VDI 3400 vs MT 11000 on RTV Masters

VDI 3400 and MT 11000 are not two names for the same sandpaper.

VDI 3400 (Verein Deutscher Ingenieure) is a spark-erosion / EDM roughness scale used on mold steel. Grades are numbered (commonly discussed as VDI 12 through VDI 45, sometimes written N12–N45). Each step is a defined texture character from fine satin to heavy orange peel. It is a *standard*, process-tied, and relatively cheap to specify on an industrial LSR or HCR *part* tool.

MT 11000 is not a committee standard. It is a Mold-Tech (Standex Engraving) catalog code in the MT 11xxx family: chemically etched or laser-mapped grains with a published depth and a supplier-recommended draft. MT 11000 itself is a very fine grain in that family (on the order of 0.01 mm depth on Mold-Tech’s published card, with a small recommended draft). Neighboring codes (MT 11010, 11020, and so on) are different depths and different looks. “MT 11000” on a drawing that meant “any Mold-Tech grain” is how you get the wrong plaque.

On this site the silicone is the cavity. You do not EDM a 10A–20A jacket. Finish the master (CNC, metal, or a sealed SLA) to the grain you want copied. A VDI callout on a poured platinum tool drawing is a category error unless you mean the *mother tool* or the master that will be sparked. SPI polishing grades (A-1 through D-3) are a third language, aimed at polish and blast, not at decorative etch. Do not write “SPI A-2 or VDI 24 or MT 11000” as if those were equivalent.

What the dump sees is the inverse of the master

Silicone copies. A pit in the master is a bump in the cavity, which becomes a pit in the dump — watch the inverse twice. LSR on steel prints a fingerprint on the *part*. RTV prints the master on the *mold*, then the mold on the chocolate, gummy, or resin.

For LSR/HCR steel tools (parts OEM):

• VDI via EDM is consistent, non-directional, and available from any decent toolroom that owns a sinker and a comparator plaque.
• Mold-Tech (or equivalent etch houses) is how you get leather, technical grains, and brand-matched interiors. The house needs the steel type, hardness, and a mask.
• Laser texture can put VDI-like roughness or a named grain on geometry EDM cannot sit on. It is still a specified plaque, not a Photoshop filter.

For RTV molds (this site):

• Grain on CNC masters: mill or blast, then sign off a plaque or a chip.
• Grain on printed masters: layer lines are not VDI. Seal, then apply the grain you actually want, or you will copy stair-step as “leather.”
• Grain on a found object / leather wrap: you are copying that object, including wear. Say so.
• Keep grain off keys and shut faces. Texture across a split is how the dump leaks and how the jacket tears.

If you ignore the inverse, the defect is a grip you specified as “recessed leather” that came out as raised warts because someone textured the wrong half — or textured the jacket instead of the master.

Do not treat texture-system numbers as interchangeable without the catalog sheet for the selected grain.

Shops circulate charts that say VDI 21 = MT 11020 = SPI D-2. Those charts are marketing, plus Ra overlap, plus wishful thinking.

Ra overlap is real: a medium VDI and a fine MT 11xxx can share a roughness number and still look different under a customer’s thumb. EDM spark texture is cratered. Chemical etch follows the microstructure of the steel and the film. Leather grains have direction and undercut. A clear resin casting will show that difference immediately. A matte chocolate might hide it.

What to do instead:

• Call one system on the face: “VDI 3400 – 24” or “Mold-Tech MT 11030” (or the actual code you meant), plus a physical plaque to sign off — on the master for RTV, on the steel for LIM.
• If a plastic housing uses MT 11000-family grain and the silicone overmold or the dump must *match*, send both plaques through the same light. Matching is a visual buy-off, not a VDI number you reverse-engineered from a blog.
• Write depth only when the house publishes it and you need it for draft. Do not invent depths for every VDI step on the drawing.

This library will not print a 45-row conversion. If a vendor’s quote depends on one, ask for their plaque, not their spreadsheet.

Draft, fill, and RTV-specific traps

Texture is draft. A common thermoplastic rule of thumb is about +1° of draft per 0.02 mm of texture depth (Mold-Tech cards often quote draft versus depth in the same spirit). It is a rule of thumb. Soft LSR can strip more grain than PC. Soft RTV *peels*, so the risk flips: a deep grain on a 0° master can tear the jacket, which is the opposite part. See the draft article in this cluster.

Fill: female pits in steel (raised bumps on the part) trap gas. On RTV, heavy grain at last-fill on the *master* traps air in the pour unless you degas and vent. Male peaks strip-drag and tear thin skins — of the part on LIM, of the jacket on RTV.

