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Easy ways to clean parts, remove broken bolts, etc.
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How to Lap Small Components

Sat Jan 24, 2009 6:20 am

Component Lapping

Rudi has asked me to show the component lapping procedure, as it would apply to a Cub carburetor body. As I didn’t have a Cub part available, I used a generic carburetor part, that was laying around my shop.

Lapping is a very simple procedure, which requires only a smooth, flat surface and various grades of sand paper. My set-up, for this demo, is a piece of ¼” tempered glass, on top of a piece of ¾” plywood. Any piece of glass will do, as long as it is on top of a flat rigid surface. I’ve used window glass many times. For this demo, I used three grades of sand paper, starting with 80 grit, next using 180 grit and finishing with 400 grit. Here’s my set-up.

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Here, I am using adhesive backed paper, but it doesn’t have to be, it just makes it a lot easier. You can put a light coat of spray contact cement or spray gasket sealer on the back of the paper, or just hold the paper in place with your free hand. Because I’m lapping a small item, my pieces of paper are small as well. If you’re lapping a large item, full sheets of paper may be required.

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Here’s the part, before starting the procedure. To make the results show up better, in the photos, I sprayed a light coat of machinist bluing on it.

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I first take a couple passes across the 80 grit, to see how uneven the part is.

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You can see, in the photo, that it only made contact in a few places.

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After a few more passes on the 80 grit, it’s beginning to take shape. As I sand, I rotate the part to sand in various directions.

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At this point, I have near full contact and can move on to the 180 grit.

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After a few passes on the 180 grit, I’m making full contact, although reflections in the picture make it look a little darker in some areas. At this point, almost any gasket would certainly seal, but for the sake of illustration, we’ll take it one step further.

Here’s the finished product, after lapping with 400 grit. In the photo, it doesn’t look much different, but is actually a much smoother finish.

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It took me all of about ten minutes, including photos, to get this part in shape. Larger or badly warped items will obviously take longer, but it’s very rewarding when you’re finished.

By the way, if you know someone who is getting rid of an old refrigerator, with glass shelves, grab the shelves, they’re good heavy tempered glass.
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