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radkins
03-29-2013, 02:33 PM
This may be a totally dumb idea but I would like to get some input on it, I got my little Sieg mini mill set up and made a few cuts to see how well it works and to see just what I have. Even after making the usual suggested mod of bracing the tilting column at the mounting location I can still detect quite a bit of vibration in the column, not measurable flex but noticeable felt vibration in the column while cutting that gets even more noticeable with heavier cuts. I was thinking that since the column is hollow would filling it with lead shot help any? How about pouring lead into it? I have plenty of small lead shot on hand already but doing this would require removing the column again in order to seal the bottom so would it be worth the effort or would it accomplish nothing at all?


If this is a dumb idea it won't hurt my feelings if someone tells me so, I have never seen or heard of this being done but I did get good results doing something similar when using lead shot to stop chatter in a rifle barrel I was machining. I know this mill is extremely limited and I don't expect miracles but it's what I have right now and I want to make the best of it so any suggestions on dealing with this vibration (which I am sure is normal for one of these things) would be appreciated.

SGW
03-29-2013, 02:46 PM
Sounds plausible to me. I'd be wary of filling the column with molten lead. If you try it be certain to remove all traces of oil and moisture so you don't get steam blowing molten lead around. An easier and considerably cheaper option might be concrete, which has good vibration-damping qualities.

derekm
03-29-2013, 02:48 PM
on one of the other forums there are entire threads devoted to filling the voids with an epoxy agregate - read concrete with expoxy instead of cement.

radkins
03-29-2013, 02:50 PM
Actually pouring lead into the column would seem like a bad idea for many reasons and I doubt I would attempt such a thing, don't know why I even mentioned doing that.

lazlo
03-29-2013, 03:43 PM
There's a series in the current Model Engineering Workshop entitled "Improvements to the Sieg X2 Mini-Mill". He covers the column brace, and a variety of other improvements.

radkins
03-29-2013, 04:21 PM
Yep I checked that out when I bought the mill and used one of the suggestions about bracing the column, this helped tremendously with flex but I still have some vibration. Holding my hand on the column the vibration is quite noticeable and I know that some is going to be normal but this is enough to cause problems I believe. Checking with a DTI before I added the column brace I could push against the top of the column using only two fingers and easily get .003 to .004 deflection measured at halfway down but with the brace it takes some real effort to deflect even .001. The only discussion I found anywhere dealing with the column vibration was one fellow who had rigged up a crude framework that attached at the top of the column and braced it with angle braces to a frame at the bottom onto which the mill was mounted, effective I guess but quite a conglomeration of bracing too!

Duffy
03-29-2013, 07:27 PM
If you decide to fill the column with shot, then I suggest that you mix it with epoxy. It would be a MUCH more dense "concrete" than granite/epoxy mix. I made some up to weight a pair of table lamps. I mixed a bit of epoxy in a zip-lock bag, added shot, worked it until it was uniformly wet, cut the corner off the bag and squeezed it into the cavity. No muss, no fuss and no cleanup. It doesnt take a lot of epoxy either. The whole mixture is sort of "gluey".

tdmidget
03-29-2013, 07:32 PM
I would try the loose shot first. It seems to me that it's ability to move might be at least part of the damping quality. Easy enough to undo. It's tough when it's full of epoxy and you're thinking "I wonder if loose shot would have been better?"

darryl
03-29-2013, 07:49 PM
I would go the epoxy route also. One thing you could do is fill the column with shot, then dump that into another container. Settle it down well, then fill with water to the height of the packed lead. Then drain the water out into a container so you can measure the volume of water. That's about how much epoxy you'll need to do the job. Of course you'll have to thoroughly dry the shot afterwards.

Consider whether it would make sense to add a pipe down the center of the column. This would give you a way to use a threaded rod through it to fasten any bracing or other attachment you might want to add at some point. I don't know what that column is like, so you would modify this idea to suit. If you were to ever want to add something, it would be good to have attachment points cast in from the start. A coupling nut with a washer bolted to one end with a short bolt would make a decent attachment point. You would drill the column and temporarily bolt these in place before you cast the lead shot/epoxy mixture. You can remove the mounting bolts later, and if you never use them- no big deal.

My take on this is that those little hollow columns can use all the stiffening and bracing you can find a way to add. Maybe a larger base can be cast in concrete, with rebar, and with nesting points for the existing base, plus added brace attachment points. Just an idea. I don't know if the rest of the machine is solid enough to make these additions practical.

By the way, if you go the epoxy route, you would seal the bottom of the column first so the epoxy can't run out, but then pour the needed amount of epoxy in before adding the shot. If you let it settle awhile before adding the shot, much of the air will rise out of the epoxy. If you then add the shot slowly, it will wet out and sink, allowing as much air as possible to leave the mixture. If you mix the shot and the epoxy, then attempt to pour that, you're just asking for messy trouble.

radkins
03-29-2013, 08:17 PM
I have lots of shot and about a gallon, which is way more than I would need, of polyester resin that's normally used for fiberglass lay-ups. Would the polyester resin work in place of Epoxy?

Black_Moons
03-29-2013, 08:21 PM
Sure its not the whole machine? My IH mill has noticable vibration everywhere when I take heavy cuts! Its just a stressful process.

Its also why we have seperate passes for 'roughing' and 'finishing to size', so the heavy roughing vibrations/twists/torques don't upset our accuracy and surface finishes.

Try a 'rougher' style endmill to help reduce that, since I doubt you want to run a multi insert facemill with so little torque.

