Molding a concrete slab to use as a base for a bench mill.

[Weldingrod1]

Fyi,granite counter top is not particularly flat or rigid. I looked into it at one point.
Casting on plastic makes crazy smooth concrete.
A layer of 1/16" plastic would guarantee your surface plates safety and still let you reproduce the flatness. Or just Visqueen sheet stuff... vacuum down for bonus points!

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[Provincial]

It seems like inexpensive machines often have bases left "as cast." If your base was not machined flat at the factory, there is little point in trying to achieve a perfectly flat top for your base.

If your base is machined flat on it's mounting surface, and you make a perfectly flat surface to mount it on, make the feet of the base adjustable so you can level the machine there and leave the mounting surfaces in full contact, with no shims.

 

[maxime.levesque]

@matthewsx , @Chipper5783 you are correct: shimming the mill on a "flat enough" surface will give the same results, with a lot less trouble, since I might end up having to shim anyways, should the concrete base end up insufficiently flat.

As a "machinist with no other purpose than to machine" (... in other words a hobby machinist...;-), I find that improving the accuracy of "budget tools" are quite interesting projects.

If the goal was to get the most accuracy and rigidity per dollar, a "real mill" (heavy second hand machine) would be cheaper and superior, but unfortunately I have the "mill must be brought in the basement" constraint, and that exclude a lot of superior (and cheaper) machines that I see on the second hand market.

So my lightweight (low rigidity, low accuracy) mill impose the initial constraints I have to work with, but that doesn't make the project less interesting.

The "crazy flat concrete base" is a component in a larger strategy to increase the rigidity: the main idea is to bolt the upper end of the mill column to the concrete basement wall, as the column is where most of the flexion occurs.

As you are probably guessing: bolting the top of the column with a rigid fixture to the wall can create serious problems if the mill itself is on a flimsy base.

A nightmare scenario resulting from such a "half genius" design be would be a sinking base with the mill holding itself to the wall by the column !

Should the base move in any direction after the column has "become one with the concrete wall", the risk of permanent deformation is quite likely.

So evidently, if the column "becomes one with the concrete wall", the base also needs to "become one with the concrete floor", which translates into a steel tube structure design for the base, strongly bolted to the wall.

An important design constraint of the fixture that links the column to the wall, is that it must not impose any movement of the column while tightening the screws, in other words it needs to adapt to the position of the column in all three axis, and not the other way around.

Even in that context, I think that your idea of just shimming is a superior alternative to obtaining a crazy flat surface (superior in that it is just as good with less effort, even if my hobbyist time is free, I prefer spending it where produces measurable results).

But I'd like to give one last chance to the "crazy flat base" idea before I discard it.

As far as I can think, a "crazy flat base" will only be beneficial *IF* (and only if) the base was co planar with the Y axis dovetail sliders after milling, and the base had distorted during transport, or as a result of stress movement in the casting. In this case, a highly planar base would correct the distortion, while shimming would maintain it.

The probability of such a "correction opportunity" seems low, and I'm not feeling the urge to put the mill on the granite to find out, so I think I will go with a "MDF board" level of flatness, and shims between the mill and the slab.

With all due respect I think you may be looking for an advantage that really won't materialize. You have a lightweight bench mill. I know that many folks get very good results with stock stands or home built stands that are no where near the flatness you are trying to achieve. Having a well built stand is definitely important but I doubt the machine you've chosen will perform any better with a precision ground, ultra flat stand.

No matter what stand you choose your leveling process will likely require shimming. Once shimmed the flatness of any stand will basically be moot. It's unlikely the bottom of your mill will be even as flat as a decent piece of Masonite so having an ultra flat surface to mount it on is probably not going to make much difference.

I could totally be wrong here, but honestly I think your efforts will be better spent getting good measuring tools to ensure the parts you make are within the spec you need.

If you really want the flattest surface possible you might be able to find a used surface plate to bolt your mill to. You could even buy a new one if you like for fairly short money.

STM 255135 | 3" Thickness x 18" Width x 24" Length Granite Inspection Surface Plate

We distribute top-quality industrial tools and machine shop supplies at the best prices. View our collection of CNC machinist supplies and tooling packages.

allindustrial.com

But, I really haven't seen anyone else trying to achieve this level of flatness for mounting a machine on. Most want to be able to adjust the mounting as needed to achieve the desired tolerances at the machine, not the base.

