Derek Korn joined Modern Machine Shop in 2004, but has been writing about manufacturing since 1997. His mechanical engineering degree from the University of Cincinnati’s College of Applied Science provides a solid foundation for understanding and explaining how innovative shops apply advanced machining technologies. As you might gather from this photo, he’s the car guy of the MMS bunch. But his ’55 Chevy isn’t as nice as the hotrod he’s standing next to. In fact, his car needs a right-front fender spear if you know anybody willing to part with one.
During my visit to the Blaine, Minnesota, shop, I picked up on a few tricks it uses to be more effective at machining micro features. Here are a few I cite in the article above:
The shop sometimes starts the creation of square-edge micro-slots by first using a ball end mill to essentially rough out the slot before coming back with a standard end mill to create the sharp corners. This minimizes the load on the standard end mill.
Pecking cycles are used for some micro-drilling operations, and the pecking feed distance depends on the material and hole size. However, Challenge Machine has found that some applications lend themselves to drilling without pecking. This is often the case for polyetheretherketone (PEEK), requiring an adjustment of speeds and feeds to generate the proper chip size per tooth so chips can be evacuated out of the hole.
The shop tries to integrate deburring operations during the machining cycle as much as possible to minimize manual deburring work. If face milling is required after holes are drilled, the shop might slowly run a drill backward down each hole to remove any burrs that milling created.
Challenge Machine also commonly provides micromachining lessons to its customers. For nearly every prototype project, the shop works closely with the customer to offer design-for-manufacturability (DFM) suggestions. For example, a part with a callout for a 0.001-inch tip radius would require the shop to use a 0.002-inch-diameter tool. If the designer can accept a 0.0015-inch tip radius, then the shop can use a cutter with a 0.003-inch diameter to speed the machining process.
Switzerland’s Reiden Technik is new to the U.S. market. Its five-axis machine tools are available through Cincinnati, Ohio’s Pilsen Imports, which also offers large Toshulin vertical turning machines and Colgar horizontal boring mills.
Reiden has developed an interesting concept it calls Double-Drive Technology (DDT). This features two separate spindle motors in one spindle housing to enable its RX series machines to effectively perform both roughing and finishing operations. A hydraulic circuit is used to engage the high-torque spindle motor via a bevel gear coupling while the high-speed spindle motor freewheels. When the hydraulic circuit is off, the bevel gear on the high-torque spindle motor retracts to enable the high-speed spindle to be used. Learn more.
I recently sat in on a roundtable discussion hosted by Gosiger that drew a handful of shop owners/managers in the Cincinnati/Dayton, Ohio area. The first question asked by Norm Vallone, president of MessageWorks who led the discussion on behalf of Gosiger, related to the prime challenges those shop principals faced. Not surprisingly, many pointed to the difficulty finding/growing good employees.
I wonder if this a problem that will be exacerbated because a growing number of young people don’t seem to be mechanically inclined or handy in general. Read this and consider commenting with your thoughts.
Louis Trumpet with Vallorbs Jewel Company in Bird-In-Hand, Pennsylvania, wrote a piece that reminds us how small turned diameters can vary from their nominal dimension when a lathe’s tool center height is off. What follows is what he sent to me (which I’ve only mildly edited).
From Louis: Very small, precision turned parts may have several different diameters, making for complications here and there. For example, when turning these small parts, you may notice that when one diameter is on the nominal dimension while others may be off by several tenths. At first, you might think this is caused by different tool pressure at the different depth of cuts, but that’s unlikely. To be sure the problem isn’t mechanical, check for backlash, flex in the machine/toolholder and the fit of the material to the guide bushing (when using a Swiss-type lathe). If everything checks out, and you’re still experiencing a differential, the likely culprit is that your turning tool center height is off. The following example shows how being off center can affect the diameters being turned.
First, let’s assume that if your tool was brought to XO, the tip would be dead on the centerline of the bar. Line “A” is how far your tool is off center. Line “B” is your programmed X-axis dimension. Line “C” is the actual distance to the cutting edge of the tool or half the actual turned diameter dimension on your work.
Imagine making line “B” longer and longer (turning progressively larger diameters), and you see that angle “A” flattens out, which in turn will make line “C” shorter relative to line “B.” In other words, the error becomes less the larger the diameter your turn is. So, when turning very small diameters, it is critical to be on center.
The Pythagorean Theorem tells us that a2 + b2 = c2. Using that information, let’s assume your tool is 0.003 inch off center and you are turning a 0.030-inch diameter (side a = 0.003 inch, side b = 0.015 inch). Side “c” is equal to 0.0153 inch because c = √(0.0032 + 0.0152), so your turned diameter will be 0.0306 inch or will be 0.0006 inch off of nominal size.
Now assume you are using the same tool to turn a 0.0125-inch diameter. Running the same math, we find that the turned diameter (rounded) will be 0.1251 inch or 0.0001 inch off of nominal size.
Since the 0.030-inch diameter was 0.0006 inch off of nominal size, we have a differential of 0.0005 inch between the two dimensions. It follows, then, that when you offset one dimension to nominal size, the other dimension will be 0.0005 inch off of nominal. All this makes it difficult to dial in the workpiece without editing the program (bad), or using two separate offsets (nearly as bad).
You can also add a macro variable to the programmed dimension, but when you think about it, all that does is provide a convenient way for the operator to edit the programmed dimension. It’s better to fix the root cause of the problem by getting the tool on center. You can use this information to calculate how far your tool is off center and correct it with an offset, assuming you have Y-axis capability. Some small-capacity Tsugami Swiss-types have a feature built into the control to calculate the tool height using this principle, but you can see it works best at very small diameters where angle “A” and the resulting error are greater.
Ever benchmarked your machine shop against others? Here’s your chance.
The online survey for the 2015 edition of Modern Machine Shop’s Top Shops benchmarking program ends February 28. Hundreds have participated thus far, so please take time to complete the survey if you haven’t already. Participants will receive a number of survey reports and have the chance to be profiled in the magazine. All it costs is a bit of your time.