Flat Machined Dovetails (related to Gerry's thread)

I was already going to post a reply to Gerry's dovetail thread but did not want to highjack it with a sidetrack idea.

I would love to use Gerry's software but unfortunately my machine does not allow for overhang machining of a vertical piece.

But this got me thinking and I spent some CAD time this morning figuring out how to cut a dovetail joint practically with flat machining only. This does not require a dovetail bit but a 30-degree V-bit (like Amana In-Groove) and a small endmill, e.g. 1/8".

The one in the rendering and video below is "half-blind" but can be done as well fully blind or fully visible. The V-bit path for the one side of the joint would need something like VCarvePro to generate. I guess it would be difficult to do a similar custom program like Gerry's for that? Anyway, I will probably do an experiment sometimes.

I hope the pic and video give an idea what I mean.
[ame="http://www.youtube.com/watch?v=B3jzjyr3Lk0"]video[/ame]

https://lh6.googleusercontent.com/-R...ovetail2Re.jpg

I've actually done a thread on this in the woodworking section about a year or so ago. It requires both a 30 and 150 degree bit to execute, as well a flipping over the part. The crv files are also posted wither there or the Vectric site.

Nice idea. Remember seeing something similar on youtube seemed to work fine

Videos here... The descriptions has the links and other info.

[ame=http://www.youtube.com/watch?v=ocNqwCRo4xE]Cutting THROUGH DOVETAILS on the FLAT with a 3-Axis CNC, part 1 - YouTube[/ame]
[ame=http://www.youtube.com/watch?v=u0BtiJka6uM]Cutting THROUGH DOVETAILS on the FLAT with a 3-Axis CNC, part 2 - YouTube[/ame]
[ame=http://www.youtube.com/watch?v=YtZrZPBdwi0]Cutting THROUGH DOVETAILS on the FLAT with a 3-Axis CNC, part 3 - YouTube[/ame]
[ame=http://www.youtube.com/watch?v=00oG0S9UMcI]Cutting THROUGH DOVETAILS on the FLAT with a 3-Axis CNC, part 4 - YouTube[/ame]

The original thread here:
http://www.cnczone.com/forums/woodwo...ue_take-3.html

Thanks, that is excellent! Looks like this is actually possible. More food for thought.

I have to look over your pictures and video again. I am a bit confused why this needs 2-sided machining and a 150 degree bit. The concept I was thinking about only needs one-sided machining, however to achieve a single 15-degree beveled cut I was thinking of a fixture to hold the board at this angle and then still use an endmill.

In the meantime I worked out some interferences and the concept looks like the following pics (fully visible and blind dovetails).

https://lh5.googleusercontent.com/--.../Dovetail3.jpg https://lh4.googleusercontent.com/-3...Dovetail3a.jpg

Thermwood sells "cnc dovetail" bits for cutting dovetails on the flat. There e-cabinet systems software can do the programming.
Thermwood Online Store - Great prices on CNC Router Supplies!

Quote:

---

Originally Posted by ger21

Thermwood sells "cnc dovetail" bits for cutting dovetails on the flat. There e-cabinet systems software can do the programming.
Thermwood Online Store - Great prices on CNC Router Supplies!

---

If I'm not mistaken, they don't make "traditional" dovetails as the tails are rounded? It almost looks like a Leigh Isoloc joint.

Quote:

---

Originally Posted by JerryBurks

Thanks, that is excellent! Looks like this is actually possible. More food for thought.

I have to look over your pictures and video again. I am a bit confused why this needs 2-sided machining and a 150 degree bit. The concept I was thinking about only needs one-sided machining, however to achieve a single 15-degree beveled cut I was thinking of a fixture to hold the board at this angle and then still use an endmill.

In the meantime I worked out some interferences and the concept looks like the following pics (fully visible and blind dovetails).

https://lh5.googleusercontent.com/--.../Dovetail3.jpg https://lh4.googleusercontent.com/-3...Dovetail3a.jpg

---

Having the bevel go the other way, eliminates needing to make a fixture to "tilt" the boards; all the boards could be lined up and beveled at the same time. Also the "notches" for interference are hidden from view.

Interestingly, I designed and drew the joint using only 2D and some quick trig.

I don't think you can just use an endmill for the bevel as tilting the board will require you making an "undercut", necessitating a 15 deg. dovetail bit.

