Materials To Know: Baltic Birch

April 26, 2016 by Gerrit Coetzee 73 Comments

Long ago, when I wanted a plywood sheet, I would go to the local big box hardware store and buy whatever was at the center of the optimization curve for cheapest and nicest looking. I would inevitably suffer with ultra-thin veneers on the top, ugly cores, unfinishable edges, warping, voids, and other maladies of the common plywood. One day I said enough is enough and bothered the salesman at my local lumber supply until he showed me one that wasn’t awful.

There are subtle clues that the Baltic Birch I've purchased is Russian. — There are subtle clues that the Baltic Birch I’ve purchased is Russian.

Baltic birch differs from other plywoods in a few ways. Regular plywood is usually made locally from the cheapest possible core wood in alternating grain layers laminated together with a hardwood veneer on the top. There are interior and exterior grades. The exterior grades are usually made with a different glue, but don’t necessarily denote a higher quality or stability. Some of the glues used can be toxic. Wear a respirator. In normal plywood, the ATSM or BB standards only apply to the face veneers used to finish the product. The core can be of whatever quality is convenient for the manufacturer.

True Baltic Birch is made in the Baltic Region with the biggest producers being Russia and Finland. Outside of the US it is sometimes called Finnish Birch or Russian Birch plywood for this reason. It is made from only top quality birch veneers laminated together with no filler wood. It is also unique in the care taken to make sure each layer of the wood is patched so there are no voids. All Baltic Birch is made with exterior grade glue, and when properly sealed will work for outdoor applications. There are grades of Baltic birch for marine applications and exceptionally void free aircraft grade plywood at a much higher cost.

The easiest way to spot Baltic Birch if you’re American is its form factor. Baltic birch comes in 1525 x 1525 mm squares, which approximates to 5 ft x 5 ft. Some people have said that manufacturers have started to produce 4 ft x 8 ft sheets specifically for the North American market, but this information comes with a caveat that these are usually lower grades made locally or in China parading under the name. The metric form factor extends to the thicknesses of the sheets. In America they will be sold as inch, but fit pretty closely to a metric form.

3 mm ≈ 1/8″ (3 plies)
6 mm ≈ 1/4″ (5 plies)
9 mm ≈ 3/8″ (7 plies)
12 mm ≈ 1/2″ (9 plies)
18 mm ≈ 3/4″ (13 plies)
– From [3] Ultimate guide to Baltic birch.

The core of regular hardware store plywood. Pretty bad in comparison.

There are some really nice practical features of Baltic Birch. One of my favorites is the absolute uniformity of the layers. This means that two pieces of birch can be laminated together and the seam between the two becomes indistinguishable. I’ve used this to make cases by CNC routing out the inside of a sheet of Baltic birch, drilling some holes for alignment pins, and then laminating the whole assembly together. We’ve covered a few readers who have had similar ideas. Since the layers are uniform you can also do interesting things when combined with a CNC router. For example, carefully milling away the layers you can get a topographic map of the object.

Baltic Birch is also significantly flatter and more stable than other plywood options. It is commonly the material used for fences on expensive tables saws. It moves less during temperature swings and changes in ambient moisture. This is one of the reasons it’s popular with fine furniture builders. This also makes Baltic birch a good option for home CNC builds, certainly better than MDF . Due to the higher quality wood and better manufacturing it is quite strong as well. It is a great structural wood.

2016-04-22_12h03_06 — Explanation of the grading scale for Baltic Birch from [1] Dan’s hobbies.

Baltic birch holds stains very well on both its faces and its edges. It’s as easy to paint and glue as any wood. As far as surface finish goes it’s important to note that as mentioned previously, Baltic Birch is graded to a different scale than regular plywood. The grades will determine how the face veneers are treated. B/B is the highest grade with both sides being defect free. B/BB is much more common and is what you are likely to find. I have not found C or CP grades in the US. My guess is that we have plenty of low grade plywoods to compete with it. It is likely found nearer to the areas where it is produced.

This is on the non-finishing side of a Baltic Birch panel. You can see the care taken to fix knots and voids. This will be done through the whole sheet. The face of the board will not have marks. This is a B/BB grade sheet. If it was B/B both sides would be without patches.

