The MDF FAQ
by Louis Lung
original
revision; June 1996 ?
revision 1.1; 21 February 1998
revision 1.2; 02 December 1998
revision 1.3; 30 March 1999
revision 1.4; 29 November 1999
revision 1.5; 03 March 2000
revision 1.6; 29 September 2000
revision 1.7; 04 November 2000
revision 1.8; 12 January 2001
revision 1.9; 21 March 2001
revision 1.10; 23 June 2002
revision 1.11; 11 December 2002
revision 1.12; 13 January 2004
revision 1.13; 7 May 2008
Disclaimer
This is
an unofficial FAQ on MDF. The information presented here is
provided as-is and is believed to be correct at the time of
its writing. No guarantees, implicit or otherwise are provided.
Neither the author, contributors, nor members of the DIY
Loudspeakers list are responsible for any injury or damage,
directly or indirectly related to the contents of this FAQ.
Woodworking
is potentially dangerous. Make sure you understand the proper
use and operation of any tool before using it. Remember -
Safety First !
Acknowledgment
Many people
have contributed contents to this FAQ though their names not
listed here. My thanks go them all.
Notice
The goal
of this FAQ is to provide information pertaining to MDF as
it relates to speaker building. When possible, generalized
answers are provided. However, in some instances, answers
have been limited to the existing scope of discussion.
Table of Contents
Q: What does MDF stand for?
A: Medium
Density Fiberboard.
Q:
What is MDF?
A: MDF belongs
to the hardboard family of products which are made
from wood fibers glued under heat and pressure. Medium Density
Fiberboard typically has densities between 33 and 50 pounds
per cubic feet while High Density Fiberboard (HDF) ranges
between 50 and 80 pounds per cubic feet. Hardboard was first
produced in 1924 by W. H. Mason, founder of Masonite Corp.
The term Masonite is therefore often used to denote hardboard
products, especially HDF.
Physical
and dimensional tolerances for MDF are specified in ANSI
A208.2-1986
Q:
What properties does MDF exhibit?
A: MDF has
many qualities that make it an ideal replacement for plywood
or particle board. It is dense, flat, stiff, has no knots
and is easily machined. Its fine particles provide dimensional
stability without a predominant "grain" (as is the
case with lumber). Unlike most plywoods, MDF contains no voids,
and will deliver sharp edges with no tearout. MDF is very
well damped acoustically thus making it an ideal material
for speaker enclosures.
Below are
some typical values for the modulus of elasticity (in million
pounds per square inch) and density (in pounds per cubic feet)
for MDF, Oak, Pine and Fir Plywood.
Material |
MOE |
Density |
MDF |
0.53
|
48 |
Oak |
1.55 |
38 |
Pine |
1.3 |
29 |
Fir
Plywood |
1.2 |
33 |
The modulus
of elasticity (MOE), also called Young's modulus, is the ratio
of stress to strain, where stress is the force per unit area
placed on the item and strain is the deformation caused by
the stress. The MOE is therefore a measure of stiffness.
Q:
What does MDF look like?
A: Here is an image of a birch veneered MDF board.
The
circular marks on the edges are caused by a 24 tooth carbide
ripping blade. Better edges can be obtained by using a more
appropriate blade (see discussion on cutting and milling).
For contrast,
here is an image of veneered particle board. Notice the much
larger and obvious particles.
Q:
Are there any drawbacks to using MDF?
A: While
MDF has been in use for almost 30 years, it is only now becoming
available to the general public. Finding MDF may end up being
the single toughest part of using it. As its density implies,
MDF is very heavy and thus potentially difficult to handle.
See the safety issues below.
Q:
What are the safety issues to consider when working with MDF?
