Crossbow Bolt Construction
This page last updated on 02/02/2002
NOTE: that the construction techniques that follow, are based on the following assumptions.
1) Arrows gain lift, in flight by "point plaining". This is the reason for setting the balance point 9% of the length forward of the center point. Crossbow bolts do not gain lift in this fashion. A crossbow bolt, falls at the same rate, no matter how fast it is traveling.
2) Crossbows by definition are center shot. So issues of arrow spine, do not effect crossbow bolts.
3) Based on the two items above, your crossbow bolt, should be as light as you can reasonably make it. The balance point can be almost anywhere, so long as it is forward of the center of drag.
The steps to making a two fletched bolt for a Iolo, or other period style crossbow, are as follows.
1) Select your shafts
Select the lightest premium grade 5/16 shafts you can find. Spine is not an issue, but weight is. The shafts must be as closely matched in weight as possible. A dozen shafts yields two dozen bolts for me.
2) Measure your crossbow
The measurement you want is the distance from where the sting is held by the nut (at full cock), to the end of the shelf or bolt rest. This distance is the length of you bolt minuses any extra for the point and nock tapers.
3) Cut the shafts
Cut your shafts to the length above adding enough extra for a point and nock taper. When finished you will want a bolt with a point that sits in front of and off of the shelf or bolt rest.
4) Taper the ends
Cut point and nock tapers on the shafts. The nock taper will be cut off the bolt after construction is complete. The nock taper will only be used to help you fletch the bolt. If in cutting the point taper, you remove too much wood, toss the shaft in the trash. At every step consistent weight in the shaft is vital to uniform performance.
5) Seal the shafts
You may paint the shaft, if you want. But unless you can dip all the shafts at the same time, you will create differences in weight that will adversely effect your groups. This fact is off set by the need to seal your bolts. Unsealed crossbow bolts will change in weight as the humidity changes. (Did I mention the fact, that matching the weight in your bolts was critical. )
6) Attach your points
Attach the points, which you have already selected. You want to use a light weight field point. Almost all target points are too light for correct balance. But, all field points are more then heavy enough. When attaching the points, try to use a consistent amount glue. Small differences in weight at any point in construction, will make a big difference in performance.
7) Friction fit the nocks
Twist nocks onto your shafts without any glue. You want a tight friction fit. After you are done fletching these bolts, you will be able to reuse the nocks.
8) Choose your fletching.
I use 2" long shield cut feathers.
9) Fletch the bolts
Set up your fletching jig with a spiral clamp set at a 5 degree off set. You want to spin the bolts pretty good. Spinning adds stability and helps balance out the fact that you are only going to have two fletches on the bolt. However, if you spin the bolt too much you create excess drag. A slow bolt is much more effected by cross winds and such. After setting the clamp type and angle, setup your jig for four fletch arrows. Then fletch the bolts with two feathers set 180 degrees apart. The fletching should be set high enough
on the shaft to clear the crossbow nut, after the nock taper is cut off and the butt of the bolt is against the string.
10) Remove the nock and cut the end
Last take off the nock that you twisted on earlier. Take your fletched bolt to a miter box and cut the nock taper off with a x-acto razor saw. Leave 1/16th of an inch of the taper on the shaft to leave a slight bevel on the butt of the bolt.
Once all of the above steps are done, take your bolts to the range and shoot them. Don't be afraid to toss any bolts that still fall out of the group.
Good luck with your new bolts
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