Frame Welding Jigs
In this section of the handbook we’ll take a look at Frame Jigs, also called Welding Jigs, and discuss the pros and cons of various configurations while trying to separate myth from reality so that the prospective builder has some solid information at their disposal as they contemplate how best to approach their own personal jig project.
The first thing you have to decide on is whether the jig is to be used for a one-off frame or intended to serve as the foundation for an ongoing enterprise since the ‘duty’ requirements are quite different. For the one-time jig you can get by with relative lightweight materials, even wood in some instances, while for the production jig you’ll want fairly heavy walled steel materials for the foundation at least.
You also have to establish some kind of initial budget for the jig, at least the major parts, as some fixtures can get pretty expensive if you’re dreaming about something that is to be fully machined and fully adjustable. You can build the foundations of almost any jig for very little money and add the refinements over time so don’t hold off on starting that frame just because the expense of the jig seems overwhelming.
A good jig is a personal tool that develops over time and isn’t ever really finished so you have to built it and refine it as you’re also building and refining your frame building expertise.
The following section of the Handbook should get you started in the right direction or at least provide the basic information you might need to get your particular project off the ground without breaking the bank.
Much of the information you’re about to read was first published on our old bulletin board back in 1988 and since that time we’ve heard from about three thousand builders, both amateurs and professionals alike, and have updated the current information to include the comments, recommendations and concerns from the feedback they have provided over these many years concerning jig construction.
As far as I am aware there is no other single source of Welding Jig information that is as comprehensive as that provided here but we encourage readers to continually submit new tips, tricks and helpful hints to the Discussion Board so that prospective builders have access to the knowledge, based upon experience, that can be provided by those folks out there who are actually building frames on a day to day basis.
What follows is a start, but it’s up to you to build upon it, as you see fit, for your particular project.
What is a Frame Jig
Many potential frame builders have the mistaken idea that the frame jig must be extremely accurate, built like a precision timepiece and yet possess immense strength for forcing the tubing sections into position for welding but in fact the base structure of the jig, sometimes called the backbone, bed, table, base table, face table or frame face can be almost any relative rigid structure.
As long as the frame bed or backbone is level in all directions the real precision and accuracy will come about through the fabrication of the fixtures that attach to this substructure or backbone and then will be adjusted and secured to position and hold the tubing and parts in place during the fabrication of the frame or chassis.
Figure 4.1 illustrates a typical jig assembly with the bed or backbone being made of two segments of box tubing with the various fixtures bolted into position.
This type of frame jig is referred to as being a ‘bottom-up’ arrangement and while it has some disadvantages it is by far the most common type of jig used in custom motorcycle frame construction. Note the point on the rod going through the stem to gauge alignment.
The following pictures illustrate a wide variety of frame jigs ranging from simple and crude homemade units to extremely complicated fully adjustable units manufactured for large chassis shops. Though the range of sophistication is wide, all of the pictured jigs can produce very accurately aligned tube frames. In fact the precision of the final product is more dependent on the builders skill than the frame jig being used and there are several custom frame builders who don’t use a frame jig to begin with preferring to use just templates and small holding fixtures.
In figure 4.2 we see a typical jig backbone, this example is made from channel and raised to knee height on cinder blocks.
Another relatively simple layout below in figure 4.3 shows two widely spaced longitudinal rails forming the backbone or bed framework.
Another typical horizontal rail or bed type of jig is shown in figure 4.4. Note that in this example, built to fabricate one specific type of frame, the fixtures are not adjustable but are welded into position on the jig bed rail made from 3x3 square tubing.
Figure 4.5 depicts a true building table, often referred to as a face or frame table. Note the leveling legs at each corner.
Figure 4.6 shows a typical jig fixture, this one used to position motor mounts.
The same table as above but with the fixtures added is shown below.
All of the jigs we’ve seen so far start with a foundation of a rail, multiple rails or table and build upward with the jig fixtures supported from below. An alternative to this scheme is the vertical jig, which is most often used in bicycle construction, but is occasionally seen in motorcycle fabrication shops especially where very lightweight racing frames are being built.
