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When setting up my new lathe I discovered that the cutter height was too low and left this nub, a common issue that is easy to fix. Click image to enlarge |
Shimming (Metal) Lathe Cutter Height
A Metalworking Lathe Basic
Text and photos by Tom Hintz
Posted – 4-19-2014
When I got my new JET BD-920W Metalworking Lathe it came with a standard 4-sided tool holder that is both common and very tough. It also puts a standard JET replaceable carbide cutter and holder well below the centerline of the work piece and we need to correct that. In most cases the cutter should have the top of the cutting edge intersecting the centerline of the material so when you make a face cut it produces a clean face without a nub at the center. My JET BD-920W Metalworking Lathe left a sizeable nub so I needed to adjust the cutter height.
Shim Stock
If you are lucky there is a source for shim stock nearby. If you are like many of us shim stock can be a bit more elusive. Automotive parts and machine shops often have shim stock. However, nearly any home center or hardware store that sells a bit of automotive or garden tractor supplies will have feeler gauge sets that are essentially made up from a range of shim thicknesses which is exactly what we need. And they are cheap.
Most of these feeler gauge sets are put together with a thumb screw or nut so the individual shims can be removed. I take the set apart and leave them apart, stored in a plastic bag. The toughest part of all this is wiping the individual shims clean as the generally come with a heavy oil on them to protect against rust between the factory and you buying them.
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Finding real shim material can be difficult but these automotive feeler gauges (left) are easy to find and work great. I(t is important that the shim stack fully support the cutter (right) so there is no rocking. Click images to enlarge |
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Shimming
Actually shimming the cutter is simple as long as you understand the pressures being applied when you lock the tool down. We always want the maximum contact area between the tool and the base so when we introduce shim material that has to be as wide as the cutter bar to it cannot rock. Most shim material, including that taken from feeler gauge sets work well here.
I began by running my cutter up to a piece of stock on which I had taken a couple face cuts that left a pronounced nub. I could then (lathe off) hold some shim leaves on top of the cutter to see what combination I needed to reach the centerline of the material. Obviously this will involve a bit of trial and error but you can get very close this way.
With the shims selected I removed the cutter and cleaned the holder and tool to be sure there are no chips. Then the shims are put down and the cutter on top of them and the screws tightened down all the while making sure nothing moves. With the cutter and shims secured I take another light face cut to see if the nub is removed. In the video I guessed very close but there was a fine numb left after the cut. I added a .010” shim to the stack and the next cut produced a clean face. Bull’s eye!
In most cases this “shim pack” will always work with that cutter as long as any replacement inserts are the same thickness. When I remove a cutter that has been shimmed I put it and the shim pack in a plastic sandwich bag to keep everything together so I can re install everything the next time I use that cutter.
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