A: MDF is
typically made with urea-formaldehyde resin totalling 9% by
weight. While most people will not be affected by this, people
sensitive to formaldehyde emissions should consider low formaldehyde
or formaldehyde-free MDF, or consider methods of controlling
these emissions through proper finishing. Finishes that work
best at controlling formaldehyde emissions are solid add-on
surfaces such as high pressure laminates, vinyl covering,
and finished wood veneers. Less effective at controlling emissions
are simple seal coats, oil and latex paints, Danish oil, and
wax. Plum Creek makes low-formaldehyde MDF, while Medite II
and Medex from Medite Corp. are formaldehyde-free MDF.
Dust is
another MDF hazard. The large amount of dust released when
working MDF makes proper respiratory and eye protection mandatory.
At a minimum, use a dust mask. A respirator is preferable.
Shop dust collection (or even a ShopVac) would greatly help
the removal of dust from not only the air but also the working
surfaces, making them easier to see. Goggles should always
be worn while using tools.
Q:
Is all MDF the same?
A: No. MDF
from different sources will vary in texture, density, color,
etc.
Q:
How is MDF sold?
A: MDF is
manufactured in sheets up to 8ft x 25ft. Typical consumer
level sheets are 4x8 or 5x8 and 1/2 inch, 3/4 inch and 1 inch
in thickness. Thicknesses can also be metric - an important
consideration when considering the use of English system tools
(such as router bits). MDF is also available with a variety
of veneers and laminates pre-applied, which may affect its
actual thickness.
Q:
What about MDO, particle board, hardboard, void-free plywood?
A: Medium
Density Overlay and High Density Overlay are
plywood products with a resin impregnated paper coating. They
are often used for exterior painted surfaces. These are not
fiber based products.
Likewise,
particle board is not fiber based; it is a solid wood composite
product. Along with flakeboard and other engineered lumbers,
composite products are made from wood flakes, chips, splinters,
etc., formed into layers and held together by resin glues
and heated under pressure. Being layered and consisting of
larger chunks, particle board does not have the uniform texture
of MDF.
While MDF
is a hardboard, the term hardboard is often used to refer
to 1/8 or 1/4 inch thick HDF, usually containing a screen
pattern on one surface. As previously mentioned, this is commonly
referred to as Masonite.
Plywood
is made from an odd number of lumber plies, each layer having
a grain direction at right angles to the previous layer. This
arrangement provides a dimensionally stable product. Void-free
plywood uses plies with supposedly no holes, thus the completed
plywood has in theory no voids (hence "void-free").
Baltic birch plywood is sometimes sold as void-free plywood
though some users have encountered small voids in these products.
Be sure to ask specifically for void-free plywood if this
is what you are looking for.
Q:
Can I build speakers with {MDF | particle board | plywood
| solid wood}?
A: You can
build speakers with whatever you like ! However, MDF is often
the material of choice. Its stiffness and density yield good
accoustical damping properties. Particle board and plywood
are cheaper and can still be used if cost is an issue. Plywood
(especially if void free) can be used in the main baffle as
a sandwich material to better hold fasteners. Plywood is also
a good material for making braces inside speaker boxes. Solid
wood (lumber) suffers from movement - the swelling and shrinking
of wood due to environmental changes such as humidity - and
is therefore not a good material for speaker enclosures. Lumber
is also not as acoustically dead as MDF.
There are
times however, when plywood, particle board and other common
sheet goods are more than suitable for enclosures. Such possible
uses include sound reinforcement, musical instrument cabinets,
and PA systems.
Q:
What should I use to cut and mill MDF?
A: MDF can
be treated much like a fine grained hardwood. Its high glue
content means that steel cutting tools will dull VERY quickly;
thus the use of carbide tools is highly recommended. Always
keep your tools sharp for efficiency and safety.
The following
recommendations are from the The National Particleboard Association
publication MDF From Start to Finish:
- For general
shop or table saw use with decent cut and good blade life,
a 50 tooth, 10 inch combination blade may be used.
