Thread: Gantry design question
First post and I'm intending to start my first cnc build soon, I'm starting to design at the moment but something is puzzling me.
Having a very rigid gantry seems to be crucial but all the designs I've seen seem to try and accomplish this by adding huge amounts of material and weight to the gantry which then means you have to start upgrading or doubling up on motors etc.
Has anyone done a gantry design by laminating aluminium honeycomb between either aluminium sheet or carbon fibre?
It would seem to provide a far more rigid solution for any given weight when compared to the mdf/plywood/aluminium builds, am I missing something blindingly obvious or would this be worth pursuing?
The cost shouldn't be that excessive if you look at the cost of honeycomb from easycomposites.
Aluminium Honeycomb Core - Stock Sizes to Buy Online - Easy Composites
MASS makes a great deal of difference to the quality and depth of cut machine can make.! . . Yes a heavy gantry does slightly restrict rapid speeds compared to a light weight gantry but the reality is that most machines spend most of there time cutting not rapiding around. (Some exceptions do apply like drilling lots of holes)
So therefore the heavy stronger gantry with it's Mass can take far deeper cuts and still give a good finish and gets the Job done quicker than a light weight gantry can due to cutting deeper so less pass's.!
The Mass dampens vibration better and vib's transfer to the finish so again better finish.
Don't get caught up in the Rapid speed light weight race it's mainly for bragging rights and very little to do with useful cutting times and quality finish.
Also the doubling up of motors has very little to do with power to move a gantry and everything to do with ease of use and turning 2 screws to allow wide gantrys not to Rack or crab which they would with a single centre or side driven screw.
It's very possible and is often used to drive 2 screws with a single motor connected via timing belts and infact my machine use's just that setup. Timing belts are very accurate and efficient regards power usage and backlash etc so don't be put off using them.
Is the extra mass adding momentum that helps the cutting process, or is it just eliminating vibration? Given the number of minute and rapid changes in direction a CNC machine must go through it seems counter-intuitive to add mass but I really do know nothing about CNC... (Damn it, where is the 'clueless dimwit' emoticon when you need it!) I kept coming back to that design direction especially after reading papers like this:
Interesting paper, but the structure they refer to in there, if I understood it correctly, is actually a support column not the moving gantry itself. While the paper starts off talking about the gantry all the study work is on the column design. So the jury is still out on whether a lightweight CF gantry beam is better. However, the information is useful as regards the gantry supports. The issue however, is for the small sizes we generally build, i.e. a gantry side 300 - 500mm high or so, does the complexity of forming such a structure give any benefit over a slab of 20mm ali?
I've had little contact with CF other than light weight motorcycle components and to be honest other than there light weight I've not been impressed.? The lower grade and quality components like covers, guards and shields etc were brittle and didn't stand friction wear very well.
The high end components like Wheel hubs, suspension parts etc were very expensive and the reason for this is down to the high manufacturing costs thru the need to use vacuum autoclave systems and high grade CF. . . . This really the reason why F1 anything that use's CF costs the earth.
So to me here lies the problem with DIY and CF.!! We don't have the budget for high grade CF and no access to equipment needed to use it correctly and get the best strength and longevity from it.
The honey comb principle I agree with and yes these transfer to CNC no problem and have been for years. IF CF gave any major performance along with even a small cost saving benefit the big boys would be all using it by now and I'm pretty sure there will be a few CF Gantry's, components or full machines stuffed in some corner of some company's R&D department.??
When it comes to Diy then light weight doesn't win over Mass and isn't easier of cheaper to acieve IME.!!
There's always got to be first that takes a gamble so with That said you go for it and we'll all watch learn.!!. . . I for one will be the first to congratulate you if it works and performs has expected. ( I'll do the Nah nah told you so has well. . . Lol)
Wish Good luck if you do.
I think maybe the best thing to do would be to design 2 gantrys, if I can get the cost difference down to £50-£100 I might take a punt just to see what happens. I was orignally intending to epoxy the surface fittings on but if I bolt through the structure instead if it all goes horribly wrong I should be able to fix it by adding a couple of thick reinforcing sheets. ( I'll engrave one with 'JAZZ WAS RIGHT!' if I do just to remind me what to do with my next good idea.)
Welcome to the forum
I am really glad you raised this question, I have thought that a CF Gantry had to be more ridgid than all the ally extrusion, when i was @ the Model Engineering exhibition a couple of year ago there was a turbine driven photo graphic aerial platform (Heli Movie Camera thingy) and its space frame was made from 8mm thick CF composite plates.
I can see no logical reason why an exreemly ridgid gantry cannot be constructed using a mould and the vacuum infusion technique.
I made an item just using fibreglass and @ 12mm thick it was both ridgid and had substantial mass.
If i ever get round to building i would certainly give it a try.
The aluminium honeycomb from there is still a good price though so I may look at doing a laminate design but it would be with thin steel or aluminium not CF, it's a shame but I'll have to shelve it for a few years and see if the price of carbon fibre comes down.
I did find a similar thread to this one on cnczone and apparently there is one company that do use composites for CNC but it is for an ultra precision machine:
DMG | DECKEL MAHO | GILDEMEISTER - HSC 20 linear | Precision Center
There is also this company making ultra high end machine components from composites beams with steel linear rails attached (look at the piccy):
Composite Machine Building Components
They both use composites for extreme rigidity, as do photographers, astronomers, sailors etc etc so I think the idea is sound but the price needs to lose a zero off the end before it comes into the reach of the dirty plebs.
I appreciate the CF rout would be the ultimate material but from my limited experience of working with fibreglass i can see no logical reason why you could not build an exreemly ridgid gantry, the project i tried to construct was a curved concrete mould, but unfortunately i could not get sufficient vacuum on the mould and it resulted in about a 400mm length being correctly cast, however this was both heavy and super ridgid, if you live anywhere near the Barrow in Furness area i would be willing to donate a roll of the FG for you to trial a gantry prototype on the understanding that we have lots of pictures and you keep us all updated, i am convinced this is the way to go, the only downside is the time it would take mould making ect.
Have a Nice Day
Just out of interest what cloth were you using to work out your costs?? For something like this you would really need a lightweight cloth & this is where the costs spiral, not just the fact that they cost a lot more to start with but the fact you need 2 or 3 times the length to achieve the same laminate thickness lol.
Don't hold your breathe waiting for costs to come down, because there is less demand for certain types of cloth less of that type of cloth is woven so costs will always remain that much higher.
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