Carbonfiber Gantry

[Jeff0000]

i used to demonstrate to people my carbon fibre bicycle wheels strength by kicking them as hard as i could. they were long fibre reinforced nylon, not woven - basically bulk moulding compound, not unlike what the tub and suspension arms of the lamborghini sesto elemento are made of.

if its made correctly, impact is a non issue. put an outer layer of basalt veil and neither is abrasion.

basically, much like casting iron, or designing a high end steel structure, you arent going to do this without good engineering and the right tools.

Now take a chunk of concrete and give that wheel a nice little rub, and then kick it.

As you said though, just pair the electronics for the weight, will surely be cheaper.

[ihavenofish]

Right. CF is not usually the only material used. Wing builds and other products I have seen that use CF also use foam core, honeycomb board, fiberglass etc for some of the structural parts. I am not sure just how many layers of CF one might need for a rigid gantry, but if it was covering some other material, then that would certainly lessen the layers needed and thus the cost.
I think the better idea would be to size the motors and electronics according to the weight of the gantry. That works very well.

hexmc has isotropic properties very similar to aluminium. regular carbon of course depends on how you lay it up, what epoxies are used, what grade fibres, etc. i dont think id do this without high grade materials and processes. a wet layup of cheap carbon would probably be very disappointing.

[ihavenofish]

Now take a chunk of concrete and give that wheel a nice little rub, and then kick it.

.

i hit many a rocks and wedges tree branches into them - the tree branches lost. i think you have a misguided notion of how carbon objects are made outside of the hobby sphere.

a normal bicycle frame, like those in the tour de france is made of a few thin sheets of unidirectional carbon, moulded to thicknesses sometimes less than half a mm. because each layer is effectively independent within the epoxy, the shear strength between those layers is limited to the strength of that epoxy. when you hit one of those, hard, the layers can delaminate, but the fibres dont break necessarily, but the frame is destroyed.

when you talk about things like a carbon gantry, you are dealing with structures that are firstly, very thick. the dmg gantry is probably half an inch thick carbon. delaminating that is an impressive feat, as i dont even think a 9mm bullet would make its way through. but on the industrial scale, like my wheels, WOVEN carbon is not going to be your primary material. moulding compounds are isotropic, or semi isotropic. there are no layers. there is nothing to delaminate. the fibres are also not continuous, so cutting one, or 2, or 10000, at the surface will have minimal impact on the overall strength. it does NOT create a significant weak point.

add that to the fact that the gantty is not in the line of impact with most items on your machine - often in fact covered up entirely - i think you are overplaying this quite alot.

[1Jumper10]

Interesting posts.

I'm still pretty intrigued and not dissuaded at all by the negatives that have been mentioned. For the DIY hobbyist it would probably only be worthwhile if the goal was to build a machine that accelerates very rapidly. I guess if your gantry could move very fast the limiting factor might then become spindle horsepower. But for 3D files, where there are lots of small movements that are too short to accelerate all the way to the programmed cutting speed, a quick gantry would save a lot of time. I know enough to know that I don't have the knowledge or ability to make one myself. But, I am in contact with one of the companies linked in this thread over in the Czech Republic that makes CF gantries. We'll see what they say. Maybe its not cost prohibitive.

[whimsical]

Interesting posts.

For the DIY hobbyist it would probably only be worthwhile if the goal was to build a machine that accelerates very rapidly.
for 3D files, where there are lots of small movements that are too short to accelerate all the way to the programmed cutting speed, a quick gantry would save a lot of time.
I am in contact with one of the companies linked in this thread over in the Czech Republic that makes CF gantries. We'll see what they say. Maybe its not cost prohibitive.

I have had it set at about 50mtr/min with very aggressive accelerations but slowed it down as it scares people
The 3D carving is the main reason I want it fast, especially for the Z.
Lots of luck getting a specialised part made cheap in solid carbon. They hear a customer ask about a full carbon part and they go immediately to the exotic car sites and start thinking about their next toy. Well it sure seemed that way when i was pricing a couple of free standing full carbon Masts and booms for the boat build.