- For those
demanding a better cut, consider a 60 tooth, 10 inch blade
with alternate top bevel (ATB) teeth at 15 degrees, 10 degree
positive hook, 5 degree side clearance, 10 degree outside
diameter clearance, and low approach angle (blade projecting
no more than 0.5 inch through top of material). \
- For an
even smoother cut, consider an 80 tooth, 10 inch blade with
15 degree ATB, 10 degree alternate face bevel, 15 degree
positive hook, and 7 degrees side clearance. This is costlier
and may result in a shorter blade life.
Q:
Where can I find MDF?
A: Availability
varies geographically so there is no simple answer to this
question. Hobbyists have found MDF from a wide variety of
sources including, but not limited to :
- large
warehouse style supply dealers (Home Depot, HomeQuarters
Warehouse, Builder's Square, etc)
- small
local lumber yards
- cabinet
shops who buy in large quantities and are willing to part
with some
- surplus
building supply dealers
Beware of
clueless store clerks trying to pass plywood, particle board
or MDO as MDF ! Note that many lumber yards can special order
MDF but may not realize this, so it never hurts to ask. Ask
them to check their price book for availability.
Q:
Who manufactures MDF and how can I contact them?
A: Some
suppliers of MDF are (company name, mill location, correspondence
address, phone number) :
- Allegheny
MDF; Hutchins Road, RD1-Box 268, Kane, PA 16735;
(814) 778-2605
- Bohemia
Inc.; Rocklin CA; 2280 Oakmont Way, Eugene OR 97401;
800-547-6065, 503-342-6262
- Georgia
Pacific Corp.; PO Box 105605, 20th Floor, Atlanta,
GA 30348-5605; 404-652-5496
- International
Paper, Masonite Building & Industrial Products;
1 S. Wacker Drive, Chicago IL 60606; (312) 750-0900
- Langboard
Inc., 1000 Springhead Road, Willacoochee, GA; (912)
534-5959; Fax (912) 534-5904; email sales@langboard.com
- Louisiana-Pacific
Corp.; P.O.Box 1525, Lake Oswego, OR 97035; (503)
624-9004
- Medite
Corp. (800) 676-3339, (541) 826-2671
- Norbord
Industries, Inc.; PO Box 26, Deposit, NY 13754
- Pan
Pacific Products, Inc.; Rt. 4, Box 371, Hwy. 3, Broken
Bow, OK 74728; (405) 584-6247
- Plum
Creek Manufacturing, L.P.; PO Box 1990, Columbia
Falls, MT 59912-1990; 406-892-6237
- Sierrapine
Ltd.; 4300 Dominguez Road, Rocklin, CA 95677; (916)
624-2473
- Temple-Inland;
TX
- Weyerhaeuser
Co.; 505 South 336th Street, Suite 100, Federal
Way, WA 98003; (800) 458-7180
- Willamette
Industries, Inc. P.O.Box 885, Ruston, LA 71273;
(318) 255-6258
Q:
How is MDF made ?
A: Take
a look at this brief description from the Australian Wood
Panel Association :
http://www.woodpanels.org.au/publications/default.asp
Q:
Now that I have MDF, what kind of joints can I use?
A: Because
MDF can be milled to just about any profile, there are many
possible joints. However, not all make sense in the context
of speaker building.
- butt
- this simplest of joints may not be ideal for furniture
but works very well for building speakers, especially when
combined with biscuits (for alignment) and screws (for holding
strength while the glue dries).
- miter
- works well when using pre-finished MDF (veneered or laminated)
thus leaving no exposed unfinished surfaces.
- lock-miter,
dovetail and other routered joints - works just like
lumber. These joints have limited use in most speaker enclosures.
- rabbets,
dadoes, grooves and other saw cut joints - same as with
hardwood. Note that these can also be cut with a router.
These joints may be useful, depending on the design of the
speaker.
