I use both Acetal and Delrin, in both white and black. Machining a batch of Delrin parts for most of this week. Did some Acetal parts last week. One-offs that turned into batches.
Delrin is a bit stronger, mechanically, and a bit more abrasion resistant, but, for microscope parts, Acetal is cheaper and you won't notice any difference in use. I guess you will need a matt black finish, so the tip about producing a matt finish is useful. Acetal will hold a decent cut thread. It's much more expensive than urethane or PVC, but much more usable for the kinds of things I make. I made a mould last week for batches of urethane (I think) washers for a run of hand-operatyed submersible pumps. The mix can be varied to give different squashiness (must be a definition of that mechanical term somewhere), and the plastics factory did a run of several specimens with different compositions, until the chap building the pumps was happy with the performance. Then I made a 64-washer mould on a single plate. I don't know how hard/solid urethane can be made. I must admit I am impressed with what can be done with some plastics. The chemistry eludes me, though. One very significant drawback with Acetal and Delrin is that they cannot be glued in any way shape or form, so that needs to be factored into the design stage. Great for one-offs and prototypes, though (until they turn into batches...) Also available in sheets, which is useful for some batches, and useful if you can machine it in the mill (saves repeatedly loading and unloading the chuck). Marcus On 23 Feb 2015, at 18:59, Bruce Layne wrote: > PS - I machine some rubbery plastic parts that have a durometer similar > to soft urethanes. I freeze the parts to make them harder, so they cut > instead of smearing and tearing. > > > > > On 02/23/2015 11:46 AM, Kirk Wallace wrote: >> I am using this site as a reference for making some telescope eyepieces: >> http://home.fuse.net/astronomy/ >> >> Larry chose to use urethane to make the blanks for machining. My >> experience with urethane is that recipes range from rubbery soft to >> pretty darn hard, but not fully hard. I need something that can take a >> .6 mm pitch thread and stand up to assembly cycles. PVC pipe is the >> wrong color, threads okay, but the threads smear easily. Acetal works >> very well, but can't be bonded or painted. Polyester resin might work. >> I'm also considering injection molding blanks from PLA. >> >> I'm wondering, are there forms of urethane that have the same >> characteristics as acetal? Are there other materials that would be better? >> >> > > > ------------------------------------------------------------------------------ > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > with Interactivity, Sharing, Native Excel Exports, App Integration & more > Get technology previously reserved for billion-dollar corporations, FREE > http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