[1Jumper10]

I know. But it cant hurt to ask.

[ihavenofish]

I have had it set at about 50mtr/min with very aggressive accelerations but slowed it down as it scares people
The 3D carving is the main reason I want it fast, especially for the Z.
Lots of luck getting a specialised part made cheap in solid carbon. They hear a customer ask about a full carbon part and they go immediately to the exotic car sites and start thinking about their next toy. Well it sure seemed that way when i was pricing a couple of free standing full carbon Masts and booms for the boat build.

engineering and tooling is complex and expensive. the end parts are somewhat cheap - at least small ones. figuring out a diy solution is the only way "we the people" would get this. the recipe i posted would be a starting point, though its still invariably going to cost more than all the traditional alternatives. you have to weigh that extra cost vs that gains in performance.

[whimsical]

engineering and tooling is complex and expensive. the end parts are somewhat cheap - at least small ones. figuring out a diy solution is the only way "we the people" would get this. the recipe i posted would be a starting point, though its still invariably going to cost more than all the traditional alternatives. you have to weigh that extra cost vs that gains in performance.

Lot simpler to use the method i did.
It is 16mm endgrain balsa with 600 gram epoxy skins each side. cost about 370aud for an 1200x2400. A roll of 50K carbon tow is about 300aud a spool weighs about 5kg and if used where it does the most good adds a huge amount of stiffness. Add in some epoxy and a bit of biaxial cloth for the taping and it is not that dear. Construction is just some rectangles glued and taped together. I put a diagonal inside the beam and can not really see any deflection jumping up and down on it. Proper tests and measurements to follow.
It was cheap for me as most is left over from the cat

[CaptainVee]

I on and of worked on a cnc that was aimed at being relatively light weight.

Went from Glass fiber reinforced epoxy concrete to steel to finally aluminium.
The last two steps were after a guy pointed out to me that no matter what you build, it will still come down to the mix of weight, stiffness and price and build time.

Only when a gantry needs to be super light weight, carbon fiber may become an option. And then it will be hard (probably even when used to the stuff as one of the previous posters must be , time consuming and expensive to build, compared to steel or aluminium.
Maybe if you need a cnc that approaches the speed of pick and place machines it is useful.

I'm now building building in aluminium box section and tooling plate.
Very quick, cheaper than epoxy concrete and super precise.

Oh, and not very heavy. It is 1250x1250 mm weighing about 300 kilos.

[ihavenofish]

well, there is a reason almost all machine are iron. its still the best mix of price, mass, damping, and ease of construction.

carbon is entertaining for something like the machine ive been mocking up (but am far off from building) which is very small, powered by linear motors, and could run at 3000-5000ipm, and 3-4G acceleration. but even as i think about it, i see issues using carbon (well, more issues with the epoxy). the biggest one is deformation under high heat where the motors connect. so ultimately that machine may end up being made of iron as well.

[nummi]

As I see it, small damage in CF won't cause failure in gantry. CF is often used in places where a large part of it's strenght is used regularly and that is why even small damage might cause failure. As gantry CF would be used as any other material using it's stiffness and only small part of total strenght.

[wizard]

There is another issue that people might not be acknowledging, going fast is hell on your linear bearings. So if the reason to go to carbon fiber is to go fast, I'm not convinced it is worthwhile. At least not in a normal cartesian arraignment of a machine tool.

[ihavenofish]

There is another issue that people might not be acknowledging, going fast is hell on your linear bearings. So if the reason to go to carbon fiber is to go fast, I'm not convinced it is worthwhile. At least not in a normal cartesian arraignment of a machine tool.

most industrial high end routers, and some mills, go 3000-5000ipm. some lasers move upwards of 10000ipm. caged linear bearings seem to be quite happy with high speeds. some of the max ratings listed for bearings are in the 600m/m range, that's up to 20000ipm.

highly preloaded and non caged bearings would have a much lower maximum limit. caged balls rub against each other generating a lot of heat and wear.

think of it this way. a 1" angular contact bearing in your 24000rpm spindle is effectively moving at over 75000ipm.

