Buying a CNC
The best possible advice to anyone considering the purchase of a CNC machine is to make sure you do your homework. Investing in the right machine can be the best thing you have ever done, buying the wrong machine will give you sleepless nights and may be a financial disaster.
When looking for a new CNC, one of the most important points is to be aware of who the manufacturer is. As in all industries, there are too many ‘home branded’ machines often manufactured in the Far East. Whilst this practice may be acceptable for standard classical machinery, for a highly technical and complex machine such as a CNC, there will be a time when you will need the manufacturers support. If the machine is being re badged and supplied by a machinery dealer, what if this dealer retires, closes or fails…? This would result in a huge problem in acquiring both parts and support. These ‘home branded’ machines will be a temptation based on price but also have very little value when second hand.
There is the saying ‘you buy it cheap, you buy it twice’ and buying a CNC is no different at all. As with all walks of life there is always a cheaper product which often carries a risk but due to the cost of a CNC, once you’ve made the purchase, it’s not just something you can say ‘oh well, that was a mistake, I’ll buy a better one’, so it is vitally important you look to buy the right machine from the outset and not be dazzled by a machine at a price.
At the other end of the scale are the ‘big brands’ where big companies have big advertising budgets, big overheads and charge big money. Stories of £4,800 for an extraction guard and customers being charged £1500 just for 1 days visit for an engineer and charges of £24,000 to extend a 12 month warranty by another year. So again, do your homework and look at the long term costs of owning a CNC.
The price for a CNC depends upon the components used during the construction which in turn leads to the longevity, accuracy and reliability of the product. Therefore, the fact is an industrial quality CNC using genuine quality branded components will start from £40k. A machine costing less than this will probably be home branded, use cheaper components and made in the Far East. If you set yourself a budget of say 25 to 35K, you have to be prepared to take the gamble that you may be buying a short term solution, then have to look at starting again by buying another machine at a later date (you wouldn’t believe the enquiries we receive from this sector)
Safety and Legality
All machines supplied into the UK should carry the genuine ‘CE’ certification. However due to the additional rules for UK health and safety which states the operator or any other person should not have access to any moving parts whilst the machine is in use means the machine should be protected to 3 sides to ensure no access and have either safety mats or a safety light barrier to the front, so the machine stops if anyone tries to approach it during use.
Unfortunately, the less scrupulous sellers ‘forget’ to mention this, and it will ultimately be the buyers responsibility to make using the machine legal.
Some suppliers say that having a slow-moving machine (upto 25m/min), bumpers are adequate as a total means of safety. Whilst this may be acceptable in some markets, the UK HSE says otherwise. These bumpers may stop the gantry from moving in the event of a collision but don’t offer much protection from entanglements or access to moving parts or even the cutter.
Also do an internet search for ‘cnc router hse enforcement notice’
It is the sellers moral responsibility to make the buyer aware of this, but unfortunately after the sale it is down to the buyer to make the machine safe to use within his environment.
There are 2 types of software on a CNC machine;
1) Machine neutral
2) Machine Bias
Ever wonder why some CNC machinery manufacturers also include their own ‘in house’ software..? The simple reason is that when you purchase a CNC you embark upon many hours learning how to use the machine, so when it comes time to buy another or replace the machine, the easiest and most cost effective route is to simply buy the same again. However of course this ‘ties’ you to that particular manufacturer and quite often support can be very expensive as you have nowhere else to go. This software we refer to as ‘machine bias’ as it is designed only for that machine.
A good example of ‘machine neutral’ software is Alphacam who are an independent and specialist software design company whose business is to provide solutions to manufacturing across all industries. This software has emphasis on the CAM to allow it to be adopted for use on any machine. Of course if you consider Alphacam as an independent product, they supply to all makes of CNC where the home grown software has become ineffective or has too many limitations.
