band saw welding techniques?

[tmt_92021]

What's the trick to a good weld on a band saw welder. I can't seem to weld them together. I get gaps in the middle of the weld. Please help!

[HuFlungDung]

Your welds are overheating and the metal is dropping out.

I assume that the moving jaw must hit a switch after the weld zone is hot enough to relax and allow the upset to occur, and the jaw to slide.

The technique may vary according to the particulars of the welder. What I would try is to preset the 'blade width' setting to that of a slightly smaller blade than I am actually welding. What this does is sets less distance for the moving jaw to travel before the current is cut off. So in effect, this is less heat time because I don't think the applied current is different from weld to weld.

[Bud Guitrau]

I agree with Hu with one addition... before welding, make certain that the blade ends are square to each other. To do this, put a half-twist on the blade before grinding (one side has teeth, the other is the back). Even though the ends might not be perfectly square to the length, they will match perfectly when welding.

Bud

[scappini]

anneal it after welding !!!

[ptkk]

i have a Ideal make welder BAS 25.
can someone guide about correct method of cutting the ends before welding so that
exact teeth profile is maintained after the weld.
do we have to take care of TPI achieved after the welding.
regards

[Abid Hussain]

Originally Posted by tmt_92021 What's the trick to a good weld on a band saw welder. I can't seem to weld them together. I get gaps in the middle of the weld. Please help!

Please explain what problem you are facing ? Which welder you are using?

[Abid Hussain]

Originally Posted by ptkk i have a Ideal make welder BAS 25. can someone guide about correct method of cutting the ends before welding so that exact teeth profile is maintained after the weld. do we have to take care of TPI achieved after the welding. regards

One teeth should be cut from end and other side from middle .
Do not hasitate if any enquery ?

Abid Hussain,

[handlewanker]

Hi, It sounds like the blade ends are not moving together when they get to red heat.

Make sure the welder clamp, (usually only one end) can move freely sideways when the lever is moved, as it's spring loaded.

The lever pulls the clamps apart sideways under spring pressure.

The blade ends are inserted in the clamps, teeth facing outwards, and butted together and clamped.

The lever is now relaxed and puts spring pressure against the blade ends.

When the weld current is applied the ends of the blade get red hot and being soft the spring pressure on the clamps make the ends weld into each other, like hammer welding a piece of red hot steel on an anvil.

If the blades were inserted without the clamps being pulled apart, (to apply pressure), when the weld current is applied the centre of the blades will just burn through.

You should see the blade ends move together when the weld current makes the center red hot, signifying that the weld has taken place.

Care must be taken now, as the blade after welding and being high carbon steel, will be brittle.

To temper the blade at the join and immediately after welding whilst still in the clamps, the welding power button is pressed very briefly a number of times to just apply enough heat to make the join area turn a straw colour, not to blue or the blade will be too soft and will rapidly shed teeth here.

If you're very carefull NOT TO BEND the blade after welding, you can remove it from the clamps and if the bandsaw has a grinding wheel attached carefully grind the weld area on both faces so that they are the same thickness as the rest of the blade, (very important).

Put the blade back into the clamps, weld area central, WITHOUT any side spring pressure on the clamps and tighten the clamps.

Finally MOMENTARILY press the weld button, using short presses of the button, a number of times to just heat the blade and make the weld area a straw colour, without it going to blue which will make the blade too soft and will shed teeth.

The tempering is a vital part of the job otherwise you just get blades that either snap as soon as tension is applied or just rapidly wear a gap in the weld area if too soft.

If you do get the join too soft, Eg it goes to blue colour, then it must be rehardened by carefully pressing the weld button untill the joint gets up to DULL red heat, then quickly grip the blade between the jaws of a pair of pliers, to act like a heat sink, and this will chill the weld area and so harden it,(carbon steel), then go through the tempering process again, you may need to polish the weld area to see the tempering colours.

I've welded blades using as much as a half dozen pieces of offcut blades when pressed for a blade, just got to be carefull with aligning the teeth as you lose a tooth or two when the weld happens.

At home I normally braze the joint by scarphing the blade ends for about 4mm and either silver solder or bronze braze them, using a special jig to make it happen, again hardening and tempering as required.

You can use a piece of brass shim and brazing flux mixed with water for the braze material, and heat the joint with a Propane gas torch.

With this method, after brazing, the joint is immediately gripped with a pair of pliers to ensure a good joint and to chill it prior to tempering

The tempering will not affect the brazed joint.
Ian.