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View Full Version : Building lathe support. Torsional stiffness

AlexK
05-23-2010, 03:34 PM
This is my lathe PM1236 (http://www.machinetoolonline.com/sitebuilder/images/PM1236_005-402x329.jpg)
http://www.machinetoolonline.com/sitebuilder/images/PM1236_005-402x329.jpg

The stand is flimsy and lathe essentially sits on top of two stands that connected by thin metal sheet.
I've bought a 9 x 25.4 steel channel that I'll put on top of cabinets to add stiffness/rigidity.
I know that closed shape(tubes) provides much more torsional stiffness.
Here is my question.
Should I consider welding a steel plate on the channel to make it into a rectangular tube? How much stiffness do I gain? Is it worth the efforts?
I don't have a welder. I'll have to pay someone to do the welding. What if instead of welding I build bolted webbing in the channel to increase stiffness and weight?

Here is the specs for my MC 9 x 25.4 channel.
http://www.tmtco.com/images/products/channels.gif
A = 9"
B = 3.5"
C = 0.45"

Any suggestion is welcome except this one: "Your lathe is stiff enough as is, stop screwing around"
For years I've been suffering :) from underweight, flexing and vibrating anorexic machinery and I'd rather overbuild than have a chance of having machine flex and vibrate under the load.

winchman
05-23-2010, 06:45 PM
It depends on how you plan to arrange the pieces of channel, and "...I'll put on top of cabinets..." doesn't really tell us much.

I'm guessing you are going to put two lengths side by side from one end to the other. That won't get you a whole lot of rigidity unless they're welded and boxed, but the extra mass will probably do a lot to steady the lathe while it's running.

Do you really want the lathe 3.5" higher than it is now? That seems rather high for working comfort.

The best approach is some sort of framework that goes between the base of the lathe and the floor. Welded is better than bolted. The cabinets themselves could fit inside the framework, but most of the sheet metal wouldn't be used.

The stand for my lathe is made of 2" x 1/4" angle welded into a framework that's 24" deep 44" long and 30" tall. It's so rigid that it will rock on uneven concrete with the 700-pound lathe on top and at least a hundred pounds of tooling inside the cabinets. I have to put shims under the legs to level it and keep it from rocking.

The Artful Bodger
05-23-2010, 07:05 PM
Hi Alex

I have a lathe which is a twin of yours and I agree it needs more stiffness, mine will twist the bed under its own weight, according to my level.

The cabinets are rather light weight but being welded boxes they are actually quite stiffer than they might appear, IMHO.

I suggest the channel steel be at floor level and well bolted to join the cabinets, my lathe is off the floor a little and the working height is just right for me, 5'11".

John

sidneyt
05-23-2010, 07:35 PM
I own a HF 12 x 36 that has the two stand arrangement like yours. IF you really want to stiffen it up, bolt the stand(s) to the floor.

http://i218.photobucket.com/albums/cc123/philt214/Lathe/8c24.jpg

I cast concrete pads to raise the height of the lathe, but this is not necessary. You can use Red-Heads or similar directly into a concrete floor. Actually, I only bolted the headstock, but that was more than sufficient to stiffen up the stand and lathe. If I were doing it again I would probably bolt down the tailstock also, but it is tricky to get the stands aligned so the bolts fit. I have read complaints before about the stands that are used with this class of lathe, but my experience is that the stands are more than stiff enough if you attach them to something solid like the floor.

http://i218.photobucket.com/albums/cc123/philt214/Lathe/44ea.jpg

AlexK
05-23-2010, 08:04 PM
Sidneyt,

what kind of cement do you use for the base?
The floor in my garage has a slope so I was planning to pour a 2"-3" high base for the lathe anyway.
Because of the sloped floor I'll have make the cement base extending to where the operator will stand.
Otherwise it'll be awkward to stand on the sloped floor while working on leveled lathe.

darryl
05-23-2010, 09:29 PM
If you welded a plate to the channel to box it, that will add more torsional rigidity than doing the webbing. You don't have to have weld all the way along, just do the ends and spot in several places between.

I was in a store the other day and noticed there was a wider range of premixed cement products than there has been before. One of those was a low shrinkage mixture. Why not fill the channel with that- after the plate has been welded on of course. Won't take much cement, and it will be even stiffer afterwards.

I never did like those metal stands. My inclination would be to build my own, and that's what I've done for virtually every machine I have. The only machine that's still on the supplied stand is the belt sander. It doesn't need to be any better than it is, so I didn't bother.

If you were willing to pay for some materials and welding, you could always make up a triangular box beam and fill that with cement. Make the three sides the same width, and wide enough so that what becomes the top plate has enough room to mount some studs to which you can bolt the lathe. Attach all hardware that you would find useful for other things, such as a back splash, or electrical boxes- whatever- before filling it with cement. You might also add some anchors to both ends of the box to give a way to mount legs. You'll end up with a lot more rigid and vibration absorbing structure, and nothing says you can't add storage shelves or drawers underneath that.

The Artful Bodger
05-23-2010, 09:41 PM
I own a HF 12 x 36 that has the two stand arrangement like yours. IF you really want to stiffen it up, bolt the stand(s) to the floor.

Hi Sidneyt, we will be moving to a new place soon and I intend to do something like you have done. Are the concrete pads bonded to the floor?

John

Evan
05-24-2010, 12:48 AM
Should I consider welding a steel plate on the channel to make it into a rectangular tube? How much stiffness do I gain? Is it worth the efforts?

The difference is extreme. I think I will do a little demonstration. Back in a while with some pictures.

JoeFin
05-24-2010, 12:54 AM
Sidneyt,

what kind of cement do you use for the base?
The floor in my garage has a slope so I was planning to pour a 2"-3" high base for the lathe anyway.

Just make sure your minimum thickness is 2" any where in the pad. Be sure to "Pummel" the existing concrete and throw in a couple pieces of rod bent over into the new pad so it sticks.

Of course if your really good at concrete you can always embed a couple pieces of C-channel flat side up where your legs are going to set. That way you can use leveling pads and the screw adjustments, and when the ground shakes as it tends to do in California your lathe can give (move) rather then absorb

Evan
05-24-2010, 01:31 AM
Here is a twist comparison of two different aluminum sections. The first is a 2x2 inch H beam and the second is a 1 x 1" square aluminum tube. The total material is much greater in the H beam but the H beam isn't a closed shape.

