[rocketflier]

Been poking around getting the itch to build something,.. ya know?

While the machines I've been looking at/following builds of have various sizes of travel for the Zaxis, what strikes me is you're still limited by distance between the base of the router and the length of the bit. So like in the photo below, a tenan may be cut, but the length of the bit would not allow a through cut.

Is this something handled by longer bits and/or how do you deal with deeper cuts (especially if they're not through)?

[CarveOne]

You can find sources for 5" DOC bits if you look hard enough, they are pricey, and the run-out may be an issue. It will be possible to cut one side of a tennon to half depth, rotate the piece 180 degrees and cut the other side using a fixture. If the tenon is not exactly centered on the piece, the gcode has to offset the second side cut by the correct amount. There is always a chance that there will be a small step inside the piece if alignment of the two cuts isn't exact.

CarveOne

[ger21]

Personally, If it's thicker than 3", I'd probably route at deep as possible on the one side, then put in on the drill press and drill out the rest with a forstner bit, then flip it over and use a flush cutting bearing bit in a handheld router to clean it up.

If you were doing a lot of them, then I'd make a fixture to locate the center, and route half way on each side and flip it over.

Really long bits like CarveOne mentioned will usually have a lot of chatter. I'd try to avoid them if possible.

[Pplug]

What about using a real tennoning drill? You could have square corners as well. But only if you have many to cut or have an extra $250 hanging around.

[Treischl]

Obviously this is a question that is not peculiar to CNC machines, but rather cutting mortises in general (the hole is the mortise, the tongue is the tenon, btw).

If you look at mortise cutting chisels/drills you will notice that they will also not cut through 5" thick material.

The reason for this is fairly obvious, why would you want to cut a mortise 5" deep unless you were doing something like timber framing, in which case it would not need to be a precision cut for your barn.

Generally speaking, the depth of a mortise should be about 1.5 - 2 times the thickness of the tenon, not the width, the thickness. Cutting through a 4 inch leg, for example, doesn't really make it stronger. It was done with craftsman style furniture as a design element. It was and is often faked.

What I have learned over the years is that if you cannot find a tool for a job, there is probably a reason that cutting tool does not exist, and that reason is that it doesn't make sense.

[CarveOne]

Obviously this is a question that is not peculiar to CNC machines, but rather cutting mortises in general (the hole is the mortise, the tongue is the tenon, btw).

You're right of course, I knew it was mortise, and can't explain why I said tenon.

I don't recommend using a 5" bit, just saying that they are available if it is required for the job.

CarveOne

[Pplug]

You're right of course, I knew it was mortise, and can't explain why I said tenon.

CarveOne

Yeah, me too! I guess I should stay off the forums on a Sunday morning!

[rocketflier]

Obviously this is a question that is not peculiar to CNC machines, but rather cutting mortises in general (the hole is the mortise, the tongue is the tenon, btw).

I'm sorry I wasn't clearer.

It has nothing to do with a mortise (mortise is the pocket, tenon the piece fitting into the mortise).

It has to do with cutting/carving negative or concave objects and depth of cut.

The mortise, however does describe the situation perfectly. You have an 8" thick piece of wood and need to carve to the inside; NOT just across the surface. In some spots, the depth of cut might be 5"

This, although a pumpkin, I'd call a convex carving:



Examples of what I'd call concave:





Granted a wheel can be constructed on a lathe or from multiple pieces. The bottom example, the samples in the center or on the right.

Actually, on the right fits best. With a router and 1" long 1/2" bit, you can cut the outer most cylinder 1" in depth. Then the step would depend on how close you can get till the chuck hits. Then ultimately, the base of the router or holder would hit the top of the part if the bit isn't long enough to completely enter the part.

And of course if it is, then you either have to switch bits, or have Z clearance for the bit to clear the top of the part.

[ger21]

Here are some 6" long bits that can cut 4.5" deep.
Vortex Tool: Pass by Spiral Upcut - Series 2300

[Treischl]

Now we are getting somewhere!

The last time I was in a pattern shop and they were using a CNC machine to cut the patterns (which was about 20 years ago), they were having their cutting tools custom made. But I am thinking that someone like around Detroit or Pittsburg must make long shank end mills for doing this type of work.

Magnate also has fairly long reach tools and will make custom tools, they supply tools for the Legacy ornamental mill which needs them. You can get larger diameter mills from them for roughing work. MicroCut also comes to mind for fine detail work.

You will really want to look at Magnate, they offer the long reaches in a ball nose style which you really need for that type of work.

Sometimes you can do the work by "slicing" which is done in software. Obviously, that is not an option in pattern work, but can be used in decorative work. Vectric software has that ability.

If you are going to hang cutters out that far, you will need to control the RPM's and the runout of the spindle and cutter, along with the cutting pressure on the tool for obvious reasons.

Hope this helped, I did not realize the scope of your original question.

Edit: I just recalled that when I went in pattern shops, they quite often bored precise registration holes that were used to "build up" the patterns after cutting them on the CNC machines. Some of the patterens would be 20 to 30 inches deep, so there was no way to cut those as one piece assemblies.

[rocketflier]

Edit: I just recalled that when I went in pattern shops, they quite often bored precise registration holes that were used to "build up" the patterns after cutting them on the CNC machines. Some of the patterens would be 20 to 30 inches deep, so there was no way to cut those as one piece assemblies.

Yes, that helps thank you. I was thinking along the lines of multi layer work because I couldn't understand how anyone would be doing it given the machines I've researched. Given the comments on chatter and thinking about a bit that long,.. spinning,.. I've more thinking to do.

20 years,... doesn't seem long, does it? What were they machining back then?