Model Engineering Glossary

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h (hecto)

The prefix h or hecto indicates the unit should be multiplied by 10².

See also: Decimal Prefixes.

Hacksaw

A few notes on using a hacksaw.

Half Male Centre

A dead center that has a portion of the 60 degree cone cut away.

See also: Centres.

Hand Reamer

The hole should be pre-drilled with an allowance of < 0.2 mm (.008 in) for soft materials and < 0.13 mm (.005 in) for hard materials.

Hardening

See also: Colour Temperatures.

Heat

If a temperature difference exists between two points heat will flow from the point at the higher temperature to the point at the lower temperature. This flow will continue until equilibrium has been reached. more......

See also: Colour Temperatures.

Heat Content

See: Heat.

Heat Flow Rate

See: Heat.

Heckenham Alloy

56 % Copper 44 % Nickel

Hercules Metal

67 % Copper 31 % Zinc 2 % Aluminium

Hertz (Hz)

Frequency in cycles per second. Named after H.R. Hertz, the German scientist who discovered electrical oscillations. In the case of Alternating Current the frequency is 60 hz in North America and 50 hz in the UK and the rest of the World.

High Carbon Steel

Carbon content greater than 0.85%.

High Speed Steel

A hard steel used for metal cutting tools as it remains hard even at dull red temperatures. It normally contains:

Tungsten 12 to 18%, Chromium up to 5% and Carbon 0.4 to 0.7%. more...

Hit and Miss Engine

An engine where the speed is governed by holding the exhaust port open and decompressing the engine when the speed goes too high, as the speed drops the exhaust is closed and the engine then draws air and fuel into the cylinder via the intake valve. Hence the engine "misses" when the speed goes to high and "hits" when the speed drops.

The photo shows a hit and miss engine built by Mick Cherry, learn more here.

Hoskin's Alloy

90 % Nickel 10 % Chromium

Hoyle's Alloy

42.3 % Lead 46.15 % Tin 11.53 % Antimony

Hydrated Aluminium

Trade name: Bauxite

Chemical formula: Al₂O₃2H₂O

See also: Chemical Table.

Hydrated Sodium Carbonate

Trade name: Soda ash

Chemical formula: Na₂CO₃ 10H₂O

See also: Chemical Table.

Hydrochloric Acid

Chemical formula: HCl

See also: Chemical Table.

Hydrofluoric Acid

Chemical formula: HF

See also: Chemical Table.

Hydrogen Cyanide

Trade name: Prussic acid

Chemical formula: HCN

See also: Chemical Table.

Hydrogen Sulphide

Chemical formula: H₂S

See also: Chemical Table.

Hypereutectic Aluminum

Used in high performance engines as it has a lower coefficient of thermal expansion and so means tighter tolerances.

See also: Pistons

Hypernik

50 % Nickel 50 % Iron

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