Have we lost the plot as far as tollerances are concerned?

[dchallender]

As another engineer I think the whole debate about tolerances is a little academic as it depends upon the individual and their skills levels. For instance I consider myself a competent wood worker but I'm not sure I could work to the level of tolerances being talked about here, however as I develop who knows.

What I do know though is that I can work to those levels in an engineering project as that is how I was taught as an apprentice and I can still replicate that in the model engineering I do.

The one thing we need to remember is context of where and when to use tolerances, as an ex head of engineering in a very large aersopace company that single fact dawned on me the first day I hit the shop floor in an aerospace factory. Having come from an automotive manufacturing background I understand tolerances and design requirements and the importance of interchangeability, as already mentioned.

The shock came for me in aerospace when I saw highly specified components that have been CNC machined, heat treated, checked, verified and treated with love and care being hit with hammers and filed with emery paper so they fit the aircraft (it's all safe by the way :shock: ) ........because a lot of parts in an aircraft are fitted. So once I realised that's how you make a plane I understood that there's a time and place for tolerances :?

So again its down to context, I think if your making a 'fine' piece of furniture then go ahead and use fine tolerances, however if you're building a piece of rustic furniture that is functional use a rule.................so context and personal preference apply, because you can buy a digital CALIPER (just in case I said vernier made that mistake once before :lol: ) from Aldi now for the price of a good steel rule :shock:

 

[tom owens]

hi all,

i'm gonna have to get stuck in on this one.

reason......i've just spent £17000 plus on a new felder cf741 professional(professional, thats a laugh) and i've just given up trying to plane something after checking the levels and clearances of the infeed outfeed tables. guess what, both tables and the cutter block are all out of true.

if a machine manufacturer can't even get the basics right, what chance have they of getting 0.00000000001 on anything.

by the way....after reading the instruction manual, i found that the machine has a working temp tolerance of +10 to +40. i rang head office to find out why....you'll love this....all the fancy moters they put on will burn out if the machine is too cold. if i had been more stupid and not chose a manual machine with good old fashioned handles, my workshop would have been shut for four months of the year.

nice one felder!

if anyone is interested in the full sorry tale of my very unhappy experience with felder, i will be posting soon.

all the best

ps: i'm quite happy with 0.25mm tolerance genarally, always cut my m/t's a bit tighter and sand if nescessary.

jeff

i bought the fox floor standing p/t similar to aximinsters for £600 and a friend of mine who,s a machinest for jewsons set it up for me.
its taking 0.19mm more of one side than the other over 250mm. its not made a difference after making a few small projects. after reading this on a machine of that caliber i presume this is pretty acceptable?

 

[mr grimsdale]

....a digital CALIPER (just in case I said vernier made that mistake once before :...

Oh yes of course - a digital caliper isn't a vernier caliper. It'd never crossed my mind. Is it a digitised vernier style caliper perhaps?
How does a digitised caliper work BTW? There must be some mechanical interface between the caliper and the digital readout, I guess.
PS http://en.wikipedia.org/wiki/Vernier_scale

 

[ajbell]

I would guess that a digital caliper may use an electrical method to determine the position of the jars of the caliper through contact with a continuous metal strip and not a mechanical method.

If it does not have a set of two scales used to read a position then I don't think you can class it as a vernier tool.

Could well be wrong - I don't want to take my digital caliper apart to find out!

Andy

 

[big soft moose]

what's a thou?

its a teeny weeny measurement only pickerd up by those dial guages

 

[harryc]

what's a thou?

its a teeny weeny measurement only pickerd up by those dial guages

Never mind the thou what is a tollerance?

 

[mr grimsdale]

what's a thou?

its a teeny weeny measurement only pickerd up by those dial guages

It's pickerd up by vernier calipers too. Mine says 0.001inches and 0.02mm.

 

[promhandicam]

tol-er-ance (noun): a fair, objective, and permissive attitude toward opinions and practices that differ from one's own.

as the title of the topic is "Have we lost the plot as far as tollerances (sic) are concerned?"

I can only assume we have all so far got the wrong end of the stick.

The answer as far as UKW is concerned is, yes, very often we have lost the plot particularly in the General Chat Forum :wink:

Steve

 

[jimi43]

....a digital CALIPER (just in case I said vernier made that mistake once before :...

Oh yes of course - a digital caliper isn't a vernier caliper. It'd never crossed my mind. Is it a digitised vernier style caliper perhaps?
How does a digitised caliper work BTW? There must be some mechanical interface between the caliper and the digital readout, I guess.
PS http://en.wikipedia.org/wiki/Vernier_scale

It works by reading a type of bar coding and measuring the movement. There was a project site that adapted one to allow for the port (which is hidden all all the cheap ones) to be read and the display positioned remotely so that you could use it say in a TS underneath with the display on top.

I tried fiddling with it for a while but then thought...WHY?!!!

I just measure it with my thumb now!

:wink:

What I find amazing is that the eye can see errors of tiny amounts....

