[Tom Brown]

Fiberglass can be extremely strong, if done properly. Perhaps some stressed fiberglass skin panels with foam or wood core would be a good material choice for some components of a DIY CNC router project. Not the bed but perhaps uprights and/or bridge.

Has anyone tried it? Any thoughts?

[JerryFlyGuy]

I haven't built a fiberglass CNC anything.. but I have built a fiberglass airplane . My recommendation would be to skip fiberglass and go w/ Carbon. For the same thickness you'd be way stiffer than glass. You could also use Kevlar 49 [or is it 29?] in it as well, Kevlar is known for its vibration dampening properties, which would be a great asset on a mill or router. I'd build the basic structure out of carbon and foam, then just wrap it in kevlar [little if any cutting of the kevlar if possible as its a realy pain to cut] and then cap that all w/ either carbon or glass.

There's no doubt that it could be made strong enough. Alot of cars now have the structural support in their bumpers, made from glass. As well as the impact beams in car doors are built w/ glass.

It wouldn't be cheap however.. But if you were going to do PCB milling or light engraving and wanted a super fast machine.. it'd be the way to go for sure. Imagine 0-1000ipm in 1/4" inch.. that'd be some acceleration eh?

My 2 cents..

Jerry [someday I just might have to try this ]

[thekm]

I'm also into planes, and about to make a machine... and it'll have glass all over it.

Carbon and Kevlar are stronger, but multiples of the price. We're not building a plane, so weight isn't quite the premium... so... with a wodden substructure, and a glass shell... methinks it'll be generally improved for the effort that goes into it. I'm also going to laminate thinner plywood pieces either side of glass and then glass the exterior... it should make the whole thing very stable to things like moisture or whatever.

...anyways, fiberglass? yes, have some!

[JerryFlyGuy]

Carbon and kevlar will be more money per foot/yard. But I think the $/psi strength actually isn't that far off. In other words, to get the fiberglass structure to be as stiff as the carbon or kevlar one, the price won't be terribly different. If you've already got the Fiberglass I'd say go for it

As far as your structure, if your using wood as a base, don't bother putting glass between pc's of wood. You'll not see any increased performance. Just bond the pc's of wood together and put the glass on the outside. If your taking about a cavity structure [ that is hollow] then glass on the inside is probably a decent idea, that is.. if mositure can get in there to attack the wood. If its an entirely sealed box, I'm not sure you'll see any advantage.

Jerry [2 more cents ]

[ger21]

This guy intends to build his machine from carbon fiber after he gets the mdf mockup running. Slow progress, though.

http://www.cnczone.com/forums/showthread.php?t=6840

[dertsap]

i've fibreglass coated a previous mdf gantry i had built ,took a fair bit to break it up to through it into the garbage bin , it was tuff and waterproof ,which was the reason i did it , lots of moisture in BC

[Splint]

Keep in mind that resin shrinks over time, as much as 5% which may be an issue for accuracy. Glass over an mdf frame would be better than pure glass as the mdf will help control shrinkage but use some thaught in the design so that whatever shrinkage occours it is exposed as equally as possible over the whole machine so that it dose not warp or bow.

Cheers
Splint

[mxpro32]

if you use epoxy resin you won't have the shrinkage issue. however, the cost will be greater.

[thekm]

Some interesting opinions, and it's good to hear dertsap's clarity of experience... it also mirrors everything I've ever done with fiberglass myself.


The gantry box has the most to gain from it. I'll be making each panel out of laminates with two layers of different oriented glass in the middle. This will make each panel much stronger alone than just an equally thick piece of wood that would be the result.

However the most strength will be gained after assembling the box, if the outside is given a shell of a couple of layers of glass: it will become very rigid. Carbon and Kevlar would be overkill. In fact, Kevlar wouldn't really provide any more strength at all, as it has different properties, and is best at resisting shearing forces. Carbon is more rigid, but for this purpose, a waste of money... carbon is much dearer lately.


Regards shrinkage... this glass CNC beast will be a fiberglass shell around a heavy enclosed wooden structure... if it shrinks it'll actually make the thing even stronger! (because the glass is strinking around the structure, making it all tighter)

...eitherway, I'm up for a bunch of glassing when the time comes.

[Tom Brown]

Kevlar is a lousy material for a router. It is strong in ways it doesn't need to be for a mill project and not strong in ways a mill requires.

Carbon fiber is more rigid than glass but expensive. I think glass could do a very good job if done properly. Vacuum bagging would be a given, on account of the high frequency vibration it would be subjected to.

One of the things that made me think of glass is that I cut a lot of aluminum and sometimes I use carbide tipped wood tools like the table saw. A carbide tipped blade or router bit will cut aluminum like butter as long as you keep the blade lubricated with WD-40.

I intend to build the Joe 2006 r2 CNC router but I worry about the compatability of MDF and WD-40 or other lubricant.

