Machined or not Machined Holes 2

[eski1]

Hi
We are manufacturing a fabricated frame to a customers supplied drawing and they are now highlighting that the holes should be put in to machined tolerances rather fabrication tolerances as we had assumed and priced.

The holes themselves don't have specific machining symbols associated to them just standard dimensions like 810mm etc
then there is a Tolerancing table in the drawing border which stipulates both Machining & Fabrication tolerances for the drawing i.e
Dimensions upto 1000mm
Machined = +- 0.5mm
Fabricated = +-2mm

There are also other parts of the drawing that have machining symbols like surfaces etc , but there are no symbols on the holes.
My question is are we right to have assumed that the holes were just fabricated tolerances , i.e we could have either got them Laser cut in or hand drill them as part of the fabrication process. Or is the customer right that they should be machined ?

I suppose the other question is what is classed as Machined ? , is drilling of any type classed as this.
I'm wondering if any of this is covered in BS EN ISO 2553 ???

Jeff

 

[eski1]

Apologies i meant BS8888

 

[TheTick]

The right thing to do wuld have been to specify processes and tolerances on the quote.

Sounds like you need to have a potentially difficult conversation with the client.

 

[CheckerHater]

eski1,

In BS8888 Fundamental TPS principles (TPS = technical product specification):

A TPS is not complete if there is more than one possible interpretation of
the specification.

Also, in in underlying ISO 8015 standard:

The drawing is definitive. All specifications shall be indicated on the drawing using GPS symbology (with or
without specification modifiers), associated default rules or special rules and references to related
documentation, e.g. regional, national or company standards. Consequently, requirements not specified on
the drawing cannot be enforced.

So, they cannot demand what's not specified on the drawing.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[eski1]

Hi
Many thanks for the replies.

CheckerHater
I tend to agree it wasn't clearly specified so what they are now asking for is unreasonable, I'm not familiar with ISO 8015 to be honest can you clarify what this Standard is called ?

Jeff

 

[drawoh]

eski1,

It is bad practice to specify fabrication processes like drilling on a fabrication drawing. They should call up a tolerance, and you the fabricator, should figure out how to do it.

If they called up the accurate tolerance on the drawings you quoted on, you should have costed for them on your quote. The customer has no business caring how you do it, short of virgin sacrifice. If you quoted on sloppy tolerances and your customer just tightened them up, then they need to let you re-quote.

--
JHG

 

[3DDave]

"we had assumed and priced."

Did that assumption make its way into the quote?

Tolerances should be explicitly assigned to features or their controlling dimensions. The designer had to look it up - they should not force everyone else to repeat that effort and potentially guess what they meant.

 

[eski1]

Thanks for the replies all.

I suppose the root cause of this issue is what's the correct answer to this question :-

Q. If a fabrication drawing on a structure with PFC ,plates etc has dimensioned holes on it i.e 4 x 18Dia holes , and then a tolerancing table like the attached then would you say these holes are to the Fabricated tolerances or the Machined Tolerances and reason for your answer?
Bearing in mind there are machining symbols where plates need to be machined flat on other parts of the drawings......

 

[chez311]

eski1,

I would say unless explicitly stated on the drawing whether or not the particular feature of interest was to be "machined" or "fabricated" the tolerance table has left it entirely up to the manufacturer to dictate what tolerance applies depending on the process they choose. I'm sure one could also have some sort of discourse on what exactly constitutes "fabricated". I would NEVER utilize such a table on a drawing and if at all possible would not make any references to manufacturing process requirements, as drawoh and others stated thats bad practice - the way a part is processed does not change the variation I would allow on a particular part, however of course the converse is often true (part tolerances will likely dictate process).

