Repairs Without Welding: Cold Metal Stitching

By Jpmort - Own work, CC BY 4.0,

What is cold metal stitching and what is it used for?

Cold metal stitching is used to repair cracked metal that cannot otherwise be mended via traditional methods, such as welding. The process of cold metal stitching implements specialized inserts that join the broken metal again across any cracks. You can use cold metal stitching to repair cast iron, cast steel, or aluminum.

There are many ways of joining metals together, whether they are of the same construction or not. While most people consider welding to be the most common way to join metals, there’s also cold metal stitching. In this article, we’re going to discuss the process of cold stitching in depth. We’ll also consider the pros and cons of cold metal stitching and when to consider this process as a potential solution to problems you may encounter. There’s much to talk about when it comes to cold metal stitching, so let’s get to it.

What is the Process of Cold Metal Stitching?

Just as it sounds, cold metal stitching laces up the pieces separated by a crack. We’re going to break down the process for you step-by-step, but if you’re looking for an audio-visual representation, check out Metalock Engineering Group’s helpful video. It’s very useful to see an example metal crack and how it is repaired via cold metal stitching.

Diagnosis of the Metal Crack

The first step in any cold metal stitching process is to consider the crack in question. There are many companies who specialize in cold metal stitching and most are able to repair cracks in materials anywhere from 3/16 of an inch to up to 1 foot in thickness. The length of the crack across the piece of metal doesn’t necessarily matter as much, but it’s important to consider what other methods can be used to repair the metal, or if it would be more efficient to obtain/create another piece entirely. In this first step, it’s important to know the pros and cons of cold metal stitching and be able to decide if it is indeed the right solution for the problem in front of you. We’ll discuss the pros and cons further down in the article but continue reading if you’ve chosen cold metal stitching as your solution.

Drilling the First Holes

By members of metalock international association - metlock international association, CC BY-SA 4.0, that you’ve decided on cold metal stitching, it’s time for the repairs to begin. The first step is to drill holes along the crack, spaced out at a specified distance. Perpendicular to the path of the crack, the holes are drilled with a guide for best results. Each set of holes doesn’t have to be the same number in total. In fact, you can have more holes at one point on the crack than you do on either end. The idea is to create strong stitching points to hold the cracked metal together.

Connecting the Rows of Holes

After you’ve drilled your stitching holes, it’s time to connect them together. This will make it easier to insert the keys you’re going to use to strengthen the cracked metal. You’ll want to use a chisel large enough to connect the holes without creating a slot in the metal. The rounded shoulders of the drilled holes will act as holding points once the key is inserted, so it’s important to maintain the outer diameter of the holes while still connecting them.

Inserting the Metal “Keys” or Stitching

By Jpmort - Own work, CC BY 4.0, metal keys are the most important component of the process. They provide the strength necessary to keeping the part together after it has been repaired. You’ll want to use high-strength metal for these keys or else you might find yourself having to repeat this process again.

Ideally, you’ll want the metal keys to be the length of the holes you drilled in the first step. That way the keys can add strength across an entire surface area to prevent further cracking from occurring. They should also fit tight enough to create a solid bond; there should be little play between the original piece and the metal keys. You may have to use a mallet to press-fit the keys in. Don’t worry if there is extra material sticking up past the surface of the original part. Dealing with that excess material is part of your finishing process.

Sewing Between the Stitches

It’s not enough to rely on the metal keys you’ve inserted in the cracked piece. While they’ll definitely make a difference when it comes to the strength of the overall piece, they are still weak enough to break under intense heat and/or pressure. For this reason, you’ll also need to install screws between the metal keys. Place them relatively closely to neighboring screws, as well as the metal stitching keys you’ve already installed. The tighter you can get the stitching, the stronger the bond between the cracked metal and the repair metal.

By Jpmort - Own work, CC BY 4.0, with the metal keys, it’s okay if there is excess metal sticking up from the installed screws. You want to have more material so that you can finish the surface as if it were one whole piece. Having material that doesn’t line up flush with the surface of the original part means you’ve got a weak spot that will likely crack again.

