3D printing replacement knobs for test gear (HP3457A and LeCroy 9370M) - Page 1
Forum section: electronics / testgear

author: saraht
author_rank: Newbie
timestamp: October 03, 2014, 10:21:59 pm
content: Hi folks,I've had a bit of success recently making replacement knobs for my HP 3457A and my LeCroy scope using a cheap and cheerful 3D printer. The knobs won't pass for originals and are frankly a bit funky looking, but they work perfectly, particularly if you're a cheapass like me and have a deep down refusal to spend more money than you absolutely have to, whilst still wanting to make old gear usable without risk of frying yourself on an exposed binding post.I picked up the LeCroy about a year ago in a pretty sad state for not much money on eBay. It had obviously been dropped on its knobs, which had sheared off a couple of them and destroyed the shaft encoders for those and three others whose knobs survived. I pulled it apart, replaced the encoders with the nearest modern equivalent (the exact ones weren't available, but a very similar model was, though it needed some minor mods using parts from the old encoders). That got me a working scope, but bought-from-Digikey replacement knobs didn't work because the encoder shafts weren't quite long enough due to LeCroy's panel design. After a few months of having them regularly annoy hell out of me by falling off all the time, I 3D printed some replacements, with shaft holes just large enough to push on while the plastic was still hot, so they got a really tight interference fit when it cooled. I didn't photograph or film any of that, unfortunately, but when I recently bought a 3457A and had it shown up with a broken binding post due to having been packed badly, I decided to do the same trick again, but this time I filmed the whole thing. There's a shot of the fixed 9370M at the end too. Irritatingly, the LeCroy needs fixing again because of some superglue-involved weirdness with the fuse holder in the power inlet (this wasn't me, I inherited that one!), but that's another story...Anyway, if you're interested, the video is athttp://www.mageofmachines.com/main/2014/10/02/m0mv001-3d-printing-a-new-knob-for-an-hp-3457a-multimeter-with-a-solidoodle-2/.

author: BobCollins
author_rank: Newbie
timestamp: October 03, 2014, 11:05:18 pm
content: Cool idea!Suggestion: I would like to see high resolution photos of your 3D printed knobs and binding posts, preferably next to an original. A video can be useful as a walk-though, but my first interest was what the final product looked like.

author: saraht
author_rank: Newbie
timestamp: October 03, 2014, 11:11:08 pm
content: Give me a minute and I'll shoot one.Bear in mind that I was going for 'working' rather than 'nice looking' or even 'remotely resembling the original'. I could probably have CNC machined a pretty accurate replica, but that would have been a couple of days work rather than an hour, so...

author: saraht
author_rank: Newbie
timestamp: October 03, 2014, 11:46:50 pm
content: OK, here goes. I've not tried adding images here yet, so hopefully this will work first try!These are both at the maximum resolution I can get out of my GH2 and my old Sigma macro lens, so I hope that works!

author: saraht
author_rank: Newbie
timestamp: October 03, 2014, 11:49:33 pm
content: For scale, each 3D printed 'sausage' layer is 0.3mm. Better printers can do 0.1mm -- I can kind of get this resolution on the Solidoodle I have, but it has an awful tendency toward the prints curling and distorting at the edges where they touch the bed, so I didn't bother and just used 0.3mm for all of these.

author: BobCollins
author_rank: Newbie
timestamp: October 04, 2014, 12:02:08 am
content: They look functional. Which is a good thing.

author: Fsck
author_rank: Super Contributor
timestamp: October 04, 2014, 12:14:21 am
content: Quote from: BobCollins on October 04, 2014, 12:02:08 ambut they kind of stick out like a sore thumb.

author: saraht
author_rank: Newbie
timestamp: October 04, 2014, 12:30:45 am
content: Yeah, I never said they were pretty. They work, however!Affordable 3D printing hasn't really hit a point where you could make knobs that look like injection moulded originals. High end 3D printing totally has, however -- I could send my design files off to Shapeways (for example) and get something much nicer back, but that costs money. I suspect that each of these knobs cost a tiny fraction of $0.01 in ABS filament to make. (Probably exactly what they are worth, but hey!)I also never claimed not to be a cheapass!

author: ivan747
author_rank: Super Contributor
timestamp: October 04, 2014, 01:08:02 pm
content: Some paint and polish will make those look great! O0Now that I come to think of it, this would make a good Hack-a-Day article, try to get published there!

author: Lunasix
author_rank: Regular Contributor
timestamp: October 04, 2014, 02:20:27 pm
content: And there is white PLA, which looks better for that.Polish is not easy, all is made with a wire, it's never smooth.

author: SeanB
author_rank: Super Contributor
timestamp: October 04, 2014, 02:57:58 pm
content: Acetone polishing works with the PLA, giving a smooth surface at the expense of slightly melting the surface. Tested video channel has some articles on doing this.CAUTION, this uses a very flammable ( and acetone is extremely flammable) solvent that is heated in an open container. Use care, do outdoors in a well ventilated area away from NAKED FLAME AND ANY SPARKS, and gave a fire extinguisher ( dry powder ABC type) handy within reach.