Guides / Choosing a Supplier

How to Check That a Shop Can Actually Take Your Large Part

September 18, 2026

Vetting a heavy machining shop is different from vetting a general machine shop. Most of the risk is physical rather than commercial: the part has to fit, be liftable, be supported, be reachable and be measurable. Work through those in order, because the first four can disqualify a shop before price is ever discussed.

Start with the four physical limits

Ask these before anything else, and ask for numbers rather than adjectives.

Table dimensions and travel. Not the machine’s nominal size, the actual X, Y and Z travel and the table surface dimensions. Then check your part against them with the fixture allowance added.

Table load rating. The maximum the table is rated to carry. A shop that works near the rating on tight tolerance parts is taking a risk with your flatness, so ask what they actually load for precision work.

Crane capacity in that bay. This catches more shops than the table does. A 20 tonne table under a 5 tonne crane gives you 5 tonnes. Ask about the crane over the specific machine, not the heaviest crane in the building.

The route out of the building. Door height and width, and whether the part can be loaded onto the transport that will collect it. It sounds trivial until a finished part cannot leave.

There is more detail on the load side in table load and crane capacity.

Then the spindle and the head

Table size tells you whether the part fits. The spindle tells you whether the features can be cut.

Spindle taper and power, which sets how hard the machine can rough
Quill or W-axis extension, which sets how deep a bore can be reached
Whether a right angle head or a facing head is available, and what it costs in rigidity
Maximum bore diameter the shop can produce, and by what method

A shop with a big table and a light spindle can hold your part and still take three times as long to rough it.

What is in house and what is not

Large parts rarely need machining alone. Ask which of these happen under the shop’s own roof and which go out:

Welding, and whether procedures are qualified for your material and thickness
Stress relief, and the internal dimensions of the oven, which is often the real constraint
Heat treatment, grinding, honing
Painting, preservation and marking
Balancing, for rotating parts

Every step that leaves the building adds transport, a queue and another handling cycle. That is not automatically bad, but it belongs in the lead time conversation, and you should know it before you compare quotes.

How they prove the part

On a small part the answer is a CMM. On a four metre part it is not.

Ask how the shop measures the features you care about. Good answers include in-process probing on the machine, a laser tracker or portable arm for overall geometry, and a documented plan that says which features are measured how. A shop that only talks about hand tools on a part with a 0.05 mm requirement across two metres has not thought it through.

Also ask what the first article report will look like and who writes it. See inspecting large machined parts.

Questions that reveal experience rather than equipment

Equipment lists are easy to copy. Sequencing is not. Ask the shop how it would run your part and listen for these things:

Does it ask about the blank and the machining allowance without being prompted?
Does it propose a rough, stress relieve, finish sequence where the part needs one?
Does it say how many setups it expects and where the datums will be?
Does it ask what the part mates to, rather than just reading the tolerances off the drawing?
Does it tell you plainly when a tolerance is unnecessary?

A shop that answers those well is a shop that has lost money on a large part before and learned from it.

Paperwork to agree before the first order

Settle these in writing so they are not a surprise at delivery:

Material certificates, and to which standard
Welding procedure qualification, if the blank is welded
First article inspection, and whether it gates the rest of the batch
Preservation and how the machined surfaces are protected in transit
Lifting points, crating and the weight declared on the paperwork
Who owns the fixture that gets built, and whether it stays for the repeat order

Red flags

A quote that arrives fast with no questions about the blank or the sequence
A capability page with no machine models or table dimensions on it
No answer on crane capacity
A tolerance on your drawing that the shop never mentions, tight or loose
Willingness to skip stress relief on a heavy weldment without discussing the risk

What to do next

Build the shortlist on the physical limits first, then rank it on the sequencing conversation. Price comes last, because on heavy work a cheap quote usually means a shorter sequence, and that is a decision you should make rather than inherit.

Frequently asked questions

Is a bigger shop always the safer choice?

No. A shop with one well matched machine and people who run that size of part every week often beats a larger shop where your job is the odd one out. What matters is whether your part is normal work for them.

Should I visit the shop before the first order?

On a first heavy job it is worth it if you can. If you cannot, ask for photos of the machine with a part of similar size on the table, and for the machine's make, model and table dimensions so you can check the specification yourself.

How do I check a shop without giving away the design?

Send a description and the envelope, weight, material and tolerance rather than the model. That is enough for a capability conversation. Release the files after an NDA if the design is sensitive.

Need a quote for a part like this?

Send the drawing with the envelope and finished weight. We match you with up to 3 shops that take parts this size and reply within 24 business hours.

Get matched with a large part shop