Field of the Invention
The invention relates to engagement and disengagement between a screw head and a screwdriver or drill shaft tip as the screw is driven into a work surface.
Discussion of Related Art
Screwdrivers of various forms are popular among homeowners, carpenters, builders, and almost anyone with a set of tools.
Most screws have similar features. The head of the screw contains a cavity of various shapes into which the tip of a screwdriver enters. The contact between the screwdriver tip and the head via this cavity enable rotation of the screwdriver to translate into rotation of the screw. The tip of the screw pierces a surface such as wood. The threads of the screw enable the screw to grip into the surface.
At a website for Home Improvement Stack Exchange, there is a discussion about techniques that help prevent slippage when driving a screw with a screwdriver. The following is an excerpt regarding five different kinds of screws:
Flat-head/slotted screws come in many sizes. Having a correctly-fitting bit helps a lot. Too narrow or too thin and you'll damage the head. Too wide and you'll damage the work. Too thick and it won't fit. Fingernails, coins, and knives are non-optimal. Make sure your bit is properly aligned in the slot. Keep the drill directly in line with the screw.
Phillip's head screws are actually designed to “cam out”. That is, when the screw stops turning easily, the bit is pushed up and out of the screw head. This is to prevent you from over-torquing the screw and damaging the work, screw, or bit. Unlike flat-head are discrete, #2 being the most common. Make sure you have a correct size. Keep the drill directly in line with the screw. Pressure on the drill is necessary to keep the bit in place. When the angle makes it difficult to apply pressure, set the clutch low and don't work too hard. When the clutch slips, turn the clutch up and apply more pressure to finish the work.
Pozidriv looks a lot like Phillip's, but has a subtly different shape that reduces cam-out. With clutches on drivers today, the chances of over-torquing are greatly reduced. Make sure you know if your bits and screws are Phillip's or Pozidriv. (Supadriv is very similar to Pozidrive.)
Torx, internal hex, and external hex are all easy to drive without much pressure and without cam-out. They also continue to work well if they get dirty or are painted over.
Square, aka Robertson, is easier to work with than Phillip's, but not as easy as Torx & hex heads.
Higher quality screws do not break or strip as easily as lower quality. Cheap screws are more likely to break or round out (i.e., strip) the head.
The following excerpt provides some practical advice:
Good-quality fasteners are worth it. Cheap screws are more likely to break or round out the head. If a driver bit slips out and damages the screw head, then you'll have a harder time finishing the work or removing the damaged screw. More torque means more damage if it slips, so be careful if you turn up the clutch. As soon as a screw is damaged happens, if you pull the screw out before it gets worse and replace it, you'll be better off than if you keep driving the bad screw.
An impact drill/driver makes driving screws much easier. The work turns to butter. They're also loud, a bit expensive, and can destroy your work if you're not careful Driving slowly lets you keep control and reduces damage when the bit slips.
Predrilling in metal/pilot holes in wood make it easier on your muscles, reduce screw breakage, reduce wood splitting, and don't reduce strength. I've heard that it may actually increase strength, but I don't know for sure. I pick a drill the size of the screw [stem].
If you're having trouble with just a few screws on something you want to look nice, you can always drill a pilot hole. This way you're just fighting the torque on the threads, rather than the torque required to displace wood around the shank and drive the threads.
Note that there are two kinds of screws, and hence two kinds of drill bits used for predrilling. Traditional screws taper evenly toward the tip, and should use a taper-point bit for their pilot holes . . . . Modern screws . . . have a constant “root diameter” until you get to the tip; pilot drills for those can be straight bits of that diameter or a bit smaller. (If you really want to do it right, you then drill a slightly larger section of pilot hole for the unthreaded portion of the shaft and, of course, countersink for the head.)
Soap can help lubricate screws in to wood, making it easier and reducing screw breakage.
You should set the speed to low, and use steady power. They sell cordless drills that have three essential features for this:
1. A really low speed setting.
2. A clutch. Whenever the screw is all the way in, it stops turning the drill.
3. Light weight; if you can't easily hold it in place, it's not going to work.
The following excerpt pertains to magnetic bit holders.