Figure 4.8 illustrates a Bringheli jig. Note the gauge rods with pointed ends used to calibrate the fixture clamps, an alignment method that can be adopted on any type of jig.
Figure 4.9 illustrates a Henry James vertical jig. This structure is often called a modified plate jig or vertical plate jig since the ‘bed’ is basically just a large flat piece of aluminum.
Figure 4.10 illustrates a motorcycle jig using both a building backbone or bed rail and a vertical panel made from spaced steel members.
Figure 4.11 is another combination jig exhibiting both horizontal and vertical primary support members.
Jigs having vertical structural members or plates are superior to horizontal or backbone based jigs in that the fixtures that clamp the individual frame components are shorter, located closer to the joints and connections, hence stiffer than the same type of clamping fixture that has to extend all the up from the base plate. For this reason it is becoming more common to see at least some aspects of the vertical plate design incorporated into conventional rail or bed type building jigs.
Another very popular fabrication technique used to improve the accuracy, rigidity and efficiency of frame jigs is to incorporate as many pieces of the motorcycle as possible into the basic construction of the jig fixtures themselves.
For example it is very common to actually build the jig around the engine, transmission, forks and wheels that will be used in the completed bike.
Figure 4.12 illustrates a typical backbone type jig with major mechanical components included into the initial jig design.
This type of jig design will produce the best ‘custom’ frame designs since the potential rider can better visualize the final product and adjustment can be made with the rider sitting in place over the motor. Needless to say accuracy will be superior because all of the component mounting points are located by the components themselves.
In our shop we use a ‘building’ jig that includes the bikes wheels, axles, transmission, motor cases and front forks for custom work and then if we decide to build more frames along the same lines we build a much smaller jig just to hold the chassis tubing.
Jigs can be extremely simple as seen below in the example used by Michael Moore
Or unusually complicated is seen in this unit used by the Harris brothers shown in figure 4.14 or the multipurpose building and alignment model shown in figure 4.15.
The jig shown in figure 4.16 is a good example of a well though out arrangement for a specific type of cycle. Note that the rear axle adjusters are used to locate the axle and that the fixtures are mounted to pieces of channel iron that can be slid fore and aft along what looks like a 3x3 tube rail.
There are almost as many jig designs as there are frame makers since each jig is usually the work of the artist building the frame. Some jigs are used over and over again producing several if not hundreds of so-called ‘custom’ frames by frame manufacturers while other jigs are only used once for a ‘one-off’ bike. Sometime a company or individual will sell a jig to another builder but without the actual plans or blueprints for the frame that the jig was built for it is almost impossible to reconstruct the frames produced by the jigs original owner. This is a hard fact for many people to believe but the sole purpose of the frame jig is to hold various bits and pieces of tubing in certain alignments and positions while they are tack welded together. The jig itself will not give you a clue as to the lengths of tubing or angles for the various bends.
As mentioned at the beginning of this section a welding jig doesn’t necessarily have to be massively built because the jig and fixtures should only be used to position and lightly clamp together the frame tubing for welding. If it becomes necessary to force a tube or fitting into position in the jig then something is wrong with your bender, your measurements or your design. Wherever possible I set up my jigs so that the frame tubes simply lay into angle iron guides so that no clamps are needed in the first place and in fact even if you do clamp down all the tubing tightly, the frame will distort anyway when it is taken out after final welding.
Quite often, especially if you’re making several frames that are similar but with minor customizations it is helpful to build separate jigs for separate parts of the frame in addition to the assembly-welding jig. In our shop for instance we use a jig to build the upper rear wishbone tubes and another for the backbone and seat post before these sections are added to the main welding jig. A good example of this type sub-assembly can be seen in figure 4.17 designed to build the backbone and wishbones before they are put into position on the main welding jig.
