Replies

1. 
   eddiefromAustralia | Apr 02, 2003 04:55am | #1

   Hi,

   MDF is made of floor sweepings, sawdust etc from the mill and contains bark pieces, dirt and a hard glue (Urea Formaldehyde).  Urea Formaldehyde releases carcinogens on heating/cutting and can cause allergic reactions also, so make sure you're working in a well ventilated area.  Keep the dust out of your lungs at all costs (very fine and toxic)

   Because of this, it's hard on blades.  The nature of the beast.

   Hope that others have a more positive response, but if you're using carbide tipped blades (usually triple chip or ATB for this), then you're doing all you can.

   Cheers,

   eddie

1. 
   Piffin | Apr 02, 2003 05:34am | #2

   Thanks for the reply. I'vew noticed in the past a lot of sparks when milling with router so I assumed it was from staples in recycled magazines or something. dirty dust explains it.

   I knew about the formaldehyde and hear that it is less in Medex versions of the sheets. I also knew about the dust. It's the most wicked stuff I know of. He has a dust system in his shop and wears a mask..

   Excellence is its own reward!

2. 
   SgianDubh | Apr 02, 2003 06:00am | #3

   Not quite what eddie said, piffin-- it's not really floor sweepings. I've visited an MDF manufacturing plant or two, and it's actually a very carefully enginered and controlled process. The board is made up mostly of smaller logs, sometimes from just one species of tree even, that are put through a sophisticated wood smashing device that produces what I can only describe best as tufted woolly twists-- the tufts look a bit like a corkscrew.

   Anyway, these 'tufts' and various additives, including glue, usually urea formaldehide which is in itself very abrasive, are put through the process and you end up with a board of MDF. The stuff has most of the materials eddie mentioned, and it's extremely hard on tooling. Naturally enough, one of the abrasive parts in the mix are all the bits of metal that are broken off from the tufting machine and end up in the board.

   I seem to recall that they have to replace the business end of the tufting machines every 24 hours or so in a factory working 24 hrs. a day-- and most lines have two or three of these essential tufting machines at the beginning: one in use, one being fixed, and one as a spare. 

   Apart from using tungsten carbide cutters, and replacing them often, and getting the feed rate optimised, I'm not aware of their being another strategy. It might be an idea to contact the moulding tool maker and see if they have a special line of tooling for handling such materials as MDF.

   Funnily enough, I read somewhere that using hand planes and the like on MDF dulls them at about the same speed as working European beech, which is interesting, because beech is not too badly dulling when it comes to hand tools. Put it this way, I'd rather saw, plane, and shape beech by hand all day than do the same with ipe, which I've found is truly a pig to work with hand tools, and even machine tools, ha, ha. Slainte.

   Website    The poster formerly known as Sgian Dubh.

   
   

   ---

   Edited 4/1/2003 11:02:18 PM ET by Richard Jones

1. 
   eddiefromAustralia | Apr 02, 2003 07:17am | #4

   Hi RJ,

   I used to live in a timber town as a kid.

   Just reread my reply as the first was hastily typed during smoko.

   I didn't mention the fact that the bulk of their feed stock is thinnings and off grade logs, thanks for picking it up.  I don't know why, but I missed that critical fact in the first reply.

   Bark went into the machine then, so the dirt & dust embedded in the bark ended up in the board.  Looks as though things have changed now, but they have had success with glass fibre, steel fibre, carbon fibre and aramide in the process.

   Here's a link outlining the manufacture process.  Looks as though acidity also is a factor on tool wear, something I wouldn't have thought of?!

   They must have cleaned up their act - by floor sweepings, I meant the sweepings from a mill floor which was mainly sawdust made up a small portion of the feed (at least, that's where we were told to put it in the holiday job I had), just to clarify my earlier statement.

   Cheers,

   eddie

   Edited 4/2/2003 12:36:12 AM ET by eddie (aust)

1. 
   SgianDubh | Apr 02, 2003 07:56am | #6

   Ha, ha, eddie. Probably a bunch more information there in that link than most of us need, but it seems to jive with much of what I recall at the plants I visited. I'd guessed you were responding 'off the cuff' and it certainly is the case that MDF is very hard on tooling. 

   It sounds like the tooling Dahoo mentioned might be the best suited for working thousands of metres of MDF, but piffins mate is just a guy hacking a few bits of the stuff up to nail against a wall in peoples houses.

   I wonder if it is that the reduced cost of the material (MDF as opposed to poplar, etc.) is offset by the increased cost of tool sharpening and tool replacement if he's going to use TC tooling on MDF as a regular thing? Just curious on that score. Slainte.Website    The poster formerly known as Sgian Dubh.

1. 
   Piffin | Apr 02, 2003 02:21pm | #8

   He's made the choice to use the MDF on this job because of the extreme wood movement we get in this coastal climate, shrinking and swelling. Not because of the cost factor. If cost were the question, he'd be losing out because of sharpenning costs and he has his own wheel for that..

   Excellence is its own reward!

1. 
   SgianDubh | Apr 02, 2003 04:56pm | #9

   Thanks Piffin. Slainte.Website    The poster formerly known as Sgian Dubh.

