Working with celluloid is much like working with cellulose acetate, but better. It is not at all gummy, nor does it chip. It is much easier to work than hard plastics such as acrylic and polycarbonate, and filled plastics, which can be notoriously hard on tooling.
For best results, keep your tool bits sharp! HSS is better than carbide in this respect: sharpness is much more important than hardness. Celluloid can be turned on the lathe without coolant, but a bit of water makes a huge difference when sawing, drilling, and milling. We strongly recommend that any power sawing of celluloid be done wet. Power sanding should be done with care, as the material can readily be heated to the point of combustion. If the workpiece begins to give off wisps of smoke (it will normally be the swarf at the surface smoking, rather than the object itself), STOP IMMEDIATELY!
It is very difficult to overheat celluloid while turning it on a metal lathe. It is much easier to overheat it on a wood lathe, so keep your tools as sharp as possible, and take clean, shallow cuts using minimal pressure. Wonderful results can be had turning celluloid on a wood lathe; we know of several Asian master pen turners who do virtually all their work in both celluloid and hard rubber freehand, including threading!
Spade drills or twist drills can be used to hollow out pen blanks. Drills with a titanium nitride (TiN) coating cut more cleanly, thanks to the self-lubricating properties of the gold-colored coating. A twist drill optimized for use with celluloid should be ground pointier, with a 60° included angle instead of the standard 118°, with 12-15° clearance and zero rake. Fast-twist drills help keep the hole clear. As with other plastics, drill speed should be kept relatively slow to prevent overheating. Don't try to do it all in one go, either: take it a half inch or so at a time, backing the drill out each time to clear the swarf and to allow both drill and workpiece to cool. Paraffin is a good lubricant for drilling celluloid; a block can be rubbed on the drill bit, or paraffin oil can be used.
Celluloid is easily glued using epoxy, cyanoacrylates, and
traditional animal glues. It may also be solvent welded with
acetone, MEK (methyl
ethyl ketone), or THF (Tetrahydrofuran).
Celluloid can readily be patched in case of damage or porosity using a paste made from scrap shavings dissolved in one of these solvents. The patch should be allowed to cure thoroughly before being worked down flush. This may take weeks, depending on the solvent, the temperature, and the size of the patch.
Celluloid doesn't have grain, but its patterning often has orientation. This is obvious in the case of laminated or striated patterns, yet it is also true for marbled and especially pearlescent patterns. Because celluloid is made in slabs, the patterns are typically laid out so that their maximum reflectivity is in the vertical axis. When cut into rods or blocks and polished, the brightness will vary as the piece is turned in the hands, giving the celluloid its characteristic shimmer and flash.
Because of its long seasoning process, celluloid objects that are made by hollowing or boring out solid stock are likely to shrink slightly after the support of the core material is removed, though no more than is typical for other plastics. For maximum precision, turn the workpiece slightly oversize, then let it sit at least two days before finishing (further notes here).
Celluloid is somewhat permeable - much more so than acrylics. Although quite a few celluloid pens of the 1930s and '40s carried their ink in direct contact with the barrel (Pelikans and Parker Vacumatics, for example), the risk of staining is real, especially when light-colored celluloids are exposed to highly penetrating inks - purples and reds being particularly troublesome. For this reason, light-colored celluloid sections on vintage pens usually were lined with an impermeable hard rubber insert, though more commonly a solid hard rubber section was used instead.
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