Wooden Coasters

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Project Timespan

September 2020 and ongoing; these are a collection of coasters I made from September to December 2020, but there’s more where that came from!

Inspiration

In my opinion, a set of well-made coasters is one of the best gifts one can give to family, friends, or lucky acquaintances. For one, they are utilitarian, protecting a bar top or table surface from unsightly drink stains. For another, they are personalizable, especially with a CNC router, and one can customize the design to fit the preferences of the giftee.

Here’s a link to another project in which I laser cut more than three hundred Philadelphia-themed coasters for a friend’s wedding. A real fun project to make!

Project Overview

Making coasters is a straightforward process on the CNC router, as the ones I typically make are logos or symbols from colleges and universities; as such, images abound online and can typically be found at high-quality resolution.

Coaster Design and Materials

The initial step is to find a high-quality image from online of the desired logo. For me, the first coaster I CNC’d was a design of the Weill Cornell Medicine logo. To properly dial in the settings for machining, the image will need to be converted into a vector format design; fortunately, there are numerous free options online for converting JPEG or PNG to SVG format.

I sourced the wood from an online vendor, Bell Forest Products, whose physical location is in Michigan. They offer a large selection of exotics at reasonable prices, and I love their “Handpick Your Board” feature as I can check for grain pattern and knots as well as be notified of any twist or warp in the board. 

As coasters are generally in the 3.5″ to 4″ diameter range, I choose a board that is at least 4″ in width. For coaster thickness, the options are limited as the majority of the wood items are at least an inch in thickness. I prefer a certain heft to the coaster – the weight of quality, so to speak – and I find that 3/8″ has a tasteful thickness to it. That being said, I’ve made coasters up to 9/16″ or even 3/4″ that look great as well, if a tad on the chunky side.

A coaster is just a flattened cylinder, if you think about it, so the design process was extremely simple in Fusion 360, as all I did was extrude the image into the top surface of the blank coaster.

Machining the Coasters

I relied on three different bits for machining – a small endmill or ball nose bit for the flat sections, an engraving bit for lines and lettering, and a larger endmill for cutting around the outside.

From loading to offloading, the time to machine a coaster (highly dependent on design, coaster thickness, coaster wood material) is from 30 – 50 minutes or so using my hobby 3018 Sainsmart CNC.

Finishing the Coasters

After lightly brushing away sawdust and small flecks of material hanging off from the face of the coaster, I then use a random orbital sander and first smooth the vertical border at 80 grit, holding the machine with my feet and rolling the coaster against the sandpaper in a controlled fashion. I chamfer the edges and lightly sand the bottom as well. Going up in grits successively from 80 – 120 – 150 – 180, I continue this process. As I don’t want to efface any details from the top surface, I generally hand sand or give it a quick go at 180 and 220 at the slowest oscillating setting. After the 180 sanding, I wet the coaster to raise the grain and I resand at 220 grit.

I really am not sure about finish for the wood coasters. I’ve used spar urethane with decent results as well as tung oil with so-so results. For the majority of the coasters, I applied mineral oil followed by a beeswax-mineral oil combination of 4:1 or 5:1 ratio, the same that I use for seasoning cutting boards. While this finish may not be the most durable, it is simple to reapply, non-toxic, and brings out the warmth of the wood and the depth of the grain.

Final Results

Let’s just say that I made a lot of coasters over a relatively short amount of time. Over the course of about three months, I machined a total of 70+ coasters. Of these coasters, the designs consisted of 37 Weill Cornell Medicine, 10 University of Pennsylvania, two UCLA, four Renmin University of China, two University of Rochester, two Ural State Technical University, one Rockefeller University, one Hospital of Special Surgery University, two Emory University, one Rutgers University, one MIT, and ten others (five Snoopy / Charlie Brown, one New York Hospital, and four anniversary coasters for my friend). I will spin off the latter three coaster designs into smaller posts down the line!

There are two widely used metrics for quantifying wood density and wood hardness, which are specific gravity and Janka hardness, respectively. Specific gravity, unitless, is the relative density of a material with respect to water at 4° C (usually). Numbers less than 1 are less dense than water and would (wood) float. Janka scale, in units of pound-force or Newton, is the force required to embed a 0.444 inch steel ball halfway into a block of wood. Balsa, one of the lightest wood species out there (though a hardwood, technically), has a specific gravity and Janka hardness of 0.2 and 70 lbf, respectively. Ironwood, a species that sinks in water, has a specific gravity and Janka hardness of 1.5 and 3,260 lbf, respectively.

For organization’s sake, I will present the wood species I used in ascending order based upon their respective Janka hardness. All specific gravity and Janka hardness numbers from the Bell Forest website.