Mcgyver
03-29-2013, 08:28 PM
its my understanding that its the very large surface area or boundary layer between two unlike materials, granite and epoxy, that gives it the superior damping properties. I have no idea what lead costs, but I can imagine where its high weight could be detrimental.

Filling it with loose material wouldn't give the same boundary layer action and filling it molten would make it really heavy but might not do much to damp vibrations. If you were not going do the epoxy thing, and just fill it loose, maybe consider sand. Cheap and easy...lot of wood lathe guys use it.

darryl
03-29-2013, 09:33 PM
Polyester resin will shrink up to 8% apparently, while epoxy is around 2%. The less additives, the lower the shrinkage also. When you factor in the fill factor of the lead shot, the overall shrinkage would be less. What would probably make sense is to fill in stages- it is usually not recommended to cast in bulk anyway due to heat build-up during cure. I think you would be fine with polyester, but maybe limit the thickness of each pour to 2 inches or so- see what happens with the first pour. If it doesn't get beyond warm as it cures, and doesn't pull away from the sides- add it layer by layer, waiting only long enough for the heat of cure to subside, not cure past the sticky point- it should be fine.

Concrete will shrink as it cures also, but I don't recall the percentage. It does of course have solid fill in it, being rocks, which don't shrink. I don't know that it adds damping, but it would add weight and stiffness.

Heck, if you really wanted to get creative you could cast some concrete rods around pieces of rebar, then place those inside the column with the polyester resin and lead shot making up the rest of the fill. The concrete get a chance to do most of its shrinkage before being cast into the column, and you minimize the amount of polyester and lead shot that's used. I think it could be good.

radkins
03-29-2013, 09:42 PM
So lead may not be a good idea? Concrete was suggested earlier would that work better than loose lead shot? I want to do whatever it is I decide on right away but obviously this is going to be a one shot affair since once it's in there it's going to be permanent, I just want to get it right the first time.

Black Moons, I'm sure it's the column and this vibration is noticeably different than the normal vibration that will be felt throughout the machine. It's no small wonder why the thing vibrates, that column is very thin walled and the whole thing weighs very little so even with the base solidly mounted now there just has to be some flex with those thin walls.

flylo
03-29-2013, 09:58 PM
I would try loose sand 1st & see if ot helps at all, if not it's cheap & easy to get rid of & the sand vibrates the tighter it packs like using around a flagpole.

darryl
03-29-2013, 10:42 PM
For that matter, try the lead shot first. If it does the job, then you can pour it out and seal the column in preparation to do the resin thing. I don't think lead is a bad idea, by the way- it does seem a waste when sand is cheap and all over the world, but if that's what you have then go for it. Lead is pretty non-resonant by itself, at least as much as any other material you might use.

If you go for it, it could make sense to test a small quantity of resin with a minimal amount of hardener first, just to make sure it will cure fully at the temperature you're at. If you're confident to mix a batch of resin for a slow but sure cure, then just do it. You do not want to mix in more catalyst than needed, as that will cause more shrinkage, and you want to minimize the heat during cure.

Mcgyver
03-30-2013, 12:01 AM
So lead may not be a good idea? Concrete was suggested earlier would that work better than loose lead shot?

careful with the nomenclature - mixtures of epoxy and granite are also called concrete. The concrete we'd normally think of, ie cement stone and water has no business in a machine tool imo. It moves around as it cures and curing kind of goes on forever, although its some logarithmic chart with most happening in the early stages. Nevertheless, for something as accurate as a machine tool it could be wreaking havoc for years. There's reasons hardinge and others put epoxy granite concrete in machines vs cement concrete. I'd speculate cement based concrete might not do much reduce vibration either ; the Portland cement and stone are not as different as epoxy and granite

Bruce Griffing
03-30-2013, 12:06 AM
The vibration of your column is related to two important factors. First is the stiffness of the column. A stiffer column will deflect less for a given force input and will resonate at a higher frequency. The second is the mass of the column. More mass lowers the resonant frequency of the column. Filling with loose shot will only increase the mass. This can be helpful if the original column resonance was at a frequency related to cutter frequency. But I don't think that is very likely. Adding stiffness is much more likely to help your vibration problems. Epoxy aggregate would be my first choice to add stiffness. All of that said, you may improve this machine, but how much effort do you want to put into that? You would be much better off buying a used but larger and stiffer machine. Then put your effort into making it better.

Mcgyver
03-30-2013, 12:22 AM
The vibration of your column is related to two important factors. First is the stiffness of the column. A stiffer column will deflect less for a given force input and will resonate at a higher frequency. The second is the mass of the column. .

I'm thinking there's more to it than that; the material and boundary layers matter a great deal to its vibration damping properties. For example, polymer concrete is 1/3 the density of cast iron and a fraction as rigid yet delivers double the vibration damping.

Evan
03-30-2013, 01:27 AM
I would fill it with loose lead shot. It has excellent energy absorption qualities which is why it is used in dead blow hammers. The very large friction surface area produces much of the damping action as well as the mass. Using loose shot also make it possible to drain it out a plugged hole in the bottom of the column should you ever wish to move the tool. I have plans to do the same although my machine does not have much flex and absorbs energy well.

When I designed my aluminum mill I used multiple layers of aluminum screwed together to make the columns. The ever so slight rubbing action between flexing layers absorbs energy extremely well. It completely eliminates the resonance usually present with aluminum structures. That was the plan and it works. The same applies to large amounts of small, dense , soft bits of material such as lead shot. It is probably about the best vibration damper available.

Paul Alciatore
03-30-2013, 02:33 AM
I would ... <snip> ...

