How Peerless Precision Selects the Right Finishing Operation for The Tightest Tolerances
Did you know that even the most modern CNC machines can’t achieve the extremely tight tolerances needed for certain parts?
In actuality, a wide range of machines and operations, both new and old, are necessary to finish parts and produce tolerances as tight as one millionth of an inch.
At Peerless Precision, we’re experts at achieving the tightest tolerances. Better yet, we reduce risk, cost, and lead time by performing many finishing operations in-house. We don’t need to outsource and forfeit control of our parts like many other machine shops.
So if you need ridiculously tight tolerances on your next project, come to the experts. Then sit back and relax while we take care of the entire process.
How Peerless Precision Produces the Tightest Tolerances
Today, we’re pulling back the curtain on how our team chooses the best finishing operations for super tight tolerances.
We’ll select one of these finishing options based on the needs of your design:
We use surface grinding when we need to create and maintain a flat surface on your part. The part’s material and your requirements for the desired finish help us determine the amount of material we will need to remove and the correct grinding wheel we will need to use to achieve the desired flatness. Grinding wheels come in various materials and grades, like sandpaper. The grinding wheels (abrasives) we use are selected based on the material we are performing the operation on and the surface flatness/finish we are aiming to achieve.
We also use surface grinding to precision cut pins that can’t be cut with a saw. Saws produce sharp edges and leave lines in the part that make the surface rough and abrasive, which makes it tough to maintain tight tolerances consistently across the part’s surface. For even the tiniest parts, we depend on the surface grinder to smooth things out, finishing edges and removing unwanted rough lines.
Cylindrical and jig grinding
We use these two grinding techniques on the inner or outer diameter of curved, circular parts. Inner diameter grinding is known as ID grinding, while outer diameter grinding is known as—you guessed it—OD grinding. ID/OD grinding options are ideal for completely round shapes.
Jig grinding, on the other hand, can be used on both the inner and outer diameters. It’s perfect for imperfectly round parts. This finishing operation is great for lopsided curves because the machine can hold the part with special fixturing to grind geometrically complex shapes. For example, we recently used a jig grinder on a set of crankcase housings, L-shaped parts with a hole in the middle. Our cylindrical grinder would not have been able to work on this part at all!
Honing is the next rung on the ladder of finishing operations. More precise than grinding, it allows us to achieve exceptionally tight tolerances of ±.00002” 8 Ra Finish.
Honing is always used on the inner diameter of a part. During this process, a special honing stone is used to maintain concentricity and achieve the desired tolerance.
We know we’ve produced a perfectly honed part when it passes our “drop test.” We drop a pin down the hollowed, honed section to ensure it falls at a certain rate and in precise alignment. If the pin fails the drop test, we hone the part again!
At Peerless Precision, we work with two different technologies for honing. One of our machines is new, but we love our older machine as well—because these machines just aren’t made like they used to be! While the newer NC Hone does the majority of the hard work for the machinist, honing is still very much an art. It requires the ability to “feel” when the parts are getting to the required tolerance. When we are working toward achieving ±.00002”, we might start it out on the NC Hone, but will finish it off on our oldie but goodie. 🙂
When you need tolerances as tight as a millionth of an inch, lapping will always be our go-to process (often in combination with honing and grinding).
There are two types of lapping that we perform at Peerless Precision: match lapping and roll lapping. Both use round parts, like roller ball bearings, pins, and pistons. Roll lapping is used when we need to remove millionths of an inch at a time on the outer diameter of round parts. We use various lapping compounds depending on the material. The most commonly used compound is a diamond compound paste, in various grades, dependent upon rough lapping or finish lapping.
Lapping is a technique that’s no longer taught in schools. Most shops won’t even touch parts that require tolerances tight enough to need lapping, and there’s no new technology to replace these older machines.
At Peerless Precision, we’ve put the work in to master this technique. Our experts have years of experience learning on the job and familiarizing themselves with the feel of a properly lapped part. We’re your one-stop lapping shop!
Regardless of the finishing operation we choose, we only quote the processes that are absolutely necessary to achieve the requirements on your drawing. That means if your project doesn’t need lapping, you’re not going to pay for it.Trust the experts at Peerless Precision to determine the proper finishes for your part’s tolerances at the best price. We have the machining know-how to get the job done right using the most cost-effective process. Request a quote today!