Concrete workbench slab for mill attempt

[WestVinTools]

Ok. So I'm hoping this will add some rigidity to my newly acquired Craftex cx601 to sit on top of this concrete slab on my workbench. If not, it looks pretty beefy sitting on top of that HSS tubing frame.

I had no intention of doing this until after I bought the mill but I figured it would be a good spot for it, and my granite surface plate on the other side.

Anyone (everyone ) think concrete top base might be overkill or a waste of effort, or no impact at all? It's 22"x22"X3" thick.

 

[DavidR8]

Holy stout! Should be fine.
How are you going to attach the mill to the slab?

 

[WestVinTools]

Holy stout! Should be fine.
How are you going to attach the mill to the slab?

Thanks ....I'm planning on drilling holes and either through bolt through the slab or epoxy the bolts into the slab. I'm leaning towards the epoxy route.

 

[YYCHM]

Thanks ....I'm planning on drilling holes and either through bolt through the slab or epoxy the bolts into the slab. I'm leaning towards the epoxy route.

Why not anchor bolts?

 

[PeterT]

I think that's a fantastic idea. Let us know how you make out with running the machine. I've read of some success stories where people have filled metal shell CNC routers frames with epoxy/concrete & it quieted the machine down substantially. I've also seen molds where people cast the locating/fastening hardware in at the time of pouring the pad. Maybe not so convenient with a heavy machine though. But I think integrating them with backfill epoxy concrete grout adhesive or similar would be fine. Give you a bit of wiggle room too so it matches the tie down points.

 

[Mcgyver]

don't know if the concrete slab with do much, but filling the HSS with epoxy granite (basically sand and epoxy) will. Its reputed to have twice the vibration damping properties of cast iron and while a lot weaker than steel it will still add some rigidity. Vibration damping comes from the boundray layer of disimilar materials - you get a lot of that with epoxy granite and its tried and true machine base filler (its what Harcrete is for example)

 

[PeterT]

That's a good point you make. I assumed the epoxy binder was more about bonding the grains together, accommodating irregular shapes & thicknesses, good strength properties, minimal cure shrinkage etc. But I can see how it would benefit vibration dampening because its wetting the grains & occupying the microscopic void space between them. Maybe kind of like millions of microscopic shock absorbers within an overall rigid silica matrix.

 

[DPittman]

I made a 8" concrete anchor block for my drill press both for height and for weight. I used concrete epoxy to glue in anchor bolts. The epoxy allows for some allowance on hole size and alignment and seems to hold like ever.

 

[Tom Kitta]

Yes concrete does dampen things - this is why under large machines you may have a huge block of it.
https://blog.reitz-natursteintechni...anical-engineering-five-convincing-properties

I think we are going to see more of "castable" raisin based machines. These are still a bit expensive - remember you need far more raisin as it is weaker then cast iron. I also expect more reinforced raisin.

Note that regular cast iron is only 50% better at dampening then plain steel.

 

[Mcgyver]

Note that regular cast iron is only 50% better at dampening

perhaps, but hopefully its about 2x the damping

I recall a study analyzing the decay of a wave through different materials. That's my recolection of it, CI is 2x as good as steel and EG 2x better than cast iron. Where did you get the 50% from?

 

[Tom Kitta]

I got it from the link in my post.

Note that not all concrete / cast iron / steel are the same. There are tolerances for both.

I also have this https://sites.utexas.edu/taleff/files/2019/10/jmatersci_v28n9y1993p2395.pdf

Here steels are medium dampening and most cast irons are in high. Mg alloys are very dampening. Also strange things, like carbon or organic glass.

Avoid Brass / Bronze / most AL. Except 6061 - T9 - that seems to be better then most cast stuff. If making a machine from AL try to use 6061-T6

 

[Tomc938]

I'm wondering how sand would work? I had an old wood lathe that had a cavity in the base that was sand filled. Would it turn the base into a large dead blow hammer? Only instead of driving the hammer forward without bounce, it would remove the bounce/ vibration it is exposed to. I know sand will disburse the power of a bullet. (don't ask how old I was when I learned this, or how I tested)

If you needed to move the base a few minutes with a shop vac and your ballast was removed.

 

[Tom O]

The sand would hold moisture

 

[Tomc938]

Probably true. Didn't think of that. Although I live on Vancouver Island, about a mile from the ocean, and after 15 years there was no sign of rust. And lathe was in an unheated attached garage.

I wonder about a cement base with a hollow core that would be sand filled before the bottom was closed up.

 

[Mcgyver]

isn't sand used in those expensive wood lathes, Oneways? It would add mass and absorb energy as you describe, just not as effectively as EG....its the boundary layer between dissimilar materials that does the damping.

There is a chap in NZ who made a concrete lathe bench, loves it. The downside I see is that concrete keeps moving it - it keeps curing and moving for a very long time. Then again that may be fretting about nothing.... even with a cast iron stand or cast iron base.....its still on a concrete slab that keeps moving about

The bagged sand you buy at the big box store should be dried, if its a concern. if the arrangement was sealed it might keep it that way....then again why would the moisture in the sand be much more than the ambient in the air?

 

[historicalarms]

I never thought it would be of interest before but seems it is.

I have a buddy that owns a machine shop with some very big machines in it (two of the biggest lathes and mills in North America) that came from a shipbuilding yard in Germany (some of you may remember the photos from an earlier thread on here). I was in the shop before the floors were poured and there was an 10' deep trough under where each machine would sit. Kerry said that this was "as per previous owners advise" he was told to install 4 ft of compacted gravel and then cover with 4-6 ft of concrete for machines to sit on...my comment was "damn those things must be heavy, especially when loaded with work"...Kerry's reply was "ya, partly for that but also very important as a dampening use"....so I guess there is relevance to everything in this thread

 

[YYCHM]

I have a buddy that owns a machine shop with some very big machines in it (two of the biggest lathes and mills in North America) that came from a shipbuilding yard in Germany (some of you may remember the photos from an earlier thread on here)

Hey Doug, do you recollect the thread those photos were posted in? I can't seem to find them.

Craig

 

[combustable herbage]

Was it this one?
Skoda Sr200 | Canadian Hobby Metal Workers & Machinists

 

[YYCHM]

Was it this one?
Skoda Sr200 | Canadian Hobby Metal Workers & Machinists

Nope...

 

[historicalarms]

I think I forwarded the photo's to johnnielson and he initiated the thread , probably 3 yrs ago now, just before a get-together at a Timmies just south of Blackfoot.