A Box Joint Jig, a Freud Dado Stack, and 1/64 inch - Woodworking Talk - Woodworkers Forum
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post #1 of 12 Old 05-23-2020, 11:46 AM Thread Starter
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A Box Joint Jig, a Freud Dado Stack, and 1/64 inch

I want to make a 3/8 inch box joint jig for the table saw. I got out the Freud SD208S dado stack, and set it up for a 3/8 inch dado. According to the chart that came with the dado stack, the setup requires two blades and one chipper. Simple, huh?

I made two test cuts in a 3/4 x 3/4 inch piece of scrapwood for test fitting the box joint pin. I measured the resulting dados carefully with calipers, then rechecked the measurements with a Starrett blade from a combination square.

The two dados (notches) are both 23/64 inch wide.

I expected 24/64 = 3/8 inch. Yeah, the dados are 1/64 inch too narrow. Normally I would not care about 1/64 inch, but with box joints, they add up. On a 3 inch box with 8 fingers, it would add up to be 1/8 inch short. That's enough to bother me.

The simple question is:
-> What next?

Here are more questions:

Box Joint Jig Questions:
* Would you live with the 1/64 error for the ease and convenience of assembling the dado stack?
* Would you shim it to a perfect 3/8 inch instead, remembering that you must shim it every time? (I can write down the shim requirements on the jig as a reminder.)

Freud SD208S Dado Stack Questions:
* Is that normal for a Freud SD208S "8 inch Pro Dado Set"?
* Is it a metric vs. Imperial issue?
* Would you call Freud to ask about it or complain?
* Would you invoke Freud's lifetime warranty for such a petty issue?

Other Questions:
* Would you make additional test cuts with different woods to make sure it is consistent?
* Am I missing something obvious?
* Is there something else I should be doing?
* Do I have unreasonable expectations? After all, this is wood we are talking about. (It's okay. Don't hold back.)

-> Any help, advice or previous experiences would be appreciated. Thanks!


Footnote:
The dado measurements remain unchanged (within 1/128 inch) outside, inside the garage, and inside the house, taken yesterday and again this morning. To the best of my knowledge, there has been no wood movement.
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post #2 of 12 Old 05-23-2020, 12:25 PM
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To shim or not to shim

Quote:
Originally Posted by Tool Agnostic View Post
* Would you shim it to a perfect 3/8 inch instead, remembering that you must shim it every time? (I can write down the shim requirements on the jig as a reminder.)

I would.


A PRO dado stack should come with shims. Good luck...Those box joints are a tricky endeavor.


Charlie
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Last edited by homestd; 05-23-2020 at 12:28 PM. Reason: Unwanted line
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post #3 of 12 Old 05-23-2020, 01:46 PM
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Did you do any investigation to determine why the blade setup was not giving the correct cut width. That is where I would start.


You say that you got out the stack. I assume that means that you have used the set before. Have you ever had a problem before?


I am guessing that the problem is most likely in your chipper. Did you measure the chipper?


Does your set include more than 1 size chipper?


You need to concentrate on how to solve the problem of why the dado set does cut the notch correctly. Not trying to come up with some kludge to make it work.



George
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post #4 of 12 Old 05-23-2020, 05:31 PM
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I have an older Freud SD308 “safety dado” set, and the finished cuts never match the chart included with the set to my satisfaction. I have a set of brass shims which I always assume I’ll have to use to get the cut I want.

I also have their box joint cutter set, which makes very accurate cuts.
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post #5 of 12 Old 05-23-2020, 05:39 PM
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Does it not have the shim set with the 208. If not you should order it.
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post #6 of 12 Old 05-23-2020, 05:44 PM
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Shim set.....
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post #7 of 12 Old 05-23-2020, 06:24 PM
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All dado sets needs shims .... or not.

All the dado sets I've owned or have seen on You Tube require adjusting the cut width with shims. You may get lucky on a particular width that does not require a shim or two. Shims are a pain in the neck and if you get them down in a thread that will throw off the width and damaged them when you tighten the arbor nut.




An accurate jig is just as important as the width of the dado set:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 05-23-2020 at 06:38 PM.
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post #8 of 12 Old 05-23-2020, 06:29 PM
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OK guys.

In a dado setup it is the thickness of the bade disks that determine the width of the cut and not the width of the teeth.

My advice is to go to a hobby store and buy a sheet of brass, 0.015 thick. Cut it with scissors and put it in the dado stack. Then you'll get your perfect ¾ dado.
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Rich
In furniture 1/32" is a Grand Canyon
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post #9 of 12 Old 05-23-2020, 08:00 PM Thread Starter
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Quote:
Originally Posted by GeorgeC View Post
(Quotes below) George
GeorgeC: Did you do any investigation to determine why the blade setup was not giving the correct cut width. That is where I would start.

TA: Okay, it makes sense to me.

My current hypothesis is that the Freud dado set is actually metric, and the printed configurations are not correct. The configurations make sense if you think of materials like Baltic Birch, which is labeled in Imperial units, but is actually slightly smaller.

GeorgeC: You say that you got out the stack. I assume that means that you have used the set before. Have you ever had a problem before?

