Newbie- same cut, both sides... please help

[grdnanthy]

We just got a new Tormach PCNC milling machine and we're having trouble using it to it's fullest extent. I am trying to make a sort of bearing block where there are two bearings set into cut outs on two opposite sides of a block. The problem that i am running into is getting those holes to line up perfectly. it really has to be exact because the shaft has to line up when it's pressed into the bearings. I tried putting the cut-out exactly in the center of the block and then flipping it in the vice. This could only get the hole lined up enough on the x-axis and we are having trouble getting it aligned on the y-axis. And yes, we triple checked our measurements, it's just not exact enough.

[One of Many]

Some dimensions like distance between the bearings, bearing bores and spacer bore between the bearings would help define your conditions.

Basic operation would be to use a boring head and machine the top and bottom bores in one setup to get the best alignment possible. This will take a custom boring bar for the bottom bore to cut upward. Interpolating a bearing bore is not as round which could distort the race if/when pressed in.

In a pinch for lightly held bearings. If the spacer bore were large enough and space between the bores short enough, one could set x,y center of the bore holes, using a woodruff cutter and interpolate the 2 bores from the top. Thereby taking advantage of the key cutter and machining in the spacer gap by dropping the cutter through the hole and undercutting the lower bore.

As you have found, when ever the part must be moved to a second operation, anything else will be a compromise to the new alignment. Assuming the block you have machined square and parallel. If you bored the bearing bore and the spacer bore in one setup, then flip it over and indicate in the spacer bore within a couple tenths, the secondary bore should still be close enough for the average application.

With a longer space between the bearings or smaller spacer bores that prevent access, flipping the part will require using a test indicator and indicating in something common to both ends to align the bores.

Creating a fixture that would hold it in 2 vertical planes would also be beneficial. Regardless how it is held, the concept is utilizing the through bore or 2 machined faces verified true to the Z axis, again using an indicator and if need be, resetting x,y zero to center on the common bore or faces. Be aware of short vise jaws and tall parts can tip with cutting forces too.

Simple center finders and edge finders just won't do if you expect near perfect alignment. The best bet is to either do it in one operation or set yourself up to make the secondary operation more reliable.

DC