Question Machine stands

[ChrisBoon]

Hi all

Years ago, as a young lad, in my uncle's machine shop, we built stands for various of his machines. He was adamant that every stand had to be as heavy as possible. Though most of his machines had solid cast bases and of course weighed a few tons each.
All about vibrations etc.
When I say long ago, I mean 50 or so years ago.
Two years ago, I built a stand for my desktop lathe. The stand weighs about twice as much as the lathe. I have just acquired a desktop milling machine weighing 330kg (700 lb.) and need to build a stand for it. I searched the internet for some ideas and was astonished at how light and sometimes flimsy some of the stands were built. Most people use square tubing for the frame. That would be fine if it was thick walled but by the cutting of it, I can deduce that it is not thick. Also, one person can lift and move it around. My question is, is a heavy framed stand really necessary or desirable.

Thank You in advance for your ideas/opinions.

Chris

 

[jwmelvin]

Desirable, yes. Necessary, less so. Heavier stands resulting from thicker structural members will be stiffer than lighter stands, for a given design. Heavier stands resulting from mass loading (e.g., filling hollow structural members with sand) will have reduced vibration. Obviously a lot changes based on design. Does the stand motion translate to cut quality? It seems to me that the stand could allow machine vibration to prosper (resonance) or could instead help resist (damp) that vibration and prevent resonance. It’s probably secondary to the machine’s internal stiffness though.

 

[projectnut]

The heavier stands will obviously be more rigid, hold more weight, and absorb vibrations better. However, I don't believe you need an 800 lb. stand for a 300 lb. machine. I built the stand for this lathe out of 3" square 1/4" wall tubing. The mounting plates for the lathe are 3/4" thick. The stand itself is in the 300 lb. range with the lathe weighing about the same.

I've been using the machine over 25 years and never had structural, rigidity, or vibration problems.

 

[Scra99tch]

There also might be something to say about the 3 point foot system. It could help focus more of the vibration into 3 points instead of 4, idea being the stand exhibits less vibration because of it being focus on 3 points instead of 4? It was a popular way of leveling a machine seeing as 3 points define a plane. But just wondering if the less points would equate to less vibration, or could it be more points share more of the load of vibration?

 

[j-becker]

It depends a lot on what the stand is for. Conceptually a lathe with the long bed will profit more from the stands rigidity than a desktop mill. And it matters a lot where the big and heavy structural members are located. For example, if you look at David Best's lathe stand, he employs a heavy U profile underneath the bed of the lathe. That is adding a lot of rigidity. Whether the rest of the frame is 1/4 or 14ga tube will not matter a lot for stiffness.

A desktop mill has a small footprint underneath an open C structure and the stand is on the short arm of the C quite a difference to the lathe. I doubt that a stand can add a lot to the stiffness. I don't mean to imply that you can't introduce a twist if the surface you are bolting your desktop mill to is flexible or otherwise poorly designed. However, the man function here is to keep up the weight. But optimizing machine rigidity and the design of stands or foundations is not a trivial piece of engineering. It involves a lot of trial and error as well as pretty sophisticated simulations if you want to accelerate the improvement cycle or fix problems. Overall bigger is better but I would not waste your engineering efforts and money on a super heavy stand for a desktop mill.

 

[ChrisBoon]

What I have on hand is 4" x 3/8" steel pipe for the legs and 3"x1.5"x 1/4" steel C channel for the top frame. The stand will be shorter than my lathe stand and therefore not so heavy. I have not decided on a design yet. I also have a lot of different sizes angle iron.

 

[benmychree]

I have a 19" swing X 56" C-C Leblond Regal lathe, it has legs made out of relatively thin sheet steel rather than cast iron, this was done during WW-2 to be used on capital ships where there had been failures of cast iron machine legs due to firing broadsides of big guns; sheet steel was substituted for iron due to its higher shear strength. It does not seem to affect the tendency to vibration in this case.

 

[j-becker]

Your materials at hand should work fine. A few more thoughts on the design: You may want to add a chip/ oil pan to the top of your stand. Somewhat bigger is better and if I had to do it again I would think about adding some means for enclosing or attaching some chip panels. It is amazing how far my mill can fling chips through the shop. Second, I designed the stand width to optimize the storage cabinets below. I choose 25.25" width between risers to optimize for plywood usage (that makes a lot of the cabinet parts <24"). Third, I designed the bottom so I could easily pick it up and move the mill with a pallet jack.

 

[gard]

Another point to consider is torsional rigidity of the stand. This may be beneficial especially for a lathe. A tube member of almost any cross section, square, rectangular or best yet pipe shaped will have orders more torsional rigidity that a similar weight C channel, flat stock or angle iron. You can easily see this effect by putting a 4 ft length of angle iron in a vice with a pipe wrench on the end. Repeat with a length of pipe that has about the same weight.
The bending strength may be similar but a huge difference in torsional strength.
Your strongest design may be angle iron or the legs and pipe or square tubing for the table.

 

[verbotenwhisky]

Hi all

Years ago, as a young lad, in my uncle's machine shop, we built stands for various of his machines. He was adamant that every stand had to be as heavy as possible. Though most of his machines had solid cast bases and of course weighed a few tons each.
All about vibrations etc.
When I say long ago, I mean 50 or so years ago.
Two years ago, I built a stand for my desktop lathe. The stand weighs about twice as much as the lathe. I have just acquired a desktop milling machine weighing 330kg (700 lb.) and need to build a stand for it. I searched the internet for some ideas and was astonished at how light and sometimes flimsy some of the stands were built. Most people use square tubing for the frame. That would be fine if it was thick walled but by the cutting of it, I can deduce that it is not thick. Also, one person can lift and move it around. My question is, is a heavy framed stand really necessary or desirable.

Thank You in advance for your ideas/opinions.

Chris

Mass is king.