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Box joint blade set no longer cuts 1/4" kerf???

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Forum topic by Dan Thomas posted 02-09-2019 09:47 PM 865 views 0 times favorited 50 replies Add to Favorites Watch
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Dan Thomas

160 posts in 508 days


02-09-2019 09:47 PM

OK, this is a really strange one, and it makes no sense at all. I’m hoping I’m just an idiot and the solution is simple, but I don’t think so. I’ll try to be thorough, in case the details help. But first, a short explanation of the problem:

My Freud 2-blade box joint set, which is supposed to cut 1/4” kerfs, is cutting them to narrow, by somewhere between .010” and .014”.

AND, the Freud dado stack I bought very recently, which is supposed to cut 1/4” kerfs when using just the two outer blades, is cutting kerfs too narrow, by about the same amount.

Two sets of blades doing the same thing, one of them basically brand new. On a SawStop JobSite table saw, in case that matters.

Details:

I haven’t used the box joint set in a while, but I’ve used it plenty of times in the past to cut 1/2” box joints using a jig I have, and it’s always worked out fine. I never measured the kerf, because I didn’t need to – it wouldn’t have worked if it wasn’t cutting 1/4” kerfs, because my jig is driven by a threaded rod, and it just wouldn’t have worked otherwise.

I probably haven’t used the box joint set since I bought my SawStop last year. And as I said, I just got the dado stack.

So here’s the obvious question:

How is it possible for both these blade sets to be cutting kerfs that are too narrow? Especially since the dado stack is basically brand new.

I can think of plenty of reasons for the kerf to be too wide, but none that explain it being too narrow.

I even toyed with the idea that maybe I was over-tightening the arbor nut, even though I can’t imagine I could over-tighten it enough to make a difference as large as .010”, but even with the nut barely tighter than hand-tightened, it makes no difference.

The only variable that’s changed that I can think of is the table saw, but I just can’t see how a table saw could cause a kerf to be narrower than it should be.

Anyone got any ideas? I feel like I’m in the twilight zone.

Thanks.

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker


50 replies so far

View Rayne's profile

Rayne

1228 posts in 2051 days


#1 posted 02-09-2019 09:55 PM

My guess would be those blades are created as close to 1/4” as possible under the Metric system (6mm is .14 less than 1/4”). The shims exist to adjust the width as necessary to get them exactly what you need. Now why they cut 1/4” before and not now, I don’t know unless the blades had debris between them or maybe your jig had enough play to fall within the tolerance. Like if your threaded rod is not an Acme rod, there’s a good chance it has enough play, but not enough to really affect your work so all seems well. Just a guess.

View Dan Thomas's profile

Dan Thomas

160 posts in 508 days


#2 posted 02-09-2019 10:11 PM

Thanks, Rayne, and that all makes sense, except that the reason I noticed this is that when I used my jig this time, the box joints didn’t fit.

As for the rod not being exact, it’s 16 threads per inch. I’m no expert, but I think if it wasn’t exactly 16 TPI, the nuts wouldn’t fit.

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker

View bilyo's profile

bilyo

854 posts in 1614 days


#3 posted 02-09-2019 10:48 PM

I’m not familiar with a box joint set, but I do have a dado stack. The two outer blades are marked as to which is inner and outer on the arbor. I don’t even know if this would make any difference in the with of the cut, but is it possible that you have gotten them turned around? Maybe the teeth are slightly off-set or maybe the plate is slightly thickened on one side ???

View Dan Thomas's profile

Dan Thomas

160 posts in 508 days


#4 posted 02-09-2019 10:51 PM

Unfortunately, no, I don’t have them on wrong. But it would have been nice if that was the problem! :)

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker

View Dan Thomas's profile

Dan Thomas

160 posts in 508 days


#5 posted 02-09-2019 10:55 PM


My guess would be those blades are created as close to 1/4” as possible under the Metric system (6mm is .14 less than 1/4”).

- Rayne

I’ve thought some more on this, and I have an idea. Suppose the box joint set always cut a narrow kerf, but my old table saw was misaligned enough to cause it to cut a wider kerf – to the point where it evened out to 1/4”? I know I tuned up my old table saw at one point, but I don’t remember if it was before or after I cut the last box joints.

