Dual Action vs Rotary: Which Polisher Should You Start With?

This question is as synonymous with detailing forums and pages as “what wax should I buy for a black car”. In truth, for most starting out, a good quality 15mm throw DA, plus a 75mm DA option for tight areas will cover most of the work you’ll need to perform, but you can be more efficient and get better results if you choose the correct machine for the task.

Your first machine purchase can open up a world of possibilities and potential income for professionals, if you

1. Get it right for the typical job

and

2. Learn how to use it effectively.

So, let’s look at the options.

It’s not a two-horse race

Let’s complicate it: there are THREE overall options. Dual action, Rotary and FORCED action (technically there are twin-head dual actions too, but only useful in very specific circumstances). But there are also combination machines, which allow you to switch between throws and actions. Small area polishers offer some unique benefits, then there are different throws, different plate sizes, cordless vs corded…

It’s not just a binary decision – though at least with rotary your backing plate size is an easy-to-change aspect.

Dual Action Polishers

E.g. Flex XFE, Rupes LHR 15, Das 6/21.

Dual action is the most sensible starting point with modern polishes and pad technology. They are more forgiving of loose technique – until you tilt too far – and they will do 95% of the work in the middle of the polishing spectrum, refining well enough for most circumstances, and cutting better than a rotary when combined with the correct technique (something covered on our Foundation Course).

You’re looking for large throw models these days for comfort and efficiency – 15mm is the standard, with 21mm available if you are covering large flat areas more. 6mm is considered short throw and were developed from orbital sanders at the time. They will take longer to achieve the same effect and are generally less comfortable due to high-frequency feedback vibration.

You are less likely to cause issues with burn through on thinner paint, and because the free-spinning action drops when there is too much friction, they are considered safer – as long as you can recognise the warning signs.

They are versatile machines capable of correction, enhancement, and LSP application with a low risk of damage. Easy to master and muscle memory is less important. Cheap starter machines are available, of varying quality. If you are only going to use it occasionally, then by all means make a saving and you can achieve a lot with relatively little effort.

If it’s going to be in regular use, you get what you pay for. Professional machines are lower vibration, lower frequency noise and more comfortable to handle. We would recommend paying the same for a second-hand professional machine over a new cheap machine if it’s coming out more than 5 times a year.

The cons are; they are almost always more expensive than the equivalent-quality rotary machines. Low heat build-up means some older non-diminishing of hybrid compounds are less suited and will struggle to work as effectively or as designed. Vibration from the machine can make it less comfortable to use over long periods.

Micro-marring is the biggest issue with dual-action machines, so heavy cutting can require the same amount of refinement as holograms do on a rotary. Pad stall is probably the most common issue you will encounter on DA, making them less useful on complex surfaces without knowledgeable technique to adjust to suit.

Backing plate choice is limited by machine, so you’ll need more than one type in order to be able to use the full range of pad sizes.

Tip – ensure you use them with foam pads featuring a hole in the middle. This reduces the torsional stress on the pads foam and prevents premature failure

Rotary

Makita, Flex PE14, Rupes LH19… the list is endless.

A universal machine which can heavy cut or refine to a pin-sharp finish. Usable with any compound, though the heat generated from friction can break down modern, DA-designed diminishing compounds too quickly. Comfortable to use for long periods as they produce little to no vibration. Pad size choice is wider as you can fit anything with an M14 thread, and it’s very adaptable, with many different sizes of backing plate and extension bars available.

It’s very difficult to find a bad rotary polisher. They are simple machines with one action, developed from an angle grinder. The issue people generally have is getting one that’s built for grinding still. High speeds, heavy weight and clunky body parts don’t make for a comfortable refinement tool.

You’re looking for one with a minimum start speed of around 600 RPM, and you won’t need it to go faster than around 1800 RPM for detailing work, so if it sits outside of this it’s probably too aggressive.

Extra weight makes it less comfortable, but like the DA, if you’re only using it occasionally you can put up with that. If it’s more than 2kg though, it will become tiresome doing vertical panels and when you get tired, you rush – that’s when results take a dip.

There are few real downsides apart from needing practice to get comfortable and proficient with them. Heat build-up and aggression can damage paintwork if used incorrectly and increase the risk of strikethrough. They require practice and the development of muscle memory to use effectively and comfortably, which only comes with time and practice.

