Parts not parallel

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rzw0wr

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I have a Smithy MI 329 mill.

When I got it the table was not parallel to the ways.

I sent the table to my son in law to clean up the top.
He is a machinist.

When the table returned I got the table adjusted to a little under .001" in about 30" or so.

I bought a vice for my mill.
I checked it for square to the quill and parallel to the table.
Both checks showed less than .001". About .0005 or so.

I put a piece of cold rolled in the vice on parallels, tap the crs piece until the parallels are tight on both ends.

I cut .010" off of the piece and the piece comes out .003" to .005" out of parallel.

Any ideas about what might cause this taper?


Thanks,
Dale
 
I just checked the part that has the taper in the vice with a dial indicator.
It shows .005" taper.

Wonder if the piece is moving in the vice?
 
rzw0wr said:
I just checked the part that has the taper in the vice with a dial indicator.
It shows .005" taper.

Wonder if the piece is moving in the vice?
Click to expand...
Put a couple of paper shims under the part on the parallels to make sure the part is seated; the best way to ensure seating is to use vise hold downs, Starrett makes them, they sit at the base of the part between the vise jaws, on both sides of the part and force the part against the parallels. Also you should indicate the seating surface of the vise bed.
 
Are you using a end mill holder as opposed to a collet? I've had end mills slip in the collet. A holder has a set screw for end mills that have the flat for it.
 
I have also had the spindle lock slip and allow the cutter to raise up along the cut making for a nice tapered part.
 
End mills can move in end mill holders, too. The cutting forces tend to pull the EM into the work, so if the top of the slot in the end mill's shank isn't in contact with the set screw it can be pulled down. This happened to me and produced a taper in the work.

Don't use a drill chuck to hold end mills. They can be worked loose by the side load and drop, with a generally undesirable result. I learned this lesson, too. Fortunately only the work (a piece of oak) was mangled. Previous to that, I had occasionally used the drill chuck to hold an EM just to avoid taking the time to install my collet chuck but now....never.

You will find folks using set screw style end mill holders claiming good results, and others using collets with good results. I use ER collets with no problem but generally take light cuts since I have a small benchtop mill.
 
like everything the devil is in the details. There is a detail to using a EM holder like you said, you need to turn the set screw in until it lightly contacts the flat then pull down till it hits the end of the flat. I've never had an EM drive up into a collet, but like has been mentioned had the quill lock slip.
 
As C-Bag says, lots of details to worry about. Take a look at This Old Tony's video here for some tips:
 
rzw0wr said:
I have a Smithy MI 329 mill.
...............
When the table returned I got the table adjusted to a little under .001" in about 30" or so.
..............
Thanks,
Dale
Click to expand...
I am curious as to what you mean by "I got the table adjusted to a little under .001" in about 30" or so". A mill table is what it is. As far as I know there is no adjustment for parallelness.

In facing with a mill the work, which is fixed of the table, moves under the stationary cutting tool. The cut will always be parallel to the ways which define the plane of the cut. In order to cut parallel faces on a workpiece, the bck side of the workpiece must be parallel to the ways. This is usually accomplished by fixing the back side of the work to the top of the table or to a surface which is parallel to the table. This assumes that the top of the table is parallel to the ways. This is not necessarily a good assumption.

To check a table for parallelness to the ways, you would mount a dial indicator in the spindle or another fixed external point and sweep the table by moving in x and y. Note that this is not the same as tramming a head. The indicator doesn't move. Ideally, the indicator will show no change as the table is swept.

If a variation is noted, there are several possible causes. One which is fairly easy to correct is loose gibs. Loose gibs can allow a table to lift when the center of gravity of the table/workpiece/fixtures moves past a point of support. Another cause can be a deformed table resulting from years of use. The cure would be regrinding the table surface. A third cause would be an improperly ground table. Again a table regrind would be the cure. A way to fix a non-parallel table without grinding would be to mount a tooling plate on the table and skim cut the surface. The surface will then be parallel with the ways and any work mounted on that plate and faced will have parallel faces. In facing this plate, a relatively small diameter end mill should be used unless one is absolutely certain that the mill head is trammed in well.

Tramming the head can be a catch 22 situation if the table has a non-parallel condition as the process of tramming is to ensure that the spindle axis is perpendicular to both the x and y ways. For that reason. I mount a plate on the table and face it with a small diameter end mill. If a mill head was out of tram by .010" over 6", the difference in elevation of a 3/8" end mill from one edge to the other would only be .0006". It isn't neccessary to face the entire plate, only the four contact points at +/- x and y.
 
As usual, This Old Tony did a good job of educating and amusing at the same time. I certainly learned a thing or two.
 
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