Are you planning to purchase plastic sheets for your next project? Cut to size plastic sheets can bring efficiency, flexibility, and a customized fit, but there’s more to getting it right than simply ordering a specific size.
Understanding how factors like material expansion and cutting tolerance impact sheet size is important, whilst also appreciating how in some cases cutting to size yourself may be a better option.
In this guide, we’ll walk you through three of the essential considerations to make with plastic cut to size, ensuring you’re equipped to make an informed choice and achieve the best results for your project.
1. Allow for Expansion and Contraction in your plastic
Plastic, like most roofing sheet materials, can slightly change size due to fluctuations in temperature. Especially in extreme UK winters!
This is called expansion and contraction. It is relatively simple to understand when heated, it can expand; when cooled, it contracts. However, the degree to which this occurs will vary depending on the type of plastic you’re using, but it’s a shared trait across all varieties, including acrylic, perspex, polycarbonate, and PVC.
Why does plastic sheet expansion matter?
If you’re using plastic sheets in an environment where temperatures fluctuate - such as outdoor installations, pool covers, or even certain indoor spaces - it’s crucial to account for these changes.
For example, a perspex sheet installed in autumn with lower temperatures, if thermal expansion is not considered when selecting your cut sizes, you may find that this is installed without the required allowance for this expansion. This will cause issues down the line when the weather warms up, potentially putting the sheet under strain.
In contrast, a sheet used for roofing where temperatures can be expected to drop considerably may contract leaving small gaps for water ingress if this contraction is not accounted for.
How to Allow for Expansion and Contraction
To prevent these kinds of issues from occurring, it’s a good practice to leave a small gap between the plastic sheet and its surrounding fixings or structure. This space allows the plastic to expand and contract as needed.
The specific gap you should allow for expansion and contraction will vary based on the type and thickness of the plastic sheets but in general, allow 2 mm on either side minimum.
When ordering plastic cut to size, discuss your intended use with the manufacturer to determine how much of an allowance might be necessary. They may be able to advise on best practices and considerations based on the specific material you’re using.
2. Tolerance – There’s a Margin of Error in cut to size
A concept that might surprise some, is the idea of a tolerance in cut-to-size plastic sheets. Tolerance is essentially a slight margin of error that occurs during the cutting process of your sheets. While professional cutting machines are very precise, achieving perfect measurements down to the millimetre isn’t ever feasible, especially when working with large sheets.
Bear in mind, the larger the plastic sheet you are ordering the bigger tolerance you should allow.
Understanding Tolerances in Cut-to-Size Plastic
When ordering cut to size plastic, most suppliers will provide a tolerance range. For example, most twinwall polycarbonate sheets will have a cutting tolerance of approximately 10mm (1cm), meaning the final size could vary slightly within this range.
It is important to note that this is generally a ‘plus or minus’ tolerance, meaning it may be slightly shorter, or slightly longer than your exact measurements.
Tolerances are necessary due to the mechanical processes used in cutting, particularly on sheets with internal structures.
The actual tolerance range can vary based on the type of plastic, the sheet’s thickness, and the cutting method used during manufacturing. Solid polycarbonate, for instance, often has tighter tolerances than twinwall or multiwall, due to being a solid material.
Why Tolerances Matter for Your Roofing Project
While a small tolerance may not seem like a big deal, it’s essential to account for it when planning your project. In certain applications, such as a roof installed with glazing bars with a tight-fitting assembly, even a minor size discrepancy can affect the outcome. Knowing the tolerance range allows you to adjust your measurements or installation method to accommodate any potential variation.
If your project requires extremely precise measurements, it can be best to leave yourself some play in the measurements you select with a view to trimming these down more accurately on site once your sheets arrive. This can depend of course on the specific material and how easy it is to work with – see the next point below.
3. Trim Plastic Sheets on Site – Achieve a Perfect Fit
If as mentioned above you choose to work with your sheets on site, one of the significant advantages of plastic sheets generally speaking is their ease of trimming, which allows for this. Unlike materials like sheet metal or glass, plastic can be trimmed using basic tools, even in a non-professional setting, if you choose the right type of plastic.
Polycarbonate sheets are generally considered the easiest type of plastic to cut, whereas perspex, petG, and acrylic can shatter during cutting.
This feature makes polycarbonate an excellent choice for most projects, as adjustments are usually necessary.
Techniques for Cutting Plastic Sheets
Depending on the type and thickness of the plastic sheet, you have several options for trimming on-site. For thinner sheets, like acrylic, a scoring knife or utility blade can often do the job. However, acrylic can split and crack when cutting so it is sometimes best to opt for a higher-quality polycarbonate option.
Polycarbonate is a great option as it will not go brittle or shatter when cutting like other, cheaper alternatives. It is incredibly easy to cut down or drill on site.
To cut polycarbonate sheets you will require:
- Jigsaw with blade (Tip: a fine-tooth blade with upward-cutting teeth is best)
- Measuring Tape
- Marker Pen
- Straight-edge or Ruler
This quick How to cut polycarbonate sheets video will walk you through the steps required!
The ability to trim plastic sheets on-site offers flexibility that is especially useful if you encounter obstacles, you did not foresee. For example, if you’re installing a roofing sheet and find you have measured incorrectly or have a pipe to work around, you can quickly adjust to achieve a perfect fit. This is a significant advantage when working with custom-cut plastic sheets because you can ensure that every piece aligns just right with your installation needs.
Conclusion
Cut-to-size plastic sheets offer convenience, versatility, and an array of practical applications, making them an excellent choice for various projects. However, understanding a few essential points before making a purchase can make a world of difference in the success of your project.
The three important things to know when buying plastic cut to size are:
- Allow for expansion and contraction
- Be aware of cutting tolerances
- Install Polycarbonate for easy trimming on site
First, remember to allow for expansion and contraction in the plastic, especially if your project will be exposed to temperature changes. This simple consideration can prevent warping and cracking over time.
Second, be aware of tolerance ranges, which account for slight variations in size due to the cutting process. While usually minimal, tolerance can impact projects requiring precise measurements.
Lastly, take advantage of polycarbonate sheets’ easy-to-trim quality. Being able to make minor adjustments on-site gives you greater control over the outcome, ensuring every panel fits perfectly.
By keeping these three factors in mind, you can confidently purchase plastic cut to size, knowing you’re fully prepared to work with the material effectively. Whether you’re tackling a large construction project or a small DIY endeavour, understanding these aspects will help ensure your project goes smoothly and meets your expectations.
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