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Thank you - the Ruland team

The Inside Story On Ruland Shaft Collars and Couplings

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Good looks are no accident- they come from paying attention to the small details- and good workmanship always looks good

Were those collars polished or prettied-up for the photographs?

 

No, they weren't. Those collars came right out of the packages, right off our finished goods shelves. They all look that way. We don't make them any other way. And that Nikon will show every pimple and every dimple.

 

Then Isn't Ruland Overbuilding These Collars?

 

We don't think so. We start with a little pride. Pride inspires good workmanship, the very best that's in a person. Good workmanship always looks good, and that is really what you're looking at. Call it over-building if you will, but it has proven to be very useful. The apparent overbuilding has resulted in a cost saving for ourselves and our customers, so our prices have stayed very competitive.

But let's not dismiss your question about "over-building"; it's important to understand a little about what collars do and don't' do and what goes into our making good collars. With a little background, "over-building" might not seem like overbuilding anymore.

First let's look at the whole family of collars we make. There are really only two groups in this family – the old-standard set screw type with the radial set screw, which we call SC, and a more recent clamp type version with an adjusting saw-cut and a tangentially positioned clamping screw. Within these two basic groups there are variations in sizes and materials. Within the clamp type group, we also have threaded-bore types, shaft couplings and two-piece take-apart types, but they all trace back to the two basic groups.

 

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Shaft collars saw few improvements until the early 1900’s when Howard Hallowell created the first recessed head set collar.

So, Where did collars come from?

 

The first mass-produced collars were used primarily on line-shafting in early mills. There were some bad accidents because the set screw had a protruding head that could catch a workman's clothing and pull him into a machine.

There wasn't much improvement until that fellow Hallowell got rid of the protruding square-head set screw back in the early 1900's and was awarded a patent for his safety set collar with the first recessed head socket screw. His product became the industry standard, and in time was copied by others.

That invention, by the way, was also the beginning of the recessed socket screw industry. Today, Hallowell's company, the Standard Pressed Steel Company, is a highly regarded maker of the "UNBRAKO" line of socket screw products and a leading producer of aerospace and high specification fasteners.

When we first looked at the industry, there were so many manufacturers and so much competition, you could buy collars so cheap that you couldn't use them.

 

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Clamp collars wrap around the shaft for even distribution of clamping forces

Who invented clamp type collars?

 

No one person invented the clamp type collar. It had been around for a long time, but was more of a bother to make than the old-standard SC style, so you didn't see one very often.

We had been producing the clamp type collar, among other things, during World War II for the bombsights and guidance instruments.

The innards of those instruments were considered very high-tech and hush-hush at that time. They were essentially mechanical with lots of precision gearing, differentials, couplings and collars in combination with electrical selsyn motors, resolvers, precision potentiometers and a smattering of electronics.

Those instruments were the fore-runners of the analog computer industry, which kept us busy in the following years, making precision components, including shaft collars. We saw the merits of the clamp collar design that wraps around a shaft like your palm wraps around a broom-handle, and knew how to produce them efficiently. We proposed to make a full clamp type product range with the largest variety of standard sizes and materials to distinguish it from the old-standard SC set screw collar.

 

Aside from looks, what's so special about Ruland clamp collars?

Many details. Some are obvious, and some others are not. For one, we maintain precise face to bore perpendicularity of TIR ≤ .002" (.05mm) during the manufacturing process. This assures squareness of that side with the bore, and we identify it with a machined groove.

 

What's so special about that?

We're the only supplier, as far as we know, who goes to that trouble. The side groove has been copied by others but the precise face to bore perpendicularity has not. If you need that squareness for, say, a mounting flange, or a bearing face, it's already there in our clamp style shaft collars.

 

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Mis-matches and Match-mates: The groove in the face helps match up the two parts of our split collars and identifies the finished machined face.

Doesn't Ruland use that groove on their two-piece shaft collars?

Yes. In fact, the two-piece collar really started the need for an identifying groove. Since the blanks for both our one-piece ‘CL' collars and our two-piece ‘SP' collars are the same, we used the identifying groove for both types, but for an additional reason, that is, to keep the two halves of the two-piece collars properly oriented.

