Hem machiningprocess pdf

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Trochoidal milling

Counterbore holes are popular for receding fasteners and seals in machined parts, especially in sealing applications, mechanical assemblies, and automotive parts. They have a non-tapered recessed area, so the heads of installed fasteners sit flush with the surface of the part.

HSM, or High Speed Machining has been around for many years in various forms. I've heard many people shy-away from even discussing HSM, since, as they put it, "I don't have high speed spindles, so HSM isn't for me".

Radial engagement milling

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A correctly executed counterbore will sit flush with the surface of a part, meaning the counterbore depth is only as deep as the head of the fastener and/or any additional parts like washers or gaskets. Counterbores allow for ease of installation (they are self-locating), a more streamlined appearance, and additional safety — things won’t get caught on fastener heads sticking out of a surface.

Some sources leave out the depth of the smaller diameter hole (the pilot hole) but, it’s a critical specification and will always be called out alongside the counterbore dimensions. The symbol for a counterbore is ⌴ , and here’s an example call-out from a drawing containing a counterbore for a binding head machine screw:

A counterbore is a cylindrical hole, with a flat bottom that is larger than and coaxial to another cylindrical hole below it. The counterbore serves to provide a recessed and flat surface for mating parts, and typically, socket head cap screws are used with counterbores.

Also, there are plenty of tables with counterbore hole sizing data (they even contain pilot hole sizing and depth as well):

Most CAD programs, such as SolidWorks, have a built-in feature for creating counterbores in your model. While this functionality ensures your fasteners will fit in the pre-defined hole, it’s still important to understand the underlying principles and standards, such as ANSI or ISO, so that control drawings are properly defined.

In contrast, the radial immersion (Radial Depth of Cut or RDOC) is kept low. Typical RDOC values in Aluminum would be 20-30% of the cutter diameter. For Steel, that would be 10-15%, Stainless 5-15%, Hardened Steels 2-7%, Titanium 3-10%, HRSA 2-8%.

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Hem machiningformula

Counterbores and their corresponding fasteners are well-defined by industry standards. As shown in the example graphic, you can easily specify the necessary features, such as angle, diameter, and pilot diameter to create a precise counterbore.

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Hem machiningpdf

The drawing shows a 1.78 inch diameter thru hole underneath a 3.97 inch diameter counterbore, to a depth of 0.81 inches.

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High Efficiency Milling Calculator

Because the time of contact is reduced, but the feed and spindle speeds kept high, most of the heat is transferred to the chip that is formed and ejected from the cut. Often after running the roughing routine with a HEM style path and just air blast, the parts are cool enough to touch. (Obviously be careful before you test this, and watch out for hot chips!)

Counterbore also refers to a tool used to enlarge the opening of a hole to create a flat bottom surface and allow socket-head screws to seamlessly fit with a part’s surface. While a counterbore may seem like a spotface, a spotface is less shallow than a counterbore. A spotface will often act as a flat mounting surface (for locating purposes), whereas a counterbore will recess a fastener head.

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Hem machiningmachine

It is for this reason that I prefer the term "High Efficiency Machining", since this technique is almost universal across the manufacturing industry. HEM involves roughing a block of material or a cavity using the entire flute-length of the endmill. The depth of each cut (Axial Depth of Cut or ADOC) is large to help spread the wear over the entire flute.

Having just returned from IMTS in Chicago, it is hard not to talk about all the different options there are for High Efficiency Machining in the CAD/CAM world these days. (Disclaimer: I was in the TopSolid booth for much of the show.) The industry jargon is thick these days, and while I'm sure the software developers would love to debate the nuances of why their particular algorithm is the greatest thing ever, much of these CAD/CAM packages have similar options when it comes to HEM.

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One of the biggest advantages of HEM style toolpaths is the control of the heat generated. Because the RDOC is low, the time the cutting edge is engage with the material is reduced, yet the feed is increased to take advantage of Chip Thinning and boost the metal removal rate far beyond what a traditional (non-HEM) style roughing path could do.

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HSM vsHEM

It’s important to note that as an alternative to countersinks, the target angle of the wall of the larger diameter of a counterbore hole is consistently 90 degrees. While CAD tools can handle this difference without any issues, you must be mindful of the specs since they can change and affect the final product. As such, it’s crucial to properly call-out the counterbore hole using the expected drawing elements to avoid any potential issues.

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It’s always a good idea to get a second set of eyes on your designs before production starts, especially the eyes of a Fictiv applications specialist. That way you’re sure that you’ve properly called out features like counterbore holes in your designs.

Determining the size of a counterbore is simple when the size of a fastener is defined. Simply add tolerance for the diameter — or largest dimension for polygonal shaped fasteners — so it can fit within the counterbore diameter. Then add a little bit of room on the height of the counterbore to fit the height of the fastener head and any washers you may be adding.

In this article, we’ll define counterbore holes, explain when to use a counterbore, and describe how to call out a counterbore hole in your designs so that it’s manufactured properly.

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You can use a drill bit to drill the pilot hole and then a counterbore cutter to make the counterbore if it’s within your tolerances for manufacturing. When CNC machining, a counterboring end mill tool is used, typically, to drill the countersink portion first, then the pilot hole.

The primary distinguishing factor for when to use a countersink vs. counterbore hole is the shape of the fastener head. Use countersink holes for conical or tapered head hardware and counterbore holes when the head is cylindrical or you’re utilizing a rigid washer or gasket.