What a DFM review actually changes, with the numbers
September 19, 2026
Most suppliers say they offer DFM. Most send back a sentence confirming the part is manufacturable, which is not a review, it is a pulse check.
A real one names features and attaches numbers. Here is what that looks like and what each item is typically worth.
What a review looks at
Internal corner radii. Every internal corner in a milled pocket carries the radius of the tool that cut it. A small radius forces a small cutter, and the whole pocket then runs at that cutter’s feed rate. Opening the radius from 2 mm to 4 mm on a deep pocket is often worth a double digit percentage on cycle time, for a change most designs do not notice.
Pocket depth against tool diameter. Beyond about four times the tool diameter, tools deflect, passes get lighter and finish quality drops in the corners. Widening a pocket by 2 mm can move it out of the danger zone.
Number of setups. Features on five faces means multiple clamping positions, each with fixturing, re-datuming and a tolerance stack. Moving one feature to an existing face can remove a whole operation.
Tolerance scheme. A blanket tight tolerance is the single most expensive line on most drawings. Replacing it with a general note and three called-out features changes both machining and inspection cost.
Thread depth and count. Engagement beyond 1.5 times diameter adds tapping time and tap breakage risk without adding strength in most materials. Three thread sizes on one part means three taps and three tool changes.
Material and stock size. A part designed around a 47 mm plate waits for 47 mm plate. Designing to a standard thickness is free.
Finish specification. Ra 0.8 where Ra 3.2 would do adds a finishing pass. A coating that has to be masked adds handling. Both are cheap to decide and expensive to discover.
What the output should look like
A review you can act on reads like this:
- Pocket A: corner radius 2 mm at 24 mm depth. Requires a 4 mm cutter at 6x diameter. Opening to R4 allows an 8 mm cutter, around 18 percent off the cycle time. Change accepted or rejected?
- Drawing carries ±0.01 mm as a general tolerance. We assume this applies to the four bores and that the outer profile is ISO 2768-m. Quoting on that basis. Confirming this could reduce inspection time noticeably.
- Three thread sizes: M4, M5 and M6. Consolidating to M5 removes two tool changes per part.
- Material specified as 7075. Function appears to be a mounting bracket. 6061 is stocked locally, anodises more consistently and would remove a week of material lead time. Your call.
Four items, each with a mechanism and a consequence. That is a review.
What it is not
- A list of everything that could theoretically be changed
- A push to redesign the part into something easier for the supplier and worse for you
- A reason to delay the quote
- A billable engineering service on a part of this size
How to get a useful one
Say what the part does. A supplier that knows the bore takes a bearing and the face seals can tell you which tolerance matters. One that only has a drawing has to treat every callout as sacred.
State what is fixed. “Corner radii are 2 mm because of a mating part, everything else can change” saves everyone a round of email and gets you better suggestions.
Ask for one change with a number. If a supplier can only name one thing, that one thing is usually the most expensive feature on your part.
Compare answers across suppliers. If three suppliers all name the same feature, believe them.
Where this sits in our process
The DFM notes come with the quote, not after the order, and there is no charge for them. We are the supplier of record, so a part that is awkward to machine is our problem as well as your cost, which is why the incentive to tell you is real.
The feature-level detail is in the DFM checklist, and the geometry limits are in wall thickness, pocket depth and corner radius.
What each change is typically worth
Rough magnitudes, on a mid-complexity milled part. They are planning figures, not promises, and your part will differ.
| Change | Typical effect |
|---|---|
| Corner radius from R2 to R4 on a deep pocket | 10 to 20 percent off cycle time |
| Removing one setup | 5 to 15 percent, more at low quantity |
| Blanket tight tolerance to general plus three callouts | Large, mostly in inspection and scrap risk |
| Consolidating three thread sizes to one | A few percent, plus lower tap breakage risk |
| Standard stock thickness instead of a custom one | Material cost and often a week of lead time |
| Ra 0.8 to Ra 3.2 where finish is not functional | One finishing pass removed |
Two or three of these on the same part is where the double digit savings come from, and none of them requires a redesign.
When to ignore the suggestion
A review is a proposal, and some features are expensive for good reasons:
- The radius is set by a mating part
- The tolerance is inherited from a customer specification you cannot change
- The finish is cosmetic and the product is sold on appearance
- The material is qualified and requalifying costs more than the saving
Say so, and a good supplier drops it immediately. Any pressure after a clear no is a sign the suggestion was for their benefit rather than yours.
Send a drawing and you get the review with the price: get a quote.
Questions we get on this
What is a DFM review for machined parts?
A named list of features on your drawing that make the part slower or riskier to machine, each with what it costs and what changing it would save. If it arrives as a paragraph saying the part looks manufacturable, it is not a review.
Do I have to accept the suggestions?
No. Every change is a proposal and the drawing is yours. Plenty of features that look expensive are expensive for a good reason, and a supplier should accept that answer without pushing.
Does a DFM review delay the quote?
It should be part of the quote rather than an extra step. Ours is, and it costs nothing, because a cheaper part is easier to make and easier to sell.
Have a part like this?
Send the drawing. We shortlist the shop we place it with that run the process and material, and answer within 24 business hours.
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