ballen
Diamond
- Joined
- Sep 25, 2011
- Location
- Garbsen, Germany
Hi Richard,
This one's for you. As you remember, at the end of your class I was working on the cross slide of my Studer cylindrical grinder. I had to put it to one side for the past weeks, but am getting back to it over the holidays.
I spent some time carefully studying the geometry. After a bit of head scratching I realised that the geometry of the top part of the slide is almost perfect except that it's warped across the diagonal. If I lay it upside down on a surface plate (ground surfaces down) then it's about 10 microns = 0.0004" high on two opposite corners. If I tap the four corners with a plastic hammer you can hear it clearly. Now here's the thing. If I push those two opposite corners down flat on the surface plate, then the geometry of the dovetail ways is really good, within a couple of microns (0.0001"). But if I don't push those opposite corners down, then the geometry is off by that same amount.
In use, the pressure from the gib and the wheel head pushes this flat. So I think this only matters if I want to use that top half of the slide (which is the longer part) as a master for the bottom part (where the geometry is off by a lot: 50 microns = 0.002").
I was thinking about your demo of bending a gib straight, and what you have told us about 3-point support and parts getting a deform set into them from their own weight. So I was wondering, can I put the top slide upside down on my workbench with a strip of wood underneath the diagonal, and use a couple of woodworking clamps to apply force (say 50 pounds) to the high opposite corners, then let it sit like that for a few days? The top slide is cast iron. Would the pressure deform it back to the correct shape again?
Best wishes for the holidays and the new year!
Cheers,
Bruce
This one's for you. As you remember, at the end of your class I was working on the cross slide of my Studer cylindrical grinder. I had to put it to one side for the past weeks, but am getting back to it over the holidays.
I spent some time carefully studying the geometry. After a bit of head scratching I realised that the geometry of the top part of the slide is almost perfect except that it's warped across the diagonal. If I lay it upside down on a surface plate (ground surfaces down) then it's about 10 microns = 0.0004" high on two opposite corners. If I tap the four corners with a plastic hammer you can hear it clearly. Now here's the thing. If I push those two opposite corners down flat on the surface plate, then the geometry of the dovetail ways is really good, within a couple of microns (0.0001"). But if I don't push those opposite corners down, then the geometry is off by that same amount.
In use, the pressure from the gib and the wheel head pushes this flat. So I think this only matters if I want to use that top half of the slide (which is the longer part) as a master for the bottom part (where the geometry is off by a lot: 50 microns = 0.002").
I was thinking about your demo of bending a gib straight, and what you have told us about 3-point support and parts getting a deform set into them from their own weight. So I was wondering, can I put the top slide upside down on my workbench with a strip of wood underneath the diagonal, and use a couple of woodworking clamps to apply force (say 50 pounds) to the high opposite corners, then let it sit like that for a few days? The top slide is cast iron. Would the pressure deform it back to the correct shape again?
Best wishes for the holidays and the new year!
Cheers,
Bruce