MEKK's Kit Car Man

Building Your Jig (Part 2)

2009-03-14T11:17:00.000-07:00

Construction Suggestions

Construct your jig with standard, new materials.

Use easily welded steel.

Recommended minimum materials must be at least as heavy as the frame materials. For example, when constructing a kit car frame of 2 x 3 inch rectangular tubing, the jig should be built using at least 2 x 3 inch tubing which is triangulated.

Construction Steps

Build the base or table. This will allow you to practice your welding. Height is an individual choice. Several sources recommend 24 to 32 inches. I think it’s important to be able to get underneath and that's impossible at 24 inches. I’m getting older, so I prefer to work standing with the work at belt to chest level. Some folks prefer sitting down in a roll around seat. Build to your preferences, but remember that it’s easier to shorten than lengthen.

You can lay out the base on a flat concrete garage floor. I’ll assume you’ll be using rectangular tubing, but the same principles apply to I-beams.

Cut two pieces of tubing a foot or two longer than your frame. A little extra here may make storage more difficult, but being able to adjust hard points and attach braces will be useful later.

Decide on the height you want and cut four (or six if your frame is long) pieces for the legs. Be careful to have each leg exactly the same length. This is important! This ensures your jig can be level.

Lay one of the long pieces on the floor. Place two (or three) leg pieces one side so the long piece is supported evenly.

Take the other long piece and use it to ensure that the layout is actually flat. Most garage floors have a slope but are flat. You may have to move stuff around to get a flat lay out.

Time spent here ensures your jig can be square and level.

The next task is to weld the legs to the long piece. The legs must be perpendicular to the long piece and stay perpendicular after welding. You may have your own technique or own giant picture frame clamps. But my approach was to buy four 1/4 inch thick 8 x 8 inch angle brackets. I then clamped two of these to each leg as shown in figure 1 below.

Figure 1
Clamping method.

Using a 32-inch framing square, I checked to ensure the legs were truly square to the long piece. They were perfect.

Now alternately tack weld the legs to the long piece. Let your tack welds cool before the next weld. This is where working on both legs is nice – you don’t feel so anxious to make that next weld.

Carefully flip the assembly along the long axis and tack the other side. Having a strong clamp method is essential for this step (or a strong significant other!)

After the second side is tacked, remove one bracket on each leg and tack the inside angle. Remove the other bracket and tack.

Using alternative welding and cooling complete the included angle welds on both legs. Complete the weld on one side of the legs also alternating your welding and allowing the joint to cool.

Again flip the assembly and weld the opposite face. Be sure to continue welding in short runs and alternate legs while letting the welds cool.

Your welding technique is very important. A welded joint tends to contract as it cools. This contraction can warp your joints leading to a twisted base.

You now have one side of the jig. Construct the other side using the same technique.

Once the two leg assemblies are cool it’s time to connect the two sides. I built mine by myself but here is where a helper can make the job a lot easier. Your helper should be old enough and large enough to hold 150 – 200 pounds of 10 plus feet of steel steady. Your 12 year old probably isn’t going to be big enough and your wife is probably not going to be willing. A teenager or neighbor friend or brother is best. Remember, this thing is going to be heavy and awkward and it will have sharp edges. You don’t want someone to get hurt.

Now it’s time to cut the cross pieces. You need at least two. Position them at the forward edge of your frame. If you’re using six legs, position a third cross piece at the center legs. My frame is fairly short so my front and rear cross pieces attached at the front and rear legs.

Figure 2
Cross pieces clamped to the two leg assemblies.

Be sure to take into account the width of the long pieces when you measure the cross pieces.

If you have enough clamps the best approach is to erect both leg assemblies and clamp the cross pieces in place. Clamping firmly is critical. Ensure your clamps don’t extend above the top surface.

Using a long straight edge (I used left over tubing), lay it on top of the clamped jig. Did I mention firmly clamped? make certain the cross pieces are exactly level with the sides pieces. You want a perfectly flat surface. You may have to reposition the whole thing if your floor isn’t level. If you have a level floor then a large level can be useful here.

You can use scrap pieces clamped at the bottom side of each leg (as shown in Figure 2 above) to hold the leg assemblies perpendicular to the floor. This is essential if you don't have a helper.

Using your now well practiced tack and cool welding method, tack both cross pieces in place.

Once all faces are tacked, remove the clamps one at a time and tack the inner edge corners.

Now go back and alternate welding all joints.

If you’ve been careful and let your tack welds cool the result should be a strong, straight, and level platform.

However, you should check for square. Using a string, measure the length between two diagonal corners and compare with the length between the opposite diagonal corners. The two lengths should differ by less than 1/8 inch. You may prefer to take these measurements before you do the final welding. Grinding a couple of tack welds out is a lot easier than correcting a fully welded joint. You can also use this method on the legs.

I didn’t think to make this measurement until I’d finished. I sweated blood when I realized just how deep the hole I might be in could be. Fortunately, my careful assembly and welding patience had created a table less than 1/8 inch out of square. Good enuf!

OK, You've now got a square, flat, table to work with. In our next installment I'll tackle the jig part of the process where we turn this table into a frame jig. Get weldin'!

Objective and Mission Supplies (Part 1)

2007-11-08T09:59:00.000-08:00

This article explains how to build a jig for making automobile frames. It is intended for the advanced hobbyist. You must have a welder and know how to use it. You need some kind of tool for cutting at least 2 x 3 inch steel of 12 gauge or heaver. You must be strong enough to handle steel materials weighing 75 to 150 pounds. You need a covered place to work with a solid, noncombustible floor – preferably concrete.

