Guides / Choosing a Supplier
What to Include on an Invar RFQ: A Drawing Checklist
September 20, 2026
Two shops quoting the same Invar drawing can return very different numbers, not because one is trying to overcharge, but because they made different assumptions about details the drawing did not specify. A complete RFQ removes that guesswork and gets you quotes you can actually compare.
Alloy and specification
State the specific alloy, Invar 36, Super Invar or Kovar, and the governing specification if you know it, such as ASTM F1684 for Invar 36 or ASTM F15 for Kovar. If you are choosing between alloys and are not sure which fits, mentioning your application’s temperature range and precision requirement lets the shop weigh in, similar to the tradeoffs covered in Invar 36 vs Kovar vs Super Invar.
Heat treatment requirement
State explicitly whether the part needs stress relief between roughing and finishing, a full stabilization cycle, or neither. This is the single detail most likely to be missing from a first RFQ and most likely to force a re-quote once it comes up, since it is one of the largest cost and lead time factors on a precision Invar part, covered in stress relief for Invar machined parts. If you are not sure, say so and ask the shop to recommend based on your tolerance.
Critical tolerances and GD&T
Call out the two or three features that actually control fit, alignment or function with real tolerance values and, where relevant, GD&T for flatness or position. Leave the rest at a standard machining tolerance. This gives the shop a realistic picture of where the difficulty actually is, rather than forcing every feature to be treated as critical, a point covered in more depth in Invar machining tolerances.
Surface finish and coating
Note any specific surface finish requirement on critical faces, and whether the part needs a coating for corrosion protection, appearance or a functional purpose like emissivity control. If a coated dimension is critical, state whether the tolerance applies before or after coating, covered in surface finish and coating options for machined Invar.
Certification and documentation
Specify whether you need a standard mill cert, which most shops include by default, or something more: measured CTE data for your heat lot, full traceability for an aerospace or space program, or specific inspection report formats. Asking for documentation after a quote is issued usually means a revised price and schedule, covered in Invar material certification.
Quantity and expected reorders
State the quantity for this order and, if you expect to reorder, a realistic estimate of future volume. This lets the shop plan material purchasing and consider whether holding fixtures or programs for a repeat order makes sense.
Operating environment
If your part will see cryogenic temperature, vacuum, humidity, repeated thermal cycling or any other specific service condition, mention it. These details, covered for a few common cases in Invar for cryogenic and vacuum applications and Invar for semiconductor equipment, can change cleaning, packaging and sometimes the process itself.
A quick checklist
- Alloy and specification (Invar 36, Super Invar, Kovar, Alloy 42)
- Heat treatment: stress relief, full stabilization, or none, or “shop to recommend”
- Critical tolerances and GD&T on the features that matter
- Surface finish and coating requirements, if any
- Certification and documentation needs
- Quantity, and expected reorder volume
- Operating environment, if unusual (cryogenic, vacuum, cleanroom, outdoor)
- File formats: STEP or IGES for the model, PDF for the toleranced drawing
Files that get accurate quotes
A STEP or IGES 3D model together with a PDF drawing carrying tolerances, alloy callout and heat treatment notes gets shops the most accurate read on your part. DWG and DXF work too, but a 3D model paired with a dimensioned drawing removes ambiguity that a 2D drawing alone can leave.
Sending your RFQ
Filling in these details up front means the quotes you receive are quoting the same part, not different assumptions about it.
Send your drawing through our RFQ form with this checklist covered, and we match you with up to three shops that quote based on what your part actually needs.
Frequently asked questions
What happens if I leave heat treatment off the RFQ and decide later that I need it?
The shop will need to re-quote, since stress relief and stabilization are significant cost and schedule items, covered in why Invar 36 parts are costly. Deciding on heat treatment before the first quote avoids a second round of quoting and a longer overall lead time.
Do I need to specify the exact stress relief temperature and hold time myself?
Not necessarily. If you are not sure, say so and ask the shop to recommend a cycle based on your tolerance and application. What matters most is telling the shop whether the part needs stress relief or a full stabilization cycle at all, since that is the detail most often left off a first RFQ.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that machine Invar and reply within 24 business hours.
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