Rusted Grub screw removal

[Top Cap]

There is a read only thread on the Forum about this, perhaps Mod will move this to it later?

Anyway, I had a problem with two rusted grub screws in the same control knob. It was purchased at the Dunstable Downs car boot sale as a replacement and no matter how I tried, the grub screws were not going to move. The control knob was soaked in oil for a couple of days, given plenty of penetrating oil but no, these little blighter's were stuck fast!
So I tried freezing in the ice box for a couple of days but that did not work so I tried the other extreme i.e. monitored short bursts in the microwave!
When the control knob was just below the point of being too hot to handle, it was found that the grub screws came out with just a slight resistance.
Obviously you can't do this trick if the knob is stuck to a control shaft but certainly can be applied to a control knob on its own that has sat in the junk box or shed for a number of years.
It would be tricky to try with a thermoplastic control knob so I would only recommend Bakelite knobs only.

[Billy T]

If the grub screw is stuck in a brass insert AND it is a thermoplastic knob, you can avoid the risks inherent in the microwave technique (lack of control over temperature level) by inserting a length of brass control shaft and applying incremental heating via a gas cigarette or fire lighter flame applied to the shaft.

If the screw is protruding too far into the shaft hole you may have to grind or file a deeper flat onto the shaft to get enough length in for fast heating

Soak with suitable lubricant for a few days first as suggested, and fit the end of the brass shaft into a small piece of wood or similar (I used an old large Bakelite knob) so that you don't burn your fingers. If you feel the plastic softening a quick dunk into cold water or a blast with freeze spray will rescue the situation.

Cheers

Billy

[percival007]

Hello,

i am assuming that the grub screws in question were metal?

When i have put something metal in the microwave (bits of tin-foil still on frozen food etc etc), usually by accident, sparks have flown!!

How did/do you overcome this with the grub screws?

Cheers, Percy.

[Top Cap]

I had worried about this sparking too but it did not occur, maybe the amount of insulation provided by the knob prevented this from happening.
Hence also the close monitoring not just for temperature but sparking.
I was just so pleased that the procedure did the trick for me and wanted to let others know about it, on previous occasions I had tried heating the grub screws with a soldering iron with little success. So before I tried this again, I thought of the microwave and very pleased with the result. Once removed, the screw holes were sprayed with switch cleaner and this caused quite a substantial wash-out of rust. I used Copper Ease as a lubricant as I have found this lubricant to be very effective on parts liable to seize.
Les

[FRANK.C]

Originally Posted by percival007

When i have put something metal in the microwave (bits of tin-foil still on frozen food etc etc), usually by accident, sparks have flown!!

How did/do you overcome this with the grub screws?

Sparking only occurs in a microwave when two piece of metal comes close to each other or two edges of the same piece of metal comes close to each other.
The cavity wall is also metal so if another piece of metal comes close to it will spark.

You can quite safely leave a spoon in liquid in the oven without any sparking occurring so long as it don't come near the cavity wall or roof.

Frank

[systemx]

Sorry if everyone knows this but always dip grub screws in silicone grease before fitting, then you can leave the microwave for re-heating the coffee you let go cold!

[Dave Moll]

The problem is usually with grub screws that were fitted by someone else about fifty years ago without the benefit of silicone grease. Unfortunately, we don't have access to a TARDIS to go back and make sure they grease the screw before fitting .

[BGmidsUK]

I often used to defrost/ pre-cook sausages in a Fray Bentos tin in the microwave, then stick it on the hob to cook them in all the juices which had come out also it's common practice when reheating meals prepared earlier to cover the bits you don't want to heat with a piece of foil. Have also left spoons or forks in containers on occasion! Not recommended unless you are watchful though.

I find if any foil is near the top of the oven or close to the magnetron sparking is likely to occur such as when a tiny bit of foil was left on a container and burnt a hole through the plastic lid!!


Back on topic, I'm assuming the bakelite expands when heated, facilitating release of the grub screw? I'm assuming the screw itself doesn't heat up and expand compressing the surrounding bakelite. This could split the knob.


BG

[JHGibson]

Put a cup of water in the microwave along with your knob etc. This will prevent most sparking.
John

[Billy T]

Just out of interest TC, was the grubscrew frozen directly into Bakelite, or was there a tapped metal bush for the shaft insert?

Cheers

Billy

[Top Cap]

The screws were seized directly into the bakelite although the other knobs I had were fitted with brass inserts and did not have the problem. I had thought of simply pouring a boiled kettle of water on it but the microwave seemed a more attractive proposition.
It's strange how the bakelite held the grub screws so tight, I know that if I had exerted more force then the screw would have probably lost half its head making removal virtually impossible. I doubt if the technique would work on a grub screw rusted into a steel insert or those plastic knobs that use a square steel nut pushed into a recess.
Les