Thread: What to use as sacrificial layer.

I use mdf, do you have a humid enviroment thats allowing the mdf to draw moisture out of the air.

I also do what rodm recommended a long time ago, I spray the sheet with some sealent, plain clear lacquer in a can

Hi Pete,
As Steve said seal both surfaces and edges and you should be OK. MDF will absorb moisture and once you have exposed the harder pressed surfaces by flattening it on the machine it is prone to moisture uptake.

HDPE (breadboard) is expensive and overkill for a spoilboard IMHO.

It might be the humidity as we have had a fair amount of rain and than heat.
I will get some laquer and seal the milled surface and see how that goes.
Thanks guys.

Personally i do the same as Rod and use sealed MDF, although depending on the size of your bed, you could also use corian. I spoke with a large supplier in Sydney as i was going to change and he had heaps of offcolour sheets and offcuts and was willing to sell them quite cheap. Good thing about the corian, if you accidently gouge the sheet, you can actually repair it with a patch kit, just like putty in wood. Unfortunately the sheets only come in bench widths (760mm wide x 3m+) and would have cost me a bit to do my machine.

Daniel

Got some of this plastic from CBC Bearings from the offcut bin.

No idea what it is or what its worth but this chunk of plastic cost me $5 cash, I recon it would be good for a spoilboard.

Nice find Chris, looks like HDPE or machinist plastic (delrin).

Hi
Might have found the perfect sacrificial layer a new product out from Nover.
It is a water proof MDF that is made from plastic (its 100% waterproof). Being a plastic I hope it to be size stable. I have put some in some cutting oil to see if it is affected.
Routes good, it does not fluff up like MDF it sand well, its paint able, glue able, It takes screw better then MDF as it does not split when putting screw into edge near a corner.
I will be looking at making a few project out of it
There going to bring it out in range of thickness of 5-40mm.
I am told a 16mm x 2440 x 1220 sheet will cost $75 (might have to add gst to that)
A joiner mate is going to get some to make some outside cabinet work for a customer. I will be searching out the off cutts

I routed there sample piece, photos attached.
The burrs on the right was when the feed rate was slow around 600mm using a spiral cutter it does come off with one wipe of sand paper. The left was with a straight cutter at 1600mm. The centre was a ball mill again a light rub and it comes great.

More as it comes
Russell

It looks promising russell, was it as hard as MDF? also did you get that nasty MDF dust or did it come off in little chunks like plastic?

I recently bought some stuff called "Insulpanel" for my new CNC project to make the gantry out of it. Old electricians (like me) would know it as "Zelemite" and most people would have seen it before as the black stuff that switchboards are made from. The new version is much better, being that the true Zelemite was 30% asbestos.

Insulpanel basic construction is from layers of paper, impregnated with an epoxy resin.
Super strong, non-flammable, non absorbent and chemical resistant. Easily cut with good, sharp tools and takes glue and screws well. Great for drilling and tapping, and very temperature stable. A little weighty, but probably on par (if not a little lighter) to the equivalent size aluminium. As an experiment, I soaked a small piece in CRC/WD40 for a week and the thickness went from 9.85mm to 9.89mm.... Pretty good in my book!

While I was talking to the salesman/tech when I picked it up, he mentioned that one of the furniture manufacturers use 6mm sheets for a sacrificial layer on their CNC's. Maybe this is an option for home CNC's

A 1200x2400 10mm sheet set me back $315 so price may be a little high for a sacrificial sheet.

Hope this helps
John

Russell,
Is the sheet actually made from plastic as the picture makes it look like normal water-resistant MDF which is similar to normal MDF except that it is treated with plastic binder which is what gives it the water repelling qualities.

Either way its definately better than spending the time to seal a full sheet of MDF with bondcrete or similar. Which is what my plans are for tomorrow.

Daniel

Ch4iS
No dust in the air like MDF just plastic shavings
twistedfuse
What I can rememberer of the data sheet was it made from recycled plastic pvc some thing like 80% does not gas off it is very inert. Have had some sitting in cutting oil for 24 hours, no change

Should get my hands on some more next week I might start a new thread as I think it would be good for prototyping before making in metal

Russell

Russell,
Sounds very promising then. Keep us informed of how it all goes.

Daniel

I don't do CNC but from the posts, I think I know what you need.

If I'm shopping for dimensionally stable, non-metallic material,
a) glazier's (glass shop). They save the best trash when they replace or rebuild windows and signs. They call it "salvage XXXXX/whatever"
b) plastics distribution warehouse. . . . by making donations to their "pizza fund," I've had a couple of very productive "swims" in the scrap bins. . . . the size of some scrap was impressive, if you get excited about odds that are 50 x 70+cm.

at my work we use MDF as a sacrificial on the CNC machines.....Unsealed....The worksheet is held down by vacuum that comes through the sacrificial from the bed.

We seal the sides of the sacrificial to not lose some vacuum.....seal with paint.