TA: No, but I have not tried using it in a precisely measured way like this before. Before yesterday, I would choose a rough dado stack size, then make two or more passes to cut the shoulders, then the middle if necessary to "cut to fit." Another use was to cut rabbets, burying the blade in an auxiliary fence. On occasion, I simply trusted the configuration chart and somehow made it work, probably by cutting or planing other parts to fit without worrying about it.

GeorgeC: I am guessing that the problem is most likely in your chipper. Did you measure the chipper?

TA: Yes. I measured the chipper and the other blade parts for you, using a digital caliper with 1/128th resolution. Here are my measurements:

Chipper body = 1/8 inch
Outer Blade body = 3/32 inch
Carbide tip extension outside the blade body = 1/64 inch (this was difficult to measure)

If the measurements are correct, the dado stack should be:
= (2 x 3/32) + (2 x 1/64) + 1/8
= 6/32 + 1/32 + 4/32
= 11/32
= 22/64

To remind you, my measurement of the actual dado slot was 23/64, which I think is within measurement tolerances. Both measurements are short of 3/8 inch.

GeorgeC: Does your set include more than 1 size chipper?

No. All three chippers are 1/8 inch.

GeorgeC: You need to concentrate on how to solve the problem of why the dado set does cut the notch correctly. Not trying to come up with some kludge to make it work.

You're right. That's why I posted the question, but your ideas helped me determine that the configuration chart included with the dado set is not accurate. If I am correct, then shame on Freud.

I made a box joint jig before and it worked fine, but it used a standard kerf 1/8 inch blade. That's too many fingers for the trays and other things I want to build now.
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post #10 of 12 Old 05-23-2020, 08:08 PM Thread Starter
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The Freud SD208S dado set includes shims. They are labeled in metric, with rough Imperial conversions in decimal, which makes it even more challenging to determine what you need for correctly sized dados. I made a chart and will post it below.

Freud includes five 0.1 mm shims, and one each of 0.2, 0.3, and 0.5 mm shims.

If you read the included configuration chart, shims should not be necessary for "standard" Imperial dimensions, but as I said above, the chart is wrong and misleading.

After doing the math, I needed a 0.4 mm shim, which is not included, so I added a 0.1 mm shim and a 0.3 mm shim.

-> The test cuts yielded a perfect 3/8 inch that I wanted.

I learned a lot, but shame on Freud for wasting my time. It isn't that the set is metric, it is that their charts are wrong, plain and simple. I wonder how much expensive wood has been wasted because people trusted the chart without testing cuts first?

P.S. Thank you to all for your helpful comments and valuable lessons!

Last edited by Tool Agnostic; 05-23-2020 at 08:29 PM.
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post #11 of 12 Old 05-23-2020, 08:21 PM Thread Starter
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As promised, here is the shim chart that I made.

The decimal inches stamped on the shims were not very useful to me. I wanted fractions, so I computed them. Please forgive the excessive precision; it was a quick copy/paste from the calculator. I do not expect anyone else to like it, want it, or need it, but it helps me.

Key:
mm (stamped on shim) = ~ inches (stamped on shim) = inch ("exact") = ~ closest fraction (fraction in decimal)

Freud Shims:
0.1 mm = ~ 0.004 in = 0.0039370079 = ~ 1/256 (0.00390625)
0.2 mm = ~ 0.008 in = 0.0078740157 = ~ 1/128 (0.0078125)
0.3 mm = ~ 0.012 in = 0.0118110236 = ~ 3/256 (0.01171875)
~ 1/85 (0.0117647059)
0.4 mm = ~ (N/A) in = 0.0157480315 = ~ 1/64 (0.015625)
0.5 mm = ~ 0.020 in = 0.0196850394 = ~ 1/51 (0.0196078431)

Freud does not include a 0.4 mm shim in the set, but I needed the measurement. Use 0.1 mm and 0.3 mm shims in your dado stack to get 0.4 mm.
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post #12 of 12 Old 05-23-2020, 09:03 PM
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Not really .......

Quote:
Originally Posted by NoThankyou View Post
OK guys.

In a dado setup it is the thickness of the bade disks that determine the width of the cut and not the width of the teeth.

My advice is to go to a hobby store and buy a sheet of brass, 0.015 thick. Cut it with scissors and put it in the dado stack. Then you'll get your perfect ¾ dado.

The width of a stacked dado is determined by two things, the number of chippers and the set of the teeth in the outer blades. the outer blades are marked right and left or inside and outside and must go on properly oriented. The chippers are stacked in "rough" order and shims are used to fine tune the width of the cut. I done that more times than I care to remember and I hated it every time. Magnetic shims are relatively a new addition to the dado set market and would be a great time saving accessory. I own several "dial a width" wobble type dado blades and they are not the easiest to set up either, but no loose parts and pieces to deal with. They are known to leave tiny bat wing looking gaps in the corners, not the best looking when the dados are visible. I wasn't aware that there is a small dado set designed for circular saws and picked up a set off Ebay. I have yet to try them out, with their HSS blades and chippers.



Of course I have tried the router against a straight edge guide and found out that any variation from a snug registration will leave a divot in one edge .... Getting the proper width dado with a router will require a two pass run or an exact width router bit for the newer Metric plywood VS older fractional size stuff. I've also used the venerable RAS for shelf width dados but of course the width is limited to the travel of the carriage on the arm.



I'm still looking for the easiest, fastest and best way ........

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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