The H beam deflects about 1 inch at the end of the lever arm.

http://ixian.ca/pics7/torquetest1.jpg

http://ixian.ca/pics7/torquetest2.jpg

The square tube deflects about 0.1" at the end of the lever arm.

http://ixian.ca/pics7/torquetest3.jpg

http://ixian.ca/pics7/torquetest4.jpg

MuellerNick
05-24-2010, 02:22 AM
Simply put:
You can't stiffen the bed with just two tubes that you put on top of your feet.
The easiest way is if your floor is a 3" slab of concrete. Bolt your lathe dwon at every hole (there should be 6) it has. This way, you can twist and even bend your bed in any desired direction.

If your floor isn't heavy enough, you have to weld something that has torsional stiffness. I welded something for a friend. In the middle was an I-beam that was closed with two C-channels (left and right). That was as wide as the bed and a bit longer.

Whatever you weld, it has to be stiffer or at least as stiff as the bed itself.
If you take the bolt-down-route, check inside those cabinets, re-weld them (you'll find a few tack welds) and reinforce them. I did that, and it made a huge difference.

Nick

AlexK
05-24-2010, 02:37 AM
Here is a twist comparison of two different aluminum sections....

Evan,

thank you for the demonstration. It is very convincing.

sidneyt
05-24-2010, 07:56 AM
I used Sakcrete that I purchased at HD to cast the pads. It was not necessary to prepare the concrete floor so that the pads stayed in place (OTOH, if I ever need to remove the pads I may have a problem). I had previously poured a pad for my mill/drill stand using 2 x 4s as forms so I knew this would work. For the headstock end of the lathe stand I used cardboard tubes in the form positioned using the lathe base to make the holes for the 1/2" studs that I cemented into place. I used Sakcrete Anchor cement to secure the bolts in the pad.

http://i218.photobucket.com/albums/cc123/philt214/Lathe/65bf.jpg

I used standard levelers on the tailstock end of the lathe.

AlexK
05-24-2010, 11:53 AM
The area that I'll be pouring concrete has 4" difference in height due to slope. Do I need to drill existing concrete and insert some rebars so there is good connection between old and new concrete?

darryl
05-24-2010, 02:13 PM
Alex, if you have a minimum thickness of concrete at the thin end of your pour, say 2-3 inches, then you won't really need to anchor that to the existing floor. Put some steel mesh into the center of your pour to help keep it an integral 'chunk', and paint the existing floor with a somewhat diluted solution of white glue before casting the new concrete. I was told that and found it a bit hard to believe, but it does work.

Because concrete continues to cure with time, it would be best to leave it untouched for several days before you put weight or stresses on it.

I don't know what you're thinking to make the form of, but you might also consider leaving it in place. Call it a kick plate or whatever- just make it look decent and be done with it.

AlexK
05-24-2010, 03:11 PM
I am planning to use plywood to make a form.
BTW How do you do rounded internal corners in the form?

Evan
05-24-2010, 03:17 PM
Use cove molding.

The Artful Bodger
05-24-2010, 04:37 PM
..... a somewhat diluted solution of white glue before casting the new concrete. I was told that and found it a bit hard to believe, but it does work.

Yes, I can confirm that.

rohart
05-24-2010, 05:05 PM
One way of "seeing" the reduced torsional rigidity of the open channel compared to the box-section is to think of one end of a twisted open section being no longer flat, one free side of the channel having moved lengthwise compared to the other. The plate welded on will stop the free sides from moving like this, taking it in shear.

But what I really wanted to say was this, and I'm not suggesting not doing the project. If the floor is not flat, then once you make the table rigid you may find the whole caboodle rocks about two diagonally opposite corners. Or worse, each end pillar does so independently. You'd better prepare yourself for having to make up shims or adjustable feet or you'll have swapped vibration for rocking !

If your gripe is really about flimsyness and vibration, then the concrete fill may be best, because it may be the extra weight that solves your problem. That solution would make it much harder to mount the channel to anything though - no through bolts.

The wooden bench I have my lathe on has grown so heavy with its supports, its drawers and everything that I do appreciate the weight. I often find that the bolts that hold the lathe down have spun loose, but I figure if it's turning straight it's better to have no bolts than for the lathe to be held down into a twist.

darryl
05-24-2010, 07:12 PM
Another way to visualize the low resistance to twisting of any non-boxed shape is to roll a piece of sheet metal into a tube. As you twist on that tube you'll see the mating edges sliding past one another. Resistance to twisting would then be enhanced if you could prevent that relative motion. Angle and channel are examples of shapes where that relative motion is not restrained at all, except where you might weld something across their edges.

It gets a bit hazy for me here, but it could be that the three sided tube is more torsionally rigid than a four sided tube for the same weight of material. Of course the four sided tube is easier to work with for bolting, drilling, and general fabrication. Welding a plate across the 'legs' of channel gives you an even more useful structural element, since you can make that plate wider than the channel and thus be able to use the flanges to bolt to.

micrometer50
05-24-2010, 08:20 PM
Another way to stiffen your lathe it epoxy concrete.

AlexK
05-24-2010, 11:18 PM
Another way to stiffen your lathe it epoxy concrete.
Do you mean building a thick heavy "top" that goes on top of cabinets?

darryl
05-25-2010, 03:27 PM
'a thick heavy top'- I don't think one made from epoxy or epoxy/granite is going to be rigid enough. If one were to layer enough sheets of fiberglass cloth and mat to build up say an inch or so, then maybe there would be a significant rigidity to help, but that gets expensive in a hurry. And you could still flex it considerably. Might as well start with a large enough surface plate and secure some mounting tabs to it to bolt the bed to.

In my opinion, if it's rigidity you want, start with a torsion tube of some kind, like heavy wall square tubing. If it's mass, then fill that with concrete, or go with a piece of steel plate. Remember though- a steel plate will have a resonant frequency, and if that happens to coincide with another machine resonance you could have another problem. Plus, you don't know that this plate will actually be flat. It probably will have some warp however small, and this might even change over time. Regardless of what method you use, you'd still want to be able to separately adjust each lathe mounting bolt. You do need to be able to do an alignment after all, and no type of stand or mounting arrangement is going to be able to ensure that for you on its own.

I don't know what you could do with a lathe bed and epoxy, except to close off the bottom of the bed, then fill it with granite/epoxy to a workable level. I think this would make an improvement, but besides the expense it might interfere with the headstock mounting bolts or other things.

Depending on the lathe you might be able to cast in a central support column under the bed at about the halfway point, and include say two of the webs within this casting. Could use either granite/epoxy for this, or concrete, but basically you'd be making just another support for the bed, and it would have to bolt to the stand in the same way as the other mounting areas. The stand still becomes an important part of the total structure.

