Introducing the X Link

X Link Far

The X Link is my adaptation of the nineteenth century scissors mechanism used with a leg vise to eliminate the need for a pin in the lower guide board. I have used modern materials and have added improvements to make it function better and ease installation. The X Link is shown used with the VX 20 vise mechanism to create a  quick action pinless leg vise. Here is a link to a YouTube video of the vise in action:

X Link YouTube Video

The X Link mechanism is designed to provide exact parallelism between the vise jaw and the vise leg. In practice however the vise jaw should be angled slightly so the top of the jaw contacts the workpiece first and clamping pressure deflects the mechanism slightly and makes the jaw parallel to the leg. Ideally this deflection should be kept to a minimum for best operation. In the video the jaw is spaced out at the lower jaw link end by only 0.040″ which is about 3/64″. This is accomplished by adding a shim to the mechanism. This small amount of deflection is easily accommodated by the VX 20 mechanism and full clamping pressure is applied in a half turn of the handle.

X Link Close

The X Link mechanism is housed in a mortise which is only 16″ long and 1″ wide. The jaw is 2-1/8″ thick and 5-1/2″ wide. In a future post I will disclose more details about the mechanism and some of the unique features which make it operate with minimal deflection and allow simpler installation.

Progress

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We are hard at work producing the parts to make the VX 20 vise. I thought I would share some of the processes that go into making the vise.The picture above shows some parts  right after machining.  After machining there are a lot of burrs and tool marks in the parts. To get rid of all of the marks and soften all of the corners the parts are put into a vibratory tumbler with little cone shaped dense plastic media. After many hours of tumbling the parts come out with a very uniform finish and all the edges are smooth. After the finishing process the parts are sent out to be anodized and then they are ready for assembly.

VX 20 Vise Now Available For Pre – Order!

Pre – order the VX 20 vise now and save $10.00! This special will only be offered for a limited time so hurry. The metal hand wheel and wooden hub with handle have also been added to the product line up. The pre – order vises will be shipped on a first come first served basis. We plan on having vises ready for shipment in early October. When the pre – order period is over the price will rise to $140.00.

We are currently working on the directions and will post those as a download as soon as we can. The VX 20 is very easy to install so don’t expect a lot of complicated directions. An assembly view and jaw and leg drawings are available here:

VX 20 Assembly With Pin Board

VX 20 Jaw Hole Dimensions

VX 20 Leg Hole Dimensions

Please note that the production vise will differ slightly from the current pictures. The color of the production vise will be black based on the huge customer response for that color. The vise will be mounted using #10 wood screws instead of lag screws as pictured. We will updated the pictures to reflect these changes as soon as we can.

VX 20 Vise With Ancora Yacht Service Chain

 

 

 

 

 

 

Ritter Chain Mechanism WEB

Jim Ritter from Ancora Yacht Service has installed his chain mechanism with the VX 20 vise and it works really well! Jim produced a YouTube video showing how it works. Here is the link: VX 20 with Ancora Yacht Service Chain

In Jim’s video the VX 20 is shown with a wooden hub and handle and the housing rotated to allow the chain to be as close to the clamp shaft as possible. I plan to offer a VX 20 specifically for the chain mechanism which will allow the wooden hub and handle to be oriented vertically when in the un-clamped state. I am going to provide Jim with the metal hand wheel as soon as I can get them in. I have a feeling the hand wheel option will be pretty popular.

I just received my own chain mechanism shown above which I will build using the VX 20. I can’t wait to see it in action for myself! The machining on the parts in Jim’s kit is excellent and all of the fasteners are high quality. It is obvious he has put a lot of time in designing the chain mechanism. Please check out his website to find out more:  Anchora Yacht Service Website

 

Help! My Scissors are Bending!

Scissors Patent jpeg

The above patent illustration is from a May 13, 1845 patent by W.H. Taylor and A.P. Norton of Waterville, NY. I guess the guys in the mid Nineteenth century didn’t like to bend over to adjust a pin either. Scissors mechanisms have been around for a very long time in various forms and have found their way into many household items. The application of a scissors mechanism (sometimes referred to as St. Peters Cross) to a leg vise presents some interesting design and engineering challenges. I have viewed some YouTube video’s with home-made scissors parallel guides that did not function well and the above inventors must have had similar problems because their patent utilizes a rack and pawl mechanism to help restrain movement.

