Drilling out a high tensile screw?

[martin collins 1]

I recently nosed my electric converted Precedent Stampe over on a touch and go and the prop adapter sheared off leaving the remains of the 3 screws behind. I have removed two off them which were sticking proud, they were reluctant to come out as i had put thread lock on them but out they came. The third one has snapped inside the motor casing so i thought i would drill it out and recut the thread but new drill bits are hardly making an impression. The screws in my opinion are much too small for a motor of this torque being only 3mm, i have tried a new 1.5mm bit but it has hardly made a mark. Any advice on getting it out appreciated, i thought about a local engineering firm but the bill would probably cost more than the £50 replacement cost of the motor!

[Erfolg]

Has the screw got to come out?

 

In the distant past, spark eroding the root diameter or ultra sonic machining could be used if financially worth while. Then prise the remaining coil out'

 

Again I did see in the past a drill that would drill HTS, although it required a lot of pressure, also it was expensive.

 

If a solution comes up other than a new motor I will be intrigued, an addition to my knowledge.

[Dickw]

The only ideas I can come up with are applying heat to the motor casing to get a differential expansion, or (depending on the motor design) perhaps dismantling the motor and working from the inside.

 

Good luck.

 

Dick

[Ron Gray]

Are you using a cobalt drill bit, they can drill hardened steel, an ordinary drill bit is no good!

[J D 8]

As above heat may help in that it will destroy the thread lock. A quick blast with gas pencil flame.

An other option would be cut a groove in the end of the screw with thin Dremel disc and turn out with screwdriver, this would result in some damage to the motor but a possible last resort to get it working again.

[Andy Stephenson]

If what you are removing the screw from is aluminium you should try using alum. Alum dissolves ferrous based metals but doesn't touch aluminium. Alum is a family of chemicals so you have to choose the correct one for the job but I'm sure with a bit of googling you can find the answer.

[Piers Bowlan]

Dicks suggestion to dismantle the motor (if possible) and work from the inside, is what I would try personally. If there is some of the screw thread proud of the inside of the motor case at least there would be something you could get a long nosed mole grip onto? Play some heat on the motor case to break down the thread lock before trying to turn it, as suggested by JD8 ?.

 One of the dangers with drilling, is of the drill bit hitting the windings once it has broken through the screw. So one way or another dismantling the motor sounds unavoidable to me and probably what an engineering company would do.

No harm in asking an engineering company for a cash price by the way. You may be surprised, £10 or £20 quid may cover it, which would be worth it.

If it was me trying to drill it out, the motor would definitely end up scrap.?

Where is Laser Engine’s Jon, when you need him, he would know how to do it.?

Edited May 28, 2022 by Piers Bowlan

[Engine Doctor]

Have you tried heating the part to release the threadlock  then turning the part with a small sharp screwdriver? Thread lock breaks dien with heat an let's go.

If time is not an issue soak the part in an alum solution. This will erode any steel or iron parts while leaving the aluminium, bronze or any non ferrous metal untouched. Any steel bits will effectively be dissolved.its often used to remove taps that have snapped while tapping threads in aluminium.

Finally, if you can find a left handed drill to attempt drilling the part out. As soon as it bites the effect will be to unscrew the part.

Good luck hope you find a fix.

 

[kc]

Mount the motor the other way round?     Most motors have the shaft one end and the bolt on prop adaptor goes on the other end.    If the shaft has been cut off then replace the shaft,  but if intact then just get a collet type adaptor.

 

Heating as suggested by others may work - I would get a soldering iron really hot and then put onto the screw - try several times with cooling in between.    Or maybe put in the freezer for a while and then heat the outer part quickly.

[PatMc]

+1 for reverse motor mount option, unless it's possible to simply reverse the shaft. 

What motor is it ?

[martin collins 1]

Thanks for all the suggestions, the motor dismantling proved a no go, i undid all the grub screws and took off the circlip but the shaft would no budge and the motor would not come apart. In the end i thought about it over a cuppa and i just rotated the ally prop adapter to another position, drilled 3 new holes and tapped them, simple solution when you think about it! The Stampe will be back in the air this week now.

[Martin McIntosh]

I used to work with CCTV cameras mounted to the top of police vans. You would not believe how often they would manage to break them off. The tilt bearings were fixed on with three M4 s/st screws and secured with atom bomb proof Loctite but a cobalt tipped drill would make start on the screws and the heat generated would destroy the Loctite. On your repair, replace the lousy Chinese screws with proper hardened ones. I had this happen in the air with a RCG 30cc petrol motor when all four prop. screws sheared.

[Ron Gray]

9 hours ago, Martin McIntosh said:

I had this happen in the air with a RCG 30cc petrol motor when all four prop. screws sheared.

?

[Stuphedd]

I have tried alum with no success  , so now I use those little diamond "drills" you get for the Dremmel , then all you need is patience , lots of it and many drills  , However if you know a dentist , a rapidly vanishing body  , they have super quality "drills"  , and try to get some worn out ones , they do last a lot longer !  A good quality tap then finishes it off . Had to do it last month on a 1984 Moulton  , ( spares as rare as dentists !!) 

[PatMc]

If you want to look for them via google, they're known as "burs" in the dental profession. IIRC they are designed to work at very high rpm.

My dad was a dental supply sales rep, I used to be able to get his demo cast offs. (Nearly 60 years ago ?)