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The flute configuration of a reamer is important. Selecting the correct configuration helps optimize tool life and hole finish.
Left hand spiral reamers should be selected for through holes. A through hole has an opening on the other end. If you put your eye up to the hole, you would be able to see out of the other side of a through hole. A left hand spiral pushes the chips ahead of the reamer and out the other side of the hole. This reduces the chances of scarring the work-piece and reduces the chance of damaging the reamer by previously cut chips. Additionally a left hand spiral helps bridge interruptions such as cross-holes or keyways. Left hand spirals are excellent for reaming hard materials and typically provide the best size and finish as compared to right hand spiral or straight flutes.
Right hand spiral reamers should be selected for blind holes. A blind hole is a hole that does not have an opening on the other end. If you were to put your eye up to the hole, all you would see is darkness. In a sense, you would be “blind” while looking in the hole. A right hand spiral pulls the chips towards the back of the reamer. This helps prevent the chips from getting packed into the bottom of the hole reducing the chance of damaging the reamer and the work-piece by previously cut chips. Additionally a right hand spiral also helps bridge interruptions such as cross-holes or keyways. A right hand spiral reamer may cut slightly oversized holes due to the aggressive flute geometry. They perform very well in highly ductile materials.
Straight fluted reamers are very good general purpose reamers. They are typically cheaper than left hand or right hand spiral reamers and work best in non-chip forming materials such as cast iron, bronze and free cutting brass. The preferred hole condition for a straight fluted reamer is a through hole all things being equal but they perform well in blind holes as well due to their non-aggressive geometry. If all the application parameters are known typically a right hand or left hand spiral reamer will provide superior results in finish and performance then a straight fluted reamer.
For additional information on left hand and right hand spiral reamers while reaming with coolant please see our previous post Reaming with Coolant.
As always if you have any questions about left hand spiral, right hand spiral, or straight fluted reaming (or any other cutting tool questions) feel free to leave us a comment here on our blog or fill out the form on Super Tool’s Contact Us Page.
Bryan Enander
Super Tool, Inc.
941-751-9677