My knob fell off...

U

UngaWunga

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UngaWunga
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Knob for channel tuning on my secondary radio came off the other day. Just spun without doing anything, then fell off in my hand. Looks like its missing a pin or something, because otherwise I can't figure out how it stays on.

Inside the knob is a screw that screws into the little metal piece next to the knob. That'll be a pain in the ass to get back together without drilling the top of the knob open.

Any idea how this all fits together to stay on?

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You should have gotten a shot for that a long time ago...

It's a little set screw that goes in the knob that holds it in place.
 
Somehow this seems like an appropriate thread for this song.


 
Really? A thread for a knob and a set screw?

Never heard of an allen wrench?

Pardon me because I grew up on a farm and I'm kind of crusty. The things people can't do nowadays bugs me sometimes.
 
What did the leper say to the prostitute?

Keep the tip.

Sorry couldn't resist :redface:
 
There's no set screw on the knob. That would be too easy. This is an airplane part, remember?
 
Yes, it does. But there's no set screw in the knob.... No hole for a set screw, either, in case you're thinking the set screw fell out...
 
GlennAB1 said:
Push the little insert back on the rheostat shaft and screw the knob back on.
Click to expand...

Can't. Won't thread on. The screw spins. Even so, there's nothing to hold the knob to the shaft.


Keep it clean. :nono:
 
Something is wrong. The part with saw cut looks like a collet. It looks like there may be a screw in the other end of the knob, the side you didn't take a picture of. You also only took a picture of one side of the collet. I'm thinking the other side is large enough to slide over the stud on the radio. Basically you slide the collet over the stud, the knob over the collet, the screw screws into the collet, pulls it into a taper in the knob which tightens it onto the stud. I'm thinking there is a removable cap on the other side of the knob hiding the screw.


Or not. Take some more pictures.
 
What I don't understand is why a guy would want to post on a public forum about a knob failure. Hey, that's part of the equipment getting old...
 
Yes, the collet does fit over the shaft on the radio. There's a pin hole in the end of the shaft, perpendicular to it. I'm guessing a pin goes through that which just prevents the collect from just spinning on the shaft.

Broke out the drillpress, put a small hole in the top of the knob to hold the screw inside the knob still so I could screw the collect back into the knob. One task done....

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Clark1961 said:
What I don't understand is why a guy would want to post on a public forum about a knob failure. Hey, that's part of the equipment getting old...
Click to expand...

Slow night. Raining outside. And cold. :dunno:
 
Oh hey, what do you know... the top pops off the knob. What a stupid, over complicated design. MX300 radio, in case you're wondering...

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I think that's a cap on the end of the knob that can be pried off. You will probably find a nut and a set screw, or a regular screw. Tighten it up on the stud.


Or you already did this, can't tell from your post.

Good luck.
 
There you go. A little removable locktite on the screw threads should keep it tight.
 
Yup, but the collect doesn't screw onto the shaft of radio. No threads on that side of it.

Now... I do have a "spare" MX300 radio. Tempted to pry the knob off of it to see how it goes on.
 
UngaWunga said:
Yup, but the collect doesn't screw onto the shaft of radio. No threads on that side of it.

Now... I do have a "spare" MX300 radio. Tempted to pry the knob off of it to see how it goes on.
Click to expand...

The collet squeezes onto the shaft, very tightly, that's what the taper is for. It's kind of like a vise. Tighten the screw to squeeze the collet down. Make sure it's not tight before you put the knob on the radio or it won't go on.
 
Testing that theory now on the other radio...
 
Well now, someone give PaulS a cookie. That's exactly how it goes on. Mystery solved.


Y'all were on the edge of your seats, weren't you...
 
UngaWunga said:
Yup, but the collect doesn't screw onto the shaft of radio. No threads on that side of it.

Now... I do have a "spare" MX300 radio. Tempted to pry the knob off of it to see how it goes on.
Click to expand...

The outside of the collet has a taper that matches the inside of the knob. When you tighten down the screw it will draw the collet into the taper and it will grip the shaft. Put a drop of blue loctite on the threads so it won't loosen up again.
 
MotoFlier said:
The outside of the collet has a taper that matches the inside of the knob. When you tighten down the screw it will draw the collet into the taper and it will grip the shaft. Put a drop of blue loctite on the threads so it won't loosen up again.
Click to expand...

Not blue. Purple. Loctite 222. For very small fasteners. Blue (242) will hold it tight enough that it will break next time someone wants it off. Red (262) would hold it even tighter.
 
That was solved way too quickly. Perhaps an argument could ensue on what type of logbook entry is required...
 
Crap. I'm not a AP. Can I fix a knob? Do I have to get a ferry permit?
 
UngaWunga said:
Crap. I'm not a AP. Can I fix a knob? Do I have to get a ferry permit?
Click to expand...

I'm pretty sure that if you fix knobs you have to have a fairy permit...but maybe the Supreme Court has said otherwise...
 
Dan Thomas said:
Not blue. Purple. Loctite 222. For very small fasteners. Blue (242) will hold it tight enough that it will break next time someone wants it off. Red (262) would hold it even tighter.
Click to expand...

Not a snowballs chance in hell of that fastener breaking from blue loctite.
 
UngaWunga said:
Oh hey, what do you know... the top pops off the knob. What a stupid, over complicated design.
Click to expand...

Really...

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When you don't understand how something comes apart or goes together, stop and think about it. Forcing it and drilling holes will usually only break things. Don't blame the designers for your lack of patience and imagination. :rolleyes2:
 
It's actually a great design. It's designed to stay together, even when a puckered up pilot grabs and turns it.
 
ollopa said:
When you don't understand how something comes apart or goes together, stop and think about it. Forcing it and drilling holes will usually only break things. Don't blame the designers for your lack of patience and imagination. :rolleyes2:
Click to expand...

You are the knob master.
 
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