Consider whether it would make sense to add a pipe down the center of the column. This would give you a way to use a threaded rod through it to fasten any bracing or other attachment you might want to add at some point. I don't know what that column is like, so you would modify this idea to suit. If you were to ever want to add something, it would be good to have attachment points cast in from the start. A coupling nut with a washer bolted to one end with a short bolt would make a decent attachment point. You would drill the column and temporarily bolt these in place before you cast the lead shot/epoxy mixture. You can remove the mounting bolts later, and if you never use them- no big deal. ... <snip> ...



This plus the three or more thousandths of sway at the top of the column raised a thought in my mind. What if you go back to concrete, real concrete mixed with cement. Add a cardboard tube down the middle and a couple of thick (1/2" or more) washers at the top and bottom with holes in the centers and an OD almost equal to the ID of the original column. When the concrete is dry and hard (a week or two, depending on the mix) place a tension rod down the center and apply as much tension as you can without distorting the original tube or breaking the rod. Measure the OD of the column before and during the tension process and stop if it increases. Otherwise go to the limit of the rod. This will produce a prestressed concrete column and should greatly add to the strength which will reduce the flexing or sway at the top. I do not know what, if anything it will do for vibration, but it can't make it any worse.

After reading some net sources, it does appear that prestressed concrete does have at least some vibration dampening properties. I can not find any comparisons to materials like cast iron. Any body else have any thoughts on this?

Evan
03-30-2013, 03:00 AM
The primary reason for prestressing concrete is to prevent it from coming under tension. Concrete has outstanding compressive strength and almost no tensile strength. By prestressing it under compression it insures that all parts of a concrete beam under bending loads remains in compression from the neutral axis to the furthest fibers.

ptjw7uk
03-30-2013, 05:42 AM
How about a threaded rod down the centre of the column and put the column into compression. Also put all your old carbide inserts in there to dampen vibrations.

Peter

Peter.
03-30-2013, 06:32 AM
How about a threaded rod down the centre of the column and put the column into compression. Also put all your old carbide inserts in there to dampen vibrations.

Peter

By the time the column was full of inserts the mill would be worn out from making chatter-marked parts :D

radkins
03-30-2013, 09:13 AM
careful with the nomenclature - mixtures of epoxy and granite are also called concrete. The concrete we'd normally think of, ie cement stone and water has no business in a machine tool imo.


I have to admit that when I saw the suggestion I thought of sidewalk material! I was a bit leery of pouring that into my mill and I would have done some more research on that one before attempting it, thanks for explaining it to me.


I know a bigger mill is the real answer and that's coming sometime this Summer but until my new shop is built this thing is all I have room for.

lwalker
03-30-2013, 09:47 AM
...I got my little Sieg mini mill set up and made a few cuts to see how well it works

So, besides the vibration, how well did it work? Is the vibration you feel actually having an impact on the quality of the finish?

Lyndon

radkins
03-30-2013, 10:03 AM
I really haven't run it enough to comment on how well it is going to work but IMO the vibration, or maybe this would be more correctly called flex, is bad enough to cause problems. There is a noticeable difference between felt vibration at the bottom of the column as opposed to the top so it's apparent that some means of stiffening the column will make a difference. I have been thinking that maybe instead of, or maybe in addition to, filling the column I could bolt a heavy plate to the back of it.

flylo
03-30-2013, 10:25 AM
Just my opinion but if your getting a big mill this summer & plan on selling this one I'd just live with it or make sure what you do is reversable before you sell it.

radkins
03-30-2013, 10:49 AM
I probably will not be selling it and I need it right now so I want to set it up to do the best it can within it's limitations, but still I will be realistic. After playing with this thing a bit it looks as if it may work out quite well if I can stiffen up the column, that appears to be the only major weak point-well that and of course size and power. Of course the point about the bigger mill is well taken and I agree completely it's just if there is something I can do until then (within reason for both time and expense) I would like to try.

Rich Carlstedt
03-30-2013, 03:30 PM
I don't think you want to get too complex here.
Mass and Dampening ability are what you want....along with simplicity !
Putting in lead shot into the column is a superb approach.
The "shot" is great, because it can guantee 100 % contact with all internal areas on the column.
Obviously There is air space between the shot, but the mass added is what changes the harmonics.
That and the dampening of lead is hard to beat !
"Casting" can work, however if the material shrinks one bit, it retracts from the surface, a no-no for effective control
Rich

radkins
03-30-2013, 10:53 PM
Ok I made a plate to fit the bottom of the column and drilled/tapped some 10-32 screw holes to firmly attach it for a good seal then filled it to the top with the lead shot (which is about equal in size to a #5 shot for a shotgun), that thing is REALLY heavy now! I tried a couple of cuts with a 3/8" 2 flute end mill and a 1/2" 4 flute both in 4140 steel. There is still a noticeable difference in vibration at the top of the column vs the bottom but it is much better than it was, overall this was apparently well worth the effort.

I know that these little mills are very limited and I don't expect too much from it but considering I have been getting by for a couple of years with a milling attachment for my lathe this just has to be an improvement!

Mcgyver
03-30-2013, 10:57 PM
I think thats great, a simple solution that gave a noticable improvement. I'd thought of sand just because its cheap and easy......lead is bought from gun supply places? is it expensive?

