Guides / Shop Practice
How Shops Decide Whether to Take the Next Large Job
October 5, 2026
A small machining centre can absorb a scheduling mistake. Move a job back a day, split a batch, run overtime. A large boring mill or gantry mill does not forgive the same mistake, because one part can occupy it for days or weeks and there is often no second machine to shift the work to.
That changes what scheduling means for a heavy shop. It is not a calendar exercise, it is a decision about which jobs the business can actually afford to take on right now.
Why heavy scheduling is different
Few machines, long jobs. A shop might have one or two machines that can handle a part in this size class. A four week job on one of them is not a line item, it is most of the shop’s capacity for a month.
A large job blocks smaller ones. Once a heavy part is fixtured, it usually stays fixtured until it is done. Small jobs that would normally slot in around it have nowhere to go until the big part clears the table.
Setup time does not shrink with the schedule. Rigging, craning and indicating a large weldment takes what it takes. A tight promise date does not change how long it takes to true up a four metre part.
Outside steps sit outside your control. Stress relief, plating, NDT and other subcontracted steps move a part off site for days at a time, on someone else’s schedule, not yours.
Demand for this class of work is lumpy. Three heavy RFQs can land in a week, then nothing for a month. A shop that schedules for the average week gets the busy weeks wrong.
Deciding on a new large part RFQ
Before a quote goes out, the honest question is not just “can we machine this” but “where does it actually sit in the schedule”.
- Check what the constraint machine looks like four, eight and twelve weeks out. Not the shop as a whole, the specific machine this part needs.
- Confirm the blank lead time against the machine’s open window. A part that needs a slow casting can be quoted against a slot that opens later, which sometimes solves a scheduling conflict on its own.
- Weigh the job against what is already booked. A smaller, faster, higher margin job already on the schedule is sometimes worth protecting over a larger one that would displace it.
- Decide early whether the promised date is real. If it depends on another job finishing early or a subcontractor turning something around faster than usual, say so in the quote rather than finding out in week five.
- Be honest about crew and crane time, not just spindle time. A job that fits the machine’s calendar can still be blocked by needing the same crane or the same setup person as another job.
A quote that skips this step is a promise made on hope. See how to build a large part quote for what else belongs in it.
The cost of idle versus the cost of overbooking
| Idle machine | Overbooked machine | |
|---|---|---|
| Visible cost | Empty spindle hours, easy to see | None, until the date slips |
| Hidden cost | Lost margin on unbooked capacity | A missed delivery date on a live job |
| Who feels it first | The shop’s own numbers | The buyer waiting on the part |
| How it is fixed | Better pipeline and mix, see below | Rarely fixable once it has happened |
An idle machine is a bad month. An overbooked machine that slips a date is a bad reference, and on large part work a missed date on a buyer’s first job with a shop tends to end the relationship before it starts. When the choice is close, protecting the date usually beats protecting the utilisation number.
Keeping the schedule honest
Track the constraint machine’s calendar in weeks, not days. Heavy jobs move in week-sized blocks. A day-by-day schedule creates false confidence on work that does not actually move that finely.
Build in the known outside time. If stress relief reliably takes a week, put a week in the plan before quoting a date, not after the part is already late.
Revisit the schedule when a quote turns into a PO. The slot you assumed when you quoted may no longer be open by the time the buyer decides. Confirm it before committing to the date in writing.
Decline or reschedule early when the fit is wrong. A buyer who hears “we can take this in five weeks, not two” in the first conversation stays a buyer. A buyer who hears it in week four does not.
Filling the machine when it is genuinely short of work is a separate problem with its own answer, covered in keeping a boring mill loaded and earning. This is the other half: knowing when to say no, or say later, before the schedule says it for you.
What to do next
Look at the constraint machine’s bookings for the next eight weeks and mark which slots are firm versus assumed. Any RFQ that would land on an assumed slot needs a second look before it gets a quoted date.
Related reading: how to build a large part quote, lead time on large machined parts and table load and crane capacity.
Frequently asked questions
Should I ever turn down a large part job because of scheduling?
Yes, and doing it early is better than doing it late. Declining or rescheduling a job in the first week costs a conversation. Slipping a promised date in week six costs the relationship.
How far ahead should a heavy machine be booked?
Far enough that a new large part RFQ has a known slot rather than a guess. Many heavy shops plan four to eight weeks out on their constraint machine, with shorter jobs used to fill the gaps around it.
Is it better to run two heavy machines at partial load or one at full load?
There is no single right answer, it depends on setup time and part mix. What matters is knowing which machine is the actual constraint, because that is the one whose schedule decides everything else.
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