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Equilateral Glass Prism: Sawn, Ground and Pitch-Polished
Frankford Arsenal, in F. E. Wright, The Manufacture of Optical Glass and of Optical Systems (1921), Fig. 77 · Public domain (US Government publication)
Charlie

Dibuat oleh

Charlie

19. Oktober 2026DE
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Equilateral Glass Prism: Sawn, Ground and Pitch-Polished

A prism splits white light into its colours, so its faces must be optically flat and its angles true. This is how the US arsenals ground prisms in 1918, as F. E. Wright recorded for the Ordnance Department in 1921: saw a blank from optical glass, rough-grind it on iron disks, set a batch of prisms in plaster, fine-grind, and polish on pitch with rouge. Wright's worked example is a right-angle prism; an equilateral prism has three 60° angles, made the same way. The picture: blocking prisms for rough grinding at Frankford Arsenal (Wright 1921, Fig. 77, public domain).
Lanjutan
2-3 days

Instruksi

1

Saw out the blank

Saw a triangular blank from a block of optical glass with a diamond saw, using kerosene as lubricant. Leave several millimetres extra on each face for grinding.

Material untuk langkah ini:

Kaca OptikKaca Optik1 as required

Alat yang dibutuhkan:

Gergaji IntanGergaji Intan
Minyak TanahMinyak Tanah
Jangka Sorong Digital 6 InciJangka Sorong Digital 6 Inci
Kacamata pengamanKacamata pengaman
2

Rough-grind the faces

Grind one triangular end flat on a rotating iron disk with 90 or 150 mesh grit. Then rough out the three side faces at right angles to it, checking the 60° angles with an angle gauge.

Alat yang dibutuhkan:

Cakram Gerinda BesiCakram Gerinda Besi
Set butiran abrasif silikon karbidaSet butiran abrasif silikon karbida
Kaliber SudutKaliber Sudut
3

Grind the ends in a batch

Wax 20 or more prisms by their ground ends onto a heated iron disk and grind the other ends together: 90, 150, then 220 mesh, then smoothing grit. Change grit only when the surface is free of scratches. Regrind to the set thickness.

Alat yang dibutuhkan:

Cakram Gerinda BesiCakram Gerinda Besi
Set butiran abrasif silikon karbidaSet butiran abrasif silikon karbida
Lilin parafinLilin parafin
Malam LebahMalam Lebah
Pelat PemanasPelat Pemanas
Jangka Sorong Digital 6 InciJangka Sorong Digital 6 Inci
4

Block the prisms in plaster

Set the prisms face down in melted paraffin on a flat iron disk and coat their backs with beeswax. Clamp a ring round them, fill with plaster of Paris and a little Portland cement (10 : 1), and let it harden about 16 hours. Cut the plaster back 1/8 in from the prisms and give it two coats of shellac.

Alat yang dibutuhkan:

Pelat PemanasPelat Pemanas
Lilin parafinLilin parafin
Malam LebahMalam Lebah
Gips (Plaster of Paris)Gips (Plaster of Paris)
Semen portlandSemen portland
Pelet Lilin LebahPelet Lilin Lebah
5

Fine-grind

Grind the block on a slightly convex plate with wet flour emery (the part that settles out of water between 10 and 60 minutes). After five minutes check with a magnifier: the faces should have an even velvet finish, slightly hollow by less than 0.001 in.

Alat yang dibutuhkan:

Cakram Gerinda BesiCakram Gerinda Besi
Set butiran abrasif silikon karbidaSet butiran abrasif silikon karbida
Lup PembesarLup Pembesar
6

Polish on pitch

Pour strained pitch with a little rosin 1/4 in deep on an iron tool and cut crossed grooves 1/8 in wide, 1 in apart. Press it true with a rouge-wetted flat. Polish the block with creamy rouge and water on the machine, usually 4–8 hours, running nearly dry at the end.

Alat yang dibutuhkan:

Pek ter kayuPek ter kayu
Damar pinusDamar pinus
Merah poles perhiasanMerah poles perhiasan
Mesin Poles OptikMesin Poles Optik
7

Test for flatness

Lay an optical flat on each face and look at the Newton colours in sodium light (salt in a Bunsen flame). Straight bands to the edge, or one colour over the whole face, mean it is flat.

Alat yang dibutuhkan:

Bidang optik datar (acuan)Bidang optik datar (acuan)
Pembakar BunsenPembakar Bunsen
GaramGaram
Lup PembesarLup Pembesar
8

Free, clean, check the angle, repeat

Break the plaster away, clean the prisms with benzene and check each angle with the angle gauge. Correct by hand on a flat tool with smoothing grit. Repeat blocking and polishing for every face, smallest face first.

Alat yang dibutuhkan:

PaluPalu
BenzenaBenzena
Kaliber SudutKaliber Sudut
Cakram Gerinda BesiCakram Gerinda Besi
Set butiran abrasif silikon karbidaSet butiran abrasif silikon karbida

Bahan

1
  • 1
    Kaca Optik
    1 as required
    Placeholder

Alat yang Diperlukan

23

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