Dovetails

Last week tried dovetails on the CNC, pics shown. Some commentary:

Dont ask me about how this clamping fixture is mounted to my machine - it was not made for it but I did it anyway. Do not recommend.

I tried various gadgets in VCarve, and looked at the paid software just for calculating dovetail joints. In the end I decided they were all either limited in customization, or saved little time vs just laying it out myself.

With some mental imagery, laying dovetails of any size/spacing you want in VCarve is a pretty straightforward exercise. Simply assign an end mill cutting bit equal to the diameter of the dovetail bit you want and have at it. For the pins just match the angle to whatever angle the dovetail bit is. These were all 8 degree.

I did use a roughing pass with a straight bit before cutting with the dovetail bit.

The pins are cut with a straight bit.

This was my first attempt, and I left the cut lines line to line with no 'gap'. They are super tight. In the future I will add some gap to design file by offsetting (once I have a pocket vector it would be simple to offset that vector by .003 or so - although there might be a toolpath setting that does the same)

In my pic you see my mickey mouse setup has an old ruler as a spacer against the clamping cam. The problem with this type of BS is that the 'operator' doesnt pay attention and of course the bit tries to cut through that hardened steel and destroys the tip of a bit. Rats. (I still suffer from the occasional crash or dive when doing something new/different, in part because I do too much mickey mouse setup stuff)

Also note - as with a router fixture - you are limited to what you can do with router bits. So the smallest pin dimension is limited by the shank end of the router bit. and you need a bit with enough cutting length to accommodate material thickness. This in fundamental to cutting dovetails with a machine. So if you dont like the looks then go with hand cutting.

The first one took a LOT longer than if I would have just cut by hand. I sold my router jig because I never used it once I got better at hand cut.

Otherwise it worked well and makes it a matter of cut, clamp, repeat until they are all done.

I may at time still decide to hand cut depending on the project, but this has a place. I have some box joints to cut and am pondering whether I CNC those one at a time or gang them all at once on the table saw or router table like I would have previously.

Am likely to keep using the CNC on this little project as a learning curve and getting familiar with the process, then decide in the future what approach fits what objective.

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Those look like really good and tight dovetails - good job! I've yet to cut any but keep saying I'll do it soon. So, I'll do it soon... :)

Looks good and from your description, it sounds like you coded things well, too.

Since you have the vertical holding fixture, box joints should be just as easy, if not easier than the dovetails to accomplish and that "repeatability" thing is nice. The same limitation applies with sizes, however...it's all about the tooling. You can do narrow box joints on thinner material no problem with, say...a .125" end mill, but there will be increased risk doing that with thicker material because of the limitations on LOC (length of cut) for the tooling and heat generated when paases get beyond that LOC as you step down for each pass.

Dovetails are both a fun and frustrating project. Here's a link to some I did back in 2008 that is all hand coded with variables using the SB3 control. Depth and width of the pins and tails could be adjusted a few thousandths from the keyboard if needed. Programming followed the geometry of a PC dovetail jig and a traditional bit.

With over 37,000 views, it has been one of my most watched videos

https://youtu.be/4Aw4lElTecg

I will try some half blind next for the drawer sides. I think it will go pretty smoothly.

Then to decide whether to cut simple grooves for drawer bottoms, runners, etc on the CNC or just run them on the router table. Clamping the workpiece down and keeping fingers away from it as the cutting happens has a certain appeal.

Before I remove the vertical clamping jig I have some additional drawers on a separate project I will at least do the pins for. Cutting away waste is tedious and the CNC is benefit
there.

Its useful. But as with many things, may not be the chosen way to do some things.

Tool Radius Compensation. G02 or G03, typically. You program to the finished part and set an offset in the control to comp' the cutter diameter.

I don't remember if VCarve supports this. But I'm sure those that have actually used it within the last 4 years do.

As for narrow box joints in thick material, there are long reach endmills with short flutes at the end of a solid shank. Much more rigid than a conventional long endmill, and the shank is relieved so there's nothing dragging where you've already cut.

Yes, V-Carve, Aspire has an allowance parameter that lets you account for the diameter of the bit, or to simply add a "fit factor" for an interference, tight, sliding, or loose fit, as you choose. It's a key feature for me in fitting parts together.

John

Duh, don't know how I screwed that up. G02/3 are arc commands. G41/42 are for cutter comp.

Before I went on to the next step of this project had a couple boards from a friends tree so decided to just double up on everything. So ran another set of through dovetails while it was set up.

Which is just a matter of clamping new boards in and letting it run. I sat and checked email and sipped a beer while it ran...

Not sure I call this woodworking. But its a way to make duplicates easily.

This cherry slid together with just the right force. The first set was a different wood (not sure what it is.. very dense, heavy, oily) so the cut seems to behave slightly different depending on what wood is being machined.

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It's woodworking, especially for joinery that is for functionality and isn't intended to be "the art" of the project. It's no different than using a Leigh or other jig to do dovetails rather than hand cutting but it has the advantage over them of precise repeatability for future projects that need the same work done. You can spend your time doing the finesse work instead of that can be pure drudgery when you have a lot of, say...drawers...to build. That's certainly subjective, but an opinion I've held for a long time.