 

What are the advantages of the two-piece shaft collar?

They hold a little better, because that area ‘b-b' on the torque charts is missing. That's the ‘dead-ban' (see Fig. 1) on a one-piece collar. It's the area of torqueing effort that doesn't do any holding, because that effort is expended in closing the collar bore to meet its shaft. In the two-piece collar all torqueing effort is available, since at the outset the collar bore is in contact with the shaft.

They are real handy to have around, for they can do everything the one-piece type can do, and more. They are more adaptable to varying sizes of shafting, and they can be assembled into a mechanism or disassembled without taking the whole machine apart.

 

Fig. 1 - Representation of Stick Slip (Not an actual record)

Highest holding power in the industry

 

Fig. 2 - Ruland Clamp Style Collars With Alloy Steel Clamping Screws
PART NUMBER BORE
(IN)
CLAMP SCREW SCREW TORQUE
IN IN.-LBS
SLIPPAGE ON SHAFT IN LBS.
CL-4-F 0.250 #4-40 15 200 (HARD)
CL-6-F 0.375 #6-32 28 600 (HARD)
CL-8-F 0.500 #8-32 49 1000 (HARD)
CL-8-A 0.500 #8-32 49 1200 (SOFT)
SP-8-A 0.500 #8-32 49 1250 (SOFT)
CL-10-F .625 #10-32 76 2400 (S0FT)
CL-12-F .750 1/4-28 170 3500 (HARD)
CL-12-A .750 1/4-28 170 3700 (HARD)
SP-16-F 1.000 1/4-28 170 3000 (HARD)
CL-24-F 1.500 1/4-28 170 2900 (HARD)
CL-32-F 2.00 5/16-24 325 8000 (HARD)
CL-48-F 3.000 3/8-24 570 8000 (SOFT)

 

Fig. 3 - Ruland Clamp Style Collars With Stainless Steel Clamping Screws
PART NUMBER BORE
(IN)
CLAMP SCREW SCREW TORQUE
IN IN.-LBS
SLIPPAGE ON SHAFT IN LBS.
CL-4-SS 0.250 #4-40 8 150 (HARD)
CL-6-SS 0.375 #6-32 15 200 (HARD)
CL-8-SS 0.500 #8-32 28 600 (HARD)
SP-8-SS 0.500 #8-32 28 900 (HARD)
CL-10-SS 0.625 #10-32 45 800 (SOFT)
CL-12-SS 0.750 1/4-28 110 1400 (SOFT)
SP-12-SS 0.750 1/4-28 110 1600 (S0FT)
SP-16-SS 1.000 1/4-28 110 1700 (HARD)
CL-24-SS 1.500 1/4-28 110 1900 (HARD)
CL-32-SS 2.000 5/16-24 190 2700 (HARD)
CL-48-SS 3.000 3/8-24 345 3700 (SOFT)

 

Fig. 4 - Ruland Set Screw Collars with Alloy Steel Set Screws
PART NUMBER BORE
(IN)
SET SCREW SCREW TORQUE
IN IN.-LBS
SLIPPAGE ON SHAFT IN LBS.
SC-4-F 0.250 8-32 15 350 (SOFT)
SC-8-F 0.500 1/4-20 75 950 (SOFT)
SC-10-F 0.625 5/16-18 165 1500 (SOFT)
SC-12-F 0.750 5/16-18 165 1600 (SOFT)
SC-12-A 0.750 5/16-18 165 1400 (SOFT)
SC-24-F 1.500 3/8-16 290 2100 (SOFT)
SC-32-F 2.000 1/2-13 350 2900 (SOFT)
SC-48-F 3.000 1/2-13 620 3100  (SOFT)

 

Fig. 5 - Ruland Set Screw Collars with Stainless Steel Set Screws
PART NUMBER BORE
(IN)
SET SCREW SCREW TORQUE
IN IN.-LBS
SLIPPAGE ON SHAFT IN LBS.
SC-4-SS 0.250 8-32 12 200 (SOFT)
SC-8-SS 0.500 1/4-20 60 500 (SOFT)
SC-10-SS 0.625 5/16-18 130 900 (S0FT)
SC-12-SS 0.750 5/16-18 130 1100 (S0FT)
SC-24-SS 1.500 3/8-16 230 1200 (S0FT)
SC-32-SS 2.000 1/2-13 500 1200 (HARD)
SC-48-SS 3.000 1/2-13 500 1800 (S0FT)

 

 

Why does Ruland still offer SC set screw collars?

