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View Full Version : My vice twisted.!!!



David Powell
01-28-2010, 01:48 PM
Ok I am a cheap fellow. I bought a cheap 6" Knock off Kurt style vice from Busy Bee tools some years ago. I use it without the swivel base and it spends most of its time clamped on my mill bed For the past couple of weeks I had it off the mill as I worked( very intermittently) on jobs that didnt suit a vice. When I went to put it back on I noticed it rocked, I thought I had maybe trapped some swarf, so I recleaned everything. After about 3 tries of this I became suspicious and brought out my ancient straight edge. To my surprise the bottom was bowed down to the ends about 5 thous. The vice ways were still straight, at least were within a thou by my rolling papers. I am in no position to buy another so simply clamped it down on the bed, ( after checking the tram of the mill) with the vice ways down and using my carbide facing cutter took it down until I had cut all over, with a light finish cut I got a reasonable finish and a quick rub with fine emery on a block got a bit of a shine. I then bolted it back on the mill, this time it sat down properly. A quick test with dial gauge shows no more than a thou difference anywhere on the top surface. So it will certainly do for my work. I can only suppose that casting strains were still in it, that they were released by it being unclamped for so long, but why did only the base warp and not also the vice ways? Puzzled David Powell.

Carld
01-28-2010, 01:53 PM
What happens is cast iron has to age before it can be machined without warping in the future. Some manufacturers aged it for 8 or 10 years before machining now I doubt the cheap manufacturers age it at all.

Chances are it will not warp again but I would keep an eye on it. Also, did you dial indicate over the flat under the moving jaw to be sure it is good and flat. If it's not sometimes you can take a light cut without hurting the clamping effect of the moveable jaw. Check to be sure before you flycut it.

Mcgyver
01-28-2010, 02:35 PM
amazing engineers, those buys bees. Even as the vise bent in a pretzle, the ways stayed true so the model engines will work as good as ever. A strange one David, a casting bending is one thing, but migrating? there's no vices affecting the vise inspection now is there? :D

Toolguy
01-28-2010, 02:43 PM
If the ways stayed the same, the bottom was probably like that from the beginning and just now got noticed. It might not show up much on the swivel base with the ends hanging off.

Doc Nickel
01-28-2010, 02:45 PM
My cheapy was twisted in all sorts of directions (http://www.docsmachine.com/projects/4vise/4vise-01.html). Not by a great deal, but the ways weren't quite straight nor perfectly parallel, and the base was almost "dished".

http://www.docsmachine.com/projectpics/4in-vise-32.jpg

I surface ground mine, but I'd bet the casting is still "aging" and I'll have to do it again before too long. :D

Doc.

lazlo
01-28-2010, 03:50 PM
What happens is cast iron has to age before it can be machined without warping in the future. Some manufacturers aged it for 8 or 10 years before machining

Richard Moore dismisses those fallacies in Foundations of Mechanical Accuracy: virtually no stress relief happens in cast iron below it's plastic temperature: 600* F.
So room temperature aging, burrying it in the ground, urine, and cycling it back and forth to the freezer doesn't work :)

When cast iron castings are commercially stress relieved, they're heated to about 100* beyond the plastic temperature: 1100*. That allows internal stresses from differential cooling to release. So if you bought the camelback castings from Stephen Thomas or Michael Morgan, they were furnace stress relieved after tumbling -- standard operating procedure in industry. If you have Mike Morgan's excellent scraping video, there's a short segment at the end showing the camelback castings being poured and stress relieved in the foundry.

