straightening without painting cues
straightening without painting cues
Straightening without painting cues
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What can we do to create the illusion of depth in our designs?
There are 2 types of depth cues
- pictorial cues — can be reproduced in a photograph or realistic painting
- non-pictorial cues — can’t be reproduced in a photograph or realistic painting
Pictorial depth cues do not have to be applied singularly to the entire design. They can be applied independently to the different elements that make up your design.
Your visitor will find depth even in a flat design so the question isn’t whether or not to be 3d or 2d, the question is which depth cues will you use.
The rest of this post will focus on some pictorial depth cues.
Pictorial Depth Cues
Below are some of the different cues we can use to give the illusion of depth being present in a design.
When one object obscures part of another object it’s clear there must be a depth of space between them. Objects that are nearer occlude (cover up) objects that are further away.
It’s important that the partially occluded objects are recognized for their complete shapes or the total composition can be seen as two shapes sitting side by side.
One way we can use the above is to organize information so that more important information partially occludes less important information.
Size and scale
We can use the above to show the relative importance of information. Less important information will take up less space and be smaller.
A ground texture can also provides a size reference for other objects.
These lines don’t need to be visible, though they can be. They can also be implied by the objects in the composition.
Perspective is by definition a technique for representing 3-dimensional objects and depth relationships on a 2-dimensional surface.
When the shadow is smaller, darker, crisper, and nearer the object casting it, the nearer the object is to the surface holding the shadow.
You can increase the depth by making the shadow larger and lighter and placing it further away from the object. Blurring the edges of shadows also increases the illusion of depth.
Location on the picture plane
Perhaps this has to do with a look at the world around us.
When we stand in our 3-dimensional world it’s those things we see at the bottom (the earth, the grass, the pavement) are those we’re physically connected with, those things that are generally closer to us.
The clouds, the sky, the stars, those things we see above are also further away from us.
Lighting and shading
Gradients, Bevels, Embosses, and the like show depth in the way light is held and reflected off a surface.
The surface of an object can also show more or less light depending on its orientation from the light source. Closer to the light source will show a brighter surface with more reflected light.
Depth of field (focus)
The closer another object is to the one with the focus, the less depth is perceived between the two. The further away on the same depth plane an object is from the focused one, the blurrier it should appear.
This is true regardless of whether or not the out of focus objects are nearer or further from you. The blurriness is relative to the difference in depth with the object in focus.
- Depth of Field: One of the most important elements in photography
- Depth of field
- Tutorials: Depth of field
Reference to nearby or known objects
The known object adds a context tied to the absolute world and as such adds scale to the picture.
The nearby object adds a different kind of context, but a context nonetheless. An object can only be small in relation to another larger object.
Degree of contrast
It also helps account for depth of field as the greater the contrast in focus and blurriness, the greater the distance.
Since the canvas we work in is 2-dimensional, we can only impart a sense of depth through visual depth cues. There are a variety of different cues you can use, each communicating in its own unique way and each with a different strength in making us see depth.
Bent Shaft Straightening
A bent shaft can occur as a result of damage during shipment, rigging, or operation. Shaft straightening methods, when properly applied, can sometimes be used to salvage damaged shafting.
Because of the different variables involved, shaft bend correction can be as much an art as a science. Each application is unique, and needs to be reviewed on a case-by-case basis.
Table of Contents:
- Measuring Straightness
- Mechanical Shaft Straightening
- Spot Heat Method
What is the definition of bent shafting?
In a perfectly straight shaft, the centers of each shaft cross-section from end-to-end of the shaft lie on a straight line. A shaft is bent if that is not the case.
In a bent shaft, the axis of the shaft is different than its axis of rotation. The range of the orbit or gyration caused by the shaft bend is defined as the shaft runout, and is typically measured in terms of "TIR" (Total Indicator Reading).
What are the consequences of operating a piece of equipment with a bent shaft?
- Shaft misalignment
- Equipment vibration due to unbalance
- Damage to bearings, seals, and couplings
- Contact, and possible seizure with, close-clearance surfaces
- Material fatigue
What causes shafts to bend?
