LIST
FEGURÐ OG VELLÍÐAN
HANDVERK
MENNING OG SAGA
SKEMMTUN
UMHVERFI
MATUR OG DRYKKUR
ÖFUGVERKFRÆÐI
VÍSINDI
ÍÞRÓTTIR
TÆKNI
KLÆÐANLEG TÆKNI
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)
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Charlie

19. október 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).
Lengra kominn
2-3 days

Leiðbeiningar

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.

Efni fyrir þetta skref:

SjónglerSjóngler1 as required

Nauðsynleg verkfæri:

DemantssögDemantssög
SteinolíaSteinolía
Stafrænn skífmælir 6 tommurStafrænn skífmælir 6 tommur
ÖryggisglerauguÖryggisgleraugu
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.

Nauðsynleg verkfæri:

JárnslípskífaJárnslípskífa
Sett af kísilkarbíð-slípikornumSett af kísilkarbíð-slípikornum
HornamálHornamál
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.

Nauðsynleg verkfæri:

JárnslípskífaJárnslípskífa
Sett af kísilkarbíð-slípikornumSett af kísilkarbíð-slípikornum
ParaffínParaffín
BýflugnavaxBýflugnavax
HitaplataHitaplata
Stafrænn skífmælir 6 tommurStafrænn skífmælir 6 tommur
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.

Nauðsynleg verkfæri:

HitaplataHitaplata
ParaffínParaffín
BýflugnavaxBýflugnavax
Gifs (Parísargifs)Gifs (Parísargifs)
PortlandsementPortlandsement
BýflugnavaxkúlurBýflugnavaxkúlur
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.

Nauðsynleg verkfæri:

JárnslípskífaJárnslípskífa
Sett af kísilkarbíð-slípikornumSett af kísilkarbíð-slípikornum
StækkunarlúpaStækkunarlúpa
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.

Nauðsynleg verkfæri:

ViðartjörubikViðartjörubik
FuruharpixFuruharpix
GullsmiðarauttGullsmiðarautt
SjónglerfægivélSjónglerfægivél
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.

Nauðsynleg verkfæri:

Ljósflötur (viðmið)Ljósflötur (viðmið)
BunsenbrennariBunsenbrennari
SaltSalt
StækkunarlúpaStækkunarlúpa
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.

Nauðsynleg verkfæri:

HamarHamar
BensenBensen
HornamálHornamál
JárnslípskífaJárnslípskífa
Sett af kísilkarbíð-slípikornumSett af kísilkarbíð-slípikornum

Efni

1
  • 1
    Sjóngler
    1 as required
    Staðgengill

Nauðsynleg verkfæri

23

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eftir CharlieDE

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