Drill for tap

[emnick]

Hi All,
I need to tap an M10 thread into 14mm aluminium should I be using a slightly smaller drill than I would if tapping steel? I was going to use about 8.5mm?? would this work. or should I be using slightly bigger diameter.

Thanks for any help

 

[William_H]

Aluminium i softer than steel so a lot easier to tap into. But is hence not such a strong thread. So you might be able to use a smaller drill bit however the diameter of the hole as made by the thread in cutting its way through the ali will be the same assuming the hole drilled is no bigger than the low valley of the thread diameter. ie the tap will cut a hole it needs regardless of the original hole drilled so use the correct drill size regarless of material. good luck olewill

 

[forelle541]

I usually go for bolt size less the pitch of the thread. Usually about the same as Mr zoooos for the engineers on here.

 

[rosssavage]

Ahhh, the little yellow and black book. Still got mine somewhere, but not used it for years.

 

[old_salt]

Have a look here and use thin oil or paraffin, kerosene or WD40 to lube:-http://www.shender4.com/metric_thread_chart.htm

 

[VicS]

Hi All,
I need to tap an M10 thread into 14mm aluminium should I be using a slightly smaller drill than I would if tapping steel? I was going to use about 8.5mm?? would this work. or should I be using slightly bigger diameter.

Thanks for any help

According to Zeus the BSI recommended size is 8.4mm

The table from Presto Tools says 8.5mm

The table from Intal gives 8.4 as the BSI recommended size and 8.6 mm for a 75% depth of thread..

I see no suggestions to use different sizes for different materials

Use paraffin as the lubricant.

 

[old_salt]

Quote from VicS.
I see no suggestions to use different sizes for different materials

You use different tapping drill sizes for course threads, fine threads.
Thats why I posted a link to a chart with the Course and Fine Sizes.
May be this is what got emnick to ask the question.

Course Thread
M10 x 1.5 = 8.50 tap drill

Fine Thread
M10 x 0.75 = 9.25 tap drill
M10 x 1 = 9.0 tap drill
M10 x 1.25 = 8.8 tap drill

 

[earlybird]

Quote from VicS.
I see no suggestions to use different sizes for different materials

You use different tapping drill sizes for course threads, fine threads
l

That's not quite the point. It's possible to vary the tapping drill size to suit material and application. Between 75% and 95% thread engagement might be commercially acceptable.
The lower figure would give easier machining and less tap wear, for say stainless steel, with minimal loss of strength.
The higher figure for soft materials or high-class work.

 

[old_salt]

That's not quite the point. It's possible to vary the tapping drill size to suit material and application. Between 75% and 95% thread engagement might be commercially acceptable.
The lower figure would give easier machining and less tap wear, for say stainless steel, with minimal loss of strength.
The higher figure for soft materials or high-class work.

Yes I agree a little leeway may be necessary due to the tools you have at your disposal.
In a backyard workshop yes very doable.
But when building a Steam turbine that is to take a ship 100,000,000 miles No.
Bin there and done both.

 

[tjbrace]

I used 8mm drill to tap 10mm threads in an aluminium backing plate for deck organisers. Worked perfectly.

 

[emnick]

Thanks again to everybody.

 

[Sailfree]

for aluminium is a coarse thread preferred?

 

[old_salt]

for aluminium is a coarse thread preferred?

Yes it has a deeper thread pattern.