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Posted by Suzy on January 8, 2008, 1:36 pm
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> Suzy wrote:
>> I know 3.3 mm is the preferred drilling for a 4 mm tap, but in practice
>> is 3.5 mm OK? My supplier only stocks "standard" taps (no starters or
>> bottomers)
>
> How long is the piece of string ;)
>
> What are you wanting to tap into?
> I tend to use a bigger drill when working with softer aluminium as I find
> the tap tends to bind less, and pushes up the tops of the thread anyway.
> And for a hard material like steel, while you will get better strength
> with a smaller hole, it still depends a bit on how clean the tap cuts.
>
> It also depends on how accurately your drill cuts as well, a 3.3mm drill
> may well cut a 3.5mm hole if slightly miss ground.
>
> So it's a little difficult to give an accurate answer on the information
> available.
>
> --
> Lester Caine - G8HFL
> -----------------------------
> Contact - http://home.lsces.co.uk/lsces/wiki/?page=contact
> L.S.Caine Electronic Services - http://home.lsces.co.uk
> MEDW - http://home.lsces.co.uk/ModelEngineersDigitalWorkshop/
> Firebird - http://www.firebirdsql.org/index.php
Thanks Lester. I'm drilling aluminium and plastic (I know -- which plastic?
Answer: I don't know but it's stock moulding from a hardware store, 15mm X
20mm section). 3.5 mm has worked perfectly in practice but as I'm writing an
article on the project I did not want to mislead my (non model engineering)
readers
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>3.5 mm OK? My supplier only stocks "standard" taps (no starters or
>bottomers)
>