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Reaming Blind Holes vs. Reaming Through Holes
Knowing the difference between the two types of holes is important when reaming with coolant. 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 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. Coolant fed reamers come in two styles coolant through the center of the tool and coolant through the flutes of the tool. Reamers with coolant through the center should only be used on blind holes. This is because when the reamer shoots the coolant out of the front of the tool it will hit the back of the hole and come back towards the reamer forcing the chips back up through the top of the hole and at the same time flood the cutting edges. If a reamer with coolant through the center is used on a through hole, the coolant will shoot out the front of the tool and out the other side of the hole without flooding the cutting edges rendering the coolant ineffective. Reamers with coolant through the flutes should be used on through holes. This enables the coolant to flood the cutting edges as the coolant is shooting out the side rather then the front of the reamer.
Right Hand Spiral vs. Left Hand Spiral Coolant Fed Reamers
The principle behind a left hand spiral reamer and a right hand spiral reamer concerning coolant is simple. A left hand spiral pushes the chips ahead of the reamer. A right hand spiral pulls the chips towards the back of the reamer. It is typically best to use a center fed coolant reamer with right hand spiral flutes on blind holes. The force of the coolant is “pushing” the chips towards the back of the reamer and is complimented by the right hand spiral that is also “pulling” the chips towards the back of the reamer. Conversely, it is best to use a flute fed coolant reamer with a left hand spiral on through holes. The force of the coolant is “pushing” the chips ahead of the reamer as the coolant floods the left hand spiral cutting edges. This action is complimented by the left hand spiral which is also “pushing” the chips ahead of the reamer out the other side of the through hole. This contributes to better hole finishes because the chips are being flushed away from the reamer/workpiece interface. Flushingthe chips away reduces the chances of scarring the workpiece and reduces the chance of damaging the reamer by previously cut chips. (Note: there are other advantages to using right or left hand helixes, which we will discuss in a future blog).
Coolant Pressure
Inadequate coolant pressure or volume can lead to tool failure. For more on coolant pressure see the previous post Drilling with Coolant as the principles regarding coolant pressure is similar for reamers and drills.
Reaming Speeds and Feeds Using Coolant
Use the same formulas for speeds and feeds that you use for reaming without coolant.
Speeds and Feeds Formulas
RPM = (SFPM*3.82)
(TOOL DIAMETER)
IPM = (IPT)*(RPM)*(#Teeth)
IPR = IPM/RPM
RPM = Rotations Per Minute
SFPM = Surface Feet Per Minute
TOOL DIAMETER = Diameter of the cutter in inches
IPM = Inches Per Minute
IPT = Inches Per Tooth
IPR=Inches Per Revolution
Here is a link to a reaming speeds and feeds chart. There are two charts one for reaming dry and one for reaming with coolant.
Check back with us next week. We will be discussing reaming speeds and feeds. If you have any questions about drilling with coolant (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.