These can be helpful. They are typically magnetic, so they hold the screw in place. They also have a sliding sheath, so it will hold the screw in place until you have completely driven the screw.
I don't like the magnetic bit holders much, because it's easy to leave the bit in the fastener. The sheaths are nice when accuracy is unimportant, but if you want the screw to be really straight, you have to hold it a different way (or pilot).
After seeing a lot of amateurs that have a different concept of accuracy, I think these are fantastic for teaching the concept of lining the drill head up with the screw. And the magnets are nice when you're wearing gloves and can't pick the screw out of your pouch.
There are two sets of forces required to operate a screwdriver: (i) the rotational force to turn the screwdriver and screw and (ii) the forward directional force to hold the screwdriver tip in the screw head and to push the screw forward into the surface.
This standard process of using a screwdriver, however, comes with a negative side effect. When driving into a dense surface, such as pressure treated wood, the amount of forward force one needs to apply on the screwdriver can be quite high. As a result, it is common for the screwdriver to slip out of the cavity of the screw head, sometimes causing damage to the screw, screw head cavity, screwdriver, surface, wall, and/or user. This is such a well-known and common problem that products exist to remove screws whose head cavity has been stripped or damaged by screwdriver slippage.
When driving many screws into a dense surface, for example, even if using a powered screwdriver, the user must still exert considerable force onto the screw to prevent the screwdriver tip slipping out of the screw head, risking greater damage, physical injury and increased muscle fatigue. Some products attempting to reduce these issues are on the market, yet all such screwdriver products fail in high force applications.
For example, one such product uses a magnetized screwdriver tip. This product is of value only to screws that are attracted to magnets. The strength of the magnetic attraction between the screw and the screwdriver tip is almost always far weaker than the sheer force required to keep the screwdriver tip inside the screw head cavity when screwing into medium or hard surfaces. Hence, screwdriver slippage is not prevented.
Another such product uses springs in various configurations to keep the screwdriver tip connected to the screw head. This only works when the strength of the forward force required to keep the screwdriver tip inside the screw head cavity is less than the strength of the spring. Once again, hard and dense surfaces often require far greater force to keep the screwdriver tip in the screw head cavity than the springs can provide.
Another set of such products use various premolded forms with prongs that squeezes the screw. These premolded forms have some limitations such as the inability to accommodate various size screw heads, various shapes of the screw head, and various diameter screw stems, and the necessity of the devices to have to flex to insert the screw. As such, these devices suffer from the same consequences as the magnetized screwdriver tip.
Creative solutions of all sorts have been proposed to keep the screwdriver tip in the head of the screw. These include using tape, glue, and other adhesives. However, none of these solutions reduce the need for the user to maintain considerable forward force to ensure the screwdriver tip remains in the screw head.
For instance, in U.S. Pat. No. 2,762,409, tips are provided to hold a screw. However, each tip is affixed to a screwdriver and does not enable one to change screwdrivers. Further, the jaws have a more limited width of a screw head to which they can grip. The jaws are attached to long straight metal lengths. One would need to stretch these apart to enable a wide screw head to fit within these jaws.
U.S. Pat. No. 5,881,613, whose contents are incorporated herein by reference, provides in part:
A conventional power screwdriver is commonly used for driving a fastener, such as a screw, into various work surfaces. Such power screwdrivers do not provide a means for automatically stopping the rotation of a spindle which holds a driver bit. To use such a power screwdriver, an operator must know when to stop applying power to the motor with a trigger switch to stop the rotation of the motor. However, when a screw is driven into a delicate material, such as dry walls, a delay in disconnecting power to the motor may damage the work surface or may result in an excessive penetration of the screw into the work surface.
