Thoughts on a 5 axis router/welder?

[MalachiLandis]

Peter,

The chinese windlass is also known as the differential capstan, so the reduction is developed not by the ratio of the two spools but as a function of the difference in diameter between them. It's similar to the way a chain fall works. So by having one side of the spool at 1.000" diameter and the other at 0.990" diameter you develop a very large reduction.

Malachi

[RCaffin]

So by having one side of the spool at 1.000" diameter and the other at 0.990" diameter you develop a very large reduction.
Not in my book, or at least I can't imagine how you could use that for a CNC. Oh that it was so easy!
Diagram?

Cheers
Roger

[MalachiLandis]

I don't have a diagram of the exact setup I'm thinking, but it's similar to the chain fall described here:

https://en.wikipedia.org/wiki/Differential_pulley

I will work on producing a better diagram. Sorry for the poor communication.

[ger21]

I used a Monarch VMC 75b when I worked at a machine shop over the summer. That machine was extremely rigid and you could take big cuts with it in steel. However, if my machine is cutting aluminum at best, with likely a 1/4" cutter most of the time, surely I don't need as much rigidity

As Peter said, you need far more rigidity than you think, and with 5 axis, it's far more difficult to achieve.

I've been on this forum for 17 years. I've probably seen less than 5 functional 5 axis machines built. And these were not hobby level machines, but near commercial grade, and far above what you are proposing.
Nobody else has been able to pull one off, other than very lightweight machines for cutting foam.

[MalachiLandis]

Gerry,

I knew that weren't many 5 axis machines that have been made and posted on this forum, but I did not know the number was as low as 5! Does this include all types of 5 axis? I feel like the trunnion style 5 axis machines must be more common. Do you have examples of people making a 5 axis similar to the ShopBot where there's an AC head?

In your opinion, would there be value in building a custom AC head that could be attached to an existing 3 axis machine?

Thanks for your thoughts.

Malachi

[peteeng]

Hi Malachi - The issues with that proposition are 1) 5 axis software 2) machine stiffness 3) getting the extra cabling to the head 4) a "normal" 3 axis machine does not have enough Z to accommodate the extra height needed for the AC head. Malachi you need to develop a machine specification for what you want to do. This will then drive all development in the correct direction. Being a cost sensitive student I suggest you design a machine to performance and forget about cost. It will take you about 6 months and 20 design rounds to sort your first machine. Then you will have a good understanding of the process and pitfalls. Then you can back down to an affordable machine. You have the brain and tools to do this. Anthro. 5 axis , trunnion all have their purposes I think you need a purpose to drive this development.... For instance metals are sort of old hat. Have a look at composite tape laying machines. Composites are the answer to so many problems but we are stuck hand laying (read very many $$$) to make parts. Aerospace and auto have pushed into tape layers big time. General industry needs economical tape layers. They will be 5 axis so that scratches your 5 itch. They either lay directly into a mould or they lay a flat preform then this is draped into the mould. So much scope in this area.... The big machine builders are already making CF composite parts and they will need tape layers...My next big project (after my current Brevis-HD build look for it here) is a mill and that will be all composite maybe I need a tape layer too (called an ATL in the trade automatic tape layer) Peter


https://www.compositesworld.com/arti...tons-and-more-

https://www.sciencedirect.com/topics...ed-tape-laying

[MalachiLandis]

On our robotics team, we find ourselves machining a lot of 2" by 1" or 2" by 1.5" hollow aluminum tubing, 0.125" wall. This is all done on our OMIO x8. What about a 4th axis that the spindle would sit on that would rotate it about the Y axis? That way, you have the tubing set up running along the Y axis and you can machine 3 of the 4 sides at one time. Would be nice for getting bearing bores concentric for the drivetrain. Just spitballing another idea.

That machine shown in your attached image, why is it so beefy? I understand for machining purposes, you need a very stiff machine. But if it's possible to lay tape by hand, I don't understand why it has to be so stiff. I have seen some of the robotic arms used for making COPVs in the aerospace industry. Actually one of my professors is researching COPVs, maybe that would be a source of funding...

Now that I think about it, could the machine do both? As in machine the mold, then lay the tape?

