MDF/Plywood able to work aluminium?

[Chrjensen]

Hi there,

I'm completely new to this, but I really find the idea of making a CNC machine an extremely interesting challange. Also, I could really use a CNC router to make some stuff for another hobby of mine - amature telescope making. The problem here is that I really need to be able to mill aluminium parts before this gets interesting.

What "grade of build" would be the minimum to work aluminium? I'm looking for something fairly simple and cheep - constructed mainly from MDF or plywood - as a first build to learn the technique. However, I'm not shure if such first build would be able to work aluminium at all?

Thanks in advance!

[hemsworthlad]

Hello,

Mdf or ply wood really are not very good materials for a machine capable of machineing aluminium, great to learn the basics cheaply but just not strong or stable enough for milling aluminium accurately.
I would recommend you either forget the wood and go straight to Steel/Aluminium for a frame work or forget about milling Aluminium build the cheaper Mdf/plywood machine as a learning exercise and then plan the stronger machine when your more informed.

Personally I would go straight to the stronger machine and take it slow, ask loads of Q's on here and learn from other builds.
This is what i did with no prior knowledge or experience of Cnc and my machine mills aluminium effortlessly and i,ve even just recently used it to mill mild steel without any problems so it can be done as a first timer.

The only other thing i would add is that to do it properly (and you will need to do it properly if you want to have any chance of machineing aluminium accurately enough for telescopes) it wont be easy to do it cheap..?
The words CNC Aluminium and Accurate and Cheap tend not to go well together.!!

Good luck it,s worth the trouble and it's very rewarding, BUT BEWARE very very very addictive.!!

[metalworkz]

Hello,
I think hemsworthlad makes some very valid comments regarding the use of MDF etc. for a machine to cut aluminum accurately. However, I do believe it would be possible to construct a machine for example from a laminated MDF and aluminum sheet stock that would in turn be very sturdy and very strong. I don;t know if anyone has attempted a build similar to this but I think one could greatly increase the strength and wear properties by laminating either a plywood or MDF and aluminum sheet metal. I have not done any build like this yet but now that I am thinking of it I may try to incorporate something like this into my next CNC build. Both the wood and the fairly thin gauge aluminum would be workable on a small CNC router with conservative feeds and speeds, and laminating them should not be too difficult. Just another idea to perhaps get enough strength and accuracy out of your build.
Regards,

[guerd87]

There is a build thread of a DIY MDF CNC over at overclockers.com.au that uses laminated MDF panels for strength.

http://forums.overclockers.com.au/sh...d.php?t=787067

Its currently not finished yet but seems to look very strong, I think the idea behind it was to try and make a CNC capable of doing light alloy work on the cheap. Not sure when he is going to finish it, he is working on some electric powered bikes etc for him to get around on currently.

Here are some various pics from the build

http://members.ii.net/~aussiejester/...n_IMG_2437.JPG

http://members.ii.net/~aussiejester/...n_IMG_2447.JPG

http://members.ii.net/~aussiejester/...ries_pic_3.jpg

http://members.ii.net/~aussiejester/...ries_pic_4.jpg

http://members.ii.net/~aussiejester/...ries_pic_6.jpg

[metalworkz]

Hello,
His build looks very strong but I don't see any aluminum sheet included in the laminated parts. I think the aluminum sheet laminated to the wood and perhaps on the outside surfaces might really beef things up and add the strength needed and basically be similar to a thick aluminum flat stock in thickness and appearance. It would produce a much tougher wearing surface than wood alone and could be finished or left bare and possibly polished. It will no doubt cost a bit more than wood alone but may be a lot cheaper than going for the solid aluminum construction.
Regards,

[guerd87]

Just re-read your post and figured out what you ment with the MDF and Alloy.

I was thinking you were just talking about Laminating 2 pieces of MDF, which is what he has done.

MDF + Alloy together would be quite good

[ger21]

Unless you're talking about 1/8" or thicker aluminum, you can get similar strength using plastic laminate (Formica) instead. It's also easier to work with. and easier to bond than aluminum.

I've been working on a design for a few years now of laminated wood and epoxy construction. They make 100 MPH and 1000HP racing boats out of wood and epoxy, so I think you can make a pretty rigid CNC from the same materials.

If going the MDF route, instead of using 3/4" MDF, you can laminate 3 layers of 1/4" MDF and you'll get a much stronger panel.

It's not so much the material used, but the total design.

[Chrjensen]

Hi guys, thanks for the advice.

So, to get this straight, the problem with working aluminium is to get the construction stiff enough? How about the linier movement system? The kind of linier rails used for "real" machines is a heck of a lot more pricy than e.g. a skate system made with ball bearings and steel pipes. Would the skate system be no-go for a machine with the capability to work aluminium?

