When you de-burr a block, you get rid of sharp inner and outer corners, replacing them with smoother inner and outer radiuses. The reason you do that is because metal stresses tend to collect at points with sharp inner or outer corners.
I have a cheap Harbor Freight 12 ton hydraulic press I use in the garage. I was trying to press a bushing out of a Honda front lower control arm, and this is what happened to the arbor plate.
Notice that the main break runs from the large right angle sharp inner cutout to the small right angle sharp inner cutout. Notice that neither of the round cutouts failed, but the sharp outer corner at the edge of the larger round cutout is where the second break occurred.
This is a graphic example of why deburring a block is a good idea:
I have a cheap Harbor Freight 12 ton hydraulic press I use in the garage. I was trying to press a bushing out of a Honda front lower control arm, and this is what happened to the arbor plate.
Notice that the main break runs from the large right angle sharp inner cutout to the small right angle sharp inner cutout. Notice that neither of the round cutouts failed, but the sharp outer corner at the edge of the larger round cutout is where the second break occurred.
This is a graphic example of why deburring a block is a good idea:
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