- Damage during rigging or improper handling
- Impact during operation
- Machine misalignment
- Unequal machining operations
- Vibration during shipment
- Improper material handling during heat-treating, rolling, forging, thermal stress relieving
- Elevated temperature during operation
What is the best bent shaft straightening method?
Unfortunately, there are no simple answers to this question. A successful shaft straightening repair is dependent on several interrelated variables, with the result that a method that is successful in one case may be unsuited for another.
In general, it is safe to say that the best method is the one that requires the fewest corrections to achieve the desired straightness tolerance, that adds the least additional stress to the shaft.
If the process restores the deformed shaft material fibers to their original state, prior to bending, the chances for a long-term successful outcome are good.
In practice, the bent shaft straightening process sometimes simply creates additional stresses in the material that oppose the material stresses that caused the initial bending. As a result, the shaft material fibers that initially caused the shaft to bend remain in a stressed condition after the repair is complete
A shaft straightened in this manner can initially indicate straight. However, the long-term success of the "balanced stresses" is doubtful and unpredictable, as those material stresses can relax over time.
To determine an appropriate approach for a particular application, it is helpful to review and evaluate the factors discussed in the next section.
What factors determine the feasibility of a successful bent shaft straightening repair?
With the urgency of an equipment downtime situation, it can be tempting to begin a repair process without fully understanding the problem or considering the consequences of the proposed correction. However, it is worth taking a few minutes to properly assess the situation to determine if the selected course of action is appropriate.
Some of the criteria that determine the outcome of a bent shaft straightening project include...
Cause of the bend
relaxation of internal stresses
Type of bend
The material from which a shaft is manufactured is a significant factor in determining the feasibility of a successful repair. Some materials are inherently more stable than others, and are therefore less susceptable to distortion. Those same materials tend to be more forgiving as they are straightened, and are therefore more suited for repair.
The shaft material is of particular importance if one of the heat straightening methods is considered. Applying heat to local areas of shafting has the unfortunate side effect of changing the hardness with the unwanted result of hard spots and possible thermal stress cracking.
Shafts manufactured of low-to-medium carbon steel material (.10 to .50 carbon) are less likely to have material-related problems during straightening. However, shafts that are hardened, or made of high carbon content steel, high alloy steel, stainless steel, or non-ferrous material need to be evaluated on a case-by-case basis.
Shaft design can include features such as keyways, tapers, shoulders, threads, holes, etc. In general, the greater the number of design features, the more challenging the bend straightening repair can be. Shaft design features act as stress risers. In addition to being a contributing factor in causing bending to occur initially, they can also affect the success of a bent shaft straightening repair.
The shaft length-to-diameter ratio is also a consideration. Shorter length, larger diameter designs are much more stable than are the long, slender types of shafting such as used in turbine pumps, for example.
type of applicationconsequences of a possible failure
For example, a shaft used in a slow-speed, low-tolerance, non-critical application obviously has a greater margin for error than a shaft that is used in a high RPM, close clearance machine.
The value of the machine downtime as well as the cost of labor to repair the damage are all factors that need to be evaluated.
Measuring Shaft Straightness
What are typical shaft straightness tolerances?
What is a bent shaft survey map, and how is it useful in a shaft straightening process?type of bendinglocationmagnitude
What is the procedure to create a bent shaft survey map?
- Support the shaft so that it can be rotated freely. To do this, the shaft can be supported using V-blocks as shown in Figure 2, or supported between centers in a lathe. In some instances, the shaft can be rotated in place in its machine housing supported by its journal bearings.
- Using a felt-tip marking pen, make a "Rotational Reference Mark" on the shaft as shown in Figure 2. The position and orientation of the marking is arbitrary, but once established, the same mark is used throughout the shaft straightening process.
- Create several evenly spaced "Axial Reference Marks" on the shaft using the felt tip pen. The number of axial markings, and their spacing distance, is not critical, and can vary depending on the length and diameter of the shaft. The axial reference marks are used throughout the process.
- Position a dial indicator over one of the axial reference marks as shown in Figure 2. Starting with the Rotational Reference Mark at the 12:00 orientation, slowly rotate the shaft. As the shaft rotates, observe the full range of travel measured by the dial indicator - also known as the Total Indicator Reading (TIR). For purposes of consistency, it is generally helpful to record the amount of the shaft deflection, which is one-half of the TIR value obtained. For example, if the Total Indicator Reading (TIR) is .004 in (0.1 mm), the shaft deflection recorded value is .002 in (0.05 mm).
