Working with Delrin

[Michael Rogers]

Does anyone have experience of, hence useful advice to impart about, making 'things' from delrin (acetal - same stuff?)? I have in mind things like drilling and shaping.

Bit difficult to explain briefly the application. It relates to aspects of junk rig, to do with sheet spans and parrels, and I think involves what are referred to, somewhat cryptically, as euphroes in 'Practical Junk Rig'. A sort of block without a sheave (incidentally, the etymology of the word 'euphroe' intrigues me. It is surely not Chinese, so whence....?). In Blondie Hassler's day they were made, presumably usually home-made, of hardwood. These days it has occurred to me that a combination of delrin euphroes and naked dyneema lines might serve rather well in terms of low-ish friction. Some applications are well served by nylon thimbles, but I'm coming across some where a different shape would help. Not critical, but quite fun, if you know what I mean. Expense will, of course, be a factor, but I thought I would research a bit.

Assistance from the experts, as always, gratefully received.

Michael Rogers

PS  I have found where 'euphroe' comes from - Dutch origin, according to Collins Dictionary. Similar word to German 'Jungfrau'.

[Alan]

Hello Michael,
Delrin is really nice to work, easily my favourite plastic! Machining is no problem, generally no need for lubricant. It's a little stiffer than nylon and does not leave a burr. Working by hand it can be cut easily with a hacksaw but you will need very sharp files to file it otherwise they just slide off without making much impression. When using a pillar drill, clamp the work securely of course and if drilling through thin sheet or through the material into fresh air instead of a piece of scrap, consider reducing the rake of the drill. This means grinding a small flat parallel to the drill axis where the helical cutting edge meets the ground clearance face. Think of the geometry of a spade drill.
When buying, it is sometimes described as POM, an abbreviation of its chemical name. Also available as homopolymer and copolymer with slightly different properties. A great source of information on engineering plastics is the RS Components catalogue but I forgot to check before writing this wether the materials data is available online.
Another low cost source of low friction plastic is high density polyethylene in the form of chopping blocks which I have bought from our local Chinese supermarket.
'hope some of this helps, Alan

[Michael Rogers]

Thanks, Alan, it does indeed help. Wish I had a pillar drill, though!

Michael