How to quote a machined part from a drawing

What do you read off a drawing before quoting?

Go through the print in the same order every time, so nothing that changes the price gets missed:

The example bracket's print gives: 6061-T6511 aluminum, 4.00 × 2.00 × .500 in, 6 holes of Ø.201, 2 of them tapped 1/4-20 UNC-2B, an R.250 corner note, general tolerances ±.01, ±.005, ±0.5°, and no coating.

How do you work out stock size from a drawing?

Take the finished envelope, add what the machine cuts away to clean it up, then round up to a size you can buy. QuotedPart's defaults for a milled part: plate under 1/2 in is used at its finished thickness; 1/2 in and thicker is sawn from the thinnest plate distributors stock that leaves at least .030 in a side to face both sides clean; length and width get 6 mm (about 1/4 in) each. A turned part comes from the next standard bar at least 3 mm over its largest diameter, cut 5 mm longer than the part to face both ends and part it off.

The bracket is .500 in thick, so it is sawn from 5/8 in plate and its blank is 0.625 × 2.236 × 4.236 in: 0.26 kg (0.58 lb) of 6061. One blank can't be bought on its own, though: a distributor cuts plate no shorter than 12 in, so a lot buys a 12 in strip at least, 0.74 kg (1.64 lb). At $9.50/lb, a one-bar price, that's $15.55 for one. At 10 the blanks outweigh the strip and are priced by weight. At 100 parts the order is a few bars and the price per pound falls toward the distributor price: $3.87 a part.

How many setups does a machined part need?

One for each face that has features on it. A through hole can be drilled from either side, so it adds a setup only when neither side is used already. A blank that's faced on both sides needs a flip for the back even when every feature is on the top.

The bracket's holes are all drilled from the top, and its .500 in blank is faced on both sides: 2 setups. The first setup is charged in full and each further one at half, because the tools and the program are already in the machine:

setup min = wc.setup_min * (1 + (part.setups - 1) * 0.5)

With the 3-axis mill's 45 min setup that's 67.5 min.

How do you estimate machining time from a drawing?

Work out the volume to remove (stock minus part: the envelope less the holes and pockets), the area to finish, the holes and their depth, and the setups. Then divide by removal and finishing rates. The default 3-axis milling formula, in minutes per part:

(part.removed_volume_in3 - part.narrow_volume_in3) / (6 * material.machinability * part.tool_scale ^ 1.5) + part.narrow_volume_in3 / (min(6, 100 * part.narrow_tool_in ^ 3) * material.machinability) + (part.machined_area_in2 - part.thin_wall_area_in2) / (8 * material.machinability * part.tool_scale) + part.thin_wall_area_in2 / (3 * material.machinability) + part.holes_count * 0.3 + part.tapped_holes * 0.4 + part.holes_depth_in / 10 + part.setups * 0.75

For the bracket:

The inputs: 2.02 in³ removed, 11.8 in² finished, 6 holes (2 tapped) 3.0 in deep in total, 2 setups. Try them in the machining time calculator, which runs the same formula.

What else goes on the routing?

• Programming. Once per job: 15 min to plan and post, 5 a setup and 4 a toolpath. Each setup faces and finishes its side, and each hole size, tap and pocket size adds its own: 15 + part.setups * 5 + part.toolpaths * 4 = 53 min.
• Deburr. A minute plus time per hole and per finished area: 2.3 min a part.
• Inspection. A first article (18 min, more with more holes) and a light check of every part (0.8 min). Tight tolerances need more, and a position, profile, concentricity or symmetry tolerance or a CMM note adds a CMM program: 30 min plus 2 a hole, up to 20 holes.
• Outside services. Anodize, plating or heat treat at the vendor's lot charge and piece price.

Which assumptions should you list on the quote?

Anything you decided that the print didn't. For the bracket:

• Holes assumed drilled from the top face through the .500 thickness.
• 1/4-20 tap drill taken as .201 (#7).
• R.250 on all 4 outside corners is called out in a note but not drawn in the plan view; treated as an outside profile corner radius, not a pocket.
• Hole locations are not dimensioned on the drawing; positions are not needed for estimating.
• Setups counted from the faces the features are machined from, plus a flip to face the back (1/2 in and thicker is faced both sides).

A buyer who sees "holes drilled through the .500 thickness" on the quote can say "no, they're blind" before the order, not after the parts ship.

How does QuotedPart quote from a PDF drawing?

The same steps, with the reading done for you and the assumptions left for you to check:

• The PDF is read by Claude (Anthropic's API) for the title block and notes: part number, revision, material, finish, general and tightest tolerance, threads, notes, quantities, and warnings about what the estimator should check.
• A second read takes the geometry: overall size, stock form, holes with counts and threads, pockets and steps, turned diameters, bores, bends and the tolerances.
• The engine, plain code and not AI, turns that into stock, setups, removed volume and finished area as above, and prices it on your own formulas and rates.
• The part is labeled "Estimated from drawing" with high, medium or low confidence, and the quote warns you to verify size, stock and features before sending.
• Everything it assumed is listed. You can correct the size, thickness, diameter, hole count or pocket volume, and reset to the drawing.
• A size the print leaves open (a dash-number table with no dash number named, or no size at all) leaves the part unpriced until you enter it, rather than quoting a minimum charge.

It's an estimate from a print, not a measured model: when the customer has a STEP file, upload it too. See CNC quoting software for the rest of what it does, and the RFQ checklist for what to check before you price anything.