How flat should a 'cast and ground' aluminium router table be?

Woodworking
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I recently purchased a fairly cheap router table on-line from a reputable supplier, but on receipt of the router table, and before assembling it, I thought I would check the ‘flatness’ of the cast and machine ground alumimium table.
I did this with a metal straight=edge I know to be true, namely a timber framing square, and found that when measuring flatness across the long dimension of the table surface, the feed-in and feed-out direction, the table deformed by 2.0mm in the centre, gradually decreasing to zero deformation at approximately 70mm from each end. There was also a similar deformation, but less severe, being 1.5mm across the short width of the table…

I contacted the seller pointing this issue out, and was told that the table was within permitted tolerances, and they stated ‘We have been selling router tables for over 20 years and we have yet to find a sub £100 router table with tolerances below those you state’…

In another email they stated that the ‘tolerance’ (i.e. 1.5mm to 2.0mm) was within the specification for the machine… but this was not mentioned in the specs for the machne on their web site or specifically in the information shown for the machine on-line, at the point of purchase…

Does anyone have any experience of this or can give advice on tolerances of cast and ground aluminium machine tables… My thoughts are if it is cast and ground, I woulsd at least expect it to be ‘flat’ to within a far less tolerance than 1.5mm to 2.0mm across a length of only 450mm max? Any Comments???

2

A 2mm deflection sounds a lot and I would personally find that unacceptable as it means that it’s nigh on impossible to accurately machine a long bit of material. However, the manufacturers state it’s within the specs for the table.
The crunch point as I see it is that they don’t appear to highlight it anywhere in the information which was provided for the table, so I think you’ve got a good case for a refund as the table as purchased is not ‘fit for purpose’.

3

Yep, I have returned the Router table and got my purchase costs back, but not the £15.99 return costs, which according to their Ts & Cs, they will only refund if the item is ‘defective’…and they consider the 2.0mm bowl in the ground table to be acceptable… I have argued that, as you state, it would be impossible to get an accurate cut on work on the feed-in - feed-out direction with this amount of tolerance…which they effectively did not respond to, merely stating that a higher degree of accuracy was obtainable on more expensive router tables, where tolerances were less…!!

I was trying to find if there was British or EU/ISO Standard that covered the acceptable tolerances of cast and ground aluminium machine tables, and see if I could find out what standard the machine in question is supposed to comply with in respect of manufacture of the table…anyone got any ideas??

4

Glad to hear that you got a refund for the table but not the £15.99 it cost to send it back; sounds to me that the particular company you’ve been dealing with is one to stay well clear of in the future.

Can’t help with the standards issue, but I would have thought that someone on the Ax Product Development team is bound to have that sort of info at his or her fingertips, or at least knows where to point you in the right direction to find it.

5

Result…Following further email discussion with the company concerned (Rutlands), they have now agreed to refund my £15.99… as a ‘show of goodwill’… but still disagree that anything on the Router Table is out of spec, or not fit for purpose… last time I shall be using them… Lesson Learnt.

Still amuses me… why would anyone go to the trouble of casting an aluminium machine table (in this case a router table), and grind it, if as they have stated, the tolerance across the 450mm long table are +/- 2.0mm… and actually are 2.0mm out across the table… absolutely mistifying to me…!! MDF would give a flatter result…

6

Said Rutlands, 'nuff said. I and others won’t touch them with the proverbial barge pole. Over the years I’ve heard so many awful tales about their service etc I’ve never bothered to deal with them.
For what it’s worth and I know it’s an entirely different kettle of worms, but I use the Ax UJK ci table which is as flat as a proverbial billiard table.

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Thanks for that, I’ll look it up and start saving… :pound:

8

As an engineer I would be devastated if my ground plane was anymore than .2mm out let alone 2mm!

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Stu93, I’m with little-reg, and although I don’t have a mechanical engineering background, I totally agree:

There must surely be some standards to which we should expect tools and allied equipment to be made to, and a 2mm off on such a small table is inadequate to be fit for purpose.

Glad you named and shamed!

Barry

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Lets hope someone from Axminster is reading this and comes up with info on the relevant standards applicable and advice on what to expect from a cast and ground table, whether aluminium or steel etc… It would be interesting to find out and to add that bit of knowledge to the toolbox…

So come on Axminster lets have some in-put here…

11

Good afternoon,

We’ve done some investigating and there are no BS or ISO standards covering this topic. Cast iron does have a tendency to move after being machined unless the raw casting is matured before machining, either by natural processes involving leaving the casting in its raw state for 9-12 months, or by artificial maturing by a process of heating and cooling in a controlled manner.

The UJK cast iron router tables have a manufacturing tolerance of 0.5mm deflection between opposing diagonal corners.

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Thanks Hannah, strange (as a layman! non mechanical engineer!) but good to know UJK at least have ‘standards’. Not good to know anyone can make almost anything and say “that’s expectable”.
I can see why leaving castings 9-12 months is not liked as an option… and too much end user cost arising!!

Barry

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I use a ci UJK router table (one of the big boys) and I could detect no discernible deflection in the top when I tested it with a metre long LV straight edge, which is as straight as a straight thing. Good also to see that the Ax team are on the ball (or the flat, whichever you fancy) and have done a bit of background research.