When I built my first prototype scissors mechanism I knew there would be some deflection (or more simply bending) of the links in the mechanism and in fact I calculated what it would be. But the scissors mechanism deflected significantly more than what I had calculated. This deflection allows the bottom part of the vise jaw to swing in and can make it feel as if you are compressing a stiff spring in the jaws. If the deflection is severe enough the top of the vise jaw will pivot away from the part being clamped causing looseness. I knew there had to be something else happening, so through much experimentation I have found the factors that cause the excessive deflection. This simple mechanism from the 19th century turned out to be quite complex. So complex that I had to create an excel spreadsheet to do all the calculations and allow me to accurately predict the performance of a scissors mechanism.

Scissors Mechanism Deflection Sketch

In a leg vise the scissors mechanism is loaded at the lower free end of the link sliding against the vise jaw. In engineering speak we call this asymmetrical loading but in simple terms the lower part of the scissors mechanism has a force on it and the upper part does not. This asymmetrical load happens because we are clamping a work piece at the top of the vise, putting screw force somewhere near the middle and trying to stop the jaw from rotating with the scissors mechanism at the bottom. The scissors mechanism resists this force because the legs of the mechanism always want to remain parallel with one another. We know the force applied to the scissors mechanism will be upwards of 300 pounds and we can calculate how much the links will bend under load. If they are properly sized this bending will only be thousandths of an inch. So let’s investigate now what is causing all the additional deflection.

When the scissors mechanism has the asymmetrical load applied to the lower part of the mechanism it will deflect inward slightly. When this happens it also allows the jaw to pivot in with the hinge point being the board that is being clamped. The upper jaw link pivot is located in the jaw that is pivoting and acts as a multiplier for any jaw rotation. So any movement of the upper jaw link pivot point is going to be multiplied and causes the scissors mechanism to further deflect. I call this phenomenon pivot factor for lack of a better name. It is very similar to what happens in an old time pantograph enlarger which is also a form of scissors mechanism. The jaw also deflects slightly at the pivot point when a load is applied and this is multiplied as well. Additionally, when the links of the mechanism deflect, this small deflection is doubled because it occurs at the center pivot pin and displaces the lower contact point of the leg link. So if you have a typical scissors mechanism leg vise and apply 1000 pounds of screw force the scissors links will only deflect 0.006” but the mechanism multiplies this and actually deflects almost 1/8”. In a screw operated vise you just make sure the top of the jaw touches the work piece first and the bottom of the jaw is angled out, and add a few more cranks to take up the deflection. In a quick action vise you don’t have the option of additional cranks and this is just wasted motion and effort anyway. With this in mind I set out to optimize the scissors mechanism to minimize deflection. Deflection can’t be eliminated entirely but there are a few ways to minimize it:

1. Shorten the links.

2. Use a stiffer material for the link construction.

3. Use a thicker jaw.

4. Decrease the mortise size in the jaw.

5. Strengthen the center pivot of the two links.

Shorter links will be significantly stiffer than longer ones and changing the material from cast iron to steel for example will increase the stiffness by 61%.

A thicker jaw will reduce the deflection of the upper pivot. I have actually measured jaw deflection using a straight edge and a feeler gage. If we have an 8” wide by 1-3/4” thick jaw and apply 1000 pounds of load to it, it will bend almost 1/16”. If we increase it to 2-1/2” thick it will only bend 1/64”. And keep in mind that this is a solid jaw for the whole length. The deflection will increase due to the mortise in the jaw and to a lesser extent any reduction in width.

The center pivot should be very solid and close fitting. Any deflection of this pivot point will be doubled at the bottom of the vise jaw.

Let’s look at two hypothetical designs and compare the performance.

Option 1: Cast iron links, 17-3/4” long, 3/4” thick and 2” wide. Centerline of screw to upper pivot is 3”. The jaw is hard maple, 2-1/2” thick and 4” wide with an 8” throat and will be the same in both cases. With 1000 pounds of screw force applied with a 3/4″ jaw opening you will get 720 pounds of clamping force, the jaw will deflect 0.038”, the links will deflect 0.006” and the total deflection of the lower part of the jaw at the link contact point will be 0.089”.