If the goal is to increase the rigidity of the bed, then bolt it to a torsion structure, whether you add the center support column or not, then carry the whole thing on legs which you can adjust. If you're going to bolt the 'stand' to the floor, that changes things a bit since you can then use the floor as a constrainment mechanism, but if the stand is expected to just sit on the floor plus add rigidity to the lathe, it needs to be very substantially built and not just some sheet metal door holders like many of them seem to be. Again, this is my opinion only, but I'd rather build a stand from scratch to include the strength, mass, and rigidity, rather than try to improve an existing stand which would probably result is some other compromises along the way.

Bguns
05-25-2010, 04:11 PM
A new stand from scratch would be best.

They cheaped out on tailstock quill/ram diameter on the PM1236. Barely bigger than the morse taper hole.... it's 40 mm diameter on my green 12 x 36... Still not a Monarch or Pacemaker...

A big issue there... almost all long work will be between centers.

Spindle brake is nice though. It will complicate stand build a little.

macona
05-25-2010, 04:32 PM
You might check out this thread:

http://www.practicalmachinist.com/vb/south-bend-lathes/concrete-lathe-bench-top-130222/

The entire stand is replaces with a concrete stand.

-Jerry

The Artful Bodger
05-25-2010, 05:07 PM
There are a lot of places concrete could be added to that lathe, fill the bed, pour a pad the same size as the drip tray and put that on top of the stands, fill the stands with concrete, pour a slab at floor level and bolt everything down, all of the above and weld the gap filler in place for good measure!:rolleyes:

rohart
05-25-2010, 05:09 PM
Alex - you've bought a length of 9 inch channel. You don't weld, so you'll be charged by the inch.

Your lathe bed is wider than 9 inches. More like 15 inches ?

This is what I'd be thinking about.

Go buy another length of the same 9 inch channel. Have the two lengths welded together, and the top of the channel closed, by two plates of 1/4 inch say 20" x 8", one at either end - use 3/8 if you want. This whole lot goes open section down under the lathe, with a 1/4" plywood or MDF platen in between to act as the bench surface. Pop in a 1/16" coolant tray here if you like, or add one later.

Build a bench with drawers for this lot to go on top of out of wood. Either 4x4s at the corners, or diagonally braced 4x2s. The weight of the two channels will hold the wooden bench solid as a rock, and act as a solid bed for the lathe to sit on. You'll hardly need to snug up the lathe's mounting bolts after shimming.

I just don't like trying to use the channel as a torsional stiffener alone. You're going to spend more time than it's worth trying to connect your torsion member to the rest of your supports, and you still won't be satisfied.

philbur
05-25-2010, 05:43 PM
Look at the channel you plan to use and then look at the lathe bed cross-section and decide what you think that channel will add.

I think you are mixing two issues here.

Issue 1: machine flex.
Issue 2: Stand vibration.

Machine flex: The lathe bed is sufficiently stiff as is. The earth is sufficiently stiff as is. The stand connects your lathe bed to the earth and may not be stiff enough for the job. So you need to add vertical structure to the stand not horizontal support to the bed.

Stand vibration: If this is the problem then it will most likely be due to the thin sheet metal of the stand. However if you have added vertical structure to the stand connecting the bottom of the bed directly to the earth it will effectively no longer be sitting on the stand so vibration should no longer be a problem. If it still vibrates then fill each leg with sand.

Alternatively throw the stand away and sit the lathe bed on two concrete towers or massive frabricated steel structures (filled with sand).

Concrete doesn't add much in stiffness unless you use really massive cross-sections (if you don't believe me look up the modulus of elasticity). Sand will give more easily achieved damping than concrete (it's self adjusting to maintain contact with that pesky sheet metal) and it's easier to apply and to remove later if/when necessary.

Just a few thoughts
Phil:)

Any suggestion is welcome except this one: "Your lathe is stiff enough as is, stop screwing around"
For years I've been suffering :) from underweight, flexing and vibrating anorexic machinery and I'd rather overbuild than have a chance of having machine flex and vibrate under the load.

darryl
05-25-2010, 06:52 PM
A few months ago I was considering a design for a sort of gantry mill, not a large one by any means, but still solid. The gantry travel would have been about 3 ft, which put the length of the bed at about 4 ft. Width wise it could have been about 12-16 inches. What I figured to do was lay 6 pieces of 2x3 square tubing, 3/16 wall, side by side with the 3 inch dimension vertical (thus giving 1 foot width) then laying a piece of 1/4 inch plate across the top and bottom of that. That sandwich structure would be fabricated using the surface plate to give the initial alignment to the assembly. I would have used epoxy and lots of flat head bolts to assemble it.

This assembly would then have been 3 1/2 inches thick, with a top and bottom metal thickness of 7/16. Two properly spaced cross members would be attached at the bottom for the leg structure, and at this point at least one of those crossmembers would have a pivot point where the legs could swing a bit. This would be to allow this bed structure to maintain its flatness, while the legs could all be touching the floor. In fact, both crossmembers could be made to allow the legs to swivel a bit, then the base unit could be levelled front to back quite easily. A wooden storage cabinet could be made to fit between the legs, and this would serve to keep the machine from buckling over sideways.

The rest of that design is irrelevant to this discussion. Basically though, this is an outline for a very rigid base unit using available materials and buildable using minimal common machinery in the shop. In my case, this would have been a machine bed, but it would also serve to mount a lathe onto. In fact for a lathe stiffener, it wouldn't even need to be particularly flat. You'd still level the lathe by adjusting shims, etc. anyway. You could still fill the tubes with something like cement for that extra solidity, and if you wanted to nothing stops you from using sand either for its damping properties.

To make a comparison, AlexK has some channel, and if a plate was welded across the open side it would basically be this structure I'm talking about, just simpler. You need legs, and the legs have to be braced, but you don't really need the 'stand' as they are commonly built. You don't 'need' vertical columns filled with cement or sand. All you really need is this solid 'ironing board' base.

The Artful Bodger
05-25-2010, 07:11 PM
All you really need is this solid 'ironing board' base.
A thick concrete chip tray?:cool:

However, for that particular lathe I really think it need either bolting the stands to the floor or some other way of increasing the footprint, if you have something heavy spinning in the chuck and you tromp on the spindle brake it almost topples forwards on to the operator.

philbur
05-25-2010, 07:51 PM
Yes but he already has a (stiff) lathe bed. Compare the cross section of the lathe bed with a top quality lathe of the same size. I doubt there is much in it. If I sit a stiff "ironing board" base on a jelly what do I have. The stand is the jelly in the sandwich. You either get rid of the jelly or you stiffen it up.