- spline,
biscuit, dowel - as with lumber, the glue joint is stronger
than the MDF. Dowel holes should be 0.002 to 0.003 inch
larger than the average dowel diameter, and 1/32 to 1/16
inch deeper than the actual depth used. Plain or spiral
grooved dowels are preferred over fluted or multigrooved
dowels. Biscuits are very handy for alignment of parts in
addition to the additional glueing surface provided.
MDF can
also be edge glued to make larger surfaces, although this
is not likely to happen except with exceptionally large speakers.
Panels can be scarfed, doweled, tongue & grooved and finger
jointed.
Q:
How may various fasteners be used with MDF?
A: While
a woodworking joint (see above) is preferred over a fastener,
some typical fasteners may be used as follows. Note however
that this increases the risk of spliting and seperation of
the material.
- staples
- Do not staple within 3/4 inch of any corner. Coated staples
hold better than smooth staples. Use a finer wire staple
if splitting is a problem. Drive at right angle to the surface
to avoid bending.
- nails
- The same rules apply to nails as they apply to staples.
Use ring-shank nails to avoid fiber raising around the nail
head; do not use smooth nails.
- screws
- Drill pilot holes between 85 % and 90 % of the root diameter
of the screw used and at least as deep as the screw. Untapered
sheet metal screws with constant size shank are good; wood
screws are not recommended. Pilot hole sizes and minimum
edge distances for common screw sizes are :
Screw
Size |
Pilot
hole (inch) |
edge
distance (inch) |
#6 |
3/32 |
1/2 |
#8 |
7/64 |
5/8 |
#10 |
1/8 |
1
|
Do not
overtighten screws and force screw heads into the surface.
Do not rely
solely on the above fasteners for building speaker enclosures.
This is especially true for butt joints. Combine glue with
screws for a simple and strong joint.
Here's another
tip on using screws in MDF.
Q:
How do I mount drivers to an MDF baffle ?
A: Screw
holes on a driver's mounting flange often do not provide enough
clearance from the edge of circular cutout to satisfy the
recommended edge-to-screw distance (see above).
Furthermore MDF is not ideally suited to hold screws as tightly
as other materials.
Some speaker
builders use T-nuts - a device inserted into the baffle that
contains an inside thread to hold a machine screw. One variant
is a "riveting
T-nut". Another possibility is to use thread inserts
such as the Tap-Lok.
Unfortunately, these devices are not always easy to use and
can still damage MDF, leaving behind a useless hole.
A better
method is to glue a material that holds fasteners better than
MDF to the inside of the baffle. This has the added benefit
of strengthening the baffle.Void-free plywood is a good choice.
If possible, it is a good idea to chamfer the inside circular
cutout edge of the plywood so as not to inhibit air flow to/from
the driver's rear.
Q:
What kinds of glues can I use with MDF?
A: Good
glues to use are gap-filling glues such as polyvinyl acetate
(PVA) typically known as white (paper) and yellow (wood) glues,
or modified PVA glues like Titebond II. Epoxy, urea, polyurethane
and hot melt glues may also be used.
Note that
raw MDF is very porous. Use a generous amount of glue to ensure
a proper bond.
Q:
How can I finish my MDF speaker?
A: For that
finished look, there are many options requiring different
levels of woodworking skills.
- The box
may be painted. Be sure to seal and prime the surface before
painting to ensure even absorption on all surfaces. A high
gloss piano finish can be made with combinations of spray
enamel, spray lacquer or other topcoats. A little experimentation
at this juncture can be very rewarding.
- The box
may be laminated. Options include melamine, Formica, or
even contact paper. Be sure the surface is clear of dust
before applying any laminate.
- The box
may be veneered. Carried out properly, veneering can yield
a very professional looking speaker. Refer to the references
below for veneering info. A veneered surface can be finished
with lacquer, varnish, oil or wax depending on individual
taste. Stains and dyes may be used to modify the color as
desired.
WoodWeb's
Finishing
Knowledge Base offers several articles relating MDF; check
them out !
Q:
Where can I get veneers and pre-veneered MDF?