Baltic birch is more expensive than the regular grade stuff. So a sheet of ¾” thick Oak veneer plywood with a pine core, interior grade, from Lowes is about 35 US dollars where a similar sheet of 18mm Baltic Birch will run around 65 dollars.

I’ll still occasionally purchase a cheaper sheet of plywood when I have a non-critical application (like garage shelving), but when I am doing something precise or nice I’ll spend the extra on the birch plywood. While I love this material, I am by no means a wood worker. Have any of you had experience with this plywood? Is there an even better plywood out there?

I’ve left my sources below for further reading. [3] Ultimate Guide to Baltic Birch is very good.

[1] Dan’s Hobbies. (2016). A baltic birch plywood primer | Dan’s Hobbies. [online] Available at: http://www.dans-hobbies.com/2010/01/09/a-baltic-birch-plywood-primer/ [Accessed 19 Apr. 2016].

[2]Wikipedia. (2016). Plywood. [online] Available at: https://en.wikipedia.org/wiki/Plywood [Accessed 19 Apr. 2016].

[3] Stephens, (2014). Ultimate Guide to Baltic Birch Plywood: Why It’s Better, When to Use It |. [online] Woodworkerssource.com. Available at: http://www.woodworkerssource.com/blog/tips-tricks/your-ultimate-guide-to-baltic-birch-plywood-why-its-better-when-to-use-it/ [Accessed 19 Apr. 2016].

MDF as a mold master. It works, but nowhere near as well as tooling board.

Materials To Know: Medium Density Fiberboard

April 14, 2016 by Gerrit Coetzee 77 Comments

MDF is the cheapest and flattest wood you can buy at local hardware stores. It’s uniform in thickness, and easy to work with. It’s no wonder that it shows up in a lot of projects. MDF stands for Medium Density Fiberboard. It’s made by pressing materials together along with some steam, typically wood, fibers and glue. This bonds the fibers very tightly. Sometimes MDF is constructed much like plywood. Thinner layers of MDF will be made. Then those layers will be laminated together under glue and steam.The laminated MDF is not as good as the monolithic kind. It tends to tear and break out along the layers, but it’s hard to tell which kind you will get.

Proper way to attatch a fastener to MDF.

MDF is great, but it has a few properties to watch for. First, MDF is very weak in bending and tension. It has a Modulus of Elasticity that’s about half of plywood. Due to its structure, short interlocking fibers bound together by glue and pressure, it doesn’t take a lot to cause a crack, and then, quickly, a break. If you’d like to test this, take a sheet of MDF, cut it with a knife, flip it over, and hit the sheet right behind your cut. Chances are the MDF will split surprisingly easily right at that point.

Because of the way MDF is constructed, fasteners tend to pull out of it easily. This means that you must always make sure a fastener that sees dynamic loads (say a bearing mount) goes through the MDF to the other side into a washer and bolt. MDF also tends to compress locally after a time, so even with a washer and bolt it is possible that you will see some ovaling of the holes. If you’re going to use screws, make sure they don’t experience a lot of force, also choose ones with very large threads instead of a finer pitch. Lastly, always use a pilot hole in MDF. Any particle board can split in alarming ways. For example, if you just drive a screw into MDF, it may appear to go well at first. Then it will suddenly jump back against you. This happened because the screw is compressing the fibers in front of it, causing an upward force. The only thing pressing against that force is the top layer of laminate contacting the threads. The screw then jumps out, tearing the top layer of particle board apart.

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Materials To Know: Tooling And Modeling Board

March 9, 2016 by Gerrit Coetzee 35 Comments

I was in a fit of nerd glee the first time I used tooling board. I’d used MDF for similar purposes before, and I doubt I ever will again. Called Renshape, Precision Board Plus, or that green stuff people on another continent buy; it’s all the same extremely useful, unfortunately expensive, stuff. It’s hard to pin down exactly what tooling board is. Most of the blends are proprietary. It is usually a very dense polyurethane foam, sometimes by itself, sometimes with a fine fiber filler.

What makes tooling board so good is its absolute dimensional stability and its general apathy to normal temperature swings. (It even comes in versions that can go through curing ovens.) It is impervious to humidity. It has good surface finish, and it machines perfectly without wearing down tools.

