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  • Ben Nordman

Replacing Your Top Plate

Updated: Feb 21, 2023



The largest spare part on a chuck, the top plate on an electromagnetic chuck is not only something that wears down over time but something that is replaceable when it does get too worn. Let’s get into the what, how, and when of top place replacements.


What is a top plate?


The top plate is the removable plate that is often the touch point of the chuck to the workpiece. Each chuck can have different top plate configurations which affects the application that it is best for. One big aspect of holding power for a chuck depends on the parts that it holds, giving the top plate an essential part of holding down parts.


The top plate is composed of both magnetic and non-magnetic material, depending on the configuration needed for specific applications.


How does a top plate get worn down?


As the chuck is used over time, there can be a multitude of reasons behind needing a new top plate. What it typically comes down to is either dressing the magnet or having to grind the top plate to make it flat and parallel.


Mistakes happen in the shop environment where a mill could end up milling into the top plate, causing it to be ground down, or a nick could be taken out of the top plate from moving a heavy workpiece and bumping it. There is a never ending list of reasons as to why the top plate needs to be replaced.


When is the right time to replace a top plate?


We estimate that once the top plate is down under 1” on most rectangle models, the user needs to consider a new top plate. This is slightly different on a round magnet, where there is a “shoulder” that comes before what looks like the top plate. The shoulder height, which is measured from the top of the magnet to the shoulder, can get around ⅛” before the user should replace that top plate.


It is always best to consult us if you need help. If you have any questions or concerns about your workholding, give our chuck doctors a call and we’ll help you get your machine running well.


Obsidian Manufacturing Industries, Inc. is a Rockford, Ill. manufacturing company and is the OEM for Magna-Lock USA workholding, MagnaLift & Power-Grip lift magnets, and Arter Precision Grinding Machines as well providing surface grinding services. They are located at 5015 28th Ave. in Rockford, Ill. with a phone number of 815-962-8700. Check out more at obsidianmfg.com/brands.


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