Hardwood flooring tongue and groove tolerance

[Phillip Mitchell]

Well, for better or for worse, I am planning to make a few thousand lineal feet of 3/4” thick flooring for my brother from 4/4 red oak that he sawed on his woodmizer and kiln dried. I will be doing it “old school” - jointer, planer, bandsaw/table saw, and shaper with power feeder for the actual T&G.

I am ordering some 6mm thick HSS knives + limiters from Whitehill to fit a 125x55 limiter block. The tongue will have small chamfers on both top and bottom of the end to ease insertion. I am also asking them to modify either the tongue thickness or the groove thickness (does it matter which?) so that there is a an appropriate amount of extra space to make install reasonable.

I have been talking with them about what tolerance I want for the groove compared to the tongue thickness. Obviously this does not / should not be dead nuts tight. We are working in mm.

So what is the ideal thickness difference between tongue and groove on typical hardwood flooring so that it will be reasonable to install but also come out as flush as reasonably possible on the top face. 0.2 mm? 0.3 mm too big? I started the conversation at 0.1mm difference which is basically 0.004”, and then thought well, that’s about the difference I aim for when machining “tight” mortise and tenon joinery with a friction fit and glue, so maybe too tight…

The floor will be installed raw, then sanded and finished after install, fwiw.

I need to make a decision on this in the next day or so, so hopefully someone has experience in this to help.

Thanks as always.

[Maurice Mcmurry]

An ambitious undertaking. I can measure some Bruce later this week. I found this on the web but that info is not included (found my glasses). The tongue has a round nose and is tapered on the products I'm familiar with. Amana does not provide that detail either. I don't know how important it is to have the bottom plowed but that feature is present on most flooring too.

Screen Shot 2023-06-26 at 1.25.45 PM.png
FREEBORN - MC-59-040 - CARBIDE FLOORING SET Shaper Cutter

Screen Shot 2023-06-26 at 1.41.26 PM.pngScreen Shot 2023-06-26 at 1.46.45 PM.png

[Phillip Mitchell]

Thanks Maurice. Yeah, curiously, I don’t see that particular dimension called out on the Freeborn drawing either.

Regarding the undertaking, a bit ambitious I suppose, mainly because of the tiny size of my shop and how completely overrun it’s going to be with the milling process. I am also fearing the amount of chips this will create and already trying to put something in place to make that a bit easier. I actually enjoy digging into repetitive work. My brother wants the wood manufactured into flooring regardless and was getting quotes from regional millwork shops that I felt ok about price matching, even if it takes me a week or so to work through the pile.

[Kevin Jenness]

I've done that, about 300 sq ft. Never again, just too inefficient without a molder. I think I left a bit more of a gap, more like .006". Is there something else the material could be used for? I'm guessing you aren't getting paid for this.

[Phillip Mitchell]

I am getting paid. I'm not in a place in my life yet to be able to work that hard for free for a week or 2, even for my dear brother . I already tried talking him out of it, then we got some quotes from regional millwork shops and I told him I was willing to match the median pricing that was coming back and squeeze it in on a much faster timeline. I will be ok from it even though I know I will be way more inefficient than a larger shop with a moulder and SLR.

I'm sure I'll have more to say about it once I get through it, maybe "never again", but I'm looking forward to the challenge and change of pace from the slow tedium of custom furniture, etc. It will be also hopefully be a nice "welcome to the shop" christening for my new/old shaper.

[Warren Lake]

its no big deal, just work, you can work fast and efficient its repetitive work not detailed custom work. The moulder people have a higher shop rate than you to pay for the machine.

[Rod Sheridan]

I made ash flooring recently, make sure your knives are for flooring and have the nail groove.

The cutters will take care of the clearances themselves.

To ensure consistent width, use an outboard fence and feeder on the shaper…..Regards, Rod

[Patrick Kane]

Im with Warren, it's just work. I did enough shiplap out of 6/4 hemlock for my shed ceiling and flooring. My takeaway after processing the lumber was, "i will buy it next time". I remember the price difference was maybe $400+/-, and it was a solid 12+ hours of work for me to plane, saw, and shape the boards. However, you are making money off it, so if it makes sense from an hourly rate, then it's a good decision for both parties. In my particular case, i remember constantly looking at the clock and thinking, "im costing myself money/time".

Definitely dont underestimate the chip load. My 35 gallon cyclone bin filled up QUICK. Finally, i dont envy you simply for the horrid smell of cut red oak. I dont know if its just me, but i hate the smell of the stuff.

Do you have any scrap flooring laying around you can measure the tenon and dado? If not, i definitely have some hard maple extras laying around my shop i can measure.

