Are you working with accurate fabrication specifications?

This is not a trick question. We all know that accurate fabrication specifications are vital if a project is going to be successful. However, experience tells us that many customers ‘copy and paste’ their specs assuming that in every respect, one-size-fits-all.

We’re used to examining our customers’ designs and making recommendations that will lead to improved functionality and, often, cost savings. It’s important that we know what our customer is trying to achieve. If we find that the wrong material has been specified, or unnecessarily tight tolerances allowed to slip through, it can make a massive difference to cost alone.

We work across a lot of sectors – aerospace, construction, retail – and the story’s the same: inaccurate specifications may prevail for various reasons, but the impact on timescales and budget is the same across the board.

In this blog, we look at some of the common mistakes we find in fabrication and component specifications.

Prioritising fabrication and component specifications

There are two issues to address:

  1. Why using the same old specification might be dangerous
  2. Why you may not have the knowledge and experience in-house to create accurate fabrication specifications in the first place

Using the same spec isn’t wrong in itself. Working in spares and repairs for aerospace, for example, we are often asked to manufacture replacement components – washers, brackets, gaskets, etc. Not unreasonably, the customer will refer to the original drawings and specs. However, these can be 20-30 years old! So whilst the component design might be the same, the material specified is highly likely to have been upgraded and could, therefore, be obsolete. Of course we might have stock of the ‘old’ material which solves the problem – assuming the upgrade isn’t more appropriate. Otherwise, it’s back to the drawing board (literally), and a lengthy approval process.

Customers are often surprised that their original spec or drawing may no longer be relevant. The prospect of changing materials can be daunting because the consequence is most likely delay – sometimes as much as 4-5 months. A new or upgraded material might have different properties such as different tensile strengths changed or it might even be ‘unweldable’.

Whilst we will pick this up at quotation stage and offer an alternative, the customer’s stress engineers will have to re-evaluate and approve the component. This will inevitably hold up production causing a delay to the project. Checking with us before the project goes though the external procurement process, would avoid such delays.

The second issue is that engineers, designers and architects are not always the best (eg qualified) person to specify the material that ensures their vision can be realised. Why should they be? Their specialism is design, not keeping up to date with materials and techniques. That’s why you use Alroys.

Just how wrong is the wrong material?

Materials, methodology and processes in the construction industry are forever changing. Architects often fall back on what they’ve used before – specifying a 75mm x 40mm box section without knowing if such a configuration still exists. Maybe it’s changed to 75mm x 50mm. At a certain stage in a project, knowing that earlier would be useful!

We’ve questioned the specified thickness of protective glass for a roof-top garden. Taking into account the strength of the wind, we felt that 21mm was stronger and therefore, safer than the specified 18mm. Just because something is specified on the drawing, doesn’t always mean this is the best solution.

The wrong material can have far-reaching consequences…

Being too tolerant of tolerances

Defining tolerances accurately gives you greater control over the consistency, precision and quality of your project. Tolerances determine your ‘room for error’ so we always check them – even if we are replicating a part – just in case the circumstances have changed.

Accurate fabrication specifications 1 - Alroys
When you define your tolerances from the start, be sure to take into account mating parts and the build up of tolerances. This will make it less likely that the assembly won’t fit, and reduce the chances of re-work or even re-make. Equally, if a part doesn’t move and doesn’t have to fit inside another component, then the tolerance can probably be a little looser, without negatively affecting its core function.

Being precise about tolerances means you’ll only pay for the manufacturing methods and labour that you actually need to get the desired end result. The tighter the tolerance, the higher the cost. It’s really important, therefore, to asses the function of the component and apply the correct tolerances accordingly.

So the question we always ask is: what is the end use for this ‘bracket’? You might be OK using a standard drawing but best not to assume the ‘default’ tolerances are suitable.

Don’t specify a ‘poor’ finish

Specifying the wrong finish can have serious ramifications. For example, for internal use, you need only clean, pre-treat and top coat for a powder coated finish. For outdoor use, however, as well as the cleaning and pre-treatment processes, we’d also recommend an epoxy primer prior to the top coat. This additional process is to protect it against the elements in case the top coat gets scratched or chipped. You may even choose to use an architectural polyester top coat which will offer even more corrosive resistance than the standard polyester finish.

Location can impact the finish in other ways. Will it be susceptible to adverse heat or salt water, both of which are key factors to take into account at design stage.

Are you qualified to specify the right materials?

An awareness of the different kinds of materials available, and their properties, is vital. For example, there are several variants of mild steel, stainless steel and aluminium. Choosing one grade of material against another can affect its performance such as welding, bending, strength, etc, so we need to know the purpose and functionality of the component.

An architect or engineer can’t possibly know all the options open to them – what will do the job well, be a more economical substitute, etc.

We’ve come across people who think that BS EN 1090 actually specifies materials as part of their compliance with the regulation. It doesn’t; you specify the material and demonstrate that your choice is safe and appropriate. Which is exactly what we achieve across all our projects, irrespective of whether BS EN 1090 is involved or not.

It makes sense to come to us at the design stage of a project and share your “I’m thinking of this…” moments. Tell us early on what you’re planning so you save time and money (no redraws, no impact on the schedule, just cost effective materials).

The impact of inaccurate fabrication specifications

The impact of inaccurate fabrication specifications can be summed up as follows:

  1. Strength and integrity
    The wrong material can threaten the integrity of a project. Even a fixing can weaken a structure because it dictates the pitch, proximity and diameter of holes to be drilled.
  2. Cost implication
    If you price up on the basis of an inaccurate specification, your budget will be wrong one way or another. Given that expenditure on spare parts and engineering materials can be as much as 45% of the total budget, accuracy of specification should be a high priority.

The current supply problems are unlikely to be relieved any time soon so, creating accurate specifications is even more important. The earlier you or your contractor share your plans with us, the more successful the project.

Further reading
Is your steel fabrication structure fit for purpose 
Without EN1090 your structure might kill someone 

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