[flojor10]

So I was thinking if I ever became a millionare one thing I would do would be to build the best Cnc machine ever! So I started thinking about characteristics I wanted and of course speed, what my current machine lacks. So would a carbon fiber moving gantry be something to consider. I mean the material is amazingly stiff and lightweight. I also thought it might contribute to resonance, and weight could help, how much weight is desirable on the gantry to have a sturdy machine? And if anyone else has any ideas to make the best Cnc machine ever we'd love to hear them.

[Devastator]

And if anyone else has any ideas to make the best Cnc machine ever we'd love to hear them.

One word.....Titanium.

[CarveOne]

One word.....Titanium.

Titanium is a distant second place to Unobtanium, but I hear it is having supplier related problems at the moment.

[RomanLini]

CF and Ti are both very springy and that's not great for a CNC machine.

What you need is something very rigid and inflexible, like stone. If you need something lightweight as well to get high performance you could use some type of hollow structure made from artificial "cast-able" stone like epoxy granite.

Or box section aluminium for lightness combined with some partial fill of a rigid material like epoxy granite.

[Caprirs]

All the big machine tool builders have settled on cast iron as the best material for numerous reasons. These are builders who sell the machines for over one million dollars per machine.

There is a tendency by some to try to reduce the weight/mass of the machine tool but this is exactly the opposite of what makes a machine tool effective. Generally, cutting performance is what matters most, not speed. If it needs to position faster, bigger servos are used.

Carbon fiber can be stiff if the fibers are arranged carefully but still lacks the mass machine tools require to dampen vibrations from cutting tools.

Titanium, although lighter than iron, is not as rigid. And again, there is less mass to dampen vibrations.

The machines that can benefit from lightweight components are those where no cutting forces are involved such as laser, plasma, and water jet.

[louieatienza]

I would agree with the others here that mass can be your friend. As far as titanium, it is lightweight and strong, but also springy and resonant. There's a reason that to this day cast iron is used, for it's excellent vibration damping properties and strength.

Anyways if you had the resources, you'd probably be able to have your machine made of cast iron and all bearing surfaces hand scraped, got the heaviest duty linear roller bearings, ground ballscrews, and drive them with powerful and fast servos. The high end machining centers are capable of moving 1-ton blocks and more at ridiculously high speeds... DMG has a 134HP spindle available for one of their machining centers. The sky's the limit!

[thefu]

the cnc plasma table i built here in my shop, at first was built lightweight. I had issues with vibrations as the gantry moved and changed directions. few tons of steel added later to the table and beefed up the gantry substantially also increasing the motor size..problem solved, now i can change directions at 360ipm with no hint of vibrations in the water table weight is your friend!

[flojor10]

Guys, I like how there were a bunch of ideas you came up with: titanium, unobutainium, epoxy granite, cast iron, and aluminum. So in essence the two best materials are epoxy mixed with anything else and metals. You guys said there are two things a solid gantry should have, strength and weight, if I was a millionaire I would add one more, good looks! There isn't one person who doesn't like the look of cf, I need to incorporate cf in the build at least on the outside. I've never worked with it, so suggest processes to add weight to a carbon fiber shell or to add carbon fiber to a metal or epoxy granite frame. Also I want to here some other unique ideas to make the best Cnc router possible, I like the 134hp spindle.

[RomanLini]

I don't think you need to go as "tons of cast iron" unless of course you want to machine metals.

As you posted in the Router Table Machines section of the forum I imagine you are talking about a high speed machine for routing wood and plastics, or maybe light cuts in aluminium?

If I wanted a fast and quite rigid machine I would copy some of the commercial machines made from welded steel box tube like this one;

[compositepro]

Carbon Gantrys are already in use

I tried to drop this hint in the epoxy granite (theoretical as no one has made anything thread) its not rocket science its composites

[crane550]

I think carbon fiber would just be a gimmick. I would stick to cast. Also concrete/epoxy machines have promise.

Weight is your friend. When people say they want a "lightweight" machine all I hear is flex.

[bebob1]

carbon fiber might have its place in some CNC machines. Its high strength to weight ratio makes it more ideal for CNCs that need high speeds and lower overall machine strength, e.g. Dedicated wood or plastic cutting. Or if its used in a laser cutter it will be great.

[OCNC]

I think what you're really looking for is stiffness. The problem with light weight stiffness is that it's susceptible to resonance. It's easier then to go with heavy stiffness as in cast iron, steel etc. If you can model the resonance issues accurately though there should be no problem with light weight stiff materials as in carbon fiber, titanium and of course unobtanium.

