Cutting Tool Engineering
June 2012 / Volume 64 / Issue 6

Tips for turning parts on manual lathes

By Tom Lipton

As a follow-up to my April column, here are additional tips for enhancing the operation of a manual lathe.

  • Be aware of the reduction in clamping force when spinning a chuck at high speed. You can lose 50 percent of the clamping force when running at a high rpm.
  • Orient rough-cut blanks from oxy-fuel, waterjet and plasma cutting with the large end of the taper in the cut to the back of the chuck. All of these processes produce varying amounts of taper, depending on the material thickness.
  • When roughing, try to get completely under the bark, or outer skin, of a bar on the first pass. This extends tool life.
  • Most lathes have 0.001"-dia. divisions on the cross-slide dial. A decent operator can control diameters to 0.0003" by interpolating between the divisions—if the lathe is in good shape. With that said, a lathe should repeat to half the smallest division on the cross-slide dial.
  • Ch05.Fig015.Lipton.DSC_3838.tif

    Multipurpose tool bits, such as this one that turns ODs, chamfers IDs and ODs and faces part surfaces, can save time when manually changing tools. All images courtesy T. Lipton.

  • Set the compound rest at a small angle to dial increments smaller than the cross-feed dial dimensions. A 5.73° angle off the Z-axis will take off 0.0002" on the diameter on the X-axis for each 0.001" dialed on the compound.
  • Try to grind special lathe tools so the tool post can stay square to the machine axes. This reduces setup time, but is not always possible.
  • Grind a couple of multipurpose tool bits. This can save time when manually changing tools.
  • Make an old-school, spring-type toolholder if you need to do large radii, use form tools with a broad cutting edge or apply any tool that tends to chatter. The spring-type toolholder, with its pivot above the centerline, backs the cutting edge off when the tool bites and starts to chatter. Typically, you can double the cutting speed using this setup. Contrary to popular thinking, sometimes more rigidity is not the answer. In the old days when planers were used to produce surfaces on plates and other large, flat workpieces, the final finishing tool was a wide, flat tool held in a gooseneck, or spring-type, toolholder. Form tools are an excellent and fast way to duplicate complicated geometry in a manual lathe.
  • Ch05.Fig016.Lipton.DSC_4337.tif
    Ch05.Fig017.Lipton.DSC_4327.tif

    Make a spring-type toolholder if you need to do large radii, use form tools with a broad cutting edge or use any tool that tends to chatter. The spring-type toolholder with its pivot above the centerline backs the cutting edge off when the tool bites and starts to chatter.

  • For jobs your shop might find overly challenging, have your local wire EDM shop cut special part profiles and difficult-to-cut geometries. Some of these are a nightmare to accurately hand grind. Good luck trying to find commercially made tooling to machine some of the crazy stuff part designers create.
  • Pull back on the tool post with a few pounds of force when backing tools in the Z-axis. This prevents leaving tool tracks in a turned surface. This also works with boring bars on the ID, but you have to push instead.
  • Make a couple of aluminum face plates that fit in a 3-jaw chuck. These can be resurfaced dead flat dozens of times and set up quickly. They can be welded or bolted together. If you bolt them, be sure to sink the heads well below the surface so you don’t face the screw heads.
  • Ch05.Fig022.Lipton.DSC_3860.tif

    Wire EDM special tool profiles and difficult-to-grind geometries.

  • A nifty hand tapping guide that fits in the tailstock chuck works well for manual or slow-speed tapping of small threads.
  • Three-jaw backing plates are great for backing up a part for heavy drilling. If you make several thicknesses, they can be used to quickly position thin, disc-shaped parts. Add three jacking screws for adjusting the plate in relation to the chuck face to hold thin, disc-shaped parts where you want them in the jaws against a parallel surface.
  • Use light cuts for a disc-shaped part by pressure-plating against a face plate. You can even use the top of the chuck jaws if you have a little help. Three pieces of double-stick tape make all the difference. Open the jaws to a radius just below what you will be turning to for maximum holding capability. Use a smaller disc with a center hole to push against the tailstock center. This method works great when you can’t apply a center drill or have a center mark in the workpiece. Double-stick tape always works better when the mating surfaces are cleaned with alcohol and the blank is squeezed into the tape. CTE

About the Author: Tom Lipton is a career metalworker who has worked at various job shops that produce parts for the consumer product development, laboratory equipment, medical services and custom machinery design industries. He has received six U.S. patents and lives in Alamo, Calif. Lipton’s column is adapted from information in his book “Metalworking Sink or Swim: Tips and Tricks for Machinists, Welders, and Fabricators,” published by Industrial Press Inc., New York. The publisher can be reached by calling (888) 528-7852 or visiting www.industrialpress.com. By indicating the code CTE-2012 when ordering, CTE readers will receive a 20 percent discount off the book’s list price of $44.95.

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