broken shaft

[Salehthefish]

Hey guyz

i need help here if anyone can help Plz. My shaft was broken and of course after i grind my shaft tip ( isaw similar thread talking about not sharpning the tip by grinder by i read that after grinding it ) anyway i bought new shaft but is there any advice for the old shaft because the tip hook was broken along with the old shaft.

The other question is about the bands. I have bought second band for my gun which is Comanche 75 cm any advice regarding the accracy? what can happen for my gun?

thanks for the answers in advance.

~~pe@ce~~

[agbiv]

Salam my friend! If you ground the tip and it changed color to a cherry red or straw yellow and did not quench (in oil) after a few seconds the tip will be softer. Use a large flat file to swipe toward the point. If still hard it'll shave just a bit. If soft it'll bite and really shave a lot. If soft then reheat wait a couple of seconds & quench. I use oil quench not water. The water cools too fast and makes the steel brittle. Won't really hurt much since it's a backup shaft and only really if you're shooting into rocky areas where a rock/wreck strike will break the tip. If it's soft it will stay sharp for about 3-4 shots on most fish.

[Salehthefish]

w/Salam Thanx for the reply. Actually the main thing is that on the tip there is a hook to keep the fish on the shaft after shooting and the tip was broken from that area so if i will file it and shoot a fish it can escape easily from the shaft

I am thinking now is to take it to latheshop where they can thread it so that i can fix one tip with thread.

[agbiv]

AHHH so clear now! It broke before the flopper! Yes get it turned & threaded. Contact any competent dive shop (like Scubaworld) and give diameter of shaft & they can give you specification on the pitch of the threads to afix a new tip!

[Jobogogin]

Hey guys, I have a question regarding shafts. Why is it bad to sharpen speargun shafts with a grinder? I didn't fully understand the reason not to.

[Salehthefish]

Hey mate

Fisrt of all i have read that thing in another thread, but it is right. In nature there are types for materials mainly brittle, ductle... brittle i think is more strong in hardness than the ductle so if u will recieve a hit on brittle material it will not bend it will break unlike the ductle which will bend.

In material science you will find a table for materials quenching if you will use a material and heat it up it will be in one point in that table and if you quench it ( Which is dip it in oil or water it will change its physical characteristics and it will be softer or harder depends.
When you oil quench material it will be softer than water quenching.
when i grind it on a grinder the tip will heat up and therefore will get softer . Thats why it was broken.

Such thing is so complicated to understand unless you study material science.

I hope this clear if you have further questions regarding this i may help.

~~pe@ce~~

[agbiv]

Exactly on the science part of the metalurgy. I learned my steps from an old blacksmith and have done some of the anvil & forge work myself. That craft uses eyesight watching color changes to determine the maleability of the metal when quenched, hence the colors I was quoting. Quenching fluid is critical too. Quench too fast & item gets brittle, too slow it's soft. For shafts brittle is bad . Snaps off easier and hit a rock or wreck it can/will shatter. The reason NOT to use a grinder is because it can easily make the very tip too hot, changing the structure of the metal. Best to use a file OR a belt sander sparingly.

[devondave]

Belt sander ? Belt sander !! Brilliant !! Why didn't I think of that ? Ah yes , I remember , it's because I'm stupid !

[agbiv]

Our meat market here has a small belt sander for putting the coarse edge on their knives followed by whetstone for fine edge & steel to maintain.

[gimewater]

I can understand the temp change in the metal but what if the metal doesn't change to the cherry red or any other color?

[agbiv]

Then it's okay...but the change can be very subtle and sneaky. IF you see blue or irridenscent color creeping up shaft after grinding you've probably changed the temper somewhat. Short grinding strokes instead of steady hard pressure (with the requisite shower of sparks) which will heat to the point of altering the temper. A dim workshop or garage is best to watch for the red/straw colors on the tip (smithies are always dark around the forge). Blue shows up in light. ALWAYS wear eye protection & gloves. Good luck. PS Stainless steel is a completely different animal and a grinder can be used for the heavier shaping and finish with sander.

[Salehthefish]

plz visit the link below its an example study for phase diagram showing the effect of temperature on the material as well as steel and cat iron content (Its a general explanation)

Iron-Iron Carbide Phase Diagram Example

~~pe@ce~~

[agbiv]

Great information. The temeratures grinding would experience goes from the 410'F to about 1000'F. Everything above that in the scale ie. 1414'F become molten and there wouldn't be a tip anymore to sharpen. Really the only way to get the spear that hot would be in the center of a smithy forge by the tuyere or with a cutting torch. Me thinks we've begun beating a dead horse.

[Salehthefish]

hahaha that's good point :P but from the diagram there i was not shwing our case exactly it is just general info and depends on wats ur alloy content but the main pint is to show that at each temperature the physical behavior of metals will vary along with temp now in our application slight change in temp will not affect while in other applications it will b with great affect.

By the way wats the story of the horse

~~pe@ce~~

[agbiv]

An old English saying (means futile effort expended) Comes from just as a jockey will urge a horse on with strikes from his crop...if the horse is dead that additional effort ain't gonna help ya win the race.