Phil:)

To make a comparison, AlexK has some channel, and if a plate was welded across the open side it would basically be this structure I'm talking about, just simpler. You need legs, and the legs have to be braced, but you don't really need the 'stand' as they are commonly built. You don't 'need' vertical columns filled with cement or sand. All you really need is this solid 'ironing board' base.

MuellerNick
05-26-2010, 04:20 AM
Yes but he already has a (stiff) lathe bed.

Believe me, that bed is not stiff. You'll discover as soon as you level it. As soon as you lean against the lathe, the bed will twist. Measure, don't guess!

Since about a century, lathes relied upon either massive beds (that still had to be twisted and adjusted by screws in the feet or by bolting the feet down into some heavy concrete slab.

That tin can cabinet is not suited for bolting down nor for adjusting the twist by weight.

If he doesn't want to take the bolt-down route, all he can do is add an additional stiffener to the bed. If you add something, that is at about as stiff as the bed, the result won't be double the stiffness, but more! It depends on how far away the added structure is from the bed's neutral axis.
The only problem with the added stiffener is, that adjusting it (getting out the twist) will be a pain. Shiming, measuring, disassembling several times. The resulting structure has to be connected to the cabinet by only 3 points, so the cabinet doesn't twist the structure again.

My Haas TL-2 (2.1 tonnes) twists by its own weight more than 0.2 mm / m.

Nick

jackary
05-26-2010, 05:14 AM
On a smaller scale I believe that the overarm connecting the headstock to the bed adds much to the overall torsional stiffness on my Stepperhead lathe.
Alan

Evan
05-26-2010, 08:17 AM
The lathe bed is sufficiently stiff as is.

For a change Nick and I agree. No chance that lathe is as stiff as it could/should be. The net shipping weight of that lathe is 1250 lbs. That includes chip tray, splash guard, enclosures, 2 chucks and a face plate, cabinet stand and various tooling. It's a 12 inch swing x 36 lathe. The shipping weight of my 9" South Bend was 450 lbs and it included nothing but a centre turning dog, everything was optional. I would guess that on a size normalized comparison that the South Bend has twice the amount of material in the bed per inch of length when you consider that volume increases by the cube as area increases by the square.

philbur
05-26-2010, 08:31 AM
Everything deflects under load so perhaps I should have qualified the term "stiff". The lathe bed is stiff in comparison to the stand and is stiff in comparison to his proposed channel stiffeners. The smaller the machine tool the greater is the ability to support its own weight. That's why small lathes are acceptable with cantilever bed design, where as a large long bed lathe can effectively behave like a piece of wet spaghetti and needs multiple supports along its length.

I think we are all agreed the essence of the problem is the stand, not the lathe. So he needs to sort out the stand, not try to compensate for a crap stand by adding something to the bed. As you point out the accepted solution for the past 100 years has been a massive stand or a bolt down. What's changed in this particular case? No matter what he adds to the bottom of the bed it's still going to be sitting on a crap, jelly stand. Also by correcting the stand he can then also use it to provide added stiffness to the bed. For improved stiffness cross-section is everything.

In the end it depends on whether he wants to do something that is simple or something that works.

Phil:)

Believe me, that bed is not stiff. You'll discover as soon as you level it. As soon as you lean against the lathe, the bed will twist. Measure, don't guess!

Since about a century, lathes relied upon either massive beds (that still had to be twisted and adjusted by screws in the feet or by bolting the feet down into some heavy concrete slab.

That tin can cabinet is not suited for bolting down nor for adjusting the twist by weight.

If he doesn't want to take the bolt-down route, all he can do is add an additional stiffener to the bed. If you add something, that is at about as stiff as the bed, the result won't be double the stiffness, but more! It depends on how far away the added structure is from the bed's neutral axis.
The only problem with the added stiffener is, that adjusting it (getting out the twist) will be a pain. Shiming, measuring, disassembling several times. The resulting structure has to be connected to the cabinet by only 3 points, so the cabinet doesn't twist the structure again.

My Haas TL-2 (2.1 tonnes) twists by its own weight more than 0.2 mm / m.

Nick

Racebrewer
05-26-2010, 01:04 PM
Hi,

How about building a triangular cross section truss into the cabinet using the two sections of channel bolted to the lathe as two of the three long beams of the truss?

I'm leaving now.............

John

Rex
05-26-2010, 01:44 PM
Back to the original post, I bought a small lathe a few years ago that came with a shop-built stand. It used a 48" X 15" section of steel C-Channel, approximately 3/8" thick. That was welded to 2 4x4 square tube heavy wall uprights, with horizontals welded to the bottom. That makes for one stout and stable mounting surface. I sold the lathe, kept the stand.

I think that stuff makes a great basis for a lathe mount. It would be nice to have it milled or ground flat before use.

AlexK
05-26-2010, 03:10 PM
If you closely look at the middle of the frame of my lathe it is apparent that it can not be stiff. There is just not enough meat in it. You might even feel an urge to put some support in the middle or it'll break in the middle under it's own weight.
From posting on other forum I've discovered that other owners of this lathe don't feel comfortable to lift it by the eye attached in the center of the mass. They worried that it will get severely bended or even break in half. :)

In my metal turning class I was using a little bit larger LeBlond. It had probably 4 times as much structure. Not even mentioning it's stand.

philbur
05-26-2010, 04:20 PM
In your first post you state: "For years I've been suffering from underweight, flexing and vibrating anorexic machinery". It seems you have bought you way into more years of underweight, flexing and vibrating anorexic machinery. If you are unhappy with the stiffness of the bed of your new lathe then possibly you bought the wrong lathe. You should have bought a used Southbend or LeBlond:o

Evan's opinion on lathe bed design should be treated with a little caution. He built a lathe with a wooden bed:eek:

Once again the correct approach is a massive stand or bolt it to the ground via a more rigid structure. If you don't have a welder then fill both columns with cement, bolt the bed direct to the cement and the stand direct to the ground. If it makes you happy bolt some additional structure between the two stand columns. You can do this in stages untill you are happy. If you just stiffen the bed it will still be sitting on a jelly.

Phil:)

The Artful Bodger
05-26-2010, 04:46 PM
I think we are all agreed the essence of the problem is the stand, not the lathe.

The stands are about 15" boxs welded from 3mm steel, at least they would be boxs if they did not have the doors in them.

