By Graham Howe

Quality and Accuracy

Posts on model engineering forums never seem to be
lacking when it comes to queries about buying a lathe or mill. It seems
 for most buyers it is a difficult and challenging process and recently
there have been many questioning the accuracy and quality of import
ed machines as compared to home grown older machines. Reading these
 concerns I decided to offer my thoughts on this and how I attempt to
rationalise all this as it is a genuinely difficult area especially for
 newcomers to model engineering.

It seems a lot of people, even very experienced engineers have difficulty
 with quality and accuracy terminology and this is very understandable as
 they seem to apply to every machine available for sale. In my computer
 career I worked in IT and, unfortunately, had to manage the quality
 requirement placed on my department by HQ who deemed that all
employees must be 'quality aware'. 
The problem was how in the world
 do you define quality?  A Rolls Royce is a quality car and so for that
 matter is a basic Ford economy car yet they are worlds apart in design,
 appearance, functionality, performance and cost. The thing is that when
 looking at any product the quality label is tailored to that product alone
 and often the term is misused as a marketing means to attract and 'assure'
 new buyers. It clearly has different meanings for different people and as
 you might expect a precision toolroom lathe operator will expect quality
 well above that of a home hobby lathe user but strangely many new
buyers fail to rationalise this and expect high quality but at a low cost.
What all this comes down to when contemplating buying a new lathe or
machine is for the buyer to first consider his needs, skills, working
environment and then cost.  For example, if you are producing work in a
production environment say for paying customers who provide product
specifications and demanding tolerances then you would look for the
 very best lathe or milling machine that can meet those requirements
 knowing the cost will be high to buy but equally high if you fail to meet  the customer expectations. 
The reason the cost is high is because the machine will probably be new, manufactured using the best materials machined on high precision machines and assembled by experienced skilled fitters.  Quality is assured, as is accuracy, in these circumstances this is easily confirmed by asking the manufacturers about their staff, products and quality control mechanisms.

Now let’s come down to earth and examine the scenario of a home hobby requirement. It is unlikely the need will be to produce parts in a production environment but it maybe a small run of specials. The end product being made is unlikely to be a large quantity and have to meet exacting specifications and tolerances. Generally, time taken to make parts is a low priority and labour costs are negligible as all the work is done in-house. Assuming this to be the case the main decisions come down to cost, needs and user skills. 

Cost is probably the key factor in most buying situations especially so for a home workshop user and unless the buyer has a lot of spare cash this is probably going to determine the type of machine. 

Used 'quality' machines

If the potential machine is used but made by a reputable manufacturer of old it all then it comes down to wear.  A machine that has visible wear will probably be unable to produce repeatable accurate work even though it was once a very expensive quality machine. The problem is that wear is often disguised by a nice paint job and shiny metal but at some time a worn part will fail and getting a replacement will be expensive and often very difficult to fit. 

If the wear is in the main bed slideway then probably impossible to resolve.  Myfords, when they were in business, used to provide a service to refurbish lathes which would include re-grinding and specialist fitting but this could be costly. There are some other things to consider, if the history of the machine is known it may have had little use and been well cared for and so this immediately becomes the bargain of the year but bargains like this are getting rare. 

If the buyer is already well experienced then he can probably determine the degree of wear and remaining life before needing replacement parts plus he is likely to have the skills needed to do any correction work and fitting.  The problem here is that it takes pre-sale time and a lot of cooperation by the seller for checks to be made but despite this a quality machine can still be found but only if you are not in a hurry. 

Assuming the buyer is new to the hobby and lacking engineering skills then buying a used lathe or mill at low cost may still be quite a good move but here the emphasis has to be on low cost and obviously it has to be in reasonable working order. A new user with little or no previous knowledge needs a machine on which to make all the mistakes that come with learning and also get to appreciate why the accuracy may not be easy to achieve but in this case the initial purchase cost is the cost of learning and any major 'crashes' will be not on a new, pristine of likely expensive outlay. This is where one has to be extremely careful when looking at ex-school or college machines which can be made to look like ‘new’ by the seller but in many cases have been damaged by students.  A teacher once commented that despite all the training a student will always find the wrong way to do things!

New Machines

These basically fall into three types, professional, hobby small and hobby medium machines. The home user will unlikely consider the professional level machines so the decision once again comes down to cost. There are prestige small and medium machines available for the hobby market such as the Myford (no longer), Southbend, Wabeco, Emco etc. but these are all quite expensive. However, one can be assured of quality, accuracy and long life.  These are the top of the buying range and also high cost, if you can afford it and have the skills to use such an investment wisely then end of decision.  There is a small problem that exists, however, and this often relates to the user needs which if that includes working with large work pieces then many of these lathes cease to satisfy that requirement and the buyer is forced into looking at professional level machines and the cost now rockets!

The market for most hobby machines, small and medium sized, is now largely satisfied by the imported machines frequently from China. These all carry a quality and accuracy label which probably is not always comparable with quality standards of older traditional machines but this does not mean that they are not suitable. 

