5/4 and 4/4?

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Forum topic by TuckerFan posted 08-08-2012 05:07 PM 1291 views 0 times favorited 13 replies Add to Favorites Watch
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24 posts in 2301 days

08-08-2012 05:07 PM

Another dumb question from me…as always. In starting a Adirondack chair using mahogany, I saw in the cutting plans the terms “5/4” and “4/4”. The 5/4 was used as a heading for a few cuts that were all 3/4” thick, while the 4/4 was the heading for all of the cuts of 3/4” thickness. I understand the term nominal, but this has me stumped.

-- I...I..have a...a...wood problem

13 replies so far

View PurpLev's profile


8536 posts in 3672 days

#1 posted 08-08-2012 05:09 PM

are all cut parts straight and square?

if there are any curved parts, than having a thicker starting point makes sense.

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

View chrisstef's profile (online now)


17423 posts in 3029 days

#2 posted 08-08-2012 05:10 PM

4/4 is 1”, 5/4 is an 1 1/4”, so on and so forth. Hope that clears it up for ya.

-- Its not a crack, its a casting imperfection.

View MonteCristo's profile


2099 posts in 2211 days

#3 posted 08-08-2012 05:14 PM

Could be an error. Happens way too often in plans !

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

View jmos's profile


839 posts in 2393 days

#4 posted 08-08-2012 05:19 PM

Any chance some of the 5/4 parts were curved? Might need the extra thickness to get the curve out of it if cut on a band saw rather than bent.

-- John

View TuckerFan's profile


24 posts in 2301 days

#5 posted 08-08-2012 05:23 PM

OK. These replies help…kinda. So should I assume that all of the 5/4’s are to be planed to and even 1”? That’s a huge amount to plane, isn’t it? The curves are only on the arms of the chair, but these curves can be done with a jig saw or band saw, true?

-- I...I..have a...a...wood problem

View Doss's profile


779 posts in 2287 days

#6 posted 08-08-2012 05:30 PM

No no. What some people are saying is if the piece is to be 3/4 and it is curved, they probably start with a 5/4 piece to have enough room to achieve the curve.

Usually, when using 4/4 or 5/4 lumber or anything denoted like this, it is not just nominal. It may be actual.

-- "Well, at least we can still use it as firewood... maybe." - Doss

View Sawdust4Blood's profile


405 posts in 3045 days

#7 posted 08-08-2012 05:30 PM

5/4 is nominally 1.25” but that is not guaranteed to be straight, flat, or uniform thickness. By the time you joint one side flat and then plane the opposite surface to a uniform thickness, you’ll probably already be a lot closer to a true 1” thickness that you think. Shorter, narrower boards can be dimensioned with less overall loss but long, wide boards may require a substantial amount of material removal before you get them straight, flat, and true.

-- Greg, Severn MD

View PurpLev's profile


8536 posts in 3672 days

#8 posted 08-08-2012 05:30 PM

you should follow the cutting plan. if the parts are to be 3/4” then you plane them to be 3/4”. 5/4 is usually 1 1/8” thick – so not really that much to plane to get it to 1” but yes, quite a bit to bring it down to 3/4” I am only assuming the 5/4 material is for the curved arm rests which – yes you cut the curve on the bandsaw, but you still need thicker boards to be able to accomplish that curved part.

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

View Enoelf's profile


192 posts in 2286 days

#9 posted 08-08-2012 05:32 PM

Not sure if it helps or not, but Chrisstef is right on the money. Those sizes are the “new” standard for talking about lumber sizes. 5/4 is 1 1/4”, I have even seen stuff stating 8/4 which would be 2”.
Probably something about taking up less characters, and reducing confusion…..
Confused yet?

-- Central Ohio, Still got 9 and 15/16 fingers!

View TuckerFan's profile


24 posts in 2301 days

#10 posted 08-08-2012 05:36 PM

Thanks, one and all. Heck, I might as well just start…this ain’t no brain surgery. I just need to do it! Many thanks, again. (I truly envy your skills and knowledge.)

