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Techtchr
04-30-2004, 07:35 AM
I hate to admit it, but I need a lesson in putting band saw blades together. I don't have a blade welder at school or home. I would like to be able to repair some good broken blades and make new from bulk stock. My attempts have met with very poor results.
I am very capable at silver soldering and brazing, but my welding stinks.

So far what I have tried is:I milled a slot in a piece of flat stock to allign the blade straight while clamping it together. Milled a relief groove where the blade gets heated. I've tried grinding the ends of the blade to make a V joint, and i've tried grinding to form a lap joint. I've brazed them and I've silver soldered (real silver solder not low temp stuff ) them. I've tried the mig welder too, but that was a disaster. After putting them together I ground the sides down and made sure any teeth filled with material were fixed.

So what the heck am I doing wrong besides being too cheap to buy a blade welder?

Thanks in advance.
Matt

Peter S
04-30-2004, 07:45 AM
Matt,
The one step you haven't mentioned in any of your methods is annealing. You might already know about this, but even the best weld done on a bandsaw welder will be brittle if it isn't annealed. This is because the steel at the point of the weld air hardens.
DoALL recomend heating the weld up to a dull cherry red colour, then let it cool. If you heat beyond dull cherry red, the weld will reharden.
They also recomend cutting off the old, brittle weld portion before rewelding blades.
I can't comment on the various methods you have mentioned, I have the luxury of an in-built blade welder http://bbs.homeshopmachinist.net//smile.gif

JCHannum
04-30-2004, 07:51 AM
When silver soldering bandsaw blades, the joint should be a lap joint, not a butt joint.
The usual method involves squaring the ends on a grinder, then twisting one end of the blade and holding the ends together side by side. This puts the inside and outside together. Grind a bevel on the ends 1/2" or longer, depending on blade width and thickness, tapering to nothing.
Clamp the fluxed blade in your fixture with a piece of silver solder in the joint and heat to braze it.
Clean and grind the joint and you will be in business.

Techtchr
04-30-2004, 08:41 AM
Pete,
I didn't think I needed to anneal after silver soldering as the metal gets heated that hot anyway. I will let cool and reheat to the proper color.

JC,
When you twist the blades and hold them together to grind , are you telling me that the 1/2" bevel ends up on each end of the blade,so I need to grind 1" or are you grinding them together for a 1/2 " and the lap is only 1/4" when you put them together? At home and school I have one of those import saws that takes the 64 1/2" blades.

Thanks again, Matt

suprdvn
04-30-2004, 09:07 AM
I am no expert but I would think that silver solder could never hold. It has little or no flexability. Also after it is ground thin enough to go through the guides the surface area it is bonded to is very small, just the butt end of the blade.

Super Dave

ulav8r
04-30-2004, 09:08 AM
By twisting the blade and grinding both ends at once, the bevels are equal length and angle. The ends are parallel to each other and are flush to each other. the teeth will be pointing is opposite directions so one bevel is on the outside, the other on the inside of the band.

Evan
04-30-2004, 09:31 AM
I braze with regular brass brazing rod after grinding in the manner that JCH describes. The amount of lap isn't critical nor is the angle of the lap. In fact, too much lap creates a fairly inflexible area to go over the wheels. It also is essential to grind the area to the same thickness or ever so slightly less that the thickness of the blade.

JCHannum
04-30-2004, 11:03 AM
I suggest 1/2" of bevel on each blade, which will result in a 1/2" long joint. A little more or less won't hurt, but I prefer the joint to be at least the same width as the blade.
Silver solder joints are plenty strong and flexible, and have been the method of choice for years for those not lucky enough to own a blade welder. Properly done, they will not fail.

darryl
04-30-2004, 05:06 PM
Silver soldering works for me to repair blades. You do need to align the ends, and angle the ends so the solder line isn't straight across, and also to feather and overlap the ends. When overlapping, position the ends so the thickness of the join is just under the blade thickness. In theory, the ends shouldn't actually be touching when everything is aligned and clamped. At this point, flux the gap, and insert a small piece of sheet solder. The blade ends will spring apart enough to hold it there while you heat. I don't have sheet solder, but what I do is hammer a piece of wire into a flat, and clean it before inserting it. I find also that it helps to first heat the blade ends, then clean them, before clamping and going through the joining procedure. If you don't pre heat and clean, it's harder for the flux to do it's job, often enough resulting in a poor solder flow.

[This message has been edited by darryl (edited 04-30-2004).]

jaybird
04-30-2004, 08:56 PM
for what it's worth, here something that may be of interest,

http://www.advancecarmover.thomasregister.com/olc/01163005/welder.htm

J

Smokedaddy
04-30-2004, 09:25 PM
Matt,

Check this puppy out ... even has a few pictures. BTW, you'll have to go nearly to the bottom of the webpage to see the article.

http://www.homemetalshopclub.org/news/dec03/dec03.html

-SD:

[This message has been edited by Smokedaddy (edited 04-30-2004).]

Techtchr
05-01-2004, 06:53 PM
Thanks!
The little welder looks interesting and the link to the metal working group was helpful.

I think my biggest problem was not using enough taper when I did the lap joint.

Matt

Paul Alciatore
05-01-2004, 08:08 PM
Smoke,

Thanks for the link. Although I'm working in Iowa now, I plan to retire to Beaumont TX (a bit down the road from Houston) and I will definitely look up that club then.

I noticed a picture of a hand powered grinder. My grandfather had one of those mounted on the center post of his garage. Used it for sharpeneing tools, of course. I remember cranking it up. I considered it fun at the time. But no safety glasses back then.

I also have had bad luck repairing band saw blades. I'm not much on welding but I hope to learn. I have several broken blades that I can practice on.

Paul A.



<font face="Verdana, Arial" size="2">Originally posted by Smokedaddy:
Matt,

Check this puppy out ... even has a few pictures. BTW, you'll have to go nearly to the bottom of the webpage to see the article.

http://www.homemetalshopclub.org/news/dec03/dec03.html

-SD:

[This message has been edited by Smokedaddy (edited 04-30-2004).]</font>

Techtchr
05-04-2004, 06:59 PM
Made a new fixture to hold blades today. Tried it on a broken blade. Did the Lap joint as suggested. Silver soldered it together. So far so good! Seems to be holding.
Thanks to All.
Matt