Tolerances in woodworking.

[Steve (Correze)]

(Character limit in the title, should really be
"Accuracy, Precision and Tolerances in (industrial) woodworking."

Was reading through some documents at work the other day that I thought may be of interest here.

For those who don't already know, I work for a fairly large furniture manufacturer in the upper end of the market, we make hotel bedrooms, offices, bars and similar, either assembled or in flat-pack, depending on price and shipping.

We work mostly in MDF and chipboard, either melamine or laminate finished.


Anyway... the other day I was looking at the guideline tolerances we use when designing pieces and deciding on machining processes, these are figures obtained through real shop-floor experience rather than the manufacturer's specifications and I think they may surprise some people...

Any machine/process can be accurate, assuming a skilled operator, but precision depends as much on the design and operating principles of the machine as the operator.

In no particular order.

CNC panel (beam) saw: 0.4mm (+/-0.2mm)
CNC router: 0.2mm (+/-0.1mm)
Wall saw: 1mm (+/-0.5mm)
Table (panel) saw: 0.5mm (+/-0.25mm)
Spindle moulder*: 0.5mm (+/-0.25mm)
Shaper*: 0.4mm (+/-0.2mm)
Edgebander* 0.4mm (+/-0.2mm)
"Festool" rail-guided saw: 1mm (+/-0.5mm)
SCMS: 1mm (+/-0.5mm)

The Festo (or similar) and SCMS are considered only suitable for one-off pieces or for use on site, the wall saw is only used for rough sizing of panels for small orders, though it's just as quick to load the beam saw and programme it.

*These machines are dependant on the precision of the stock arriving from the previous operation.

Most of the machines are actually or theoretically capable of producing work to far higher tolerances, but these figures assume average set-up and operation.

So, for example, pieces that have to fit together "perfectly" (no visible gaps/joints) are only rough-sized on the beam saw before being cut to their final dimensions by the CNC routers, it takes longer, but the result is noticeable. In another example, our beam saws are always set to cut 0.2mm undersize for production runs, as a piece with undersized components will assemble more successfully than one with oversized parts. A really skilled operator or designer/programmer will work out which pieces should err toward undersized and which would be better oversized and adjust the dimensions accordingly.


I don't have any figures for hand tools, though I suspect that so much depends on the operator...

 

[woodbloke]

I don't have any figures for hand tools, though I suspect that so much depends on the operator...

Interesting. This one had a good airing some time ago... workmanship of risk vs workmanship of certainty perhaps? - Rob

 

[Aryanmasoud]

(Character limit in the title, should really be
"Accuracy, Precision and Tolerances in (industrial) woodworking."

Was reading through some documents at work the other day that I thought may be of interest here.

For those who don't already know, I work for a fairly large furniture manufacturer in the upper end of the market, we make hotel bedrooms, offices, bars and similar, either assembled or in flat-pack, depending on price and shipping.

We work mostly in MDF and chipboard, either melamine or laminate finished.


Anyway... the other day I was looking at the guideline tolerances we use when designing pieces and deciding on machining processes, these are figures obtained through real shop-floor experience rather than the manufacturer's specifications and I think they may surprise some people...

Any machine/process can be accurate, assuming a skilled operator, but precision depends as much on the design and operating principles of the machine as the operator.

In no particular order.

CNC panel (beam) saw: 0.4mm (+/-0.2mm)
CNC router: 0.2mm (+/-0.1mm)
Wall saw: 1mm (+/-0.5mm)
Table (panel) saw: 0.5mm (+/-0.25mm)
Spindle moulder*: 0.5mm (+/-0.25mm)
Shaper*: 0.4mm (+/-0.2mm)
Edgebander* 0.4mm (+/-0.2mm)
"Festool" rail-guided saw: 1mm (+/-0.5mm)
SCMS: 1mm (+/-0.5mm)

The Festo (or similar) and SCMS are considered only suitable for one-off pieces or for use on site, the wall saw is only used for rough sizing of panels for small orders, though it's just as quick to load the beam saw and programme it.

*These machines are dependant on the precision of the stock arriving from the previous operation.

Most of the machines are actually or theoretically capable of producing work to far higher tolerances, but these figures assume average set-up and operation.

So, for example, pieces that have to fit together "perfectly" (no visible gaps/joints) are only rough-sized on the beam saw before being cut to their final dimensions by the CNC routers, it takes longer, but the result is noticeable. In another example, our beam saws are always set to cut 0.2mm undersize for production runs, as a piece with undersized components will assemble more successfully than one with oversized parts. A really skilled operator or designer/programmer will work out which pieces should err toward undersized and which would be better oversized and adjust the dimensions accordingly.


I don't have any figures for hand tools, though I suspect that so much depends on the operator...

Hi,
Do you know if there are specific standards for determining general tolerances in the carpentry process during the design and engineering of furniture structures?
Thank you

 

[Spectric]

The tolerance you work to will be dependant on what you are making and how it is fixed together. Using man made boards that are essentially butted together will need tighter tolerances than say the panel in a frame and panel assembly. It is also determined by the material, again man made boards are a lot more stable than a length of redwood and there is no point in trying to work to the nearest mm if the wood movement is far greater.

 

[Jacob]

Hi,
Do you know if there are specific standards for determining general tolerances in the carpentry process during the design and engineering of furniture structures?
Thank you

Some things have to fit nicely for structural reasons, like mortices and tenons, but many things simple have to look as though they fit nicely and may be faked by undercutting, or planing down to match etc.