That said, I doubt the above will win you any favors with your customer. The first step would be to have them re-submit a drawing with the correct tolerances explicitly applied to the features and removing any reference to manufacturing process. If they are requiring that the tighter tolerance be applied to the hole, you have only two choices - (1) re-submit a quote reflecting the explicitly applied tighter tolerances, presumably at a higher piece cost, with the potential to lose the bid or (2) eat all or part of the increased cost. Either way, someone ends up unhappy. Take this as a lesson to never assume anything on ambiguous drawings, if theres any portion of a drawing that is unclear it will benefit everyone in the long run to make a call and ask the customer - better to bug them than end up with having to make the choice you're currently stuck with.

 

[looslib]

How are they differentiating 'Fabricated' versus 'Machined' features?
All features are fabricated, just that some may require tighter tolerances and thus have been marked with either a surface finish symbol or a machining symbol. If a feature, hole, outer shape edge, etc., is not marked, it is left o the fabricator to determine the most cost effective method for manufacturing the part. This should be conveyed in the quotation. If the customer then comes back and adds machined surface requirements to the design that had been assumed to be fabricated, that would require a re-quote.
Specifying a manufacturing process on the engineering drawing is not allowed. The design requirements need to be conveyed through the use of dimensions, tolerances and GD&T callouts. Also holes have generally not been toleranced and left to be controlled by the tolerance specification of the drill itself, which is usually tighter than most holes would be dimensioned to anyway.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[MintJulep]

My question is are we right to have assumed that the holes were just fabricated tolerances , i.e we could have either got them Laser cut in or hand drill them as part of the fabrication process. Or is the customer right that they should be machined ?

Neither. You are both wrong.

You are wrong for quoting work that you did not understand.

Your customer is wrong for sending our an ambiguous drawing.

How much extra will it cost you to give the customer what they want? Hundreds, thousands, millions?

Get some adults together and make a deal. Getting defensive and argumentative will take longer, cost more and create bad will.

 

[Burunduk]

How are they differentiating 'Fabricated' versus 'Machined' features?

They fabricated a differentiation.

 

[TheTick]

Get some adults together and make a deal.

 

[jassco]

Hi, eski1:

Generally, you don't do critic to customer prints.

You are supposed to provide quotes per the prints.

If some dimensions and/or features on the prints are not clear, you need to make assumptions and note them in the quote accordingly.

Best regards,

Alex

 

[eski1]

Thanks again for the replies all

What i would say is from our position the drawings were clear to us that they were Fabrication drawings and the holes were to be to the Fabrication tolerances and only where they had stipulated machining symbols were we too machine these as this is just what the norm is.
So from that stand point is wasn't a question or Technical query (TQ) we needed to raise at any point , I suppose you could say we presumed something but when something looks clear cut then I'm not so sure it is a presumption TBH but it is a fine line.

We are trying to work this through with our customer as Adults , which is good and hopefully will have a favourable outcome in the end.

Jeff

 

[TheTick]

Generally, you don't do critic to customer prints.
You are supposed to provide quotes per the prints.

This is how the worst vendors operate. I avoid them.

If a vendor does anything that shows they have carefully considered the print, it's a good sign that you have a competent vendor and a good vendor/client relationship.

It's a partnership. Client has needs. Vendor has capabilities. They need to line up. Sometimes it takes a bit of work.

 

[TheTick]

Generally, you don't do critic to customer prints.
You are supposed to provide quotes per the prints.

True story from my very last week as a machinist...

Working night shift, manually milling and drilling parts to order for a plastics supplier. Other machinist comes to me and says, "Tick, you're almost an engineer. What do you make of these prints?"

I looked at the prints and saw dimensions for mating pieces were off, and there was no way parts could fit together. Together we call Bob the GM at 2:30AM to inform him of the problem. His response: "#@^*%^@*!! your job is to make parts to print! Now go do it!"

We had no choice. So we went back, tweaked the CNC router until parts were running almost perfectly. Parts pass 100% inspection. Customer receives parts. REJECTED! because nothing fit.

Two days later, there is an emergency all-hands meeting at the end of my shift. Bob the GM is frothing. He holds up our parts and yells "This is the kind of $#!+ that's going to kill this company! None of these parts fit together!"

I resigned that morning.