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Help with frame and panel calculations, please

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Forum topic by 1tacoshort posted 02-27-2019 03:22 AM 418 views 0 times favorited 9 replies Add to Favorites Watch
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1tacoshort

38 posts in 1208 days


02-27-2019 03:22 AM

Hi all,

I’ve been working on this arts and crafts project for forever and I’m coming in to the final stages with some questions. I need to plane dados in a number of rails and stiles so that they may receive panels. The exposed portion of the QSRO panels are roughly 6.5 inches across so, if I’ve done my math correctly, we’re talking 1/64 inch shrinkage or expansion in width (1/32 per 12” perpendicular to the rings—which is the width of QSRO) and negligible wood movement in length. This makes 1/128 on a side but, really, I question my ability to cut things to a greater precision than, say, 1/32. This is a wet winter so I imagine that the wood is at its maximum size right now (though, I’ll still leave a scootch of room just because). I figure the dado depth to be 3/16”.

If I’m right about all of this, I’m thinking I’d be safe if I ripped my panels to be 1/16 shy of the 6.5 (visible) + 3/8 (dado depth x 2) or 6 13/16 wide.

Is this about right or am I missing something, here? After all the time, effort, and money I’ve put into this project, I’d hate to honk it up at this late stage.

Thanks!

-- Wade


9 replies so far

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TungOil

1169 posts in 824 days


#1 posted 02-27-2019 04:14 AM

You are working way to close. It’s winter so the wood panel is as small as it will be all year, so allow for some expansion. Even then I like 1/8”-3/16” clearance on each side so I have room for space balls. I like 1/2” deep grooves to accept the panel. That gives you a decent length stub tenon on the ends of the rails for strength as well.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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therealSteveN

2362 posts in 903 days


#2 posted 02-27-2019 04:22 AM

^^^^ What he said. Trying to guess absolute wood movement is going to leave you cracked and split more often than loose and rattle prone. Space balls are the deal for any solid wood panels, and aren’t wrong on a plywood panel, when it comes to rattle control.

-- Think safe, be safe

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Rich

4263 posts in 918 days


#3 posted 02-27-2019 04:54 AM

Those are grooves, not dadoes. The standard is 7/16” deep. Cut your panels for a 1/4” insertion depth (1/2” over the opening in the frame) and use space balls. They are 1/4” dia and will fill that left over 3/16” space perfectly since they are designed to work in compression.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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1tacoshort

38 posts in 1208 days


#4 posted 02-27-2019 05:03 AM

Thanks so much for the help!

So, I was curious: how long are space balls expected to last? I have delusions of grandeur on this project and I was hoping to pass it down to my daughter.

Ah, right—dados are cross-grain. Sorry.

So wood expands when it gets dry? Huh!

I really appreciate all of y’all’s help! Thanks!

-- Wade

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AlaskaGuy

5193 posts in 2638 days


#5 posted 02-27-2019 05:10 AM

What TungOil laid out for you is perfect in my opinion. When I make doors I use style and rail shaper cutters. They cut 1/2 in deep groves and stub tenon. I’ve always left the panel clearance at 1/8 inch on each side, top and bottom. 3/16 would be fine too and would give you added safety if you live with wide humidity changes.

Don’t forget to post picture when you ” got er done ’’

-- Alaskan's for Global warming!

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1tacoshort

38 posts in 1208 days


#6 posted 02-27-2019 06:23 AM

Absolutely will, AlaskaGuy. I’ve been working really hard on this project (that was really more than I could handle—I’ve learned a lot on this) and I’m anxious to get it to a state where I can show it off.

-- Wade

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TungOil

1169 posts in 824 days


#7 posted 02-28-2019 02:24 AM


So, I was curious: how long are space balls expected to last? I have delusions of grandeur on this project and I was hoping to pass it down to my daughter.

- 1tacoshort

They will outlast us all…

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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1tacoshort

38 posts in 1208 days


#8 posted 02-28-2019 03:52 PM

> They will outlast us all…

Nice!

-- Wade

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Manitario

2747 posts in 3212 days


#9 posted 02-28-2019 05:29 PM

This is something that you don’t want to guess at; there are many great online calculators for estimating wood expansion/contraction, eg. http://www.woodweb.com/cgi-bin/calculators/calc.pl

The main factor to consider is how the moisture content of your wood will change seasonally. I live in Ontario; hot summers, cold winters. The moisture content of the wood changes from a low of about 4% in the winter to a high of about 9% in the summer. For me, QSRO will fluctuate at least 3/32 per 12” yearly. You’d also want to leave a tiny bit of “extra” room, so again, I’d be looking at leaving at least 1/16 on each side of a 12” panel.

There are many great stories on this site of cracked panels from those of us that have not calculated wood expansion properly…myself included.

-- Sometimes the creative process requires foul language. -- Charles Neil

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