The CNC set-up I coaxed precision molds out of.

This stuff is really tops as far as machining goes. I got super precise molds out of a very basic CNC machine at the LVL1 hackerspace. Renshape cut easily at a high spindle speed, and put practically no load on the machine. Climb and conventional milling were equal load wise with no immediately perceivable difference in finish. In the end I hit the precision range of my cheap digital calipers: +-.005mm, when the temperature is right, the battery is a charged, and the planets align.

I like to do resin casting when I get serious about a part. If you are making a master mold, there’s nothing better than tooling board. I’ve used both Renshape 460 and Precision Board Plus. Both impart a very light matte pattern, equivalent to a light bead blast on an injection mold. There’s no finishing required, though I mistakenly bought Renshape 440 at first and had to sand it a little to get the finish I wanted.

Tooling board is great for masters in metal casting, and is often used in the industry for just that, especially if quick and accurate prototypes are needed. It’s also tough enough to last through a few rounds of metal stamping in the home shop.

If you are doing lay-up for carbon fiber, fiberglass, or leather, this is also a very good choice. It will be unaffected by the chemicals, heat, and vacuum you may use in the process. It is tough enough hold alignment pins for proper set-up without premature ovaling. It is also a very good choice for vacuum forming.

Tooling board is, unsurprisingly, really good for tooling. It’s a great material for soft-jaws, alignment fixtures, and assembly fixtures, especially if you are doing delicate precision assemblies.

If you’re made of money, tooling board can be used for models, signs and props. It sands, shapes, and files extremely well. It bonds well to a lot of substances. It also takes paint very well with none of the absorption properties of wood or MDF. Most professional model shops will use it.
The one big flaw of tooling board is its price — this stuff is expensive. There’s no good DIY version that I’ve scrounged up so far. If you’re making a mold master, a fixture, or anything where you need tooling board’s properties and you are likely to get a few uses out of the board, then it’s probably worth it. Also, be careful of sellers selling plain “Renshape” it is probably going to be the lower grade Renshape 440 and not the more expensive Renshape 460 (or equivalent), where you start to really see the surface finish advantage of the material.

Tooling board is an industrial material. Typically you can call up a supplier and tell them what you’d like to do with it and they will be able to help. If you are making tools for carbon fiber quadcopter frame lay-up, let them know and they’ll have a formulation for that. If you are resin casting, there’s a formulation that gives superior surface finish.

It’s a pretty common material in the industrial scene, but I don’t see it a lot on the hobby scene. This is almost certainly due to its cost, as well as a shortage of small quantity re-sellers. (If someone starts selling assorted sizes on eBay for a reasonable price you have at least one buyer in me.) However, after using it in the niches it is designed for, I really don’t use anything else. I used to hack MDF to fit, but MDF is awful to paint, has no dimensional stability, and dulls tools really fast.

Are you a fan of tooling board? Have a good source? If you have anything to add, let us know in the comments.

Materials To Know: Acetal And Delrin

March 3, 2016 by Gerrit Coetzee 65 Comments

Delrin, Acetal, and its many trade names is a material properly known as Polyoxymethylene or POM. It is one of the strongest plastics and is a good go-to material when you want the best properties of plastic, and don’t need the full strength of a metal part. It was originally formulated to compete with Zinc and Aluminum castings after all.

I won’t go too deep into the numbers behind POM. If you need the Young’s Modulus, you probably don’t need this guide. This is intended to be more of a guide to its general properties. When you’re looking for something to fit an application it is usually easier to shift through the surface properties to select a few candidates, and then break the calculator out later to make sure it will work if you’re uncertain about the factor of safety.

The most popular property of POM is its ease of machining. While doing this research every single site I came across referred to it as the most machinable plastic. That’s about as objective as subjective praise can get. It doesn’t tend to grab tools like, for example, HDPE. It also chips nicely unlike UHMW and Nylon. Some plastics, like UHMW, have the unfortunate tendency to render the dials on a mill or lathe meaningless as the plastic deflects away from the tool. POM does not do this as much. Of course these other plastics have their strengths as well, but if any plastic will do, and you’re machining, POM is a very good choice.

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