Better Base for a Benchtop machine

[analogman]

In my quest for a smooth finish, I noticed that my RF45 sitting on the stock stand using "hockey puck adjustable feet" is very far from a rigid setup. So I am going to get rid of the adjustable feet and make a concrete base/stand.

I have seen some steel stands on casters and such, but I want something heavy, rigid and "at one with the floor".

Has anyone built such a base? Please post pictures if you have them.

thanks
AM

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[blkexp98]

I'm looking forward to your build. I have been planning on something more rigid as well but set my goals a little lower using wood.

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[cyclestart]

Has anyone built such a base?

I've never seen one. Concrete and granite tops but not complete stands.
The idea doesn't seem unreasonable unless you're thinking solid cube, that would be crazy heavy.

[Hypnotoad]

I've been questioning how rigid my G0704 stand is and whether that matters much for what I'm doing. I have it bolted to the concrete but there's quite a bit of flex to it. What's the effect of that? The machine itself is much more rigid.

[blkexp98]

I have the G0619 SX3 and currently have it mounted to an old metal craftsman table with 2 layers of melamine. My little machine will shake it pretty easy. That's why I wanted to make a heavy wood one. Concrete seems kind of overkill but I'm sure it would work.

You could always get a large and small piece of sonotube and make a large hollow pillar. If you were really going for it you could put some studs in the existing concrete and pour onto that to tie it all in.

[hanermo]

Fwiw .. hope this helps.
I made a big heavy base/stand for a small 7x lathe.
Then rigid mounted the lathe, perfectly fit, onto the stand.

Rigid mount is important, in this context.
Perfect fit is very important, in this context.

Ie my contact points were floating, when fixed onto the lathe, and as such conformed to the lathes feet/contact points, without bending/twisting.
The feet are 120x12 mm mild steel flats, first bolted onto lathe, floating. About 50 cm / 19" long. X axis direction.
Then drilled/tapped onto second slats, identical. The second slats were spot welded, at corners. Underneath. One at a time, with cooling.
Thus, the heat does not move/distort anything, since its
1. far from contact and
2. lots of metal to absorb the heat and
3. very small spots wrt the whole size/mass.
Once cool, unbolt first feet, lathe, and then weld the bottom slats into frame.
Face/face on 120x500 mm slats is very repeatable, I guess 1-2 microns or so.
Ie the surfaces are not flat, straight, rigid or conformal.
But 6 mm bolts will repeat the registration of the face, to pretty much identical, every time, since top surface will always conform in the same way to bottom surface, over such a wide area.
A 6 mm bolt will easily bend 12 mm thick steel, to lie flat on a largish surface area.

The stand was then carefully built around these, until finally rigid enough for full finishing.

Lathe is 40 kg.
Stand is 150 kg.
120x12 mm mild steel, on its side, so the stand 120 mm thick steel slats, all around.
Flat box.
15 mm redbar, 3 of, cross welded, then heavily preloads the stand.
One end, and middle, of rebar welded into inside stand.
Then heat rebar with torch, until rebar is hot.
Then weld last ends inside box.
The cooling rebar preloads the box, by approx 1000-2000 kgf, my estimate.

The slats/mount points were fixed once the box was done.
Used a heavy 20 kg hammer drill on vibrate/no rotate, to vibrate the concrete mixture.
Had the thing face down, with a granite floor slab 30x30 cm/12" as surface, granite cast as integral part of structure.

Worked really well.
3x less noise, 3x more rigid.

[hanermo]

Second example.
I scratch built a big cnc mill, now a VMC.
Steel frame.
1600 x 500 mm (1000) work area.

The bottom was 50x50x5 mm mild steel tube. Rectangle. 2000x600 mm.
Spilt in middle with 2 inside tubes, for a box-in-box.
Cross x braced, inside. With extra Y brace in x axis direction.
Welded everything, except last corners.
Heat bracing with torch, weld last corners.
Cooling steel makes heavy 1000 kgf preload into frame.

Slap onto melamine tabletop, pour concrete onto structure. Vibrate.
When done, its == 150 kg, very rigid, wont vibrate, "sing" or twist.
About 2000 x 600 x 50 mm.

Concrete and granite is not strong, and will easily bend. But they dont crush or compress.
Thus, a strong steel structure, preloaded, filled with concrete or epoxy granite, is immensely strong, absorbs vibration very well, is easy to do, not expensive.
The melamine scrap office tabletops made the surfaces flat and pretty, and came off without any effort (not stains, even).

I made the base about 10 years ago.
Imo today. its too thin re: 50 mm, and today I would use approx. 15x150 mm F1 (a basic accurately-sized tool steel, here in Spain), on its side, rather than tube.
Or a tube 150x150/8, with a tool steel flat, welded onto it on outside. At that size, filling just the tube would likely be enough.
In a unibody the mass would be a problem, re moving it, maybe 600 kg.

The current v.3. VMC frame is now nearing completion.
New stuff is approx another 1200 kg in mass, all tool steel of 2-3 cm thickness.
Its a bridge mill, with moving y axis table.
I hope to be able to use 2-3 kW of spindle power.
Spindle is 7 kW ISO30 industrial, 7000 rpm, toolchanger.
35 mm linear guides, double on front (8 trucks, 4 rails on front).

Total mass approx 2000 kg.
Brushless AC servos, 1:3 belt drive, 0.266 microns step size, 32/4 mm ballscrews.

It is possible I may be able to use the full 7 kW of power, but anything over 500W will be enough, for my uses.
The frame rigidity is likely equivalent to most commercial stuff, today, typically C frames on vertical VMCs.
Measured rigidity pre new vertical columns was 0.05 mm / 80 kgf, or 16 N/um.
I expect to get about 0.01 mm, or 80 N/um, with new columns.
Commercial stuff design goal for machine tools is 20-70 N/um.

The machine is a tech demonstrator for commercial purposes.
Ie I sell stuff.
So no pics, at the moment, until sheetmetal, guards, chip shields etc are in place.

I plan to put a 1-3 kW servo on the spindle, so it can do rigid tapping.
Maybe with brake, for cnc broaching.

[analogman]

Thanks Hanermo, just what I was looking for.

Based on your comment "Concrete and granite is not strong, and will easily bend. But they dont crush or compress.
Thus, a strong steel structure, preloaded, filled with concrete or epoxy granite, is immensely strong, absorbs vibration very well, is easy to do, not expensive."

I am doing a similar thing. The existing steel base will used as a mold for the concrete & rebar. The stand will be bolted to the floor and the mill bolted to the stand/ It will weigh 1000lbs, but that does not bother me at all.