WTB knob for a 3/8inch 0.375inch shaft - Page 1
Forum section: electronics / general

author: tggzzz
author_rank: Super Contributor
timestamp: June 30, 2022, 11:51:13 am
content: I've some old Muirhead D-805 decade resistors, some without knobs. I'd like to put some knobs on them so I can change the resistance without using pliers.Traditionally the knobs are large, chunky and probably bakelite or phenolic plastic, but I'm not too fussy about that. Oneexampleis shown below.The main problem is that the shafts are not the standard 1/4in (6.3mm) diameter, but are the larger 3/8in a.k.a. 0.375in (9.5mm) diameter.Anybody know where I could get some at a pleasingly low price? No, I'm not prepared to pay £35 each!

author: mag_therm
author_rank: Frequent Contributor
timestamp: June 30, 2022, 04:23:09 pm
content: I looked on SurplusSales Nebraska but very few with 3/8" and the price is highIf the shafts are grounded, a set could be made on a lathe. I have done some in aluminum and brass would be good too.Knurl the head and pointer line can be milled and filled with black paint.Maybe check with machinist hobbiests or steam engine builders etc.

author: tggzzz
author_rank: Super Contributor
timestamp: June 30, 2022, 04:30:10 pm
content: Thanks.Another possible source is hamfests, but they are obviously hit and miss.

author: PaulAm
author_rank: Frequent Contributor
timestamp: June 30, 2022, 05:30:02 pm
content: A lot of these types of knobs have a brass insert and there may be enough in there to drill it out to 3/8.You'd probably need to do it on a lathe with a boring bar to get a flat bottom on it. Or use a drill and then finish the hole with a 3/8 mill to get the flat bottom. You could do that with a drill press but you'd need to make sure the knob was rigidly held.

author: tggzzz
author_rank: Super Contributor
timestamp: June 30, 2022, 07:15:23 pm
content: Hm. Hadn't thought of that.My concerns would be thatone of the old knob's plastic might be too brittle to withstand the forces. Gentle slow grinding with a dremel might ease thatit would be difficult to guess whether the brass insert was of sufficient thickness to allow it. Not a major issue if the knob was cheap or it could be inspected in personDefinitely one to keep in mind.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: June 30, 2022, 10:57:24 pm
content: HiWhen I was at school many years ago now 0.375 of an inch was 3/8 of an inch not 3/4 of an inch.Maybe the new maths has changed that.G Edmonds

author: dew
author_rank: Contributor
timestamp: June 30, 2022, 11:26:03 pm
content: Vintage 2" Black Bakelite knobs for Ham Radio, Amplifier, Transceiver 3/8" shaftThis lot looks like a good fit for a decade resistor box

author: tggzzz
author_rank: Super Contributor
timestamp: July 01, 2022, 12:09:32 am
content: Quote from: George Edmonds on June 30, 2022, 10:57:24 pmOh, picky picky picky. What's a factor of two amongst friends.Maybe I've changed the title, maybe not.

author: tggzzz
author_rank: Super Contributor
timestamp: July 01, 2022, 12:11:05 am
content: Quote from: dew on June 30, 2022, 11:26:03 pmIt does, doesn't it.Unfortunately when postage is included, the cost is around $35/£28, which exceeds my enthusiasm!

author: AVGresponding
author_rank: Super Contributor
timestamp: July 01, 2022, 05:10:16 pm
content: Not exactly what you're after, I just wanted to post a picture of a wing knob...https://www.ebay.co.uk/itm/165553976756

author: TimFox
author_rank: Super Contributor
timestamp: July 01, 2022, 05:16:46 pm
content: I have (carefully) used reamers in a drill press to enlarge 6 mm ID knobs to 6.35 mm/0.25 inch for American shafts, but that is a small increase in a brass bushing or solid aluminum knob.I did this when I wanted to match knob appearance with a mixture of 6 mm and 0.25 inch shaft controls on a panel.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 01, 2022, 05:52:35 pm
content: I'd be tempted to try and make one with a combination of 3DP and some 3/4" brass bar stock.

author: tggzzz
author_rank: Super Contributor
timestamp: July 01, 2022, 11:25:14 pm
content: Additive printing has its attractions, but the difficulty would be creatingreliableways for the knob to "become one" with the shaft.From a different project, I'm not sure whether to aim to 3D print the unique red/blue/white connector below, or to put a very wide skirt on a simple knob.

author: AVGresponding
author_rank: Super Contributor
timestamp: July 02, 2022, 10:36:33 am
content: I'd use a 2-part resin. That stuff makes two things become one really well.

