i have a few 8mm threads to tap on the rs200 chassis,i have the taps but am unsure what drill size to use.
is there a drill/tap size guide out there?,i have googled but kept coming up with bath taps
cheers
dave

 

drill size is 6.75mm

 

thanks,dave

 

For next time:

http://www.wisetool.com/manufacturing/drill.htm

.

 

I usually use 7.2mm

You want the hole to be big enough that the tap then goes in easy, but not so big that there is no thread left. It will vary on the type and thickness of the material.

Drill a smaller hole and try the tap - if it's too hard, go for a bigger hole

 

no problem Rodney

 

cheers

has all the sizes i need now

dave

 

K5SSY it's actually 6.8mm for a 8mm thread

 

If you're ever REALLY unsure - just go 1mm under the size of the M

That's not a particularly professional thing to do - just gets you out of a tight spot

 

always works though!

 

Yup

 

This will help you for future referance

METRIC COARSE SIZES

----------------------------
TAP DRILL
SIZE SIZE
----------------------------
1mm x .25 .75mm
1.1 x .25 .85
1.2 x .25 .95
1.4 x .3 1.1
1.6 x .35 1.25
1.7 x .35 1.3
1.8 x .35 1.45
2 x .4 1.6
2.2 x .45 1.75
2.5 x .45 2.05
3 x .5 2.5
3.5 x .6 2.9
4 x .7 3.3
4.5 x .75 3.7
5 x .8 4.2
6 x 1 5
7 x 1 6
8 x 1.25 6.8
9 x 1.25 7.8
10 x 1.5 8.5
11 x 1.5 9.5
12 x 1.75 10.2
14 x 2 12
16 x 2 14
18 x 2.5 15.5
20 x 2.5 17.5
22 x 2.5 19.5
24 x 3 21
27 x 3 24
30 x 3.5 26.5
33 x 3.5 29.5
36 x 4 32
39 x 4 35

METRIC FINE SIZES

----------------------------
TAP DRILL
SIZE SIZE
----------------------------
4 mm x .35 3.6mm
4 x .5 3.5
5 x .5 4.5
6 x .5 5.5
6 x .75 5.25
7 x .75 6.25
8 x .5 7
8 x .75 7.25
8 x 1 7
9 x 1 8
10 x .75 9.25
10 x 1 9
10 x 1.25 8.8
11 x 1 10
12 x .75 11.25
12 x 1 11
12 x 1.5 10.5
14 x 1 13
14 x 1.25 12.8
14 x 1.5 12.5
16 x 1 15
16 x 1.5 14.5
18 x 1 17
18 x 2 16
20 x 1 19
20 x 1.5 18.5
20 x 2 18
22 x 1 21
22 x 1.5 20.5
22 x 2 20
24 x 1.5 22.5
24 x 2 22
26 x 1.5 24.5
27 x 1.5 25.5
27 x 2 25
28 x 1.5 26.5
30 x 1.5 28.5
30 x 2 28
33 x 2 31
36 x 3 33
39 x 3 36

need anymore?

 

tried this when i was trying to drill a hole for M1 x 0.25 tap, can't get the tap into the hole tho!

easy way to remember, if your tap says M12 x 1.75 for example subtract the 1.75 from the 12 to give the tap drill size, in this case it'd be 10.2mm

 

 

depends on the pitch of the thread, but for metric its usually the pitch minus the diameter

so for a 8mm dia with 1.25mm pitch, a 6.75mm drill will be fine

but you can oly get prolly a 6.7 or 6.8 - either will be fine tho

 

buy one of those, and stick it in your garage toolbox



http://cgi.ebay.co.uk/BRAND-NEW-PREC...QQcmdZViewItem

 

Correct!

ps,
Working as cnc operator in sweden, drills a lot of holes and thread´s them
ds.

 

Not always true for Imperial pitches though

 

you'll never need anything else, i've used mine every day for over 16yrs. the first thing i ever bought as an apprentice.. £5 now... blimey i got mine from whsmiths for 95p

 

think you will find it wasnt, seen as though he didnt say what pitch it is i was correct as stated in later posts on this thread.

 

sigh...you take the addendum and dedendum of the thread and adding them up thus giving the thread depth or .86603xp to give the fundimental triangle minus the basic crest radius,minus the basic root radius.
Take 60% of this depthx2 then take this figure away from the tap diameter, that should be about right for the hole size to be drilled.

 

but normally we dont say the pitch of the imperial threads we say the teeth per inch, and of cause to work out thread depth from TPI you need the thread angle as well! i know you know this and thats why you said it though

 

 

oops double post lol

 

i'll take your zeus book and raise you the "mechanical yearbook 1969" think it was 11d if i remember correctly

 

Ill raise you to "mechanical year book 1930 something "
which i have in my locker at work