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Model Forum / General / Models / April 2009Making waterproof cable connector on lathe - which plastic?
Fancy making some waterproof connectors (similar to http://www.qvsdirect.com/fiximages/files/weatherproof_accessories/aqua_safe_conn ector_large.jpg) so wondering what plastic to use. I've heard that Nylon will soak up water, so would acetal or Delrin be better? > Fancy making some waterproof connectors (similar tohttp://www.qvsdirect.com/fiximages/files/weatherproof_accessories/aqu...) > so wondering what plastic to use. > > I've heard that Nylon will soak up water, so would acetal or Delrin be > better? Delrin is just the DuPont trade name for acetal. I wouldn't be too concerned about nylon in water (unless your lathe is on a submarine ). It is hygrascopic, which means it absorbs water, but it doesn't have too much of an effect and it will only absorb a certain amount. It changes size slightly and gets tougher, but looses some of it's tensile strength -neither to an extent that would effect this application though. If buying it for the job then I'd prefer to machine acetal, but if you've got some nylon lying around use that. There used to be someone on ebay who sold cheap offcuts of plastic bar, don't know if they are still there -worth a look. Regards Kevin > > Fancy making some waterproof connectors (similar tohttp://www.qvsdirect.com/fiximages/files/weatherproof_accessories/aqu...) > > so wondering what plastic to use. [quoted text clipped - 15 lines] > Regards > Kevin As far as I know, Delrin and acetal are different, Delrin is stronger but acetal is less hygroscopic. There's a place near me that sells PVC rod too - is that easy to work with? I've got a Myford Super 7 and use indexable tools. Worth getting some bits of each in anyway, plenty of other projects to start (need to make a threaded adaptor for an American pump - need to cut 11.5tpi internal thread) >> > Fancy making some waterproof connectors (similar tohttp://www.qvsdirect.com/fiximages/files/weatherproof_accessories/aqu...) >> > so wondering what plastic to use. [quoted text clipped - 22 lines] >of other projects to start (need to make a threaded adaptor for an >American pump - need to cut 11.5tpi internal thread) Delrin is Acetal. DuPont invented Acetal Homopoylmer, and the other manufactureres developed Acetal Copolymer (which has randon ethylene oxide molecules dotted around the chains) to get around the patent, but both are PolyOxyMethylene (POM) or Acetal in laymans parlance. The homopolymer (Delrin) is marginally stiffer, but is less suitable for applications where it will come into prolonged contact with HOT water, where thermal oxidation can rapidly cause failure. Both are hygroscopic to the extent they must be dried thoroughly before moulding, but compared to Nylons their absorbtion is insignificant in terms of application and use. Anyway, Nylon/Acetal/PVC/ABS are all suitable as long as you use an elastomer seal to prevent ingress. Peter If buying it for the job then I'd prefer to > machine acetal, but if you've got some nylon lying around use that. > There used to be someone on ebay who sold cheap offcuts of plastic > bar, don't know if they are still there -worth a look. > > Regards > Kevin I'm still there, just moved the store to .com is all; http://stores.shop.ebay.com/The-Great-Industrial-Garage-Sale__W0QQ_armrsZ1 Nylon can absorb up to 25% of its weight in water - UHMW absorbs virtually zero and delrin only a few percent. If that connector is going to see any rough use, I'd suggest UHMW because it's virtually unbreakable. >I'm still there, just moved the store to .com is all; > [quoted text clipped - 5 lines] >If that connector is going to see any rough use, I'd suggest UHMW >because it's virtually unbreakable. Absolute bollocks. Nylon will absorb around 2.5% of its weight in water at equilibrium conditions, and a maximum of around 8%, but only in super-saturated immersion conditions. It will then release the absorbed water and give up its weight and reverse the size change as the conditions ger drier. If you get a hydrolysis stable grade (developed for automotive use) it will still absorb some water, but without the molecular dis-association that leads to size changes. Acetal will absorb around 0.25% at equilibrium and a maximum of around 0.85% in saturation, but the size change in Acetal is neglible. UHMW-PE, to give it it's proper name (Ultra High Molecular Weight POLYETHYLENE) ie extremely tough though, so correct on one account. Peter > Absolute bollocks. Now then Peter, no need to beat about the bush. Tell us what you really mean :) Cliff Coggin. > If buying it for the job then I'd prefer to >> machine acetal, but if you've got some nylon lying around use that. [quoted text clipped - 5 lines] > >I'm still there, just moved the store to .com is all; No, the relevant seller us Ringwood Precision:- http://stores.shop.ebay.co.uk/Ringwood-Precision-Engineering Selling from New York isn't relevant to ukrme :-| Mark Rand RTFM > If buying it for the job then I'd prefer to > [quoted text clipped - 14 lines] > If that connector is going to see any rough use, I'd suggest UHMW > because it's virtually unbreakable. UHMWPE is a fantastic material for some uses, mainly involving wear resistance. But it is an absolute pig to machine and requires razor sharp tools. I wouldn't reccomend it for this application, massivly over specced. Virtually any engineering plastic would do. Quite agree with Peter regarding water. Regards Kevin > > If buying it for the job then I'd prefer to > [quoted text clipped - 23 lines] > Regards > Kevin Think I'll just get some Acetal - it's not too critical whether it absorbs water or not - the threads it will screw onto aren't formed very well anyway so I'll probably have to fudge it with PTFE tape anyway |
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