How to get flat bottomed dados with a BT3?

[JimD]

I have a jig like that which I use occasionally. I use a top bearing flush trim bit with it so I can put the space to be cut out right on the layout line. But I only do little location type dados with it. 1/8 depth or less. I do not like routers for deep dados, it seems like the router doesn't have the power. But you can make multiple passes. Or you can use the router for a final cleanup cut after removing most of the material on the table saw.

I have a HF dado set too but I do not use it for multiple reasons. It is 8 inch diameter which is not so good for the BT3100, it is not rated to handle the rpm of the BT3100, and the blades are not ground very well so there is no way mine will make a flat bottomed dado. It would be OK for crude stuff if it wasn't for the other issues.

It would be better to shim the blade position with a washer if you are having trouble staying on the smooth part of the shank than it is to try and wrap tape on the threads or something like that. 5/8 washers are not very expensive and for smaller adjustment you could use stack dado shims.

Jim

[JR]

I have used the router method and it is very effective. In fact, with a properly adjustable jig you get perfect fit every time.

I also have a good technique for dado blades on the BT using a micro-adjuster. Get as much of the dado stack as you need, but taking care not to stack them on the threads. Make a pass at the correct depth, then use the micro-adjuster to move the fence. This will give good results, getting the width of the groove just about perfect.

JR

[SARGE..g-47]

I use the same T square jig CB uses except mine is "not" cut out in the middle of the cross-priece for the bar clamp... well not until about 2 PM today when I will cut it out. That's a very clever way of clamping the set-up. My way is good but not as quick to clamp as that.

BTW.. for any considering... you can make a pass on one side of the T with say 3/4" to get your dead zero mark.. then use the other side of the T for say 1/2". Just use the sizes you use most frequently which will may just be 3/4 for most. I cover 1/4" and 3/8" with my Freud Box Joint Cutter Set as mentioned.

I wouldn't consider making asking a 3/4" straight bit to dig 3/8" to 1/2" deep for a dado in one pass and my Milwaukee plunge is 2 1/4 HP.. Trying to do deep in one pass is asking for trouble.. bit scorthing.. etc.

Anyhoo.. the jig is easy to make and dead accurate...

[JR]

I llike Cabinetman's jig, but there is a limitation. It assumes you have router bit that matches the thickness of the material you will be installing in the dado. There are plenty of circumtances where that will work just fine, but also plenty of times when you have skinny plywood or whatever.

If I were making that jig today, I'd make it so one of the long legs is adjustable. In use I'd run the router down the center between the legs, using a top bearing straight bit. To set it up you put a piece of your plywood between the two legs, move the adjastable piece until it's snug, then plow out the middle. Easy and perfect fit. Somewhere I have a pic...

Ah, here it is. This jig is fully adjustable for width of the dado and length of the piece to be cut. There are stop blocks clamped in place to limit the length of the dado. It is still imperfect in that I failed to fix one of the end pieces square to the long parts. It's TOO adjustable for quick setups.



JR

[cabinetman]

BTW.. for any considering... you can make a pass on one side of the T with say 3/4" to get your dead zero mark.. then use the other side of the T for say 1/2". Just use the sizes you use most frequently which will may just be 3/4 for most. I cover 1/4" and 3/8" with my Freud Box Joint Cutter Set as mentioned.

If the other side of the "T" is used, the routing direction would have to be from the end towards the "T".

I wouldn't consider making asking a 3/4" straight bit to dig 3/8" to 1/2" deep for a dado in one pass and my Milwaukee plunge is 2 1/4 HP.. Trying to do deep in one pass is asking for trouble.. bit scorthing.. etc.
Anyhoo.. the jig is easy to make and dead accurate...

I find a 1/4" deep dado sufficient for most applications.
.

[dbhost]

My problem with dadoes / router is certainly edge guide related. I use a Milescraft 1203 , well okay the Craftsman branded version of this, and the knobs have been upgraded to regular Rockler star knobs... I usually find out the guide isn't locked down tight around the same time that the dado is completely screwed up...

Rumor has it that accessories for the PC690, including the 42960 Edge Guide fit my Hitachi KM12VC. I may just try that out...

[tseavoy]

I just run a sharp chisel along the bottom of the dado.

Tom on Marrowstone

[SARGE..g-47]

If the other side of the "T" is used, the routing direction would have to be from the end towards the "T".

Correct.. once the cut slot is aligned to the mark on the T side.. I move to the opposite side of the fence and pressure is exerted by a pull to the fence for left to right movement. On the 3/4" side I exert pressure to the fence with a push toward it moving left to right.


I find a 1/4" deep dado sufficient for most applications.
.

Depends in my shop.. how much weight is going to be exposed to the piece that will fit into the dado.. how much space in between dadoes only supported by the dado and the thickness of stock dadoed into. If you are using 7/8" or 1" stock on a side panel being dadoed into as I do often with some of the A & C pieces I build.. why limit the depth when the panel will accomodate more depth which means more glue surface.

In 3/4" ply which I don't use.. 1/4" should be sufficient as it is cross plied in most situations I can think... again I don't use ply to build anything but utility construction items with exception of drawer bottoms and chest backs.

[Mr__Bill]

I just run a sharp chisel along the bottom of the dado.

Tom on Marrowstone

Now that's a stealth gloat if I ever heard one... good one Tom




Bill
now I have to find a 17mm chisel so I can follow Tom's lead

[cabinetman]

Depends in my shop.. how much weight is going to be exposed to the piece that will fit into the dado.. how much space in between dadoes only supported by the dado and the thickness of stock dadoed into. If you are using 7/8" or 1" stock on a side panel being dadoed into as I do often with some of the A & C pieces I build.. why limit the depth when the panel will accomodate more depth which means more glue surface.

In 3/4" ply which I don't use.. 1/4" should be sufficient as it is cross plied in most situations I can think... again I don't use ply to build anything but utility construction items with exception of drawer bottoms and chest backs.

The jig is designed to do dadoes in sheet goods. For stock thicker than 3/4", in which a deeper dado could be appropriate, the dado in the "T" would be compromised for its depth of cut (1/4").
.