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.

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FREEBORN - MC-59-040 - CARBIDE FLOORING SET Shaper Cutter (https://ballewsaw.com/freeborn-mc-59-040-carbide-flooring-set.html?gclid=Cj0KCQjw7uSkBhDGARIsAMCZNJvPNkPQJHZ fHgdBuuuV0C0djQE2uFhlzpArRyyh-g-e59DaiXPxoD0aAkh6EALw_wcB)

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[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 :D . 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.
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[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.
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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.

[Thomas McCurnin]

The T&G joint isn't akin to a mortise and tenon, which should be sort of snug, the T&G is only to allow seasonal movement and hide gaps, there is no structural benefit of having a super tight T&G, and indeed, when dealing with long, 10-12 foot length boards, having a tight T&G is really a pain because any fluctuation in the tolerances makes fitting the boards together a pain, and often the tops of the tongues have to be trimmed with a block plane. So one wants the boards to slip together easily over the entire length with a rubber mallet and you don't want to be pounding and trimming.

My guess is about a 32nd of an inch clearance, but honestly, I never measured it, as we have the boards commercially milled.

[Joe Calhoon]

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.

Phillip, the nail groove with proper clearance will allow use of a flooring nailer. The first floor I did for myself on the shaper I used groovers and rebate cutters stacked as you describe. Got the fit too tight on that one and very difficult to install. Second time I used the Garniga Multiuse cutter that allows chamfering the tongue in one pass. It was a little better but still tough. I’m not a carpenter or floor installer, these were just projects for myself.
Below is a picture of the insert cutters I now use on the moulder. The rounding of the tongue and groove plus the offset shoulder make everything easier. I don’t do much custom flooring anymore but these cutters are handy for wall and ceiling paneling, bead board and a few other things.

If this is a one off that you think you will never do again corrugated knives from Neil at MT tooling would be the most inexpensive route. Then use his setting magnet to fine tune the fit in the head. Don’t know the cost of the Freeborn head above but that is probably a good setup if you thought you might do more of this.

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[brent stanley]

Hi Phillip, if you look in the catalogue or web page you'll notice Whitehill makes carbide insert style flooring heads for moulders and have about 8 different profiles available with clearances common in the industry drawn and labeled. Chamfers are included as well as offset shoulders on the back and of course any of these styles can be mimicked in the HSS knives for limiter heads or HSS for their chip limiting corrugated blocks. The majority of their HSS knives in the catalogue are made for furniture or cabinet work and not for flooring, but like I said anything you want can be done and I believe they said the flooring profiles you want will not be charged custom rates.

As I expect you are discovering, there are no universal standards accepted world wide for the "correct" way to do t&g flooring as different installers have different standards for how they like it and I have had people spec different clearances depending on the actual floor they are looking at. Rough uneven subfloors get larger tolerances etc, so I would caution you about "expert" advice that say theres only one way to do it.

The knives you order can include nail grooves if you want and if you want they can be tipped in carbide for longevity. You can have profile and counterprofile done on one set of knives if you want, it's often a little less expensive and works the same as individual provided you have the room for profile you want on the 55mm blank. To get the same accuracy as a carbide insert head you may need to set them up with a dial because the affixing system for the knives is less sophisticated. It is your trade off for having access to thousands of profiles for one head for peanuts per profile vs big money for every profile.

Whitehills carbide insert heads of course use carbide insert mounting/affixing systems that position the inserts perfectly with minimal user input but the nature of the beast means fewer profile options are available without having new blocks made to properly back up the brittle and fragile inserts. This is a trade off people working with tooling have to make all the time. Cabinet door grade, piston fit accuracy won't be required for flooring so with whitehills grinding I would just throw the limiter knives in properly and do a test run and you should be fine. Whitehill's Corrugated is easier as the radial positioning is done for you with the corrugations and axial with the end stop they make on their blocks, no need for a jig but you may be buying more steel than you need.