Some power screwdriver is equipped with a clutch mechanism to either transmit or disconnect the rotation force from the driver motor to the spindle. The clutch mechanism includes a fixed clutch connected to the driver motor and a movable clutch, which engages or disengages the fixed clutch in response to the pressure applied to a housing surrounding the driver bit when the housing is pressed against the work surface. During the disengaging operation, the separation of the clutches is usually abrupt and causes early wear of gear teeth. Similarly, when two clutches reengage each other, the gears or teeth of two clutches grind against each other to foster early wear.
There is a need for a device that enables one to insert a screwdriver through the center, holding the screwdriver tip in the screw head cavity with sufficient force so that when the screw drives through the surface of the material it is going into, the force required to go into the surface will not cause slippage. Such device will not strip the screw face cavity and must be able to hold each individual screw during the screw driving operation and then release the screw after it is screwed into the surface so that the device may then hold the next screw for the next screw driving operation.
One aspect of the invention is a device and method that includes an assembly that retains an engagement of a shaft tip and a screw head as the screw stem penetrates a surface and that releases the engagement in response to a force applied against an end of a retention sleeve by a working surface that has been penetrated by the stem of the screw. After the release, the screw head may continue to be screwed to penetrate the working surface.
For a better understanding of the present invention, reference is made to the following description and accompanying drawings, while the scope of the invention is set forth in the appended claims.
In this example, as depicted in
As shown in
Given the gearing 28, the tighter one turns the exterior bit contact sleeve 26, the tighter the bit contact jaws 30 hold the drill bit or length/shaft of a screwdriver 18. Turning the bit contact sleeve 26 in a counterclockwise rotation releases the grip of the bit contact jaws 30 from the bit 18. It is noted that it is common for chucks (i.e., for a drill or a screwdriver handle) to have rotating sleeves to control gearing to hold a bit. Such chucks with rotating sleeves are also used in other products such as some flashlights that are controlled by sleeve rotation. There are considerable modifications that can be made to the exterior bit contact sleeve 26, the gearing 28 and the bit contact chuck 24, along with other modifications to enable the connection to the bit or screwdriver length/shaft 18 and still fall within the scope of this invention.
As shown in
However, in the present art, there are no such notched chucks with rotating sleeves to hold a screw 10 as part of a screw stem grasping assembly to effect the relative movements shown in the progressive views of
As depicted in
Screw Contact Jaws and Screw Contact Sleeve
Alternatively, the manner in which the jaws tip 42 move away from each other in response to the exertion of force on the underside of the jaws 40 may arise, for instance, if the construction of the jaws tips 42 is substantially incompressible and the jaws 40 are held either in a resilient manner against the screw stem or to have some give such that the jaws tip 42 follows the angled incline of the screw head to move apart from each other. Turning to
As a further alternative, as shown in
In an embodiment where the device 20 does not have the screw contact sleeve 46 extending beyond the screw contact jaws 40, so that the screw contact sleeve 46 does not come into contact with the surface 60 before the jaws 40, the screw 10 will be held in place by the screw contact jaws 40 until the jaws contact the surface 60. At that point, the user can manually turn the screw contact sleeve 46 counterclockwise to release the jaws 40 from the screw 10.
The device 20 is comprised of non-stretching and non-bending material, such as metal, that uses gears 28 and the like (for the screw contact chuck and sleeve) to position the jaws 30 and 40 and grab the bit 18 and screw 10, respectively. The gears 28 and the like are well established as means to tightly hold items without slipping or stretching such as gears associated with jaws to hold a drill bit. The problem with prior art products wherein pressure forces the screw 10 to be released from the hold of the device 20 is solved because the like gearing is such that the jaws 40 will hold the screw 10 and only release in accordance with the actual pressure applied by the surface 60 being screwed or drilled into. There is no such pressure until the screw 10 is completely into the surface 60 or, at least, well into the surface 60, which depends on how far down from the tip 12 of the screw 10, the user closes the screw contact jaws 40 and jaws tip 42.
For instance, U.S. Pat. No. 5,881,613, whose subject matter at col. 6 lines 38-67 is incorporated herein by reference, describes a screwdriver that provides an automatic disengagement mechanism to prevent excess penetration of the screw into a work surface.