Chris

[bebob1]

All structures have resonant modes and resonance occurs under dynamic loads. Theoretically a mechanical structure has infinite number of modes due to essentially infinite degrees of freedom.

A light and stiff structure has higher resonant frequencies than the same geometry of a low young's modulus and higher density material.

Resonance is not an issue if dynamic loads are not at the resonant frequency. Sometimes you cant avoid resonance for example due to an impulse such as an instantaneous strike has all frequencies. But you can damp the vibrations out to make their magnitude of oscillation essentially negligible given the acceptable accuracy required.

[louieatienza]

I think though in the end aluminum and steel are so much cheaper, easier to work with, and proven for what most DIYers use CNC routers for.

To give an example, Onsrud's Extreme Series fixed bridge router is capable of over 6000ipm rapids and up to 4000ipm cutting feedrate. The 40HP spindle alone has to weigh a couple hundred pounds, let alone the other parts of the carriage and other spindles (line boring head, etc...). There's no carbon fiber anywhere on the machine. If CF was such a benefit to a woodworking machine they'd save money and use smaller servos to move that carriage.

I could see composite parts used in vinyl plotters, plasmas, lasers, waterjets, pick-and-place machinery, etc. where acceleration and speed are beneficial, and there is no heavy forces placed on the drive system.

I guess you could wrap metal parts with CF to make a cool looking design, but I don't know if the benefit would outweigh the cost....

[bebob1]

yeah and carbon fiber can be a PITA to create parts out of. Requires more steps and unconventional techniques to cut fibers and to impregnate with resin and cure etc. Also you are likely gonna need more assembly of parts when using carbon fiber vs machining it out of a single block which may cause engineering issues too due to need for more assembly.

[shedbob]

Check out the links composite pro gives on the epoxy granite thread,post 4645 page 388.
They show strength,weight and damping advantages of carbon fibre graphite materials.
Great if your a big company with lots of dollars for r+d and good engineers.Cost,design
and construction inexperence sadly put it beyond my understand the
principle/empirical/experimental approach though.

[CaptainVee]

I think though in the end aluminum and steel are so much cheaper, easier to work with, and proven for what most DIYers use CNC routers for.

If CF was such a benefit to a woodworking machine they'd save money and use smaller servos to move that carriage.

I could see composite parts used in vinyl plotters, plasmas, lasers, waterjets, pick-and-place machinery, etc. where acceleration and speed are beneficial, and there is no heavy forces placed on the drive system.

This and what others have written is conventional thinking to reason why new and unconventional ideas will not work.
Not that conventional thinking is bad but if you want new ideas to work out you will need to use new ways to get to the desired result. Conventional thinking will be in your way.

When the first boat was proposed to be made from steel the designer was laughed at because everyone knew that steel does not float.

I have developed a system in composites for leisure boating that had been made in welded stainless steel and/or (cast) aluminium for decades. In the process I have reduced the number of custom made parts by about 50%, cutting weight and cost significantly.

Based on what I know from that, and cnc, I think that resonance is the only problem you may face when building a cnc from CF.
And that will only be known if someone will try it.

And it may be unsure if that is a BETTER cnc (in any way) than heavy ones that are common.

[rowbare]

Check out the links composite pro gives on the epoxy granite thread,post 4645 page 388.
They show strength,weight and damping advantages of carbon fibre graphite materials.
Great if your a big company with lots of dollars for r+d and good engineers.Cost,design
and construction inexperence sadly put it beyond my understand the
principle/empirical/experimental approach though.

The CF comes out looking pretty good there but they cherry picked the other items in the comparison. Yes it did better than steel but steel rings like a bell. I think the conclusions of a damping comparison to grey cast iron or E/G wouldn't look so good.

That said, I have often wondered how a machine with an E/G bed and a CF gantry would perform. The bed's weight and damping would keep the machine stable and the light gantry could be accelerated at insane rates. I suspect it would be something like a race car though. It would work very well within its design parameters but be a pain to use outside of them.

bob

[OCNC]

When the first boat was proposed to be made from steel the designer was laughed at because everyone knew that steel does not float.

I hope this isn't true...as it was well known for a long time before the introduction of the steel or iron hull that the weight of the boat only need be less than the weight of the volume of water that the hull shape will displace. Successful metal hull building was I believe more a matter of construction methods than an understanding of hydrostatic principles.

Chris