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.
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.
Mike Burchill, president of Marshall Manufacturing in Minneapolis, stands next to the GL 170G gang-tool lathe that Romi provided for winning its IMTS 2014 machine giveaway.
Mike Burchill, president of Marshall Manufacturing in Minneapolis, is the winner of Romi’s IMTS 2014 “It’s time I had a Romi in my shop” machine giveaway.
I know. You’re thinking, “IMTS was months ago…why are you just now announcing this?”
Well, there’s a reason.
You see, the prize Romi offered was a C 420 turning center. However, Mike says that particular model is a larger, more heavy-duty machine than Marshall could effectively use in production. Learning this from him wasn’t surprising because I had visited Marshall some time ago to develop this article about its machining (and bending) capabilities geared primarily toward medical customers.
So, Marshall and Romi worked together to identify options for swapping that lathe for a smaller, higher-speed model that was better suited for the work that flows through the shop. Mike explains that in the end, Romi generously honored the shop’s request to substitute the C 420 with a GL 170G gang-tool lathe, which Marshall is currently using to machine extruded ABS core tubes for reverse osmosis water filters. Mike says the new lathe is much more reliable and productive than the 20-year-old machine it replaced.
So, congrats to Marshall for winning the contest, and kudos to Romi for providing the shop with an alternative machine.
Another element of Top Shops is an Honors Program that highlights successful participating companies in each of the survey’s four primary sections: machining technology, shopfloor practices, business strategy and human resources. Honors Program winners are profiled in the pages of Modern Machine Shop and on our website. Ogden, Utah’s JD Machine was a winner in 2013, and Matthew Wardle, company president, says that the resulting exposure helped net a nice contract from a new customer.