I've posted this extensive Naval Research Lab study of cat iron stress relief on PracticalMachinist:

Stress Relief of Gray Cast Iron (http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD620556&Location=U2&doc=GetTRDoc.pdf)

Abstract : The report describes a number of experiments on the stress relief of gray cast iron. One set of experiments consisted of making relaxation tests and using the rate of relaxation as a means of evaluating stress relief. These studies showed that: (1) the rate of stress relief is most rapid during the first hour at temperature; (2) the rate of stress relief is very slow below 1000 F, but increases as the temperature is raised; and (3) initial stress and alloy composition have an important influence on the rate of stress reduction by heat treatment. Observations of heat treatments on highly stressed cast wheels revealed that (1) indoor aging and low-temperature (600 F) heat treatment are ineffective for stress relieving, (2) furnace cooling after heat treatment produces lower residual casting stresses than air cooling, and (3) relaxation tests agree closely with results of stress-relief heat treatments of experimental castings.

That said, I had identical experiences as the OP and Doc with my cheapie Kurt-clone vise: it was not stress relieved after casting, and the base wasn't even close to flat w.r.t. the bed rails.

EVguru
01-28-2010, 05:52 PM
It was my understanding that traditionally castings were rough machined and only then left to 'season' before finish machining. That stresses were in the surface layer chilled by the mould and for instance machining the top surface of a cast slab would cause it to bend.

Kibby
01-28-2010, 06:04 PM
Over the years I have mused over all the tools and machinery from emerging Asian countries that need a lot of work to be up to our standards. I'm glad I found this forum because there are a lot of you out there just like me, with a lot of talent and not so much money to bring it out. One of the questions I have been formulating in my head to use for starting a new thread is, "Of the non-USA-made machinery, is there one brand that is better than the other"?

If anyone can answer that, I think we'll all breath a sigh of relief. :)

MotorradMike
01-28-2010, 06:25 PM
"Of the non-USA-made machinery, is there one brand that is better than the other"?

If anyone can answer that, I think we'll all breath a sigh of relief. :)

I think a willingness to buy Chicom indicates a willingness to accept some risk that the published specs are not met. There was a recent thread about a guy who found his mill table slightly out of spec and the dealer offered to accept it back but at huge inconvenience to the buyer.
If I found something new from Tektronix or Fluke out of spec I'd be pretty shocked and not a little upset.
You get what you pay for.

To answer your question, in my opinion, Craftex from Busybee is the best. It's not easy being green.


Mike

Kibby
01-28-2010, 06:50 PM
I think a willingness to buy Chicom indicates a willingness to accept some risk that the published specs are not met. There was a recent thread about a guy who found his mill table slightly out of spec and the dealer offered to accept it back but at huge inconvenience to the buyer.
If I found something new from Tektronix or Fluke out of spec I'd be pretty shocked and not a little upset.
You get what you pay for.

To answer your question, in my opinion, Craftex from Busybee is the best. It's not easy being green.


Mike

I agree. In fact, I do believe it will be a long(er) road for me to recoup my machine shop because of this. Smart people learn from their mistakes, and I really do not want to go through everything again like I did with my turret mill and my Jet 9x20. It felt like I was working as much on them to make them run like they should have. I was constantly making fixtures and jigs to make these machines perform beyond their limitations or level of quality. Never again.

Carld
01-28-2010, 08:40 PM
Kibby, the Taiwan machines are very good, the Polish machines are too. There is some good machines from China but they are the pricey type, not home shop machines.

When I was in the Boy Scouts we went to visit the Ford factory. They showed us stacks of engine blocks and the guide said they were aging and left there for a few years. It may have been bull**** but it sounded good. As I followed in the mechanical and machining career I was told cast iron has to be aged or stress relieved. It's sometimes hard to separate truth from fiction, or is that friction.;)

chipmaker4130
01-29-2010, 12:38 AM
A subtler difference lies in the quality of the material itself. Some of the offshore products look great, but don't stay that way due to the use of inferior grade materials througout. (low-strength castings, unsuitable gear materials etc.)

