In the Shop: Hot Torch Tips

12:27AM Feb 12, 2014
( )
Dan Anderson

If the only use for an acetylene torch in a farm shop is to cut steel or iron bars, tubing or pipe, that torch is underused. Used correctly, a torch is a precision tool with multiple uses.

It might sound odd to call a torch a "precision" tool, but that’s the best way to describe its use as a bearing cutter. The process looks unsophisticated and a bit frightening to bystan­ders, but it has the potential to quickly remove a bearing without damaging its shaft or housing.

To start, remove all flammable debris from the area and make sure a water supply or fire extinguisher is handy—just in case.

Put on tinted glasses or a face shield to allow careful monitoring of the cutting process. Heat the edge of the inner or outer bearing race until it’s cherry red. Trigger the oxygen valve to start cutting; notice that as liquified metal blows away, the cooler and therefore darker surface of the shaft or bearing housing is revealed.

With patience and a steady hand, it’s easy to melt and cut the bearing’s races without nicking the shaft or housing.

Also, if a large drill bit is unavailable, a torch is also a fast way to create large-diameter holes in metal. Mark the center of the desired hole and hold the torch tip above that mark until the metal under the cutting tip is reddish-yellow. Trip the oxygen trigger and gently work the jet of flame in a tight spiral from the initial hole to create a 1" or larger hole.

Holes larger than 1" in diameter can be made more round and smooth-edged by using a large nut, a spare bearing lock collar or other large donut-shaped object to serve as both a way to keep the torch’s heat confined and as a template to outline the hole being cut.

Cutting or melting metal is only part of an acetylene torch’s repertoire. The abil­ity to apply intense heat quickly can work magic when removing wheels, gears and pulleys that are frozen to shafts.

It's helpful to use a gear or wheel puller during the removal process. The puller applies tension to the wheel, gear or pulley while the torch’s heat expands the hub and releases its grip on the shaft.
If a wheel puller isn’t available, use a pry bar, crowbar or some other tool to pry against the hub while heat is applied.

No matter how tension is applied to the hub, set the torch’s flame "hot" to heat the hub. The goal is to heat and expand the hub while the shaft stays cool.

Hubs on tapered shafts, especially if kept under tension with a wheel puller, often release with a literal "bang" or "pop" long before the torch brings a glow to the hub’s surface. Hubs on straight shafts are often more stubborn and can require the hub to reach cherry-red color before things begin moving.

It’s well known that torches can supply sufficient heat to allow steel bars and straps to be bent in circles and strange shapes. It’s less well known that careful application of moderate heat can magically straighten subtly bent metal bars, tubes or even sheet metal without the use of physical force.

The technique is called "flame straightening," "heat straightening" or "offsetting," and it is closer to being art than science.

The theory is to apply heat to the outside (convex) curve of a bent piece of metal until it’s dull red. Expanding the metal in one small location while keeping surrounding metal cool creates stress that literally bends the metal ("offset" the metal) before your eyes—without touching it with a hammer or tool.

The tricks are not overheating the metal and knowing how far to allow the piece to bend beyond straight so that it is "true" when the metal cools.

Old-school blacksmiths were artists with acetylene torches who could flame-straighten metal to within fractions of an inch. They knew that cutting metal is just a small part of what an acetylene torch offers anyone who isn’t afraid to apply heat in the proper quantity and right location.


Cool Tool

It’s possible to use a cutting tip on an acetylene torch to remove hubs or sheaves from shafts, but a rosebud tip applies more heat to a broader area faster. Price: $50 to $150 at welding supply shops.



An experienced farm mechanic by day, Dan Anderson’s practical shop tips, tricks and fixes are tested and true. Contact Dan:

E-Mail: [email protected]