Malachi

[peteeng]

Hi Malachi - In a word NO. machining is a dirty process ATL is a very clean process you never mix these operations. It has to be beefy as it moves fast and has large inertia loads imposed on it, It has to lay a 0.25mm thick tape to better then 0.1mm probably 0.01mm so the tapes are exactly edge to edge, rigidity gives you accuracy. You don't want the head to wobble an iota. You need to get your head around dynamic and static stiffness. Anything that moves needs more stiffness then its static stiffness due to inertial loads, poor damping and other factors like jerk and programming smoothness. You have a long road to understanding so keep at it. Ask people with plasma cutters about wobbly cuts with light machines. There is no contact loads with a plasma (or laser) but they still can cut wobbly... Also you need to flick aluminium and get into carbon for your robotics...Peter

The rule of thumb for machine design is the rule of 10. If you need 1 unit of accuracy you need to build the machine to achieve 1/10 unit accuracy or better. Same goes for stiffness generally you will need a machine 10x stiffer then you "think" you need.

[MalachiLandis]

It seems to me that a machine capable of machining the mold and laying the tape would be attractive as it would combine 2 machines in 1, but you're probably right. I can't imagine trying to get one of those large molds clean enough for laying tape.

Are you familiar with FIRST robotics? You have 6 weeks to build a robot for competition, so not sure if composites will ever really take hold. Plus it's hard enough to get the students to build anything in aluminum.

Malachi

[machinedude]

With plasma a light gantry is needed to get the fast acceleration needed to maintain the high feed rates in the corners so they don't end up blowing out from excessive heat build up when slowing down to make the turns. But at the same time the gantry has to be stiff because the high acceleration rates exert a lot of forces on the frame work of the machine. with lots of acceleration and no rigidity you end up with shutter that shows up in your cuts. so what Peter is saying is are valid points about the relationship between frame stiffness and accuracy. something you don't think about until you see it happen first hand then you put two and two together and it all makes sense.

[peteeng]

Hi Malachi - No but I just looked it up and they also do First in Australia. Einstein said something like if I had one hour to solve a problem I'd think about it for 55mins then solve it in 5mins so your 6 weeks so 42 days so actually you have 3.5 days to solve it heaps.... I worked for a company that bought a large router which also was used as a prepreg cloth cutter. They used it as a cloth cutter primarily. One day they used it as a router and after that they never used the router head again, took a week to clean it up. I think they eventually sold the router head. I've attached a video of a large router which I'm working on commercially at the moment. They are recommissioning it and will upgrade the z axis. The gantry is 7m wide and it has a 3.5m Z. The columns in this case have been moved at 0.2g . The head consequently vibrates for over a second at 17m/s/s to start with which is 1.7g. That wobble creates all sorts of problems for cutting. This is what you are up against.... Peter

Also economically you don't want to be waiting around for the mould to be cut if you have tape to lay or vice versa. A tape layer needs to be working all the time to make $$$. So they are economically and logistically and mechanically mismatched.

[ger21]

I was talking about 5 axis gantry routers, not trunnion machines.

With plasma a light gantry is needed to get the fast acceleration

You don't need light weight to go fast, you just need more power. There are plenty of industrial routers that are crazy fast, and weigh 10,000 lbs or more. And these probably cut much faster than a plasma cutter. 2000 inches/min or more.

[machinedude]

I was talking about 5 axis gantry routers, not trunnion machines.




You don't need light weight to go fast, you just need more power. There are plenty of industrial routers that are crazy fast, and weigh 10,000 lbs or more. And these probably cut much faster than a plasma cutter. 2000 inches/min or more.

yeah that's true but it adds extra cost. with plasma you don't need the extra weight with that process it just has to be rigid enough to suit the need of the task at hand. so my point is just simply know what you need out of it from a structure stand point and make it as big and heavy as needed. with plasma the bed of the table has to support a lot of weight so that part need to be pretty robust but he gantry being light and rigid at the same time allows you to keep the motors a lot smaller keeping the cost of the electronics down.

[hanermo]

What peter and others said re_rigidity is SPOT ON.

Ex.
Don´t think of it as *rigidity* because all Your/our understanding of rigidity from everyday life is completely wrong.

Think of it as strength, and accept that it *needs to* be 100x stronger than the max load you will ever use.
Any commercial machine tool is typically used at max 2% of their "strength".

Strength as in failure point loads aka plastic deformation aka "it broke".

So a modern cnc lathe or VMC machine tool typically uses about 32 mm ballscrews with 1500 kgf max loads, aka max push.
(Lika a HAAS ST10, 11 kW, HAAS VF3, 25 kW, etc.)

The frame is thus strong enough to take about 75 metric tons of load before failing, if evenly loaded.

[RCaffin]

Hi Hanermo

Welcome back!
How are things going? Any pics of your machines?

re 'strength' - it is when you make a programming mistake and plow the table into the endstops with a G0 that you find out about strength!
My mill is not large, but it was designed to take students. Yeah, solid!

Cheers
Roger