Build Your Own Classic Crossbow.pdf

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It was the "hot setup" during the Crusades

and it's going through a new revolution today.

An archer might consider it kin to a fire-

arm

. .

a shooter, on the other hand, most

likely would think it a stock-mounted

bow.

and you wouldn't need a poll to know the

gen-

eral public's feeling: It looks sinister enough

to be a lethal weapon!

In short, there's not much doubt that the

modem crossbow suffers an "identity crisis,"

but-regardless of the mystery that still sur-

rounds this curious hybrid-it's been gaining

in popularity among hunters and targeteers

alike

. . .

and that trend hasn't gone unnoticed

here at

MOTHER.

With several avid bowhunters on the staff,

and a research department eager to take on

such an interesting challenge, it wasn't

too

difficult

to get the ball rolling on a project

that we figured might be a first in the field:

designing and building a quality crossbow

testing its range, accuracy,

from scratch

and overall effectiveness

. . .

and then com-

paring its performance to that of traditional

recurve and compound bows.

The

Classic

Crossbow:You

Can

Build

...

ABOVE: Our fieldpiece

looks-andf functions

-like many of the more expensive manufac-

tured crossbows. RIGHT:

The

front sight is

strap of aluminum fitted with a bead. The

steel cocking rodgives the cocking lever (BE-

LOW) a forward mount when the string is be-

ing drawn. FAR BELOW: i'2isprototype

has

no trigger safety, but one can be added.

QUICK

ANALYSIS

The contemporary crossbow shares little

beyond a basic design with its forebear, the

medieval arbalest. Though both launch

ar-

rows (bolts) by means of a short bow trans-

versely futed to a stock, the superiority of

modem materials-along with the improved

geometry made possible by the use of such

lightweight plastics, alloys, and composites-

has turned what was a crude but effective

weapon of war into an admirable piece of fair-

ly uncomplicated technology.

Over the past few years, crossbow design

has received considerable attention from var-

ious manufacturers, with the result that the

old standard has been modified to run the

gamut from a paramilitary-looking assault

piece to an artistic expression of classical

physics. And although these developments

represent improvement in most cases, they're

beyond the ability of all but the best-equipped

crafts people to duplicate.

We chose the path of least resistance and

used the simplest common denominators in

our design. The stock of our crossbow con-

sists of a center spine covered on each side

by a strengthening flank. As a bolted-together

unit, this flat-aluminum assembly serves as

a combination barrel (or

chase

crossbow ter-

minology), trigger housing, handgrip, and

shoulder extension.

The bow, or prod, is set into the nose of

the

forestock, and the two-piece trigger mech-

anism, cut from 114" plate steel, is pinned

be-

tween the right and left flank pieces just

below the receiver. Walnut stock inserts were

trimmed and shaped to mate with the stock

Your

Own!

on either side of the shoulder extension.

NOSE DETAIL

Since the string does contact the barrel and

is thus subject to friction, we added a pair

of shoulder slides to the sides of the chase to

reduce string wear and increase bolt veloci-

ty. Though these could also

made of wal-

nut, we used Delrin (a Du Pont acetal resin)

because it possesses an inherent lubricity.

Our crossbow's open sights consist simply

of a front frame made of aluminum strap, and

an alloy rear ring mounted to the receiver,

Socket-head cap screws threaded into each of

these brackets provide sighting beads, and the

rear unit can be lowered or raised as neces-

sary to zero the piece in at a specific range.

As far as we've been able to determine, a

telescopic rifle sight is inappropriate on a

crossbow for three reasons. First, the weap-

114' $1'

1-114'

on's effective range is limited to 50 yards or

ALUMINUM

PROD

BLCXX

so in all but an expert's hands, and at that

distance, beads and the practiced naked eye

The takedown version

either a pistol

lot~g

arm.

should be sufficient. Second, a fired bolt's

TRIGGER AND

SAFRY

DETAIL

trajectory is such that, beyond 15 or more

632

X 1-1R'

SOW(ET+lEAD

025'

318'

yards, its drop is enough to lower the point

CAP

SCREW SIGHTING

POST

SPRINGSTEELTANG

of impact many inches from the line of sight

(see sidebar)

and since most scopes are

calibrated for rifles, the range of adjustment

may be restrictive or the zeroing-in process

tedious. Finally, a scope narrows the field of

view and adds weight as well.