Another example of a separate building fixture is pictured below. In this case used for not only the assembly of wishbones but notching the fish-mouths as well.
I’ve also seen this same type of sub-assembly complete with fixtures for the seat-post tube and this approach to frame construction is in many ways far superior to the old method of trying to do everything in one single frame jig. More and more production shops are taking this route since it’s usually a faster process and more accurate as well.
For true custom bikes it is very likely that you’ll wind up designing and building the frame and the frame-welding jig all at the same time developing individual elements and components of both the frame and jig in sequence. For example you sketch out the backbone curve full scale on the shop floor, build a large-radius bending jig to shape the tube and then weld up a jig fixture to hold the backbone in position over the seat post with both tubes held in alignment with the steering head fixture.
In addition to building and welding jigs it is often very helpful to build full-scale mockups of frame components or in fact complete frames from wood dowels before you commit a design to steel tube. Building a wood mockup is extremely useful in helping you decide on the sequence of construction, devising easy methods to position tubes for notching, pointing out ways to build effective fixtures and allowing you to visualize the form of the completed chassis before you spend hard cash on the steel. In a similar fashion try to build templates and patterns for components that are repetitive from one frame to another.
Each builder has his or her own ideas about what constitutes the ‘benchmark’ or ‘base-point’ that all measurements are taken from on the jig. Some fabricators start at the steering neck and base everything about this point working rearward. Others use the rear axle and work forward. To my way of thinking about the only thing that usually doesn’t change on a custom V-twin chassis is the center point of the motor so I always set a ‘kingpost’ at the vertical reference centerline of the engine and work fore and aft from this point. I believe this gives me far more freedom in planning and designing than having either the steering neck or rear axle as a fixed point on the jig.
A really good frame jig will never be finished. It will always remain a work in progress being tweaked and modified as the builder hones his or her skills and begins to develop their own unique construction methodology and artistic style. The key to good jig design is repeatability. Every time a part goes into or comes out of the jig everything should be absolutely identical.
Let your imagination be your guide.
Many people have asked us what dimensional tolerances we work towards in building both jigs and finished frames and while each maker has their own concepts about accuracy in our shop we strive for absolute perfection but we will accept dimensional discrepancies of up to 1/4 inch in an overall frame length or 1/8 inch in width if we have to. Between any to closely positioned components 1/32 inch is considered acceptable but anything over those ranges and we scrap the piece and start over. In reality it is almost impossible to detect defects caused by inaccuracies in the range of 1/8 inch over the entire length or width of the frame and if the axles are perfected parallel to one another and the steering neck is perfectly perpendicular the relative accuracy of the all the various interconnected tubes is actually immaterial which brings us back again to jig and fixture strength. Remember that large portions of the jig don’t necessarily have to be very accurately fashioned. In fact the fixtures don’t have to be precise either so long as the precision is used where it counts and that is at the frame tubing connection points and mount points. In other words the degree of accuracy or acceptable tolerance goes from gross to fine in ascending order up from the base rails into the connections. Dimensional accuracy is far less important than angular precision where everything is plumb, perpendicular or parallel.
It is imperative that the tubes are properly cut to length, bent and mitered so that the joints are as close to perfect as possible. If this is done they can be positioned and held very lightly in place while they are tacked and if the welding sequence is done correctly no heat distortion will change the angular or dimensional alignment of the various tube members. The jig and fixtures no matter how strong or rigid cannot resist the bending and warping stresses caused by improper welding sequence or inaccurate initial layout and fitting once the frame is removed from the jig.
One way to test your building skills is to fabricate a frame and then saw through some tubes near connection points at various places on the frame. If the sliced tube end suddenly springs away from the other end or springs to one side or another at the point of the cut it indicates that your frame has a lot of built up stress caused by poor welding sequence, too much welding heat or poor structural design considerations. If you cut an unstressed tube the hack saw will pass through the member and nothing happens, both ends stay in perfect alignment separated by about a sixteenth of an inch of air space.