-- I...I..have a...a...wood problem

View Sawdust4Blood's profile


405 posts in 3045 days

#11 posted 08-08-2012 05:48 PM

I think you’ll find that the notation normally tells you something about the degree to which a piece of lumber has already been milled. If I see a piece listed as 4/4, I expect to find a piece of lumber that is at most surfaced two sides (S2S) one edge straight. I anticipate that I will have to joint and plane it to true dimensional lumber and it should yield a piece that is .75” thick (if straight). One the other hand if I see a piece listed as a 1×4, I assume that piece to already be fully dimensioned (S4S) to a true size of .75” by 3.5”.

Likewise, 8/4 should be somewhat close to 2” rough cut but will require milling before use. Meanwhile a 2×4 is already fully dimensioned to a true size of 1.5” by 3.5”

-- Greg, Severn MD

View HerbC's profile


1763 posts in 2882 days

#12 posted 08-08-2012 06:21 PM

First of all the 4/4 and 5/4 (and all the other #/4) notations are nothing new. They are typically used to specify the size of rough lumber, especially hardwoods but also used in softwoods.

Second, the curves in a typical Adirondak chair arm are not in the “plane” of the thickness of the lumber but rather in the wide (width x length) surface of the lumber, therefore the specification of 5/4 lumber for those parts cannot have anything to do with having enough wood thickness to cut the curves (that is, the curves are cut with the board laying flat rather than cutting into the edge of the board.

My guess is the plan calls for 5/4 on the arms and you should plane it to a full 1” finish thickness and that the reason for the spec is (1) cosmetic, the thicker arm looks better than a thinner one or (2) the designer just felt it would be “better” if the part was thicker.

Will be some nice chairs. Mahogany is pretty and nice to work with although a bit expensive for outside pieces on my budget.

Good Luck!

Be Careful!


-- Herb, Florida - Here's why I close most messages with "Be Careful!"

View SteviePete's profile


226 posts in 3326 days

#13 posted 08-08-2012 06:28 PM

Hang on there, Newt. If the material is true mahogony – Honduras mahogony I would save it for fine indoor furniture. (Not so much if Luan-philippine mahogony, or Khaya – african mahogony) I use cypress with better results than with cedars or hardwoods-black locust. Ages to silver, less moss and lichen too.

I buy some odd lots of lumber. I do not trust what people tell me they have. Always more BF, # of boards, length width and species in mixed lots. I measure length, width and thickness as well as identify species. Check the hardwoods grading manual for the full story- google it. I stack the boards I buy and measure the pile for the board feet. I take mostly full piles (they negotiate more readily when they know its gone.) The Book says 4/4=3/4” planed and dry. 5/4=1 1/8” planed and dry. 8/4= 1 3/4” planed and dry. They will argue with you over less than 3/4”—costs just as much to saw as full 1”. I give no slack on thickness with private parties or picked over piles at commercial establishments—I just reduce the scale to cover the shortage. Reputable hardwood sales outfits will give a measure closer to the rules in the book. I do take boards with defects but expect no charge—a grade with a defect usually drops it 1-3 grades—almost a give away price. This is also a good way to make an enemy. I just keep saying that we both want the transaction to be fair. All the hardwood rules have many exceptions, interpretations, etc. and they always know more technically. Only rule I follow is “I’m the only one here with a checkbook, I will agree to a price.” Doesn’t hurt to walk away. p.s Be very careful with lumber with insect damage, rot, or pith/young wood in the boards.

p.p.s. This is much harder than rocket surgery. Especially when you get a know-it-all. Good luck buy lots of local lumber. It keeps a neighbor off the dole. If you haven’t had enough yet I have some facinating Butternut stories.

Truely Full of Myself,
Steve Johnsen

-- Steve, 'Sconie Great White North

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