You've probably already noticed that our

photos show two different crossbows. The

first, detailed in this article,

a functional,

no-gadget rendition that's not overly compli-

cated to assemble, which should serve as a

fine fieldpiece or target piece. The second is

a multiuse version that has some interesting

features, but for the most part it's best suit-

ed to range shooting or backyard "plinking."

It sports a folding front handgrip, a remov-

(3)

In'

3 4 '

EXPANSION PINS

able shoulder stock extension (which allows

lySrl'

STEEL

TRIGGER

the long arm to convert to a hand piece), and

-no doubt the most practical feature of all-a

'5i32'

X 1

COMPRESSION

SPRING

positive trigger safety. (This last item, by the

(10)

NO. 6

314'

W I N E

SCREWS

way, can be added to our standard crossbow

if desired.)

NOTE: Though we did build and

test both of our crossbows, the

po-

tential for injury from any weapon

is enough to compel us lo say that

whoever builds and uses this tool

does so at his or her own risk.

PIECE BY PIECE

You might

interested to know that we

spent about $102 making our fieldpiece; that

breaks down to approximately $14 worth of

114"

aluminum flat stock (available at a scrap-

yard or a metals distributor);

in Delrin;

$6 for the walnut billets; about

in assort-

ed bolts, pins, and other minor hardware;

and-here's the kicker-$67 worth of prod

and Dacron bowstring.

Admittedly, it would have been nice if we'd

been able to construct our own short bow by

using common materials

and believe us,

(continued on next page)

COCKINQ LEVER

(3)

114'

314'

MACHINE

BOLTS

118'

24'

FLAT-STEEL

HANDLES

\(2)

114' X 1

MACHINE

BOLTS

l l B '

5112'

FLATSTEEL

COLLAR

Crossbow:

Fact

and

Fiction

Just how effective is a crossbow? To an-

swer that question, several of MOTHER'S

staffers took to the field with our project pro-

totype equipped with a 175-pound prod

. .

the smaller takedown model with a 75-pound

draw weight.

. .

a $449 Bamett Comman-

do (a quality commercial crossbow) rated at

175 pounds

. .

a recurve bow rated at 54

pounds, full (30") draw.

. .

and a 7Gpound

compound bow. We were interested in each

weapon's range, accuracy, and penetrating

power.

but, ultimately,

were search-

ing for the crossbow's proper niche in the or-

der of things.

Now we weren't interested in testing head-

to-head with the Barnett offering, and we

couldn

fairly pit a hand-held bow against

a brace-mounted crossbow. So what we did

was make a series of test firings with our

standard model at distances of 10, 20, 30,

- . .

40, and 50 measured yardr. Each group con-

sisted of five shots with the same 24.94-gram

overall (126.3-grainfield point) Easton 14"

aluminum bolt, and the resulting patterns

then were measured and recorded. The cross-

bow was mounted and leveled in a sturdy

brace, and a surueyor's transit was used to

establish a direct line of sight to a given point

on the target. The deviation of the points of

impact from the sighting point was also

noted. Wind conditions were fairly calm

throughout the test.

The chart below encapsulates our findings.

As you can see, the homemade crossbow held

a respectable pattern, even out to 50 yards.

(We suspect it would

the same beyond that

point, but thar's considered expert's range.)

A t that distance, drop was considerable (i.e.,

the weapon's barrel would have to be elevat-

ed in order to hit a target in a level line of

sight)

but the same situation existed in

thecaseofthe more traditionalhand-heldbows.

Penetration was never a problem with any

of the weapons we tested, since

all

the shafts

buried themselves-some

the fletching-

in the 12" of extruded polystyrene we used

for a target backing. Considering the differ-

ence in draw weights between the tradition-

al bows and the crossbows (and accounting

for the standard arrows' additional mass),

we could infer that prod strengths of more

than 125pounds amount to overkill; the ex-

tra power probably offers little, but taxes

strings, bolts, and cocking convenience heav-

ily.

