Milling Shafts for Knobs

Here's a case where the Internet is your friend. Search for the knobs you intend to use or for other devices (switches, etc.) that use these knobs. Sooner or later, you'll come up with a drawing of the shaft they're supposed to fit. That will answer all your questions.

There is probably a MIL-SPEC on this, but I don't know what it is...

Jerry

First you need to measure the amount milled off of the 1/4 shaft. I would measure a potentiometer or something for the distance or you can do trail and error till you find a good fit to your knob.

Set up a parallel in the milling vise, sung the shaft and tap it with a mallet so that the parallel is snug. Mill the flat to the depth you require.

Plan B might be to scrounge some long shafted components and lop the pre-made D shaped shaft to the length you require.

Darren,

If I understand you correctly, you want to be able to move the knob inward and outward, without removing it from the shaft. If it's acceptable for the screw that restrains the knob to be either set loosely, or to be tightened between operations, all you have to do is cut the D portion of the shaft within the area you expect to move the knob, leaving the end a full circle. The limited D portion will self regulate the travel in both directions, and prevent the knob from being removed.

If that's not what you wanted to know, can you rephrase your question?

Harold

Hi, Darren. The "D" shafts you are thinking about are made for knobs with flat springs in the shaft hole. they are made that way so they can be pulled off. Just the opposite of what you want.

First, who is going to be pulling on the knob? You may need two set screws at 90 degrees apart for gorillas. A single set screw will work for normal people.

Assemble the knob and shaft and tighten the set screw to mark its location on the shaft. Drill that location just enough to make a socket like hole for the set screw. Be sure the set screw goes into the hole when you assemble the thing and tighten it. Now the gorilla will not be able to pull the knob off.

I have seen this done on several pieces of military electronic gear as well at Tektronics instruments with push/pull controls.

Good luck, Paul KD7HB

snipped-for-privacy@mail.c> I'm working on a project that will require me to mill down some 1/4"

Even easier - and better. Cross drill and install a spring pin instead of a set screw. Or make a special "grub screw" with an unthreaded tip to fit the cross-drill

Knobs with set screws are readily available.

--Save a step: go with a round shaft, install the knob and crossdrill for a rollpin.

The D shafts are designed for push-on knobs. You can generally use the setscrew knobs on the D shafts, but the setscrew should seat on the round part, which might put the pointer in the wrong direction. If you use the regular knobs, you won't need to mill the shaft.

There are also collet style knobs which generally have a removable color cap at the end. Underneath is a nut to tighten the collet. Probably more available with a 6mm nominal ID (0.236") than 0.25".

Best regards, Spehro Pefhany

Thanks everyone,

I was thinking about what everyone was saying, and then when Ed posted it dawned on me that simpler is better.

I have an opportunity to pick up a lot of "D" shaft knobs for cheap, but when I think about it, milling down shafts would cost more in time and effort. So it is probably best to find knobs that accept round shafts.

The oppossite end of each shaft must be 1/2" square, but I guess that it is easier to start with a 1/2" square rod and then turn down one end for whatever knobs I can find.

Since I'm new to this, perhaps a relatively easy to work with metal like aluminum will be easier to drill for set screws.

Thanks.

Darren Harris Staten Island, New York.

steamer wrote:

I like brass for that kind of thing, or HARD aluminum like 6061T6 SERIES.

I used to use this exact method myself, & it works very well. One other tip is to add a drop of Loctite or nail polish to the grubscrew thread when replacing the knob, to prevent it loosening over time.