# Chuck keys



## DTR (20 Jul 2015)

Greetings all,

How does one work out what size chuck key to buy? 

I recently bought a model-maker's bench drill from the wife of an enthusiastic engineer who had sadly passed on. The drill is most likely home made from raw castings. (I also came home with a Cowells hand shaper, but that's another story!). The drill chuck has a capacity of around 3/8" (I think), and the hole for the spigot part of the key is 5/32". Despite searching high and low in his workshop, no key was to be found. 

Can anyone please point me towards what size key I need? Thanks!


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## AndyT (20 Jul 2015)

Last time I needed one I just took the drill to the toolshop and asked for a key to fit. That is what I would do, but I understand that there might be no proper tool shops in Essex. [I think I recall seeing mention of a good one in Leigh on Sea, where my old aunt used to live, but I digress...]

More helpfully, this page from Chronos will at least give you an idea of the sizes that are available so you could buy one and try it.

http://www.chronos.ltd.uk/cgi-bin/ss000001.pl?page=search&PR=-1&TB=A&SS=chuck+key&ACTION=Go


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## Phil Pascoe (20 Jul 2015)

Is there a way of working out the number of teeth on the chuck key from the number of teeth on the chuck?
Anyone?


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## AndyT (20 Jul 2015)

In case it is any use I have just gone and measured the key on my old B&D Electric Drill which also has a 3/8" chuck which was probably a common one in the 70s. The pin is 15/64" and the pitch of the teeth, measured in the middle of the taper to give an average size, is about 3/32", so probably not what you need. 

You could measure the pin by using a set of drills as gauges and checking which drill fits, presuming that you have a set of imperial sized bits. And assuming it's an imperial sized chuck...


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## marcros (20 Jul 2015)

i bought a key from eBay for a couple of quid that had 4 sizes on it. Predictably, it was made of cheese and broke the first time I used it, but something similar would tell you the size to buy a decent one of.


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## DTR (20 Jul 2015)

AndyT":2rah9o11 said:


> More helpfully, this page from Chronos will at least give you an idea of the sizes that are available so you could buy one and try it.



Chronos was the first place I looked but I still managed to miss that page..... either one of the 4mm chucks might do it



AndyT":2rah9o11 said:


> You could measure the pin by using a set of drills as gauges and checking which drill fits, presuming that you have a set of imperial sized bits. And assuming it's an imperial sized chuck...



I've already measured the pin, it's 5/32"  (or 4mm in new money)



marcros":2rah9o11 said:


> i bought a key from eBay for a couple of quid that had 4 sizes on it. Predictably, it was made of cheese and broke the first time I used it, but something similar would tell you the size to buy a decent one of.



I thought about that but even the smallest looked too big. Are the sizes labelled on each key?


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## marcros (20 Jul 2015)

DTR":1cror1r1 said:


> AndyT":1cror1r1 said:
> 
> 
> > More helpfully, this page from Chronos will at least give you an idea of the sizes that are available so you could buy one and try it.
> ...



I think that they were. if they weren't, i knew the 4 sizes that I had bought from the listing.


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## DTR (15 Aug 2015)

DTR":2ikh8ya2 said:


> AndyT":2ikh8ya2 said:
> 
> 
> > More helpfully, this page from Chronos will at least give you an idea of the sizes that are available so you could buy one and try it.
> ...



So I ordered the two sizes of 4mm chuck.... and they both fit equally well :-k 

The larger key has a slightly different tooth profile, so it still meshes ok. Learn something new every day.

I mentioned this briefly in another thread. I originally thought that the drill was home-made from castings, but something wasn't quite right. There were parts that were obvious diversions from the original design, but I just assumed that the original owner had used whatever parts he had to hand. Later on I realised that it was actually a conversion of a hand cranked drill.







I still need to install a table and an NVR switch, but I'm looking forward to using it.

Thanks for the help chaps


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