Who Orders Fixtures
Fixtures for Injection Molders and Stampers
A new part number means a new fixture, and a tool launch means several at once. Both are quoted from your prints.
Molders and stampers need a check fixture per part number, and a tool launch brings several at the same time. The fixtures have a shared problem: the part is not rigid and not exactly repeatable, so the fixture has to locate on real datums without forcing a flexible part into shape. Locators are soft where the part is finished, hardened where a trimmed edge rubs. Send the part prints; a person quotes in 24-48 hours, standard lead time 4-6 weeks.
Updated September 2026
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Why the fixture count tracks the part count
A check fixture is tied to one part number. It reproduces that part’s datum scheme and checks that part’s features, so it does not transfer to the next job. For a shop running a few dozen tools, that means a standing need rather than a one-off purchase: every new mold or die that comes in brings a fixture with it, and every part revision that moves a datum or a checked feature brings a fixture change.
A tool launch makes that visible all at once. Several part numbers arrive on the same date, each needs its own fixture, and they all need to exist before the first production run is judged. Sets of three to ten are quoted as one order here, which is also the only way to be sure they are made to the same conventions. There is no minimum either way, so a single replacement fixture is just as normal an order.
The molded part problem: draft, shrink and a part that flexes
A molded part is not a machined part and a fixture built as though it were will fight it. Wikipedia’s Injection moulding entry (en.wikipedia.org/wiki/Injection_moulding) covers why: draft is designed in so the part releases from the tool, so almost no wall is truly perpendicular and a pocket cut square to the part model does not fit the part that comes out. Shrink means the part is not the model, and how much it is not depends on the resin, the wall thickness and the process window. And a thin-walled molding flexes, so clamping it hard will make it pass a check it should fail.
The practical answers go on the print. Locate on the datum features the part print names under ASME Y14.5 (asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing), usually a set of pads and two holes or bosses, not a general profile. Contact at defined pads rather than around a whole outline. Clamp lightly, toward the rests. And where the fixture has to swallow shrink variation, say how much: a stated allowance is quoted, a hoped-for one is not. Check and inspection fixtures covers the general build.
The stamped part problem: springback and a moving edge
Stampings bring their own version of the same issue. Springback, described in Wikipedia’s entry on it (en.wikipedia.org/wiki/Springback), means a formed angle relaxes after the press opens and the amount changes with the coil, so a fixture that locates on a formed flange is locating on the most variable feature of the part. Trimmed edges carry burr and a cut line that moves with die wear. And a large panel is flexible enough that how it is supported changes what it measures.
So the same rules apply with different specifics: locate on the pierced holes and the flat datum pads rather than the formed edges wherever the print allows, support a large panel at defined points so it sits the same way every time, and treat flush and gap at a formed edge as the attribute check it is. Where the fixture also has to check trim, a hardened edge or profile block is what survives; drill and trim jigs covers guided trimming.
Not marking a finished part
Molded parts are often cosmetic, and a Class A surface that a locator has scuffed is a reject. Stamped parts may be plated, painted or pre-finished coil. Either way the fixture faces that touch a show surface go to acetal or UHMW, usually as inserts pocketed into a metal base so the fixture stays stiff and the soft faces can be replaced when they wear.
Mark on the part print which surfaces are cosmetic and the split follows automatically. Delrin and UHMW fixture details covers which plastic goes where: acetal where the detail also locates and has to hold a size, UHMW where the part slides or drops onto the face. Hardened steel stays where a trimmed or unfinished edge does the rubbing.
What the quote covers, and what it does not
The quote covers the machined base and details to the tolerances on the print, the hardware the print lists, and assembly where the print shows an assembled fixture, as one order with one contact. Ground and hardened details bring precision grinding and heat treat onto the same job. Anything that cannot be made or inspected as drawn is named in the quote instead of being substituted.
Two limits worth stating plainly. No design service is offered, so if a fixture print does not exist the quote lists what is still missing rather than drawing it for you; sending the part model and print with the datums and checked features marked, plus a dimensioned sketch, is what moves it forward. And the tooling itself, molds and dies, is not quoted here. This is the fixture that checks what comes out of them.
Duplicates, customer copies and lead time
Two situations produce duplicate orders. A second press or molding cell needs a second identical fixture, and a customer’s incoming inspection often asks for a copy of the fixture the supplier uses so both ends of the shipment measure the same way. Both are quoted together with the original where possible, so they come from the same setup and actually agree.
Standard lead time is 4-6 weeks from approval with the quote back in 24-48 hours, and rush at 1-2 weeks is quoted when a launch date is fixed, and extended is 6-8 weeks when timing is flexible. Fixture lead time explains what moves a build toward either end, and custom fixture cost covers which lines on a print move the price. Vendor setup takes a day: W-9, NDA, net terms available.
Questions
Before you send a job.
01 How should a fixture handle draft and shrink on a molded part?
By locating on the datum features the part print names, usually pads and two holes or bosses, rather than on a general profile cut to the model. Contact at defined pads instead of around the whole outline, and clamp lightly toward the rests. Where the fixture has to swallow a shrink allowance, state it as a number on the print so it is quoted rather than assumed.
02 Where should a stamping fixture locate, given springback?
On the pierced holes and the flat datum pads wherever the print allows, because a formed flange is the most variable feature on the part. Support a large panel at defined points so it sits the same way every time, and treat flush and gap at a formed edge as the attribute check it is rather than a dimension.
03 Will the fixture mark a Class A surface?
Not where the print says it must not. Faces touching a cosmetic or plated surface are machined from acetal or UHMW, usually as inserts pocketed into a metal base so the fixture stays stiff and the soft faces can be swapped when they wear. Mark the cosmetic surfaces on the part print.
04 Can you quote a whole launch set at once?
Yes, and it is the better way to buy them. Sets of three to ten part numbers are quoted as one order, which keeps the conventions consistent across the set and means one delivery to plan around. There is no minimum, so a single replacement fixture is equally normal.
05 Do you make molds and dies as well?
No. What is quoted here is the fixture that checks, holds or trims what comes out of the tool, not the tool itself. That keeps the scope honest: a check fixture, a trim jig, a CMM holding fixture or an assembly nest, made to your print and inspected against it before shipping.
06 What if we do not have a fixture print yet?
Send the part model and print with the datums and checked features marked, plus a dimensioned sketch or photos with a ruler in frame if you are replacing something, and the quote lists what is still missing before a build-to-print number can be given. No design service is offered here, so the quote will not draw the fixture for you.
Related
Where to go next.
Custom machined fixtures
The hub: every fixture family, quoted from your print.
View →Check and inspection fixtures
The general build, datums, locators and the 10:1 rule.
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Guided drilling and trimming on molded and formed parts.
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