Weld 3mm plate where the doors are and fill the things with concrete.:rolleyes:

The Artful Bodger
05-26-2010, 04:56 PM
Meanwhile :-

http://farm3.static.flickr.com/2541/3822189664_39d66036dd_o.gif

My lathe of the same family is bolted to 4 bits of 4x4 which stop it toppling over and brings it up to the height I prefer.

My Czech machinists level says the bed is not twisted and I seem to be able to make parts that fit each other.

Further than that I do not have the experience to comment.;)

[Hmmm... they might actually be 4x3s!]

Evan
05-26-2010, 06:58 PM
Evan's opinion on lathe bed design should be treated with a little caution. He built a lathe with a wooden bed

Just so newcomers don't get the wrong impression here is the lathe with the "wooden bed".

Note also that the bench it sits on is not in the slightest rigid and contributes nothing at all to the rigidity of the lathe. It isn't even bolted down. The cast iron it is cutting isn't gray but tending much more toward white, meaning it is very hard. The wood in question is one of the hardest there is and must be milled, drilled and tapped just like metal.

http://ixian.ca/pics7/ixlathe22.jpg

http://ixian.ca/pics7/ixlathe23.jpg

Stiffening the bed will produce the most improvement for the least amount of money and time spent.

J Tiers
05-26-2010, 11:19 PM
I will admit to being a little puzzled......

OK you said

Any suggestion is welcome except this one: "Your lathe is stiff enough as is, stop screwing around"

We are on our second page and so it's time to ask teh question, and maybe say "Your lathe is stiff enough as is, stop screwing around".............

Looking at the picture, I see a lathe with what appears to be a deep and 'chunky" bed, a bed which one would expect to be rather stiff in and of itself..... You might expect it to be stiff enough to sit on 3 points like a 10EE.....

If so, the cabinet of 1/8" steel should be almost irrelevant. Lots of people are using Atlas lathes with a bed depth maybe 1/3 of that, and a width at most 3/5 of that.... meaning much less stiff.

if you are having problems with chatter and so forth, maybe it is not the lathe bed or support....... could be fit of parts, choice of tooling, work support, etc.

If you are NOT having a specific problem, why worry?

Any answer is acceptable EXCEPT "just because I can and it's none of your business if I do"....... (on principle of what's sauce for the goose.........)

Evan
05-26-2010, 11:34 PM
Jerry,

The weight of the lathe tells the story. It just isn't heavy enough to have enough metal in the bed to be "rigid enough".

S_J_H
05-26-2010, 11:36 PM
Nice pic Evan. I think that is one of the reasons you built it, that is to face or turn much larger parts than your SB9. Looks like it is working well for you.

I have always admired the design of my Old Artisan 11x24's bed.
The bed is a massive anvil like form. I can move the lathe all over the place in my shop and the bed never seems to twist even a little. The stand is cast iron with tension rods. The machine is heavier for sure than my SB9A. A good 500lbs or so I would guess and most of it is in the bed.
It'll face a 18" disk in it's gap like Evan shows on his lathe with no troubles. It's an odd one for sure, but I really love this machine.
Steve
http://i109.photobucket.com/albums/n48/S_J_H/vintage%20Artisan%20lathe/Artisanlathe007.jpg
http://i109.photobucket.com/albums/n48/S_J_H/vintage%20Artisan%20lathe/Artisanlathe006.jpg
http://i109.photobucket.com/albums/n48/S_J_H/vintage%20Artisan%20lathe/restoredArtisanlathe006.jpg

The Artful Bodger
05-27-2010, 12:28 AM
Jerry,

The weight of the lathe tells the story. It just isn't heavy enough to have enough metal in the bed to be "rigid enough".

Arrrh.... I do not think that is true. You have already demonstrated how the torsion stiffness of an object relies as much on its cross section as on the weight of material used.

Rich Carlstedt
05-27-2010, 12:39 AM
Years ago, my Mentor had a bench model Southbend that was so incredibly smooth and vibration free, that I thought it was "One of a thousand".
You could hold cuts to wiskers..It was a joy to run
When he passed, I found out that he had placed a 2 foot by 4 foot plate of steel 2 inches thick under the plywood bench top. This 600 pounds or so made a huge difference in rigidity and smoothness. and is easy to do.
Rich

J Tiers
05-27-2010, 08:49 AM
Jerry,

The weight of the lathe tells the story. It just isn't heavy enough to have enough metal in the bed to be "rigid enough".

Possibly, possibly not.

1) As you of all people should know, the size (outside dimensions) and geometry have quite a lot more to do with stiffness than pure mass of material. The same mass can be in a flexible shape or a stiff one.

2) that bed appears to be deep, and is wider than an S-B or Atlas by quite some margin.

3)if 1250 lb is nowhere near sufficient, then your wood-bed lathe is useless....... which you have shown is not true.....

4) 1250 lb is the weight of several Atlas machines, and the deep-bed geometry is going to make it a lot stiffer than the shallow, thin, and bouncy beds of a Southbend or Atlas. The basic stiffness of that bed should be at least 8 x more than any of the small-shop S-B other than the industrial series. probably 16x or more stiffer than an Atlas, with NO support from the base.

If 1250lb of machine are the new "9 x 20", then apparently I have strayed into the wrong forum, this must be the "Monarch" forum on PM...........

Feh...........

When he passed, I found out that he had placed a 2 foot by 4 foot plate of steel 2 inches thick under the plywood bench top. This 600 pounds or so made a huge difference in rigidity and smoothness. and is easy to do.

not sure it was all the weight, although with plywood between, it was as much more rigid...... yet even so, the rigidity of that plate when added to the bed would have been many times better than the thin, limber, and bouncy bed of the basic Southbend*, plywood notwithstanding.

*Which isn't all that limber and bouncy, really.

Evan
05-27-2010, 08:53 AM
If 1250lb of machine are the new "9 x 20", then apparently I have strayed into the wrong forum

How much does the lathe weigh?

philbur
05-27-2010, 09:51 AM
You should already know the lathe weight, you said It just isn't heavy enough to have enough metal in the bed to be "rigid enough". What on earth did you base that pronouncement on, your magic eye:o

Looks like we need to start your lesson 2 in torsional rigidity. Rigidity is primarily a function of geometry and the modulus of elasticity not of weight.

If your magic eye can see that the geometry of that particular lathe bed is not "rigid enough" then you need to identify: not rigid enough to do what. Seems all you guys with Asian 9 x 20 may as well just put them in the craper, Evan says they're not rigid enough.

