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- Aug 13, 2020
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I've got an RF-31, round column mill clone. I detailed before how the table is not flat, and how I used a grinding cup to get it that way. That thread is here:
www.hobby-machinist.com
Well, after all that work, the table was still had a grade of about 2 thou across the width. I didn't have a power feed and had got to the good enough point. So I trammed up the mill to the table and called it quits.
The trouble is that tramming a mill to a table that isn't square causes all sorts of weird effects. The worst of which is that you will NEVER cut anything square. Forget about it. It ain't gonna happen. My problem was that as I was grinding the table flat, the cup grinding wheel was cocked forward and to one side, so that it only ever cut on side of the wheel.
So, this evening what I did was sweep the table with a tenths indicator, writing the measurement directly on the table every few inches. Then I picked what looked like the flatest spot for tramming. I marked out a square that matched the bolt pattern on the column base and put circles on each corner. Picked the highest one, positioned the dial over it, and set the dial to zero. Then I moved the dial to each of the others and wrote the dial reading on the table.
Now, at each of the corners I had two numbers. The difference of the dial indicator from the zero position, AND the difference caused by the table not being square. A little math gave me a number that was the amount of shim thickness I needed to change under teach bolt. For instance, the front right corner needed an extra 1.5 thou. The left rear needed an extra 8 tenths. The left front got a slip of aluminum foil.
With the shim changes made (God bless feeler gauge sets), I set about doing something about that 2 thou difference from front to back. Put the cup grinder back in, but this time I have a power feed and a 3Hp motor (vs the 1Hp I had before). I've not swept the table yet, but it is obvious that the cup is cutting on both sides at the same time, and the cut pattern isn't really shallow troughs. Not sure I can describe it, but it wasn't cutting all the way from slot to slot before. Not it is.
I'm looking forward to sweeping it out tomorrow. I'll tram again then. I'm fully expecting that I won't have to change anything.
Word to the wise: Take bed flatness into account when tramming.
Cheap mill abuse...don't choke
My mill table was shaped like a bowl. I think it was shipped that way from the factory. It's a round column mill, and the pattern is what you would get from letting a block get too hot will grinding. The center swells from the heat more than the sides, the grinder cuts it flat in that...
www.hobby-machinist.com
Well, after all that work, the table was still had a grade of about 2 thou across the width. I didn't have a power feed and had got to the good enough point. So I trammed up the mill to the table and called it quits.
The trouble is that tramming a mill to a table that isn't square causes all sorts of weird effects. The worst of which is that you will NEVER cut anything square. Forget about it. It ain't gonna happen. My problem was that as I was grinding the table flat, the cup grinding wheel was cocked forward and to one side, so that it only ever cut on side of the wheel.
So, this evening what I did was sweep the table with a tenths indicator, writing the measurement directly on the table every few inches. Then I picked what looked like the flatest spot for tramming. I marked out a square that matched the bolt pattern on the column base and put circles on each corner. Picked the highest one, positioned the dial over it, and set the dial to zero. Then I moved the dial to each of the others and wrote the dial reading on the table.
Now, at each of the corners I had two numbers. The difference of the dial indicator from the zero position, AND the difference caused by the table not being square. A little math gave me a number that was the amount of shim thickness I needed to change under teach bolt. For instance, the front right corner needed an extra 1.5 thou. The left rear needed an extra 8 tenths. The left front got a slip of aluminum foil.
With the shim changes made (God bless feeler gauge sets), I set about doing something about that 2 thou difference from front to back. Put the cup grinder back in, but this time I have a power feed and a 3Hp motor (vs the 1Hp I had before). I've not swept the table yet, but it is obvious that the cup is cutting on both sides at the same time, and the cut pattern isn't really shallow troughs. Not sure I can describe it, but it wasn't cutting all the way from slot to slot before. Not it is.
I'm looking forward to sweeping it out tomorrow. I'll tram again then. I'm fully expecting that I won't have to change anything.
Word to the wise: Take bed flatness into account when tramming.