Option 1

Option 2: Steel links, 14-7/8” long, 1/2” thick and 1-1/2” wide. Centerline of screw to upper pivot is 2-13/16”. The jaw is the same. With 1050 pounds of screw force applied with a 3/4″ jaw opening you will get the same 720 pounds of clamping force, the jaw will deflect 0.031”, the links will deflect 0.005” and the total deflection of the lower part of the jaw at the link contact point will be 0.074” a 16% reduction.

Option 2

Option 2 will require a 16” long by 1” wide mortise of 20 cubic inch volume. Option 1 will require a 19” long by 1-1/2” wide mortise of 49 cubic inch volume. Option 2 reduces the mortise volume by 59% which will make the jaw stiffer and reduce deflection on a similar sized jaw. The drawbacks to option 2 are that it will require a half pound more force applied to an 8” diameter hand wheel with a 4 thread per inch screw and it has slightly less clamping force at the widest jaw openings. I think that is a good tradeoff for a stiffer and more compact scissors mechanism.

We will put option 2 to the test and see how it actually performs when paired to the VX 20 vise mechanism. Check back later to see the results.

 

 

 

Contact page email now working

We finally have the contact page email working. If you have sent an email through the contact page on the website recently and have not received a reply please re-send your message as our email was not working properly. Sorry for the problem, we are not ignoring you!

More About the VX 20

VX 20

There will be some very minor changes to the VX 20 between the vise shown and the production unit. The mounting will change from four ¼” lag screws to four #10 pan head wood screws. For this application the lag screws are overkill and the #10 screws will package better and be easier to install. I am considering changing the color of the housing to black instead of the gold and adding the Hovarter Custom Vise logo to the housing in white letters. If you have an opinion on the housing color I would like to hear it.

Here are some additional specifications on the VX 20:

The mounting base is 3” wide by 4” long and the housing is approximately 2-1/2” high. The maximum jaw opening is 11-3/16” when used with a 1-3/4” thick jaw and a 3” thick leg. The carburized and hardened steel clamp shaft is designed to be fully retracted flush with a minimum 3” thick bench leg. The 20-1/4” long clamp shaft may be lubricated if desired. A coating of wax will help prevent corrosion and improve the sliding action. The clamp shaft is retained by the housing and can’t be removed without dis-assembly of the housing. The vise mechanism provides clamping action similar to a 4 thread per inch screw and will provide high clamping forces for a minimal force input to the handle.

The vise is virtually maintenance free. The totally enclosed housing prevents dust and dirt from entering. The aircraft grade anodized aluminum housing will not corrode and the machine screws which hold the housing together are stainless steel to prevent corrosion. All internal wear parts are constructed from steel for long life. If any maintenance or cleaning is ever required the housing can be simply removed by un-screwing the four Phillips head machine screws.

Introducing the VX 20

The VX 20 is the culmination of years of development work to produce a robust, economical quick action leg vise that is also simple to install. This versatile vise mechanism can also be made into a quick action face vise or be used just as you would use a conventional vise screw and nut. The VX 20 is constructed from aircraft grade anodized aluminum, steel and stainless steel to provide a lifetime of service.

See Video Here

To install the VX 20 simply drill holes through the bench leg and vise jaw and screw the housing assembly to the back of the leg. A Delrin bearing is screwed into a counter-bore in the front of the leg. The vise handle is attached to the shaft with a quick release pin which allows the jaw to be removed entirely in seconds. The pin system also allows you to select either a wooden hub and handle or a metal hand wheel to customize your vise. Other options are in development and will be introduced at a later date.

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VX 20 Housing

Perhaps the greatest feature of this vise will be the price. The VX 20 vise assembly will start at $140.00! The hand wheel or wooden hub will be sold separately to allow the consumer to fully customize the vise. Please check back often to see the latest developments and look for a pre – order discount!

