[RockBoy]

I've just finished building my first MDF machine, things were going well until i noticed that the humidity of summer has caused parts of the machine to swell. The biggest impact this has had is the fact that my x-axis lead screw now has a bow in it (just threaded rod) and the machine is vibrating.

So now i'm about to start my second build and I'm against the idea of MDF, it just isn't working for where i live. I don't have the equipment to work with steel/aluminium so I'm wondering if plywood is a viable alternative. Why do i rarely see it being used by members of the zone?

[gmfoster]

I've just finished building my first MDF machine, things were going well until i noticed that the humidity of summer has caused parts of the machine to swell. The biggest impact this has had is the fact that my x-axis lead screw now has a bow in it (just threaded rod) and the machine is vibrating.

So now i'm about to start my second build and I'm against the idea of MDF, it just isn't working for where i live. I don't have the equipment to work with steel/aluminium so I'm wondering if plywood is a viable alternative. Why do i rarely see it being used by members of the zone?

Plywood moves as well. Seal what ever you are using, that is keep the moisture out. In fact most all wood moves with temp and humidity.

Garry

[ger21]

The only plywood I'd recommend is Baltic Birch. It's what I'm using for my first machine, and the next one I'm working on. It's the only plywood that'll stay flat, and it's extremely strong. But it is 2-3 times more expensive than MDF.

[Drools]

What Gerry said +1

[bogiestl]

From my speaker building experience, I prefer MDF for dimensional stability, and elimination of possible "lose" vibrating pieces... And yes, I've also used Baltic Birch...

But everything that is wood/porous will change with weather. You could try disassembling it, and sealing it... Or maybe make a rough-cut (you don't have to machine it...) frame/platform of angle, and then attach it to the MDF, and screw to other stuff to it...

[drhanger]

The only plywood I'd recommend is Baltic Birch. It's what I'm using for my first machine, and the next one I'm working on. It's the only plywood that'll stay flat, and it's extremely strong. But it is 2-3 times more expensive than MDF.

I'm making mine from Baltic Birch plywood as well, what is a good product to use to seal it?

[ger21]

Epoxy, followed by polyurethane.

If you skip the epoxy, a lot more will soak in, especially on the end grain edges, and you'll need more coats for a good finish.

[bobsch]

Epoxy, followed by polyurethane.

If you skip the epoxy, a lot more will soak in, especially on the end grain edges, and you'll need more coats for a good finish.

Zinsser SealCoat http://www.rockler.com/product.cfm?page=10310 also works well to seal MDF before applying poly.

[PropNut]

I have several machines made of MDF, including my 4x8 CNC router. I seal them with garage floor (concrete) paint, I have had no problems with the very humid west Michigan weather. Gerry is correct on sealing plywood though, you really need a sealer coat on the end grain when working with that material.

A bit off topic but isnt it ironic that the cheapest plywood that I use in my cabinet shop has always been baltic birch and now it is the most expensive? I used it for all my cabinet carcase assemblies and then veneered it to whichever species that the customer desired (outside finished ends, etc). In the last couple of years it has become that most expensive. Supply and demand I guess, and a building boom in east asia.

Edit: I used BB and BBBB grade but even those are getting too expensive these days to show a profit on unless I want to raise my prices, and it is already hard to compete with cheaply made cabinet from the big box stores.

[Big-tex]

I have several machines made of MDF, including my 4x8 CNC router. I seal them with garage floor (concrete) paint, I have had no problems with the very humid west Michigan weather. Gerry is correct on sealing plywood though, you really need a sealer coat on the end grain when working with that material.

A bit off topic but isnt it ironic that the cheapest plywood that I use in my cabinet shop has always been baltic birch and now it is the most expensive? I used it for all my cabinet carcase assemblies and then veneered it to whichever species that the customer desired (outside finished ends, etc). In the last couple of years it has become that most expensive. Supply and demand I guess, and a building boom in east asia.

Edit: I used BB and BBBB grade but even those are getting too expensive these days to show a profit on unless I want to raise my prices, and it is already hard to compete with cheaply made cabinet from the big box stores.

I remember days when baltic ply was coming from Finland then from russia.
Now days we have plenty of imports coming from China and indonesia.
Be careful this stuff is just like Chinese toys with lead paint. Formaldahide, barium, arsenic. Arsenic wasn't that what Napoleon was poisoned with?
Now day we kill our population with same chemicals....my $0.02.

I agree with Garry all wood products should be sealed at end grain this is where moisture gets absorbed. As per any kind of ply all edges since ply construction is odd number of layers for balancing and cross grain layering for warping.

[dkirtley]

I really can't see messing with MDF. The only real thing that it has in its favor is being cheap and fairly uniform. It doesn't hold fasteners well. It doesn't glue very well. It is really weak in comparison to most things in just about any direction except compression. It has all kinds of nasties in the binder that just are not very healthy. Even with an epoxy coating, it is not impervious to moisture. Epoxy will slow absorption, not stop it entirely.