A.K. Boomer
01-29-2010, 01:23 AM
Back to the vise,,, never clamp objects in one side of a milling vise (without something the same width on the other side) as this too can cause the bed to warp out, I say this because many people may drag the habit over from standard garage vise use...

whitis
01-29-2010, 05:00 AM
I've posted this extensive Naval Research Lab study of cat iron stress relief on PracticalMachinist:

Stress Relief of Gray Cast Iron (http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD620556&Location=U2&doc=GetTRDoc.pdf)

Abstract : The report describes a number of experiments on the stress relief of gray cast iron. One set of experiments consisted of making relaxation tests and using the rate of relaxation as a means of evaluating stress relief. These studies showed that: (1) the rate of stress relief is most rapid during the first hour at temperature; (2) the rate of stress relief is very slow below 1000 F, but increases as the temperature is raised; and (3) initial stress and alloy composition have an important influence on the rate of stress reduction by heat treatment. Observations of heat treatments on highly stressed cast wheels revealed that (1) indoor aging and low-temperature (600 F) heat treatment are ineffective for stress relieving, (2) furnace cooling after heat treatment produces lower residual casting stresses than air cooling, and (3) relaxation tests agree closely with results of stress-relief heat treatments of experimental castings.


That is an interesting study but its goals were rather different.

Often, what we are concerned about is not truly relieving all the stress in the material but relieving that stress which can relieve itself over time under normal environmental conditions. Sure, we would prefer that the piece be perfectly stress relieved so we could cut it and it wouldn't move (though we are adding stress when we cut it).

If much stress relief doesn't occur below 950F, how much do we care for material that we aren't going to subject to elevated temperatures? Apparently some stress relief does occur over time at normal environmental temperatures or we wouldn't be worried about parts warping after the part is finished.

Fig 9 suggests something interesting. If you look at 72F line, you see that most of the stress relief that is going to occur (at least during the first 16 hours) at room temperature, does so in the first two hours. Also it is clear that on those graphs some stress relief occurs before time 0 on the graph, so the magnitude may be higher. Which suggests that if you wait a couple hours between roughing and finishing passes, you might get better results. if you can't do stress relief. Of course, a graph with higher vertical resolution and time scales of years would be desirable.

Grinding your vice from start to finish, a delay, then regrinding all surface might have some benefit. Effectively, that is what Doc did except the first grinding occured in china. Here is what might have happened. Raw casting from foundry is machined and ground without stress relief. The removal of material removed the skin more in some areas than others relieving some stress asymmetrically by the process of simply removing some of the stressed material but the vice is not allowed to relax. Some additional stress is introduced by the cutting itself. The vice is unclamped from the fixture/chuck and instantly warps like a pringle. Then they ship it. Doc then regrinds the vice countering the warp. He is removing less material and may not be pushing as aggressively as a production shop so he may introduce less new stress and relieve less old stress. Doc has thus made an actual milling vice from what was really only a kit, and it might actually be reasonably stable.

Now Moore would be more concerned about what we are (though to extremes), but when he said that stress wasn't relieved at low temperatures what was the context? It sounds like he is saying that stress isn't relieved much below the plastic temperature. Same thing NRL said. But again, we aren't going to heat much of our stuff over the plastic temperature after machining, either. If you are making a $250,000 machine, then getting that last bit of stress out that might later crack the casting or result in a slight shift is worth spending $2000? to heat treat the casting.
"room temperature aging, burrying it in the ground, urine, and cycling it back and forth to the freezer doesn't work" - looks like you inferred that. What didMmoore actually say about those practices? I would think burying in the ground wouldn't be too good because the temperature is too stable. The NRL document mentioned corrosion did relieve some skin stress, so maybe urine has a small effect. Room temperature wouldn't be expected to be as good as outdoors where there is more deviation. Freezer? Well cryogenic treatments are used today. However, you may need to go to -300F and slowly warm to relieve most of the stress. I did read recently that in some metals (certain tool steels), the tempering process isn't finished on cooling to room temperature but the parts have to be cryo treated (http://www.crucibleservice.com/eselector/general/generalpart2.html) to get rid of the last 20% of austenite. What happens to such a half tempered part if it is subjected to frigid conditions after being machined to size?

