Baltic Birch ply + MDF build, which material for which part

[nicanor76]

I started to consider what my 2nd build will be. I've searched through the past threads and hear lots of points about MDF vs Baltic Birch. For the sake of the argument, let's say the price is the same for both materials so price difference won't come into play.

My build won't be a super huge machine, probably 24"x24" moving area for X and Y. Also it will be an open table, moving gantry. And it will probably be transported (moved locations) more frequent than others so construction build needs to stand up transportation stress.

What part of the CNC would you prefer to use with MDF and which parts for Baltic Birch to result in the best combo build?

[High Seas]

Stability - in humid conditions or changing humidity
Rigidity - stable and won't bend or sag (mind you small - but expect you want good/constant repeat-ability at different sites)
Durability - no glue failure due to moisture intrusion
Mechanical - ease of attaching fittings, screws, etc..

Looks like Plywood - of good quality -- would be the choice NOT MDF

Jim

BTW Baltic Birch isvery nice -- but you can use other solid core ply - with good glues -- ie marine ply -- a little cheaper but not always as pretty as Baltic Birch!

[nicanor76]

I'm an industrial design student so I get a discount on the wood supplier (or at my school's workshop but they're closed for the summer), but still won't be as cheap as MDF (considering I can get MDF discounted as well). So I don't mind building the entire thing out of baltic birch, but through older threads some people still prefer MDF, at least for some parts.

Which reminds me we have a metal shop and get decent discounts on metal too... Weight would be a concern to me since I may transport it to my home to school (not too often but will probably happen a few times until I graduate in 2 years). So I'm trying to figure out the best material to use for specific parts. Pretty much the best bang for the buck with weight concerns.

[ger21]

Did you read this?
Thoughts on MDF & Torsion Box Design

[High Seas]

I'll add: there may be a place for plastics in the your design as well.
High density plastics have good mechanical properties and some machine with common tools easily.
Maybe not for the entire structure - but as sub system.

Jim

[nicanor76]

Originally Posted by High Seas I'll add: there may be a place for plastics in the your design as well...

That's kind of my main question. What part would be prefer to be made of MDF/Baltic/Plastic? From past threads it sounds like some people say a mixture of materials would be optimal (instead of an all MDF build) , but which part for which material?

In other words....

What would be the best for the X axis rail supports: My guess would be Baltic Birch Ply since it's the most stiff to keep things aligned and square better

The gantry side supports (for the Y axis): Baltic since it's the most stiff?

The Y axis: ?

The Z axis: MDF since it's the most vibration absorbent?

[ger21]

What would be the best for the X axis rail supports: My guess would be Baltic Birch Ply since it's the most stiff to keep things aligned and square better The gantry side supports (for the Y axis): Baltic since it's the most stiff? The Y axis: ? The Z axis: MDF since it's the most vibration absorbent?

I personally would not use plastic for anything, except maybe bearing blocks or something similar.

I think that the design is far more important than the material used. If you design to make up for any shortcomings in the materials, you shouldn't have any problems.

If you plan on using a single 3/4" thick panel for your gantry side, it won't really matter what you use, because it will have too much flex no matter what you do. If you're building torsion boxes, than mdf will be fine, and will only cost 1/2 as much.

One advantage of Baltic Birch is that it will hold screws better, and won't split when screwed into the edges as MDF can easily do. But, if your careful with MDF and know what you're doing, you can still get comparable results using MDF. But MDF probably require a little more care when drilling and assembling.

One downside of MDF is that if you don't store it lying perfectly flat, it'll start to sag or warp. But if you cut it right away, this is really not an issue.