[thegimpster]

Which is stronger to use, MDF or the expensive Birch plywood that is used in cabinet making? I know MDF doesn't have a grain or layers to contend with. But I think the wood might be stronger. Or maybe it just depends on the application.

[ger21]

I prefer Baltic Birch, but MDF is slightly more stable, a little easier to work with and half the price. Baltic Birch holds screws better and is more durable. As for strength, Blatic Birch is probably a bit stiffer.

[jdell42]

Birch sould be stronger...but with the different grades and quality its tough to tell sometimes. Strength is not always the primary concern as stability tends to be high on the list too. As Gery mentions MDF tends to strip if you torque a screw too much.... but Birch.. espcially good baltic birch will be stronger and stiffer.

[Gir]

If I remember correctly, MDF is going to be a good bit stronger but will flex more than the Baltic Birch. However, Baltic Birch is a whole heck of a lot lighter, and as ger21 mentioned will hold screws much better. On the other hand, MDF is cheaper! So it really depends on the application. If you need a lightweight box/frame/whatever than Baltic Birch is the way to go. If you need a heavy (or weight doesn't matter) box/frame/whatever for cheap, than MDF is probably the way to go.

Also worth mentioning, MDF will inflate like a sponge if it gets wet, so that may be taken into consideration. When working with MDF it's probably best to use wood glue with optional screws. As for screws, I've found #8 with a 3/4" shank is the best when working with 3/4" MDF so that it will really pull the two pieces together for a very solid connection since there aren't any threads that could keep them separated.

[rlrhett]

As jDel42 mentioned, there is Birch and then there is Birch. Home Depo sells "Birch" plywood, but it is very poor quality. There are many voids, etc. If you buy birch plywood and want the stuff that makes Birch popular, you are going to have to get it from some lumberyard that sells to cabinet makers. It won't be cheap.

If you pre-dirll and use non-tapered drywall screws MDF will hold a screw well. Also, you can use barrel bolts (IKEA like breakdown hardware). They are very strong and don't depend on ability to holding a screw.

MDF is also more sensitive to moisture. It can't sit outside unless it has been thoroughly primered and painted. Of course, neither can your electronics!

Considering the price of "real" Baltic Birch plywood, I probably would advise MDF for any jig making. If you really want strong, light and stable the next step up would probably be aluminum extrusions.

[martinw]

Dear gimpster,

I do not think that there is any question about Birch ply being stronger than even the best quality MDF. Over here, the very best ply is Finnish Birch, and ,I think it has at least 11 plys (plies?) in a 3/4" thickness. It also takes screws a whole lot better into the face and edge compared to MDF. The centre portion of MDF is pretty much mush. The faces are higher density, but when it comes to screw withdrawal loads, decent ply always wins.

As regards flexural strength, take a peek at this...

http://www.woodbin.com/calcs/sagulator.htm.

The reason why people use MDF is simple.

1) If you buy a sheet of 3/4" MDF, it will be pretty much spot-on as regards thickness over the whole sheet. Birch ply may well not be.

2) A sheet of reasonable quality MDF costs about 35% of the ply equivalent (and there is still the thickness issue).

Best wishes,

Martin

[dmoore]

I completely agreee with you on the issue of attachment of screws to MDF - poor at best. I *highly* recommend using dowel nuts or cross dowels. You can see samples of how they attach here:

http://buildyourcnc.com/Step2.aspx

When purchased in quanity, they can be reasonable and they allow you to take apart your CNC machine (and you WILL take it apart several times) and reassemble without stripping out the holes. Yes it does take more prep time and drilling than screws alone but they work great!

[thegimpster]

Im actually going to build the cnc from that sight, so im quite familiar with it. I was just wondering which it would be better to go w/. thanks