MDF or Birch

[Dave Vigness]

So, I've been almost exclusively working with Premium MDF, 90% 3mm with a few 6mm and 9mm pieces thrown in. I've had some inquires about Birch ply, I'm assuming the Premium Birch Plywood.

My big question is how big of a difference am I looking at?

My Premium MDF is dimensionally stable as all hell. I've not had good luck with box store plywood, but I've never tried Premium plywood, much less Premium Birch.

Secondary question is the physical weight. There is a good chance I will be shipping a number of smaller pieces. Is there a major weight difference? Can it even be had in something resembling 3mm / 1/8" or do I have to start with 6mm / 1/4"?

I'd appreciate any info those of you that have worked with both might be able to pass on. Pro's and con's of the Birch, and nightmares to watch out for, that kind of thing.

[Tim Mellor]

I just checked some numbers on 3mm MDF against 3mm Birch (Laser Grade adhesive) and the MDF is about 15% heavier. viewtopic.php?f=112&t=4065 so Postal weight isn't going to be an issue. It might be a bit hard to tell from the photo but I weighed each of the samples (200x120mm) and wrote the weights on them.

Voids, cavities and adhesives however can and most likely be an issue. Typically good quality Birch Plywood (not Birch Veneer) should be fairly free of voids as it is meant for furniture and finished products. Basically you need to be a bit careful about what is in the middle more than the outside layers it is fairly common to use softwood cores to save $. The general adhesive used on Plywoods is also very dirty compared to a more Laser friendly one, I won't be putting standard Ply near my Laser if at all possible.

[Dave Vigness]

Yeah, I've seen the horror stories of standard ply. I've seen a fair amount of laser cut birch plywood that looked pretty nice so I would assume it was the premium, but no guarantees.

I've got a good supplier of mt Premium MDF and was going to give them a call about the birch ply but thought I'd throw it out here to laser guys first. Good to know it's actually lighter that the MDF. Wondering how it compares to stiffness. I can get some pretty thin cuts with the 3mm MDF and still be fairly strong. I know it's not going to be like Balsa, but if I have to make large changes in my cutting widths for established patterns I might have to take another look at it.

Any experience in warpage? I've seen some 1/4" make good boat boards, not sure what 1/8" wold do. The again, if it's a bit lighter, I may be able to cut thicker material than I can with the MDF.

[Tim Mellor]

Even my 40W Laser will do 3/8" Ply but struggles beyond 6mm MDF.

Much as this is aimed at non Laser it is a good primer on Plywoods as is the rest of his channel if you like playing with wood. Low on BS and slightly quirky https://youtu.be/Es9uKC6o_LQ

[Willy Ivy]

I guess this one is a matter of opinion. I on the other hand use mostly 3mm plywood because the stuff I make needs to have a nice wood grain and mdf would look like crap.
If I want a smooth look after painting then I sometimes lean to mdf but painted plywood gives a nice painted grain effect.
Birch does not have enough grain character for most of my projects.
Yes mdf is heavier than plywood of the same thickness.
Yes plywood may have a void now and then.
Yes plywood may be full of glue and even a string now and then.
Yes you may have to recut a new piece now and then.
Yes plywood can smoke a lot and cause some sticky goo.
You need good extraction and a bed that is quick and easy to clean.
I have probably cut around 20 sheets of 4'x8' 3mm plywood over the last 2 years and plan on cutting at least that many before the end of this year alone. In the same time period, about 1 4'x8' 3mm mdf.
Oh, did I mention that I DO NOT use laser grade birch plywood. Most of my projects are cut from cheap Home Depot utility plywood at less than $10 for a 4'x8' sheet. I may pull down 100 sheets to purchase 4 because I like to choose my wood grain and quality of the outsides. I then restack the 96 or so sheets back as I found them and sometimes better than they were stacked to start with. I do not like you guys who choose lumber and then leave it where it does not belong. If you are not going to restack it, take what is on top.
I also like to use reclaimed lumber (mostly fence material) milled down to 10mm but plywood is my first got to.