How to extend pot shaft? - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: November 15, 2015, 02:12:31 am
content: I need to extend the shafts on some volume controls. Strange I've never had to do it before; was always able to move the pots. It's a common 0.25 inch (6 mm) split shaft with axial grooves to grip the knob. Am thinking of set-screw coupling, aluminum or delrin shaft, and set-screw knob. Have to toss the existing knobs, which are friction fit. Anyone try heat-shrink instead of set-screw coupling for this? Could make a little ridge on one end of the extension which would fit in the slit in the existing shaft to avoid slippage. Other methods?Mike in California

author: Someone
author_rank: Super Contributor
timestamp: November 15, 2015, 02:29:50 am
content: If the new shaft is otherwise constrained I've had good luck with cutting a slot in each shaft and putting heat shrink over a key coupling them.

author: Muttley Snickers
author_rank: Unknown
timestamp: November 15, 2015, 03:40:48 am
content: Very hard to advise without an indication on how far you need to extend the shafts and what load they may be exposed to, If you were close and handy I could readily knock you up something on the lathe but that's not going to happen. If it's only a slight extension then taking some material off the rear of the existing knobs will give the female receptacle more grab on the fluted shaft otherwise find a thin walled 1/4 hex bit extension from your drill accessories and see how that fits, this I have done before as a temporary measure.Muttley

author: helius
author_rank: Super Contributor
timestamp: November 15, 2015, 04:31:36 am
content: Is this enough extension?

author: crispy_tofu
author_rank: Super Contributor
timestamp: November 15, 2015, 04:40:55 am
content: Are you okay?

author: Bud
author_rank: Super Contributor
timestamp: November 15, 2015, 04:50:29 am
content: A used pen and a TV cable clamp did it for me ....15 years ago...

author: djQUAN
author_rank: Frequent Contributor
timestamp: November 15, 2015, 05:04:47 am
content: http://sound.westhost.com/pcb/pes250.htm

author: calzap
author_rank: Frequent Contributor
timestamp: November 16, 2015, 04:35:43 pm
content: Thanks for all the replies. I went the quick and dirty route of using heat shrink. This pot won't be adjusted very often, so heat shrink should last a while. If it slips, I'll use a set-screw coupling. First pic shows pot and Al extender with precision-milled ridge on end (Dremel plus mill bastard!). Second pic shows them together before heat shrink, and third pic shows after heat shrink.Mike in California

author: Ian.M
author_rank: Super Contributor
timestamp: November 16, 2015, 04:53:16 pm
content: What happens when someone pulls on the knob slightly?I'd have slotted the end of the extension shaft fairly deeply and used a strip of steel as wide as the shaft bridging both slots. However, assuming a conventional through panel bush and knob is used, either it needs a setscrew coupling or a collar on the shaft just inside the bush, or a much 'grippier' sleeve to positively retain it. Two layers of adhesive lined heatshrink would probably do it.

author: drussell
author_rank: Super Contributor
timestamp: November 16, 2015, 05:50:57 pm
content: If you're using heat-shrink for the coupling, you could certainly try the stuff with the internal adhesive in it.That stuff is actually pretty strong glue.

author: calzap
author_rank: Frequent Contributor
timestamp: November 16, 2015, 06:04:29 pm
content: Quote from: drussell on November 16, 2015, 05:50:57 pmYes, I've used heat shrink with hot snot in it for below ground splices on video coax, and it worked well. I would have used it for this task, but didn't have any of the right size on hand. If the regular heat shrink doesn't hold, I'll go straight to a set-screw shaft coupler.Mike in California

author: calzap
author_rank: Frequent Contributor
timestamp: November 16, 2015, 06:14:15 pm
content: Quote from: Ian.M on November 16, 2015, 04:53:16 pmYes, it could come off with a good pull. This unit will be in an equipment compartment in a slow-speed, non-highway EV on my own ranch. It will not be easily accessible to users and will probably be adjusted very few times during its life. It will be pointed upward at about a 45 degree angle, so even the effects of vibration and gravity won't be great. I'm just curious how this quick method will hold up. Worse case, I'll just have to install a set-screw coupler.Mike in California

author: biosonar1
author_rank: Newbie
timestamp: November 16, 2015, 06:50:15 pm
content: If you're not completely out of funds, 50K pots built with extended shafts are easily purchased. I've usually had the opposite problem and had to cut mine down!

author: nctnico
author_rank: Super Contributor
timestamp: November 17, 2015, 12:00:20 am
content: I strongly recall having seen shaft extenders in the past. I could use a few as well but have no idea where to buy them.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 17, 2015, 12:51:20 am
content: Automotive flexible fuel line is quite often used as a "quick 'n dirty" solution.

author: zapta
author_rank: Super Contributor
timestamp: November 17, 2015, 01:30:38 am
content: A 3D printer or a service can solve your problem. Design an extender and print it.

author: bson
author_rank: Unknown
timestamp: November 17, 2015, 06:46:25 am
content: A 6mm rod and a 6mm shaft coupler (or tubing/heat shrink). Cut rod to size with a hacksaw. Brass is easy to work with.

author: xReM1x
author_rank: Regular Contributor
timestamp: November 17, 2015, 07:04:36 pm
content: Quote from: vk6zgo on November 17, 2015, 12:51:20 amI would probably get a steel rod or something and drill the inside with a drill bit just smaller then the shaft, then heat the steel so it will expand and then press fit it, or just use glue.if I could not get a rod I would think of something stupids that works. should not be a problem

author: dom0
author_rank: Super Contributor
timestamp: November 17, 2015, 08:58:22 pm
content: Quote from: nctnico on November 17, 2015, 12:00:20 amMentor produces 4 and 6 mm shafts and 4/6, 4/4, 6/6 couplers with set screws made from brass.Except for H.V. insulation purposes I don't see a need for plastic shafts ; I just cut a part of a M6 threaded rod off.

author: Ian.M
author_rank: Super Contributor
timestamp: November 17, 2015, 09:14:40 pm
content: Obviously, if you've got the right metalworking tools, you can make up a custom friction-fit splined coupler, but as the 6mm or 1/4" shaft extensions and couplers are reasonably readily available, why bother? The only thing I would add, is that if using a grubscrew coupling on a split splined shaft, you should file a flat + solidly pack the split otherwise it *WILL* work loose.

author: vk6zgo
author_rank: Super Contributor
timestamp: November 19, 2015, 07:30:00 am
content: If you can find one,cut the splined shaft off a "dead" pot.If the "donor" shaft is long enough,you can cut the splined part off your good pot,& use a "grubscrew" type coupler,with no further work.If it isn't,you will have to try the various ways of making the coupler fit,as described by earlier posters.With the extension shaft a splined type,you can use your original knob.