The increased heat can cause rebound issues on Ultra High Solid (UHS) clears so you’ll need to learn to adapt your technique to the situation. Use on surfaces such as GRP can go badly without experience, as heat dispersal is reduced by the substrate.

Myth-bust – Burn through is actually quite hard to do by accident on sound original paint if you ignore all the warning signs, rotaries are only as damaging as the people who use them, and if used in the correct manner can actually give you more control and a safer experience than DA polishers.

Forced Dual Action

e.g. Flex XCE/VRG, Rupes Mille, Vertool

Forced action machines have a very specific niche. The utility of them are overlapped by the above for only slight gain, so you can quite easily perform all tasks without ever picking up a forced action, but in the right situation they can be useful. In a choice of the three polisher types, Forced Actions are probably the fourth or fifth choice we would buy, with a small-area polisher or nano polisher and a cordless machine or longer-throw DA all stronger contenders.

Known as forced DAs, a positive-action drive machine combines some of the safety of a DA, keeping heat and friction lower, with a lot of the consistency a rotary gives you.

They don’t stall on panels, regardless of their curve, due to the gear-driven rotation, and act as a safer alternative to rotary polishers on curved or inverse surfaces, allowing you to remove more defects, use larger pass areas, and cut quickly and efficiently. They can create heat useful in heavy correction, whilst being gentle enough to use as an application tool if needed.

Micro-marring can be an issue, as it can be with dual-action machines due to the eccentric action on the surface. They can also break down some compounds too quickly, as with a rotary, due to the higher friction and heat generated, which leaves them less effective with modern diminishing compounds.

They will require some muscle memory to master as they can pull you around a panel, and some of the popular versions spin the opposite way, making it feel odd and tricky to master for those used to rotary rotation.

Only really useful over and above rotary and DA in certain scenarios though – for example, we have used them on the curved interior of helicopter windscreens and with a large pad to speed through a LWB van side panel when it only needed a quick lift rather than a full correction. Niche.

Tip: you can load up a pad with more compound and spread further with a Forced Drive – perfect for large areas and more efficient “flick over” polishing.

So what machine should I buy?

All of these machines, including the ones we don’t go into detail on, have their place. If you are a professional or aspire to become one, you should aim to be proficient in all types of polisher so as to be able to correct a vehicle as efficiently and as effectively as possible.

If you have the time to spend mastering it, and you have expendable panels available to practice on, Rotary will give you the broadest range of use with the most comfort with low vibration output. Lower-end machines are cheap due to their simple production design and are often noisy and heavy. A more expensive machine will make polishing easier and more comfortable once you have learnt the basics and is a worthwhile investment.

If, however, you are “earning and learning” – that is, you have practised but need to perfect your technique on paying jobs, you should probably go with a dual action machine. These are forgiving enough to allow you to make minor, easily fixed errors without too many consequences when used sensibly. They are capable enough for 95% of the jobs you will encounter, and provide a uniform finish with reletive ease.

Cheaper machines, whilst enticing, are a bit of a false investment. Not only will they offer less cut and potentially need replacing sooner, but if you think the vibration from a good dual action is harsh, wait until you try a cheap one. Your body, and therefore your efficiency, will thank you for investing in a quality machine early on.

Forced action, despite seeming to have the best of both worlds, is probably the last machine you should buy. It squarely covers the middle 80% of the polishing field, and whilst extremely useful in the right circumstances, you can achieve the same results and more with a combination of the other two machines when needed.

So, which machine polisher is best to start with?

For most people starting out, the best option is to purchase a good quality dual action machine and a smaller 75mm dual action polisher, which will cover most enhancement and minor correction scenarios. Once you are comfortable with your first machine, look to purchase a Rotary and spend some time practising on scrap panels to get a feel for how it pulls and travels.

A course such as our Foundation Machine Polishing course is ideal for getting to grips with DA polishing, or, if you are an existing user looking to progress, the Advanced 2-day course will get you up to speed on techniques for all machines, getting the most out of these tools with proper pad and compound matching along with technique and handling practice in the workshop.

Either will help you gauge what to expect when you do expand your range, so you are ready with the correct technical knowledge to progress. All in the safety of a classroom environment where you can make mistakes without dire consequences.

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