Joel
03-31-2013, 12:11 AM
Ballistic products usually has good prices for reloading supplies. Looks like the going rate for lead shot is around $47 for 25 lbs. Obviously shipping would be a major issue. Last time I had the need, I got lucky and found some on clearance locally, not that it was particularly cheap.

http://www.ballisticproducts.com/Magnum-Chilled-Lead/products/68/

Peter.
03-31-2013, 06:00 AM
You can buy 1 gallon tubs over here for filling diving pouches.

radkins
03-31-2013, 07:55 AM
In my case the lead was free, I have a couple of hundred lbs of it that was taken out of some old coal mining machinery where it was used as a sound deadener. It is very soft lead and I have used a lot of it to add to lead wheel weights for bullet casting alloy.

radkins
04-02-2013, 07:37 PM
So, besides the vibration, how well did it work?Lyndon


I have run it enough now to make a few observations and overall it's about what a person might (or at least should) expect. If by asking how well does it work you might be thinking of buying one I would not recommend it, at least not a new one. I got mine for only $450 with at least $600 worth of add-ons, mods such as a belt drive conversion, tooling, etc so I can't complain but it's about what I expected. This thing came with a power feed drive from Little Machine Shop that's a total waste of money, it's worse than just don't work because about all it's good for is rapid feed and breaking end mills! The motor is too small and the unit is geared too high, I suppose to get the rapid feed, so when it's first turned on the motor stays stalled until the current is turned up high enough to produce enough torque to start turning at which point it will take off at much too high of a speed. Basically the only way to achieve a slow enough feed rate to use the thing to mill with is to start out fast and then slow down but even then the rate is erratic, you had better be a good distance from engagement with the work when that thing is turned on! The ways are a joke and if the gibs are snugged up enough to take out the play there are tight spots that simply makes feeding by hand very tiring especially with those tiny feed wheels, loosen the gibs enough to get even a reasonably easy and smooth feed and there are loose spots with enough play to cause chatter. I am not complaining about this thing but rather just pointing out some of it's annoyances, I managed to get the column stiff enough but it looks as if I still have a lot of work to do to make this thing usable. I am going to junk that power feed and use the gear box for another project I have but the next thing I am going to do with the mill is to attempt to smooth up the ways in order to get a decent feed without requiring so much effort.

Evan
04-02-2013, 08:30 PM
You need a pulse width modulated drive for the feed motor. It sounds as though they are using a simple rheostat.

radkins
04-02-2013, 08:44 PM
Not sure about the electrics but that motor is tiny and very light so I would be surprised if it puts out any torque to amount to much. For what I intend to use this mill for I doubt I will miss the power drive very much, it would be handy of course but not worth the effort and expense for the fairly short time I intend to use this thing. I think if I can get the ways cleaned up enough to smooth things up so that manual feeding won't be such a chore I should be able to do what I need with this little outfit until I get enough room for a real mill.

GNM109
04-02-2013, 09:02 PM
How about a threaded rod down the centre of the column and put the column into compression. Also put all your old carbide inserts in there to dampen vibrations.

Peter

This is an excellent suggestion. My first mill was a Harbor Freight Mill Drill. I worked with it and learned quite a bit about stability (or lack of it) during the ten or so years that I owned it. At the time before I had planned on moving to a machine that would be larger and more stable, I had thought of turning a steel disc for the top and bottom of the column with something like a 5/8" or 3/4" threaded rod down the center of the column so as to put it under compression. I went so far as to turn the upper cap and was going to disassemble the column to look at the bottom and make another disc when I got very ill and spent some time in the hospital. When I returned, I had totally lost interest in the machine and decided to move up to a BP or clone so it was sold.

I do think that this would be the easiest solution and would also, unlike concrete or epoxy, be removable and perhaps tunable with slight variations to see what could be done to make the assembly even stiffer. With sufficient torque placed on such a rod, it should add at least a modicum of stability, although there are other issues on round or other type small column mills, especially in the area where the column enters the base.

J Tiers
04-02-2013, 11:02 PM
Well, I am surprised that it made that much difference.

My first thought was wrong...if I had commented before reading the results, I probably would have said shot filling was unlikely to do much good. Usually you can;'t get enough in to change the mass much, and the small mass of shot hasn't much damping effect. You may have found the sweet spot where the added mass was able to tune and damp enough to work because of the extreme lightness of the rest of the structure...

I've tried shot, and similar things before, and in general it has been so small in effect as to be virtually worthless. On the other hand, the vibrations we wanted to fix were pretty bad, with a good bit of power behind them, and they were already driving a large mass, so that may explain our lack of success.

I'd have suggested bolting the biggest weight you could locate to the top of the column, with the idea that the mass would tune the column much lower than the "driving source", making its flexibility absorb the vibration. Maybe the lead does both sufficiently to work for you.

In any case, good work.

lwalker
04-02-2013, 11:31 PM
If by asking how well does it work you might be thinking of buying one

No, I've had one for a few years. I was asking if the vibration and flexing you noticed had a effect on your work or if you were just expecting it to.

In my case it doesn't. I've been meaning "eventually" to make braces for the column, but I make up for it by trying to keep the workpieces as close to the table as possible to reduce flexing. For what I do, mostly aluminum and plastic, it works very well.

One of the problems with making comparisons is that there seems to be a large variation in the quality of these mills. I probably got one of the better ones.

Evan
04-03-2013, 12:35 AM
Clamping the column itself in compression will make it less stable. At some point it will buckle and at any point it is closer to buckling than it was uncompressed. Buckling occurs as the resonant frequency decreases because the stiffness decreases, similar to slackening the tension on a wire. In this case as the resonant frequency goes down the required exciting force goes down as well. Just before failure is reached the exciting force is very close to zero.

