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Thread: taps and dies

  1. #1
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    Default taps and dies

    hi,

    I was wondering if anyone had a link to what size drills to use with metric taps.

    what I mean is, if for example I have an M10 bolt and I want to tap a hole for it in some mild steel, obviously I cant use a 10mm drill or there will be no steel left for the tap to cut a thread into.

    on the other extreme, the largest drill bit I have that will fit into a hole threaded for an M10 bolt is 8.5mm. (Drill bit set has .5mm increments)

    I have searched google and only got imperial data. surely there is a metric chart out there somewhere? the action of tapping probably reduces the diameter of the hole a bit, so I am thinking if I drilled it at 8.5 it would be too small so is it 9mm or 9.5mm?

    If I go too small I risk placing too much pressure on the tap as it is in use and risk breaking it or if I go too large there wont be enough metal in the hole to tap properly and it will strip too easily.

    Does anyone have access to a chart for metric threads? greatly appreciated if someone can help me.

    Doug

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    Just do a search for metric tapping drill chart,if thats to hard look at the tap or taps you will be using,they are marked showing diameter of the tap and the pitch of the thread,for metric threading subtract the pitch from the tap diameter and that will be the size to drill the hole.
    This is far to much information allready given for something that is all to excessable on the net.

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    Doug,

    Here you go mate Tap Drill Sizes

    For your 10 mm thread the 8.5mm drill will be fine.

    I'm happy to help

    Ignore 'pipeclay' seems he's a misserable so & so

    Dave'H

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    Doug,

    This one is in PDF form so you can download it and print it.

    http://www.boltsupply.com/catalogue_...ta/pdf/022.pdf


    Dave'H

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    Quote Originally Posted by pipeclay View Post
    Just do a search for metric tapping drill chart,if thats to hard look at the tap or taps you will be using,they are marked showing diameter of the tap and the pitch of the thread,for metric threading subtract the pitch from the tap diameter and that will be the size to drill the hole.
    This is far to much information allready given for something that is all to excessable on the net.
    Why is it too much information?

  6. #6
    Dave J Guest

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    Hi Doug,
    Metric is the easiest of them all, like Pipeclay said you subtract the pitch from the tap diameter. So say for a common metric 6 x 1mm you just minus the 1 from 6 giving you a 5mm drill needed.
    For general purpose threads around the home etc this system works fine, but you can get into different fits of threads in the engineering side of things, and it's gets a bit more complicated.

    Here is another chart
    Tap Chart Metric Threads

    Dave

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    Quote Originally Posted by pipeclay View Post
    This is far to much information allready given for something that is all to excessable on the net.
    Then why give it.
    What's happening pipeclay, this is not the normal you??

    Phil

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    Generally its not far off the mark for me.

    I am a believer in trying to help yourself first.

    People shouldnt be spoon fed,if they are they will never try to help themselves.

    Going by the way this thread was worded there was a knowledge shown of some form.

    The search that was conducted on google must of been very short and limited.

    By just using a few of the words in the posted thread results on google were achievable.

    From the way the thread was written the poster has a basic knowledge of what they are attempting to do or achieve.

    The thread also showed an amount of reasoning and thought,in my opinion enough to be able to search google to find the desired information.

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    Default thanks for the help

    Good morning everyone.

    Thanks to the two Dave's for the links to the charts. That is exactly the information I was asking for.

    Pipeclay, I think you might have stayed up about half an hour past your bed-time last night and got a little grumpy. But thanks for recognising that I had acquired some basic knowledge of the process, that knowledge was all thanks to google and other research I did yesterday. But try as I might I just could not find any metric charts.

    Thanks again to those who helped

    Doug

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    Doug, don't worry mate, after a few years you'll learn to ignore the idiot responses on this board, it seems some people seriously need a root ... or something.

    With regard the tapping drill size, the problem with metric is that the tapping drill is not normally included in standard drill sets with 0.5 mm rises such as the type you'd buy at a hardware store. Off the top of my head I think M6 and M10 are the only exceptions in sizes most people would commonly tap. However in the charts you now have you'll note the quoted tapping drill is designed to give full thread depth. Most of the time we don't need that, and the fastener will still function perfectly and be very nearly as strong if the hole is drill slightly oversized. "Proper" quality taps will come in a set of 3, and they will allow easy tapping to full thread depth, however cheap taps don't function nearly as well, and drilling the tapping hole slightly oversize will save a lot of frustration (and possibly broken taps). For example instead of drilling M8 6.75 mm (a size btw I've never seen and is a stupid figure to quote) drill it 7 mm, a size you'll have. Likewise M5 you could (carefully) drill 4.5 mm and so on. Just be careful at the small sizes or in critical applications or you'll lose too much strength. If it's important, then go to an engineering supply house and buy the correct size drill for that tap size, or if you're feeling wealthy buy a set in 0.1 mm rises ... and then guard them with your life

    Hope that's of practical help.

    Pete

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    Thanks, Pete,

    I have a good quality set with the three taps, taper, plug and bottom. I gave up buying cheap tools years ago. I dont even go into the tool shop at bunnings any more. I bought the tap and die set from Hare and Forbes and it was not the cheapest set they had.

    With the background information you gave me, obviously gained from hands-on experience and the charts kindly provided by the two Dave's, I am sure that I will be able to complete my current project and many more to come.

    As for grumpy people on forums, yes I have encountered them before and generally I believe they are a nice person having a bad day, they may have a problem in their personal life or had too much to drink or whatever. On the net as in real life I take it with a grain of salt and move on. After all next time I need some help they may be the one to provide the answer.

    If you look at this thread http://www.woodworkforums.com/f36/forum-149396/ members are agreeing that you can ask the most basic question on the forum and people are all supportive and provide help. I agree that this is generally the case.

    thanks again Pete

    Doug

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    On the subject of special size drills for metric taps, H&F sell a set of metric (coarse) taps, 3 each for sizes 3-12mm, with matching drills all in a metal case.

    The other thing I have is a set of 115 drills that has all the Letter drills, all the Number drills and Imperial drills up to 1/2" in 1/64" steps.
    Whilst these are not top notch quality they nonetheless come in very handy as they cover most of the sizes needed. I just drill a hole close to the final needed and then use one of these to drill to the final size.

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    Quote Originally Posted by Pete F View Post
    ... and drilling the tapping hole slightly oversize will save a lot of frustration (and possibly broken taps). For example instead of drilling M8 6.75 mm (a size btw I've never seen and is a stupid figure to quote) drill it 7 mm, a size you'll have. Likewise M5 you could (carefully) drill 4.5 mm and so on...Pete
    Question for Pete or anyone who knows, how does this apply to different materials being tapped? I will be tapping cast iron and mild steel in the near future and possibly other metals as the need arises.

    I would imagine that cast iron being more brittle would be more difficult to tap than mild steel. Does this mean that it is more desirable to tap oversize on cast iron so there is less of it to tap, or would it be better to leave as much thread in the hole as possible, because it is more brittle, even though that will make the tapping harder and increase the risks of breaking a tap in the hole?

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    Doug,
    Get yourself an engineer's black book. It's the most used "tool" in my workshop. As for drill sizes for metric taps, imperial 1/64 sets cover most of the unusual sizes needed.
    Ewan

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    CTC tools sell individual drill bits in 0.1mm increments, quite cheaply. The quality is usually ok too. I say usually because I had one that wasn't heat treated or something because it was soft as. The others (4 or 5) have all had good geometry and performed well. Results for Cutting Tools: Drill Bits

    Attached is a chart I like because it gives some guidance on thread depth.

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