- With the dial indicator positioned as described in the previous step, note the orientation of the Rotational Reference Mark that corresponds with the "high" point of shaft deflection measured by the dial indicator. For example, if the dial indicator shows that its maximum deflection occurs as the Rotational Reference Mark is at the 3:00 orientation, record the 3:00 position on the survey map.
- Repeat the above steps at each of the Axial Reference Mark locations on the shaft so that a value for deflection and orientation is recorded for each location.
- Review the survey map to determine if there is a trend in the data. Whether the shaft has a twist, a gradual bend, a simple bend at a single location, or perhaps more than one bend, the survey map data should help to identify the type of bend present in the shaft.
- Determine a location to perform a bent shaft straightening correction. The best location is typically the single point on the shaft where the greatest deflection occurs, and may not be at one of the locations previously recorded. By reviewing the survey map, move the dial indicator to axial locations where the data trend suggests that the greatest deflection may occur. By trial-and-error, locate the spot of greatest deflection and mark it.
In the set-up shown in Figure 2, the dial indicator is positioned very close to the shaft support V-block. What is the purpose of taking a reading at that point? Shouldn't the runout measured near a shaft support always measure zero?
Any shaft support runout issues need to be resolved before proceeding to create the Survey Map. Otherwise, those errors will distort the mapping data obtained.
In the set-up shown in Figure 2, won't gravity cause the shaft to sag in the middle? Will the sag affect the Survey Map data?
if the shaft is of uniform cross-section
Bent Shaft Straightening Methods
What are some typical bent shaft straightening methods?
- Mechanical Shaft Straightening
- Spot Heat Shaft Straightening
- Peening Shaft Straightening
- Opposed Heating and Cooling Shaft Straightening
Mechanical Shaft Straightening Method
What is the Mechanical Shaft Straightening repair procedure, also known as "Cold Shaft Straightening"?
- Create a Bent Shaft Survey Map to determine the location and amount of bend correction required.
- Install the bent shaft in a suitable press as shown in Figure 3. Rotate the shaft so that the "high side" of the bend with the greatest magnitude of deflection is positioned directly under the ram of the press. Mount a dial indicator as shown in Figure 3 to monitor shaft deflection.
- Slowly actuate the press to apply a force to the shaft while monitoring the amount of deflection on the dial indicator. To get a feel for the responsiveness of the shaft to bend correction, it is a good practice to work in increments and then back-off the press to observe the result.
- Repeat the process until the desired shaft straightness is obtained.
What are the advantages and disadvantages of the mechanical shaft straightening method?Advantages:
- Of all the shaft straightening processes, the mechanical method comes closer to correcting the root cause of the problem for many applications. For this reason, the mechanical method is often considered the first choice approach.
- With a proper set-up, the repair cycle of the mechanical method can be performed relatively quickly. The results can be monitored easily and directly throughout the process by observing the dial indicator reading. For a given shaft, the amount of required correction is relatively consistent and repeatable.
- Because the mechanical shaft straightening method does not require the use of heat, it can be used on a wider range of shaft materials than the spot-heating process.
- The mechanical shaft straightening method requires a press of adequate capacity to correct the bending in the shaft. For large shafts, the availability of a suitable press and material handling equipment can be a limitation. For these same reasons, this process can be difficult to perform while the shaft is in-place.
Spot Heat Shaft Straightening Method
What is the procedure to straighten a bent shaft using the Spot Heating method?
- Create a Bent Shaft Survey Map to determine the location and amount of bend correction required. Rotate the shaft so that the "high side" of the bend with the greatest magnitude faces upward as shown in Figure 4. Part of the success of the spot heat shaft straightening method relies on the weight of the shaft itself to assist in correcting the bend.
- Position dial indicators adjacent to the bend location as shown in Figure 4. If the shaft is supported between centers in a lathe, relax the center preload slightly so that the shaft can flex during the shaft straightening process without binding.
