Daft mechanical question

I don't know the full answer, but you can always start by making the holes too small. Right?

It should also be plain that the tap determines the size of the screw. If the tap won't fit a (say) 2.5mm plain hole, then you need to enlarge the hole a bit.

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Per this useful chart, for a 3 mm thread tap, you want to drill a 2.5 mm hole.

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Get a 3mm nut to make sure you didnt mess things up when you cut the head off the screw. You may need to file it gently to make the thread work.

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Use a long set screw instead of a cut-off bolt.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 
845-480-2058 

hobbs at electrooptical dot net 
http://electrooptical.net

Ah, thanks for that.

I think I might have used a tap and die once in Metalwork class at school.

Gareth.

Gareth Magennis Inscribed thus:

Look up "Taping & Threading Chart" !

A 3mm dia rod can be threaded M3 and a M3 tap requires a 2.45 mm hole (2.5mm is close enough)

--
Best Regards: 
                          Baron.

ext -

Wouldn't it be easier to just get a new/replacement antenna? Or, as many of us do, are you making it into a fun(sort of) project?

Not really. The antenna snapped off at the base - it's one of those roof mounted ones that sits above the middle of the windscreen and faces backwards. (Ford Focus)

To replace the entire unit, I would have to remove the base mounting from the car roof. This might be a simple job, but I suspect it is a complete nightmare as its mounting bolts are probably inside the car, meaning I would have to remove the interior roof lining, and I will then probably then have to go to a Ford Main Dealer to have the ECU reprogrammed to recognise the "new" antenna. (that last bit was a joke, by the way)

I suspect that by far the easiest and cheapest solution would be to "glue" back the snapped off antenna. It will cost me the price of a 3mm Tap and a few minutes of my time, and I will now know how to drill a hole and tap it.

And I will not have a detached roof lining that I can't put back, causing me to crash every time it falls onto my face.

Gareth.

Hmm, I might spend a few extra minutes on this problem first.

Could be the stud that has snapped off the roof mounting, or the stud that has snapped off the aeriel.

Gosh, how exciting.

Gareth.

...

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My car dealer that would wash the car as a gratis extra service would routinely unscrew the similarly designed antenna to prevent damage. I didn't realize this till I picked up my antennaless Golf one day, and they had to retrieve it from some drawer.

I have never washed my cars on principle, it is wet enough in the UK to do it for you on a regular basis, I am not "car proud", and consider car washing a vanity and a complete waste of resources.

However, I had parked it under a tree over the course of a few months, and it developed a horrid sticky coating of sap, particularly on the roof. Also the rubber window seals started growing a fine crop of moss.

I took it to a hand car wash, which I considered to be the least objectional form of car washing rather than doing it myself ( I am lazy, and the illegal immigrants could probably do with the job if the truth be known). However, all they did was use a Mickey Mouse pressure washer which did not shift any of the sap. Or the moss.

I figured an auto car wash would probably do a better job, but actually it didn't, and it ripped off my aerial out of spite instead.

It wasn't the roller brush that did the damage though. After all that rolly soapy rinsey stuff, the machine decided to dry the car with an air blowy thing, that comprised of a square section beam the width of the car that was passed from the back to the front, directing a blast of air vertically downwards. Now, these machines have sensors to detect where the various parts of the car are, so it can avoid any contact, but it didn't detect the aerial, and the square drying thingy was forced underneath it. I heard a weird kind of Boing, and saw the aerial flying through the air to land some

20 metres from the car. Good job it didn't perforate somebody's skull I reckon, these machines are dangerous.

Gareth.

For any size thread you plan to tap, to find the hole size just subtract the pitch of the thread from the diameter of the thread. For an M3x.5 that would be 2.5, for a 1/4-20 it would be .25-1/20, .25-.05, or .2 (#7 drill is .201), etc.

Blimey, that is such a simple rule, and one I will probably not forget. Makes all those huge charts look rather silly now.

(I'm glad the UK uses the Metric system though, yours looks a total nightmare!)

I received my 3mm Bottoming Tap today, and now my aerial is back on the car.

Thanks,

Gareth.