First Chess Set With My CNC Lathe: Fischer's Dubrovnik Chessmen

When my copy of Bobby Fischer and His World by IM John Donaldson arrived in the mail, the first thing I did was look in the table of contents and the index for any information he may have found on Fischer’s long lost Dubrovnik set.  After skimming the massive book for an hour, I didn’t find anything and finally started to read from the beginning.  He has a lot of detail about the contents of Fischer’s delinquent storage container that was auctioned off.  Fischer’s manager of the storage unit tried to hunt down all the contents but no chess set was found. My suspicion is that the owners, or somebody, knew that was Fischer’s container, and kept the set for themselves.  They never tried to sell it because the only way to prove it was Fischer’s would be to prove it was from his storage locker, a bit self-incriminating.

After the 1950 Dubrovnik Chess set design gained popularity, a new version, designed by Andrija Maurović (source: bestchessmenever.com/blog), was released for higher volume production.  Some say it was a “cartoony” version of the 1950 version.  Bobby Fischer obtained one of these sets in 1968 or 1970.  That’s why I refer to this set design as Fischer’s Dubrovnik (FD).  

I used reference photos of actual FD chessmen and the video of Bobby using this set to prepare for the 1972 World Chess Championship to model the design in CAD.

With this being an experimental, first attempt at making this set, I decided to make the black pieces from bocote wood instead of staining the maple as in the original design.  

This was the first set I would produce with my homemade CNC lathe.  I had invested a lot of time and money converting my manual mini metal lathe to be CNC and there was a big question in mind the entire time:  Would it work for woodturning chessmen?  

A lot of people demonstrate their CNC metal lathe capabilities by turning chess pieces from aluminum.  But there are more challenges when turning wood.  The grain can tear leaving a horrible surface finish or even chip out.  The wood can burnish and close up the pores, causing dark spots that finish doesn’t penetrate well.  



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Chip out and grain tearing

Splotchy Finish Penetration From Burnishing

When woodturning by hand, a human can angle the cutting tool in many degrees of freedom.  You can opt between making a shearing cut or a scraping cut depending on the grain direction, angle of the cut, and wood species.   However, with a 2-axis CNC lathe, the cutter is in a fixed orientation, limiting the type of cut.

There isn’t much information available about using CNC lathes for cutting wood.  The main industry use is for larger parts, like railing banisters, or round chair legs.  But with chessmen, the details are much smaller and have sharp angles. 
  
I figured if the CNC conversion of this mini metal lathe didn’t work for making chessmen, then at least I would have a CNC lathe for cutting metal.

The first program I ran on the lathe was a Fischer Dubrovnik pawn out of pine.  I used pine for many trial runs as it’s cheaper than maple.  I knew I would need multiple cutters to reach all the sharp corners of the pawn geometry but figured I would first try it with a single cutter.

First Attempts in Order from Left to Right

I was elated that the lathe and program I created in Fusion360 actually produced something that resembled a chess pawn and not a popsicle.  I rewrote the program to use more cutters.  I was grinding high speed steel by hand to make the cutters.  Ultimately, I found that I could do everything with a right hand cutter, a left hand cutter, and a narrow parting tool.  The only exception was top of the rook that required a forstner bit and a boring bar.  ​

Right Hand Tool, Left Hand Tool, Parting Tool

Extra Tools for Rook: End Mill and Boring Bar

Steady Rest For Manual Turning

After decapitating a few pieces from having the wrong tool offsets, the pieces were better but one flaw still remained,  chip out on the thin collars.  No matter how slow of a cutting feed rate, the collars would chip out.  However, my reaction time to dodging flying pawn heads was ninja level.  

I noticed when making a straight plunging cut there was no chip out on the sides and chip out only occurred when making a cut at a slight angle.  I decided to modify the collars in the CAM program to be straight cuts and finish the angle by hand with a skew.  This may be because the cutter was not executing a perfect shear type of cut and maple is not forgiving in this.  Now an online search shows there are CNC wood lathe knives to buy that have a steep angled v-shape.  This may be a solution to the problem but adds expense to the tooling. Nothing beats the economics of grinding high speed steel tool blanks.

Once the CAM program and cutters were dialed in, the machining time per part was 8 min.  Add an additional 3 min to make the skew cuts on the collar, plus sanding, and it’s about 20 min/piece.  That may seem slow but remember that the majority of the material removal is done up front with the right hand cutter, and I only have to be present to change tools at the end. 

I can’t explain the strange joy of doing other things while the lathe is running.  First I did obvious things like prepare the next wood blank, organize the workshop, and sweep up sawdust.  Then I started to do more things for the irony that I was simultaneously making chessmen.  Since the cycle time was 8 min until a tool change, I could squeeze in a 3 min game of online blitz.

A Trade-off to Form Tools

Chessmen manufacturers in India can turn a piece using a couple of form tools in less than a minute.  Recently, a video was posted showing a machine carving out a piece with two form tools in just a few seconds.  Was I jealous?  Yes.  That puts my single-point cutters on the CNC lathe to shame.  The only advantage of single-point cutters on the CNC lathe is that it can be programmed to turn any piece, any size, any time.  It can turn a 3.5” Dubrovnik rook one minute and turn a 4” St. George King the next.  With form tools, there is an initial investment, and that tool can only produce that one piece.  Once the form tool starts to dull, it can be re-sharpened, but will start to lose dimensional accuracy (unless weld build up and re-ground).  Also, I believe my CNC lathe could be fitted with similar form cutting tools.  

CNC Knights?

The knights were still carved by hand.  These are the first attempts that turned out okay but I may remake them someday.

To carve the knights with a CNC router, I believe the best approach is to look at it as a relief carving from the side, carve half of the symmetry, rotate the piece 180°, and carve the other half.  The final cuts on all surfaces should be made by hand to remove tool marks and look authentic to the originals. I didn’t make a 3D model of the knight from this set. (There is already a pretty good model of Fischer’s Dubrovnik set on thingiverse).  

Here are a few pictures of the completed set.  The varying shades of maple were due to trying several finishes as well as pulling from different wood sources.

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Weighting

Fischer said he preferred the unweighted Dubrovnik sets because they were better for travel.  I don't plan to do much travel with the set, and since I already used a different wood than the original, I though I might as well weight the set. 

I had been scheming an over engineered method for weighting chessmen that I will explain in another article...

Weighting