GNM109
04-03-2013, 12:46 AM
Clamping the column itself in compression will make it less stable. At some point it will buckle and at any point it is closer to buckling than it was uncompressed. Buckling occurs as the resonant frequency decreases because the stiffness decreases, similar to slackening the tension on a wire. In this case as the resonant frequency goes down the required exciting force goes down as well. Just before failure is reached the exciting force is very close to zero.

You opinion is interesting. Why then do they produce cast concrete columns with tubes inside of them that contain cables to place the columns under tension (compression)? I presume that such columns are only placed under enough tension to prevent buckling and not so much as to induce it.

It's only a guess on my part but I would think that a column with a rod secured in the center would increase stiffness rather than decrease it. As I said, I never completed the project.

Just curious.

J Tiers
04-03-2013, 01:03 AM
because concrete can stand almost NO tension.....

The cables take ALL the tension, and the concrete provides the compression strength. It allows making a beam for a bridge out of concrete. Even rebar isn't nearly as good as "pre-stressing".

Evan is perfectly correct, although as a practical matter I am not sure it would matter much in the end. The tubular column is almost certainly stronger than any but the largest size rods to fit through the middle, unless it was made VERY thin, or very long in comparison to its diameter.

Pre-stressing the column might actually do something.... whether or not it is better than a solid column is open to question and calculation. I have no opinion, it's acalculable thing

Evan
04-03-2013, 01:13 AM
Why then do they produce cast concrete columns with tubes inside of them that contain cables to place the columns under tension (compression)?

The scenarios are not similar. In the cases of the compressed concrete it is of utmost importance to avoid allowing the concrete going into tension. The tube prevents the cables from being locked to the concrete and also prevents corrosion as well as adding bending resistance and strength. The concrete is compressed nowhere near to its compressive limit although it will have the same effect of lowering the resonant frequency. What it buys is protection from tensile failure in an application it could not serve in otherwise.

In the case of a mill column with a bolt down the center the bolt is under tension but none of the resulting increase in resonant frequency is transferred to the column as it is only attached at the ends.. The only result is to lower the resonant frequency of the column and to reduce the exciting force needed to make it vibrate. There is no associated benefit.

GNM109
04-03-2013, 01:28 AM
The scenarios are not similar. In the cases of the compressed concrete it is of utmost importance to avoid allowing the concrete going into tension. The tube prevents the cables from being locked to the concrete and also prevents corrosion as well as adding bending resistance and strength. The concrete is compressed nowhere near to its compressive limit although it will have the same effect of lowering the resonant frequency. What it buys is protection from tensile failure in an application it could not serve in otherwise.

In the case of a mill column with a bolt down the center the bolt is under tension but none of the resulting increase in resonant frequency is transferred to the column as it is only attached at the ends.. The only result is to lower the resonant frequency of the column and to reduce the exciting force needed to make it vibrate. There is no associated benefit.

I would have to do some testing to be sure.

philbur
04-03-2013, 05:23 AM
Plus 1 on the loose shot. The shot will always maintain intimate contact with the column and the internal friction between individual shot will provide better vibration dampening. I think wet sand would work even better as a vibration dampener. The trick is to get the vibrational movement to rapidly dissipate as heat (due to internal friction).

Phil:)



I would try the loose shot first. It seems to me that it's ability to move might be at least part of the damping quality.

philbur
04-03-2013, 05:35 AM
Strength and flexing are different properties. Prestressing does nothing to reduce the ability to flex whereas it may well improve the ultimate "bending" strength of the composite, due to the fact that the concrete has little strength in tension. This is classical beam theory.

Phil:)


This will produce a prestressed concrete column and should greatly add to the strength which will reduce the flexing or sway at the top. I do not know what, if anything it will do for vibration, but it can't make it any worse.

GNM109
04-04-2013, 05:58 PM
Well, if this much work has to be done to stabilize a machine, it's probably time to sell out. It worked for me.

Lots of nice theories here however.

philbur
04-05-2013, 07:26 AM
Take an empty wine class, mine usually are, place it on a table and hold it on the table with two fingers on the base. Tap it with a spoon. It rings like a bell. Fill it with damp sand and tap it again. Clack, no ringing, no vibration, complete damping.

If you are concerned about column stiffness rather than vibration then either bolt the column to the wall or otherwise brace it externally, or buy a bigger machine. Epoxy composite is a relatively flexible material and will add little to the stiffness inside a cast iron column. Yes it is used in commercially produced machines but then the geometry of those machines is specifically designed to minimise the negative effect of a low modulus of elasticity. You don't have that luxury with an existing configuration.

Phil:)

928gene928
04-05-2013, 09:22 AM
Radkins,
The trick when filling something is to be sure that the filler does not shrink as it dries. On of the best products to use is machinery grout. One trade name that comes to mind is Embaco 636. There are many of these types of products, and this type of grout is easy to use and it does not shrink. It can be mixed in almost a liguid form, or heavier like regular cement. I have used these products for 45 years in all sorts of applications with excellent results.

Evan
04-05-2013, 12:54 PM
I've never found lead shot to shrink all that much.

ckelloug
04-05-2013, 03:02 PM
Shrinkage in epoxy-granite "polymer concrete" is approximately nil. Shrinkage with polyester resin can be non-nil. Shrinkage could create odd stress states in the mill if things remain bonded or completely decouple the damper you just added to the rest of the mill by causing an air gap if the material unbonds fromt he column. Epoxy granite damps because in E/G the boundaries between the particles and the resin cause the vibrations to reflect at the boundaries due to difference in density. The granite particles are like masses and the epoxy like a spring and damper. Because of the wide variety of particles sizes and the random orientation, E/G is a very broad band damper. My studies also indicate that the graphite particles in Meehanite offer a similar damping mechanism to what I just explained about EG. Because the epoxy provides another interface with the mill column, it provides an additional dissipation mechanism in addition to making the entire column behave as a larger mass: I would predict (haven't tested) that lead shot in epoxy would probably do better than just lead shot. Almost any epoxy granite formulation other than one with half epoxy or something will work just fine for filling a column. The insanity about which I have something like 2500 posts on CNCZone is based on maximizing strength and stiffness while also damping. . .

