Monday, 12 March 2018

Yet More Cross Prod Work


The Ipe from my mate Matt at Cambridge Longbows has come in very handy, as well as using it on flight arrows there was enough to make a pair of belly laminations for one of my crossbow prods. I have 2 prods on the go, the slowest one being used for experimentation. That one had a bamboo belly which I've taken off using my new draw knife and carefully taken down to the Yew core.

The Ipe was sawn on the bandsaw with some care to try and get nice clean parallel strips. It's not as simple as one might think, some careful set up and a suitable blade helps enormously. Contrary to what one might think, I've found a narrow blade seems to allow the wood to follow the guide best.
I'm using a 1/4" x 0.025" 4 tpi AS Hakansson Silko blade. (From Justbandsawblades)
That's a general purpose carbon steel blade, 4 teeth per inch Alternate Set. The alternate set cuts a slightly wider cut and helps avoid friction. Being a 1/4" blade it also allows you to follow quite tight curves, the down side is that it's not as rugged as a wider blade and you wouldn't rip down logs with it.

I still have the former from the last glue up of the prod, but the Ipe is too stiff to bend easily to shape without some heat bending first to get it about right. Once the Ipe was hot (using a hot air gun) I clamped it to the former to get the bend. As I heated the Ipe, it changed colour, going darker and tiny specs of oil came out of the wood. I have heard people suggesting that some oily woods be de-greased before glue up, but others suggest a fresh sanded surface is fine. I went for the fresh sanded surface. The Yew was lightly scored and all traces of the old glue removed. Glue up was with my usual Cascamite (Resintite) and plenty of clamps. (Picture shows starting to clamp it up starting near the centre to ensure it is nicely butted up against the centre riser block)

I've had the prod up on the tiller clamped up between two thick aluminium mounting plates, as it will be when mounted on the stock, to ensure it doesn't break at the shoot through cut out.
I've pulled it to about a 13" draw (measuring from the Aluminium mounting plate nearest the archer) and it's pulled about 125-130# I'm not sure if I dare pull it much further.
One consideration is that although the latch is at 14 1/4" one has to pull it beyond that to actually cock it and engage the latch, also because it is being pulled with two hands on the string that effectively shortens the string slightly pulling it even further.
I can always take 1/2" off the end of the stock to reduce the draw, I don't know yet, I'll proceed slowly.

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