I have had some folks use a set of knives for a job and have it perfect, then the subfloor is worse on the next job so they deliberately offset the knives a bit to loosen up the fit and it's perfect. You will be just fine with the approach you are using, and thousands of linear feet of flooring are done every day that way without issue. The clearances are hard to give advice on because it will dependin on your stock going through the machine and the eveness of the subfloor but I would start with common ones seen in the catalogue and tweak from there. Are you jointing and planing the stock before feeding or just planing? Accuracy of machining (not just thickness) will determine accuracy of positioning of the profile on the edge of the stock.

Brent

[brent stanley]

Here are a couple of pics of the relevant pages in the catalogue for their moulder heads. They are designed to be flexible precisely for the reasons I describe....every installer will want a slightly different clearance. Not that you want moulder heads of course, just to give you a sense of the range possible.

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[brent stanley]

This is what the heads look like if anyone is curious...

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[Maurice Mcmurry]

It is neat that the flooring will be for a family member. Hopefully installed in place Phillip will get to visit. Regarding chips. Dad still tells the story about the gentleman that preceded him in the cabinet business. Leon Foley, he had the shaper right in front of a window with a chute that fit under the sash. The mountain of chips outside the window was impressive. It caught on fire once. The foley descendants tell the story of how franticly they all shoveled smoldering wood chips while they prayed that the Firemen would hurry. Several of my clients have Foley kitchens. The sons made some doors for a remodel I did recently and seemed to really enjoy using their dads old profiles again. Turns out that my client now owns their Grandma's former house.

[Rod Sheridan]

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Above is the knives I used, they fit a 40/50mm Euroblock head.

http://www.mouldingknives.com/

Above is the contact info for the company..........Regards, Rod.

[Mike Stelts]

Sorry for jumping in, but I'm thinking about the same topic. I'm reflooring a summer kitchen where about 120 sq ft are missing. The existing floor has one cut nail on either side of the board per 2 ft joist.

I used a cutter set on hand for the tongues and grooves, hoping for the best. I think I'll relax the tonue to provide wiggle room during assembly. My bigger concern is expansion and contraction of the 12-15" boards. A 2% moisture change in eastern white pine would change the width 1/16". They've been in a 50% humidity space for about two weeks after resting in the barn for years. I'd prefer them tight, but I wonder if installing before the summer humidity will cause them to bow. Is there a strategy here, or just nail 'em in?

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[Rod Sheridan]

Hi Mike, I would measure the moisture content of the flooring before installing it

The bottom edge of the piece with the groove should be reduced so the top fits tight with a small gap at the bottom, this is to guarantee that the top joint has no gap.

Regards, Rod

[Mike Stelts]

Thanks, Rod. I will plane the bottom edge. Moisture of the new boards is ~11%. The existing floor (circa 1850) is 12-15%. An old board I took inside to repair less tha a week ago is 11%. I think I'll let them sit in the summer kitchen for a week, install tight, and try to install the HVAC this summer.

[brent stanley]

Thanks, Rod. I will plane the bottom edge. Moisture of the new boards is ~11%. The existing floor (circa 1850) is 12-15%. An old board I took inside to repair less tha a week ago is 11%. I think I'll let them sit in the summer kitchen for a week, install tight, and try to install the HVAC this summer.

Moisture content is part of it of course but you'll probably find the newer material will change dimensions more than the old due to faster growth in the newer material all else equal. 15" wide material in modern lumber may be challenging to keep well behaved depending on a number of factors.

[Phillip Mitchell]

I thought I would update this thread with some photos and a few details about the actual job/process. It went well. Loads of time milling with even more wood chips. I had a wild-ass-guess of (22) 55 gal drums of wood chips when looking at the stack of rough lumber initially. The final tally was (24) 55 gallon drums, so pretty close. Even knowing that, the waste management was probably the worst part of the process, relatively.

1/8” passes of the jointer - 1 face and 1 edge
Rip 1/8” over final width at bandsaw
Plane down to final thickness 1/8” passes - no photos somehow

Shaper setup with outboard fence to take the profile cut + 1/16” of width off each side - hence roughing 1/8” oversized initially. I ran 2 1/4”, 3 1/4” and 5” widths. Normal outfeed fence was flush with the outermost cut on the profile. Then the outboard fence was set referenced off of that with spacers made from scrap plywood. I ended up using corrugated flooring knives from Neil at MT Tool. They had good tolerances and performed great. My estimate was ~2,000 - 2,500 linear feet run through each set.