You don't actually need to add a lot of mass to improve damping by a fair margin. Any time you have a material interface where two materials with different properties are forced to share a displacement across a surface, you get a damping element. See for example this paper from the Varanasi research group at MIT: https://docs.google.com/viewer?url=http%3A%2F%2Fweb.mit.edu%2Fkripa%2Fwww% 2Fpublications%2Flwsm_jsv06.pdf

radkins
04-05-2013, 03:20 PM
I have not had much to add to this thread but I have read every word and as usual I am learning a lot more than I asked! Much thanks to everyone who replied.


BTW, could someone please explain the proper way to pronounce "Meehanite"? I know about Meehanite castings and it's common uses but over the years I have heard it pronounced several different ways by people who should be very familiar with it, I asked Mr Google a few moments ago but no help on that one.

johnd
04-06-2013, 07:32 PM
I have no worthwhile info to add, just a somewhat related story. Many years ago I worked for a company making and selling automotive machine shop equipment, some of which was imported from Italy, and all of the bases were fabricated from steel plate as opposed to the big heavy / expensive cast iron bases of American made machines. The Italian machine for reboring engine blocks had a tendency towards high frequency chatter and the engineers solution was to fill the base with sand. This did improve the performance of the machine and the problem was considered solved. The sales department even quoted the heavy weight of the machine as a sign of quality! One day a customer bought a new one and went to drill a couple holes to mount an electrical disconnect box or something and ended up with a huge pile of sand on his floor. Customer service had a bad day!
A couple replies mention filling it with your old carbide inserts. The local sawfiler saved me the remains of the worn out carbide teeth when new ones were brazed into saw plates. My plan was to someday use them for tumbling media for cleaning rusty old wrenches and stuff but when I stumbled on an outfit paying $10 pound I decided to stick with the wire buffing wheel I used for years. I put 57 pounds of them in a flat rate box and sent them off, check came in 4 days and they even added $11 for the postage! If you have a bucket full of inserts sitting around they might be worth enough to buy a new machine. Apparently tungsten is expensive to mine!

Ernie
04-06-2013, 10:02 PM
Having read all of this, it seems the idea is to have whatever filler is used to be in hard contact with the walls of the column. What about making a shouldered plug for the bottom, fitted with a threaded rod long enough to extend past the top of the column. Fill the column with the lead shot, making sure the threaded rod stays centered. Fit a thick disc which just clears the inside column wall over the rod and use a nut on the rod to compress the lead shot. A short piece of bar stock and nut at the top would prevent the whole mass from falling out the bottom. You could check once in a while to see if the shot settled and tighten the nut as needed or even add shot if needed. It would be a lot easier to undo than the cement or resin etc. Just a thought.
Ernie

elf
04-06-2013, 11:13 PM
Having read all of this, it seems the idea is to have whatever filler is used to be in hard contact with the walls of the column. What about making a shouldered plug for the bottom, fitted with a threaded rod long enough to extend past the top of the column. Fill the column with the lead shot, making sure the threaded rod stays centered. Fit a thick disc which just clears the inside column wall over the rod and use a nut on the rod to compress the lead shot. A short piece of bar stock and nut at the top would prevent the whole mass from falling out the bottom. You could check once in a while to see if the shot settled and tighten the nut as needed or even add shot if needed. It would be a lot easier to undo than the cement or resin etc. Just a thought.
Ernie

I'd say it's the exact opposite of what you want :) This was discussed earlier when melting the lead was suggested. Sand works well because it's free to vibrate.

J Tiers
04-07-2013, 12:46 AM
Take an empty wine class, mine usually are, place it on a table and hold it on the table with two fingers on the base. Tap it with a spoon. It rings like a bell. Fill it with damp sand and tap it again. Clack, no ringing, no vibration, complete damping.


Phil:)

As you know, this is totally different from the important part of the vibration, so it's on to your scenario #2.

And that is why I am surprised that there was a noticeable difference in surface finish from the lead shot. All I can figure is that the mass of the shot was enough to move the resonance out of the offending range.

Adding a sufficient mass would also have some of the effect of external support in the case of impact or intermittent momentary forces, such as the edge of the tool "taking a bite". But a narrow, flexible column would typically have little volume available to get a reasonable mass into.

Anyhow the person with the problem is happy......

Evan
04-07-2013, 02:21 AM
Lead shot will tend to eliminate any resonance. Since it is free to move it will not permit resonating oscillations to exist. Even if not free to move it is a very good damper. Try ringing a lead bell.

Elninio
04-07-2013, 02:31 AM
Lead shot will tend to eliminate any resonance. Since it is free to move it will not permit resonating oscillations to exist. Even if not free to move it is a very good damper. Try ringing a lead bell.
I know from boring bars, it's better for the lead to be under compression. How much so for columns?

darryl
04-07-2013, 03:50 AM
There's always the option of lining the inside of the column with carbon fiber/epoxy - then add the loose lead shot.

J Tiers
04-07-2013, 12:29 PM
Lead shot will tend to eliminate any resonance. Since it is free to move it will not permit resonating oscillations to exist. Even if not free to move it is a very good damper. Try ringing a lead bell.

