Monday, 15 October 2018

Finished Crossbow Prod Mount


The mount is finished and it's holding the prod very securely, there is sheet rubber beneath the limbs and elsewhere too. I've removed the shim of 3 ply from under the stock to get the string sitting just a whisker above the track. (see pic)

I think it looks a tad Brutalist with maybe a hint of Art Deco. I might round some corners and remove some excess metal later to improve the aesthetics.
With the masking tape removed, the limbs look rather handsome with the Maple showing through the clear glass.
I took a quick full draw shot...
I'm not entirely happy with it as it is working hardest mid limb, but the outers are flexing. I could maybe take a few mm off the underside of the last 6", tricky to see with out a decent comparison with the unstrung shape.
The close up of the nock shows the construction. There is a wedge of maple adding thickness to the wooden core, a horn piece is overlaid over the glass backing, this is then recessed slightly and bound with carbon fibre/epoxy to minimise the risk of the string splitting down the nock. These are lessons leaned from earlier prods.

I haven't actually measured the poundage at full draw (it's difficult to set it up for such a measurement) and measuring it won't actually effect the reality! It's relatively comfortable to draw, so my guess is about 100# or a tad over, it certainly seems to have decent speed vs draw weight. (255 fps at last measurement)
I'll have to try it through the chrono' again later, as the improved rigidity may have given it another couple of fps, mind I might not get round to it as I have a cold and may retire to my bed!
Update:- Just tested it 258.5 fps :-)
And here's the unstrung pic for comparison.
I've combined the 2 pics here:-





Thursday, 11 October 2018

A Waiting Game

I've done a lot of work on the crossbow prod mounting and it will be much more solid when finished, the limbs won't be able to lift at all at the tips. I've had one more test shot at a fractionally lower brace and it was about 1.5 fps faster which is a refreshing change from the natural material prods which lost speed with each shot.
Once the mounting is finished, I've made a new string and optimised the brace height it should be pretty respectable... I recently saw a 175# crossbow advertised as having 145 fps which makes mine look rather good as it's prob only about 100-120# tops.
I've had to order a variety of screws for the prod mount and while I'm waiting for those, I've taken a little more off the Elder primitive. I've also had a chuck of wood with a nice natural curve which I'll use to make short levers for the Elder drying out on a radiator, still not sure if it's Ash or Willow, but once I start working with it, I'll probably find out!
That's about it really, done some pruning and tidying in the garden and generally been enjoying the fine weather.

Done some more and cut the splice for the levers, here's a pic of one dry assembled.




Saturday, 6 October 2018

Successful First Crossbow Shot

I made some new deflex wedges for the crossbow limbs with less deflex, I made a couple of stringer clamps too.
That all took longer than it should as I had one of those days where I couldn't pick anything up without dropping it and I couldn't put anything down without losing it! I wanted to take a tad off one of the wedges using the belt sander. The belt was drifting to on side and wouldn't adjust ??? Then the bracket that mounts the adjusting screw fell in half, damn... I set to and made another.
Finally I tried to sand the wedge but the belt sander wouldn't switch on!... It would run while I held the button, but the relay wouldn't latch on.
I opened it up, cleaned and tightened the connections, then finally it worked... but where had the wedges gone? Arrrrggghhh! I tided the bench, looked everywhere, even emptied the rubbish bin... nope.
There was only one possible place they could be, down the slot in the table of the table saw where the blade comes up (the table saw gets used as a secondary work bench). I shone a torch in there.. yes! I had to lie the table saw on it's side, take the bottom off and clean it out. Having recovered the wedges I stuck some duct tape over the slot in the table saw as I only use it about once every 10 years as I tend to use the bandsaw or my circular saw.
Anyhow, I eventually got the crossbow all back together and glued on the string catchers which I'd salvaged from the previous prod. Ready for testing, once I could brace it, and that took an age, the first stringer string just stretched too much, eventually I used an old crossbow string with the clamps I'd made and got it braced to a decent height and tried a first test shot. It seemed pretty good and didn't shake itself to bits. The string settled down a couple of mm above the track, so the prod mount will need a little adjustment, but that's no problem.
Video here:- https://www.youtube.com/watch?v=XcI_GfUmB1A&t=38s

Next step will be to inspect it all to check it's all secure, then make some improvement to the prod mount and to adjust it a bit.
I've already checked to see if the prod has taken any set, it has, but just 1/2mm over the straight central section of each limb, and I feel that's ok.
I'll shoot it some more and measure the speed through the chrono'.
Update:- I shot it through the chrono' 255fps I'm very pleased.
The limbs are tending to twist upwards slightly as the string line is above centre, the limbs being tapered up from the lower edge. Some tweaking to the prod mount should sort that out.

Tuesday, 2 October 2018

Prod Tweaking Progress


I got the prod mounted, but it's almost impossible to brace. I got a string on as tight as I could and videoed it to see how it was moving.
It looked a bit stiff at the inner area where the limbs thicken up, but rather than jump in and remove material from the bow I've made up a couple of wooden wedges which fit between the limbs and the mounting, effectively angling them back towards the archer as if deflexed by about an inch and a half. That doesn't seem like much but it allows me to get a taut string onto it at a low brace and it look promising.
It's difficult to quantify the effect, but string movement (draw) on a braced bow, is about 3 times the tip movement, so it's quite significant. Bear in mind a crossbow is high poundage short draw so, say 120# at 12" draw is going to be 10# per inch of draw, so angling the bow back may have taken 45# off the draw weight!
So, it may be that the final arrangement is a smaller wedge.