[ger21]

linear bearings will last a lifetime at 2000-3000ipm in a DIY machine.

[keffer322]

I am currently building a fixed gantry mill and am using carbon fiber to cover the quartz counter top I am using for the build. The local quartz dealer has remnants for $10 a square foot so I have all the material I need for the build for $270. The mill has a cutting area of 20" x 20" by 8". The carbon fiber I am using is 0.011" thick and the 10 yard roll I purchased is 60" wide, cost was $220. The gallon resin I just purchased should cover the 150 square foot of carbon fiber and was $150 with the pumps. So for a cost of around $700 for the frame materials I think its very competitive with other materials. The quartz is less stiff than aluminum on its own but when you add 8 layers of carbon fiber it is stiffer. The two materials complement each other with the carbon on the outside in tension and the quartz on the inside in compression. I have read that epoxy quartz is twice as good a cast iron in vibration dampening. One disadvantage is that you have to add inserts for all your tapped holes then go back and drill and tap after the epoxy has set. Anyway I am having fun with the build so far.

[1Jumper10]

Sounds pretty interesting. Do you have any pics?

[keffer322]

I am documenting the build here in this thread - Quartz Counter top for Mill Base.

[peteeng]

I've read this whole thread. And the thing that keeps coming to mind is that cf is damaged so easy and it's nearly impossible to fix once damaged. So why would you want to use it where a little bump can cause significant damage?
I've done enough maintenance in machine shops to notice one thing, not a single one looks showroom condition.

I know this is old but CF is easily fixed if damaged. In the case of a machine part firstly you would dress it just like a damaged metal part and leave it be. The CF part is likely to be very well over designed for stiffness which means its uber designed for strength. CF is ideal for making machine parts, its come of age and understanding. The argument that weight is great is an old paradigm. Modern design using simulation can sort all sorts of vibration issues before the build. If you build a straight rectangular CF tube you will not compete with aluminium but if you build a mould and have all the required features for fittings, taper the part and have very little post work then you will be well ahead of any metal for the job. To build such a mould means you would need to make many parts so for a one off part this is prohibitive. Peter

[wizard]

You have waken up an old thread here.

The negative with respect to CF are many when it comes to home built machines. One of the biggest problems is finding good information on its usage. It isn’t like metal working where literally hundreds of resources exist to assist even a novice builder. This especially when you consider very viable machine structures can be created with out computer intensive modeling of the structures. Consider my local situation where literally hundreds of machine shops and various sheet metal and allied shops exist. If you are willing to pay for it you can easily have critical work done for you. With CF I know of no local help if I wanted to go that way.

Understand here that I’m not knocking CF, in fact I’m always interested in alternative ways. The problem isn’t so much the positives with respect to carbon fiber but rather the lack of experience and the potential to waste a lot of money. In this respect I’d like to see a well documented build that would allow one to learn the techniques from the ground up.

I know this is old but CF is easily fixed if damaged. In the case of a machine part firstly you would dress it just like a damaged metal part and leave it be. The CF part is likely to be very well over designed for stiffness which means its uber designed for strength. CF is ideal for making machine parts, its come of age and understanding. The argument that weight is great is an old paradigm. Modern design using simulation can sort all sorts of vibration issues before the build. If you build a straight rectangular CF tube you will not compete with aluminium but if you build a mould and have all the required features for fittings, taper the part and have very little post work then you will be well ahead of any metal for the job. To build such a mould means you would need to make many parts so for a one off part this is prohibitive. Peter

[peteeng]

Hi Wizard - I appreciate what you say. You either jump in or stay with what you know. Depends on your nature. Happy to answer Q's on composites, pick a part and we'll talk it through. I started making steel bicycle frames some 30 years ago, then CF frames then decided that was too hard so built 1000's of aluminium frames then moved into marine composites then industrial composites. Now I'm commercially into huge steel mining machines, the wheels turn.....and my own small CNC machines... Been an interesting journey. Peter