Easy measurement conversions?

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Forum topic by rhybeka posted 478 days ago 690 views 0 times favorited 10 replies Add to Favorites Watch
View rhybeka's profile


261 posts in 1758 days

478 days ago

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 :)


-- aspiring jill of all trades

10 replies so far

View Loren's profile


7464 posts in 2285 days

#1 posted 478 days ago

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


467 posts in 705 days

#2 posted 478 days ago

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


261 posts in 1758 days

#3 posted 478 days ago

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.

-- aspiring jill of all trades

View rrww's profile


263 posts in 750 days

#4 posted 478 days ago

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

View MrRon's profile


2809 posts in 1880 days

#5 posted 476 days ago

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


82 posts in 1041 days

#6 posted 476 days ago

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

View PurpLev's profile


8476 posts in 2285 days

#7 posted 476 days ago

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


636 posts in 2729 days

#8 posted 476 days ago

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


5352 posts in 2222 days

#9 posted 476 days ago

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


261 posts in 1758 days

#10 posted 475 days ago

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.

-- aspiring jill of all trades

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