Wear: EDM VDI on hardened stainless holds up in LSR better than a deep etch on mild steel. On RTV, the grain wears when the *master* polishes off or when the jacket tears at a barb. Recast the skin; do not pretend a 20A face is a Mold-Tech insert.

Medical and food parts: texture that traps residue can fight cleanability even when the grade is ISO 10993 or FDA 21 CFR 177.2600. A matte VDI to hide scratches is not free on a surgical grip that must wash — or on a gummy tray that must release.

RUUIPON Mold Structure Decision: Flat back? → open-back, grain on the master face. Deep undercuts plus leather? If the silicone cannot peel safely → two-part / plug. Large wet dump? → mother mold so the grain does not stretch as the tray sags.

Common mix-up: VDI on the jacket drawing

A lot of RFQs put VDI 24 on the RTV cavity line. In the shop that usually means the pour lead ignores it or guesses a blast on the master. Put the code on the master process.

What to ask when you're buying

• Faces, one system and code, plaque for sign-off?
• Master process: CNC, sealed SLA, metal — who textures it?
• Extra draft already added for grain depth?
• Grain kept off keys and the split?
• Must the dump match a plastic neighbor under the same light?

Worked example

You're copying a 90 × 60 mm soap with a leather back, 8-cavity platinum RTV, about 1,200 dumps. Texture the CNC master to a named grain (or wrap a real leather and say it is a copy, not MT 11030). Add draft on the master walls. Pour 12A–18A, resin jacket. Do not EDM the rubber. If production later is an LSR grip that must match a Mold-Tech PC housing, that plaque buy-off lives on the steel tool at the parts OEM.

We would not recommend a VDI callout on a poured 20A jacket with no master process

We would not recommend a 45-row VDI-to-MT conversion as the contract, grain on the split, or milling scan noise and calling it Mold-Tech. We would not add 5° “because texture” on a shallow, soft, optical-adjacent master without a plaque.

Typical shop values

Reference values only. Confirm material-specific limits against the supplier’s technical data and agree project acceptance criteria before production.

| Item | Typical shop value | | --- | --- | | MT 11000-class depth | On the order of 0.01 mm on the published card — confirm the *code* | | Draft thumb rule | About +1° per 0.02 mm texture depth — start, then adjust | | RTV cavity Shore | 10A–20A with a jacket; deep grain can tear a 0° peel | | Platinum shrink | About 0.1–0.3% — grain still copies | | Untextured RTV master draft | Often near 0° on a peel; protect the jacket on deep grain | | ISO 3302-1 | M2 common on the dump; grain is a visual buy-off |

Copy this into a texture RFQ

• Faces; one system and code (VDI 3400 grade *or* MT code *or* SPI polish)
• Plaque for sign-off; extra draft already added
• Process: RTV from a textured master or LSR/HCR steel
• Confirm “MT 11000” means *that* fine grain, not “the 11000 series”
• Which half is textured (master vs steel cavity vs core)

Send the face list and a plaque or chip. We'll put the grain on the master and keep it off the keys. Custom RTV molds.

Related: draft vs texture depth, silicone mold texture options, surface finishes.

FAQ

Is VDI 3400 the same as Mold-Tech MT 11000? No. VDI 3400 is an EDM roughness scale; MT 11000 is one fine grain in Mold-Tech’s catalog family, with a published depth and recommended draft. They can overlap in Ra and still look different. Specify one system and buy off a plaque.

Can I convert every VDI grade to an MT number from a chart? You can find charts; they are approximate at best. Spark craters, chemical etch, and leather undercuts do not map 1:1. For a visible face, use the actual plaque. For a hidden industrial face, a VDI grade is usually enough and cheaper than a decorative etch.

Should an RTV silicone mold be specified in VDI 3400? Only if you mean the rigid master or mother tool that will be spark-eroded. The flexible jacket copies the master. Put the grain on the master finish. A VDI callout on a poured platinum mold, with no master process, will be ignored or guessed.

Does MT 11000 need extra draft on RTV the same as on plastic? The catalog draft is a thermoplastic-oriented starting point. Soft RTV peels, so extra draft is often about protecting the *jacket* from a 0° deep grain on the master. Deep grains, tall walls, and robots on LSR parts often need more than the card. Treat +1° per 0.02 mm as a thumb rule to check.

Will texture on the parting line help hide flash? It will help hide a witness and will help the dump leak. Keep grain off keys, shut-offs, and sealing lands. Hide flash by seating the split, not by etching camouflage into a gap.