- Working quickly, heat an area of the shaft about .5 in - 1 in. (12mm-25mm) diameter using the welding tip of an oxy-acetylene torch. The objective is to achieve a temperature differential, or local hot spot, between the area being heated and the surrounding area. Therefore, apply the heat evenly and steadily while monitoring the dial indicators.
It is really important to watch the dial indicators during the entire heating process as things will happen quickly, usually within several seconds.
As the shaft is heated, the dial indicators will climb - indicating that the amount of the bend is increasing, temporarily. This is the desired result, even though it seems counter-intuitive.
- When the dial indicators show that the desired deflection is achieved, remove the heat and allow the shaft to cool. To speed-up the process, the cooling cycle can be accelerated by various methods such as pouring water on the shaft, or by the use of compressed air, a spray mist system, or by simply using a wet sponge or wet cloths.
If the shaft is straightened in a machine with a water-based flood coolant system, that can also be used to cool the shaft as shown here.
As the shaft is cooled, the dial indicators will move in the opposite direction as they did during the heating process. Continue cooling until the area that was heated is the same temperature as the rest of the shaft.
- After the cooling is complete, measure the magnitude of the bend that now exists in the area that was just straightened. Compare this new value with the previous bend deflection prior to the repair.
If no improvement in the bend is measured after the first repair cycle, repeat the spot heating process by increasing the heat-induced deflection in small increments of .010-.020 in (.25-.50 mm) more than used in the previous attempt.
NOTE: At any point, if the amount of heat required causes the shaft to become dull cherry red in color without having an effect on correcting the bend, the spot heating approach in unsuited as a repair method for that particular shaft and an alternate process needs to be used.
- Repeat the process until the desired shaft straightness is obtained.
Photo courtesy of Machinist's Inc.
How does the spot heat shaft straightening process work, in principle?
Experienced welders are familiar with metal distortion, known as "drawing" or "heat affected zone", that occurs during the welding process. Spot heat shaft straightening uses the same principle. The mechanics of the process are as follows:
- A small area is heated quickly so that the material in the localized area is in a softened, semi-plastic state while the surrounding material remains relatively cool and solid.
- The spot-heated material expands as it is heated. Because the locally heated area is surrounded by solid (cooler) shaft material, the thermal expansion causes growth in the only unrestrained space available... toward the surface of the shaft. This expansion creates the raised bump on the surface of the shaft that is characteristic of the process.
- As the shaft is cooled, it would be natural to assume that the material in the raised bump would return to its original state prior to heating. In actuality, the exposed surface of the bump cools the most quickly - and becomes solidified in the raised condition.
- The very center of the heated spot is the last to cool and, as it cools, the material contracts. At this stage of the process, the center spot is surrounded on all sides by material that is in a cooler, solidified condition.
- The contraction of the center creates a tensile stress at that location that is very close to the yield point of the material. The localized tensile stress exerts a force that pulls on the surrounding material and causes the shaft to deflect.
In Figure 5, the red lines indicate the shaft forces generated as a result of the localized area of tension. When performed properly, in the correct location, the tension forces can pull the shaft toward straightness.
What are the advantages and disadvantages of the Spot Heat bent shaft straightening method?Advantages:
- The method uses readily available industrial repair shop equipment.
- If necessary, the process can be performed in-place where the shaft is located, whether installed in the equipment in which it operates or in a machine tool such as a lathe.
- The process creates high material stresses in concentrated areas. The stresses can relax over time and affect the straightness of the shaft.
- Spot heating can create a heat-affected zone that is undesirable in critial application shafting. The tendency of creating localized hard spots or stress cracks limits the shaft materials that are suited for this process.
- Spot heating creates a slightly raised bump in the shaft material in the area that was heated. The bump needs to be carefully removed prior to using the shaft, particularly if located in the area of a bearing or seal surface.
- The process can be very time-consuming. After each heating cycle, the shaft needs to be completely cooled to a uniform temperature prior to assessing results.
- There is not a precise method of determining the amount of heating required. The amount of heat needed for each project is best determined by trial-and-error. Several iterations are typically required to achieve the desired result.
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What can you find on YouTube:Jacoby shaft adjustment tool. how to straighten warped pool cue shafts easy No Steam!