After years of using a single rail jigs we have decided to start using a base frame made from two parallel rails. Since we build frames for a variety of bikes and not just Harley’s we feel this gives us more flexibility since fixtures can be mounted between the rails for centerline type fittings or outside the rails as may be needed. Figure 4.19 below illustrates the basic foundation of this setup.
Many people are surprised to find out that a jig will cost more than the frame that comes out of it. In fact a good professional level jig with machined adjustable fixtures will cost about four thousand dollars to build if you have to farm out the machine work. Machining, done in-house can shave maybe two thousand off that figure. If you work for free and deduct the cost of your own labor you can knock another fifteen hundred off the budget which means a good jig will cost you about five hundred in materials and incidentals if you do all of the work yourself. Compare this to the hundred bucks in materials you need to build a frame.
Always remember that you are better off without any jig at all rather than being forced to use an ill conceived one. A good jig can’t be built in a day and most will take at least a week to put together properly. Final fixture clamp accuracy is paramount so go slow, measure twice and cut once. Watch out for welding distortion. It is better to err on the short side as anything can be shimmed out to final dimension where it is much harder to grind something down and still maintain precision.
As mentioned above it is far more expensive to build a jig than to build a frame. It is also far more complicated to build a jig than a frame and it takes far more time to build a jig than it does to build a frame. For these reasons many people are tempted to bypass a jig altogether and try to weld up a frame without using a jig. There is nothing wrong with this if you’re a good experienced fabricator and you have a lot of time on your hands since it takes longer to build without the assistance a good jig provides. There are some good builders who fab every frame from scratch but for every successful frame built this way by professionals there are probably ten built by amateurs that don’t work out so well and have handling problems if they even make it to the engine stage in the first place.
The one point I forgot to mention is that it’s a good idea to plan on how you’re going to get your frame out of the jig after it’s welded together. You would be surprised how many novice builders have welded their fixtures to the rails in such a manner that the frame gets ‘locked’ inside the jig after the tubing runs for the frame are ‘closed up’.
Many first time builders hold off on starting their own chopper frame project because they feel that they need a very fancy and complicated jig in order to do good work and simply don’t have the extra cash needed to put together such a jig. In reality you can get started very quickly and cheaply with just a rudimentary jig and refine it over time.
Before you begin the actual construction of a welding jig it’s important to remember that any piece of manufactured square or rectangular tubing, or any typical structural shape, such as I-beams, Angles or Channels typically don’t really have any perfectly flat surfaces. As the steel in such members is usually hot formed the surface tends to ‘cup’ when cooled. An example of a section of square tubing, drawn at an exaggerated scale, is shown below to illustrate the problem.
The distortion in most tube sections is usually confined to cupping. If you put a square on tube sections you will usually find that the member is indeed ‘square’. In other words at least all of the corners are at right angles to each
Structural steel shapes such as channels, angles and beams also have the additional problem of manufacturing distortion in the angular relationship between the flanges and webs in that the corners aren’t necessarily square and this is why we don’t recommend their use for jigs since you have to make more corrections to begin with. You’ll have to take into account the cupping and the problem with out of square flanges both top and
If you’re using square or rectangular tubing all you have to worry about is providing an easy way to get a ‘flat’ surface on the jig to take your measurements from and this is usually accomplished by just using sections of thick bar stock ‘gauge-blocks’ that will span over the concavity.
Some builders take this one step further and build all of their jig fixtures with adjustment screws in the base plates as shown in the illustration below.
This system, when using four adjustment screws in fixture base-plates or measuring blocks enables the builder to achieve limits of accuracy measured in the thousandths of an inch regardless of the basic inaccuracy of the bed rails or component mounting tubes, uprights or runners.
While this may seem a complicated procedure remember that this limit of accuracy is only needed in three areas for a typical welding jig.
A good example of this system in action can be seen in the snapshot provide by Concrete-Guy, shown below, where he has incorporated small adjustment screws between the base-plates of his axle holding fixture.
