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The Weight Limits That Disqualify a Shop Before Tolerance Does

September 10, 2026

Buyers check tolerance first and weight last. Shops check weight first, because a part that cannot be lifted, supported and moved is not a machining problem at all.

If your part is heavy, four numbers decide the shortlist before anyone looks at the drawing.

1. Table load rating

The maximum mass the machine table is rated to carry. It exists because the guideways and the drive underneath deflect, and the machine’s calibrated geometry assumes they are not deflecting much.

Two things follow from this.

The rating is not a target. A shop can put a part at 95 percent of the rating on the table and machine it. Positioning accuracy and flatness across a long face will not be what the machine’s specification says. Shops that do precise work keep well below the rating for tight tolerance jobs and use the top of the range for roughing and loose work.

Ask two numbers, not one. The rated maximum, and what the shop actually loads for the tolerance you need. A straight answer to the second question tells you a lot about the shop.

2. Crane capacity over that machine

This catches more shops than the table does, and it is the question buyers forget.

The part has to be lifted onto the table, turned over between setups, and lifted off. Every one of those needs a crane that reaches that specific machine. A workshop with a 30 tonne crane at one end and 8 tonnes over the boring mill has 8 tonnes of real capacity for boring mill work.

Ask about the crane in the bay, by capacity and by hook height. Hook height matters because a tall part on a sling needs headroom that a short one does not.

3. Floor loading

The workshop floor has a limit in tonnes per square metre. It rarely binds on a table machine, because the machine spreads the load over its own foundation.

It binds on floor plate work, where the part sits directly on the shop floor and a floor type boring mill drives up to it. It also binds when a heavy part has to be set down next to the machine while a fixture is changed. Ask about it only when the part is genuinely large, but do ask, because it is the reason some shops decline work they otherwise have the machine for.

4. The route out of the building

Door height and width, and whether a truck or a low loader can get to that door.

This sounds like a joke until a finished part cannot leave, which does happen. Any part that needs oversized transport should have its route out confirmed before the order, along with the lifting arrangement at the far end. See shipping oversized machined parts.

Why weight and tolerance interact

There is a second reason table load matters, beyond whether the part physically fits.

A heavy part on a table loads the machine’s structure asymmetrically as the table travels. The deflection changes with position. On a short part that variation is inside the noise. On a four metre part machined at the extremes of travel, it is a real contribution to the geometry.

This is one of the reasons positional tolerance across a long part is harder than the same tolerance on a short one, as covered in tolerance across a large part. Weight is part of the accuracy question, not only the logistics question.

The one email that settles it

Send this to every shop on the list before anyone starts quoting.

Part is approximately 2 400 x 1 100 x 900 mm and about 3.2 t finished, roughly 4 t as a blank. Can you confirm:

Table dimensions and X, Y, Z travel on the machine you would run this on

Table load rating, and what you would load for a 0.05 mm positional requirement

Crane capacity and hook height over that machine

Door dimensions and whether a low loader can reach them

Happy to send the model and drawing once you confirm the part is in range.

Four answers, one email, and the shortlist sorts itself out in a day. Shops appreciate it too, because it saves them quoting work they cannot take.

What to do next

Get the weight before you get the quotes. If you do not have it, calculate it from the model volume and the material density and say it is an estimate. A stated estimate is useful. A missing weight means every shop either asks or guesses, and guessing makes quotes expensive.

Frequently asked questions

Why does loading a table near its rating hurt accuracy?

Because the guideways under the table deflect under load. The machine still runs, but the geometry it was calibrated with no longer holds, so positioning and flatness across a long face drift. Careful shops keep tight tolerance work well under the rating.

Does the crane really matter if the table can take the part?

Yes. The part has to get onto the table and off it again, and be turned over between setups. A shop's real capacity is the smaller of its table rating and the crane over that machine.

What is floor loading and when does it matter?

The weight per square metre the workshop floor can carry. It becomes the limit on floor plate work and on very concentrated loads, and it is the reason some shops can machine a part they cannot set down next to the machine.

Need a quote for a part like this?

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