JMHO,

John

 

[matthewsx]

I still think effort would be better spent on actually making parts with the machine and measuring the results. If you go through this exercise before using the machine without the "crazy flat base" and attachment to the wall you won't know if you improved it, made it worse, or did neither.

Lots of folks have moved full size mills and lathes into their basements. Not knowing your situation I can't say if it would be possible or not. I suspect you will get acceptable results even with a small machine if you take the time to learn it's limits and work within them. Lots of folks do and without heroic efforts to re-engineer the base machine.

Of course, as a hobby we can all do as we please. My wish for you is to succeed in whatever endeavor you choose to pursue. Simply pointing out that to know if one has achieved a specific goal there must first be a baseline measurement to compare against.

John

 

[dabear3428]

@matthewsx , @Chipper5783 you are correct: shimming the mill on a "flat enough" surface will give the same results, with a lot less trouble, since I might end up having to shim anyways, should the concrete base end up insufficiently flat.

As a "machinist with no other purpose than to machine" (... in other words a hobby machinist...;-), I find that improving the accuracy of "budget tools" are quite interesting projects.

If the goal was to get the most accuracy and rigidity per dollar, a "real mill" (heavy second hand machine) would be cheaper and superior, but unfortunately I have the "mill must be brought in the basement" constraint, and that exclude a lot of superior (and cheaper) machines that I see on the second hand market.

So my lightweight (low rigidity, low accuracy) mill impose the initial constraints I have to work with, but that doesn't make the project less interesting.

The "crazy flat concrete base" is a component in a larger strategy to increase the rigidity: the main idea is to bolt the upper end of the mill column to the concrete basement wall, as the column is where most of the flexion occurs.

As you are probably guessing: bolting the top of the column with a rigid fixture to the wall can create serious problems if the mill itself is on a flimsy base.

A nightmare scenario resulting from such a "half genius" design be would be a sinking base with the mill holding itself to the wall by the column !

Should the base move in any direction after the column has "become one with the concrete wall", the risk of permanent deformation is quite likely.

So evidently, if the column "becomes one with the concrete wall", the base also needs to "become one with the concrete floor", which translates into a steel tube structure design for the base, strongly bolted to the wall.

An important design constraint of the fixture that links the column to the wall, is that it must not impose any movement of the column while tightening the screws, in other words it needs to adapt to the position of the column in all three axis, and not the other way around.

Even in that context, I think that your idea of just shimming is a superior alternative to obtaining a crazy flat surface (superior in that it is just as good with less effort, even if my hobbyist time is free, I prefer spending it where produces measurable results).

But I'd like to give one last chance to the "crazy flat base" idea before I discard it.

As far as I can think, a "crazy flat base" will only be beneficial *IF* (and only if) the base was co planar with the Y axis dovetail sliders after milling, and the base had distorted during transport, or as a result of stress movement in the casting. In this case, a highly planar base would correct the distortion, while shimming would maintain it.

The probability of such a "correction opportunity" seems low, and I'm not feeling the urge to put the mill on the granite to find out, so I think I will go with a "MDF board" level of flatness, and shims between the mill and the slab.

keep in mind that concrete floors and wall move with ground movement and any attempt to use the wall/floor intersection to create a solid 90 deg joint (in the specific intent of machining) is doomed.

 

[verbotenwhisky]

I just received my Weiss32B mill, and my first project will be to build a cabinet.

I want the top of the cabinet to be as planar and rigid as possible, because the casting is kind of lightweight (the whole machine weights only 240kg), and I want to avoid any source of distortion. The mill base is the same as a PM30V (same manufacturer), the base rests it's rectangular contour.

A concrete slab for the cabinet top seems like a good choice, for it's rigidity and low cost.

I happen to have 24x18 granite plate (grade A accuracy), which could be used as the base of a mold for the concrete slab, with wooden walls around it. The slab should have one face pretty close to the granite.

The challenge is to not ruin the plate ! So I want to cover it with "something", to prevent cement from touching the granite surface. I might also put a film of oil on the granite for extra safety, because I have an almost emotional attachment to the granite plate ;-)

I would like to have suggestions of covering material that is both solid enough to not puncture, and that has a consistent thickness, so I don't loose to much accuracy.

I would not use the granite plate. I would consider melamine board, set it on a solid level surface and build your form around it out of the same material reinforced. Melamine board is cheep, easy to use and will provide a flat smooth surface, we use it for epoxy layups.

 

[maxime.levesque]

I still think effort would be better spent on actually making parts with the machine and measuring the results. If you go through this exercise before using the machine without the "crazy flat base" and attachment to the wall you won't know if you improved it, made it worse, or did neither.

