Which tap??

Ok so what's the score with coarse v fine ? Which category does a standard metric bolt sit in?!

Also can you hand tap with a spiral point?

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Originally Posted by JoeHarris

Ok so what's the score with coarse v fine ? Which category does a standard metric bolt sit in?!

Also can you hand tap with a spiral point?

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I believe the standard preferred metric screw thread is the coarse thread. Fine is generally used when wall thickness is less than you'd ideally like.

No idea about the spiral tap, I'd guess tho that it's mostly for drilling with a hand drill. I put my tap in a cordless drill when I had 48 M8 holes to tap when I was doing some bits for my early design (which has since been scrapped)

Attachment 7420

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Originally Posted by Lee Roberts

Typically I just buy what I need size wise as and when I need them

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...and end up spending more in the long run than if you had bought a set. I bought one with had the standard 3 of each tap, and dies from M3 to M12 a couple of years ago and it's been invaluable. I've since replaced a few, generally with odd ones I find at the car boot sale.

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Originally Posted by Lee Roberts

I think some people use a little lube when tapping, personally I don’t bother.

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Then you're missing out. Use something with a low viscosity (WD40, coolant, tea...) works well for aluminium and a tapping paste for hard materials. It will make the taps last longer and increase productivity since if the tap is lubricated you can often get away without periodically reversing.

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Originally Posted by JoeHarris

Also can you hand tap with a spiral point?

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Yes, so long as it is not a blind hole a spiral point tap is generally the best choice for aluminium.

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Originally Posted by njhussey

I believe the standard preferred metric screw thread is the coarse thread.

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Correct

P.S. Anyone want to come and tap about 1000 M8 holes for me ;) ?

I bought a set of taps from a hardware store about 12 years ago...only one of each size from M3 to M12 with M8 & up having a few different pitches...they're mostly (haven't a clue if they're all still there) all in a rusty pile in my tool box (the partners son borrowed my tool box when I was away and left it out in the rain for a weekend :( ) I know I have M8, M6 and M4 as I've just looked but will treat myself to some new ones for my build :)

I use cutting fluid I've borrowed from work...must take it back...

Thanks everyone, really helpful. Jonathan, I am excited about getting my first set and learning how but you can keep your 1000 holes!