Finishing Steps

The last few steps in this process are perhaps not your most favorite. Chisel away the excess material from both the metal keys and the stitching screws you’ve inserted. Remove as much material as you can with the chisel and then come back with a grinding tool to sand the rest down. You can then refinish the piece as it was originally, as most of the evidence of repair should be hidden beneath the ground-down excess metal.

What Can Cold Metal Stitching Repair?

Cold metal stitching is more popular than you might think. Really, it is an ideal solution for repairing structures than cannot easily be dismantled or replaced. Construction workers may implement this process during restoration of old buildings to conserve the original handiwork of the builder or architect, while still creating a safer place for any inhabitants or visitors.

Another application for cold metal stitching is inside a ship. During dry-docking, these types of repairs can occur with little downtime. Sometimes the engine blocks crack and rather than install a completely new engine in such a tight space, cold metal stitching may provide the easiest, most cost-effective solution. Cold metal stitching impacts industries like the automotive and construction industries, the agricultural world, transportation, trucking, mining, large-engine machinery, and many other applications as well.

Pros of Cold Metal Stitching

There are many situations in which cold metal stitching is the only cost-effective solution. Think about a sheet of metal as the windshield in your car. When you get a cracked windshield, you don’t always have to replace the entire glass. In fact, you can often call in a service to fill the crack (as long as it is the right size, of course), rather than paying for a completely new piece of glass. Cold metal stitching is similar to the process of filling in windshield cracks, except in metal instead. It’s often easier—and cheaper—to repair the existing metal than rebuild the entire structure itself.

Another benefit of cold metal stitching has to do with pressure release points. Cracks often appear where stresses are highest, as they overcome the surrounding metal. If you can repair these areas and effectively make them stronger, you allow the stress to release where it already wants to while still preparing the metal for extra strain. This prevents further cracking in other (potentially weaker) areas as well.

When done properly, cold metal stitching does not mar the surface of the broken piece either. After the initial repairs are made, you can simply sand down the stitching. Finish the now-fixed piece of metal as you would normally, painting over it if necessary or desired. Best of all, the alignment of the original pieces shouldn’t be affected, since you drill within the metal as it stands. You won’t use any heat necessarily to perform the repair either, so there’s no concern about heat distortion.

Cons of Cold Metal Stitching

Speaking of heat distortion, certain metal parts such as engines and heavy equipment that experience hot and cold temperatures on a varying basis may not benefit from cold metal stitching. The stitching materials and the original metal may not be of the same makeup or perhaps even not the same type of metal. Each metal heats up and cools down at its own rate, so unless you use the exact same materials for stitching as the original piece, cracks can reoccur due to the stresses of hot and cold. Therefore, it’s best to use cold metal stitching in spots where varying temperatures do not exist; however, in some instances cold metal stitching may be the only alternative.

When Should I Use Cold Metal Stitching?

Cold metal stitching saves many companies and corporations large amounts of money when it comes to repairing large machinery. Think about your own vehicle for a second. If you had to replace the entire engine in it, chances are it would cost you anywhere from $5,000 to $10,000. Now consider how much companies who maintain large mining trucks, transportation semi-trucks, and even railroad locomotives would have to spend to repair their enormous fleets of heavy-duty equipment.

It all boils down to the cost-effectiveness of the repairs in question. Will the replacement part exceed the cost of the repair via cold metal stitching? If that’s the case, then that expense might be put off longer with the repair costs associated with cold metal stitching. On the other hand, there are cases in which partial or full replacement is necessary. It could be required by law or circumstance or just make more sense for all the factors involved.

Where Can I Go to Learn More about Cold Metal Stitching?

If you’re looking for a do-it-yourself alternative to welding, check out Cast Iron Crack repair on YouTube. also has a great video on repairing an engine block yourself. There are a number of videos and tutorials available on the web. Just search “cold metal stitching” to check out what other people have done to repair their cracked metal pieces.

For examples on how cold metal stitching can be used on architecture, check out this website. There are a lot of applications in terms of housing and restoration where the integrity of the dwelling itself can be improved with some modern fixes. Many companies specialize in their own methods of cold metal stitching, so google to see if any are located near you. You never know, cold metal stitching might just be the answer to your prayers.

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