Silver Soldering Bandasw Blades

[wannabe]

Silver Soldering Bandsaw Blades

I broke my bi-metal bandsaw blade yesterday. The blade is still sharp and at $50+ I thought it would be worth having a go at fixing it.
I’ve read a couple of threads here http://www.woodworkforums.ubeaut.com.au/showthread.php?t=21148&highlight=Joining+Bandsaw+blades (http://www.woodworkforums.ubeaut.com.au/showthread.php?t=21148&highlight=Joining+Bandsaw+blades) and here http://www.woodworkforums.ubeaut.com.au/showthread.php?t=48642 (http://www.woodworkforums.ubeaut.com.au/showthread.php?t=48642) plus numerous other ones that it is possible and easy. Yeah right. Easy for them. I've had no success.

What I’ve done is :-
Ground the blades with about a 30 degree scarf joint.
Made up a jig out of aluminium to hold the blades in alignment.
Cleaned up everything using metho.
Fluxed everything up.
Applied heat from below using a pencil flame from a propane torch.
The result is that the joint is very weak and breaks as soon as you flex it..

Tried doing it three times with varying degrees of success but the end result is always the same. A weak joint.

Are there different types of silver solder? I got this silver soldering kit from Bunnings with a roll of silver solder and flux. It states it’s for plumbing and refrigeration and also stainless steel. The solder has a melting point of 495 degrees F.

[watson]

Silver Soldering Bandsaw Blades

I broke my bi-metal bandsaw blade yesterday. The blade is still sharp and at $50+ I thought it would be worth having a go at fixing it.
I’ve read a couple of threads here http://www.woodworkforums.ubeaut.com.au/showthread.php?t=21148&highlight=Joining+Bandsaw+blades (http://www.woodworkforums.ubeaut.com.au/showthread.php?t=21148&highlight=Joining+Bandsaw+blades) and here http://www.woodworkforums.ubeaut.com.au/showthread.php?t=48642 (http://www.woodworkforums.ubeaut.com.au/showthread.php?t=48642) plus numerous other ones that it is possible and easy. Yeah right. Easy for them. I've had no success.

What I’ve done is :-
Ground the blades with about a 30 degree scarf joint.
Made up a jig out of aluminium to hold the blades in alignment.
Cleaned up everything using metho.
Fluxed everything up.
Applied heat from below using a pencil flame from a propane torch.
The result is that the joint is very weak and breaks as soon as you flex it..

Tried doing it three times with varying degrees of success but the end result is always the same. A weak joint.

Are there different types of silver solder? I got this silver soldering kit from Bunnings with a roll of silver solder and flux. It states it’s for plumbing and refrigeration and also stainless steel. The solder has a melting point of 495 degrees F.

There are many, many types of silver solder..and I've probably had a go at them all using basically the same method........with one exception.
One the joint is done, still in the jig, I reheat the joint to just under the solder melting temp of the silver solder, and then let it cool slowly. So far no probs.
But I do use high silver content solder.
If nobody answers with more technical info, I'll find my files on the subject in the morning (they're up the shed) and send them to you.

[Metal Head]

Hi Wannabe,

I haven't read the additional threads you highlighted. I have seen them brazed and TIG welded together with success. I know when they are resistance welded they have to be annealed (tempered) to reduce the hardness that is induced by that type of welding process. I wouldn't have thought at the temperture you mentioned that would be a problem:(.

Regards
MH

[Grahame Collins]

Hi,
There has been been quite a few posts,including my own, on silver soldering of bandsaw blades. The new search facility should find them easily.

A suitable grade to use is 245 blue tip which must be used with flux. I would say your failures might be because you have over heated the silver solder. When successfully completed the silver solder will be smooth and shiny.

If it is grainy/sandy looking it has the zinc boiled out of it during the brazing process, therefore any strength is gone. Don't use too much, a 3mm long length is more than adequate for a 12mm wide x .75mm blade.

Will it last ? The ones I did for school have lasted up to 9 months being used daily, many times.Most were damaged by cutting too small a radius or by cutting nails.

Bandsaw blades aren't that hard because I cut them with a pair of snips to achieve the scarf angle.30 degrees is about right but not square cut as you minimise the length of bond and maximise the strain as the joint passes over the wheel.

An important point is to peen down the twisted edge that the snips cause.Don't be concerned about flattening the set as those 2 or 3 flat teeth won't matter.

Try not to bruise the metal,ie make it thinner than it already is. The mating surfaces must be flat and level with each other. A jig of some sort is necessary.See my posts for a picture. A commercial jig is available through Mc Jings.