Some old time practices, like outdoor aging, involve prolonged exposure to temperature extremes that are wider than those the parts is likely to experience in normal use. The NRL study showed that outdoor aged parts still deformed during machining/cutting as much as unaged parts. But what about their long term stability? They didn't test for that. May not be any benefit. But if the major stresses didn't change by more than 1% sitting outside for 1-1/2 years, how much will the stresses of the finished part change sitting in your shop if it was machined twice to compensate for stresses? Cutting: 0.0089" change. Sitting outside for a year and a half: 0.0000" change. What does that suggest about the relative benefits of machining in such a manner that you take into account that the major changes are going to happen right then vs stress relief?

If we are going to accept that this study disputes the benefits of outdoor aging, then we also have to consider that it also casts doubt on the notion that finished parts distort as they age at normal environmental temperatures. If one is an old wives tail, what about the other? Could observed changes be due to abuse, wear, or thermal gradients at the time of measurement in either the part or the surface plate rather than internal stresses? Were they the result of just measuring on the wrong day while the surface plate or the part wasn't in equilibrium? Or was it just that the study was not testing the components of aging/stress relief that really matter for either situation? I.E. the small portion of total internal stress that might actually change with time? Is that getting dwarfed by the major stresses that don't and the short time scales?

However, alternating between the icebox (0 degrees F) and the oven (200 degrees F) for for cycles with 2 hour exposure did produce a measurable, if small effect. The deflection when the part was cut dropped by 5% (0.0018 less deflection. These results, incidently, were about as good as 600F for 24 hours. Was an extra hundred degrees on the cooling side as good as an extra 400 degrees on the heating side? Corrosion induced stress relief was also of a similar magnitude.

Stress relief might follow the 80/20 rule: 80% of the cost is in getting the last 20% of the results. In a home shop environment, we may usually be interested in getting the 80% of results at 20% of the cost or that can be achieved without additional equipment.

Aside from surface finish, how much of the benefit of machining and then grinding a part (without heat treating in between) comes from the part being removed from one machine, allowed to relax, and then all critical surfaces remachined on the surface grinder? What happens if we put it back on the milling machine instead of the surface grinder, for those that don't have a surface grinder? How much do we really care about surface finish on a vice, for example, as long as the bearing surfaces are flat? Except perhaps when dragging a dial indicator across it. If one is going to harden a part then you can't do the post-oven-pringle-effect machining without a grinder.

Vibration is another method of stress relief. A vice on a milling machine may be subject to vibration in use which could result in more change than would normally happen at those temperatures.

Evan
01-29-2010, 06:01 AM
Cast iron is fairly unique in one respect. It has a very high glassy transition temperature compared to other engineering alloys/metals. What effect this has on ageing is hard to say but ageing is a very important part of the development of properties in many alloys. Even mild steel undergoes significant changes in properties after plastic deformation such as bending. Once the plastic limit has been exceeded and the crystals have slipped along boundary planes it take hours and days for the bonds to be realigned and for the properties to return to "normal".

The glassy transition temperature of cast irons is generally above zero F and in some cases even above freezing. Placing cast iron specimen outside will do two things. It will ensure, in moderate climates, that it repeatedly undergoes the glassy/ductile transition in the course of a year and it will therefore repeatedly undergo the induction of coefficient of expansion strains while in the glassy condition. In the glassy condition the notch toughness of most cast irons is reduced to as low as 10% of the "room temperature" notch toughness. In the glassy condition dimensional changes due to temperature changes can induce microcracks along crystal boundaries that will "heal" when the material changes to the ductile state.

It is this type of fatigue cycling that is likely to produce a measurable effect on the dimensional stability of cast irons.

This chart show the transition temperatures for a range of cast iron alloys.

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