A: Veneers
are available from many sources in a wide variety of species,
cut and color. Veneering your own cabinets can give your speakers
a look that might otherwise be difficult or impossible to
obtain commercially. Some pre-veneered MDF is also available,
some in very exotic veneers. Sizes and thicknesses vary. Here
are a few of sources :
Q:
Are there any other tips for using MDF in speaker enclosures?
A: Some
members of the DIY
Loudspeakers list have submitted the following tips for
working with MDF.
- Apply
the finish to the enclosure after assembly. Then cut the
speaker holes. This gives the best appearance for the least
work.
- Use shelf
braces to stiffen the box and to further support edge joints.
Also use 3/4 x 3/4 inch lumber along the inside of edge
joints for extra strength and for stiffening.
- Use a
table saw for dados and grooves when possible. This usually
gives better, straighter results.
- On large
panels with no bracing or shelves attached, reinforce the
panel with one or more 3/4 x 3/4 inch ribs.
- If using
particle board, fill exposed edges with spackle or wood
filler. Then sand all surfaces thoroughly to get a smooth
surface. Prime before painting.
- Two coats
of yellow glue applied 10 minutes apart may be used to seal
MDF edges.
- Wood
or autobody sealer may also be used to seal MDF edges.
- To avoid
stripping threads when mounting drivers to MDF baffles use
threaded inserts such as T-nuts.
- Excess
glue may be removed before it dries with a damp rag. For
pre-veneered MDF, care should be taken to avoid smearing
glue into the wood grain. An alternative method is to scrape
off the glue in its semi-hard state.
Q:
Where can I get more info on MDF or related woodworking information
as it relates to speaker building?
A: Here
are some useful references and resources for speaker builders
interested in enhancing their woodworking abilities :
- Enclosures
Materials, by Jonathan Nihil.
- The
World of Engineered Wood by the Composite Panel Association
and the PB-MDF Institute. This is a great industry site
pertaining to particle board and MDF that has many links
to other industry related sites.
- The
Australian Wood Panel Association web site.
- The
Woodworking Catalog
- Understanding
Wood by R. Bruce Hoadley, (c) 1980 The Taunton Press,
ISBN 0-918804-05-1
- A
Manual of Veneering by Paul Villiard, (c) 1975 Dover
Publications, Inc., ISBN 0-486-23217-4
- Understanding
Wood Finishing by Bob Flexner, (c) 1994 Rodale Press,
ISBN 0-87596-566-0
- Wood
Finishing With George Frank by George Frank, (c) 1988
Sterling Publishing Co, ISBN 0-8069-6563-0
- Fine
Woodworking on Marquetry and Veneer (c) 1987 The Taunton
Press, ISBN 0-918804-74-4
- MDF
From Start to Finish. 1980, National Particleboard Association,
Gaithersburg, MD
- Sheet
Goods for the Woodshop by William Duckworth; Fine Woodworking
magazine, April 1996
- Veneering
a Tabletop by Michael Burton; Fine Woodworking magazine,
October 1995
- Basics
of Vacuum-Bag Veneering by David Shath Square; Fine
Woodworking magazine, December 1994
- Easy
Veneering with a Household Iron by Mario Rodriguez;
Fine Woodworking magazine, October 1994
- A
Woodworker's Guide to Medium-Density Fiberboard by Jim
Hayden; Fine Woodworking magazine, February 1994
- New
Tools Make Laminating Easy by Monroe Robinson; Fine
Woodworking magazine, April 1993
-
Forest
Products Laboratory. 1999. Wood handbook--Wood as
an engineering material. Gen. Tech. Rep. FPL-GTR-113. Madison,
WI: U.S. Department of Agriculture, Forest Service, Forest
Products Laboratory. 463 p.
Q:
Where do I send comments and corrections on this FAQ ?
A: Use the
"About" page on this site to send comments and corrections.
Original
HTML version compiled by Dylan Kelly
|