The wear problem associated with used machines does not exist and the cost is often low even for a new machine, more so when one takes out the costs attributed to shipment from China, middle supplier, taxes and seller profits, the cost is ridiculously low!  

Low cost readily equates to manufacturing and labour costs being 'trimmed' and possibly the use of mass production techniques.  Another crucial area open to trim costs is a lack or reduction of quality checks and this often shows up as inconsistent part dimensions and fitting problems. 

The fact these machines are mass produced does sometimes offer a ray of hope in the accuracy of major parts such as the main bed ways which are sometimes machined on large modern milling and finish grinding machines capable of very high accuracy. 

This factor, in  my opinion, was a crucial requirement for development and success of import machines.  As new and better production techniques have evolved the quality and accuracy of imports has radically improved. Consider a lathe, if the main bed ways and headstock, spindle etc. are wrong, the end product can never be accurate even to basic requirements. I understand from others who are more knowledgeable about this that some of the typical machining centres currently used to machine the major parts are cutting edge technology and often supplied from European machine tool specialists. So we can generally feel more comfortable that a purchase of an import machine is these days likely to be accurate with regard to the major parts of the machine but is this quality and is the sum of all the parts quality? In order to keep costs to a minimum manufacturers of import machines only the essential things which directly affect the fundamental accuracy of the machine will be carried out using specialist tooling. 

Unfortunately, other parts are less well prepared such as rounding corners, fettling castings or applying ‘traditional’ pleasing appearance.  Does this matter? well I like to see attention to detail and good finish on premium machines but this adds considerably to the cost and provides really no increased accuracy advantage other than that of final appearance. It is no strange coincidence that most import machines are ‘box-like’ with 

chunky square-cornered parts usually over sized.

The next area of cost trimming associated with import machines is all the other parts assembled to make the final machine. This includes, in the case of a lathe, parts such as the tailstock, cross slide, compound slide, gearbox, gears, leadscrew, electrical bits etc.  These are mostly reasonably well made and sometimes very well made but there is often a lack of consistency between parts when it comes to dimensional accuracy. In other words parts rarely seem to be fully inter-changeable should one order a replacement. On my import lathe I was pleasantly surprised that most of the parts were machined reasonably well but then again some were also in need of some further attention. The fitting of parts was adequate but lacked any attention to detail so the performance and hopefully accuracy of the overall machine could later be enhanced. 

It should be said that as delivered the lathe was ‘fit for purpose’ and thus one could say it was a quality machine but quality is a term having many levels of definition and so while in the basic quality grade with some extra work it could potentially become better quality!

Areas where costs have been trimmed to produce parts are just adequate and often badly fitted and so fail by my definition of quality yet the sellers always claim their products are of highest quality. What is quality to one person is trash to another but the good news is that for the basic home hobby user most of these machines, as delivered, are capable of producing good work. Even better news is that if some additional work is done by the buyer to improve the fit of parts the quality and accuracy of the machine can be transformed from an adequate machine into a reasonable quality machine able to produce consistent accuracy. 

Many people (new buyers) in the forums seem to expect high quality but always at low cost and this is not going to happen. However, if the buyer is prepared to add time and effort to improve the machine then quality and accuracy can be achieved at the same initial purchase cost.

The other thing that I think many newcomers need to be cautious about is when they are buying a new machine based just on the marketing material and product appearance alone. To explain this further, marketing is all about perception and not always reality so in the case of buying a lathe for example, is it always essential the lathe has a gearbox to change speeds and feeds etc. Remember the manufacturers have trimmed the costs and so additional parts and added complexity will also be trimmed when it comes to quality. 

The marketing hype readily appeals to most buyers who can save time by pulling knobs and levers to change gears but forget that this added complexity to the design saves time but increases the likelihood of potential problems in the long term. It is my opinion that fitting is always a problem with imports because parts are lacking machined dimensional accuracy and consistency and in many cases there is no time to correctly ‘fit’ parts together (assuming they have the appropriate skills). The solution is to weigh up the pros and cons of the 'marketing goodies' against need, cost and long term reliability. Problems can be minimized of course by spending time to inspect and rectify bad fitting or buying a less complex machine. 

I bought a belt drive import lathe which is a basic and simple design having few parts, the advantage being that if a part fails or needs replacing it is not a major task to re-make and fit. I recently examined the highlight features for one of the successor lathes to mine which now incorporates a gearbox for rapid speed changes and feeds however it was a surprise to see that selecting different screw-cutting requirements now required pulling gears used for the feed and replacing them with the appropriate screw-cutting gears. This now takes additional time whereas on mine for a large selection of feeds and screw-cutting I need only move a couple of gear selectors and not disturb the back end gear train.  

The marketing did not mention this additional time consuming step but all the extra goodies added 50% to the cost as compared to my basic lathe yet added no additional machining functionality. When buying a new lathe, whether it be used or new, the crucial thought process must be to ignore all the marketing stuff and concentrate on user needs giving special consideration to cost. Take into account any additional checking and fitting work needed and if saving time is really essential. 

Quality is difficult to define whereas accuracy can easily be measured but be in no doubt sometimes additional cost does not add either quality or accuracy.