Fluffy mdf

[Steven W]

I am new to the world of cnc but have been woodworking for years. I have been making models out of mdf for a few years now and have been routing these using a handheld or table top router. I have been using standard grade 18mm mdf from local B&Q stores etc with no issues. Using the same mdf on the cnc the finish cut is very poor. The core (centre part of the board) goes extremely fluffy and you can see a slight step where the cutter has moved to the next cut down. I have been reading that there are different grades of mdf and maybe the stuff I have been buying is not dense enough. The other observation I have made is following the feed speed calculator the router moves very quickly over the piece. I am wondering if anyone else has experienced this problem and can offer a solution

Thanks Steven

[jcb121]

Make sure the mdf isn't damp.

I have.the same problem

[Steven W]

Thanks jcb. Mdf is bone dry in my workshop. As mentioned above I don't have any issues routing the stuff manually only on the cnc

[GEOFFREY]

If the same material machines well wiTh a hand router, the problem must be with the cnc. Never mind the calculated speeds ctc. try to replicate the hand router conditions, speed feed same cutter etc. If the problems persists it sounds to me that it may be a rigidity or vibration problem. G.

[Steven W]

Thanks Geoffrey. It's a brand new machine albeit from the cheaper end of the market. I have routed all sorts of other types of softwoods and hardwoods and they have been perfect. I think the speed of the router has a lot to do with it. Will try slowing down the feed rate. Steven

[richie00boy]

You might find you have to slow the CNC down to a snails pace. The MDF from B&Q and the likes is the lowest grade. Go to Wickes or Jewson and get the moisture resistant type. This is about the best you can get easily. If you have a good wood merchant they should be able to get you deep router grade which makes B&Q MDF look like toilet paper. It will be double the price though, but the reduction in messing about with sorting the edges can make it good value.

[Neale]

I think you probably have an ER11 or ER20 collet on the end of that spindle. Extra collets aren't very expensive (take a look at Arc Euro Trade, for example) and it's well worth using the right ones. In theory, one collet will handle nominal size shanks or up to 1mm smaller but especially in the smaller sizes they don't like compressing that easily so I also use a mix of metric and imperial size collets. 6mm shank cutters go in a 6mm collet and the 1/4" cutters (nominal 6.35mm) go in a 1/4" collet rather than using the larger collet for both. You only have to save one broken cutter to make up the cost of a collet!

[Jonathan]

Yes, Arc Euro is a good place to get individual collets. I got a set in 1mm increments off eBay, then got 1mm, 1/8" and 1/4" collets from Arc. You can put a 1/4" cutter in a 7mm collet, but it'll wear out the collet faster and takes longer to do up the nut!

With the ER collet system you should never try and clamp a cutter that's bigger than the diameter of the collet, even if it's just 0.1mm bigger. Depending on the size, they can clamp 0.5-1mm smaller than the nominal diameter.

[Shinobiwan]

I'm a bit late to the party here but do have a long running love hate relationship with MDF. Love it because its cheap, hate it because its cheap! lol

As others have said, the furring is because B&Q supply cardboard badged up as MDF - yes its really that bad. Complete junk and I'd avoid it at all costs, I've never got a decent edge finish from this stuff yet.

Medite is ok at the budget end though thickness's above 25mm do have a rather mushy core and again you'll get some furring but nothing like as bad as B&Q rubbish. At the top end you have Valchromat and I love this stuff. Zero furring, retains very small details and can be sanded smooth - almost like plastic when sanded upto 1200 grit. Its expensive though at £80 for 25mm thick 8x4ft sheet.

For reference I mostly cut at 7m/min 11,000rpm and 100% cutter diameter for DOC. Use carbide tooling and you can get amazing tool life, not sure how long exactly but a few months of use almost day in day out for me in MDF. Key to increasing tool life is keep your rpm low and your feedrates high.

[nbowes]

I have cnc and manual routers. to do away with fluff on any material, I use down cutters whenever I can. feed speed max my cnc will do is 70 in per min.