Forces in a Leg Vise

For as long as I can remember I have always read about the remarkable clamping force generated by leg vises. When I began to design leg vises I found out that this is not necessarily the case. If you think I am going to start bad mouthing leg vises you are wrong. I like leg vises but you need to understand the shortcomings and not overlook their faults. I like to understand all the forces involved in the leg vise so I can make it operate at its maximum potential. Let’s take a look at the forces generated in a leg vise and see what is really going on.

Leg Vise Forces Capture

A leg vise is typically characterized by a very deep throat (the distance from the very top of the vise jaw to the screw or clamp shaft) of 8” or more. Where you clamp the work piece in the leg vise greatly affects the clamping force generated. If you clamp a board so that the bottom portion of the board rests on the vise screw then nearly all the clamping force will be applied to the work piece. See FIG. 2. If however you clamp a relatively thin board flatwise at the top of the jaws then you will have reduced clamping force. See FIG. 1.  This is the worst case clamping scenario for a leg vise. When I design a leg vise this is the clamping configuration that use.

Now let’s go through some simple math and figure out just what’s going on in a leg vise. From my last blog we found out how much force is generated by a vise screw. We will use the last example, a 4 TPI (threads per inch) screw with an 8” diameter hand wheel. This screw will generate approximately 1000 pounds of clamping force when you apply 10 pounds of force to the rim of the wheel. For the vise jaw we can assume a 9” throat and 16” from the screw centerline to the parallel guide pin board. The distance from the screw centerline to the parallel guide pin board is called the fulcrum length.  As force is applied to the work piece to clamp it the bottom of the leg vise wants to pivot in as if the jaw was hinged to the work piece so we counteract that pivoting by pinning the lower parallel guide. What we end up with is a screw force acting in towards the bench and two reaction forces acting in the opposite direction. One of the reaction forces occurs at the work piece and is used to clamp and the other occurs at the parallel guide and is wasted on stopping the jaw from rotating. To calculate the forces a simple proportion will give you the reaction force and the parallel guide force. Here is an example for the worst case with a board clamped at the top of the jaws as shown in FIG. 1.

CLAMPING FORCE = SCREW FORCE X (FULCRUM LENGTH / OVERALL LENGTH)

The fulcrum length is the distance from the screw centerline to the parallel guide pin board. The overall length is the throat length + the fulcrum length. For our example this is:  9” + 16” = 25”. So for our 1000 pounds of screw force we get:

CLAMPING FORCE = 1000 X (16/25) = 640 pounds of clamping force.

The parallel guide force is simply 1000 – 640 = 360 pounds. The parallel guide force and the clamping force must equal the force applied by the screw. This 360 pounds of force is wasted on preventing the jaw from rotating.

Now let’s take a larger board that is almost resting right on top of the vise screw as shown in FIG. 2. The throat length is now 1” and the overall length is 17” (1” + 16”). With the same screw force of 1000 pounds we now get:

CLAMPING FORCE = 1000 X (16 / 17) = 941 pounds of clamping force!

Obviously from our calculation it makes a big difference where in the vise jaw you clamp your work piece.

Let’s look at the effects of a longer fulcrum length. In our previous example our fulcrum length was 16”. What happens if we increase it to 24” while keeping everything else the same and clamping at the top of the jaw?

CLAMPING FORCE = 1000 (24 / 33) = 727 pounds of clamping force.

With the 16” fulcrum length the clamping force was 640 pounds. Increasing the distance between the screw and the parallel guide board will definitely increase the clamping force of our theoretical leg vise. We will never get the full 1000 pounds of screw force but to get the most out of your leg vise make the fulcrum length as long as possible.

So let’s summarize what we have discovered and look for ways to optimize our vise design.  Leg vises do not generate remarkable clamping forces, in fact they are the least efficient of any vise type because of the wasted force on the parallel guide. There are three ways to compensate for the reduced clamping force; Increase the number of threads per inch (TPI) of the screw. A 4 TPI or greater screw will help reduce the amount of force you have to apply. Increase the length of the vise handle. The increased leverage will reduce the amount of force you have to apply. Two tooth per inch wooden screws typically have a very long vise handle for this very reason.  If you have a hand wheel you are just going to have to apply more force by hand.