If you look how my sample is assembled in the video you'll see the bevel. It cannot be cut in one setup because the 30 deg. bit leave a "draft" on the walls between the tails, which have to be "mimicked" on the tenon end. In fact even the tails have a "draft" on the walls, which makes the joint somewhat non-self-locking in one direction, but there actually is more surface area for glueing. If I "squared" the bottoms of the tail end then it would ruin the look of the dovetail, unless I stopped short and whittled the rest, which to me defeats the purpose of doing it this way.

I didn't see the small flat (shoulder) at first, though I think that just adds another setup and complicates things a bit.

I like the blind joints. It is a great way to hide that you are using laminated pieces of ply instead of real wood.

Quote:

---

Originally Posted by louieatienza

If I'm not mistaken, they don't make "traditional" dovetails as the tails are rounded? It almost looks like a Leigh Isoloc joint.

---

These aren't actually "traditional" either. Given the choice, I'd probably go with the thermwood type, as there are no visible clearance gaps.

Quote:

---

Originally Posted by louieatienza

If I'm not mistaken, they don't make "traditional" dovetails as the tails are rounded? It almost looks like a Leigh Isoloc joint.

---

I have been experimenting with Isoloc style joints a while ago (did not know the name though). They are pretty and functional but so far I did not come up with an idea to machine a 90-degree joint of that style with both parts flat. That is why I picked up on the more traditional style dovetails.

But I made an experiment with an inline joint (or butt joint) of 3/4" plywood. After the glue set I whacked it with a mallet in a vise and it broke right next to the joint. The joint itself held up, seems to be a really strong connection.

https://lh4.googleusercontent.com/-c...2/DSC01241.JPG

Quote:

---

Originally Posted by ger21

These aren't actually "traditional" either. Given the choice, I'd probably go with the thermwood type, as there are no visible clearance gaps.

---

Mine do not have clearance gaps (other than layout error) either...

JerryBurks stated:

I would love to use Gerry's software but unfortunately my machine does not allow for overhang machining of a vertical piece.

Here are some ideas on how to accomplish a vertical mount by going through the table/spoil board.


Legacy method

[ame=http://www.youtube.com/watch?v=WKu6OC47Qv8]Legacy CNC through dovetails.mp4 - YouTube[/ame]


Hole though spoil board

[ame=http://www.youtube.com/watch?v=ccS2W2O9CJY]Cutting Dovetails on a Joes Hybrid 4x4 1/2 - YouTube[/ame]


Mount router head horizontal? [This is timber framing, but shows idea}

[ame="http://www.youtube.com/watch?v=7RNo0ESFsl4"]Arunda dovetail assembly system - YouTube[/ame]


Ancillary thought: It would be great fun to get you high level creators and problems solvers in one room and see what you would accomplish. :cheers:

We are in one big room. ;)

I have actually mulled over ideas and techniques for doing dovetails on the flat. It seems most would either require rotating the spindle (possibly requiring large Z axis clearance,) 3D movements (requiring expensive CAM or tough hand-coding,) or leaving visible "defects" (which would be unacceptable for a through dovetail.)

With my method, everything can be done in 2D CAM with readily availabe tools (the 30 degree and 150 degree bit can be purchasedd at ToolsToday relatively cheaply.) You won't be able to make a blind dovetail with this method, as having the corners butted up as in a manual dovetail jig would probably be the best way.

There is a company that sells a jig called a WoodRat or something like that, and they sell dovetail bits that have a very narrow tail ends which mimics hand cut dovetails better. They also have an interesting take on carbide vs. HSS.

Dovetail Wizard CNC

Dovetail Wizard CNC

found this, did not read much, but its a lead.

Cambium Machines youtube video of cutting dovetails. Works with SketchUp.

[ame=http://www.youtube.com/watch?v=2gT5icRbjc8]Introduction to Dovetails - YouTube[/ame]


https://www.cambiummachines.com/home.html

I continued some design over the holidays (traveling and no access to the shop for some real useful stuff). It occurred to me that the "classic" dovetails are shaped to accommodate manual cutting and not really optimized for CNC machines. Therefore I simplified the shape so that it should be possible to machine this flat with an end mill and a small roundover bit. I think I will give this a try once I am done with a few other projects in the pipeline.

https://lh6.googleusercontent.com/-w...SquareDove.jpg