In a preferred embodiment, as shown in
Prior art products are designed for low pressure, low torque screw holds. This device 20 is designed for any pressure including high pressure, high torque screw holds.
Conventional devices, such as that described by U.S. Pat. No. 6,857,343, are based on spring loading to hold the jaws around the screw. Like above, if the pressure required to keep the screwdriver tip in the screw head cavity is greater than the strength of the spring, then this product will fail. The spring will have a limited strength and, over time, like all mechanical springs, loses its strength as it is repetitively stretched and returned.
The invention is designed for high pressure and high torque screw holds. As shown in
U.S. Pat. No. 7,779,734 is a screwdriver-starter. It initially holds a screw but, like the above described prior art, is meant to initially hold the screw and does not support high torque continuous holding of the screw. It uses a spring to push a screwdriver tip into the screw. Like the above prior art, it is not designed for high pressure, high torque screw holds and is not designed to automatically disengage once the screwdriver tip reaches the surface into which the screw is being driven.
Here, the inventor uses a set of screw contact jaws 40 whose tips 42 are extended inward toward the center so that, as the screw contact jaws 40 come together, the extension tips 42 grip the shaft of the screw 10, preferably just below the screw head 12. The screw contact jaws 40 hold the screw 10 in place throughout the process of drilling or turning the screw 10 into place. These jaws 40 automatically disengage once the jaws 40 or the screw contact sleeve 46 hits the surface 60 due to friction causing the screw contact sleeve 46 to stop its rotation in the clockwise direction, seemingly rotating in a counterclockwise direction relative to the rest of the device 20 that continues to rotate in the clockwise direction. This is because, when the screw contact sleeve 46 hits the surface 60, there is friction sufficient to stop the clockwise direction of the screw contact sleeve 46, which triggers its release of its engagement of the screw head 10 due to the like gearing driving in a counterclockwise direction relative to the clockwise rotation of the device 20. This action causes the contact chuck 44 and jaws 40 to open in accordance with the friction created by the force exerted on the surface 60.
As in a standard drill chuck, the screw contact sleeve 46 around the screw contact chuck and jaws 44 and 40, respectively, is turned to open or close the jaws 40 around the shaft of the screw 10. The like gearing for the notched chuck 44 and the screw contact jaws 40 are positioned such that closing the jaws 40 around the screw 10 requires the screw chuck sleeve 46 be turned in the same rotational direction of the screw 10 to be driven into the wall.
Again, it is noted that
Bit Contact Jaws and Bit Contact Sleeve
At the end of the screw bit holder chuck 24 into which one inserts a screw bit or screwdriver 18, a preferred embodiment comprises a set of jaws 30 similar to drill chucks so that as the jaws 30 come together, the jaws 30 grip the shaft of the screw bit or screwdriver 18. In this way, the device 20 can be slipped onto any drill bit or screwdriver because of the cylinder 32 and cavity 22. Then, at one end, the device 20 can be tightened onto the drill bit or shaft of the screwdriver 18 via the bit contact jaws 30. Turning the bit contact sleeve 26 allows the jaws 30 to tighten and grip the bit or shaft 18.
The positioning of the bit contact jaws 30 prior to the turning of the sleeve 26 is typically such that the distal end of the device having the screw contact jaws 40 and sleeve 46 will grip the shaft of a screw 10 just below the head 12 of the screw.
Variations of the dual sleeve jaw system can be created. For example, the bit contact jaws 30 and the bit contact sleeve 26 can be permanently assembled to a screwdriver. A drill assembly can have the dual sleeve jaw system as well. In any variation, the notched chuck 44 is provided to hold the screw 10 in the novel manner described herein.
While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various changes and modifications may be made without departing from the scope of the present invention.
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Entry |
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“What is the best technique for using a drill to insert screws”, Home Improvement, http://diy.stackexchange.com/questions/7524/what-is-the-best-technique-for-using-a-drill-to-insert-screws, Jul. 8, 2011. |
Number | Date | Country | |
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20180147704 A1 | May 2018 | US |