Cast iron bed crack - options

[DonInReno]

I picked up a  damaged Juki lu-562 as a project...keep in mind this is a project machine and not a mission critical money maker.

It seems to have been squished under something heavy and the underside of the bed has a crack running the entire width of the bed, but not completely through to the top.  The nose of the bed is bent upward about 1/8", which not surprisingly, has the shafts half bound up.  On the plus side the shafts do not appear to be bent since rotating them by hand produces even resistance.

Its easy to argue the most proper fix is replacing the bed and or entire head from a donor machine.  Are beds and upper portions matched and/or machined as a unit?  Im sure there are some damaged upper heads with intact beds that would be free or nearly so.  Even if they are mated early in the manufacturing process it doesn't seem outrageously complicated to machine off a little to shrink the neck, or cut a shim to raise it.

Along the same lines are all 562's the same?  How about 563's - do they share most parts with the 562 other than the larger hook, or have a number of other bits been upgraded?  

The crack doesn't cross any bearing bosses or other spots that might omit welding or brazing as options.  Proper welding techniques on cast iron are well documented by all the big venders - a lot of preheat, nickel rods, long drawn out post heat slowly bringing the temperature down over many hours.  I've never heard if arc or TIG produces better odds of success?

Brazing options seem to be either lower strength silicone bronze (doable with a dc TIG, which I have), or much stronger aluminum bronze (requires AC TIG similar to what's required for aluminum welding).  I'm not a huge fan of brazing since it has to be built up more than the original iron and will always look like a repair every time the head is tilted back for oiling or cleaning.

 

[Gunnarsson]

1 hour ago, DonInReno said:

Proper welding techniques on cast iron are well documented by all the big venders - a lot of preheat, nickel rods, long drawn out post heat slowly bringing the temperature down over many hours.  I've never heard if arc or TIG produces better odds of success?

Brazing options seem to be either lower strength silicone bronze (doable with a dc TIG, which I have), or much stronger aluminum bronze (requires AC TIG similar to what's required for aluminum welding).  I'm not a huge fan of brazing since it has to be built up more than the original iron and will always look like a repair every time the head is tilted back for oiling or cleaning.

A proper brazed repair should normally have a higher breaking strength than cast iron, so it can be superior in strength to both the original item and a welded repair. And if you use the proper method and grind a groove where the crack was and braze it up nothing prevents you from grinding any protruding material and painting it to make the repair more or less obvious. (All repairs require stop drilling the cracks and grinding a groove, really - both welding and brazing.)

You did not mention the brazing method using an oxygen/acetylene torch, with the proper brazing bronze. Unlike TIG, you can use the torch to preheat the area before brazing. 
Actually, it could be O/A welded too - in some cases it's still the best method. It does not use a nickel filler like when arc welding cast iron, rather you use actual cast iron rods for filler (such as Kastweld 111). The upside is that after the repair you still have a 100% cast iron item, that can be drilled, tapped and machined as before if the proper slow cooldown was used. The downside? The part needs to be stripped down completely. Complicated shape items such as cast iron cylinderheads are welded using this method, but those complicated shaped require ALOT of preheat - we're talking the entire head being bright red. After that the machined surfaces need to be re-machined, but your crack looks like it's in a "better" area requiring way less preheat.

I'd go for brazing, partly because it's the lower temperature option. But the warp in the bed worries me a bit, the repair would probably pull it a bit straighter again but exactly how much is hard to know. And if you try to force it back, even after stop drilling and grooving the crack out, it might be enough to break the bed completely off. On the other hand, then you could bolt the halves together and stop worrying about welding or brazing.

[DonInReno]

I wonder if it's more prudent to cut through the bed completely or just grind until the crack stops and leave the top surface intact?  Hmm...

[Uwe]

You could probably simply ignore the crack, too. If the machine sews fine, just put it in a proper, very strong table top and use it. That tiny crack at the 10" mark on your ruler should not affect functionality. Any hot welding fix attempts may just make matters worse. Properly supporting the machine may be all you need to do. Most tables only support the machine at the corners, but you can machine an edge that supports the machine along the "lip" instead of just the corners.

The most likely cause of that crack is a bowing table top that only supported the machine at the very left and right edge. Many cheap industrial table tops are simply too weak to support the sewing machine without bowing in the middle. That big hole in the middle weakens the table top considerably. Especially particle board table tops are only straight for short while after you cut a big hole in them and drop 70 lbs of weight on them repeatedly.  

If the machine is supported only at the ends and you let it drop down often enough, a metal fatigue crack will develop in the unsupported middle on the underside. Fixing the crack without fixing the table top will only buy you a little time.

Putting the machine in a proper, very sturdy table top, may keep the crack from getting worse and if the machine sews fine as it is, there may be no need to "fix" the crack. 

I had a machine with a similar crack in the bottom ridge that worked just fine. I built a new, straight, and sturdy  table top for it (two layers of 3/4" plywood glued and screwed together). It's been performing well in a production environment going on two years now.

 

Edited January 24, 2018 by Uwe

[CowboyBob]

I've welded a lot of beds over the years & on this one it would be best to v-grind it for more contact & either braze or heat & I've used nickle rod,brazing is the best,with a torch.

[brmax]

I am a bit curious and would really like to see a few more photos of that area and particularly the bottom generally.  My thoughts honestly are that crack if pulled together, would not result in a flat surface on top. I would discuss more and figure a way to relieve the stress it has, if any more! 

Good day

Floyd

[480volt]

Is this worth repairing? LU 562s and similar are not difficult to find. You could go to the trouble to weld/braze it and the shafts could still bind.

[GPaudler]

I've had good luck using silicon bronze and TIG brazing cast iron but you might consider drilling, tapping and epoxying a steel doubler on the underside, if there's room. It would save disassembly and repainting after burning-off the paint.

[Gregg From Keystone Sewing]

22 hours ago, CowboyBob said:

I've welded a lot of beds over the years & on this one it would be best to v-grind it for more contact & either braze or heat & I've used nickle rod,brazing is the best,with a torch.

This is old school, and how we do it, too!  Lot's of them.  Many of them in this location in the bed as well.  Clear sign of a drop.  The machine will never break on it's own unless it's a stretch and the weld gives out.  Maybe some did break the frame under normal use, but I don't know.  No two machines are the same.  

Edited January 24, 2018 by Gregg From Keystone Sewing

[DonInReno]

I feel much better since you guys have some track records fixing this kind of crack! I did pick up a $10 thrift store  machine to break and practice on. Lol

In a kitchen remodel we removed enough maple butcher block for my three machines - a nice stiff table seems to add something intangible.  Having said that, I'm always amazed at how durable high pressure laminate (like Formica) is on even a sagging table.