Some places carry MDO, which is the stuff they make signs out of. Some places use it for concrete forms. There are some phenolic laminated plywoods that are pretty nice but they are hard to glue together into thicker members. If you have it available, marine grade ply is really nice also but tends to get pricey but still cheaper than a lot of materials. It is put together much like the old baltic birch you used to find. BS 1088 is the nicest grade. It does not have any voids.

Hardwood plywood is much better suited to structural use. If you seal it well, plywood will last as long as just about anything else and it is much stronger per unit weight that just about anything you can name that is commonly available.

Don't discount using real honest to goodness solid wood as well. If you orient the grain properly, the expansion is not really an issue. It doesn't change much at all in length, moisture makes it expand radially.

[PropNut]

To each his own I guess. Everyone has an opinion, as I said, MDF works very well for me. My machine has been in operation for about a year now under pretty regular use. Could I have built it out of aluminum or steel? Sure, but I wanted to build it cheap (part of the fun for me) and MDF fit the bill (pun intended). No, it is not a perfectly precise machine, I will never get it to .0005 accuracy but it is close enough to cut cabinet parts and PCB's for hobby electronic projects. I was working with 1/2" aluminum the other day and am very happy with the results. Does this mean that I am "stuck in the Dark Ages"? Perhaps, but perhaps there is more than one way to get the job done.

[dkirtley]

Yeah, I know the story of everyone having an opinion Mine stink up there with the rest of them.

Hopefully mine will be cutting stuff out soon as well. At present, I only have a little Roland CAMM-3 that I brought back to life at work to play with that has a cutting area of 120mm x 100mm.

What software are you using to design the PCBs? Everything I have seen so far has been geared toward etching boards. The closest I have come so far is with Fritzing and it comes up with weird artifacts.

[mmcp42]

I use Eagle
it has a handy plugin pcb-gcode that spits out gcode directly from the layout

you can set cut width and copper clearance required

(I have no interest other than a happy user)

[dkirtley]

I have seen other people recommending Eagle as well. I tried it a bit, but honestly, I couldn't make heads or tails out of the interface. Maybe I need to just lock myself in a room with it and not come out until I create a PCB that works the electronic lock on the door

[PropNut]

I do it the hard way I measure my components and make DXF files in DesignCad. Eagle looks really good and I have installed the free version but I have not taken the time to mess with it. I make very few PCB's so CAD works for me. If I were to do it regularly I would definitly teach myself to use the proper program.

[dkirtley]

I do it the hard way I measure my components and make DXF files in DesignCad. Eagle looks really good and I have installed the free version but I have not taken the time to mess with it. I make very few PCB's so CAD works for me. If I were to do it regularly I would definitly teach myself to use the proper program.

The little Roland machine I have been using doesn't use G-Code. It basically uses a variant of HPGL, so I have been doodling in Inkscape. They do have one CNC router table at work for cutting PCB but it has been a steaming pile of garbage. It has been down more than it has been up. It has either had a dead spindle, ridiculous contortions to set the cutter height, or my personal favorite -- pads being offset by about 1/4 in. from the holes from their awful software. I can't say that it has successfully cut a board since they day that they had it.

[harryn]

Hi, I think you under estimate your ability to work with Al. It does require some changes in approach, but not that many. I was surprised that working with Al 6061 was not all that much different than working with a hard oak.

I don't recommend trying to rip saw it, but as far as using a chop saw or drilling it, it is largely a non event. Just go slowly through the material using a carbide tipped blade just used for this kind of work.

Clamping becomes a much bigger deal than with wood. When wood cuts, it breaks away with less grab, but with Al, more power is available to move things around. Don't even imagine that you can hand hold it down by hand.

One thing I do recommend is to add some safety equipment - a full face shield and use it ALL of the time when cutting this stuff. When I used a wood chop saw (power miter box) the hot chips came right back at me vs following the normal path that the wood saw dust follows in the blade guard.

Keep the area clear so it doesn't kick and hit someone, similar to how you would work with a hard wood with knots.

Don't bother trying to route this stuff with your router. Yes it can be done, but it is slow and will likely just damage your existing setup. The speeds are just way too fast.

As far as joints - if you use 6mm or thicker walls, you can tap it, which is really handy. Epoxy the joints and it is fine. Even off the shelf, industrial quality angle, channel, and and rectangular tubing are quite straight and stable, compared to nearly the best wood products you can buy.

I am building my router "wood prototype" from plywood. It is ok for testing, but it warps from what I consider moderate stresses. MDF is a non starter for me for lots of reasons. I don't own a single piece of that - uhm - product. One the wood proto version is working, it is just a matter of moving the design to Al.