Btw, you would be surprised that accuracy, while of cause desireble, is not that importent for making parts for telescopes.

Also, some of you are talking about laminating plates for stiffness. Have you considered carbon fiber? It's not that hard to do (except that the resin coating can be quite messy). This material is often used in telescpe making because it is light, stiff and has very little termal expansion.

I would not expect a construction out of pure CF, but laminated with MDF I would think it could be VERY stiff, and it would be fairly easy to make. Just sandwich some layers of CF fabric and resin between two MDF plates and screw it together. Leave it to dry and trim the edges, and you are done!

[metalworkz]

Hello,
Linear rails are normally and excellent choice and require very little maintenance.
I think a cheap alternative can be formulated to use something like skate bearings and pipe if your design incorporates a means to support the rails/pipe.
Even CRS flat bar or round stock might be a better alternative than pipe as it has a more accurate surface for the bearings to ride on than pipe, but either way I think supported motion guides is a better design than un-supported. I had started making some round bar bearing races to use with skate bearings and had already about 6 sets laser cut from .375" steel and assembled when I started looking for the round bar and found the cost was going to put me close to Thompson supported rails available on eBay. I stopped there with the assembly and ended up buying some linear rails for the Z, thomson rails for my X and a THK actuator for my Y axis. If you can find the different parts needed at a reasonable price you may be able to do better cost wise by making your own. I still have the bearing races designed to fit a 1" round bar and may end up using them in another build. Design your own and build it with the extra strength included and it will probably do fine. Keep in mind if you use a router motor for a spindle you may end up using minimal cutting depths and feeds anyway so that will impart less force into the machine also. A regular spindle will work better for aluminum and other metals, but for most things and aluminum the small router motor will get you buy.
Regards,

[hemsworthlad]

Hi

Yes Stiffness is key for working harder materials but there are lots of other factors to take into concideration when working metals over wood, esp with regards to linear motion options and MDF.
These factors are mainly coolant and metal chips both of which can be major problems for the cheaper ways of doing things.!!

Most Diy linear systems tend to be open systems were the bearings run on rails or tubes etc this leaves them wide open to chips and fillings which will ruin a set of cheap skate bearings in short order then there's the clogging and jamming of the bearings causing missed steps etc.
This can be a problem even with wood as many who have gone this route will testify so it will be magnified several times with aluminium chippings because belive me milling aluminium flings chips everwhere and lots of them.!!

The other issue is coolant swelling the mdf, you dont need flood coolant to mill Aliuminium but you do need some light spraying if you want a decent finish and to help extend cutter life, again while your not using lots of coolant it still flys everywhere and gets into every nook and cranny.
Mdf wont last long in these conditions even if you seal it, sooner or later the moister will find it's way into the mdf through any cracks or cuts in the surface.
Personally I dont like mdf for anything other than spoil boards or making the fire.!!
I do understand why peeps use it regards cost but to me it doesnt take much more money to do it right using real longer lasting materials.?
Steel is a resonably cheap material and perfect for making the base frame and obviously mega strong, mixed in with a few pieces of intelligantly placed aluminium which again if carefully scrounged or ebay spotted can be had cheap and you will have a machine that can handle most materials.
The motors/drivers required will be the same wether you use MDF or steel/aluminium combo if designed right, the extra weight differance is not as much as you would think because you have to use much more MDF to get any decent strength and Mdf aint the lightest of stuff.!!

Regards linear rails, like M-works says the cost wont be a lot cheaper using skate bearing etc if you look hard enough and be pateint and buy used rails, and the differance is worlds apart not just in motion but in longevity and hassle free useage.

Regards C/F Mdf sandwich . . . .Why bother the cost wont be much less than steel and the work/mess involved ???. . . . Well dont need to say much more really.!!

A.T.B
Dean.

[hemsworthlad]

Hi,

What size of machine do you have in mind anyway, by this i mean usable cutting area.?

[Chrjensen]

This is great stuff!

I was also concerned about the coolant causing problems with the MDF, but I didn't think about the chips, but that seems an obvious problem. Obviously, a metal water pipe has lower tolerances than a precision machined rod, so the acuracy af the machine would naturally suffer. Also, I figured that lack of strength in the construction can, in part, be compensated by cutting slower.

I am probably still far away from actually starting construction, so I have a lot of time investigating design options. One thing I could be tempted to do, is to construct a fairly simple design, like the JGRO, to learn the basic principals of operation before moving on to a more complex - and expensive - design. Eventually, I would like to end up with a machine with a working surface of approximately 15'x15'