How to remove the OBS knob from a gauge.

[No Longer Active]

Hi there,

I have purchased 2 real dummy gauges for the right side of my cessna cockpit. However I am struggling to remove the rotary knobs from the gauges so I can fit them into my MIP.

I have the Bendix King VOR2 and ADF and it appears that the way to remove the knobs is by unscrewing a tiny hex screw on the side of a knob, however my smallest hex key which is 1.5mm is a fraction too big, and I am struggling to find a 1mm hex key to fit it.

Can anyone offer any advice as to a tool that can remove the tiny screw to remove the knob. It appears a such simple task, but the smallest key I can find is 0.5mm too big. AHHHH! LOL

All the best,

Alex

[smendlik]

Alex - Just curious if you have solved your problem yet or not? Are you sure it's a hex screw and not a hollow pin? I've been fooled by things like that before. Looking up hex sizes there is indeed a 1mm size, so your solution might be to find someplace that sells them that small.

[Ronson2k9]

Why not drill out the knob anchor with a bigger drill bit. If you go about half way you will have 'removed' the anchor making a slightly bigger hole in the knob. Small Allen Wrenches can be found at hobby shops. Many of the small models and electric motors require small tools. You could also see if there is an installation manual for the gauges you have and found out how/if the knob is removable. If you go the drill route you could check Dremel tools they have small size bits that could be what you need. Also make sure your target is securely clamped small drill bits break pretty easily.

[LH784]

On my (real) instruments the little hex screws are indeed used to tighten the knobs. They are opened /unfastened by unscrewing that little headless screw and then pull the knob away to the front.
Since my 727 instruments seem to use inch sizes and over here we use mm, it is sometimes a bit difficult, but there are all kinds of different tiny sizes and those screws usually are not extremely tight. Also, I have already used tiny allen wrenches with slightly inclined heads so it will slip into the screw's head until it finds a final tight position.
Reagrds, Florian

[No Longer Active]

Hi All,

Indeed it is a hex key, because of the hex shape of the screw, I have just managed to find a 1mm hex key online for £2, so will hopefully have that in the post asap and can get the knobs off to put the gauges in my new MIP....

All the best,

Alex

[Meridian]

Alex, make sure that the 1mm Allen key is the correct size i.e not too small, otherwise it will damage the screw by 'rounding' the hexagon and then you will have a real problem. It could be that the screw is an Imperial size and not Metric in which case the Allen key that you need could well be 3/64 inch (1.19mm). If the 1mm key is too small try one at 3/64 inch.

Andrew

[Ronson2k9]

A quick check as to where the gauge was manufactured should answer that question. If it's north American then probably imperial if not then probably metric.

[No Longer Active]

Hi Ron, my gauges are bendix king so can only assume they are american.

The 1mm hex key i bought is now too small :(

[Ronson2k9]

2 questions.

What is the gauge you are trying to take knob off of?
Do you want to keep the knob to re-install it back in gauge?

There are some schools of thought out there that you should not remove the set screw that is hold the knob in place only loosen.

Check this out.. Model Fixings (http://www.modelfixings.co.uk/tools.htm#allen%20keys) They have a pretty good size selection. I believe you would be looking at the 1.3mm hex key. 1.5 is to big and 1 is to small. You really would need a metric micrometer to get the exact size without getting an install kit for the gauge itself. I was thinking you could drill it out with a dremel but if you want to use the knob again you would need to tap the hole and put in new set screw or get new knob.

The other alternative would be to file/grind down the larger hex key till it fit your set screw. You could use a mounted dremel and a grinding wheel to do that. This would change the dimension of the hex key but you could tag it or something for specific use for BK knobs. Don't through it away. If filing seems like a good option. Just go for a box don't try to make a hex .. This will drive you crazy. 4 sides should be sufficient given the circumstances.

Best of Luck
Ron

Found a BK wrench.. It's 0.050" or 1.23mm
49r Communications (http://49ercommunications.com/store/bendix-king-wrench-allen-0050spline-p-284.html)

You could file/grind a 1.3mm wrench down or get the above one one.
- Company is located in Nevada City California BTW.

Other sources could be closer by?

IMO .. I would file/grind one down to that size. You need a micrometer to do it though. Or just drill it out if you aren't using the knobs or they are only dummies/eye candy as you said earlier. At least now though you know what you need size wise.. hehe

[No Longer Active]

Hi Ron.

Thanks for your informative answers. In the rut to achieve the task, I have purchased a 3/64" hex in the hope that that will do the job. I believe that the 3/64" is inbetween the 1mm and 1.5mm range. I just hope that this does the trick.

I want to be able to loosen the hex screw to remove the knob from the rotating shaft. The knob will not go back on but will be used on my encoder knob panel as these knobs are the real deal.

Again, many thanks for your research, I secretly hoped that you would have an answer as your pretty much spot on and you have some great ideas.

Anyway, when the hex arrives I will give you a heads up and lets see if the bugger comes off! haha!

All the best to you pal...

Alex

[Ronson2k9]

Well 3/64 of an inch is 0.046875 inches. So seems really quite close. 3.2 thousands of an inch smaller then the hole or 1.6 thousands smaller on all sides. As the hole is presumably 50 thousands across seems like it will work. Take it slow though. Wrench is very small and could twist/brake so keep that in mind. I'd almost be inclined to use a pin vice and cut and clamp into vice. This will reduce the amount of torsion coming back up the wrench as it's much shorter. Keep that as option two if the wrench twists and or breaks. Set screw can't be in there that hard though.. not really thready and short. To tight would strip the threads in the plastic knob.

Best of luck
Ron

BTW Model Railroading and Flight Simming have a lot in common from the electronics to working with small items, gear ratios and the like. Both are seeking to control a model of the physical world except one is in the computer the other is on a table top...

[No Longer Active]

The 3/64 is too small, and the 1.5mm is too large, so looks like I am going to have to file down a 1.5mm :(