Howmer, an understrength prod would

even less desirable unless

was matched

with a short, lkht bolt. Our takedown ~ i s t o l

model uses %-pound prod and a 6;' alu-

minum bolt, and has a power stroke of

6-1/4" compared to the larger weapon's

8-1/2".

fine for target shooting, but not

really useful for hunting.

Regardless of draw weight, string life can

be extended and bolt velocity increased slight-

ly by applying a lubniative wax to the string

and the barrel's shoulder slides.

In summary, much as we hate to burst a

romantic balloon, we'll have to concede to the

facts: Although a crossbow has the advan-

tages of compactness and mechanical cock-

ing and locking (it can be held at full draw

without strain on the user),

is really no

more accurate than a conventional bow in

proficient

hands

. .

can't

loaded

and fired

as quickly

and doesn't even

approach

the overall effectiveness of a rifle. Nonethe-

less, it's a valid sporting tool that's slowly

but surely coming into its own once again.

(continued from preceding page)

we tried! But the laminated fiberglass prods

we laid up just didn't have adequate draw

strength or the resiliency to stand up to re-

peated use, possibly because we weren't able

to duplicate the heat-and-pressure curing

process used by commercial manufacturers.

At any rate, we were pleased to learn that

Barnett International

(1967

Gunn

Hwy.,

P.O.

Box

934,

Odessa,

33556)

will sell prods,

strings, bolts, and other accessories to any-

one who orders the company's

$2.00

postpaid

catalog.

T o ease construction, we've outlined the

crossbow's major pans and drilling points

within a grid, which will allow you to make

up-scaled templates for the metal pieces. But

play it safe by matching the templates per-

fectly

before

taping them to the metal and

scribing theit outline

. . .

and be even more

carehl when actually cutting the aluminum

stock, since

[I]

the pieces must join closely,

or you'll be spending a lot of time with the

FIELD TEST RESULTS

OVERALL LENGTH: 31"

file, and

[2]

the center spine's weak spot-

MODEL TESTED: Homemade, aluminum frame;

OVERALL WIDTH: 26"

the trigger guard-should not

any

thinner

walnut inserts; Delrin shoulder slides

POWER STROKE: 8112"

than

7/32".

PROD: Barnett Commando, heatlpressurecured

SIGHTS: Open, adjustable rear post

The best way to trim the parts accurately,

fiberglass, 175-pounddraw

BOLT: Easton,

14"

aluminum, 24.94 grams overall

by the way, is to use a band saw equipped

WEIGHT:

pounds, 5-112 ounces

including 126.3-grain fieldpoint

with a metal-cutting blade. Because the

smooth operation of the trigger and string

AVERAGE

catch depends in great measure upon the per-

AVERAGE

WINDAGE

fect alignment of the three stock components,

RANGE

DROP

ERROR

PATTERN

NOTES

we suggest that you postpone drilling the

10 yds.

+I'

full penetration

314'

flank pieces until you've bored the

9/64"

post

'14

yds.

rsm

trajectory point

holes according to the center points indicat-

20 yds.

11.114'

tight pattern

yds.

30"

9.iM'

ed on the template. Once those sockets are

bolt wobble

t30

yd8.

21.112"

Its8 bolt wobble

complete, clamp the aluminum center spine

yds.

50.314'

6.314'

pattern improved

to one of the flanks and recheck the align-

yds.

83'

pattern Improvemen(;

ment, using the template cutout from the trig-

rxcellmt penetration

ger housing. Then drill corresponding holes

Zero trajectory point

Barnett Commando comparison

the one flank piece.

With that done, use No.

314"

machine

screws as temporary locating pins for the two

bored components, and clamp the second

flank piece in place. When you're satisfied

that all three parts are evenly mated, drill the

final member. Since the post screws are re-

cessed, you'll need to countersink the exteri-

or openings with larger bits according to the

design ofthe screws and nuts you've chosen.

