Low Point On Milled Surface

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Zoltan

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I milled a face on a 2.5"x3.5"x1.5" block of 1018 steel and a 3/16"x3.5"x1.5" 1018 steel plate. The two milled faces will be fastened together. I used a 5/16" HSS end mill at 1,100 RPM, 7"/min feed, lubricated with Boelube paste.

When I checked fitment of the plate to the block I noticed a slight gap at one corner (~0.002"). Regardless of how I turned the plate the gap remained in the same place, so it appears the block has a slight low point at that corner. The affected area is approximately 1/8" deep by 1/4" long.

I plan to re-mill the surface of the block tonight, but I'd like to get some idea of what caused that low point so the same thing doesn't happen again. Any ideas?
 
Could be that milling relieved some built up stresses.

Tom S
 
Pictures please. What type of milling machine? What kind of clamping was used? 1/8" deep problem??
 
Solid column mini-mill and just recently trammed. The block was clamped using a 3" screwless vise; no parallels were needed.

By 1/8" deep I mean the ~0.002" low spot extends toward the center of the block from the edge by about 1/8".

I won't be able to post pictures until late tonight.
 
Zoltan said:
Solid column mini-mill and just recently trammed. The block was clamped using a 3" screwless vise; no parallels were needed.

By 1/8" deep I mean the ~0.002" low spot extends toward the center of the block from the edge by about 1/8".

I won't be able to post pictures until late tonight.
Click to expand...

Which face of the block did you mill? What was the final depth of cut? Did you use the end or the side of the cutter?
 
The 2.5"x3.5" face.
DOC of the final cut was 0.01".
The end mill was perpendicular to the face being milled.
 
You may have your table trammed but the vice isn't- if you have any swarf etc under the vice it may not be square. I have also seen where a vice wasn't perfectly square. Put something like a 123 block or small granite surface plate with known dimensions into it and indicate it before you re-cut the piece. It is amazing how the smallest particle under the vice can effect things...
 
But even if it isn't trammed perfectly, shouldn't it still give me a flat surface (though obviously out of plane)?
 
If it isn't trammed, one side will be higher. If it isn't trammed in 2 directions ie diagonally not square you can have a corner lower - since your part is rectangular, it may not show up on the thinner width axis, depending on how good your measuring device is. Mic the block on all corners - are they all the same thickness or is there just a depression on a portion of the block?
 
There is a depression on that corner of the block. The rest of the face sits flush against a flat surface.

In regards to tramming, if the mill is out of tram in two directions the corner might be lower in relation to the other corners, but they'll all still be in the same plane. So the block would sit flush and without gaps when that face is placed on a flat surface.
 
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