Crossbow Building Wiki
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Introduction[]

This lock mechanism is the simplest possible variation of the catch lock. Unlike the original versions of the sixteen century and later, this one does not have set trigger, and only has a few parts:

  • Tumbler
  • Trigger
  • Return springs
  • Lockplates (optional)

As this mechanism uses a long lever trigger, it looks more medieval than the original 16th century (and later) catch locks that had a set trigger. For more details on those, take a look at the following books:

  • Alm 1998: 59
  • Payne-Gallway 1990: 169-173
  • Sensfelder 2007: 52

The process step-by-step[]

Start by making a fake lockplate from thin metal (e.g. aluminum). The top of the plate should simulate the top of bow, complete with the angled catch that holds the bowstring with help from the catcher. Also make a model of the tumbler from the same metal, and drill several pairs of holes on top of each other through both of them while the tumbler is in correct, locked position:

Making a simple catch lock - 01.jpg

Next make a model of the trigger lever, place it in correct position and drill several holes through it side-by-side near the eventual axle hole:

Making a simple catch lock - 02.jpg

Now test how the lock operates, depending on which holes you use for axles:

Making a simple catch lock - 03.jpg

Usually, the goal is to place the trigger's axle as close to the tumbler as possible, so that the trigger pull is smooth. Similarly, the axle of the tumbler should as high as possible to mimimize pressure on the trigger's hook.

Once the tumbler and trigger models are ready, it's time to make the real ones. First mark the outline of tumbler and the correct axle hole to a piece of steel suitably thick (5mm+):

Making a simple catch lock - 04.jpg

Making a simple catch lock - 05.jpg

Do the same for the trigger, though leaving it straight instead of curved at this point. Cut and/or forge both to shape and drill the axle holes.

Next drill bigger axle holes to the fake lockplate:

Making a simple catch lock - 06.jpg

Attach the tumbler and trigger to the lockplate using their axles and verify their correct operation:

Making a simple catch lock - 07.jpg

Making a simple catch lock - 08.jpg

If necessary, file tumbler's and trigger's contact surfaces until they work perfectly.

The easiest way to curve the trigger is to heat it with a blowtorch and then bend it using a hammer:

Making a simple catch lock - 09.jpg

At this point the lock should look like this:

Making a simple catch lock - 10.jpg

Making a simple catch lock - 11.jpg

Next you need to widen the top of the tumbler: this helps avoid bowstring wear and the bowstring from slipping away from the catch on the sides.

First cut a rectangular piece of fairly thick (~3mm) steel and cut a deep slot to it:

Making a simple catch lock - 12.jpg

Insert the tumbler into the slot and squeeze the whole package between the jaws of a vise:

Making a simple catch lock - 13.jpg

Making a simple catch lock - 14.jpg

Grind grooves that follow the border of the plate and the tumbler and then weld both together:

Making a simple catch lock - 15.jpg

Making a simple catch lock - 16.jpg

Next grind off excess material:

Making a simple catch lock - 17.jpg

If necessary, adjust the angle of the plate and the tumbler. This can be done by by attaching the tumbler upside down to a vise and giving the tumbler light strokes using a hammer, until the angle is correct:

Making a simple catch lock - 18.jpg

The final step is to cut the plate to form. First cut away the part of the plate that extends beyond the jaws of the tumbler, i.e. cut it to length of the original slot. Then mark the outline of the plate:

Making a simple catch lock - 19.jpg

Making a simple catch lock - 20.jpg

Cut, file and polish and the results should look something like this:

Making a simple catch lock - 21.jpg

Making a simple catch lock - 22.jpg

Making a simple catch lock - 23.jpg

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