The steel trigger components have to be

thinned by 1164" in order to allow them free-

dom of movement within the stock. Once this

is done, those parts can be drilled where in-

dicated with a 118" bit, and the 1/8"

314"

expansidn pin pivots can be pressed in and

centered. The pivot pins ride in 9/64" sock-

ets drilled into the right and left flank pieces;

to be on the safe side, you might want to use

the trigger-housing template cutout to posi-

tion those openings accurately.

As we mentioned before, you can install a

trigger safety mechanism according to our de-

tail. Both the trigger and the safety catch are

returned by small compression springs set in-

to slots c i t through the central spine.

Before assembling the stock for good, you'll

want to bevel the inner surfaces of the bar-

rel, and round the entire frame's outer edges.

The rough work can

done with a grinder

or file, and rhe metal then can be smoothed

with emery cloth. Save the final extra-fine

polishing for later, after you've bolted and

pinned everything together and completed the

cosmetic work.

The next portion of the project includes set-

ting the bolt tang (the spring-steel leaf that

holds the projectile snug against the barrel),

adding the wooden (or Delrin) slides to the

flanks, and cutting, shaping, and fastening the

walnut inserts that dress the shoulder exten-

sion. (These pieces can be cut to shape using

the template as a guide, then rounded with

a sander and bolted or glued to the aluminum

spine prior to being finished with varnish or

tung oil.)

The front sight is a piece of

1116"

518"

6-112" strap aluminum bent into an open

frame configuration so the bolt can pass

through it. It's fastened to the top of the fore-

stock with two No. 6

1/4" machine screws,

and a short cap screw locked through its

crown serves as a bead. Though we used a

machined ring at the rear (to provide a hous-

ing for an experimental scope sight), you can

make an excellent sighting post by simply

drilling and tapping a hole at the top of the

receiver to accept a

6-32

socket-head cap

screw about 1-112" in length. This can then

be adjusted up or down for sighting.

We ordered a prod with a draw strength

of 175 pounds

. . .

but even if you choose a

lighter bow to lengthen string life, you'll

probably need a cocking lever to pull it into

position. You can make one by bending four

sections of 118" X

flat metal to create a

two-armed, bolt-together yoke that uses

mechanical advantage to ease cocking (see il-

lustration).

pair of slots in the stationary

part of the lever hook into a 5116"

steel

rod fitted into rhe crossbow's forestock (this

should

located as indicated on the template

and pressed in place before you install the

prod), and another set of slots cut into the

short "jack zrms" catch the string. The ful-

crum's just a movable collar that can be

locked into the optimal position.

The prod is held in place by a 114"

1-114" block of aluminum famd with

strip

of hard rubber.

similar pad, glued to the

rear of the prod socket, provides additional

cushioning, and the metal block is forced

tightly against the bow's face by a 114" X

1-314'' cap screw threaded into a tapped hole

at the nose of the stock.

Once the prod's installed, you'll have the

pleasure of stringing it. Unless you're extraor-

dinarily muscular, we'd suggest you purchase

what's called a

bastard

string along with the

regular Dacron cable. This set of strands is

longer than the service string and thus can

slipped onto the prod more easily. It's then

used to draw the bow's ears back to the cocked

position so the real string can be looped in

place. When that's done, both strings can be

released with the trigger and the bastard re-

moved. This is the

only

situation in which

the crossbow should

"dry fired," since that

practice car! split the prod.

It should be quite obvious that your fin-

ished project has a lethal potential and should

be handled with the same caution that you'd

give to any longbow or firearm. Don't load

it until you're ready to fire it, and don't fire

it without an adequate field behind your tar-

get to safely absorb any overshots. Too, if

you're interested in exploring the crossbow's

capabilities for hunting, check your state's

game laws before you build

. .

it could save

a lot of

disappointment

later. Meanwhile,

you might want to look over the sidebar ac-

companying this article to see what kind of

results you could expect from your modern-

day arbalest!

EDITOR'S NOTE:

I f

you're intaesred in

making the croshaofearured here (or the smaller

rakedown version) bur would prefer detailed,

step-by-step insrrucrionh

set of building

plans-complete wirh full-size curring te7nplates

-is available at a cost of

$10

plus

$1.00

for

shipping and handling from Mother's Plans,

Crossbows,

P.O.

Box

East

Flat

Rock,

28726.8

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