What a load of old cobblers.

Phil:)

How much does the lathe weigh?

Evan
05-27-2010, 12:08 PM
I know what it weighs with the accessories. I take it you aren't as good at reading english as you are at writing it.

Looks like we need to start your lesson 2 in torsional rigidity. Rigidity is primarily a function of geometry and the modulus of elasticity not of weight.

Lesson in physics, MASS not weight. Geometry is highly constrained by usable design. Are you saying then that even the very light lathes may be as rigid as the heavy ones? How did so many manufacturers go so far wrong?

Now, to repeat, how much does the lathe weigh? Is your MAGIC EYE able to see the actual configuration and distribution of matter in the lathe bed as well as the density and type of material used?

Please enlighten us master of Mud.

AlexK
05-27-2010, 02:10 PM
Just to clarify ... We are talking about 12x36 lathe. Not 9x20
1200 lb for 12x36 is not that much.
Another factor to consider is the cast iron quality.

If I am not mistaken someone on this forum had a Kurt vise clone with dimensions and mass as original Kurt. But unlike Kurt it broke when it was tightened "too tight". The clone had several cavities in the cast, not to mention that it was porous too.

Having said that we can assume an average Chinese lathe bed has some cavities. So to achieve "old American iron" rigidity a Chinese lathe have to be actually larger and more massive than old iron. Who knows how big are the cavities in my lathe bed or how porous it is?

S_J_H
05-27-2010, 02:14 PM
If 1250lb of machine are the new "9 x 20", then apparently I have strayed into the wrong forum, this must be the "Monarch" forum on PM...........

lol, But it seems these import 12x36" lathes are really closer to around 850lbs. The PM 12x36 comes shipped with an impressive amount of extras-
6" 3 Jaw Chuck with Reversible Jaws
8" 4 Jaw Chuck with Reversible Jaws
Face Plate
Coolant System
Work Light
Foot Brake
Tailstock Drill Chuck
Live Center
4-Way Indexable Tool Post
Splash Guard
Stand with Chip Tray
Add in a skid and packing too.

And speaking of the 9x20's, Here's the Artisan's spindle resting on my old 9x20's bed. Sort of gives you an idea how small and light the 9x20's really are.
http://i109.photobucket.com/albums/n48/S_J_H/vintage%20Artisan%20lathe/Artisanspindle.jpg
Steve

J Tiers
05-27-2010, 10:38 PM
Lesson in physics, MASS not weight. Geometry is highly constrained by usable design. Are you saying then that even the very light lathes may be as rigid as the heavy ones? How did so many manufacturers go so far wrong?

You are misconstruing the argument.... I think I put it a little more understandably.....

The SAME weight (mass) of material can be distributed to be limber and flexible, OR relatively rigid. The difference between these may be 50:1.

IF a machine is BOTH heavier (more massive) AND has the material distributed in a manner to make better use of it, then one would expect that machine to be stiffer than the comparison item..... The difference may be a little, or a LOT, depending on the difference in weight (mass) and the distribution of it.

The fact that it is a "12 x 36" is somewhat significant.......

The 12" part is less relevant for bed stiffness..... that is headstock height and affects the lever arm, and also subtracts a little mass at both HS and TS......

The 36" may be highly relevant...... or not. A longer bed takes more material even if made the same size otehrwise.

To PROPERLY make a longer bed as rigid as a shorter, you must also increase the sections to increase the rigidity..... it should be wider and deeper.

Now a "comparable size" Atlas of 12 x 36 weighs perhaps 350lb. If so, and that is a WAG off of the weight of smaller machines, it is less than half the weight of this machine.....

In other words, the bed can be made considerably wider and deeper, to the extent of close to doubling its weight, with the overage going towards HS, TS and carriage. length is approximately the same.

if you double the depth of a beam, you very significantly increase its stiffness..... If you also increase the section out at the "ultimate fiber", you gain another increase, and you can afford to do it, since the "web" can be relatively thin..... and increasing its depth adds a lesser amount of material.

The minimum stiffness increase I can see as credible is 4:1 over the example Atlas. Quite possibly it is 6:1, could be more.... depends how the bed was made, proportioning, etc.

There is another benefit as well... when you increase the stiffness out of proportion to weight, you raise the resonant frequency, and that will tend to push it out of the chatter range.... doubling your benefit.

The Artful Bodger
05-27-2010, 11:29 PM
How much does the lathe weigh?

Nett, 450Kg.

dian
05-28-2010, 07:53 AM
i am just finishing a bench for my little lathe. the top is epoxy concrete and weights roughly 300 kg. it is floating on five soft hockey pucks.

http://i973.photobucket.com/albums/ae218/romandian/mkbohrer034.jpg

Evan
05-28-2010, 10:19 AM
There is another benefit as well... when you increase the stiffness out of proportion to weight, you raise the resonant frequency, and that will tend to push it out of the chatter range.... doubling your benefit.

You don't want to raise the resonant frequency, you want to lower it. That is what mass does. You can't raise the resonant frequency above the expected range of excitation from a lathe but you can lower it below the usual modes. Adding stiffness reduces the excursion possible. It would be possible to build an extremely stiff lathe using carbon fiber composite construction. It would weigh almost nothing compared to cast iron. I wonder why they don't do that?

Evan
05-28-2010, 10:20 AM
Dian,

That is a beautiful bench. May I ask what lathe will be going on it?

S_J_H
05-28-2010, 11:30 AM
Dian,
Holy sh\$t ,that is one hell of a bench top!! Fantastic job!

I have my SB9 bolted down on a stainless table top. The table is heavy and braced from the underneath and covered with what looks like some sort of thick asphalt covering. I have no idea where it originally came from. It was in my garage when I bought my house 20 years ago.

There are steel plates sandwiched between lathe and table top and then the lathe is bolted down through the plates, table top and into the cast iron logan lathes. I then bolted and tac welded steel plate to connect each leg.