This same system can be used to provide not only very accurate positioning but also rather major adjustability as the central bolt that supplies tension between the upper and lower bed rail plates can also serve to clamp fixtures into various fore and aft locations on the bed rails themselves.
Fixtures and Sub-Fixtures
Some builders prefer to have every little bit and piece of every fitting and every possible connection point built into the main body, or at least, into the fixtures of their jig and these usually include the motor and transmission mount points and I used to do the very same thing at one point in time. There is a group of builders however who choose to build completely separate jigs, or at least major sub-assemblies specifically designed to handle the chore of positioning the motor and transmission mounting plates.
We already covered the importance of keeping the steering neck perpendicular to the rear axle shaft and this feat is usually accomplished on the main jig itself with the construction and placement of the tail stock axle fixture and steering neck post. Since the steering neck and rear axle shaft are separated by a considerable distance in space very slight problems with alignment between the two points won’t usually show up as major problems in the final frame. When we get further down the ladder however and get closer to the drive train parts of the frame it gets a little more complicated.
It is imperative that the motor-transmission and rear axle assemblies are as close to plumb and square as is humanly possible. This isn’t to say that these components have to be plumb and square to the frame itself. In fact the mount points can be pretty skewed in relation to the frame just as long as they line up both vertically, horizontally and longitudinally with the rear axle shaft.
This is the point where huge portions of mass-produced frames fall apart. The motor and tranny mounts may indeed be spot-on, as advertised to an accuracy of .003”, but they’re out with respect to alignment with the rear axle. If you’re not familiar with this problem you’ll usually end up thinking that the mounts are wrong and spend days trying to shim the motor and tranny into position when the real problem has to do with the axle, more accurately, the sprocket alignment because the axle plates are tweaked.
The sketch shown below represents a typical v-twin motor/tranny and rear sprocket when viewed from the front of the bike. Keep in mind that considerable ‘artistic license’ has been used for these illustrations which are intended to be educational and not especially technically accurate.
As you can see the X and Y axis are at right angles to one another so everything lines up perfectly.
In Figure 4.24 however the rear axle shaft is out of plane and you can see the sprocket in the background canted at an angle to the motor and transmissions shafts.
To get this frame to ‘work’ you’d either have to rebuild the axle plates or install the motor and transmission mounts so that they’d be aligned with the axle shaft.
Depending upon the amount of misalignment it’s usually easier to install the mounts to match the axle no matter how they set in relation to the frame rails.
Figure 4.25 illustrates the four basic alignment conditions that the frame builder typically faces. The first graphic, ‘Condition-A’, is what we’re all striving for; Perfect alignment between the motor, transmission and rear wheel sprocket or pulley.
Condition-B, is our worst nightmare since this type of misalignment usually means our frame is crooked. You can see that motor and tranny are aligned but the rear sprocket is skewed to one side or the other.
Condition-C isn’t as bad since it appears that the only problem is with the transmission mount, which appears crooked in relation to motor and the rear wheel.
Condition-D is similar but in this instance the motor mounts are off with respect to the tranny and the rear sprocket.
Notice that the frame itself is not shown in these diagrams.
When there is a misalignment problem it is usually minor. A really major problem may mean that something’s out of whack by about an eighth of an inch. This is indeed a huge problem with respect to the components; mount points and the mechanicals of the bike but ‘visually’ it means almost nothing. You can move the parts around within the frame by this amount and the average bystander will never notice it but your chain and sprocket will thank you.
The easiest way to avoid these problems to begin with is to build or buy a set of motor and transmission ‘Plates’. Theses plates are bored to match the factory motor and transmission bolt patterns and can be either permanently affixed to the jig or built as a removable fixture or sub-fixture. You can buy these plates from several sources listed in the back of the manual or as shown on the links page of the website. You can also build them yourself using the mount point dimensions shown in the reference material section.
Figure 4.26 shows a typical motor plate in position. This particular unit is sold by Bitter End Old School Choppers. They sell a variety of both motor and transmissions plates for internal or external applications with respect to your jig.
