homemade bowstring jig

© 2010 Justin Ross of 8

This homemade, three-post, one-arm endless bowstring jig (for recurve) has gone through many alterations in an attempt to reduce bending and increase practicality. It will make a string up to 70” and has a post height clearance of 115mm (more than enough room for a Beiter winder). These instructions have been written for my own records but also to share the knowledge I have gained over three months of tinkering, getting the jig to what it is today. Use them at your own discretion and, dare I say, risk. PARTS LIST Qty Part Size From Part no: 1

Slotted steel channel (e.g. Unistrut)

41mm x 21mm. 2.5mm thick. 3m (118”) long.

City Electrical Factors (www.cefonline.co.uk)

0024-4600

3

Square bracket 10mm hole. 40mm x 40mm.

City Electrical Factors (www.cefonline.co.uk)

0024-4237

2

Flat coupling plate

2 hole City Electrical Factors (www.cefonline.co.uk)

0024-4240

4

Non spring channel nut

M10 TLC Direct (www.tlc-direct.co.uk)

UV NS10 (or UV SS10 and remove spring)

1

Wing knob M10 female brass insert

Components Direct (www.comdir.co.uk)

KN0014


4

Studding connector

M10 x 30mm Wickes (www.wickes.co.uk)

156645

5

Flat washer M10 Hardware store -

3

Repair washer M10 Hardware store -

1

Wing nut M10 Hardware store -

1

Cap nut M10 Hardware store -

1

Hex nut M10 Hardware store -

1

Hex nyloc nut M10 Hardware store -


2

Hex nyloc nut M5 Hardware store -

2

Machine screw M5 x 10mm Hardware store -

2

Hex bolt M10 x 30mm Hardware store -

3

Hex bolt M10 x 60mm Hardware store -

3

Rawplug Throughbolt (R-SPT)

M10 x 130mm (includes nut and washer)

Hardware store -

Note: If you can’t buy bolts to exact length, buy the next size up and cut down. You may have to cut some bolt heads down by half for clearance inside the steel channel.


CUTTING, DRILLING AND WELDING (or riveting/glueing) When measuring and cutting the slotted steel channel, take into account that the drill holes needed for the ‘pivot arm’ and ‘feet’ should be through solid parts of the base. Don’t use slots as the bolt holes. Cut the slotted steel channel into four pieces: 58.5" (main channel) 27" (pivot arm – ensure its centre at 13.5” is solid, i.e. not a slot) 14" (foot – ensure its centre at 7” is solid, i.e. not a slot) 14" (foot – ensure its centre at 7” is solid, i.e. not a slot)

At least 7” in from both ends of the ‘main channel’ drill a hole suitable for an M5 machine screw. At the centre of each ‘foot’ (7”) drill a hole suitable for an M5 machine screw. At the centre of the ‘pivot arm’ (13.5”) drill a hole suitable for an M10 hex bolt.

This part isn’t essential but reduces the tendency for the 'pivot arm' to lift toward the end post. Weld a flat coupling plate to the bottom of the ‘pivot arm’ so that one hole is directly under the central drill hole of the ‘pivot arm’. The other half of the flat coupling plate should protrude at a right angle to the ‘pivot arm’. This flat coupling plate could be affixed in other ways, e.g. small bolts, rivets or glue. Note: If small bolts are used to affix the flat coupling plate to the 'pivot arm', don’t let them foul the 'main channel' or the 'pivot arm' won’t sit flat.

Use a flat screwdriver to open up and remove the metal sleeves from the throughbolts.


ASSEMBLY


End post

Screw an M10 x 60mm hex bolt into a channel nut and do up tightly. Slide into one end of the ‘main channel’ and put a square bracket onto the bolt followed by an M10 flat washer and studding connector. Tighten up firmly. Screw on a second studding connector and tighten up firmly. Finally, screw in a throughbolt with its washer and nut included. Tighten up.

Pivot arm post 1

Screw an M10 x 30mm hex bolt into a channel nut and do up tightly. Slide into one end of the ‘pivot arm’ and put a square bracket onto the bolt followed by an M10 flat washer and studding connector. Screw in a throughbolt with its washer and nut included. You’ll need to move this post so don’t tighten hard.


Pivot arm post 2 and tying off point

Screw an M10 x 30mm hex bolt into a channel nut and do up tightly. Slide into the other end of the ‘pivot arm’ and put a flat coupling plate onto the bolt with one half over the ‘pivot arm’, the other half off the end. Put an M10 flat washer onto the bolt followed by a studding connector. Screw in a throughbolt with its washer and nut included. You’ll need to move this post so don’t tighten hard. Put a repair washer on an M10 x 60mm hex bolt and place up through the overhanging second hole of the flat coupling plate. Put a repair washer onto the bolt and tighten in place with an M10 hex nut. Screw an M10 wing nut upside down onto this bolt, followed by two M10 flat washers. Screw an M10 cap nut onto the end of the bolt to finish the tying off post.

Pivot arm

Screw an M10 x 60mm hex bolt into a channel nut and do up tightly. Slide into the ‘main channel’ and put the ‘pivot arm’ onto this bolt. Screw on an M10 hex nyloc nut for enough for the ‘pivot arm’ to be rotated and slide along the ‘main channel’ without the channel nut coming free. Place a square bracket followed by a repair washer, onto the bolt, and screw on the wing knob. This is what locks the ‘pivot arm’ in place. Measure outward from the central bolt or wing knob of the ‘pivot arm’ to each ‘pivot arm’ post. Make the distance equal on both sides and tighten down the posts’ studding connectors and nuts.


Feet

Put an M5 machine screw down through one of the M5 machine screw holes in the ‘main channel’. Take one of the ‘feet’ and tighten in place with an M5 hex nyloc nut so that its base is against the base of the ‘main channel’. The ‘foot’ should rotate when moved by hand. Repeat at the other end of the ‘main channel’ with the other ‘foot’. The ‘feet’ can be rotated in-line with the 'main channel' for easier storage. The jig is now complete and you’re ready to start building bowstrings.

homemade bowstring jig

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