Guides · 23 October 2026
Quoting machined parts from the customer's 3D model
More and more requests for quotes arrive with a STEP file next to the drawing. The model will not give you a price, but it answers the first questions of every quote quickly and exactly: how big is the blank, how much metal comes off, and how many holes are there. Here is how to use it, and where it stops.
What the model gives you
- The part's envelope. The smallest box around the part, in its own orientation, is the starting point for the blank. For a turned part, the smallest cylinder around it gives the bar diameter and length.
- The part's volume. Blank volume minus part volume is the metal you will remove: a good guide to how long roughing will take.
- Holes. Round holes by diameter, count and depth. Diameters such as 4.2, 5.0 or 6.8 mm are tapping drills for M5, M6 and M8, a hint that those holes are threaded.
- Pockets and slots. Closed pockets and slots with their size, depth and corner radius tell you which cutters you need and how much milling time to allow.
What it does not give you
- Tolerances and fits. A Ø20 H7 bore and a Ø20 clearance hole look identical in the model. Read the drawing.
- Threads. Most models show the tapping drill, not the thread. The drawing says which holes are tapped, to what size and depth.
- Surface finish, coatings and heat treatment. These drive outside processing costs and sometimes the whole process route.
- The revision. Check that the model and the drawing are the same part and revision before you price either.
From model to blank: a worked example
An aluminium cylinder mount measures 80.5 × 43.5 × 18 mm, with a volume of 52,821 mm³. It has six Ø4.2 holes 6.5 mm deep (M5 tapping drills), two Ø10 dowel holes and a Ø22 bore.
| Machining allowance: 2 mm per side | 84.5 × 47.5 × 22 mm |
| Rounded up to whole millimetres | 85 × 48 × 22 mm |
| Blank volume | 89,760 mm³ |
| Metal to remove: 89,760 − 52,821 | 36,939 mm³ (41% of the blank) |
| Blank weight in 6061 with 3 mm saw kerf: 88 × 48 × 22 × 2,700 ÷ 10⁹ | 0.251 kg |
From there the material cost is weight × price per kg plus the cutting charge, and the holes become a drilling operation and, once the drawing confirms the threads, a tapping operation.
Round up to stock you can buy
The model gives an exact size; your supplier sells standard thicknesses and diameters. A 22 mm thick blank usually means 25 mm plate. Price the stock you will actually buy and the extra material you will take off it. The allowance per side depends on the stock: sawn plate needs more clean-up than precision-ground flat bar.
A quick routine for every RFQ with a model
- Open the model and the drawing side by side; confirm part number and revision.
- Take the envelope, add your allowance, round up to the stock you buy.
- Note the removal volume, the holes and any pockets.
- Read tolerances, threads, finishes and notes from the drawing.
- Build the routing and price each quantity the buyer asked for.
A word of caution: do not accept models or drawings under export controls (such as ITAR or Australia's Defence and Strategic Goods List) unless your shop is set up for them.