A lead bell is another totally separate issue. 90% of what lead shot does in the way of damping would be just as well done with brass shot.... and brass can make a good bell.

It is the friction of the shot rattling around, and the fact that it isn't connected to the object, so it acts independently, that does the damping. Lead adds a poor "rebound" to the mix as well, and its density increases the "M" term in the "M*V^2" expression of the energy transferred to any individual piece of the shot. But the fact of having loose bits absorbing energy and losing it as frictional heat is the "first order" effect.

As for "not permitting"...... that is certainly a very relative statement..... it may be true to an extent, or it may be 100% false.

The part about "tend to" is correct...... it has the "tendency" to damp oscillations. Whether it DOES damp them or not is totally dependent on conditions.

1) amount of lead (or brass, steel, whatever) shot..... compared to the moving mass. It must be significant, even "dominant" mass-wise, or it will have no great effect. The volume inside the column is often so small that it is no contest, the vibrations win because the column is larger in mass than the amount of shot you can put in.

2) Power behind the oscillations. If there is a minor amount of power driving the oscillation, you may have an effect. With a lot of power, the damping simply cannot handle it.

3) amplitude..... if there is a small amplitude driving a much larger oscillation (similar to low power, not identical to it) then shot damping may have an effect, because it is a high "Q" system, and lowering the "Q" will also lower the amplitude of the resonance out at the end of whatever is resonating. This would be like a vibrating table having a long tube attached to it.... damping the tube will reduce the amplitude of the oscillations at the end, assuming the tube was at resonance.

Boring bars with internal damping can have the "#3" effect..... although the energy input point is different.... but old-time machinists ALSO would hang a piece of some old steel or CI junk on the bar, loosely, and that would have the same effect, or possibly more.

yes the shot thing can work. But it is certainly no "slam-dunk" guaranteed solution.

Evan
04-07-2013, 01:11 PM
90% of what lead shot does in the way of damping would be just as well done with brass shot

I doubt it. You are making a WAG which is probably incorrect. Lead absorbs energy efficiently because it is very soft. Brass isn't and does not.


then shot damping may have an effect, because it is a high "Q" system...

Precisely the opposite. The Q is nearly nil.


The volume inside the column is often so small that it is no contest, the vibrations win because the column is larger in mass than the amount of shot you can put in.

You are joking, right? Any hollow column that might be used in a milling machine is easily outweighed by the amount of shot it will hold. The counterweight for the head on my mill is about 3.5" x 3.5" x 10 inch and weighs 55 lbs. Lead shot will be about half that for the same volume, still very considerable.

J Tiers
04-07-2013, 01:33 PM
I doubt it. You are making a WAG which is probably incorrect. Lead absorbs energy efficiently because it is very soft. Brass isn't and does not.



Precisely the opposite. The Q is nearly nil.



You are joking, right? Any hollow column that might be used in a milling machine is easily outweighed by the amount of shot it will hold. The counterweight for the head on my mill is about 3.5" x 3.5" x 10 inch and weighs 55 lbs. Lead shot will be about half that for the same volume, still very considerable.

The entire point of the addition of shot, or sand, or many types of filler is two-fold.

a) it adds mass and changes the resonance. Solid lead would do that as well, probably better, as it has no voids in it, more lead less air, more change of mass by addition.

b) It causes frictional losses as each of the shot pieces rubs against its neighbors, wasting at least some of the energy as heat, maybe even enough of it to make a difference.

Yes, a wag..... a good one..... borne out by the experience of the old-timers who used other items to damp vibrations in a similar way. Lead has properties that make it better, but it is not as if no other material will work. SAND , for instance, is often suggested, and it works as well. It is notable that sand is much harder than lead, and less dense as well.

I think you misread something.... the Q of the SYSTEM *without* the shot may be high.... The effect of the shot is to lower it, which is the entire point, and not at all "precisely the opposite".

Not joking..... The "total amount" of shot may be irrelevant...... some very good reasons.....

1) Presumably the column has a large and massive (by comparison to the round column) milling head on it..... The shot system must absorb the energy of that fairly massive object moving, since ultimately, that is the item which affects the finish quality due to vibrations. And it is also the SOURCE of the vibrations, as the cutting edges strike the work, and release as they exist. The shot in the "working area" is unlikely to outweigh that head, except in the case of the most lightweight of the "mill drills" and "mini mills". however, ANYTHING is likely to help that sort of machine, so by all means try it.

2) The key issue is where the shot is. A lot of it down where there is little movement anything from 1/3 to 1/2 can be essentially out of the picture. The important part of the shot is in the part of the pipe which is moving significantly, and which therefore can jostle the shot and cause frictional loss of energy.
If the machine is on a lightweight stand, that may be less true, but the shot vs the more massive base and x-y table is the issue there.

3) The shot has relatively little effect on torsional vibrations. Almost nothing in some cases. And a mill-drill, with the head out at some distance from the axis of the spindly round column, will have a lot of mechanical advantage.

It's WORTH TRYING.....

IT CAN WORK................... apparently it did "enough" in the case of the OP to make the machine tolerable.

A slam-dunk solution is is not, and shouldn't be expected to be.

radkins
04-07-2013, 05:36 PM
Just for info here, the column has very thin walls and is about 2.250"x4"x24", the weight of the lead shot greatly exceeded the weight of the empty column. One must remember this thing is almost a toy and is extremely light weight in construction so I am thinking the improvement I got is probably a lot more noticeable compared to what it would have been in a machine of more substantial construction. Also it is solidly mounted on a steel cabinet with a 3/4" thick plate for the top, the weight of the cabinet is about 3 times the weight of the machine in case that might make a difference?