Even stranger....it doesn't see the errors in the component parts as you are cutting....only in the result when assembled.

The art of the apprenticeship is to determine when errors are likely earlier on...that is my view!

Jim

 

[dicktimber]

Just a couple of comments.

If we have moved on in terms of measuring say from rules to digital calipers, and machines can achieve these levels of fine tolerances we try to achieve, similar to tolerances that mechanical engineers expect when working metal..

Why don't we bring our drawings up to the same standard?
We are saying on one hand we should work as closely as we can to dimensions, yet fail to produce a drawing that reflects these dimension tolerances.?
For instance, an aircraft can be a couple of foot )and more) longer when it is completed because of the plus/minus tolerances build up on individual components when assembled.
Many people now use sketch up, but dont reflect these tolerances when designing in wood.
Should we not be putting plus and minus, or in some instances zero minus tolerances on dimensions, when we have the machinery and measuring facilities which make this possible?
Should we not be concerned at tolerance build up, which affects the overall size of the part...which as explained can make the finished part longer, or shorter...?
It appears we are only doing half a job.
Trying to work to engineering tolerances in wood, but producing a drawing that does not alow us to work to those tolerances because we do not incorporate them into the drawing?

My other point which has not been commented on is......
If we do work to these fine tolerances, what about woodmovement in service?
I think we are fairly lucky in our climate which is fairly stable. Make something in the south it will be in the about the same climatic conditions for moisture pick up as in the north ( would have cost half the price in the north though :wink: :wink: )
But I don't think we should have this same situation if we were in say the USA, because the country is so large and the climatic conditions vary so much if too tight a tolerance is used there would be problems IMO with splitting etc.

Please be aware these are my views only, and I personally think it is a good topic for discussion, and there is not right or wrong just personal views.

 

[mark w]

I`ve just read most of the posts in this thread and something has just occurred to me, if our machines are set accurately and we measure things with engineering tools and work to tolerances normally reserved for the aerospace industry do we need hand tools at all?
If say you have made a frame with mortise and tenon joints cut by machine and you have worked as stated above, then every thing is going to fit and everything is going to be flush, job done. In particular are you going to need one of Karls planes, if you go by his working ethic then surely the answer is no.
Another question I have is does anyone out there use a Holtey plane in their day to day making, I have read many articles in various magazines and not one shows the author using a Holtey plane. there must be someone, Karls waiting list must be proof of that.

Kind regards, Mark W

Ps Please do not take this post too seriously!

 

[Mike Wingate]

Be as accurate as you can. I make jigs for routing and build into them a tolerance to allow for the thickness of polish, when fitting the part into the routed cavity that I have cut with the jig. When I started these jigs, parts fitted really tightly, then when polished, needed treatment to bring them down to size to fit again. I know that wood moves, but you can only do your best with it. Anticipate.

 

[devonwoody]

MarkW, I think I can make a box without a handtool, (I think I do have a tape measure in my hand when I go hunting for the piece of timber to use )

So those handtool fellows here I am sure will respond to this post :wink:

 

[Chris Knight]

I think people have overlooked the fact that the most accurate metalwork is traditionally done by hand - surface plates for example were hand scraped not milled or ground - see here for example. IIRC the same applies to lenses and mirrors.

http://en.wikipedia.org/wiki/Hand_scraper

 

[Ironballs]

With regard to the point about handtools being obsolete, the answer for me is no they're not, but they have a different role than they might have done in the past. For instance I will dimension all my timber with power saws and a planer/thicknesser, but to remove the machining marks and imperfections I will go over it with a handplane.

Similarly roughing out a tenon is done on a bandsaw and finished by plane and chisel - for me

 

[stuartpaul]

Never mind the thou what is a tollerance?

All the previous responses are wrong, - it's the look on the wife's face after I've visited Axminster!!

I tend to agree with others on this. If it looks right and feels right then it probably is right.

Whilst I do own digital measuring devices I rarely use them preferring instead the old metal rule. I genuinely don't believe I have the skills to work to some of the tolerances mentioned. That doesn't mean that I won't work hard to try and achieve them but often my desire to achieve perfection is outstripped by my abilities. That doesn't stop me trying.

I've spent ages trying to get the mitres spot on for picture frames, boxes etc. and generally can. It doesn't come easy or naturally to me . The pile of offcuts and sawdust is sometimes bigger than the finished product.

Owning good machines certainly helps. I couldn't do it without them as my handskills really aren't up to it. Although on my latest project I tend to find myself reaching for hand tools rather than resorting to machinery. Something that has surprised and pleased me.

Regardless of any of the above I do genuinely love my woodwork. With all sorts of other 'stuff' going on in my life it is my escape and my sanity.

Is it the cheese eating surrender monkeys (am I allowed to call them that?!) who say 'vive la difference'.

 

[ondablade]

OK... So how's about this.

1. There's two drivers of all of this - function (whether or not it works) and aesthetics. (does it look nice)

2. Whether we work to tight tolerances or not we have to stitch together a set of parts in a way that 'works' - that functions.