Software application and Training
Many manufacturers already have their own CAD package for designing cabinets etc and probably have several years catalogue they want to use rather than having to start designing and drawing all over again. This is where the software applications engineer can save you hundreds of hours and get you up and running in the shortest possible time. Whether you use Autocad, Solidworks, Sketchup, Articad etc, the software applications engineer can show you how to convert your designs into optimised manufacturing data in the quickest and easiest way.
We cannot stress the importance of this when purchasing a machine. Does your machine include remote access to their technical support team..? Typically an operator may write or import a program which ‘doesn’t work’….so, what do you do…? Call and book an appointment for an engineer to visit which means the machine will not be working for a number of days..?
These days you connect remotely to the technical support team who can connect to your machine, read the program and diagnose if there is an incorrect depth, speed or tool being used. The technical support team can not only read through the programs but also the machine software and run diagnostic checks to see if there may be something like a proximity switch needs adjusting. This is what we refer to as the first response which is the quickest way to resolve any issues.
The second response is of course if an engineer is required who will be fully versed to the problem as diagnosed by the technical support team and will be able to make any necessary adjustments required or be equipped with any part that may be required. This system using today's technology of connectivity ensures the fastest and most cost-effective solution to support your CNC.
The CNC should be a long-term investment due to the nature of the cost and invested time in learning the software. Spending a little more now could save you having to purchase a ‘better’ machine in the future, therefore consider the following points as to what you need and where you want to be.
1) For a flat bed machine, one of the primary goals is to keep the components from moving during cut. Therefore the size of the vacuum is important (usually at least 250 m3 on 8 x 4 and 10 x 5 and twice that on jumbo sized machines). Just as important yet quite often overlooked is the design of the vacuum bed, namely the ‘matrix’ or ‘chocolate bar’. As it is only the vacuum that is holding the workpiece in position, the design of the matrix is of paramount importance. The larger the matrix or chocolate bar, the less vacuum hold is generated and therefore the less effective it will be.
2) Power of the router head and a rapid linear speed will also give greater flexibility to the work being processed and as time goes on will allow faster processing times (yes, there will be a time when your CNC will be working flat out, so if a faster machine can process a sheet 2 minutes quicker and a typical nest takes 10 minutes per sheet, this equates to 12 minutes per hour, or 96 minutes per day or 8 hours per week or based on a 48 weeks per year a whopping 384 hours…if this time is equated to man hours and a typical wage being £15/hour, the faster machine will save you £5,760 per year…..or give you an additional 384 hours’ worth of capacity to bring in more work). Usually a 9Kw is considered as standard….there is nothing more frustrating than having to nest a sheet at slow speed and in 3 or 4 cuts if the motor isn’t big enough.
3) Linear speed, these days 70 m/min should be considered as a minimum, not only for speed of tool change to reduce cycle times but as tooling technology increases, a machine working at say 25m/min may not be able to cope. A typical example is one of the nesting tools we supply can cut at up to 50 m/min on MFC and 25 m/min on MDF. Some manufacturers give their machines a ‘Vectoral Speed’ which is a little misleading. Linear speed is actual speed in a straight line whereas vectoral speed uses the X and Y dimensions from a ‘zero point’ but uses the actual distance travelled, for example on a machine bed 3.2m x 2.1m, starting from zero and travelling the opposite corner they will use 3.2 + 2.1 = 5.3m ‘distance travelled’ when in reality the head has moved 3.83m (the hypotenuse), i.e. suggesting the machine is over 30% faster in operation as opposed to the corresponding linear speed.
4) The PC and software, at first you may want to cut shapes and nest some sheets but once you understand the capabilities of a CNC you may want to import a complete kitchen as a ‘solid model’ have the software break it down into component form, use whatever choice of fixing whether it be pilot holes for screwing together or one of the face fixings currently available, then have the machine optimise, cut and drill multiple sheets. Do you have the possibility to upgrade software to allow this as opposed to the afore mentioned machine bias software which works on the theory of ‘one shoe fits all’. Does the machine’s PC have enough power and speed to process such demands..?
The purpose of this guide is to offer assistance and information so hopefully you can avoid some of the pitfalls of making what could be your largest manufacturing investment.