I spent a deal of time making some stringer brackets, but they tended to slip along the limbs. I'll probably make some more like the ones I made for the 275# steel prod on my repro' medieval light sporting bow which can bee seen in this post unfortunately those clamps are won't quite fit on these limbs.

Saturday, 29 September 2018

Crossbow Prod Mount

The prod and mount is coming along nicely, my little mill is proving very useful and it's also good to still have the pillar drill on the other end of the workbench.
I'm getting it built up slowly, it will obviously have the corners rounded , decent hex head bolts, chunky washers, rubber wear strips etc, but the pics give the general idea. There will also be vertical angle bracing to the side of the stock, so plenty to do yet.
The prod is maybe a tad long at the moment, but it's been made such that the limbs can be shortened at the mounting end by about 1/2" an new holes drilled, if I want to shorten the bow and increase the draw weight a tad. Conversely, if I want to reduce the draw weight I can machine wedges to go between the mount and the limb to angle them into a slight deflex position. Having individual limbs gives a lot more room for manoeuvre, it also makes it a bit simpler to get matched limbs.

I might have it all mounted up by the end of the day, but I haven't cut nocks in the limbs yet, they will require some thought as I don't want them splitting. I'll probably add a little sliver of wood to the back to allow a nice rounded shape and also bind some carbon fibre and epoxy round for security. There is also the issue of string catchers/buffers.

Wednesday, 26 September 2018

Crossbow Limb Glue Up

I got the clear glass laminations and EA40 epoxy from 1066archery shop
I did the glue up very carefully as the laminations can slip and move as clamps are applied. You can never have too many clamps but even so it's a relief when they are removed and the masking tape taken off the glass and you can see if the glue line is good (it's clear glass).
It grieves me deeply when I see people gluing up laminated bows with great gaps between the clamps... if you don't have enough and can't afford more, scrounge some old inner tubes and use rubber strapping between the clamps. It's daft to scrimp on the early stages, a bit like building a house but not using any cement between the blocks in the foundation.

Once cured I took off the clamps and peeled off the masking tape which I'd applied to protect the glass. The glue up looks great, I was amazed how clear the glue and glass was, it just looks like polished maple... which reminds me of one guy on FB who got upset when I laughed at his indignant claim that his bow was Yew when it was a Yew core with clear glass laminations on back and belly, he didn't like me calling it a glass bow, but it's the glass that's doing all the work, ok, some core woods are better than others, but a glass faced Yew bow ... isn't a "Yew bow".

I've run the first limb through the bandsaw to put a slight taper on it, sawing away the lower edge and leaving the top edge straight. I clamped it up in the vice and gave it a gentle flex, it seems suitably stiff, but it's all guess work.
I tried a bend test on the triangular off-cut, clamping it in the vice... blimey, it bent a hell of a way back and showed no sign of breaking, it seemed to recover too, which is very encouraging!
(Note:- I put masking tape on the limb for sawing, to protect the faces)

Meanwhile, I took a sunny stroll over to the woods where they have been opening up a corridor alongside the brook, to let more light in and promote some young growth. There is a great variety of trees and some had been cut and roughly piled as a dead hedge. I looked in it for some curved timber to make levers/siyahs for the Elder primitive. I found a couple of bits, but I'm not sure if the lighter stuff is Willow or Ash. Willow is
rated as useless for bows, but seeing as how the siyahs just want to be light and stiff, it might be suitable. Anyhow, they will not be long levers. I found three pieces and suspect I have Ash, Willow and Blackthorn. I've reduced the wood substantially so it can be seasoned quickly on a radiator and tested to see if it is tough enough.

Sunday, 23 September 2018

Onwards and Upwards

I was a bit miffed that the monster warbow exploded, but I had my suspicions about the wood as there was a good deal of discolouration between heart and sapwood also some areas that were neither one thing nor the other. I do wish more people understood how to season wood. Get it off the ground, somewhere dry and airy and don't drape a tarpaulin over it. I'd paid reasonable cash for the Yew and spent a deal of time collecting and sawing it up... but hey ho, I get given some too.
I took down another stave from that same tree and reduced the sapwood and roughed it out. Not enough width for a warbow and with the slightly suspect timber, I'll use it for a 50# bow.

While I was rummaging through the staves, I had a look at the Elder I cut in December 2016 and roughed that out, removing the bark and sawing away the belly side. It's got the makings of a nice bow, and I may add little levers like on Monkey bow.
I didn't want to rush into too much work, so it's good to rough out a couple of bows so that when I'm in the mood I can pick them up and get onto the fun bits. It also allows me to ponder the possibilities at my leisure.
I've started doing a dry run jigging up the crossbow prod limbs ready for glue up. Preparation is the key with any glue up, so I'm taking it slow, especially as it's stonking down with rain, more conducive to armchair bowmaking.