[Albert Lee]

I have installed 400sqft of blonde oak 2 years ago and roughly 250 sqft of purple heart flooring just recently.

Regardless how long you leave the flooring to aclimatise to its environment, it will always move. obviously the longer you aclimatise the less movement.

[Phillip Mitchell]

I made ash flooring recently, make sure your knives are for flooring and have the nail groove.

The cutters will take care of the clearances themselves.

To ensure consistent width, use an outboard fence and feeder on the shaper…..Regards, Rod

The nail groove is not something I had thought to specify in the T&G knives. Thanks for bringing that up. I am customizing a few sets of knives for this specific task. Their standard T&G profiles are not intended for flooring but Whitehill is willing to make to whatever specs I supply.

Do you have any dimensions or figures for what size the nail groove should be? Should it be placed in the inside corner of the top side of the tongue - meaning where the tongue turns the corner onto the topmost shoulder on the tongue side? I have installed enough flooring in the past with a pneumatic nailer to see how this could be a big deal during install in certain dense woods, nails not fully setting, etc.

[Richard Coers]

Also on flooring, the bottom shoulder of the groove does not touch the shoulder on the tongue side. This makes sure the top shoulder is tighter.

[Phillip Mitchell]

Im with Warren, it's just work. I did enough shiplap out of 6/4 hemlock for my shed ceiling and flooring. My takeaway after processing the lumber was, "i will buy it next time". I remember the price difference was maybe $400+/-, and it was a solid 12+ hours of work for me to plane, saw, and shape the boards. However, you are making money off it, so if it makes sense from an hourly rate, then it's a good decision for both parties. In my particular case, i remember constantly looking at the clock and thinking, "im costing myself money/time".

Definitely dont underestimate the chip load. My 35 gallon cyclone bin filled up QUICK. Finally, i dont envy you simply for the horrid smell of cut red oak. I dont know if its just me, but i hate the smell of the stuff.

Do you have any scrap flooring laying around you can measure the tenon and dado? If not, i definitely have some hard maple extras laying around my shop i can measure.

Thanks Warren and Patrick. Work is work and I will be paid fairly for it so all should be well.

Somehow I do not have any scrap flooring laying around my shop to reference or measure. I did some more research in the cobwebs of Woodweb and saw a flooring “standard” figure of 0.010-0.015” tolerance between tongue and groove thickness, so I think I better amend to 0.3 mm over in groove thickness.

Attached below is what I have come up with so far for a knife grind, with the only blank being the optimal dimensions for a nail groove. Anybody care to critique?

[Joe Calhoon]

Phillip,
0.3 mm or a little more is correct. First time we ran flooring on the moulder we got it too tight and a red faced contractor showed up the next day with the 2000 sq ft load and we had to re run everything through the shaper to enlarge the groove.

I Like Whitehill blocks for profiles but anything profile - counter profile is fussy to set up. If you use them don’t do stacked profiles like the picture they are even harder to dial in. The correct knives will make the job easier. Early on I did a couple floors just using T&G cutters on the shaper. It worked but a bear to install.
ACEAA09C-49CC-4D1A-9D76-7131B2AEDEE3.jpg

[Phillip Mitchell]

Phillip,
0.3 mm or a little more is correct. First time we ran flooring on the moulder we got it too tight and a red faced contractor showed up the next day with the 2000 sq ft load and we had to re run everything through the shaper to enlarge the groove.

I Like Whitehill blocks for profiles but anything profile - counter profile is fussy to set up. If you use them don’t do stacked profiles like the picture they are even harder to dial in. The correct knives will make the job easier. Early on I did a couple floors just using T&G cutters on the shaper. It worked but a bear to install.
ACEAA09C-49CC-4D1A-9D76-7131B2AEDEE3.jpg

Thanks Joe. What do you recommended or would you consider the right knives for the job?

I was planning on HSS stacked T&G cutters with my own customized dimensions for the proper fit.

What are your experiences / thoughts about a nail groove in the tongue?

I do already have 2 different sets / sizes of nice, insert carbide adjustable groovers and one of them is reversible for smaller tenoning (tongue cut.) That would net me a very simple T&G with no tongue chamfers, offset lower shoulder, or nail groove, but I guess I could do it with what’s on hand in carbide.

[Warren Lake]

never had a nail groove. I used a heavy crown senco 1 1/2 - 2" stapler. Told it had been used to put a brazillion rosewood floor down past. They said it had the attachment that you strike with a hammer. It was an expensive ad on that I didnt think I wanted. I eye ball the angle. No safety on the gun its got a lot of kick to it. Its a weapon.