Figure 4.27 shows a pair of plates built by Weyland Smith installed over a stock frame mounted in the jig.
The important point is that you install your motor and/or tranny plates or fixtures so that they are adjustable relative to the rear axle shaft and not the frame rails or the jig bed itself.
Fixed verses Adjustable
Among frame builders there are two schools of thought concerning basic jig design. One camp holds that the so-called ‘fully adjustable’ jig is superior as you can adjust, align and reposition every single part to suit a wide range of frames. The other side claims that a ‘fixed’ type of jig is better where the fixtures and sub-fixtures are swapped in and out of the jig bed as needed to suit different frames. In this case you need to build a separate set of fixtures for every type of chassis you intend on building.
I’ve personally used both types and even combinations of these two basic design concepts and find that the ‘fixed’ type of jig with specialized sub-fixtures is better suited for the way I happen to work. The problem with fully adjustable jigs is that it’s very hard to get repeatability unless you keep a ‘master-frame’ or mocked-up skeleton around the shop so the jig can be reset after it’s changed. With the ‘fixed’ fixture method you know for sure that once the fixture is in position the part will be identical to every part that’s ever been made in that particular jig.
A typical example of the ‘fully-adjustable’ jig type is pictured below. This particular unit is based upon the designs provided by BCC Orlando.
Another example of this same design is shown below and with the frame mounted you can get an idea of what the ‘arms’ are intended to do.
An excellent example of a ‘fixed’ fixture jig type is illustrated in Figure 4.30 posted by Bolle at the discussion board.
It’s apparent even at first glance that a tremendous amount of thought went into the design of this particular jig, set up here for a softail frame. Every fixture is substantial yet removable or interchangeable with no flimsy adjustable brackets or extension arms to worry about even though the individual fixtures all have provisions for minor adjustment to insure accuracy. The individual fixtures can be swapped out for different types of frames.
The ‘ultimate’ jig would probably incorporate ideas from both types of setups.
The important points of this section, in my opinion, have been first and foremost, that the foundations of the jig, the bed rails, or table platform if that’s the direction you decide to take have to be as rigid and square as you can possibly make them. This is the only piece of the jig that typically won’t be changed or modified over time and that’s why’s it’s often called the ‘backbone’ of the system. All of the various fixtures can, and probably will, be modified and rebuilt dozens of times over the years that a jig is typically in use but the backbone will endure several generations of use if built with care. When I first started building frames I used a backbone that was originally built in 1952 and handed down to several other builders before it finally got to me. I used that set of rails for almost tens years before building a set for myself and as far as I know those original rails are still being used today by other fabricators. I have been in several shops that are using jigs built in the fifties and sixties so I know for sure that a well-built jig will endure almost indefinitely.
Keep in mind that a jig is constantly exposed to weld spatter and grinding dust and as a result any finely machined parts, especially adjustable parts, need protection if you want them to continue in operation. In the production environment ‘simple’ jigs will outlast ‘fancy’ jigs at rate of about fifty-to-one.
Don’t rush to build your jig. The construction of the jig is as important as the construction of the frame that comes out of it. Spend a lot of time doing research. Browse all of the discussion boards that have a section about jig building. Visit all of the sites that provide jig plans and start a notebook of ideas and pictures that you’ve downloaded. Think about how you typically work and what it is you actually expect your jig to accomplish. If you have even the slightest inkling that you may want to build more than one or two frames try to do some long-range planning about the types of frames you’ll likely encounter.
A super fancy, fully adjustable, totally machined jig will not make up for poor tube fitting or poor welding technique and sequence no matter how much time and money is spent in the construction of the jig itself. The quality of a jig really makes little difference in the quality of the frame that comes out of it as long as the fabricator is skilled in his or her craft. Ninety percent of all ‘bad’ production frames that are produced every year come out of very expensive fully machined adjustable ‘fancy’ jigs that are extremely accurate. Unfortunately some first-timers think that ‘the jig makes the frame’ but in reality it’s ‘the fabricator that makes the frame’.
