Fitting 6.26mm pot shaft to a 6mm knob - Page 1
Forum section: electronics / projects

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 19, 2017, 08:28:30 pm
content: Hi,I have this knob:https://www.dfrobot.com/product-978.html- it has a retaining screw.I want to fit this knob to a 6.26mm shaft pot, but the knob has a hole with diameter of exactly 6mm, and because of that it doesn't fitI really like this knob and would like to use it, so I thought about maybe drilling it, but I don't have exact 6.2mm drill and I don't want to buy one locally because I wont find one or wait a month to get it from eBay, I have 6.4mm drill I think and I tried just drilling the hole bigger but because of the angle of the drill I could not drill it all the way, and the hole was really not square so the knob was wobbling on the pot a lot and it didn't fit all the way to the end, I only have a hand drill..It's not the end of the world if there is no way to fit it on the shaft but its such a nice knob that I doubt I will find something similar locally.Anybody got any idea to how to fit the knob on the shaft?Thanks, Shay.

author: danmcb
author_rank: Regular Contributor
timestamp: April 19, 2017, 08:36:13 pm
content: it just sounds like a world of pain. I wouldn't ...

author: CM800
author_rank: Frequent Contributor
timestamp: April 19, 2017, 08:40:59 pm
content: Easy, if you can't change the diameter of the knob... thin the shaft out!if it's plastic, just use a knife to evenly scrape it thinner, else grip the end of it with a drill, then spin it around and use a small file to make it smaller! (cut the end that was clamped off or just file the last bit by hand if you need to.)

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 19, 2017, 08:47:23 pm
content: Quote from: danmcb on April 19, 2017, 08:36:13 pmI live on the edgeQuote from: CM800 on April 19, 2017, 08:40:59 pmIt's not plastic, it has a metal shaft and 10 turns. your average 10 turn pot. fileing sounds challenging but possible, I will try it tomorrow and report back. I think i'm going to ruin the shaft somehow but fuck it you learn from mistakes.

author: rob77
author_rank: Super Contributor
timestamp: April 19, 2017, 08:56:42 pm
content: grind or file the shaft down to 6mm.. if you don't have a grinder then use a grinding stone or file and do it manually.

author: Ian.M
author_rank: Super Contributor
timestamp: April 19, 2017, 09:11:40 pm
content: *DON'T* file the shaft - its far to easy to FUBAR it + the shaft must be supported in a V block so you don't stress the bearing or wiper mechanism excessively, and tape used to stop filings and grit getting into the pot. Also, unless you are an expert at precision hand-fitting, you are almost certain to get it out of round, and tapered, convex or concave so the knob wobbles like a friday night drunk.The knob needs to be bored out to 6.3mm. To do this with hand tools without messing up the knob is really difficult - you really need the help of someone with a lathe or mill, or at least access to a pillar drill + a spare 6.3mm drill bit you can grind the point off to finish the bottom of the hole. 6.4mm is over-size - you'd need to shim the shaft with some very thin metal sheet wrapped round it. Try Aluminum foil tape.

author: rob77
author_rank: Super Contributor
timestamp: April 19, 2017, 09:35:01 pm
content: you don't need a fancy V-block. just use some masking tape and use a vise to hold the shaft (if needed use 2 pieces of wood between the jaws of the vise and the shaft to make it fit) if you do the filing in small steps and carefully it will be round enough (tip.. always file the high spots to make it rounder and rounder).btw.. everyone says you need fancy tools.. but how did people do all the amazing mechanical stuff before the existence of fancy tools ?i know it's faster and better to use tools... personally i would bore out the knob on my micro-lathe.. but the OP has only hand tools available.. so filing down the shaft is not a bad option.another good option would be to create a jig for holding the hand drill straight (two pieces of wood making a corner to hold the drill bit against) and try to drill a new knob...yet another option would be to just drill the knob over-sized and use repair putty to glue it centered.

author: danmcb
author_rank: Regular Contributor
timestamp: April 19, 2017, 09:36:52 pm
content: right. and this is why I think this is gonna be *really* hard to do. You'll either end up with a sloppy knob that wobbles all over the place (oo-er!) or a knackered pot. Or both. there is just no way you will file that round enough to feel right by hand - if you can do it at all (many pot shafts are very hard steel).(don't let me spoil your fun though ... )

author: danmcb
author_rank: Regular Contributor
timestamp: April 19, 2017, 09:39:32 pm
content: and a knob glued on the pot shaft, to me, is a total head-slap. i would *hate* the person that did this enough to want to slay them and 7 generations of their offspring.I mean - there are like 74567890876 different pot knobs for a 6mm shaft online ... is it *really* worth it?

author: rob77
author_rank: Super Contributor
timestamp: April 19, 2017, 09:42:13 pm
content: Quote from: danmcb on April 19, 2017, 09:39:32 pmbut what if you like the one you already have so much ?

author: danmcb
author_rank: Regular Contributor
timestamp: April 19, 2017, 09:43:57 pm
content: I tells ya Rob, that's the only pot knob in the world for me!

author: Muttley Snickers
author_rank: Unknown
timestamp: April 19, 2017, 09:50:18 pm
content: Seriously, some people need to get a grip.

author: Nusa
author_rank: Super Contributor
timestamp: April 19, 2017, 10:26:14 pm
content: Classic Imperial vs Metric problem. Shaft intended for 1/4" hole vs 6mm hole.Easiest way to use that knob: Replace the pot with one that has the correct shaft for the knob.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 19, 2017, 11:20:23 pm
content: Saw 2 cross-cuts in the pot shaft - should then be able to squeeze it down to fit.

author: james_s
author_rank: Super Contributor
timestamp: April 19, 2017, 11:27:44 pm
content: Wrap some sandpaper around a rod that is a bit smaller than the hole in the knob. Tape one end of a strip and then just roll it around the rod, put that in a hand drill and spin it inside the hole in the knob. With a bit of patience you can make the hole larger. Shouldn't take too much work to enlarge it by 0.26mm.

author: Delta
author_rank: Super Contributor
timestamp: April 20, 2017, 12:11:37 am
content: Just get a hammer and whack the thing on, it's only a quarter of a millimetre out, and an aluminium bush.....

author: danmcb
author_rank: Regular Contributor
timestamp: April 20, 2017, 12:15:08 am
content: head down to the tracks, position it on the rails, with the knob upwards, just balanced on the end of the shaft. Wait for the next train ...

author: rdl
author_rank: Super Contributor
timestamp: April 20, 2017, 12:23:32 am
content: Both #13 and #14 sound feasible to me. Either way may give results that are "good enough". I would probably just find knob and pot that actually fit together correctly. That knob style can't be too hard to find, even RadioShack sold similar.

author: TimFox
author_rank: Super Contributor
timestamp: April 20, 2017, 08:24:00 am
content: Have you tried using a proper reamer (in a tap handle) to enlarge the hole?The metal in the knob is much softer than the shaft.

author: Fungus
author_rank: Super Contributor
timestamp: April 20, 2017, 11:37:13 am
content: I usually work the inside of the knob with a drill bit held in an electric screwdriver (ie. low-RPM). Hold the drill bit stationary and rotate the knob on the end of it.Works for me.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: April 20, 2017, 01:17:55 pm
content: I got it! Fuck yeah!I filed a flat side on the shaft and shoved it into the knob and it worked! maybe I didn't need to file the shaft but only to push it harder, but neither way it worked.now I need to cut ~4mm from the edge of shaft because it is too long.Thanks everybody for suggestions!