Shopsmith Forums

It's a power issue.

A dado stack is generally much wider than a saw blade. So given the same feed rate and depth of cut, it will remove material much faster than a sawblade. But the power demand rises roughly in proportion to the material-removal rate. The PowerPro is more powerful than a conventional headstock in the sawing-speed range, and so it can cut more agressively than a conventional headstock.

A Mark V doesn't have enough power to zip through a wide & deep dado cut at full speed. But it does have a variable-speed transmission, which acts as a torque multiplier at low speeds. It may take longer, but when you crank the speed down, there is plenty of torque to drive a wide dado stack.

With an appropriately shallow depth of cut, a Mark V headstock should be able to make dado cuts at sawing-speed RPM's. A 3/4" wide dado cut 1/8" deep will require roughly the same power as a 1/8" saw kerf through 3/4" thick material.

I haven't tried it, but I'd bet that you could minimize tearout by taking a light/shallow dado pass at sawing RPM, and then cranking the speed down for a full-depth cut on the second pass.

The 'Magna dado' was a heavy wobble blade.

BuckeyeDennis

Unfortunately using the Incra-I-Box jig you don't have the option of making shallow cuts. Once you set it up, the set up remains the same until the total job is done. Otherwise it would be a "Real Hassle" changing set ups and run the risk of making a minor error and ruining the whole job in the process. Since I am only using two blades instead of a stack, I am gong to increase the speed until the head-stock shows any sign of bogging down.

Don G

JPG wrote:The 'Magna dado' was a heavy wobble blade.

Here's what the Magna Dado instructions have to say about proper RPM's. They are referring to use on a 10E/R.

I have the Freud box joint set. I really don't see needing to run it at excessive speed, just because it can run at 9000 rpm doesn't mean it needs to.

Keep in mind most saws do not have a speed adjustment. Blades are designed to run a what ever speed the saw provides. Like wise the blade designers are designing for those saws and not for a shopsmith. The damping and vibration controls are like wise figured for maximum effect at typical saw speed.

I have the powerpro and this is what I did to come up with a speed to run the box joint blades. I wanted to have a speed in rpm to equal the tip speed of a standard 10" blade. This is pretty simple math.

If I had a 10" blade running at 3450 rpm then then C=pi*d or C=3.14*10 or 31.4 inches. Now we add the rpm to find that distance traveled in one minute =3450*31.4 or 108330 inches.

Knowing that we can now work back to find the rpm need to match that for an 8" blade. Again we know that C = pi*d so C = 3.14*8 or 25.12. Now if we want to solve for the rpm it becomes 108330/25.12 or 4312.5 rpm.

From this I try and just think 4300 rpm and so far so good.

I would really question anything over this. Again just because you can doesn't mean you should.

Ed

jsburger

John I have to ask you a real dumb question. I have been playing around with this Incra-I-box jig while waiting on Freud blades and the correct miter bar and have run into a problem. I noticed you cut the slot for the bottom of your box before you cut the finger joints (I think anyway). After assembly it would appear that you would have half of the finger (Maple) at that slot that would need to be replaced with a plug. Is this true or am I losing my mind.

I have tried in vain so far in being able to slot the box so this problem doesn't happen ???

A better solution may be to use 3/8" or 1/2" fingers so you could cut the slot in the middle of a finger. I am assuming your box is 1/4".

Don G

dgreen810 wrote:jsburger

John, if you don't mind, will you post what RPM are you turning your Forrest box joint blades? I assume you are using your Power Pro so if you can relate the RPM of the PP to a Mark V speed dial. I have never quite understood why the speed dial on a Mark V has a setting for "Magna Dado" which is considerable slower than the "Saw" setting which contributes to unwanted tear-out. Even when using a good solid backer. I am using a Freud "Super Dado"stack set two blade configuration for 1/4" dadoes and experience minor tear-out and think the "Saw" setting would help the situation but am a little leery unless someone can explain why not??

I haven't been able to find the max RPM for the Freud "Super Dado" set I have but think they can be turned to 7000 RPM safely as well but don't know for sure???



PS: I ordered a Freud 8"Box set that should help since Freud says they can be turned to 7000 RPM.

Don G

I have a Powermatic PM2000 table saw also. That is what I use the I-Box on. The arbor speed is 4300RPM. On the standard MK V "U" is 4200RPM and "V" is 4400RPM. I see no reason not to try that speed. Also slower feed rate should help and putting a strip of painters tape on the stock should also help. FWIW, I get no tear out with the Forrest blades.

John

Will do. Address the othr question about plug please!!

Don G

dgreen810 wrote:jsburger

John I have to ask you a real dumb question. I have been playing around with this Incra-I-box jig while waiting on Freud blades and the correct miter bar and have run into a problem. I noticed you cut the slot for the bottom of your box before you cut the finger joints (I think anyway). After assembly it would appear that you would have half of the finger (Maple) at that slot that would need to be replaced with a plug. Is this true or am I losing my mind.

I have tried in vain so far in being able to slot the box so this problem doesn't happen ???

A better solution may be to use 3/8" or 1/2" fingers so you could cut the slot in the middle of a finger. I am assuming your box is 1/4".



Don G

The box is 1/2" thick stock and the fingers are 1/4". The bottom is 1/4" Baltic Birch. The slots were cut after the fingers were cut with the I Box. The slots were cut on the router table with a 1/4" straight bit. The Baltic Birch is just shy of 1/4" so the fit is perfect. As you can see in the picture I did a stop dado on the maple pieces centered on the first 1/4" pin.

jsburger

Where is the nearest optometrist??? Just kidding, believe or not I didn't notice the stops on the slot dado. Can you believe I have jacked around since noon yesterday trying to cut the slots on my radial arm saw and not end up with "Missing wood" on two pins. I almost am reluctant to post this reply.

I have watched maybe 10-12 videos of guys making boxes and to my knowledge not one mention of using stops on the slot for the bottom. Maybe I missed one.!!

Don G