A lot of people get all geared up to build a frame but rapidly loose interest when they are faced with the challenge of building the welding jig itself and try to take shortcuts and this fact alone accounts for almost all of the failed attempts experienced by home builders or small independent builders when they tackle the job of that ‘first frame’ project. To be successful you can’t jump from step 1 to step 5 without something going wrong somewhere down the line. The reason is usually a matter of economics. A jig costs from two to ten times the amount spent on materials for a frame so it’s tempting to short circuit the program. What we’ve tried to illustrate here in the handbook, if properly implemented by the average builder, will enable them to not only build a good welding jig but also one, perhaps two, frames for the same amount of money they would otherwise have spent on a single mass-produced frame and in the end there should still be a little money left over.
Keep in mind that anything you see here in steel can be duplicated to some extent in wood if the jig is intended for a one-off frame project but you do have to take more care when working with lumber and I personally wouldn’t recommend building bed rails from two by fours for instance.
When it comes to so-called welding jig ‘plans’ I personally don’t give them much credence even though we sell a set ourselves as part of out frame plan package. What a frame jig builder needs is frame plans since the dimensions of the jig absolutely have to come from the dimensions of the frame itself. Jig dimensions by themselves are virtually worthless to the fabricator. The fancier the so-called jig plans are the more worthless they become with respect to producing a specific frame. It comes down to what you want to build, a fancy jig or some nice frames. Plans will at least give you a base line to start from but don’t take them as gospel.
The prospective builder has to do research, investigation and background study. What we’ve provided in this section is perhaps only 60% of the total amount of information needed to fully understand jig construction. There is a ton of information out there on the Internet and even more good information contained in various books about motorcycle and racecar frame fabrication that one can purchase in almost any bookstore. In addition I strongly urge anyone interested in building frames to visit as many shops as possible so they can see first-hand the equipment and procedures used by professional fabricators in their own shops.
It’s my personal belief that you can’t build a jig without first having at least a few test ‘tubes’ to put into it. As a Webmaster I see all kinds of submitted jig pictures but very few with partial frames in the snapshot, and perhaps more importantly, some ‘reject’ tubes in the background.
You really do need to get a tubing bender before you start to build your jig. As we mentioned earlier it’s far easier to build the first frame and the first jig simultaneously. Without the frame tubes how in the world can you test the jig as it’s under construction? It’s like putting the cart before the horse. The jig is intended to position the tubes but without tubes how can you build a really good jig?
Regardless of whether you decide to build a fancy jig or a plain jig you should be aware that you could buy ready-made fittings and accessories to make precision slides and v-blocks from a variety of sources but I’ve had good luck with McLean Products machined slides. These v-block slides come in 1, 2, 3 and 4-inch widths and almost any length and are specifically designed to be used by fabricators who want to build their own precision tools and fixtures.
You can also try web searches for a huge variety of extrusions, clamps, small vices, adjustable collars, shaft collars, shim stock and just a huge range of pre-made parts that can save you time and make life a little easier. You could spend at least two entire days just searching the McMaster-Carr on-line catalog.
The frame jig you eventually build will be ‘your’ jig and that’s the way it has always been. The jig itself is just a tool used by the individual fabricator and as such is truly a unique personal piece of ‘equipment’ that can’t be ‘store-bought’ in the form of plans or even pre-made as often seen on eBay.
When I see somebody using a carbon copy of my jig, or Joe McGlynn’s jig or the jigs sold by BCC Orlando or those provided by Mechwerks I can’t help but think that the owner didn’t spend much time in really customizing the product for their specific application.
Chopper building is a unique individual endeavor leaning more towards an art form than a pure technical or engineering exercise in the creation and assembly of various mechanical parts. The welding jig should be your personally tailored tool whether it’s built from scrap steel or from custom machined billets.
Plans for our latest version of the jig that I use are located here:
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