It makes for a very rigid SB9. At the tailstock end are 2 setscrews which are used to adjust out any twist.
It's rigid enough to where I was able to use this multi tooth form tool I made from 3/4" acme stock and plunge straight in without chatter. I consider that pretty impressive for a SB9.
http://i109.photobucket.com/albums/n48/S_J_H/misc/formtool004.jpg

Here's a shot of both of my SB9A and the Artisan 11 x 24-
http://i109.photobucket.com/albums/n48/S_J_H/compares004.jpg
They are similarly powered, 3/4hp Leeson DC motor on the SB and 1hp Marathon 3ph motor and VFD on the Artisan.
The Artisan will take a deeper more aggressive cut than my SB even though the stand is pretty lightweight.
The unusual cast in and scraped support pad for the Artisan's carriage further helps when doing cuts on very large diameter work-http://i109.photobucket.com/albums/n48/S_J_H/vintage%20Artisan%20lathe/artisan2ndway001.jpg
http://i109.photobucket.com/albums/n48/S_J_H/vintage%20Artisan%20lathe/artisan2ndway002.jpg

About a year ago I went to the trouble of mounting my SB on my main workbench which is made of wood as I needed the floor space. The bench is very heavy and overkill on the bracing. But the lathes performance was noticeably degraded compared to the all steel and iron mounting. The lathe was also much louder running on the wooden bench. I removed it the next day and remounted to the steel table setup.

I have read several old books on lathe and lathe bed design which I found very interesting.
I think most small lathes performance can be improved with a well thought out solid mount.
Steve

Tony Ennis
05-28-2010, 11:44 AM
dian - that's gorgeous!

Tony Ennis
05-28-2010, 11:58 AM
What do you all think of a benchtop made of 3 sheets of 3/4" plywood over 2x4 'joists' on 6" centers, wrapped in an apron of 2x8s, and sitting on legs of 6x6s?

Or, version 2, replace the 2x4 joists with a 1/2" plywood torsion box. Total depth of the torsion box would be about 3.75" with a 6" spacing between parts. Torsion box would sit on a lip made of a 2x2s all the way around the bottom of the apron. I can make the torsion box thicker at the expense of using a 2x10 for the apron or making the top thinner.

This would be for a 12" Craftsman with a 48" bed - it's perhaps 300# and as we know, prone to vibration.

I hate to under-build when overbuilding is only incrementally wasteful :)

darryl
05-28-2010, 05:55 PM
IMHO- I'd be disinclined to mix 2x4s with plywood if the intent it to create a rigid and stable structure. I think you would do better to use a single layer of plywood for the top, plus also a bottom layer, with lots of well-fitted diagonal bracing between those. The surrounding panels should also be of the same plywood. Those sides and all the bracing would be all the same width, so you are mostly just cutting the length of those pieces to form the sides, and for internal bracing you are also cutting lots of angles. All pieces should fit well to give as much wood to wood contact as possible for the glue. Coffee table epoxy might be a good glue to use as it won't introduce any moisture into the wood.

A project like this often takes a fair amount of preparation, then some help during assembly. Cut your top and bottom pieces out, and match them up for squareness, etc. With enough 'strips' cut out to make the sides and internal bracing, then cut lengths for the sides and ends. Make the long sides full length and the ends to fit between. Assemble one long side to the top, then fit the ends, then lay this on the surface plate with the last edge hanging over a bit. Weight it down or whatever to get any twist out of the plywood top, then fit the last side. Leave it like this until the epoxy has cured.

From there, determine where your mounting bolts will need to be, then fit some diagonal bracing that will surround those bolts. This bracing should come directly from the inside corners of the box, and should meet up. A crosspiece is placed to coincide with this junction. The box should be kept in contact with the surface plate while all this bracing is glued, placed, and pinned. The end result should be lots of triangulated openings, and basically no gaps in the construction.

The final step is to make sure there's no bumps on the top edges of the sides and bracing, then heavily wet the edges with epoxy, temporarily lay the bottom in place to mark the glue lines, lift that off and saturate the glue lines and edges again, then assemble the bottom, weight it to ensure the top surface is laying flat on your surface plate, then pin the whole thing. Let cure fully before you move it.

I've only gone into this much detail explaining a construction method to suggest how important it is to have triangulation as opposed to boxation, and close fitting construction, moisture-free gluing, and achieving a flat top. When this is done right, every part of that construction is able to resist the entire structure against deformation from twisting forces. There are no separately stressed areas, and there is no reliance on any 90 degree junctions to resist a bending of that junction, except for the corners where you can't help that. Most all of the stresses are taken up either directly in tension or in compression in-line with the materials. Securing the mounting bolts will also not be tending to warp any surfaces, as the tension will be directly inline with some of the bracing.

There you have a most solid and rigid base structure. Adding legs becomes a secondary and separate part of the project. They can be attacked to the bottom of the lathe mounting bolts, since those will be sticking out the bottom of the torsion box already. As far as those bolts, it would be most helpful to epoxy them in as well. Those points will be responsible for transferring the rigidity of the torsion box to the mounting points on the lathe bed. Because those bolts are surrounded by closely fitted bracing, there won't be much volume to fill with epoxy to fully surround the bolts.

As for the plywood, start with a good grade and be picky about the flatness of the sheet you get. More laminations is better than less, and if you choose to double up the top, this should be the last part of the building process, after the torsion box is built and cured. More epoxy of course to fill in the gap for every thru-bolt.

Last point- to a point, the thicker you make this box the more rigid it will be. You should probably make it about 3 to 3 1/2 inches deep for every 8 inches of width.

The Artful Bodger
05-28-2010, 06:18 PM
So now I am thoroughly confused!:confused:

I will be moving to my new shop in a few months and am thinking I should have a concrete monolith poured in the middle of the room to put my 12x36 lathe on.

A block the size of the chip tray and to a comfortable working height will be 0.8cu metres and will weigh as near as dammit 2 tons, I think that will that be quite sturdy enough.:)

I guess I could make it a bit heavier by putting local iron sands in with the mix.

Evan
05-28-2010, 06:58 PM
Darryl,

You are making it much to complicated. Sure, what you propose will work very well but so will a much simpler approach.

My lathe bench top is a stressed skin panel. That's a fancy name for a box of 2x4s and plywood. It has 2x4s on 8 inch centres and 3/4" 5 ply each side which is glued and screwed. I used a product called Liquid Nail to do the gluing. It is very strong and it has no perceptible flex. The lathe stays very well aligned regardless of season.

The main item though is the length of heavy channel iron to which the lathe is mounted. I didn't box it although that would be even better but I didn't have and couldn't afford the material or a welder at the time.

http://metalshopborealis.ca/pics/shop1a.jpg

Tony Ennis
05-29-2010, 10:33 AM
a stressed skin panel. That's a fancy name for a box of 2x4s and plywood.

Even a thin sheet of plywood will add enormous strength, especially where racking is a concern. Plywood is also dimensionally stable, even as the humidity changes.

As I am finding out, it is easy to over-design a bench :D

darryl
05-29-2010, 02:10 PM
It may be easy to overdesign a bench, but it sure is nice when it's totally solid, and you know you can beat the crap out of it and it will remain solid. I've never regretted any constructional 'overkill' that I've implemented.

