led red plastic screen cover replacement - Page 1
Forum section: electronics / general

author: sjl
author_rank: Newbie
timestamp: November 11, 2019, 03:39:43 am
content: I am restoring a Keithley 617 Electrometer-- recapping, replacing 2 lug with 3 lug triax, etc. The biggest challenge however is that it needs a new red plastic LED cover. Firstly, do these screen covers have a more appropriate name besides 'old style led screen red plasticy cover thingy?'See the attached screenshots-- I'm not sure if this is acrylic or poly-carbonate. I have tried polishing it but one of the legs is cracked and the damage runs pretty deep.One thought I had was to purchase a sheet of this:https://www.amazon.com/gp/product/B074MHHY1P/and score/cut it, but getting the legs and the beveling would not be easy without something like a laser cutter or water jet. I could always just cut a square and tape or glue it behind the opening but then it would not be flush / a bit of a hack job.Or does anyone know some reasonably priced plastic fabricators that would do a 1 off or any other suggestions?Thank you!

author: BrianHG
author_rank: Super Contributor
timestamp: November 11, 2019, 03:47:28 am
content: Quote from: sjl on November 11, 2019, 03:39:43 amDisplay Bezels, Lenses.https://www.digikey.com/products/en/optoelectronics/display-bezels-lenses/93https://www.google.com/search?q=LED+DISPLAY+LENS+BEZEL+RED+&ie=utf-8&oe=utf-8&client=firefox-b-e

author: beanflying
author_rank: Super Contributor
timestamp: November 12, 2019, 02:57:29 am
content: The issue will be one of cost if you want a replica. Laser cutting the profile from Acrylic will be fine but you then need a second step of setting up and CNC milling the step. Either that or it is a slightly more complex two step cut with a CNC router.The cheaper solution would be adopt the thickness of the stepped portion overall and forgo the flush fit on the front panel rather than the current version. Then it is just a Laser cut Acrylic job. Material cost a few $ and if you can do a Cad drawing (generally DXF or SVG will do) the production cost will be low.If they have to do the Drawing then that will stack up too.If I was given a drawing and it was a straight 3mm Red see through then I could mail you one to the USA for $20'ish if you can't find a local. The panel below is the 3mm red I have on hand so the display should punch through it fine.

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2019, 06:12:57 am
content: You don't need to CNC mill that step. For a one-off a rookie with a manual mill could mill could do that in about 2 minutes. Lacking a proper mill, a drill press with a cross slide vice or even a carefully adjusted table saw could do it.

author: beanflying
author_rank: Super Contributor
timestamp: November 12, 2019, 06:19:09 am
content: So you reckon a Table Saw Leftie?The biggest issue with small stock even on a CNC table is holding it in place let alone trying to hold it in cross vice. It can be done but it is a PITA.

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2019, 06:23:33 am
content: You adjust the blade so it's just poking up through the table, and set the guide so it's *just* about to touch the blade. If that's too tight then you can clamp a straight piece of wood against the guide. For milling plastic bits like that I use good double sided tape to stick the stock to a scrap of something more substantial. Never try to hold onto something that small directly while machining it.Even if you have a CNC mill you still have to come up with a fixture to hold the material.

author: beanflying
author_rank: Super Contributor
timestamp: November 12, 2019, 06:25:39 am
content: Normally on a CNC mill you do the actual cutout of the piece last or even leave partial tabs to hold it in place PCB style then snap it out.

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2019, 06:33:47 am
content: It depends on what you're trying to do, but with small parts you almost always run into a tricky situation where you have to find a way to hold onto the part while trimming it out of the rest of the stock. Friends of mine run a CNC shop and have all sorts of tricks, making the fixturing is a significant part of the process. If I were trying to produce a bunch of those I might try to use a vacuum table, it's surprising how little surface area it takes to hold a sheet of something down with a vacuum pump pulling out the air under it. For a one-off it's hard to beat double sided tape though, tape it down to a scrap of aluminum bar stock and you can clamp that in the vice on a mill and it's not gonna go anywhere.

author: beanflying
author_rank: Super Contributor
timestamp: November 12, 2019, 06:43:51 am
content: I do have a Vac table planned when I get my larger CNC router back up and running. For a bulk lot of these or similar it would make a lot of sense to hold the panel down and leave them tabbed in place.The issue for a single job like this is the material is cheap as chips but the setup and potentially the CAD time will tip it toward theprice for the OP. The actual machine time is not much at all.I have a very healthy respect for table saws so many chippies missing bits of fingers or like a mate of my Dads had a dopey moment and dropped most of four fingers next to the timber he was cutting after having the Table for a few decades