This was the first larger run/project I’ve used the new (to me) Wadkin BEM shaper on and I’m quite pleased with the machine. Smooth as silk and stout as a post.

Thanks to everyone for the input previously in this thread. Very helpful all around.

[Phillip Mitchell]

A few more. Aside from the stop and go nature of emptying the dust collector so often during milling, I actually really enjoyed the process and repetition. It was a nice break from tedious custom furniture work, which I also enjoy but can be draining and sometimes feel like a lot of bouncing around in terms of process. This was so linear and focused and repetitive that I was able to get into a great mental flow and groove. Also helps that I enjoy milling rough lumber and have good machines to do it on.

A notable thing is that I used up the last of my last can of Johnson’s Paste Wax, which has been discontinued. I have since bought a can of Trewax and it seems good, but the Johnson’s paste wax has been a staple for me since I started woodworking and I know others much older than me who have had it around for decades. End of an era and I will save the last empty can somewhere in the shop for a memory way down the road.

[Warren Lake]

did you make the bottom relief cuts

[Phillip Mitchell]

did you make the bottom relief cuts

No bottom relief cuts or end matching on this run. Though I had plenty of time while milling to contemplate about what it might take to do.

Here’s photo of the end / bottom of a 5” flooring board from a batch of factory flooring for reference. The bottom relief cuts look to be ~3/8” wide x ~1/16” deep and there are 5 of them on this width board.

I realize that everyone making flooring with any scale and consistency is pushing rough blanks through a moulder, but how would the old school shop like mine efficiently approach the bottom relief cuts? My best thoughts were maybe small diameter saw blades (~4” or so) stacked with spacers on the shaper…obviously in a different setup / machine than the T&G portion. Or a similar setup on the table saw with a dado stack though my table saw arbor is much much shorter than my shaper spindle and this would require multiple passes / fence settings / spacer blocks and no power feeder on the table saw…or to just have a corrugated or other type of profiled knives made specifically around these relief cut dimensions, though limited to ~4” height if corrugated and ~half that or less if in a profiled Euro block.

The end matching is not something that I am set up to do efficiently. I’m not sure how necessary it is on flooring that is ~5” wide or less.

[Warren Lake]

ive done them with dadoe blades, on the woodmaster with a knife ground to do that, or even single saw blade cuts will relieve some strength. you want to break the back of the material

[brent stanley]

No bottom relief cuts or end matching on this run. Though I had plenty of time while milling to contemplate about what it might take to do.

Here’s photo of the end / bottom of a 5” flooring board from a batch of factory flooring for reference. The bottom relief cuts look to be ~3/8” wide x ~1/16” deep and there are 5 of them on this width board.

I realize that everyone making flooring with any scale and consistency is pushing rough blanks through a moulder, but how would the old school shop like mine efficiently approach the bottom relief cuts? My best thoughts were maybe small diameter saw blades (~4” or so) stacked with spacers on the shaper…obviously in a different setup / machine than the T&G portion. Or a similar setup on the table saw with a dado stack though my table saw arbor is much much shorter than my shaper spindle and this would require multiple passes / fence settings / spacer blocks and no power feeder on the table saw…or to just have a corrugated or other type of profiled knives made specifically around these relief cut dimensions, though limited to ~4” height if corrugated and ~half that or less if in a profiled Euro block.

The end matching is not something that I am set up to do efficiently. I’m not sure how necessary it is on flooring that is ~5” wide or less.

I had Whitehill make me a set of knives a long time ago for a 100mm limiter block, tipped in carbide for longevity, that machines a few rounded reliefs on the bottom, when run on edge, against the fence on the shaper. Quick and dirty, because accuracy isn't as important for something like that. All the T&G work I've done has been small runs for historic homes, reproducing existing, or making authentic looking material that suits even if none was there. I've also done some wider work so I have two sets of knives, kne for standard strip width and some for wider material.