Easy measurement conversions?

  • Advertise with us

« back to Designing Woodworking Projects forum

Forum topic by rhybeka posted 05-11-2013 10:36 PM 1100 views 0 times favorited 10 replies Add to Favorites Watch
View rhybeka's profile


3904 posts in 3087 days

05-11-2013 10:36 PM

So I’m probably going to show my newbieness here but I’d rather be safe than sorry. I’m working from a set of plans for Modular Tool bins (seems to be in every The Complete Small Shop magazine and at least one Woodsmith book I own). The dimensions call for 3/4 and 1/2 in ply. Since this is going to be residing in my garage, I went and picked up a sheet of 15/32 and 23/32 ply. Since this is mainly to do with thickness of the ply, I’m assuming the only place I need to make accommodations is where I’m cutting my dadoes for the shelves, right? Thanks all :)


-- Beka/Becky - aspiring jill of all trades, still learning to not read the directions.

10 replies so far

View Loren's profile


10262 posts in 3613 days

#1 posted 05-11-2013 10:42 PM

Undersized plywood is common. 23/32” is 3/4”
in common parlance among cabinet makers. All sheet
materials used in cabinetmaking have variances.

Anyway, you can buy “undersized” plywood router bit
sets from places like MCLS for not much money –
I don’t use mine much because I don’t do a lot
of dado joinery, but when I need them they are
just the ticket.

View Bogeyguy's profile


548 posts in 2033 days

#2 posted 05-11-2013 10:52 PM

You got it Becky. Don’t assume dimensional lumber is actually what it is said to be. Measure and adjust as needed.

-- Art, Pittsburgh.

View rhybeka's profile


3904 posts in 3087 days

#3 posted 05-11-2013 11:19 PM

Gracias :) off to go measure and get my pieces cut hopefully before the sun is completely down! @Loren – Thanks for the heads up – I’m still on the fence about how to cut the dadoes. I have a wobble dado blade that I have to go pick up from woodcraft (just had it sharpened since I’m sure my dad never did), or I do have a 1/4 in straight bit for my router and a straight edge.

-- Beka/Becky - aspiring jill of all trades, still learning to not read the directions.

View rrww's profile


263 posts in 2079 days

#4 posted 05-12-2013 06:14 AM

I would use the router. I never had good luck with the wobbler.

View MrRon's profile


4717 posts in 3209 days

#5 posted 05-13-2013 06:19 PM

The undersize plywood router bits work OK, but plywood is never uniform in thickness. It is usually 1/32” undersize from the nominal size, but can vary from different suppliers. I like the dado blade best, as I can dial it in for a perfect fit with the plywood I’m using. If using a router bit, best to go with one that is 1/8” or more under the size of plywood used and sneak up on the width of the dado. For example, use a 3/8” router bit for a 1/2” dado. Always use a scrap piece to dial in your dado width. A dial caliper is a real convenient tool for measuring plywood thickness. Don’t assume a 1/2” panel is always 15/32” or a 3/4” panel is 23/32”.

View junebug's profile


101 posts in 2370 days

#6 posted 05-13-2013 06:51 PM

i would use the router bit. make yourself an exact width dado jig first. I use mine all the time

View PurpLev's profile


8534 posts in 3614 days

#7 posted 05-13-2013 06:54 PM

here’s a tip – measurements on plans almost never end up on the actual product even if you do have 3/4” and 1/2” material. measure your part (thickness) and cut dadoes accordingly. if you don’t have undersized router bits you can use a smaller router bit and do several passes with it (as in 2 passes with a 1/4” bit to make a 1/2” dadoe – but overlap those passes to get you under 1/2” per se).

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Nicky's profile


695 posts in 4057 days

#8 posted 05-13-2013 07:03 PM

The wobble dado would not be my first choice for cutting dado’s. Aside from not creating a flat bottom and a higher level of tear-out, most of the ply that I buy is not flat, and I find it difficult to get good results on the table saw. If you are using a high quality plywood (not from the big box stores, disregard the comment.)

You own a router, and have a strait bit, maybe time to expand its capabilities. Take a look at this video . One of the better videos with an in depth explanation.

I built a similar jig many years ago, and have used it countless times.

-- Nicky

View SCOTSMAN's profile


5849 posts in 3551 days

#9 posted 05-13-2013 07:20 PM

I have never used a wobble head cutter and have always thought them to be inferior and slightly dangerous technology.However obviously plentyof people use them so they must be ok they are with Dado blades forbidden by health regulations in Europe as a guard cannot be used with them.Still I would definately advocate the router myself. as at least you get a flat bottom Wow did I say that naughty naughty Alistair lol

-- excuse my typing as I have a form of parkinsons disease

View rhybeka's profile


3904 posts in 3087 days

#10 posted 05-14-2013 12:29 PM

Thanks guys! :) Nicky – I’ve been poking around for a jig like that – thanks a bunch!

Lol @Scotsman – I’ve never used one – this one came from my dad with the table saw and I figured it was better than nothing. I trust the router idea a bit more than the wobble dado but I’ve never used either for dadoes. I have a 3/4 in straight bit and a 1/4 in straight bit which is what I believe I will be using and taking the weo passes as suggested by PurpleLev. I was looking at building a bigger router base or a jig to help me balance the weight for the rabbets on the ends of the top and bottom panels, or maybe just using the TS for those. I’ve got a bit of scrap so I can test it out before trying it on the real thing.

-- Beka/Becky - aspiring jill of all trades, still learning to not read the directions.

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics