The MDF FAQ

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

• What does MDF stand for?
• What is MDF?
• What properties does MDF exhibit?
• What does MDF look like?
• Are there any drawbacks to using MDF?
• What are the safety issues to consider when working with MDF?
• Is all MDF the same?
• How is MDF sold?
• What about MDO, particle board, hardboard, void-free plywood?
• Can I build speakers with {MDF | particle board | plywood | solid wood}?
• What should I use to cut and mill MDF?
• Where can I find MDF?
• Who manufacturers MDF and how can I contact them?
• How is MDF made ?
• Now that I have MDF, what kind of joints can I use?
• How may various fasteners be used with MDF?
• How do I mount drivers to an MDF baffle ?
• What kinds of glues can I use with MDF?
• How can I finish my MDF speaker?
• Where can I get veneers and pre-veneered MDF?
• Are there any other tips for using MDF in speaker enclosures?
• Where can I get more info on MDF or related woodworking information as it relates to speaker building?
• Where do I send comments and corrections on this FAQ?

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.

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 :

• Woodcraft
• The Woodworker's Store
• Constantine's
• Boulter Plywood
• B&B Bare Woods
• Woodstock
• McGinnis & Associates
• Flamingo Specialty Veneers
• Certainly Wood
• Alta Resource Wood Suppliers

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.

13-January-2004

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