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Harold Hall

Workshop Projects

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Design Changes

Having completed the milling head I chose to run a few tests even though I had already purchased the castings, etc.  for a mid size stationary steam engine to put it through its paces.  However, after some initial doubts regarding the design, which resulted in the changes mentioned below, the results are quite acceptable for such tasks. For the benefit of readers who may consider making this milling head my experiences may be of help, especially should the reader consider making changes to suit his or her situation. For those just reading the article, and I anticipate this will be the majority, my findings will no doubt add to the interest.

 

When powering up the unit as initially made and machining  mild steel using a 12 mm end mill, the amount that could be removed without signs of stress was less than I would have liked. Of course, it was necessary for me to realise that the system could not be the equal of the robust mill/drill that I normally used. Even so, I felt that better results should be possible.

 

Most noticeable was the fact that the end of the milling cutter could be deflected back and forward at right angles to the lathe's bed. This with a fair degree of force required I must add. It was though much more robust if force was applied along the length of the bed. This is of course not surprising as obviously the spindle mount will twist much more easily than it will bend across its width.

 

I decided that there were three areas that may stiffen up the assembly.

 

1. To increase the thickness of the spindle mount.

 

2. To reduce the overhang of the spindle from the column assembly and

 

3. Reduce the height of the column. In terms of benefit the three items are I consider in the order that would have the most effect. Actually, I was confident that item one would have by far the most effect with Item three having only marginal effect.

 

To test my theory regarding item three, I placed a bar some 1.2 M long between diagonal columns at the top and applied a substantial force in an attempt to twist the assembly. Whilst I did not measure the effect at the end of the cutter it was visually only just apparent.