5 axis question

[turmite]

I didn't know where to put this so I though here would fit the best.

does anyone here have any experience with 5 axis. I am primarily interested in the 4th and 5th axis at the moment and in particular which design is best for stiffness. I am not even sure of the proper names but I think it is trunnion (sp) and yoke. What type of system is used to give them their movements. I have seen pics of them that appears to not have a motor on them at all. If someone here has design their own 5 axis from scratch without using the sat units I would appreciate any input.

Mike

[Dan B]

Hi Mike,

We have extensive experience with both trunion style and rotating head type 5-axis machines.

The trunion style is by far the most rigid and accurate of the various designs out there. If the trunion position is fed back to the machine by use of glass scales, then the machine will be extraordinarily accurate. Our Hermle uses this system and we can put holes in all day long within .001". However, we are talking about a $500,000 machine here. The Haas trunion style machines don't use the glass scales, so the accuracy is not as good. And from what I hear, it degrades as time goes on. But to be fair, it is half the price too.

The rotating head designs sacrifice rigidity and accuracy. While some are better than others, I would be surprised to hear of any that can match the rigidity and accuracy of a trunion machine. Our 5-axis head is capable of around .004" accuracy.

Does this help?

Dan

[Evodyne]

Dan,

I'm sorry, but "trunnion style" to me doesn't mean a thing to me. For the newbs could your make reference to some pics of the different 5-axis configs, or perhaps attach a quick drawing? Like Turmite, I'm looking into what it would take to add this to my design. I was wondering how many different approaches there are to solve the same problem-and their merits/faults.

Lance

[Dan B]

Take a look here:

http://www.hermle.de/fs_hermle.php?sprache=en&page=168

navigate around a bit and you will see some drawings and photos of trunion style machines.

Dan

[turmite]

Dan thanks for the info and the link. Keep watching cause I'll be back!

Mike

[Evodyne]

Ditto on the thanks!

Lance

[Dan B]

No problem. Just ask away, and I'll do my best to answer.

Dan

[jcolley]

Mike,

I am in the middle of a design of exactly what you are talking about. My machine will be used heavily for aluminum and steel, and will experiment with "superalloys" if the rigidity proves to be sufficient.

My design is a modified gantry style using four upright columns to support the X and Z axis spindle assembly. The cradle assembly (I think is what you referred to as trunnion) moves in the Y direction on THK linear ways. The cradle has a rotary stage which positions the A axis +/-120 degrees. On the cradle, a servo driven ratory table handles the C axis.

I debated how to drive the A aixs for a while and decided to custom build the rotary drive stage using a standard fine pitch worm gear and dual worm pinions in an anti-backlash configuration. I plan to use dual loop feedback with rotary encoders both on th servo and on a rotary encoder directly connected to the A axis. The software end is posing the greatest challenge atthis point though, as dual loop is not readily available on an affordable hobbyist scale.

As I have said many times before, I base all my work on absolutely nothing and have zero building experience to this point, just some hair-brained ideas and Pro/Engineer Wildfire to hash it all out for me.

Jim

[turmite]

Dan and jcolley after re-reading your posts and thinking about what I ask...........I think I ask the wrong question. Trunion is not what I am wanting. I think Dan called it a rotating head. What I am looking for is ideas as to how to rotate the two axis and where to mount the motors? I think I can get the torque great enough by using harmonic drives but where do you put the motors?

Mike

[Evodyne]

Mike,

As I have said many times before, I base all my work on absolutely nothing and have zero building experience to this point, just some hair-brained ideas and Pro/Engineer Wildfire to hash it all out for me.

Jim

Well, you've got a lot of company! It's amazing how far a little common sense can take you though (as if I'd know). You'll have to keep us up-to-date: it sounds like an interesting project.

Lance

[jcolley]

If it is a dual rotating head you are looking for, check out this conversion ( 5 Axis ) for a Bridgeport style machine. The best I can tell (guess) is that they use cross roller bearings ( THK ) on the head assembly and using bevel gears on each side about the same size as the outer diameter of the bearings. These two bevel gears would be driven by a bevel gear up inside the stationary part of the head. They would then drive a fourth and final bevel gear on the spindle.

Now the actual axis motion would be controlled by a second set of bevel gears on the rotary part of the head, one for the rotating axis and one for the angular axis. I'd have to think about it for a bit, but it doesn't seem that hard to figure out.

I actually have no idea how the one in that link works, but that makes sense to me and if I designed it, that's how it would work.

Again, reference my first post for my actual qualifications to speak here...there are none...

Jim

[Evodyne]

Dan and jcolley after re-reading your posts and thinking about what I ask...........I think I ask the wrong question. Trunion is not what I am wanting. I think Dan called it a rotating head. What I am looking for is ideas as to how to rotate the two axis and where to mount the motors? I think I can get the torque great enough by using harmonic drives but where do you put the motors?

Mike

Mike,

Despite exposing my complete lack of artistic ability, I thought a scribble might stimulate a little conversation. No laughing! Even though this might well be a new low for attached "artwork", it's the thought that counts, right? BTW, it's still a little early to tell, but I think I scored a couple of harmonic drives! Boy will I be honked if I DON'T get them. Any how, take a peek and let's do some brainstorming...

Lance