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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 848 views 0 times favorited 16 replies Add to Favorites Watch
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MrRon

3926 posts in 2705 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

3097 posts in 1113 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

6565 posts in 1612 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

3926 posts in 2705 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.

View WhoMe's profile

WhoMe

1464 posts in 2705 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 -

View Ger21's profile

Ger21

1047 posts in 2593 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

486 posts in 1082 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.

View sepeck's profile

sepeck

314 posts in 1603 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

4822 posts in 2510 days


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

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

-- Bert

View hotbyte's profile

hotbyte

841 posts in 2437 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


View bbasiaga's profile

bbasiaga

754 posts in 1457 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.

View SignWave's profile

SignWave

318 posts in 2497 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

3926 posts in 2705 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

8 posts in 262 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

393 posts in 681 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

303 posts in 1924 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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