Barrel replacement services update!

[ithacaartist]

The interference fit is great--it will never be shot loose, and there's no mess to clean up.

I had occasion to take such a joint apart some years ago. I was working in a local fabricating shop and, to the owner's specs, had made a short set of special dies for the press brake. The whole assembly was too short, it turned out, and the screws that moved the upper frame up and down to adjust it were extended so far that the force of the stroke offset the few threads that were turned into the socket by about .003". The threads would bind when running the screw upward due to this offset portion.

The socket component was held by a large resistance fit pin to an offset hole in a large wheel. We heated the dickens out of the material surrounding the pin and applied the output of a CO2 fire extinguisher to the exposed end of the pin--and off she came. The offset threads were trimmed by the machinist, and the parts were heated and cooled similarly for re-assembly. The moral of the story is that such a joint can, indeed, be manipulated, rotated, or undone.

Another way to get a hefty bond is to create a slick slip fit. Then apply three evenly spaced rows of center punch dimples to "strawberry" the O.D. of the inside piece for a tap fit into the corresponding hole. When the inserted piece bottoms out, rotating it slightly positions it so that the strawberry marks resist being drawn back through fresh material. But at this point, I think I like the heat/cool joint, for this job.

[sheepherder]

Originally Posted by ithacaartist

The interference fit is great--it will never be shot loose, and there's no mess to clean up.
<snip!>

Cool story!

I have one too...

Back when I was a millwright, one of my recurring jobs was rebuilding pulverizer gear reducers for the boiler in our paper mill. Coal dust got in everything (especially lungs ) and gummed the reducers up to the point they would break 3" shafts. To replace the bearings we'd heat up the cast iron gearbox, refridgerate the race overnight, and press the outer race (about 6" dia) in with a six foot hydraulic press. The outer race was an interference fit. You only had one chance to get it right. If you got it wrong, the race had to be torched in half and do it all over again.

To get the cast iron gearbox to expand the exact amount needed to drop the race in, we'd use two oxy-acetylene torches with rosebud tips. The millwright heading the job [me] would run a Tempilstik [pic below] over the area. The stik was like a candle but only melted at a specific temperature. 262º F in this case. When it melted & ran when you touched it to the gearbox, you [me again] dropped the race over the gearbox shaft opening, slammed a long steel sleeve over it, tilted it under the hydraulic ram, and started pumping like Hell!!!

I did at least a dozen rebuilds...I don't recall ever having a hangup...But there was evidence in at least one of the four reducers we had that it had happened (torch cut in the cast iron body)...

It was a four man job...And once the ram slammed down we all took turns pumping...Welders, millwrights, machinists - anyone walking by!!!

It was a stressful job...Lots of time spent by the machinist making the shafts...Expensive bearings...6" in dia, 3" wide races...

A reducer lasted about three months...We always had one standing by for when one of the two in use failed...The dust got in the oil ways and made a hard paste that had to be drilled out...

IIRC, the interference fit was ~1 1/2 thousandths [.0015"]...You couldn't let the reducer body get any hotter or it would take the hardness out of the bearing race...We had to have air hoses ready to start cooling the reducer down as soon as the press reached 20 tons...

They had all been painted gray originally...I had our painter paint them different pastel colors to tell the four apart...Baby blue, pink, light green, and gray...My way of rebelling against conformity...