Boring with the Right Angle
Matching lead angle to application is just as important to quality and productivity requirements as other modular boring tool components. Jack Burley
There are so many factors to consider when specifying the components for a modular boring tool: select a boring head, decide on what size of tool, how many extensions are needed to make it long enough, then find the right spindle adapter for the machine. One might think that these choices are the most important and critical to boring success, but there is still work to be done. Considerations for selecting the right insert holder and lead angle for the application must also be looked at based on the application. Conventional wisdom says to use the longest lead angle possible, thinning the chip because it allows you to increase speeds and feeds. We view it differently. We prefer lead angles closer to 90 degrees, because it applies the least amount of radial pressure against the tool. This is a much better approach for combating chatter and vibration, which go hand and hand with part productivity and tool life. The rough and fine boring tools and insert holders we make reflect this approach. The rules for twin bore roughing and single point fine boring are similar, but not the same. Twin cutter rough boring tools come with a choice of two types of insert holders.
Rough Boring Balance
Rough Boring Step
Zero-degree lead or 90-degree square shoulder type with a diamond shaped insert such as CCMT inserts with two cutting edges will produce a true 90-degree shoulder in a bore for a bearing or seal assembly to fit to a precise depth.
First is a zero-degree lead or 90-degree square shoulder type with a diamond shaped insert such as CCMT inserts with two cutting edges. This will produce a true 90-degree shoulder in a bore for a bearing or seal assembly to fit to a precise depth. While CC-type inserts can be used for balanced cutting, the first choice for setting up a twin bore is to use stepped cutting. This provides the least amount of radial engagement resulting in more stable cutting forces on longer tools exceeding L/D ratio of 5:1. Twin cutters with CC inserts can also be used for through hole applications. However, when the tool is almost exiting the bore, there is likely to be a ‘punch out ring’ and these can cause havoc with the chip auger. Also, the bore will have a very
rough edge and require a heavy chamfer to clean up. This makes our second option, SCMT inserts, the better choice for through-hole applications whenever possible.
SC types have four cutting edges and a 6-degree positive lead. These are traditionally used for edges and a 6-degree positive lead. The positive lead angle reduces thrust forces upon exit, avoiding the ‘punch out ring’ and breakout where the bore ends. SCMT inserts are the better choice for through-hole applications whenever possible. SC types have four cutting
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