Getting clean cuts on dimensioned parts

Tips to reduce chips and tear-out when shaping dimensioned parts. June 14, 2000

We run lineal chair parts in cherry, removing 1/8 of an inch of stock on a Bacci two-sided, reciprocating-table shaper, then use a Prosand power-feed sponge sander at 120 grit for cleanup.

On the uphill side of the curves we get microchips, tiny chips that will require extra sanding. If we kept running them through the Prosand until the uphill curves were clean, we'd sand the part down to a smaller dimension.

The microchips are only in a few spots on about half of the parts, therefore an extra step of close inspection and hand touch-up on the drum sander is necessary. Because of the sheer numbers of parts, we need to optimize our shaper time as well as sander time and minimize the close-inspection time.

What gives the most chip-free finish: climb cutting with a straight brazed tip head, or a conventional, into-the-wood cut with a multi-tipped, spiral-pattern head?

Any time the cut can be broken up, you're better off. For many applications, the use of carbide-insert tooling provides a better cut.

One major key is the use of sharp tools. Many people over-use their tools to the point of being over-dull. The use of an ampmeter on the cutting spindle will help in determining the dullness of the tool.

Tearout is also caused by the wood itself. To reduce the effect of this tearout, the cutter should be designed to remove a smaller chip. This is often done with cutters that have many knives that do small sections of the cut, as compared to a full-length knife that is cutting the entire wood piece at one time.

In general, I have found that insert tooling does a better job than brazed-on tools. Even though this is not always true, it is well worth looking into. The proper hook angle and tool design is also critical.

Climb-cutting versus conventional straight cutting: The most important thing to consider here is the safety factor. Is the wood part being held so that the it cannot move while being cut? If so, then climb-cutting can reduce the tearout. I much prefer to use the proper cutting tool first, and climb-cut as a last resort.
Dave Rankin, forum moderator