We sent out sample kits with both the "old" and "new" styles. We soon learned that customers were interested in the old SC style as well as the new clamp style. So we continued to offer both types.

The set screw collar is a familiar component because it has been around for a long time. It costs the least, and does a fair job if properly used. When its holding power is exceeded, there is axial movement followed by an increase in slip resistance. This warning is not apparent in the clamp style.

We didn't expect the SC collar to become an important item for us, but went ahead anyway as part of our one-stop shopping concept. And now, many years later, while most of our activity is in the various clamp type designs, the SC style enjoys a lasting popularity.

 

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The collar that remembers: On soft shafts, it may be difficult to make slight axial adjustment with a set screw collar, because the screw will “home” into its previous indentation. An advantage sometimes, but frustrating at other times.

What's so special about your set screw collars?

We have always provided all-forged socket set screws on every carbon steel, aluminum and stainless steel SC collar we make.

You may be aware that the length of the set screw used in every SC collar size is shorter than the length needed for full performance of that size screw. The socket depth must be reduced, because of this shorter overall length, and, in the case of the conventional drilled-and-broached method of manufacture, the depth must be further reduced to allow for the chip pocket that's required with this method of manufacture. So the maximum permitted torque is lowered.

It may seem like a minor matter, but one advantage of a forged set screw is that it is made by a chipless method of manufacture, so there is no need for the space allowed for the chip pocket. That permits the socket to be formed to a greater depth so the screw can be torqued to higher ratings, with correspondingly better holding power.

When we look at the making of better stainless steel style SC collars, the all-forged process for the set screws becomes a real winner. More about that later.

If set screws do the job, why is Ruland making clamp style collars?

There is a need for both types. The old-standard set screw collar uses a combination of friction and shaft penetration by a hardened screw to achieve its grip on the shaft. Most of the holding ability is accomplished by the penetration of the point of the screw into the shaft.

The SC collar doesn't do a good job in certain areas – it is much less effective on a shaft that is harder than the set screw, because there is little or no penetration.

Because holding power is linked to penetration of the set screw into its shaft, there are set screws available with points having knurls or other trick configurations, all to make a deeper penetration into the shaft. That takes the worst feature of the set screw collar and magnifies it. It can be quite a nuisance for that person who has to remove components from a shaft that was assembled with set collars. And, of course it doesn't do a thing for you if the shaft is harder than the screw.

SC collars aren't as readily adjustable, because of that "memory" matter shown in the illustration. Any and all of the above are solved with the clamp style collar. That's why we make both types.

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Stainless Steel Set Screw Collar

What about stainless steel set screw collars?

We have talked about the heat treated set screw and its making its mark on a shaft to achieve holding power. We now lose most of that capability if we elect to use a stainless steel "SC" product, with a stainless steel set screw because the true stainless steels, which contain high percentages of nickel and chromium, do not respond to the common heat-treating processes used to harden, that is, increase the strength of, carbon-containing steels.

When the screw is even marginally harder than its shaft, there is penetration of the screw point into the shaft. The only method of achieving a higher strength in these austenitic stainless steels is through work hardening – a process than can be induced through excessive kneading of the metal. By utilizing the cold forging process, which shapes the metal by pushing it around, rather than by cutting, we achieve some work-hardening at each step in the sequence of operations. The work-hardening effect is cumulative and the result is a stainless steel set screw of elevated hardness.

So, we have chosen this more expensive cold forming process for our set screws. The screw body, the hex socket, and the screw threads, all are cold forged.

We have found on every stainless set screw collar that we have tested (except our own) that the set screw supplied was of the same hardness as the shafting. This means little or no shaft penetration and a holding power that is minimal.

To our knowledge, we are the only maker of style ‘SC' collars in stainless steel who supply them with socket set screws having this elevated hardness. This results in a level of improvement in holding power that is unique in the industry.

How can you tell if the set screw is harder than the shaft?

