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Milling Two sides of a part but they don't lineup

Message 1 of 5
278 Views, 4 Replies

Milling Two sides of a part but they don't lineup


I am a hobby person who is into model engineering, building small engines, at the moment I am trying to machine a water pump housing.

I am machining the bottom side first because it is flat and then I bolt it to a plate and machine the top, but after machining the two side are not lined up, they are not far out but the is a bearing top and bottom and they are not in line after machining

Would appreciate any ideas you may have as to why this is happening

I do have a subscription to Fusion360


Message 2 of 5

What are you doing to align it on the second operation, and what style of machine + workholding are you using?


I can't see where you've machined any reference surfaces to probe or sweep with an indicator, so I wouldn't expect any sort of accurate alignment when flipping this part.


The only way I can see you bolting it to a plate is if you tap the holes in the part, and bolts alone won't give you a good enough alignment. If you can machine the plate while it is clamped in place, and machine holes for dowel pins that could mate with holes machined in the first operation, you would get betted alignment, but you would need to access the bottom of that plate while it is still clamped to install the bolts.


If you need to remove the plate in order to install bolts, then you would need to machine reference surfaces you can reach with a probe/indicator once the plate goes back in, and align it that way.



Message 3 of 5

entered by accident

Message 4 of 5


Thank you for the reply

The first operation is to machine the bottom and the stock is held in a vice, not on any type of jig or fixture 

After machining the bottom the 4 holes are taped and then it is screwed to the jig, it is a firm fit in the jig and when the Allan bolts are tightend its is soled, then the top is machined

The X0,Y0 are set from the stock for both operations not the jig

The machine is a knee mill retro fitted to CNC

Stock is machined on all four sides, top and bottom first, remeasured and the exact measurments are then put in to the setup so the stock is the correct size  

Message 5 of 5

found a work around

Changed some of the tool paths, deleted the bearing hole from the top

I machined both sides and then made a mandrel to fit in the bottom bearing hole and turned the top bering hole in the lathe

Came out perfectly in line.

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