Lots of folks have moved full size mills and lathes into their basements.

I was lucky enough to get my hand on a well preserved Hardinge HLV, and the "descent into the basement" went much better than I thought.

It seems mills that are comparable in size and quality are much more rare, at least in my area, the "quality mills" that I see are a big step up in size.

Not knowing your situation I can't say if it would be possible or not. I suspect you will get acceptable results even with a small machine if you take the time to learn it's limits and work within them. Lots of folks do and without heroic efforts to re-engineer the base machine.

Of course, as a hobby we can all do as we please. My wish for you is to succeed in whatever endeavor you choose to pursue. Simply pointing out that to know if one has achieved a specific goal there must first be a baseline measurement to compare against.

Those are great advises, I still have much learning to do in simply achieving the potential accuracy of the mill, even before trying to improve it.

But given that I need a bench for the mill (because I chose to go DiY for it, and working on the floor is not so pleasant), I have to decide if I go "dirt cheap", I have plenty of scrap wood to build a wooden bench, or If I go with a steel tube structure with concrete slab.

What I like of the steel tube + concrete is that it is upgradable later on (because it permits wall bolting).

As far as measuring the effects of the "concrete wall assisted column", I think it is easy enough to measure, by simulating a sideway pull on the head with a rope, pulley and a weight, while I measure the flexion with a dial indicator.

 

[verbotenwhisky]

Its probably not welcome but I have talked several times about adding mass and everyone seems to think that if the mass isn't part of the machine it isn't helpful and I refuse to argue with folks that have their mind made up. In this case I will put forth my thoughts and feel welcome to comments as the question was about concrete for flatness and rigidity, that is my understanding, correct me if I am wrong. Below is a photo of our large wood lathe, it weighed 400 pounds out of the box and the first time we put a piece of wood on it that wasn't balanced it tried to walk out of the garage. Please note shelf under it which is attached to the legs, that is actually a form with 300 pounds of concrete in it and the 2 buckets are an additional 120 pounds. this added mass and lowered the Center of gravity, it changed the entire personality of the machine, now a piece of unbalanced wood just causes a bit of vibration and working the machine is far easier.



Adding mass is a worthwhile endeavor.

 

[matthewsx]

I was lucky enough to get my hand on a well preserved Hardinge HLV, and the "descent into the basement" went much better than I thought.

It seems mills that are comparable in size and quality are much more rare, at least in my area, the "quality mills" that I see are a big step up in size.



Those are great advises, I still have much learning to do in simply achieving the potential accuracy of the mill, even before trying to improve it.

But given that I need a bench for the mill (because I chose to go DiY for it, and working on the floor is not so pleasant), I have to decide if I go "dirt cheap", I have plenty of scrap wood to build a wooden bench, or If I go with a steel tube structure with concrete slab.

What I like of the steel tube + concrete is that it is upgradable later on (because it permits wall bolting).

As far as measuring the effects of the "concrete wall assisted column", I think it is easy enough to measure, by simulating a sideway pull on the head with a rope, pulley and a weight, while I measure the flexion with a dial indicator.

Nothing wrong with building a sturdy stand, most find it useful to incorporate some tool storage as well. Actually, loading the base with tools will increase mass if the machine is bolted to the stand.

Others have built concrete bases for their machines as well so you can search for their experiences here. I still think Melamine will be plenty flat/smooth enough for this purpose for reasons stated above.

As for measuring things I'll defer to the pros here, they'll be able to assist with how and why to measure the machine and parts made with it.

John

 

[matthewsx]

Its probably not welcome but I have talked several times about adding mass and everyone seems to think that if the mass isn't part of the machine it isn't helpful and I refuse to argue with folks that have their mind made up. In this case I will put forth my thoughts and feel welcome to comments as the question was about concrete for flatness and rigidity, that is my understanding, correct me if I am wrong. Below is a photo of our large wood lathe, it weighed 400 pounds out of the box and the first time we put a piece of wood on it that wasn't balanced it tried to walk out of the garage. Please note shelf under it which is attached to the legs, that is actually a form with 300 pounds of concrete in it and the 2 buckets are an additional 120 pounds. this added mass and lowered the Center of gravity, it changed the entire personality of the machine, now a piece of unbalanced wood just causes a bit of vibration and working the machine is far easier.

View attachment 485285

Adding mass is a worthwhile endeavor.

Actually, that is part of the machine since it's bolted to the base.