008” DOC actually left a noticeable raised area over one half the path of the cut. While this reduction in cutting diameter might mean you can’t surface the whole width of the part in one pass, it’s better than getting chatter! If you love the “one pass” look of fly cutting, but your holders are not rigid enough, you can make your own oversize tool.I’ve been trying to level and finish surface a 6” x 10” bit of 1” plate to use as a base for a shop made tapping fixture.ĭecided to try a 2.5” fly cutter that’s been laying around in my tooling cabinet for a couple of years.ġ) each finish pass (.003” doc) leaves a little bit of edge overlap on the sides -I can feel the lip with my thumb.Ģ) one fairly deep finish pass- maybe. If the tool is sharp, the next step is to reduce the amount the bit is extended from the holder. The surface after this cut felt “fuzzy” and rough, instead of smooth and soft. In this case the tool extension was very short, but the dullness of the cutter caused a less-than-clean cut, which induced a vibration. A dull tool can also cause chatter and weird-looking moiré patterns (see photo). If you are taking a very light pass (0.010 inch or less) and getting chatter, double-check that the bit is correctly sharpened and that the cutting angles are correct for the material. Tool chatter or a rough finish could be the result of one issue, or a combination of issues. The finish is about as close to “glass smooth” as you can get with a machine tool. The depth of cut is 0.010 inches and the rpm is 1000. The fly cutter is set to a 2-inch-wide cut for 1/8-inch overhang per side. This width of the piece is 2 inches wide. Using a small fly cutter on the mini mill. It may take a few passes to get a feel for what produces the smoothest surface. Vary the feed rate as you turn the handle and evaluate the cut as you go. For aluminum, set the spindle rpm to 800-1000 (target removal rate is 500-600 surface feet per minute) and do the same test: Set the depth-of-cut to just scrape the surface and do a test cut. Don’t worry about getting that exact number! Just know that its achieved by a relatively slow spindle rpm and relatively slow X-axis (left to right) feed. The target removal rate for fly cutting steel is 80-100 surface-feet-per-minute. Set the depth-of-cut to just scrape the surface, and do a test cut. Using a 2-inch diameter fly-cutter as an example: For steel and cast iron, start with a spindle rpm of 150-200. The spindle rpm and feed rate depend on the material. Vibration is bad, not just for cutting quality, but also for the machine. It’s also possible to set the tool out so far that it creates a noticeable out-of-balance vibration, especially on smaller machines. The farther out you extend the tool, the more likely you will get chatter. For additional information on grind angles visit How far you can extend the tool depends on the holder diameter and bit length. This diagram shows the basic face (10), end (9), and flank relief (5) angles. I planed aluminum for the examples in this article, so that is what is depicted in the diagrams. For planing with a fly cutter, you can use the same basic angles that apply to single-point HSS lathe tools. All it takes is a few minutes at the grinder to fix an edge on the tool. The high-speed steel (HSS) tool bits that come with fly cutters typically need to be both shaped and sharpened before use. On a mini mill or benchtop machine, 0.005 to 0.020 might be the limit. A 0.050-inch pass on a 5-hp Bridgeport knee mill would be a light cut. What’s a light cut? It depends on the machine and the size cutter. Attempting to whack away huge chunks of material can stress the tool, the holder, the machine and even the part. Fly cutting tools and holders are designed for light-duty interrupted cutting. Often fly cutting is done with the tool overhanging one or more edges of the part. Getting good results with a fly cutter requires that the cutter geometry be correct for the material you’re working with and, if you’re surface planing, the mill head must be properly trammed (set square to the table) to assure the cutter is square to the mill table.įly cutting is primarily for final dimensioning or finishing, and not for making heavy roughing cuts. Shown are two size extremes: a 2-inch-diameter fly cutter with a 5/16-inch square bit and a -inch-diameter fly cutter with a 3/16-inch square bit. Fly cutters are pretty basic: A cutter is fixed into a slot in the head with setscrews.
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