Grahame

[wannabe]

Hi,
I found two posts on here relating to repairing the blades unfortunately the pictures have disappeared except for one and it’s that small I can’t see it properly.
I made an alignment jig up out of 30mm x 10mm aluminium and milled a 10mm wide x 0.4mm deep step in it to act as an alignment face for the back edge of the blade. This allows the teeth to hang over the edge and not interfere with the alignment. A couple of aluminium clamps hold the blade in this position. A 19mm wide groove is taken out of the centre which allows access to the underneath side of the blade.
I scarfed the blade by lining it up, clamping it together then ground it on the bench grinder. This ensures the joint is as true as I can get it.

I may be over heating the solder. One thing I just realised is that the blade is thin so it shouldn’t take a lot of heat to get it to temperature.
The flux I’ve got is a paste. A couple of seconds after I apply heat to the bottom of the blade the flux turns liquid and clear then bubbles. It then goes a gluggy black before the solder will melt. This I don’t think is a good thing. It seems to be overcooking the flux before the melting temp is reached.

With my first attempt I flattened it out to wafer thin and wedged it between the join on assembly in the jig. The results looked good but as soon as I took it out of the jig it flexed and broke. With the remaining attempts I just tried feeding the solder on by hand. Visually the results didn’t look as good and the strength was the same or worse. One looked ok but as soon as I started to grind off the excess it parted.

I have concerns this solder kit I got is not suitable for what I’m trying to do and as Watson said there are many types. It says it’s a Lead Free Plumbers Kit suitable for plumbing, refrigeration and stainless steel. The brand is Kester. Don’t know what type of silver solder it is and the flux is Kester SP-50. I’ll have another go tomorrow and if that doesn’t work I’ll go looking for some of the 245 blue tip solder and a flux.

[Grahame Collins]

I have no doubt about it. The silver solder you are using is the wrong type.It is a low temperature silver solder.

The key is to use the General purpose flux No 1 and grade 245 .
Place the 3 to 4mm long chip of s/solder in the middle of the fluxed joint. Be careful with flux placement making sure it is only where you want the S/solder to flow.
Heat from below the blade. A shiny clean finish off the file or grinder is all thats needed.

I should also mention that snips probably won't cut the bi metal blade -I didn't read the post throughly,did I?

The heat zone is the size of say an old 1 cent coin and takes a second or two to melt the s/s and allow it to capillary through.As soon as fusion occurs remove the flame as the excess heat will flash off the zinc in the s/s alloy.You will know from the white dusty deposit it will leave behind.

Allow a few thou gap between the blade fit up for the s/s to flow through.

I am not sure how this will go with propane as I have used Oxy acetylene to do my blades. Using a tip that concentrates the flame to achieve pin point heating is what is needed. Some of the tips used by ,say plumbers to s/solder pipes may spread the heat too broadly.

I hope it goes well for you.

Grahame

[wannabe]

Thanks. I had a feeling it was the tools and not the operator. It couldn't be the operator :rolleyes:

Yeah it's a bi metal blade. At $14 for a normal blade I don't think it would be worth the effort but at $50 it's worth a try.

I have to head over the other side of town on Friday so I'll see if I can track down some of the 245 solder and flux then. I'll give it a try with the propane torch and see how I go. Nothing to lose.
I've been eyeing off one of those MAPP torches for a while now. If the propane doesn't work it might be a good excuse to get one. I just have an aversion to things that use disposable cylinders. They get expensive after a while. It's like using the disposable cylinders on the MIG. Suppose it's still cheaper than hiring the bottles for the amount of work I give them.

[wannabe]

Does anyone from Canberra know where I could get the 245 solder and flux from. Gasweld and BOC are two that come to mind. Anywhere else?

[bobsreturn2003]

mate plumbers solder is around 2-5 o/o silver and is brittle . blue tip should be ok and lpg should melt it . when you have the blade and solder joined ,usually you squeeze it together ,this chills it and keeps the join close ,then clean it up and reheat up to blue and let cool , this aneals it and leaves it flexable . then file to size . dont leave back of blade with a step , good luck .bob

[Grahame Collins]

While I freely admit I have not silver brazed a bi metal blade, I would still be extremely careful heating the blade after the operation.

However I probably have brazed up to a hundred or so of the carbon steel blades while a Man Arts teacher.Kids are tough on bandsaw blades.

The critical points I found were:


Alignment which you have covered with a jig.Feel the mating edge together between thumb and index finger.

Correct preparation which seems identical to what I was using ie 30 degree scarf and 30 degree contact bevel on each blade.

Adequate cleaning( shiny bright ) and and GP No 1 flux
Warning -where ever you put the flux the alloy will flow to.

