He removed a tool changer/toolpost turret from a very large CNC lathe,
took it to a shop to repair a cracked casting properly and then
reassembled it. 9" spindle bore, probably threading oil well drill
string pipe fittings or something. Probably 100HP spindle. Big MF.
jon_banquer fired this volley in news:665d3f6e-
Jon,it was abundantly clear if you read the notes on the Picasa page:
"So they had me pull the turret and take it to one of the best machine
repair guys I know, Jim at Quality Machining, Chino California...to
reweld the assembly. "
If the weld is done properly the repair will be as strong or stronger
than the original material. The trick is knowing what the material
actually is and which weld procedure to use.
In this case it sounds like it was cast iron, and that the repair was to
grind it out and weld it plus add pins across the weld to withstand the
Cast is fun stuff, especially in areas where it lives in lubricants or oils.
I pulled down the lathe, removed the turret, took it to another shop,
stripped it empty, then a guy put it up on one of his big horizontal
mills, drilled and tapped the side of the casting (base) and put in
stripper bolts, which drew the busted pieces together, then welded it
all up with bronze. Then he put it back on the horizontal mill,
remilled and put everything back to factory specs visa vis flatness
I then reassembled everything, adjusted clearences by experience (no
manual available) and reinstalled it on the lathe. I then aligned the
turret to within .001 of alignment with lathe axis and then rewired
and made operational.
I had about 20 hrs in it. Jim had about 10 hrs in it. Plus taking it
on a 70 mile round trip on my trailer.
The original morons had put in (2) .5" dowel pins..but had only set
less than .375 in the far side of the crack..and had never pulled the
crack back together and when they welded it..they never got the body
of the casting hot..so they managed to simply put bronze on the small
side and it had NO bond with the body of the turret. When we ground
out the original braze..a big "chunk" of bronze popped out..the crack
never was bonded..it was just "puttied" and that chunk of bronze was
supposed to be bonded to the turret body. It wasnt. That chunk of
bronze was oily..and you can see in the photo..the crack was pretty
In fact..its visible in the photo with the crack, to the right side
laying loose on the body of the turret.
Now we expect it to be as strong as the original cast iron as a unit.
If not stronger.
The original guys had put on a plate of steel..just to keep the dowel
pins from falling out. Pissed us both off when we pulled that plate
off and the dowels were not even bonded with the bronze...yet they had
been welded in. Piss poor welding...zero skills with cast iron or
machinery. Unfortunately..it had been done 10 yrs ago..so we couldnt
go back after them. The machine came from another shop recently..my
clients bought their entire machine shop, and we moved it to their
building and we set it up for operation. They do plastic and steel
pipe threading and slotting etc etc for the oil and environmental
industry, along with chemicals etc etc
It is an ART to repair a casting that won't crack again! A big part of
that is in the pre-heat and cool-down phases of the weld. I've had
mostly good luck but a bit of bad luck. A lot depends on the metal and
the phase of Venus.
Indeed it is an art. When the welding equipment companies, or other
researchers, do a metallographic analysis of cast iron welds, the
results will leave you wondering how it ever works at all. The weld
and heat-affected zone typically is like a layer cake of weirdness.
Anyone who can get good results *consistently* is worth his pay.
BTW, the guy who allegedly was the highest-paid c.i. welder in the
world, an Italian who did nothing else, was hired and shipped in many
years ago by Bill Harrah to weld a crack in the block of his priceless
Bugatti Royale. He did it with O/A and c.i. rod. It worked, even
though it doubtless had oil in the (then) 60-year-old cast iron.
I don't know how he did the pre-heat or stress relief.
Yeah the haz in a cast weld gets interesting. Areas of carbon migration,
grain structure changes and lot's more.
Gas works real good for thin wall iron. You have to watch your flame
real close and only fill enough to ensure a good bond. Then watch it
real close for contraction while it cools. Add enough filler and you get
a good bond and repair, go under and it will crack again due to the
tension stress at the site. If you go over it will probably crack in a
different area due to the stress the extra material adds as it act's
like a wedge.
That sounds like things I've read, but I've never attempted it. I have
enough to keep me busy with mild steel.
It must require a combination of experience, knowledge, and a
highly-developed feel for the materials and the work. And I'll bet
that several senses are working at the same time -- touch, vision,
hearing, and even smell.
As they say, it's quite an art.