Large Part Machining for Parts That Do Not Fit a Standard Mill
Send the drawing with the envelope and the finished weight. We match it with shops whose table, spindle and crane can take the part. Reply within 24 business hours.
Why buyers send large part work here
It comes down to the match: shops that fit your part, from the first quote.
Matched by specialisation
Your RFQ goes to up to 3 shops that machine large parts regularly, picked for your part size, weight and material. Not a general directory.
Professional suppliers
Shops in the network quote to your drawing, communicate clearly and keep you updated while your parts are made.
You deal with the shop
Quotes, terms and delivery are agreed between you and the shop. Free for buyers.
Is your part a large part job?
Size alone does not decide it. Weight, the number of faces that have to line up and what the blank is made from matter just as much. Tick what applies. Two or more ticks usually means a standard machining centre is the wrong shop to ask.
Parts that come through this route
- Machine bases and bed castings
- Welded frames and gantries
- Gearbox and mill housings
- Large flanges and tube sheets
- Press platens and bolsters
- Ring gears and bearing housings
- Crane and winch drums
- Hydraulic cylinder bodies
What these have in common is not shape. It is that the part has to be craned onto the table, indicated in once, and then machined in as few setups as possible, because every extra setup adds handling time and another chance to lose position.
Horizontal boring mill or gantry mill?
Most large parts go to one of these two, and the choice usually follows from the shape rather than from the size. Knowing which one your part wants tells you which shops are worth asking.
Horizontal boring mill
The spindle works horizontally and the part sits on a rotary table that indexes it to the next face.
- Right for housings and cases with bores on several faces
- The rotary table holds position between faces without re-indicating
- Long spindle reach for deep bores, at the cost of some rigidity
Gantry or bridge mill
The spindle hangs from a bridge that travels over a fixed table, so the part never moves once it is clamped.
- Right for plates, platens, mould blocks and welded frames
- Large flat areas machined in one pass pattern, so flatness is easier to hold
- Weak on deep horizontal bores unless the head is a right angle type
Round parts follow a third route. Rings, flanges and drums over roughly 800 mm go on a vertical turning lathe, where the part turns on a horizontal table and the tool comes down onto it.
Machine classes used for large parts
Envelopes below are typical of each class, not a capacity we hold. They are here so you can tell us the right thing in the RFQ. The shop that quotes you confirms what its own machine takes.
| Machine class | Typical envelope | What it is used for |
|---|---|---|
| Travelling column mill | 3 000 to 8 000 mm X, 1 000 to 1 500 mm Y | Long frames, beams and weldments machined along their length. |
| Horizontal boring mill | 2 000 to 5 000 mm X, spindle 110 to 160 mm | Bores on several faces of one housing, held in position by the rotary table. |
| Gantry or bridge mill | 3 000 to 12 000 mm X, 2 000 to 4 000 mm Y | Plates, platens, large mould blocks and anything wide and flat. |
| Vertical turning lathe | 1 000 to 5 000 mm swing | Rings, flanges, drums and housings turned and bored on the same table. |
| Heavy horizontal lathe | 600 to 1 600 mm swing, 3 000 to 12 000 mm between centres | Shafts, rolls and cylinder bodies that are long rather than wide. |
| Floor plate and portable machining | Set by the plate, not by a table | Parts too heavy for any table, or work done on an assembled structure. |
Materials and tolerances on large parts
On a small part the material decides cutting speed. On a large one it also decides how much the part moves while you cut it. These are typical ranges, not promises.
| Material | What changes on a large part | Typical tolerance |
|---|---|---|
| S355 / A36 structural steel | Most weldments and frames. Cheap and easy to cut, but it moves after welding unless it is stress relieved. | ±0.1 to ±0.3 mm over a metre |
| 42CrMo4 / 4140 alloy steel | Shafts, pins and gear blanks. Often quenched and tempered before machining, which slows the cut. | ±0.05 mm on bearing seats |
| Cast iron GG25 / GGG40 | Machine bases and housings. Damps vibration well. Needs a sound casting and a known ageing history. | ±0.05 mm on bores |
| Stainless 304 / 316 | Marine, food and chemical equipment. Slower cutting and heavy tool wear on thick sections. | ±0.05 to ±0.1 mm |
| Aluminium 5083 / 6082 plate | Large light structures and chambers. Releases rolling stress as material comes off, so it needs re-clamping. | ±0.1 mm, more on thin walls |
| Bronze lined bearing parts | Shells and bushings. Usually bored in place after the housing is finished so the bore matches the seat. | ±0.02 to ±0.05 mm on the bore |
Tolerance on a large part is two separate questions. One is what the machine can hold on a single feature, which is rarely the problem. The other is what survives across two metres of steel once the part has been craned, re-clamped and allowed to reach room temperature. Say which of the two you need and the quotes get much closer to each other.
