Tuesday, October 25, 2011

Finish Boring vs. Reaming

By Mike Smith, Product Manager – Reaming and EPB

Drilling the perfect hole is nearly impossible, making it necessary for precision finish tools to follow the drill operation and complete the job. Fine boring heads and reamers are two popular tools used for finalizing the holemaking process. While both styles of tools can finish the hole, the design of each tool has significant advantages that can be optimized depending on the needs of the component.

When selecting the right technique for your holemaking operations, you should consider hole diameter and length, interruption within the hole due to internal cavities and the required straightness, size, tolerance and surface finish of the hole.

My intent here is to compare finish boring and reaming just enough to help steer you in the right direction as to what might be the better choice for your operations.

Finish Boring
Liteline Fine Boring Head
Finish boring is ideal for short-run jobs and situations where more stock is remaining in the hole. When compared to reaming, finish boring is more flexible when machining different hole sizes using the same tool. Also, precise hole positioning is less critical than in reaming because if a drill does not drill the hole straight, a finish boring head will true up the hole.

A reamer only follows the existing hole. In terms of hole quality, finish boring heads typically achieve tolerances within IT 5 and surface finishes above Ra 1 micron. The main drawback to a finish boring head is feed time as it only has one tooth for cutting. Also, with one tooth doing the cutting, tool life is generally less than with reamers. Once the insert wears, size and finish can diminish quickly.

Precimaster Exchangeable Head Reamer
Reaming works with pre-machined holes that have small amounts of stock. When compared to finish boring, a reamer holds tighter tolerances for longer periods of time because the cutting is generally spread out over multiple flutes. This also allows for faster feeds over finish boring heads.

Real-World Example of Finish Boring vs. Reaming
I once had a customer using a finish boring head to machine 256 holes in each of the large plates his company was producing at high volumes. These holes had very tight tolerances, requiring an adjustment of the finish boring head after every fourth hole due to insert wear. We were also able to feed the reamer five times faster than the boring head due to the reamers multiple flutes that drastically cut the production time.

We determined that finish boring would have been the better option if they were machining five holes in a 10-piece job. At which point, you could set the finish boring head, run your holes and then put it away for a different component later on down the road. 

Finish Boring and Reaming Together
There are instances where both finish boring and reaming must work together in order to get the job done right. For example, I once worked on a gun component project where the manufacturer required true positioning and very tight tolerances. The company attained the tight tolerances through reaming, but first had to use finish boring to straighten the holes before the reamer could accurately do its job. 

Holemaking and Machines
When it comes to reaming, it’s best to have a newer, accurate machine because the goal is to minimize runout. Because runout is such a big enemy of reaming (and all holemaking operations for that matter) I recommend using high accuracy toolholders, such as hydraulic or shrink fit holders.     

If a machine has a lot of runout at the spindle, finish boring is more forgiving than reaming because you have some adjustment in the boring head to compensate for the runout.

Holemaking Tools
When it comes to holemaking, whether through drilling, finish boring or reaming, Seco has a wide variety of world-class tooling solutions for small and medium batch production, large batch manufacturing and difficult-to-machine materials.

If you have any questions about what method is best for you or how to maximize an existing hole finishing application, you can contact your local Seco technical specialist or me. We’re always happy to help!

About the Author
At Seco, Mike is the product manager for reaming and EPB tool holders, which includes EPB’s line of rough and finishing boring heads. In his spare time, Mike enjoys spending time with his wife and two daughters as well as running when he gets a chance.

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