When Is 1/4" Not 1/4"? - Router Forums
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post #1 of 46 (permalink) Old 02-04-2016, 04:14 PM Thread Starter
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Default When Is 1/4" Not 1/4"?

Please explain why 1/4" plywood does not fit into a dado cut with a 1/4" router bit. I had to move the fence and rout twice to get the bottom to fit into the dado. Obviously the plywood is to thick, or the 1/4" dado is too narrow. The difference is too small for me to see. Which is more likely?

It's time consuming to have to cut the dado three times (shallow cut, full-depth cut, widening cut). The plywood came from Lowe's. There's nothing special about it.
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post #2 of 46 (permalink) Old 02-04-2016, 04:25 PM
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I think it has to do with different tolerances between sheet goods manufacturers and the finishing they go through? Sanded vs unsanded. Just a guess..

A set of calipers or a micrometre would allow you to determine the exact thickness and choose an appropriate size but I've only ever made multiple passes. More work but a custom fit each time. Good luck!

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post #3 of 46 (permalink) Old 02-04-2016, 04:42 PM
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What kind of plywood is it, Mike?
Sanded one side Fir sheathing?
Not being critical, just looking for more info. I have no problem using sanded sheathing for shop stuff myself.
Can't get decent Hardwood plywood up here on the Sunshine Coast, so if it isn't critical to me...
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post #4 of 46 (permalink) Old 02-04-2016, 05:02 PM Thread Starter
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What kind of plywood is it, Mike?
Sanded one side Fir sheathing?
Not being critical, just looking for more info. I have no problem using sanded sheathing for shop stuff myself.
Can't get decent Hardwood plywood up here on the Sunshine Coast, so if it isn't critical to me...
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post #5 of 46 (permalink) Old 02-04-2016, 05:30 PM
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Quote:
Originally Posted by patlaw View Post
Please explain why 1/4" plywood does not fit into a dado cut with a 1/4" router bit. I had to move the fence and rout twice to get the bottom to fit into the dado. Obviously the plywood is to thick, or the 1/4" dado is too narrow. The difference is too small for me to see. Which is more likely?

It's time consuming to have to cut the dado three times (shallow cut, full-depth cut, widening cut). The plywood came from Lowe's. There's nothing special about it.
WTB one (bit or ply) is metric and the other (ply or bit) is Imperial...
save work...
cut the dado on the TS...

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post #6 of 46 (permalink) Old 02-04-2016, 05:53 PM
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I'm a little confused, you are saying the dado you cut with a 1/4" bit is too small for 1/4" big box plywood? That is completely backwards from what I've seen. Usually the plywood less than 1/4" thick and the dadoes are loose. maybe you had 3/8" which is about 1/16" over 1/4".

Calipers would be a good idea anyway.
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post #7 of 46 (permalink) Old 02-04-2016, 06:20 PM
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Calipers will tell the tail, but in the link Mike posted the spec sez the 1/4" ply 'Actual Product Thickness' is 0.47" (just over 15/32).
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post #8 of 46 (permalink) Old 02-04-2016, 06:25 PM
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Quote:
Originally Posted by Ratbob View Post
Calipers will tell the tail, but in the link Mike posted the spec sez the 1/4" ply 'Actual Product Thickness' is 0.47" (just over 15/32).
I saw that too, and thinking closer to 1/2". They should have said "At least /4" thick"

Herb

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post #9 of 46 (permalink) Old 02-04-2016, 06:31 PM
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I guess great minds think a like Herb, not sure how I got included in that though. I guess even a broken watch is right twice a day.
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post #10 of 46 (permalink) Old 02-04-2016, 07:03 PM
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I saw that too, and thinking closer to 1/2". They should have said "At least /4" thick"

Herb
Sounds like little more than an advertising error. They meant 1/2" it seems.
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