Guides / Cost
Why Invar 36 Parts Are Costly and How Shops Price Them
September 20, 2026
An Invar 36 quote often surprises buyers who know what the same part costs in stainless. The gap is real, and most of it comes from five places: material, cutting time, heat treatment, inspection and paperwork. Once you see where the money goes, you can read the quote line by line and change the drawing where it helps.
Material
Invar 36 is about 36 percent nickel, and nickel is expensive. Bar and plate cost several times more per kilo than 304 or 316 stainless. Fewer mills produce it, so stock in odd sizes is thin and thick plate can take weeks.
Two details on the drawing move this line more than people expect:
- Stock size. If your part is 52 mm thick and the nearest plate is 60 mm, you pay for the 60 mm. A few millimeters of design freedom can drop to a standard size.
- Yield. A ring cut from solid plate throws most of the material into chips. A shop may suggest a tube or a ring blank for repeat orders.
Cutting time
Invar is gummy and work hardens, so shops run it at slower speeds than steel and change tools earlier. Chips are stringy and need clearing. A part that takes an hour in aluminum can take several in Invar. For small quantities, programming and setup still dominate the price, just as with any CNC part. For larger quantities, cycle time takes over.
Heat treatment
A precision Invar part is usually machined in stages: rough, stress relieve, finish. That means:
- A furnace run, either in house or at a heat treater
- Handling and packing the part in and out
- A second setup to finish, with fixturing that does not re-stress the part
If the drawing calls for a full stabilization cycle, add more furnace time and a longer lead time. This is the line buyers most often question, and it is the one that makes the part behave like Invar after it ships. The buyer’s guide to Invar machining explains why the sequence matters.
Tolerance and inspection
Tight features cost more in any material. With Invar there is an extra point: to trust a flatness or position number, the part has to be measured at 20 °C after it has soaked in the room. That means waiting time and CMM time on every critical part, not just a quick check at the machine.
Loosen what does not matter. A mirror mount needs the mounting face and bores tight. The outer profile can usually be ±0.1 mm.
Certs and records
A mill cert with chemistry comes with the material and costs nothing extra. These cost more:
- Measured CTE data for your specific heat lot
- Full dimensional reports on every part instead of first article only
- Heat treatment charts and traceability packs for aerospace or space programs
Ask for them when your program needs them. Say so on the RFQ, because a shop that learns about them after quoting will have to re-quote.
How the lines add up
Every shop builds its quote differently, but the logic is the same. Take a small batch of ten Invar 36 mirror mounts, milled from plate, with a flat mounting face and three tight bores. Roughly, the quote splits like this:
- Programming and setup for roughing and finishing, paid once
- Material, a plate cut to size plus the allowance for stress relief
- Roughing time on the machine
- Stress relief, one furnace load for all ten parts
- Finishing time, with a second fixture and light passes
- Inspection, first article plus the critical features on every part
- Certs and packing
On a stainless version of the same part, the stress relief line disappears, the material line shrinks and the machine time drops. That is where the gap comes from. It is also why asking two shops to quote without stating the heat treatment gives you two numbers that cannot be compared: one shop may have left it out.
Lead time and price
A short deadline costs more in any material. With Invar it can cost more than you expect, because the shop may need to buy material at a premium, push a furnace run into a busy week or run inspection overtime. If the deadline has room, say so. A shop that can batch your stress relief with other work can quote lower.
Repeat orders
The second order of the same part is almost always cheaper per piece. The program exists, the fixtures exist and the shop knows how the part moves after stress relief. If you expect to reorder, mention the likely yearly volume on the first RFQ. Some shops will hold material or quote a price for a blanket order.
How quantity changes the price
| Quantity | What dominates the price |
|---|---|
| 1 to 10 | Programming, setup, furnace run and first article inspection |
| 10 to 100 | Setup spreads out. Material and cycle time take a larger share |
| 100 and up | Material, cycle time and batch heat treatment. Fixtures pay back |
Heat treatment is often charged per furnace load, not per part. Ten parts in one load cost little more than one part, which is another reason small orders look expensive per piece.
Drawing changes that lower the quote
- Tolerance only the features that affect function
- Use standard hole sizes and inside radii the shop has tools for
- Avoid thin walls and deep narrow pockets that need special fixturing
- Design around standard bar and plate sizes
- Say “shop to recommend” on heat treatment when you are not sure, instead of specifying the longest cycle
- Give a realistic yearly volume so the shop can plan material
When a quote looks high
Before you push back on price, ask the shop three questions:
- Which line is largest? A shop that has done the work can tell you whether material, machine time or heat treatment drives the number.
- What would you change on the drawing? Shops that cut Invar often suggest a thicker wall, a standard radius or a looser tolerance on a feature that does not matter to function.
- Does the quote include stress relief and inspection at 20 °C? If one quote includes them and another does not, the lower quote is not cheaper. It is a different part.
Most of the time the answer points to one or two lines you can influence. A tolerance loosened from ±0.005 to ±0.02 mm on a non-critical bore, or a pocket made 1 mm shallower to fit a standard tool, can move a small batch quote noticeably.
Getting comparable quotes
Quotes are only comparable when every shop quotes the same thing. Put the alloy spec, heat treatment, critical tolerances, certs and quantity on the RFQ. When we match your request, each shop sees the same details, so the quotes you receive line up.
Frequently asked questions
Why does an Invar part cost more than the same part in stainless?
The bar costs several times more, it cuts more slowly and a precision Invar part usually needs a stress relief between roughing and finishing. Each of those adds cost that a stainless part does not carry.
Can I skip stress relief to save money?
On parts that are not thermally critical and have loose tolerances, sometimes. On optical, metrology or tooling parts it is the step that keeps the part stable, so skipping it usually costs more later.
How can I get a lower Invar machining quote?
Tolerance only the features that matter, design the part to be cut from standard bar or plate sizes, avoid thin walls that need special fixturing, ask for measured CTE data only when you need it and give a realistic yearly volume.
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