Mahogany (Genuine aka Honduran / African)

Specific Gravity: 0.59 / 0.53 |  Janka Hardness: 800 lbf / 1100 lbf

Region or Country of Origin: From Southern Mexico to central South America / West tropical Africa

This was the first time I had ever worked with either mahogany species. Mahogany is one of those wood families whose name rolls off the tip of the tongue – a word that adds a 10% luxury tax to whatever item you had just described. However, I found that both species were too open-grained and did not hold detail well, nor did the color stand out in any way compared with the other species I explored.

Total made thus far: 22

Maple (Soft)

Specific Gravity: 0.63 |  Janka Hardness: 950 lbf

Region or Country of Origin: North America

Simple, cheap, utilitarian species that works well  if one accentuates with color (see anniversary coaster project – to come). It can be difficult to appreciate fine design details in the light tone of maple, but I find that this wood is certainly underappreciated!

Total made thus far: 6

Redheart

Specific Gravity: 0.68 |  Janka Hardness: 1200 lbf

Region or Country of Origin: Southern Mexico to southern Brazil and Paraguay

Redheart is such as beautiful wood species with its brilliant pink-red hue that exudes luxury and elegance. Very easy to work with and finishes so nicely! The only gripe I have with it is that the sawdust produced can color whatever it settles upon in a pink dusting that makes a mess of things, so watch out for that!

Total made thus far: 11

African Padauk

Specific Gravity: 0.72 |  Janka Hardness: 1970 lbf

Region or Country of Origin: Central and tropical West Africa

A pretty, pretty wood that starts off as bright orange-red but darkens as it oxidizes. I have used padauk frequently in cutting boards, and I’ve had a good time with it in coasters as well. It has a nice, consistent grain that shows well the details.

Total made thus far: 4

Padauk has a similar appearance to redheart, and I didn’t take any great pictures of the padauk coasters – the two Penn coasters at the top of this image are padauk, and the remainder are redheart.

Gonçalo Alves (Tigerwood)

Specific Gravity: 0.86 |  Janka Hardness: 2160 lbf

Region or Country of Origin: From Mexico southward to Brazil

With a Janka hardness level in the 2000s, gonçalo alves has a beautiful streaked pattern of light and dark brown, hence its other name, tigerwood. This wood species holds detail well, is not too hard to work with, and has a beautiful contrasting pattern.

Total made thus far: 6

Chakte Viga

Specific Gravity: 0.85 |  Janka Hardness: 2250 lbf

Region or Country of Origin: Tropical areas of Mexico and Central America

Chakte Viga has a beautiful orange hue with small pores that hold detail well. I really enjoyed working with this wood, and I find the color really warm and inviting. Probably my favorite species overall to work with, though I have made only a few coasters from this wood.

Total made thus far: 3 if I recall

Katalox (or Mexican Royal Ebony)

Specific Gravity: 1.04 |  Janka Hardness: 3660

I had never heard of this wood species before, but the extremely dark grain with occasional streaks of light yellow caught my eye. There is a noticeably greater heft to coasters machined from this species. It holds details very well given its tight grain, so it is excellent for calligraphic text, though its extreme hardness does challenge the tools. I hope to incorporate this species into a cutting board one day.

If I were to make a two-colored set of high-end coasters for a friend, I would go for a combination of katalox and redheart.

Total made thus far: 10+

Lessons Learned & Improvements

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I have gone through several iterations of trial and error by now, and while I am sure that there still remains much I can do to improve my process of making coasters, I will share some of the lessons I learned. 

 

1. Never rush with machines – make sure you double-check test all the settings you dial. This also goes with the speed settings – I have had several bits break on me when attempting to cut through extremely hard wood species.

 

2. Have fun with wood species – it’s exciting to move away from the standard maple, oak, or cherry. I had never heard of Goncalo Alves before machining a set of Cornell coasters from that species. A distinctive grain pattern for sure!

3. Be liberal with bit changes – they make bit sets for a reason, so choose quality over expediency and select the optimal bit for the task at hand.

 

4. Work during normal working hours – the machine can get very noisy, so if you don’t have a noise enclosure (like me), I’m sure the neighbors would appreciate it the CNC machine is turned off during the nighttime hours!

5. Flatten the workpiece beforehand – whether through purchasing pre-finished material or using the CNC, the piece should be level so that any engraving, in particular, will be of uniform thickness. 

6. Orient the grain horizontally – somewhat of a personal preference, but I find that by aligning the grain with the horizon, one’s eyes can make out better the details of the coasters

With regards to improvements, I strive to combine multiple media in my projects – for example, I have dabbled in epoxy with coasters, and that is a project that I will touch upon later. One feature that I would like to incorporate is inlay. There are great tutorials online of inlaying projects with V-carve and other programs, but I have not yet been able to delve deep into these tutorials. 

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Reflection

As I have mentioned above, I find giving gifts to be such an enjoyable activity, and so far everyone who has received a coaster has really enjoyed them. I am certainly not a live-to-eat type of person, but I do enjoy sitting down and getting know better an acquaintance, friend, or family member over food and some drinks. So, now that I have made the coasters for the drinks, time to get cranking on placemats for the plates!

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