Tools

There are several tools you'll need. Some come in a choice of types as well as brands. Based on my experience I'll comment on the types I found best. If you don't have one of the tools you should beg, borrow, or buy one. While I do buy harbor freight tools, your should consider how much you'll use the tool and well you expect it to work. Harbor Freight C-clamps are fine. My plasma torch is a $1,200 commercial unit. My mig welder is a midrange US-manufactured unit that I can get parts for locally. My mechanics tools are Craftsman from Sears and old quality tools from rural auctions.

Welder [Choose one]

A mig welder is best and easiest to use for nubies

Stick welder

Tig if you can afford it

Acetylene (last choice unless you’re an expert)

Metal cutter [Choose one]

Cutoff saw - a circular saw with cut off blade will work – poorly

Or metal cutting band saw - the very best My Harbor Freight saw works well

Or heavy jig saw with metal cutting bits

Or Saws All with bi-metal blades

A plasma cutter is nice but it's difficult to make a smooth edge - not recommended

A oxy-acetylene torch requires real finesse - not recommended

Heavy gloves

Welding helmet (Boy is an auto darkening helmet the way to go!)

Face shield (better than goggles - you’re not prettier with steel bits in you face)

Sturdy C-clamps

A variety of sizes
A bunch - you can never have too many C-clamps

Square - I have a couple of each of these

Large framing square is best

Big speed square

6” or larger machinist’s square

Portable Grinder - I have all of these

Electric is my preference and what I use the most
Air-driven grinder - great for low volume small areas
Air-driven cut-off tool - makes great narrow cuts

Tape measure

Steel is it

Marking pen or pencil

High visibility on steel is needed

Paper for notes

Material for patterns

Thin cardboard - flip chart backers work fine
Plastic sheets - pricey but very durable

Spray paint

Anti-rust primer especially for those welds
Light color so you can write on the jig

Characteristics of a Frame Jig

Whatever your approach to building a frame jig, there are several characteristics that the jig must have. It must be:

Rigid
Strong
Square
Dimensionally stable and accurate
Provide hard points for all critical points in the frame
Support a method of clamping or securing the frame to the jig (tack welding can be used)
Have clamping strong enough to preserve frame dimensions during welding

General Purpose Jigs

General purpose frame jigs are needed by shops that work on or build a wide variety of frames. These are great but are also very expensive. Building one is beyond the scope of this article. All general purpose frame jigs:

Provide a method of changing/adding hard points
Are large enough for all frames
Have a variety of fixtures that bolt onto the basic jig
Usually come with measuring attachments

Nice Jig Features

While not strictly necessary, the following features can make using your jig easier.

Wheels/casters
Height adjustment

These features bring with them certain limitations, so stop and consider whether you can live with them before incorporating wheels or height adjustment into your frame jig. Wheels or caster must be strong enough to support their share of the weight of the combination of supporting table, jig, and an assembled frame. Allowance should be made for a 200 pound assembler leaning on the jig. Even with a six-leg table, the resulting weight leaves you no choice but metal wheels - substantial metal wheels. Metal wheels will also limit flexing which detracts from the dimensional stability of your jig.

Wheeled jigs are never as stable as jigs without wheels. One compromise is to attach wheels to the table support legs using a lever. When the jig is in use, it rests firmly on the floor. When you're not using it, you can lever down the wheels and roll it out of the way. You can also use add-on wheels if you're muscular. Add-on wheels require you to pick up each leg of the jig and place a wheeled extension on the leg.

Levered add-on wheels have the disadvantage of potentially 'tweaking' the jig as each leg is levered up.

Height adjustment is another nice feature that brings its own problems. It's difficult to design a height adjustment method that retains the dimensional stability of a fixed height jig. The jig could also be tweaked as each of its legs are adjusted.

So, nice-to-have jig features may be convenient, but they come with limitations that you may prefer to avoid.

Now close your eyes for a moment. Can you visualize what your jig will look like and what features it will have? Have you weighed the pros and cons of all the features? Do you own or can you borrow (or beg) for the tools? Do you have the space to do all this in?

Your first assignment is to make sure you can answer "yes" to all of the above questions. When you have, you'll be ready for part two, where we start building the frame jig itself.

Copyright (C) M.E.K.K. Autoworks, Inc.

Intro to the First Series - Making Your Own Frame

2007-10-30T13:21:00.000-07:00

I'm going to start this blog with a series about how you can make your own kit car frame (It's suspiciously similar to the one MEKK is selling but the boss says that's OK!).

Watch here each week for the next episode - sometimes success, sometimes disaster. I'll provide all the dirty details, step by step, forward and sometimes back, as I build a hobbiest version of a sturdy, reliable, kit car frame. It uses VW front suspension components and bolts to a Neon FWD donor for propulsion and rear suspension.

It's a unique approach (hence MEKK's byline "A unique frame for your unique car.") that replaces the WWII era engine, suspension, transaxle, and brakes with modern (well late '90s) components.

The Neon donor provides a reliable computerized, fuel-injected engine that doesn't need monthly valve adjustments and starts in cold weather (mine starts in 40 below temps here in South Dakota). The Neon's front disk brakes are adequate for a car its size so they are awesome as the rear brakes in a 1600 pound kit car. Instruments aren't a problem either. In later additions I'll show you how to reuse the Neon instruments in the kit car.

Stand by, the first article should be available this week...