drilling mm

[Lorenz]

Hello,

I'm from Holland and we work here with mm (milimeter)

I have got plans in inches and I try to calculate them in mm.

In the instructions stands: drill the hole, ( 1/8 inch. )

Now I calculated: 1/8 = 12.5% ( 100: 8 x 1 )
so 12.5 % = 0.125.

0.125 x 1 inch (25.4 mm) = 3.175 mm

is that a hole from 3 mm? 3,1 mm? or 3.2 mm?

that is very importand to know.

I hope my post is clear

thanks!

 

[Blogwitch]

Lorenz,

Usually it is a round UP exercise. So in your situation 3.2mm.

I have attached a couple of charts for you to print out, that will make things a lot easier for you.


Blogs

View attachment Drill Diameters.pdf

View attachment Fraction_Decimal_Metric_Conversion_Chart.pdf

 

[Jasonb]

If the hole is for a rod to pass through then you would be better off using 3.0mm as that is a readily available metric size, far easier than trying to turn down 4mm material to 3.2mm.

The same applies if its a clearance hole for a thread, as you will likely substitute an M3 thread instead of 1/8" whitworth, 5BA, 5-44, etc.

Jason

 

[Omnimill]

Very true, you need to consider standard stock sizes available to you for things like shafts etc. You could of course buy imperial (inch) stock AND drillbits though!

Vic.

 

[prof65]

Hi Lorenz

When I get plans in inches, I convert them with 1" = 24 mm; so 1/4" = 6 mm, 1/8" = 3 mm, 1/16" = 1.5 mm... no more problems with standard size for drills, mills, reamers, etc.

A simple Excel sheet makes the conversion fast & easy.

The engine is 5% smaller than the original, but it's not a problem for me.

For threads I use the standard metric size closer to the plans.

Cheers

Roberto

View attachment 1 inches to 24 mm conversion.xls

 

[Lorenz]

oke! thanks for the reactions,

The tabels are very useful,

I like the way from roberto, that is easy to use.

thanks a lot! Thm:

 

[Jasonb]

Robertos method is useful for bar stock designs but may present problems when working with castings.

Also it does not equate well to stock sizes once you work on larger engines as 1" would be better converted to 25mm (stock size) than 24mm.

Jason