Press-in threaded inserts - Page 1
Forum section: electronics / projects

author: asgard
author_rank: Regular Contributor
timestamp: March 06, 2013, 10:32:31 pm
content: Hi, guys. I am working on the design work for ruggedized enclosures for the wireless power project. Doing this kind of 3d design is well outside my typical comfort zone, but some common checklist items are foremost in my mind right now:1. Some sort of bosses to support the board assemblies, with tapped holes and a press-in threaded insert (the screw is M2sized). Any ideas about particular sources for the inserts? I looked at Grainger but was pretty disappointed by the selection.I was feeling queasy about going to the "one hung low" market for those, and they typically want minimum orders of 10000parts.2. The material ought to be HDPE or HDPET or polycarbonate, which should have similar "hand feel" to most bench handinstruments. Any thoughts about using high-density ABS, as would be used in a 3d printer or some such process?3. I am really trying to avoid going the sheet-plastic and hole-cutting process, as that obviously would have no environmentalintegrity, and I have always disliked seeing screw-heads hanging outside a box.3. I do not have any "purpose-made" 3d design tool for plastic injection molding as I have zero experience with that. CanSketchup be adapted for that purpose, or do I have to knuckle down and buy something like Autocad to do that?

author: MikeK
author_rank: Super Contributor
timestamp: March 06, 2013, 11:31:22 pm
content: McMaster-Carr has just about everything.

author: daedalus
author_rank: Regular Contributor
timestamp: March 07, 2013, 03:26:09 pm
content: 4) Last things first, unless all you are doing is a rough sketch to hand to the engineer who is doing the production design, then drop sketchup, it really isn't suitable for this sort of work. I know solidworks quite well, and that has the kinds of features you need (proper parametric lips, bosses, ribbing tools, draft analysis, etc..)1) inserts come in several different flavors, but first a question, do you really need them? inserts up your cost in terms of materials, production and assembly time. Redesigning to a self tapping plastic screw is usually cheaper and quite sufficient for a product where the pcb is only getting inserted / removed a dozen times over its useful life.You want to look at dedicated inserts for plastic injection molded parts. There are some that are ultrasonically welded in place, some that you have to insert into the mold before injecting the plastic (which ups your molding costs as operator has to do this on small runs), and some that are press-fit (however these are more problematic as you are press-fitting into a thin, soft material, so holding strength can be complicated).a quick google with "ultrasound insert plastic" will find you dozens of suppliers, here is one that comes to mindwww.spirol.com2) couldn't recommend 3d prints enough for prototype testing, however none of the 3d print technologies are going to produce parts that are usable in the field. FDM and SLS produce porous parts, and whilst SLA parts are watertight, they tend to take on moisture and warp, and don't hold up well to UV. Your best bet for small runs of parts is either to have them milled out of plastic, or use a rapid injection tool. EDIT: forgot to mention, if you can live with the extra design constraints, then vacuum casting of resin parts may be viable for small runs, such parts are quite usable however have differing material properties to ABS.3) there is a half way option, and that is to take an IP rated enclosure, and have a custom lid machined out of aluminium to replace the stock one. One good option is pelicases, which can be purchased with a watertight bulkhead mounting. You then just make an aluminium faceplate with your silkscreen and controls on it. This is massively cheaper then injection tooling until you are into the thousands of units.now a few extras:a) have you considered what IP rating you want to achieve?b) have you considered how you are going to seal the case halves together? Do you want a custom gasket, form in place seal, etc?c) are your controls, sockets, etc IP rated as good as if not better then your case spec?d) does the instrument need to survive drop testing? if so you need to do some simulation work for that, solidworks simulation can do a reasonable job for such testing.e) are you doing CE testing on this? if so what class is the device?Personally my view is that designing something like this is full of traps for the new player, so if this is a one-off job, you might be better off engaging with external engineering services to do the work. If its something that you want to learn, then I would still recommend finding a consultant on freelancer etc to give you advice on your design along the way. Things like the location of a single hole wrt to the part line can add 40% to your tooling costs.

author: G7PSK
author_rank: Super Contributor
timestamp: March 07, 2013, 05:07:03 pm
content: Go to your local production engineering company and get them to run of exactly what you want. Should not cost a lot.

author: asgard
author_rank: Regular Contributor
timestamp: March 07, 2013, 07:03:48 pm
content: Quote from: daedalus on March 07, 2013, 03:26:09 pm

author: daedalus
author_rank: Regular Contributor
timestamp: March 07, 2013, 09:04:23 pm
content: ok, well your production volume likely rules out injection molding, to give you an idea the last small enclosure mold I designed came back with quotes around 10kusd for tooling and a small initial run. Now after that investment the parts were a matter of cents each, but you have to make a lot to pay off the tooling costs.what I was suggesting as a low volume alternative is vacuum casting, this is different from vacuum forming. Here is a video showing the technique.The upfront costs are much lower than injection, but the tools wear out quickly, so the per-part costs is higher.

author: metalphreak
author_rank: Frequent Contributor
timestamp: March 08, 2013, 02:29:31 pm
content: I just bought 1,000 threaded inserts off Aliexpress because I couldn't find a cheap source anywhere. Was only $50 and I'm sure I'll use more than a few of them.http://www.aliexpress.com/item/M4-x-8-Insert-round-nuts-Brass-Rohs-PASS-1000-pieces/745532609.htmlThey are M4 thread, 8mm deep. I'm more than happy to send a few your way if you pay for postage. Might be a few weeks before they arrive thoughI'm making an MDF board to mount on my CNC's bed, with those inserts on a small 5CM grid for holding down smaller parts.

author: DaveW
author_rank: Frequent Contributor
timestamp: March 09, 2013, 05:20:22 pm
content: For the inserts, have a look at PEM fasteners. They work nicely for mounting and are pretty rugged

author: asgard
author_rank: Regular Contributor
timestamp: March 12, 2013, 04:22:11 pm
content: Because these projects are getting so much smaller (the mounting holes for all components here is only 2mm) it is a wonder that there are so few suppliers of M2 threaded fasteners and other mounting hardware. I though Grainger or McMaster were "it". I looked around at Alibaba, and while M2 fasteners are available almost all of them required stupid huge orders at minimum (one supplier in China had a 1 ton minimum order sizeSince my location is in Redding (not Reading, Davethere would be not insubstantial cost to transporting that much material here, especially when it comes off the slow boat. That would nearly cancel out the savings of buying fasteners so cheap.J.R. Stoner

author: metalphreak
author_rank: Frequent Contributor
timestamp: March 13, 2013, 01:49:23 pm
content: http://www.aliexpress.com/wholesale?SearchText=m2+insert&catId=0&initiative_id=SB_20130313054716You need to look on AliExpress for smaller quantities. Alibaba is for major importers bringing in large volume. AliExpress is essentially the ebay style sister site for small volume orders.There is plenty of M2 inserts available in quantities of 1000. I don't see $50-70 being unreasonable large for a business order %-B