Variac dial mount -- what's missing?

[mdubinko]

Question: I picked up an open-frame variac from surplus. The reverse of the knob is as shown in the attached. The variac has a split shaft with a hole through it--a hole with no threading that I can see. What is the name of the missing piece I need to mount the knob? Some kind of cotter pin?

73
AJ6BD

[ArthurDent]

It's a metal dowel pin. You can use a piece of an old drill that just fits through the hole and carefully break it to the correct length with pliers or find a screw that just fits through the hole and cut it to the correct length with a hacksaw. Any metal  will work.

https://sc01.alicdn.com/kf/HTB1.fXuasnrK1RkHFrdq6xCoFXa8/oem-shaft-machining-tolerance-0001-inch-hight.jpg_350x350.jpg

[Ian.M]

I'd bet it originally had a roll pin.  If the slot width is greater than the hole diameter, there was also a metal clip to retain the knob and stop it turning slightly, banging the roll pin from one side of the sllot to the other when you run into the end stops.   If you cant fabricate something suitable to stop it slopping around, you will be in for a whole world of grief and with use, it may even bust out the hub on the dial!

[mdubinko]

A 3mm drill bit fits into the shaft with an annoying amount of slop. A 3.2mm bit (is it weird that I have this laying around?) doesn't fit at all. An imperial 1/8" bit seems like it could fit with help from the rubber mallet of care.

I'm wondering if a nylon pin would be strong enough to do the job and still have enough give to not break...

The slot on the dial measures just about 3.2mm wide with calipers. So yeah, it seems like some kind of clip would be needed to hold the dial in place. My google-fu has failed me, though, and I can't find an image of what that might look like. Anyone got an idea?

[Ian.M]

I'm betting a 1/8" roll pin will fit it very nicely. If you cant get one, improvise with a brass pin, turned down (or sanded while chucked in a Dremel) to fit then knurled in the middle to retain it, which can be done by hand by rolling it on a hard block of wood under the edge of a largish flat file, with considerable pressure) as I suspect a nylon or aluminum pin will sheer too easily.   With only a fraction of a mm slop, gooping the ends of the pin with a few drops of impact adhesive will probably keep everything slop-free and together, however if you need to remove the knob in the future, you'll need to lever it pressing on the center hub, not the rim.   

[pinyoro]

Question: I picked up an open-frame variac from surplus. The reverse of the knob is as shown in the attached. The variac has a split shaft with a hole through it--a hole with no threading that I can see. What is the name of the missing piece I need to mount the knob? Some kind of cotter pin?

73
AJ6BD

I think it is called a split pin

Sent from my WAS-LX1A using Tapatalk

[SilverSolder]

They have roll pins at pretty much any hardware store.

[eKretz]

The ones you guys are thinking of are called "split roll pins" - there are also a different version that are like a roll of wrapping paper made of metal. Those are called "spiroloc" or something to that effect.