[Amps] What is it called?

[Will Matney]

On Sun, 23 Jan 2005 13:02:11 -0500, <G3rzp at aol.com> wrote:

> Will said:
>
> "My guess is because 4-40 screws have more holding power than a 4-36  
> screw
> does. This is due to more threads in the thickness of whatever it's
> screwed into, either tapped material or a nut. Fine threads are always
> used in places where more holding power is needed in a thin section.
> Coarse threads are for thicker sections."
>
>
> This is true up to a point. It's generally reckoned that if you have  
> three threads engaged, that will give sufficient strength in most  
> materials. However, softer materials benefit from using a coarse thread,  
> because although the core and overall diameters are the same, there's  
> more meat in each thread.

Correct, fine threads are for metallic uses like steel and aluminum  
(tapped or with a nut). Deep, coarse threads are used for wood,  
fibergalss, and composite materials like the insualtion board in mention.  
That is if it is to be tapped and used without a nut. But if a nut is  
used, the unified thread system is then used with either coarse or fine  
threads. Some of the other threads like Buttrus and Acme are used for  
linear motion or in jacks, etc.


All of which is why I tend to use Unified
> coarse threads (or even BSW!)in places where I'm using soft materials  
> like aluminium, teflon, tufnol, polythene and even fibreglass. The last  
> is very rough on tools, blunting them very rapidly, and carbide tipped  
> tools are desirable. However, I haven't seen any carbide taps yet!!!


We have carbide taps here and others with a TIN (Titanium Nitride)  
coating. Just that carbide and TIN costs more than a HSS one. Carbide can  
be bad to break off to so they have to be used with that in mind.

>
> One point worth remembering is that plain carbon steel is harder than  
> HSS (High Speed Steel) at low temperatures. HSS is used extensively  
> where speed of metal removal is important, as in industrial machining,  
> but for a lot of the stuff we do in home brewing, it's not worthwhile -  
> certainly for taps and dies which are only used in hand tools.

Generally most tool steels in the rough are soft or as annealed. After  
they are shaped into a tool they are then hardened before they are ground.  
There's two types available here, water and oil hardening. HHS blanks  
(like drill rod) though are soft and not worth a quarter if not hardened.  
There are pre-hardened HSS blanks for boring bars and for use in fly  
cutters though. They are already shaped and made to be ground away as they  
are used up.


>
>
> 73
>
>
> Peter  W6/G3RZP (where it's warm and sunny, for you guys in the mid west  
> and on the east coast!)
>
>
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Will

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