Industries that send large part RFQs
Different industries bring different paperwork. Mention material certificates, welding procedure qualification, first article inspection or painting specs in your RFQ so we match shops that already work that way. Each sector has its own page with the parts, the machines and the records it expects.
Machine tool builders
Bases, columns and cross rails where flatness and squareness carry the whole machine.
Mining and quarry
Crusher frames, mill housings, drums and large gear cases.
Power generation
Turbine casings, bearing housings, frames and flanged joints.
Marine and offshore
Stern tubes, rudder parts, winch drums and welded deck structures.
Steel and metal processing
Roll housings, chocks, press platens and furnace equipment.
Material handling
Crane girders, sheave blocks, slew rings and conveyor drive frames.
How it works
One RFQ from you. A short list of shops that can physically take the part. No bidding platform and no middleman on the order. The full method, including what a shop sees of your drawing.
Send your RFQ
Upload a model or drawing and tell us the envelope, the finished weight, the material and when you need it. Takes about five minutes.
We match up to 3 shops
We check the part against table size, travel, spindle, crane capacity and the process steps it needs. You hear from us within 24 business hours.
Shops quote you directly
Each shop contacts you with a quote. You compare, ask questions and place the order with the one you choose. Nothing passes through us.
What drives the price of a large part
Six things decide most heavy quotes, and they are not the same six that decide a small milled part. If a price looks high, one of these is usually the reason.
- Machine hoursOn a large part the machine is occupied for days, not minutes. Table time is usually the biggest single line on the quote.
- Handling and craneEvery turn over needs a crane, slings and often a second operator. Shops price handling separately, and a part that needs four setups costs more than one that needs two.
- Stock removalMaterial cost matters less than how much of it has to come off. A heavy weldment roughed down to size burns hours before any finishing starts.
- Stress relief and sequenceRough machine, stress relieve, then finish. Skipping the middle step is cheaper until the part moves and the bores go out of position.
- Tolerance across the partA bore tolerance is easy. Holding two bores in position 4 metres apart is not. Say which one you actually need.
- Transport and packingOversized freight, crating and lifting points can change the landed price more than the machining. Give the delivery address early.
Have a drawing ready?
Send the short version now. We will ask for anything missing. If you would rather give full details up front, use the full RFQ form.
Your files go only to the shops we match. Ask for an NDA and nothing is shared until it is signed.
Machine large parts? Get RFQs that fit your table.
Shops see a preview of each request before paying for it, then talk to the buyer directly. We take no commission on the order.
Questions buyers ask
Something else? Email .
Do you machine the parts yourselves?
No. We are a matching service, not a machine shop. The shops that quote you own the boring mills, gantry mills and vertical lathes, and you place the order with them.
Is this free for buyers?
Yes. Sending an RFQ and receiving quotes costs you nothing. Shops pay us for matched requests. Price, terms and delivery are agreed between you and the shop.
How big a part can be quoted through you?
It depends on the shop, not on us. Tell us the envelope and the finished weight and we match against shops whose table, travel and crane can actually take it. Parts past any table are quoted as on-site or floor-plate work.
Who sees my drawing?
Shops first see a short preview with part type, material, size, weight, quantity and tolerance. It does not include your name, company or files. Your contact details and files go only to the shops we match, up to 3. If you ask for an NDA, we hold the files until it is signed.
What do you need in the RFQ for a large part?
Overall envelope, finished weight, material and condition of the blank, the tolerance that actually matters and whether the blank is a weldment, a casting or solid stock. A 3D model plus a PDF drawing with datums gets the most accurate quotes.
Where are the shops located?
That depends on the part and on the region you pick on the RFQ form. You can ask for shops in North America, Europe, Japan, Korea or the rest of Asia, or leave it open and let us match on capability alone. On heavy parts, freight often decides the answer.
Guides for large part buyers
- Process
How Laser Tracker Inspection Works on Parts Too Big for a CMM
A laser tracker measures parts that no CMM can hold. What it can and cannot prove, what affects its uncertainty and how to write the inspection into an RFQ.
- Process
Large Ring Gears and Gear Blanks From Turning to Hobbing
A large ring gear starts as a forged ring and passes through turning, heat treatment and tooth cutting. Where each step sets accuracy and what to specify.
- Process
Machining Large Pump Casings and Valve Bodies
Pump casings and valve bodies are pressure castings machined for flanges, seats and bores. Porosity, finish, pressure testing and what to put in the RFQ.