A shorter throat will generate more clamping force. When possible you can also clamp your work lower in the vise jaws. A longer fulcrum arm will similarly generate more clamping force. Obviously the fulcrum length is limited by bench height and other factors but longer is definitely better.

Leather lined jaws (or anything that will increase friction and offer some compliance) are a requirement on a leg vise for two reasons; the increased friction helps overcome the reduced clamping forces generated. The compliant leather lining helps grip when the jaws are not exactly parallel with the sides of the part being clamped. This is especially true for leg vises which use a parallel guide pin board because it is difficult to get the jaws precisely parallel with the work piece.

 

Use the (Vise) Force Luke

My youngest son Luke never tires of my use of phrases from Star Wars. “Use the force Luke” is my favorite. I sometimes modify the phrases a little bit to suit the shop environment like, “Use the clamp force Luke.” or “Use the vise force Luke.” Luke doesn’t think a lot about forces generated by the vises in the shop. Do you ever wonder how much force is exerted by a screw operated vise on a work piece? My guess is that you, like my son, probably don’t. So that’s why we have engineers, to help answer all these inane little questions.

Drawing1

 

In your typical vise the screw acts as a force multiplier. A simple way to look at a screw is like a ramp wrapped around a shaft. The steeper the ramp is the quicker you get where you want to go but it is a harder climb. The other part of the force multiplication comes from the handle which is really just a lever. A longer lever means lower forces need to be applied but you have to turn it a much longer distance. As with most things in life tradeoffs need to be made. In the case of a vise the tradeoff is quickness of movement verses applied force to the handle to clamp your part. Ideally we want the vise to move quickly as we turn a small handle and apply lots of clamping force with only a small hand applied force to the handle. We know we can never get to this ideal vise so we try to balance things out to a level that is acceptable. So let’s look at how we can figure out the clamping force for a screw operated vise and see the tradeoff’s for a few example vises.  As it turns out there is a very simple formula to let you figure out the vise clamping force.

CLAMPING FORCE = 6.3  X  HANDLE FORCE  X  HANDLE RADIUS  X  SCREW TPI

The handle force is just the amount of force you apply to the handle with your hand. The handle radius is the distance from the center of the screw or hub to where you are applying the force and screw TPI is the number of threads per inch of the screw.

Let’s do an example of the Record 52-1/2 ED vise:

The Record has an 8” radius handle and a 4 TPI screw. Assume you apply 10 pounds of force to clamp a work piece, the clamping force works out to:

Clamping force = 6.3 X 10 X 8 X 4 =  2016 pounds of clamping force.

Most large wooden screws have a 2 TPI screw and they are desired for the quick movement when turned to clamp. But this faster movement comes at a price; higher force is required on the handle for clamping. To overcome this, wooden screws typically come with an extra-long handle of about 15”. Let’s look at a wooden screw example with a 3-1/2” hub, 15” handle and 2 TPI thread with the same 10 pounds applied to the handle:

The handle radius is actually 15 – (3.5 / 2) = 13.25     (you have to subtract half of the hub diameter to get the radius to the center of the screw.)

Clamping force = 6.3  X  10  X  13.25  X  2 = 1670 pounds of clamping force.

You can see that if you apply the same amount of force to the extra-long clamp handle you still come up short…..about 17 % less clamping force than the Record vise for the same amount of applied handle force.

Let’s look at one last example, a vise with 4 TPI screw and an 8” hand wheel. The handle radius in this case is going to be 4”. So for 10 pounds of force applied to the handle you get:

Clamping force = 6.3  X  10  X  4  X  4 = 1008 pounds of clamping force.

This is half the force you get with the Record vise. Or another way to look at it is that you would have to apply twice as much force to the hand wheel to get the same clamping as the Record vise.

You might be asking why I care about screw vises when I don’t even sell them. This little exercise points out the beauty of the quick action vise. You get quick action when moving the jaw up to the work and you get lower handle force with more clamping power. I also design my vises to mimic the action of vise screws so this formula is useful. I typically design my vises to work like a 4 TPI screw because that gives the best balance between low applied handle forces and good clamping force. May the vise force be with you……