2. 
   StanleyNiemiec | Apr 02, 2003 07:19pm | #10

   If your friend is concerned about "extreme wood movement", he should be aware that composite fiber-based panel products have one thing that real wood does not  -- linear expansion (LE).

   As such, he should expect that there can be considerable dimensional changes along the length of the "board" which can result in gaps developing at end joints when pieces are butted together.  The other alternative (depending on panel EMC conditions at installation) is that buckling is possible.  LE values (for 8 foot lengths) can be in the range of 0.2 to 0.4 inches and are the result of the randon orientation of the wood fibers in the panel.  Tests were determined between 50 and 90 percent RH conditions.

3. 
   Piffin | Apr 03, 2003 02:51am | #11

   Thanks for all your very thorough information. I have printed and faxed to him. For me it brings a lot of understanding to the process.

   I'm surprised at how much linerar expansion you mention. My experience has been about 1/8" in eight feet Max.

   Is this also thermal expansion or is it mostly from moisture?.

   Excellence is its own reward!

4. 
   StanleyNiemiec | Apr 03, 2003 07:41am | #12

   The data I cited came from the old Wood Handbook and this most certainly represents a range that includes many different manufacturers.  If you need to be specific, I would suggest requesting that data from the manufacturer through your supplier.

   If your experience is different, it may be that the manufacturer is adding stuff to the furnish to reduce LE, or you have not been making measurements over the same range of RH/EMC.  Those are pretty severe conditions of exposure and it is suprising the length of time necessary to actually fully equilibrate samples.  And in most shop/home/office environments, there is a lot of fluctuation in both temperature and RH  --  you may hit the test conditions for a period of time but they likely do not remain constant.

   With that said, 0.125" is still a huge gap and unsightly.  It might be advisable to end-match the boards (say with a T&G joint) but the problem with this is that any water in the adhesive will likely cause swelling in that area and you end up with something that is non-planar.  Maybe the urethane adhesives would minimize this because of their low moisture content.  But even with a good joint, the reality is that the LE remains the same and if you have joined two eight foot boards into a sixteen foot board, something will still have to give somewhere. 

   Thermal expansion of wood is almost negligible.

   In my mind, MDF and such have their uses  --  being a solid wood snob though, I have yet to think of any!! 

3. 
   cabman | Apr 02, 2003 07:35am | #5

   Hey Piffin try looking for PCD. Poly Crystalline Diamond cutters are about the best you can get for cutting MDF. It's expensive, but if you are doing high volume on any moulder it is well worth the expense.

   Regards, Darren.

4. 
   StanleyNiemiec | Apr 02, 2003 08:09am | #7

   MDF these days can contain almost anything as the furnish (the "official" name for the fiber base) is sometimes produced from recycled products including construction debris and old pallets.  The recycled wood from urban wood reclamation centers is most often sent to fiberboard producers instead of the land fill -- nails and all.  I guess that good in a way but it also means its hell on tooling.

   If you are going to carbide, then you also may need to consider that carbide can never attain the same initial "sharpness" as HSS.  The carbide will wear less quickly than HSS but it does not start out as sharp. 

   MDF is also considerable more dense than most real woods and as such the tooling angles need to change to produce suitable surfaces.  Generally you need to have a larger sharpness angle (the actual cutting angle on the tooling).  You also generally increase the sharpness angle with the more dense wood anyway but with MDF it is almost mandatory.  If the cutterhead set-up does not change, then the end result is that the clearance angle (the angle between the bevel angle and the wood) gets reduced and with post machining instantaneous wood springback, hammering can occur.  The only way to avoid this is to change the cutterhead set-up so that the rake angle is reduced.  This probably would required getting the cutterhead remachined to hold the tooling at a different angle.  And if you change the cutterhead configuration, you will also slightly alter the resulting profiles a given knife will produce.

   The most logical solution however must involve the number of knife marks per inch.  This is a function of the number of blades in the cutterhead, the RPM of the cutterhead and the feed rate of the stock.  You probably can obtain a very suitable surface in the range of 36 to 48 knife marks per inch  --  any more and you are likely generating an excess amount of rubbing and therein excessive amounts of heat induced tool wear.  You probably cannot change the number of knives in the cutterhead but it may be possible to either slow down the cutterhead or increase the feed speed  --  this may provide a better end result.

   Needless to say, depth of cut is another issue that should be considered.  The deeper the cut, the more problems (relating to both tool wear and surface quality) will occur.  And with regard to depth of cut, you must also realize that MDF is not a product of uniform density.  The closer you are to the core of the board, the less dense it becomes and as a result, more fuzzing is likely to occur.  Part of this is attributable to the way the mat is consolidated in the presses but it is also a function of adhesive distribution within the board.  Generally the mat is laid down sequentially with three of more "felting" machines.  In my experience, more adhesive is added to the furnish for the bottom and top layers than is added to the core.  It makes for a smoother surface and this keeps overall adhesive costs down.

   The issue is that you don't get something for nothing.  MDF is certainly less expensive than lumber but to compensate for the cost differential, additional investments must be made relative to machining variables.  This is basic fact and the first increase will be relative to sharpening costs.

   I hope this helps.

   Stanley Niemiec  --  Wood Technologist

   MS - Penn State '79