It's an interesting oddity, but in two metals that differ from each other by only a small percentage in hardness, the slightly harder one will make a good impingement on the other. If you remove a set screw from an assembly and examine the rim around the cup point, the rim itself will retain its sharp profile if the set screw is harder than its mating shaft. If the set screw is softer, or only as hard as the shaft, the rim will be flattened, indicating no impingement.

What else have you observed?

You might expect, as a starting point, that the axial hold of a collar would be a reflection of the size of the clamping screw and the torque applied to that screw. It isn't always true. When we first tested collars, we found a surprising variation in performance, both in ours, and in our competitors'. Our first job was to identify the causes of this variation, and work on its reduction. We have made considerable progress in this area and much of the contents of this booklet relates to this matter.

What is the major cause of this variation?

Some collars of the same type, applied in the same way, showed variations in holding power. One of the major contributors to this variation is what we call stick-slip.

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Fig. 1 - Stick Slip (Not an actual record)

What is stick-slip?

It's the false impression you get that a screw has been tightened to an appropriate stress level when it hasn't. Instead of the screw rotating uniformly as the torquing effort continues there can be a point before final torque readings have been achieved, wherein this uniform rotation converts to a stop-and start pattern. The torsioning effort on the screw is being absorbed as excess friction between the threads or the under-side of the head and the mating parts of the clamp body, instead of contributing to stress in the joint elements. If the stresses are low, that collar will not hold well. The stick-slip condition can be elusive. A silky-smooth operation of the clamping screw during torquing is your best assurance that stick-slip is not present.

Do torque wrenches help overcome stick-slip?

No. in fact, the springiness of the most torque wrenches invites this condition.

How does plating degrade holding ability?

Electroplating, especially cadmium, zinc, tin, nickel and even some phosphate coatings, perform like high film strength lubricants and can alter the holding ability dramatically, because they reduce a joint's friction coefficient. Any plating deposited on the bore surface will alter this index, but these differences are easily determined. The more serious matter concerns any plating on the screw thread elements. Any change on these surfaces produces a shift in this index that makes it much more difficult to predict the outcome. If the normal torque is applied to the screw, the most likely result would be an over-torquing of the system, with the risk of sudden failure.

We discourage any change to the finish on our collars or their fasteners unless you have the time and the patience to go the whole distance and establish your own torquing parameters.

Incidentally, plated wrenches are not a good idea, either. You will find that they have a shorter useful life, and more of a tendency to "cam-out" or "ream-out" than an unplated wrench of equal quality. Caution: Plating is just another level of complication.

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Proprietary black oxide process produces a fine glossy finish while increasing holding power and resisting corrosion.

What about the many stick-slip compounds that are available?

The problem with all of these we've seen is that they contain "extreme pressure" (EP) additives and these compounds or additives alter the tightening characteristics of the screw. You could end up with broken screws or damaged collars. That's why we did some research and came up with a process that minimizes stick-slip without moving the tightening characteristics off the chart.

Why do you make such a big deal about stick-slip and plating?

Because Ruland would like to disassociate itself from any unrealistic expectations of performance based on published numbers, and would like you to be aware of some elements to consider for a successful and safe design.

Why are you so insistent in using the black oxide finish?

The black oxide finish on our carbon steel collars is there for a reason. It's not any old black oxide, it's formulated as part of the total performance of the collar. It affects the holding ability, the anti-stick slip characteristic and helps keep the torque rating of the screw within its design parameters.

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Positive Location: Machine a groove 1/16” or 1/8” under the shaft diameter to width of an SP collar. Great for impact loads!

Is the black oxide finish a good enough rust preventative?

Not as good as we would like. It's intended to be an internal environment protective finish, not an outside weather protective finish. But it has better rust resistance than the standard alloy socket screws that everyone accepts. And it is part of our anti-stick-slip system.

Is there places where a collar might be used but shouldn't?

Yes. They shouldn't be used to limit impact loads where people or property could be endangered if the collar failed. In designing any mechanism that calls for a person to be near moving parts extreme care should be taken to ensure that those moving parts are constrained to do exactly what they are supposed to do and nothing else. A collar is not always enough.