Of course, I do enjoy the building of stuff, so for me it's not so much a waste as it is a pleasure to create, and then use. I'd rather have some fine German craftsmanship than an ordinary 'made in six countries' tool, even though both may be able to get the job done. I don't like flimsy, I don't like 'good enough'-

dian
05-29-2010, 02:45 PM
evan, the lathe going on the bench is probably not worth iit, i bought it 10 or 15 years ago new for almost nothing in a german do it youself market and havent seen it for sale ever since. at that time i was into racing and the main purpose was to face brake discs (and drums), which it did nicely. ill see what it can really do, after its bolted to the new bench.

by now, the project looks like this:

http://i973.photobucket.com/albums/ae218/romandian/DSC00404.jpg

RussZHC
05-30-2010, 07:36 PM
As I sloooowly try to bring life back to an old Sheldon, the time has given me opportunity to read a lot on this site including this particular thread.
I have considered most types of structure, many types of materials including some home brewed "composite/sandwich" mix of metal and wood, as well as the epoxy concrete.

Anyone's thoughts on

http://en.wikipedia.org/wiki/Epoxy_granite

I was particularly interested in the vibration absorption qualities and locally granite is not all that difficult to get though can be \$\$\$, hence the thought of the combo of epoxy and granite (heh, pounding scrapes of granite into near dust would be stress relieving and cheaper than slab :rolleyes: .
In the link they talk about how it has been used by some companies in Europe for years...input from anyone, esp those with direct experience...

dian
05-31-2010, 07:50 AM
do you know the endless thread on cnc zone? (something like 350 pages)

Kibby
05-31-2010, 08:27 AM
Why not go to a stoneworks or quarry store and have a large chunk of granite cut? You could have them drill holes and pretty much whatever you ask for.

http://i485.photobucket.com/albums/rr220/pallymcgee/slab.jpg

Weld up a stand for it to sit upon, and you are good to go.

RussZHC
05-31-2010, 09:57 PM
Dian:
no I don't know the "endless" thread...

I had/am considered going to a memorial mfg and just getting a solid chunk but one of the things that fascinated me about the granite epoxy is the wiki entry made a particular point of how that composite has several things to its advantage, including vibration absorption...if it would not be for the shipping cost, I would just go with a used surface plate {also on the "consider" list if anyone cares, slate destined for a pool table and a relatively thick granite counter-top} am currently leaning towards concrete.

J Tiers
05-31-2010, 11:17 PM
You don't want to raise the resonant frequency, you want to lower it. That is what mass does. You can't raise the resonant frequency above the expected range of excitation from a lathe but you can lower it below the usual modes. Adding stiffness reduces the excursion possible. It would be possible to build an extremely stiff lathe using carbon fiber composite construction. It would weigh almost nothing compared to cast iron. I wonder why they don't do that?

You may not be thinking about that correctly.

You want to make the resonances available be OUTSIDE the range that will be reinforced, WITHOUT compromising the lathe operation. Going up OR down would work, but there are "issues"...... Or simply making the resonances "irrelevant" also works.

To LOWER the resonance, you need to either make the mass MORE, but leave the stiffness alone, OR leave the mass alone, but make the stiffness LESS.

if you raise mass, AND make the stiffness higher, you may actually not change the resonance..... you just lower amplitude.... see below....

And you need to consider the right mass, and the right stiffness.......... You can add mass or stiffness some places and have no effect whatsoever.

Now, I don't know about YOU, but I think the stiffness of many lathes has been made low enough already...... Atlas, etc......

The basic stiffness and mass in question is the bed. A lathe with a rubber bed would have a low resonance frequency, but would not likely be of much practical use.

it is necessary for the bed to do its job of supporting and guiding, which implies a certain amount of material of a stiff nature, and typically higher density. You almost cannot make it low enough in mass-stiffness ratio to get "out the bottom" of the range of driving vibrations, as that goes to a few Hz only, depending on the minimum RPM of your machine.

But by simply adding mass to the base, the table, you do NOT ONE THING for the flexibility of the bed, or the tendency to chatter. The change occurs when you start bolting the lathe solidly TO that base...... At that point you may begin to stiffen up the bed, assuming the 'feet" have a flat enough and wide enough under surface to be stable on the base.

I have considered both concrete and a slab of 80 lb steel plate as possible bases. I figured that 3" or so of concrete, or 2" of steel, would add a lot of stiffness to a lathe in the 400 lb category, if the 'feet" are solidly supported over their entire surface (not usually true of wood tops)

Replacing a bouncy rattling base, such as the cabinets the OP has, may or may not make a big difference. But it LOOKS as if the basic bed of the machine is at least 2 x deeper (if not more) than a 12" Atlas or 10" Logan, and half again wider than an Atlas (Logan is already at about 7" wide).

As such, it may be already as much as 4x stiffer. And by increasing the stiffness 4x while the mass increases less in proportion (about 1.5 to 2x, apparently), the resonance frequency should go UP.

One other thing you may NOT have considered is resonance AMPLITUDE. (you alluded to it in passing, but may not appreciate the application)

A stiffer machine with ANY resonance frequency is likely to have a much smaller AMPLITUDE of the resonance, in terms of movement of the tool tip. Higher frequencies should normally have smaller amplitudes.

At some point, there may be a resonance, but it is so small that it has no effect on the cutting action, the amplitude is lost in the small random variations that exist as a result of cutting. As mass increases somewhat , and resonance frequency goes up with increasing stiffness, the amplitude of movement will drop, until it may not be important to operation. It may be lost in the way oil film, damped in the materials, etc, etc.

This may not be so with lower frequencies, in which typically the same energy is represented by a larger movement.

And, remember, the "mass" has to be mass that matters in affecting resonances that actually move the tool tip.... A lead weight on the toolpost might actually be rather effective in some cases ..... A lead weight clamped on the bed also might..... Both are cases of lowering the resonance, and would work best on machines of lightweight and limber, bouncy bed construction..... On an already stiff machine, the change might be minimal, or the parts in question already so massive and large in size as to make the needed added mass huge.

As for the carbon fiber..... it's expensive, but it might work if done properly..... That has already been done to an extent, with weldments of proper design replacing large sections of cast iron, making machines equally stiff, but considerably less massive. They have performed well in most cases. The problem is in making the higher frequency resonance amplitudes actually smaller, and less well transmitted...... That could be a problem with carbon fiber.