.

-- The quality of one's woodworking is directly related to the amount of flannel worn.

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MrRon

4120 posts in 2905 days


#3 posted 03-15-2016 04:38 PM



It hasn t been a full 3/4” for many years now. Use an exact width dado jig as was said.

- jmartel

I realize that, but it was always 1/32” less in thickness. Router bit makers made bits that were 1/32” less to match the plywood. This “metric” plywood is still smaller yet. The only way to cut dados is with a dado stack set or a smaller router bit and a jig.

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WhoMe

1547 posts in 2905 days


#4 posted 03-15-2016 04:43 PM

Ahh, more perils of being one of only 2 countries still not on the metric measuring system.

Personally, I think it is the manufacturers trying to squeeze out as much wood without actually going down a physical size in plywood thickness

-- I'm not clumsy.. It's just the floor hates me, the tables and chairs are bullies, the wall gets in the way AAANNNDDD table saws BITE my fingers!!!.. - Mike -

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Ger21

1071 posts in 2793 days


#5 posted 03-15-2016 04:54 PM

If you bought enough sheets, I think that you’d find that the thickness can vary by more than .01”

I’ve done jobs with 100+ sheets, and found that dados that fit with the first 40 sheets were much too small on the next bundle.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

View LiveEdge's profile

LiveEdge

517 posts in 1282 days


#6 posted 03-15-2016 04:54 PM

Was it birch plywood? That traditionally comes in mm because it comes from Northern European countries.

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sepeck

331 posts in 1803 days


#7 posted 03-15-2016 04:59 PM

Random from memory the Wood Whisperer had an exact width dado jig.
http://www.thewoodwhisperer.com/videos/exact-width-dado-jig/

I have seen ads for router bits sized for these, but yet another investment and I don’t have any.

-- -Steven Peck, http://www.blkmtn.org

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b2rtch

4830 posts in 2710 days


#8 posted 03-15-2016 05:07 PM

I have a set of undersized router bits from Freud just for this reason

-- Bert

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hotbyte

942 posts in 2638 days


#9 posted 03-15-2016 07:09 PM

I think MrRon is saying he now needs an undersized, undersized bit :(


I have a set of undersized router bits from Freud just for this reason

- b2rtch


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bbasiaga

901 posts in 1657 days


#10 posted 03-15-2016 08:40 PM


I think MrRon is saying he now needs an undersized, undersized bit :(

I have a set of undersized router bits from Freud just for this reason

- b2rtch

- hotbyte

Or an oversized 18mm bit…. :)

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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SignWave

383 posts in 2697 days


#11 posted 03-15-2016 09:07 PM

It’s been a long time since I’ve seen plywood marked as 3/4”. It always says 23/32. That would be .71875 which is pretty darn close to what you measured. Was it marked as 18mm?

-- Barry, http://BarrysWorkshop.com/

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MrRon

4120 posts in 2905 days


#12 posted 03-17-2016 04:04 PM



It s been a long time since I ve seen plywood marked as 3/4”. It always says 23/32. That would be .71875 which is pretty darn close to what you measured. Was it marked as 18mm?

- SignWave

The plywood came from Lowes and labeled “Top choice”. It was stamped on the edge stating it was .710” thick. It has 11 plies, but the face layer is the thinnest I have ever seen on plywood.

View marshallLaw's profile

marshallLaw

10 posts in 462 days


#13 posted 03-18-2016 06:24 AM

MrRon, you answered your own question – the reason you see a difference is your buying source. The big box stores are buying bulk, lower quality plywood.
If you check regular, honest to god lumber yards you will find better quality 3/4” plywood measuring in at 23/32”. They are known for under selling which causes grief for customers coming in wanting us to price match them I gently inform them that we can ‘t price match because our quality is better.

View tomsteve's profile

tomsteve

506 posts in 881 days


#14 posted 03-19-2016 11:55 AM

yer shopping for plywood at lowes and expecting cabinet grade quality maybe?
it is “top choice”..... for lowes.

ive been workin on afew projects with plywood from menards. not needing super high quality 13 ply for the projects, so menards ply will work.
i found the thickness in one sheet varied 1/32”.

View Logan Windram's profile

Logan Windram

325 posts in 2124 days


#15 posted 03-19-2016 01:41 PM

Buying stock from lowes was the biggest problem.

showing 1 through 15 of 16 replies

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