MDF or ply?

[EddyCurrent]

For mine I'm thinking 25mm Birch Plywood with sacrificial MDF tops. If this proves not so good I'll probably move to a T slot bed with MDF sacrificial tops.
I was planning on screwing down my work pieces to the top but I may drill the birch at regular intervals and use bench holdfasts such as these Buy Axminster Bench Clamp from Axminster, fast delivery for the UK but they may not hold the piece well enough.
For some work I plan to use a small vacuum bed that will clamp onto the main bed, I was also need some raised beds to bring thin stock up to the cutter so that the Z axis is not way down when cutting.
So my thoughts are that the main bed would be more for support than work piece fixing. One good thing about the bed is that it can be changed later with minimal disruption.

[John McNamara]

Hi

MDF has a bad tendency to sag over time, Just place a scrap length say a metre long between two supports and leave it for a few days it will sag by its own weight and stay bent. If you do use it use plenty of supports under the sheet

Concrete form ply is worth looking at. (Not the cheap home hardware store kind) I went to an engineering exhibition recently and found a product called Doka Xlife Plywood the sample I have is 20mm thick and is made up of about 15 ply's including a plastic wear surface on one side.

I have it on my list as a Router bed material. I plan to drill the bed (With the CNC router) with a 50mm spaced hole pattern for threaded M8 metal inserts, available from cabinet hardware suppliers. This ply is extremely dense. I am sure other competing form ply suppliers will have similar product.

I have no connection at all to the company.

Regards
John

[EddyCurrent]

John,
Funny how you overlook things you've used before, the M8 inserts is a great idea, I'd recommend these too, Toolstation > Screws & Fixings > Nuts & Washers > Pronged Tee Nut
It's true that MDF is iffy stuff and I normally avoid because of dust and Urea-formaldehyde release but for a sub-bed that is fully supported it's relatively cheap and flat.
For now I'm sticking with Birch Ply for the main bed + M8 pronged nuts and I'm going to investigate foamex.
alex, does the foamex compress much ? I imagine that over a large area it will not.

[Jonathan]

John,
Funny how you overlook things you've used before, the M8 inserts is a great idea, I'd recommend these too, Toolstation > Screws & Fixings > Nuts & Washers > Pronged Tee Nut

If anyone wants to buy some of those for a good price let me know as bought a box of 1000 for my router bed and never used them.