Knurling

Host  Neil Butterfield

February 25^th 2006

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The meeting was held at Neil Butterfield's shop.

Neil gave us some basic insight into knurling, followed by a demonstration on his lathe.

There is not much written material about knurling.  Many project descriptions give detailed instructions about how to make parts, but when the knurling is involved, they often just say knurl the part.

Neil has developed his ability to knurl and offers these basic first rules to get the job done successfully

• Don't hurry.  Take your time and pay attention to detail
  
• Use the slowest speed your equipment will turn the work piece
  
• Keep the work piece and knurl wheels clean.  Flush and brush away any buildup before it marks the work piece
  
• Use oil.  LOTS OF IT
  
• Take light cuts.  Don't try to force deep penetration
  

Once you start a knurl, do not raise the cutter from the work piece until you are done.

Knurling is primarily material displacement.  It is not material removal like making chips.  The displacement requires high pressure on the work piece and the equipment.  Light equipment does not handle the pressure as well as heavier equipment

Neil showed us several types of knurling tools.  

He recommends using the scissor type knurling tool for best results.  This design relieves some of the pressure the equipment must absorb in the process by the 180 degree opposed action of this tool.

ENCO's latest sale flier shows this tool model number DR505-4518 for $48.99.  

(Special Note  as of  28 February 2006,  This price is in error and should be some $70+ dollars.  ENCO is honoring the advertised price now however. )

To increase tool rigidity and minimize the possibility of tool movement during the process, Neil modified the mounting of the scissor type tool.  He removed the bar that would be used to mount the tool in the traditional tool holder.  He replaced this with a custom made mounting block that attaches directly to the cross slide.  The mounting block also has a lip on 1 side that bears against the side of the cross slide for alignment and added stability. 

• Neil stressed that 1 pass or a minimum number of high pressure passes does not work well in steel.  
• Neil's rule of thumb is to advance the scissor adjusting screw ¼ turn for each knurling pass in steel.
• Use a live center in the lathe tail stock to minimize material flex during the knurling operation.
• Plan the knurl section so you can trim the ends of the knurl section after the knurling operation is complete.  The very ends of the knurled section will have some incomplete patterns.  These points should be trimmed away for a better looking finished product.
  

Once the work piece is center drilled, clamped in the headstock, the live center is brought up to the end of the work piece, and the scissor knurl tool is placed on the work piece at the starting point for the knurl, you are ready for the knurling operation.

• Lube the work generously with oil.  For steel, Neil uses Mobil cutting oil # 4F977.  The can says Mobilmet Omicron Non Staining Oil.  It is available from McFadden & Dale.  4647 South 32nd Street: Phoenix  Telephone 602-304-9141.
• With the lathe headstock rotation at the slowest speed. Start the machine.  Engage the half nuts and allow the knurl to travel the length of the knurl section.  
• Neil recommends .024" lead screw travel per revolution of the headstock.
• When the knurl reaches the end of the desired knurl section, stop the machine. 
• Reverse the direction of travel.  DO NOT remove the knurl tool from the work piece.  Leave it in place.
• Restart the machine and allow the knurl to travel back to the starting point.
• When the knurl has reached the original starting point, stop the machine, reverse the direction of travel, 
• thoroughly clean and lubricate the work piece and the knurl wheels.  
• A small brush and solvent may be needed for cleaning.  
• Re-lubricate the work piece and knurl wheels with cutting oil.  
• Tighten the scissor knurl tool clamp nut ¼ turn.  
• Then restart the machine.
• Repeat this knurl cycle until the desired knurl is achieved.

When selecting the knurling wheel size to use, keep in mind the need to have the knurl size fit the diameter of the work piece so you make only full diamonds all the way around.  If you miss this step in planning and selecting you knurling wheel, you will not get a satisfactory knurl.

Neil passed out a worksheet for figuring the knurl wheel size to use.  This sheet is available on request.

Updated 3/01/06