Thinking about designing a 5 axis machine, what about an AB head?

I have been thinking about designing a 5 axis CNC router and I was wondering about designing an AB head rather than the standard AC head. I know, designing any CNC machine is a whole can of worms and it's far more likely that nothing sees the light of day than a machine gets finished, BUT, I do have a question.

Does anyone have links to images or videos of a purely AB CNC machine in operation? One that does not use a C axis at all (i.e. no rotation about the Z axis).
Would Mach4 be able to operate such a setup? I'd imagine an AC setup is more common.

Thanks for any input,

Malachi

never work...1933

Can you clarify what you mean? AB heads must exist somewhere, I just haven't seen any. Zimmermann sells an ABC head and in their advertisement they compare it to an AC and an AB head, so someone must make one.

I've used AC and BC and as posted,AB won't work.

A is X axis rotation B is Y axis rotation. That would require a double jointed head.

Mean while A C or B C means you can rotate around the Z-axis and then tilt in any other axis.

Hi - Is this what you mean't? and what do you intend to machine with it? Usually the mechanics are "easy" but the software is hard...Peter

Yes, I do mean rotation about the X and Y axes. I had a sort of specific use case in mind that I will describe below that makes an AB head seem attractive.

Imagine you were to machine a cylinder whose axis is parallel with the Z axis. I would like to use an endmill to machine the side of the cylinder with the flat of the endmill. On a typical BC head, I would rotate the B axis 90 degrees and progress around the cylinder by rotating the C axis and moving in X and Y as normal. My understanding is that if you wanted to move continuously around the cylinder, you would need slip rings or some other method of supplying power, etc. to the spindle and B axis motor through the C axis connection.

Now, if we instead used an AB head, I think you could complete full continuous rotation around the cylinder without needing any fancy connections. It is hard to picture how this will work and I may create something in CAD to explain. Basically, I think that with at least 180° of rotation on the A and B axes, you can coordinate them in such a way that this movement around the cylinder can be accomplished continuously. From the perspective of someone building their own machine, this narrows some of the mechanical issues of continuous rotation down to partial rotation, which could be advantageous.

I agree that the software would be the difficult part, and I am not well versed in what happens between the CAM and the post-processor as far as how calculations are done for a normal BC head.

My intent with building a custom router is to machine aluminum parts, but I am aware that is not only a high goal for a DIY machine, but particularly so for a 5 axis DIY machine. So even if something like this could only cut foam, I would be happy with that result.

Hi Malac - What you describe needs the C axis? Do you rotate the part? or is the part stationary? Can you do this on a trunnion? Peter

https://www.cnczone.com/forums/attac...d=446466&stc=1https://www.cnczone.com/forums/attac...d=446468&stc=1https://www.cnczone.com/forums/attac...d=446470&stc=1

The first image is the normal orientation of the head if you were to use it like a regular CNC router. The router mount is shown in orange, so normally the bit is coaxial with the Z axis.

The second image shows the milling of the side of the cylinder when you are at 0°. The cylinder is fixed. You can image that as you progress to 90 degrees, shown in the third image, the only axis turning is the B axis in order to keep the flat of the tool tangent to the cylinder. Once we reach 90°, we must rotate the A axis, as well as complete other moves in X and Z, because the B axis has 180 degrees of travel. Then as we continue to progress around the cylinder, the B axis rotates in the opposite direction.

Does this help?

Yes - but you have an inflection at 90deg. The AB can't go round a circle in one go it has to stop and retract, change sides then re-engage to do the opposite side. If the Z rotates there is no inflection?

To best cut the circle the AB will have to do one side (180degs, step down, -180deg step down etc) then inflect then do the other side is this the intent?

Regards Peter

The proposed approach looks like a lot of work to produce a weird and ineffective machine.The fact that the proposed axes don't have a common centre of rotation would make the software more than a bit challenging to develop.there may be a reason why such a machine hasn't already been developed.

Unless I misunderstood, could you not do this by mounting a large rotary table on the machine table and then mounting a normal 4th axis on that? I guess that would be a "CA" concept in your terminology, rather than an "AC".

LinuxCNC would give you the flexibility to define whatever axes you wanted. CAM post processing may be a challenge perhaps?

Quote:

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Originally Posted by nlancaster

A is X axis rotation B is Y axis rotation. That would require a double jointed head.

Mean while A C or B C means you can rotate around the Z-axis and then tilt in any other axis.

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https://uploads.tapatalk-cdn.com/202...d17b8683f9.jpg
Something like this perhaps?
Routers aren’t mounted, but 2 heads are better than none.


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Peter, I was thinking that this inflection point could be handled without having to do a full retraction. You could coordinate motion between the A, Z, and X axes to sort of freeze the endmill in place and successfully rotate the A axis 180°. If you were surfacing something where the angles were less than 90° than this is less of a problem area. I have seen 5 axis heads for waterjets that function as I describe, though they max out at less than 10°.

Routalot, this head from Zimmermann includes a B axis in addition to A and C:
https://www.f-zimmermann.com/en/milling-heads/m3abc/
They seem to have lined up the centers of rotation well, though I agree that it would be a challenge to control something like this.

Muzzer, my intent was to design a milling head that would give the additional 2 degrees of freedom rather than something mounted on a table.

Rob, I can't quite tell from that photo, but are you mounting two routers side by side with each on its own Z axis? I've seen that on production machines but that's not my goal here.

Thank you all for the excellent input.

The Zimmermann head with three axes is a fine piece of engineering.It also has one more axis than you are likely to need,but that wouldn't be the C axis.

Quote:

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Originally Posted by MalachiLandis

Peter, I was thinking that this inflection point could be handled without having to do a full retraction. You could coordinate motion between the A, Z, and X axes to sort of freeze the endmill in place and successfully rotate the A axis 180°. If you were surfacing something where the angles were less than 90° than this is less of a problem area. I have seen 5 axis heads for waterjets that function as I describe, though they max out at less than 10°.

Routalot, this head from Zimmermann includes a B axis in addition to A and C:
https://www.f-zimmermann.com/en/milling-heads/m3abc/
They seem to have lined up the centers of rotation well, though I agree that it would be a challenge to control something like this.

Muzzer, my intent was to design a milling head that would give the additional 2 degrees of freedom rather than something mounted on a table.

Rob, I can't quite tell from that photo, but are you mounting two routers side by side with each on its own Z axis? I've seen that on production machines but that's not my goal here.

Thank you all for the excellent input.

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You’re welcome.
Yes, I misunderstood your direction
My bad!


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I will just leave this here.
https://youtube.com/channel/UC9G-YIPOe7p_KDRTuheotlg