Would it be possible for a table saw to be misaligned enough to cut a kerf wider by .014”, and not be noticeable otherwise?

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker

View Redoak49's profile

Redoak49

4190 posts in 2500 days


#6 posted 02-09-2019 11:19 PM

I would not worry and just use shims.

One thing I have found is that I have to adjust finger joints for the wood I am using. I need a little different set up if I am using oak, Ash maple etc.

View Dan Thomas's profile

Dan Thomas

160 posts in 508 days


#7 posted 02-09-2019 11:25 PM

I think you show a lot of wisdom. But I want to know why this is happening!!!! I suppose I should just shrug it off and do what you say. It’s probably not worth the aggravation.

Thanks!

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker

View Rich's profile

Rich

5001 posts in 1101 days


#8 posted 02-09-2019 11:27 PM

Rayne hinted at it, but the first thought I had was to just add shims.

View Rich's profile

Rich

5001 posts in 1101 days


#9 posted 02-09-2019 11:28 PM

.

View Dan Thomas's profile

Dan Thomas

160 posts in 508 days


#10 posted 02-09-2019 11:28 PM

Well, yeah, I already did that. I just wanted to know why this happened. I’m thinking now to just “let it go”. :)

Thanks, by the way. :)

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker

View Rayne's profile

Rayne

1228 posts in 2051 days


#11 posted 02-09-2019 11:49 PM



As for the rod not being exact, it s 16 threads per inch. I m no expert, but I think if it wasn t exactly 16 TPI, the nuts wouldn t fit.

- Dan Thomas

A good way to test this is can you wobble the nut on your sawstop arbor when loose? You shouldn’t be able to. Now do the same to the nut on your regular threaded rod. You should have some play. This can make a small difference. If you had your old saw, you could have tested it by using a standard blade and cut a slot in a scrap to measure the width of the slot to the actual, widest width carbide tip on the blade to see if there was a difference.

View Dan Thomas's profile

Dan Thomas

160 posts in 508 days


#12 posted 02-09-2019 11:52 PM

OK, I hear you. Good thing I’ve decided to take Redoak49’s advice and just let it go. ;p Sometimes, ignorance really is bliss.

-- Newbie Dan, https://www.youtube.com/c/thenewbiewoodworker

View corelz125's profile

corelz125

858 posts in 1488 days


#13 posted 02-10-2019 01:07 AM

I have the Freud dado set and it is off from what the directions say for the setup. I add a shim.

View BlasterStumps's profile

BlasterStumps

1425 posts in 951 days


#14 posted 02-10-2019 02:21 AM

I’m late to this conversation but was wondering how you made the determination they are cutting too narrow?

-- "I build for function first, looks second. Most times I never get around to looks." - Mike, western Colorado

View Lazyman's profile

Lazyman

3977 posts in 1899 days


#15 posted 02-10-2019 03:16 AM

I guess I am a little like you, I want to know why…
Did you make the jig or did you buy one? Here are the things that occurred to me to look at. I assume that it is the gaps and not the fingers that are too thin? Is the finger to finger spacing exactly 1/2”? Measure it across an entire board and make sure that there is no cumulative error.
To get measurements in thousandths of an inch, I assume you are using a caliper. Is it possible that your jig is not perfectly perpendicular to the blade? I can imagine a way of cutting a 1/4” slot at a slight angle and then when you measure with your caliper, if you insert the blades perpendicular to the face of the board, it would measure slightly narrower and the finger joints won’t mesh properly. Shimming your blade may not fix that problem. You might get sloppy joints. Note that is a different problem than if your blade is not parallel to the miter slots. This is where the backer board of your jig is not perpendicular to the blade.

Finally, I can’t image that it would make that much difference and I don’t know what the thermal linear expansion of carbide is like but what is the current temperature of your shop? Even if it isn’t cold enough to measurably affect the width of the blade, I wonder if a really cold temperature could affect the length of the threaded rod that is being used to control your jig? Just thinking about variables that could theoretically affect your finger joint jig.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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