Using just the right volume of alloy 3 to 4mm length of 1.6 diam 245.

Leaving a hairs breadth gap for complete fusion from the top surface to the bottom.

Using the correct length of heat.As soon as fusion occurs withdraw the flame.Just a fraction too much and your nice brazing work will be undone.
.

Thinking about it, would it not be better to anneal the blade ends first before joining them? Once you stuff it up its very difficult to rejoin to the standard required without a full removal of the brazing alloy.

Grahame

[wannabe]

Ended up at BOC today and got some 245 silver solder and a No:2 flux. I know Grahame said No:1 flux but they didn’t have any and the guy said No:2 would be ok. For 5 rods and flux cost $64. Not cheap. Could have bought a new bi metal blade for less but I can always use the other rods for something else. It’s all about learning anyway.

Still had some troubles but we have success. Whether it will last is yet to be seen.

I ended up having about 5 goes at. Each time the soldering went well. I would mount it, turn on the saw and bang. It broke. After a few times (I’m not slow :D) doing this I figured out that I wasn’t flattening out the excess enough so all went well until it got to the guide wheel, it tightened up, put excess strain on it and it broke.
The saga goes on but with a bit more attention to detail I finally got there. Trouble is now I’ve ground that much off the length I had to take the washer off the adjustment bolt so I could just get the blade on.

Grahame:
I’ve been grinding the blade with a 30 degree angle as viewed along the narrow edge of the blade. Are you saying it should also be 30 degrees as viewed along the wide side of the blade also. If that makes sense.

Bob:
Only read your post tonight. Will try the grabbing it with pliers next time. Think it will have to wait until I break another blade though. I've run out of length on this one.

[watson]

Just a question.
If the blade joint needs annealing, does this not occur at a lower temp than the soldering??
This leads me to think that the annealing should occur after the soldering???

Another thing to ponder

[Grahame Collins]

[ all went well until it got to the guide wheel, it tightened up, put excess strain on it and it broke.

If it won't fit through the guides , the blade edges are EITHER not aligned with one another or there is too much build up of solder on the joint faces.Lightly gripping the blade between thumb and finger and drawing it through will tell you instantly if there is a variance in height /thickness.

To ensure this I found that they needed a bit of a file so there is no excess .Also if there are a few teeth flattened on either side of the joint it obviously allows the file to file flat. To my way of thinking, taking that temp up to a dull red and flattening those teeth serves the purpose of annealing as well.

To test the annealing has occurred , file a piece of un annealed stock ,the file should slide off .On the truly annealed bit it should bite. Re Watson's question about annealing.The temps need to be substantially higher than soldering temps to anneal. Some commercial band saws have blade elders attached .They are a flash butt weld fitted with a grinder and an annealer.To use the annealer ,the blade is gripped and induction heated to a red temperature around and either side of the weld.

We found at Tafe that the bi metal blades benefit from a double anneal as many of the single anneal ones were more liable to break.If done with a flame this should not be a worry however.

Any way you now have plenty of practice material.

I would try a few more joints and dress them and check they will pass between the guides.

Re the 30 degree preps I have included a diagram in MS Paint. The long scarf joint on the broad face allows the blade joint a less pronounced flex as it passes over the wheels. Normally when a blade breaks with out any force applied ,it is usually for this reason. If a joint is parallel to the wheel axis the stress forces are concentrated on that line each time it passes over the wheel. A scarf also gives a longer joint length and a stronger bond.

Grahame

[watson]

To test the annealing has occurred , file a piece of un annealed stock ,the file should slide off .On the truly annealed bit it should bite. Re Watson's question about annealing.The temps need to be substantially higher than soldering temps to anneal. Some commercial band saws have blade elders attached .They are a flash butt weld fitted with a grinder and an annealer.To use the annealer ,the blade is gripped and induction heated to a red temperature around and either side of the weld.

Grahame

Thanks Grahame..that's cleared that up for me.

[wannabe]

When I was re-read everything I thougth you were saying you bevelled the blade both ways! I only bevelled mine across the edge. Wouldn't have had enough length to do it the other way anyway but I can see that it would be far larger area to spread the load. Rather than buy a pre made bi metal blade next time I might just see if I can get some stock and make my own up. Will try the two bevels then.

Not paying enough attention to detail was my fault for not levelling out the excess properly . I used a Dremel and ground it down. It felt ok but I had the guides up too tight plus a little bit of variation in thickness = break. Filing the blade to get things level in the area is a good idea.

I think my blade got heated up that many times that it's definetly annealed. :D

I started on Simso's Pan Brake Folder today so the saw got a good workout and the blade is still intact. Looking good.

Thanks for all the help guys.