Question Machine stands

[verbotenwhisky]

There are both good and bad points to consider if using 3 feet. 3 points are the least number of point required to create a plane, simple geometry, this is the concept a tripod is based upon. By using 3 points having an equal load on all points cannot be avoided, this is good, and leveling becomes very simple, this is why large granite plates are setup with 3 points of contact. If you use 3 points/legs there will be a greater load per contact point and you'll need to spread the feet out a bit to avoid the possibility of exceeding the foot print with enough mass to topple the mill, you can also add mass to the base to mitigate this issue. If you built the base so that it is big enough to allow the foot print of the mill to be within the triangle and place 2 point under the table it should be stable.

As a matter of practicality look around your shop and see how many of the machines have been designed to be supported at 3 points.

I have 2 dozen machines in the shop and not a single one is supported at only 3 points. By in large they have 4 mounting points. Some gave 6, and some have 8. The only thing that has 3 contact points isa 24” x 36” cast iron surface plate

When using a 3 point system the load has to be centered and balanced to avoid stress and vibration. The load on a mill or lathe are rarely centered or balanced

I always get myself in trouble when I put thought candy out there. I am not advocating either way, if there is a will and/or reason there is a way, a 3 legged stand will topple if not spread out and can apply to much point load if your foundation isn't good. Some times I try not to be negative I simply throw the information out there and lit the person evaluate it on there own. I have seen large equipment set on 3 points, normally if you see that it is because being level is ultra critical and that is the way the designer/engineer decided to achieve the goal. I have seen the 3 point leveling done then they grout it in.

With all of that said I would not mount a mill on a milk stool, if you exceed its foot print it will likely topple.

I think you're assuming a symmetric machine with its center of mass in the center. The point you're making about 3-point support, I believe, is that adjusting the feet does not change the load distribution. That does not mean the load is shared equally among the three feet.

I understand/stood what you were saying, if the legs are close together and you have stuff cantilevered outside the foot print it can become heavy on one or 2 legs but you will still be applying a very similar load as opposed to a four+ point mount where you can have one or more with very little load. But you are correct I am assuming the machine is within a set of legs which are spread out with a reasonable symmetrical load if all the weight is within the foot print....

 

[Scra99tch]

As a matter of practicality look around your shop and see how many of the machines have been designed to be supported at 3 points.

I have 2 dozen machines in the shop and not a single one is supported at only 3 points. By in large they have 4 mounting points. Some gave 6, and some have 8. The only thing that has 3 contact points isa 24” x 36” cast iron surface plate

When using a 3 point system the load has to be centered and balanced to avoid stress and vibration. The load on a mill or lathe are rarely centered or balanced

I do notice on some of my pre 1950 machines that the 4 point system was incorporated. On the 1950's German Fortuna grinder I believe they call out in the manual using wedges to level machine and to just use 3 wedges. I'll have to double check that. I wonder at what point they got good enough to cast these bases to alleviate weight but not sacrifice rigidity.

 

[verbotenwhisky]

I do notice on some of my pre 1950 machines that the 4 point system was incorporated. On the 1950's German Fortuna grinder I believe they call out in the manual using wedges to level machine and to just use 3 wedges. I'll have to double check that. I wonder at what point they got good enough to cast these bases to alleviate weight but not sacrifice rigidity.

That is a good question...

 

[projectnut]

I do notice on some of my pre 1950 machines that the 4 point system was incorporated. On the 1950's German Fortuna grinder I believe they call out in the manual using wedges to level machine and to just use 3 wedges. I'll have to double check that. I wonder at what point they got good enough to cast these bases to alleviate weight but not sacrifice rigidity.

I don't think it's a question of technological advances. It's more of a question of price point. Most shops aren't going to pay a premium price for a machine that can be trued and balanced using 3 points when 4 points or more accomplish the same thing at a fraction of the cost.

Using Hardinge as an example their new machines start at $50,000.00 and go to well over $100,000.00 depending on size and features. Kent lathes on the other hand start under $15,000.00 to a maximum of about $50,000.00. A well-equipped Summit 14" lathe is around $50,000.00. It would be a waste of money to buy the Hardinge if you don't need the ultra-precision.