3. After that it's about what it looks like to the observer.

Function imposes some fairly absolute ('must do') requirements, but after that it's a lot to do with personal perception.

The trouble with perception is that many of us are not that good at perceiving beauty as such - we tend much more to go for what our eye has been trained to like. It's not easy to stay open enough that we're not influenced by what society, media and the like conditions us to 'like' - so that we won't recognise beauty expressed in a form we're not used to.

Perhaps it's the good stuff that endures, although in the case of furniture some styles have been around so continuously and for so long that we're trained to consider them 'respectable'. e.g. most conservative types tend to default to something 'period' - although there's a few too that will default to contemporary for similar reasons.

:shock: Then there's the little matter of 'distressing'. Harvey Norman for example are selling furniture here that looks like somebody took an angle grinders to it (they probably did!) - and yet it's selling. Lurker on the other hand got hassle for making 'too perfect' furniture....

Perhaps the mistake is to get blindly hung up on producing by default one or the other end of the scale (precision or it'll do, or what's only fashion/style) - when in practice 'rightness' is the result of a unique and holistic blending of everything to do with the design, material choice and making of each specific piece...

ian

PS i suspect that much in the same way the collectors of really high end tools are not at all the same people or driven by the same motives as makers....

 

[jimi43]

Interesting post Ian...and set me thinking about aesthetics.

I will pose these two question if I may:

Does a Tudor building look right if it is NOT straight?

Does an Art Deco building look right if it is anything OTHER than straight?

Well since we all know the answer to these questions....what ARE aesthetics of tolerances....what is right?

We all know mock Tudor looks rubbish.

Art Deco that is not constantly whitewashed and painted looks just dingey.

The same can be said with furniture...or motor car engines...

All have examples where tolerances which are way out of kilter are quite literally...tolerable and even preferable!

We often forget with wood...even antique masterpieces...the visible beauty often is just a veneer! (pun intended).

You only have to restore a Longcase clock to know that...

Building guitars...I find that some things are visually required but others are critical...the angle of a neck for instance can make or break the action of an instrument or the distance between frets can determine whether it will ever play in tune over the entire range.

I am finding this thread highly educational and entertaining....

Great to have such different viewpoints...

Jim

 

[ondablade]

Hi Jim. I suppose that straight lines are very much a part of the Art Deco look, but that a Tudor look can get away with curvy roof lines and the like. (the gingerbread house look - hope i've reflected back what you had in mind) What makes Art Deco work is why mock Tudor can look so crappy.

I guess people have been trying since the ancients to quantify beauty - the ancient Greeks took it all very seriously. Stuff like harmonics, ratios and the like - the golden mean which is often written about

It works to a point - at least at the level of simpler shapes like rectangles which you can apply these proportions to. It's an interesting question as to whether or not the same applies to much more complicated stuff - if you could only figure out the maths.

Yet the ability to recognise and create beauty is intuitive too. The spiritual traditions suggest that it originates from higher knowing - that when too much thinking mind gets into the situation so that the resulting excessive focus on a small part of the total picture e.g. financial considerations blocks this ability you get ugly stuff.

The average cityscape or industrial estate tends to bear this out - not only are they ugly, they clearly are the result of a failure or unwillingness to seriously consider aesthetics, and the subtler aspects of function. It's clear too that this trend has strengthened greatly in modern times as we have become mentally much more intense - even cottages from years ago had a more integrated look.

There's the old saying that suggests that form and function converge as the design becomes more highly refined too - e.g. like in aircraft.

Guitars are an interesting case. Like most enthusiast pursuits (even those that claim uniqueness) there's such an emphasis on conformity. A Strat is a Strat is a Strat - they have hardly changed in 50 years.

It's hard not to wonder how much of this is fashion (people wanting the accessories just so to prove they have bought into and belong to a particular sub culture - an ego driven motivation); how much is function (it needs to be that shape to work properly); and how much is the result of a genuine appreciation of beauty.

Maybe they all coincide in a perfectly designed instrument for a realised person??? :wink:

ian

 

[chipchaser]

I would be grateful if somebody would clarify the accuracy aspect. I understand from the posts in this thread that some of you have machines that can thickness and saw to very fine dimensions. So all the bits that can go through the planers and saws could be accurate to a thou or two. What is the maximum size of component that can be cut to this accuracy? For example, if you had to make a joinery carcase say 2.1m high by 1.3m wide, to what accuracy could you cut the framing pieces with those dimensions?

What is the correct answer to “Does a Tudor building look right if it is NOT straight?”? Straightness wouldn’t be a valid parameter for me but now I am confused, should I like the twisted by age example or the one that time has been kind to standing straight and true?

What have you guys got against mock Tudor anyway? Google Moseley Old Hall to see how good it looks when done properly. A gingerbread house by the by would be more of a “cottage ornee”. Anything can look rubbish if done badly……. or charmingly naive.

Did the Greeks really take geometry of buildings and the golden section very seriously? There are apparently well informed folks out there who say not.

Graham