If there are shock loads present, these should be taken into consideration. The clamp type collar is more sensitive to shock loads than the set screw style. And keep in mind, that a collar that resists several hundred or even thousands of pounds in a static test, can be shifted with a two-pound hammer. To absorb these shocks, the use of Belleville washers, or a resilient buffer may be in order.

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Instant hinges: Four set screw collars.

Is it practical to weld these collars?

We have seen some excellent examples of MIG and TIG welding: Wheelchair parts, exercise machines, printing equipment. Because our steel and stainless steel materials contain Sulphur and other additives, the lowest possible current and adequate ventilation should be employed. Be sure to remove screws before welding.

Why does Ruland ask the designer to do his own thing?

Ruland can do a good job of manufacturing at this end, and can make some tests, simulating ‘normal' conditions, but can't design at a distance, supervise at a distance, or decide what is safe and proper, as well as the person who is standing there.

Ok, so what has all of this got to do with overbuilding?

When we are making a product, we can detect flaws in a fine finish much more easily than in a rough finish. It is easier to measure a part with a good geometry than one with poor geometry. Take for instance the difference between measuring a billiard ball and a potato. The true diameter of the billiard ball is easy to define so less time is spent measuring. By comparison, it can take several trials to obtain useful information about the diameter of the potato. The earlier in the manufacturing process that variations are recognized and resolved, the more economical it is to produce good collars. So, what looks like over-building costs less, sells for less and installs for less.

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When we are making a product, we can detect flaws in a fine finish much more easily than in a rough finish.

How would you sum up what you've told me about shaft collars?

I mentioned something at the beginning about pride being a real asset, but I didn't answer your question fully. Pride does inspire good workmanship. Good workmanship always looks good, and that's what is so obvious in our photograph. And it isn't expensive; it actually save money. Beyond that, pride supports a certain awareness that, if you pay attention to the internal and hidden attributes of a product, the outside will take care of itself. That's why we didn't have to polish or pretty-up our product for the family photograph.

How should shaft collars be installed?

Here are a few rules to follow:

  1. IF YOU CAN, USE COLLARS AS YOU RECEIVE THEM. Wiping the bore, and applying a thin coat of light oil to the shaft may be advisable. Do not de-grease.
  2. Allow yourself some testing time, especially if you plan to plate, lubricate, or rework.
  3. Unplated (black) wrenches are best.
  4. Never use a pipe extender on the handle of the wrench.
  5. As a preliminary to production applications it's advisable to use a torque wrench to establish proper torquing parameters for that specific application.
  6. For maximum holding performance on Nomar® style collars it's advisable to tighten the collar until a slight resistance to rotation is felt, wring to final position, then tighten to final tension. This ensures maximum squareness, good seating, and maximum holding ability.
  7. Observe lower torquing standards for stainless steel hardware, or on threaded elements that have been plated.

What can you tell me about rigid couplings?

Rigid couplings are intended as compact, light-duty components for the timing, joining or aligning of shafts at lower speeds and torques, particularly where zero-backlash is desired. They are not intended for use as a critical part of a drive line or as a substitute for flexible or universal joints and other power transmission devices.

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Rigid Coupling with Nypatch®

Why does Ruland use Nypatch® on its rigid couplings?

The Nypatch® feature is there for safety; if a screw is inadvertently left free of its load, the frictional drag of the Nypatch® feature will keep that screw from further loosening, and possibly fouling or flying out of the assembly. If any screw loses its frictional drag, it should be replaced.

The clamping screws are arranged in pairs, and are fairly close to each other. As a result, there is mutuality in the hoop stress developed in the coupling by each screw in each pair. So, as each screw is tensioned, it tends to relax any tension developed by its companion. Hence, we recommend that the coupling be installed by tightening the paired screws alternately, in several steps, so the tension is distributed more evenly. Likewise, on disassembly

What do you call your screws Nypatch®?

We weren't satisfied with the consistency of the products we could buy, so we developed our own standards, and obtained a registered trademark from the Patent office.

What about shaft misaligment and rigid couplings?

Rigid couplings shouldn't be used on misaligned shafts. The lateral forces working on the coupling as a result of misalignment could lead to premature failure of the shafts, bearings or couplings due to wear and metal fatigue.

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