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Hey, Hannah…

Thank you for taking the time and trouble to see if there are any standards applicable…actually I find, as an Engineer myself (but not a Mech Eng), thta its astounding there appears to be no applicable standards, knowing that usually there are standards (British, European and International) for just about every dimension of engineering production you care to mention, including safety conformity in operation and use…

I find it somewaht amusing to think, as I would suppose, that cast tables (of any metal or alloy) are presumably ground to a ‘flat’ surface on some form of milling machine, but there should be such wide tolerances in the ‘flatness’ produced… I would have presumed that a milling machine, if within its own specs would produce a ground surface to within at least a few thousands of an Inch / microns of a Millimeter…

I guess I must accept (begrudgingly) the arguement that cheap machines are not going to be as accurate as those that are considerably more expensive, but cannot get my head around why, cheap machine or not, would set out to end up with a standard for grinding a casting (as in a machine table) that is not ‘flat’, or as flat as the milling machine or whatever process is used, could make it…surely they would not go to the lengths of actually ‘building-in’ deformity… it just makes no sense to me…!

I think this question deserves a little further investigation and a search in respect of standards that might be applicable, such as for the machines used to mill or create ‘flat’ surfaces in such castings.

Lastly, yes i am aware of the ‘normalisation cycles’ for castings, but annealing, heating up and allowing the casting to cool, is usually associated with enabling the course grains of the metal/alloy to blend, and reduce brittleness of the metal/alloy (so it is not so easy to break). Generally, once a casting is cast and cooled (and perhaps annealed if required to reduce brittleness), it is not going to move, and the grinding process, as in obtaining a ‘flat’ surface would not normally affect the castings shape (unless it was ground so thin that it could either bend/deflect slightly under load, or the pressure of the grinding equipment whilst grinding the surface(s) was such that it caused deformation to occur during this process, which would appear to defeat the object of the exercise of grinding ‘flat’ in the first place…!

An interesting condundrum that awakened my will to live and try and find out the facts…:wink:

15

In some cases an upward bulge of a router table at the centre (where the router hangs underneath) is deliberately engineered in so that the table goes flat when it sags slightly under the weight of a large router. This wouldn’t be necessary with a cast iron table but other designs have less stiff materials as the basis of the table.

As I understand it, the Veritas router table is manufactured with a degree of upward bulge as it’s made of 1/4" sheet steel and so sags very slightly under the weight of a 1/2" router. The bulge is not as gross as 2mm however, just a fraction of a millimetre. Mine is flat with the router in and not quite without.

Which way did this aluminium table bulge? Or was it already sagging down? In all events, if it wasn’t flat by 2mm when the router was mounted it couldn’t possibly route anything accurately. There doesn’t really need to be a British Standard to tell anyone that!

Lataxe

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Hi, Lataxe… the router table had a 2mm downward ‘bowl’ in the centre of the table…which started from about 70mm from the edge of the table from all corners…

It was returned to the supplier and money spent on it, and cost of return eventually redeemed… supplier was Rutlands, as mentioned above…who stated it was ‘as per specification’…but never included the fact that the table had a 2mm deformation in their sales details…just that the table was ‘cast aluminium’…so you tend to expect that if a manufacturer has gone to the trouble of casting a table, they would grind it flat…and not grind a huge dish into it, so anything machined on the table is out of true… but hey, you live and learn…

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Mr 93,

Although we do “get what we pay for” there is law that states a thing sold must be fit for purpose. The table you describe isn’t. As to the claim by the seller that it was “within spec” this begs the question, which spec? It seems they have made one up that basically says: “any old rubbish will do”.

Is it illegal to sell such dross? Probably; but the cost and difficulty of bringing a case means a case won’t be brought.

Once we had civil servants who both set and tested for standards, including those pertaining to the fitness of sold goods. Naughty dross-sellers were had-up before a beak and discouraged. Alas, these fellows have been done away with as unnecessary bureaucrats spoiling the profit-gathering efforts of Exploiters-R-Us.

Lataxe

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Trawl back through this thread to see where the router table came from…

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If it’s the fifty quid item from Rutlands, it hardly seems surprising that it was poorly-made. It’s a lot of stuff for a mere £50 so perhaps most of the value is, appropriately, the scrap value of the metal?

There’s a section titled “Specification” which gives dimensions et al … but nothing about it’s degree of flatness. So what text are they using to say the 2mm sag is “within spec”? No router-table tester and spec-setter would write such a spec, anyway. Perhaps their retort to the OP’s complaint was merely a euphemism for “you get what you pay for”? (Scrap, in this case).

I wonder what they did with the returned one? :open_mouth:

Perhaps we should buy the Axminster ones and measure them? :slight_smile: Shirly they will be as flat as the water in a fish-free aquarium, situated in an earthquake-free zone with no children running up & down the stairs or a bloke digging up the road outside with a jackhammer. Of course they will!

Lataxe

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Interesting comments…but I think I covered the gist of this previously…my main point was why bother to cast and grind it in the first place, if the result is just about as good as a couple of planks glued together…or probably worse…lol…

Next time I go to Axminister I shall take my steel straight edge and micrometer, and some paper to put your theory to the test