Blind cavities and forms a cutter cannot reach.
Sinker (ram) EDM sinks a shaped electrode into the workpiece to produce blind cavities, internal splines and forms — and to remove broken taps and drills without scrapping the part.
Sinker EDM erodes a cavity by advancing a shaped electrode into the workpiece rather than removing stock with a rotating cutter, so it reaches geometry a mill cannot: blind pockets with sharp internal corners, internal splines, textured cavities and forms sunk into hardened tool steel. The electrode carries the negative of the finished shape, so cavity accuracy tracks electrode accuracy.
It is also the most reliable way to remove a broken tap, drill or reamer from an otherwise finished part. Because the process erodes material without contact, it removes the broken tool without damaging the surrounding thread or bore — often saving a part that would otherwise be scrapped.
We quote sinker EDM against the print and the electrode geometry it requires, including whether an electrode needs to be machined in-house first. Send the drawing and the material and hardness, and we will confirm fit and lead time.
- Process
- Sinker (ram) EDM, electrode-formed cavities
- Best suited to
- Hardened tool steel, blind and internal forms
- Typical work
- Blind cavities, internal splines, broken-tool removal
- Quantities
- Single pieces and low-volume tooling work
- Sinker (ram) EDM for blind cavities and broken-tool removal
- In-house milling and turning for electrode fabrication
- In-house inspection for cavity and form verification
- 01
Print and feature review
Cavity geometry, hardness and required finish reviewed to confirm electrode strategy before quoting.
- 02
Electrode fabrication
Electrodes machined in-house to the negative of the required form.
- 03
Sinking
Cavity eroded to depth and finish, with a finer electrode pass where the print calls for it.
- 04
Final inspection
Cavity dimensions and form verified against print datums before the part ships.
- Hardened tool steel (D2, A2, S7, H13)
- Stainless steel (303, 304, 316, 17-4 PH, 15-5 PH)
- Alloy and carbon steel (4140, 4340, 1018)
- Titanium (Grade 5 / 6Al-4V)
Sinker EDM, answered plainly.
Can you remove a broken tap without scrapping the part?
In most cases, yes. Sinker EDM erodes the broken tool without contacting the surrounding thread, which is why it is the standard remedy for this problem.
Do you machine the electrodes in-house?
Yes — electrodes are machined on our own milling and turning equipment to match the cavity geometry called out on the print.
Can sinker EDM produce a textured surface?
Yes, using a textured electrode, though this is quoted case by case depending on the required pattern and depth.
Wire EDM
Wire electrical discharge machining for tight-profile forms, keyways, slots and tabs in hardened tool steel and other conductive materials that resist conventional cutting.
View capability →CNC Milling
Ten vertical machining centers running prototype through production quantities, with milled features held to a standard ±.001 in and critical callouts to ±.0001 in where the print requires it.
View capability →Secondary Operations
Tapping, drilling, grinding, deburring, assembly and laser marking in-house, with anodize, passivation, plating, heat treat and NDT coordinated through approved sources.
View capability →