[JerryFlyGuy]

Guy's can you explain a bit more why Kevlar is such a bad choice for a mill? I'm not following. Anything that I've read would lead me to think it would be a great choice for a fairly stiff structure which needs as much vibration dampening as possible.


Curious..

Jerry

[Tom Brown]

The disadvantages of kevlar are poor compressive qualities, it is stretchy (particularly grade 29), the fibers absorb moisture, very difficult to work with (difficult to cut and drill through, even when cured).

Being so nasty to work with is what makes it great at what it does best. I've used it on boat keels and areas where abrasion resistance is desireable.

I think epoxy/glass is the answer. It's cheap and extremely strong.

[JerryFlyGuy]

Tom, I guess it depends on how you look at the picture.. [half empty or half full] I can see area's where it wouldn't be the best but I can also see where it'd be great.. anyway.. To each their own..

Jerry

[miljnor]

Weight is generally an asset to machinery as it dampens vibration and stops machine movement. The weight is a big benefit to smoothness of cut.

Of course the same thing that gives you the benefit causes a lot of grief. i.e. accel/deccel allot of mass takes some $$$.

I personally hate working with resins and what not and find steel and aluminum very friendly, but if you don't have machinery to start with the glass/carbon route will get you up and running, so I say, Go for it!

[thekm]

Kevlar's tension strength is awesome, but we're not talking about excessive loads for a machine. Sure, discus launched RC gliders need a bundle of tension/torsion strength in the wings at a minimum weight, so kevar is in its own. But, as for glass on a CNC machine... it's just not the same beast. My suggestion isn't really to replace a great deal of the wooden structure with glass... just to make a glass shell. Vacuum bagging would also be over the top, as the big benefit from that for composites is to remove all possible excess resin as well as improve adhesion to whatever you're quishing against it, but it's mainly about removing excess resin. Here, we don't need that Nth degree of weight reduction, and adhesion wont be hard. Just roughing up the surface with sandpaper, squish resin into it, then lay up a couple of layers of wet glass, and squegee out the excess, make sure that it's all laid down properly... let this dry, and voila.

Composites on a machine would be great, but I don't think there's any need to get fancy on it to get the benefits.

[dertsap]

Tom, I guess it depends on how you look at the picture.. [half empty or half full] I can see area's where it wouldn't be the best but I can also see where it'd be great.. anyway.. To each their own..

Jerry

aluminum would be far better and cheaper alternative to Kevlar ,it s a pretty simple question the man asked , it sounds to me he has a project that he would like to be cost effective with the use of everyday materials



[half empty or half full] logic can pick apart that text book question

[lgalla]

Fiberglass and polyester would shrink too much and warp the substrate,unless the two skins were in perfect balance.Epoxy is a better choice.Carbon or kevlar would be too costly.Aluinium plate would be cheaper.Besides there is a world wide shortage of carbon fiber almost impossible to get.
If you want to make an extremely stiff panel laminate 3/4MDF both sides with .050 formica It will be so stiff if you knock on it it will ring like steel.Also it will not be messy like raw fiberglassing and look good to boot.
Larry

[dertsap]

Fiberglass and polyester would shrink too much and warp the substrate,unless the two skins were in perfect balance.Epoxy is a better choice.Carbon or kevlar would be too costly.Aluinium plate would be cheaper.Besides there is a world wide shortage of carbon fiber almost impossible to get.
If you want to make an extremely stiff panel laminate 3/4MDF both sides with .050 formica It will be so stiff if you knock on it it will ring like steel.Also it will not be messy like raw fiberglassing and look good to boot.
Larry

i disagree ive worked a lot with fibreglass and can t see that as being an issue ,as far as epoxy goes , the stuff is tuff but absolutely sucks to sand off the runs and any uneveness on the surface ,though an excellent alternative,
a laminate would make a nice table top (router) but if a guy isn't carefull he can easily warp the structure while applying the laminate ,more so than fibreglass

[OCNC]

If you want to make an extremely stiff panel laminate 3/4MDF both sides with .050 formica It will be so stiff if you knock on it it will ring like steel.Also it will not be messy like raw fiberglassing and look good to boot.
Larry

I've always wanted to try vacuum bagging two Formica skins to an MDF panel using epoxy resin as the adhesive. Has anyone tried that? The vacuum bagging would just be for uniform clamping pressure. It seems like it would be many levels stiffer than using contact adhesive.

Chris

[lgalla]

Yes Chriss that is the way to do it for max strength.I have been vacuum bagging fiberglass for 30 years and for quick, cheap, not dirty ,formica on MDF with epoxy adhesive, vacuum baged is the way.I did not suggest bagging as I dont know how many members are familiar with the process.Chriss,give it a try if you have the equipment.It will only cost a couple of bucks and you will be amazed.