J Tiers
04-07-2013, 06:54 PM
How heavy is the head? That has to be added, but if the column is thin, and the head is smallish, you probably had just about the ideal setup for shot damping.

In any case, it worked well enough, and that's what matters.

philbur
04-07-2013, 08:22 PM
Thats a strange way to look at it. The head is not the source of the vibrations, the action of the cutter on the work piece is the source. The head is just another mass that helps damp vibrations, as does the column, table, base and of course the lead shot. The shot doesn't need to out-weigh the head, it just needs to add mass.

Phil:)



1) Presumably the column has a large and massive (by comparison to the round column) milling head on it..... The shot system must absorb the energy of that fairly massive object moving, since ultimately, that is the item which affects the finish quality due to vibrations. And it is also the SOURCE of the vibrations, as the cutting edges strike the work, and release as they exist. The shot in the "working area" is unlikely to outweigh that head, except in the case of the most lightweight of the "mill drills" and "mini mills". however, ANYTHING is likely to help that sort of machine

darryl
04-07-2013, 09:18 PM
Some of the discussion here seems akin to mounting a V8 in an Austin mini, or in a case I know of, a V8 in a Hillman- originally an 8 hp vehicle. I'm sure we are mostly aware, as is radkins, that the machine in question is a lightweight. you can dampen vibrations to some degree, maybe a high degree, but you can't prevent the column and other parts from flexing under load. I wonder how much gain there would be by stiffening only the column. How sturdy are the mounting points and the rest of the structure that can't be easily strengthened or dampened?

I'm mainly wondering how much it could be worth doing, or how much and what else could be done to make more effective improvements to such a machine-

I look at my own round column mill, and I know where some of the flex points are. The machine would be significantly improved if I could stiffen up the base and brace the column with an overarm and support pillar to the base. Such a thing would make it awkward to get around unless it could be placed at the rear of the machine. A significant re-build of the base would be needed to accommodate this, but it would be an improvement. Of course I could fill the column and empty spaces in the base with shot or sand, etc, for better damping, and any box tubing used in the reinforcement could also be filled.

Sigh. At what point do you just bite the bullet and purchase a more solid machine- and if you are keeping the old machine, how far should you go towards improving it- where do you draw the line?

I don't know- whatever seems worthwhile to the individual I suppose. I often try to weight this out as cost vs time- if I can buy a more solid machine for less than my cost of parts and times-worth to bring one up to speed- I can work for weeks or months at some job and spend what I earn on a machine, or I can work less of that time at a job and spend more of it in the shop- I start to look at is as which passtime do I enjoy more.

I've taken a bit of a tangent here, I know, but some of this is relevant.

J Tiers
04-07-2013, 11:49 PM
Thats a strange way to look at it. The head is not the source of the vibrations, the action of the cutter on the work piece is the source. The head is just another mass that helps damp vibrations, as does the column, table, base and of course the lead shot. The shot doesn't need to out-weigh the head, it just needs to add mass.

Phil:)

Ah... but it is NOT so strange, if you look at it correctly.

The head is the source, because the vibrations get INTO the column in only two ways..... (we can disregard thru air) generally both at once.

a) they come through the head into the column, so the head is shaken "first", and the head shakes the column. (of course it is really simultaneous)

b) They come through the work, into the cross-slide table, base, and bench (this isn't a knee mill, I assume), and that shakes the column.

With any luck, the table, base and bench are heavier than the head, and the majority of the vibration is input through the head. They may be comparable, depending on the motor, in which case both paths may be active.

In any case,..... the cutter vibrates the head, and the vibrations of the head are transmitted into the column. Vibrations of a more massive item like the head is (comparatively more massive than the column, at least) are harder to damp with a small amount of friction-enhancing material, lead shot, sand, whatever. The vibrations already are more energetic, since the forces are enough to drive the head into vibration, despite its generally much larger mass vs the column alone.

So when you have the head plus column going, it is a different problem to the column alone. A solution which would effectively damp the column might be ineffective against the combination.

And, of course, there is a significant torsional component, due to the overhang of the head, and that is not particularly affected by shot in the column. If you bolted a box of it to the head, out at the end, that would be presumably an improvement to torsional vibrations as well.

There is also the issue that the lead shot acts differently if it is jammed-in so as to act as a solid mass, vs acting as particles.

it's pretty complex, actually.

For the BEST damping, one should likely take a lesson from seismic dampers used in large buildings. They have plates bolted-on with a visco-elastic material between. As the building deforms, this material is in shear, and does a good job of absorbing energy.

One could do a similar thing, with a mass, or a solid support, on one plate, and the other on the column. In the shear direction, then, that would be a good absorber. You would probably need to do both X and y, and possibly a rotational plate as well.

Or, get a bigger, more massive and rigid machine. Rather than trying to spin a silk purse out of pig leather, that might be a good plan. The OP is doing that, and the machine he has, which he improved enough to work, is not his long-term solution.

danlb
04-08-2013, 01:25 AM
While it's not sensible to put hundreds of hours into making a small machine act like a big one, it is a good idea for a home shop owner to make the best bof what he has.


When all I had was a micro mill it was pressed into service for all my milling, from car keys to car parts. Minor tweaks and upgrades made it useful for quite as while. I still use mine for second ops and as a precision drill press.


Once you clean them up, adjust and address the sliding surfaces you can do some reasonable work with a mini mill.

Dan


Dan