author: theHWcave
author_rank: Regular Contributor
timestamp: July 02, 2022, 04:54:02 pm
content: There is currently a Muirhead A-201-D with 4 knobs on Ebayhttps://www.ebay.co.uk/itm/324779468686for £55 (free UK delivery). If the knobs fit yours (I have not checked!!!) that's £13.75 per knob and you get a voltage divider in a wooden box ...

author: AVGresponding
author_rank: Super Contributor
timestamp: July 02, 2022, 05:10:42 pm
content: Which would just leave you with the problem of where to find replacement knobs for the voltage divider...

author: tggzzz
author_rank: Super Contributor
timestamp: July 02, 2022, 07:45:52 pm
content: Quote from: theHWcave on July 02, 2022, 04:54:02 pmThey would fit, since that is simply four of "my" dividers in a single case.Regrettably AVGresponding has hit the nail on the head. I could also take a knob offmy5 decade Muirhead resistance box or some of myotherMuirhead decade resistorsNo, I do not have a psychological problem w.r.t. old decade resistors. Oh no. Certainly not. Perish the thought.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 02, 2022, 09:50:53 pm
content: Just for the heck of it I sketched up a knob for 3D printing. Dimensions are just eyeballed. I have had great success doing these kinds of knobs. Surface finish will be slightly different unless you take the time to seal and paint. This is set up to take a standard (traditional units) set screw collar. As said earlier with a good glue or epoxy these will hold fine. If you want extra assurance knurl the collar.The files in the zip are an stl ready for printing, and the model in FreeCAD format. The model allows you to change dimensions to exactly match your existing knobs.

author: tggzzz
author_rank: Super Contributor
timestamp: July 02, 2022, 10:23:17 pm
content: What material do you use, and where is the part fabricated?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 02, 2022, 10:38:09 pm
content: I print my own, on an Ender 3 filament printer, which cost about $250 including upgrades. Use PLA or PETG which have both been more than up to the task for knobs. If you haven't gotten into 3D printing yet you are missing a great tool. I've had mine for over two years now, and have only printed two of the statuettes/geegaws that seem to be the rage on these printers. Knobs for TE. Feet for TE. Faceplates for TE. Adaptors to allow old tools to use modern batteries. Replacement parts for kitchen gadgets. Project boxes. Jigs to hold complex parts for machining operations. And many other things. The printer has paid for itself many times over and I still haven't started doing investment castings with printed forms.If you don't want to do your own printing there are shops that will do it for you. Prices vary, but I would guess that a knob like this would run $5-$15. The direct cost of printing your own is about a dollars worth of filament plus some fraction of a kWH of electricity. How you amortize the machine cost will depend on how you use it and how you do the accounting.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 02, 2022, 10:49:18 pm
content: The attached model has the parts used to make up the whole model named to make it easier to update dimensions. Just like software documentation helps.(FreeCAD format. FreeCAD is free and open software.)

author: AVGresponding
author_rank: Super Contributor
timestamp: July 03, 2022, 08:13:24 am
content: Quote from: tggzzz on July 02, 2022, 10:23:17 pmI suspect there are a number of people in TEA who would be willing and able to do so, including myself...

author: tggzzz
author_rank: Super Contributor
timestamp: July 03, 2022, 11:43:31 am
content: Quote from: CatalinaWOW on July 02, 2022, 10:38:09 pmThe principal cost would be my time and space. My house is full with test equipment "treasures" amongst other things, and I'm not prepared to spend my little remaining life fettling with 3D printers! In addition, I've used PLA, nylon, SLA photopolymer, and brass. Having printers for that lot would be "amusing"For me the starting point is choosing the material, then working out where to have it fabricated.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 03, 2022, 05:19:40 pm
content: Quote from: tggzzz on July 03, 2022, 11:43:31 amI understand. If you want to send actual dimensions for the knob I can update the model to match. Diameters, hight of cone section. Etc.I wouldn't mind printing some for you, but postage to your end of the world is as you are aware outrageous. But as AVG says there is a a good chance of someone local and willing. If not there are sure to be print houses and/or maker spaces in all major cities in Australia which should at least make shipping reasonable.

author: tggzzz
author_rank: Super Contributor
timestamp: July 03, 2022, 10:19:42 pm
content: Quote from: CatalinaWOW on July 03, 2022, 05:19:40 pmThat's a kind offer, but my desire is not urgent and not sufficient for me to feel comfortable putting other people to trouble.I'll keep an eye out on fleabay and at hamfests, to see if there's any scrap equipment I can dismember.

author: jorgeh
author_rank: Regular Contributor
timestamp: July 07, 2022, 05:42:07 pm
content: HiI have a bunch of front panel from different devices that i scrapped. if there is a knob that you would like let me know.I added more different front panels