Double contact steep taper system
At the end of the 1980s, the Japanese company Big Daishowa developed a spindle system with simultaneous taper and face contact between the machine spindle and tool holder.
This was standardised in 1992 and marketed as the Big Daishowa Big-Plus® spindle system (also known as BBT® or BBT BIG-PLUS®). Later, a version with a taper according to ISO 7388-1 (formerly DIN 69871) was added. BBT is the designation for the BIG®PLUS® BT taper, and BDV is the designation for the BIG®PLUS® ISO 7388-1 (formerly DIN 69871) taper. BCV corresponds to the CAT taper.
The double-contact steep taper system is based on the latest available standards in ISO 7388-1 (formerly DIN 69871) and ISO 7388-2 (formerly JIS B6339). With a conventional steep taper interface, the taper base is the strongest possible connection point. With a double-contact tool holder, however, simultaneous support on the taper and flat surface is possible, which significantly increases stability. The double-contact steep taper system outperforms other spindle concepts and at the same time offers interchangeability with existing machines and tool holders.
- Higher stability compared to conventional steep taper mountings
- Reduced vibrations at high radial forces
- No axial displacement at high speeds
- High repeat accuracy
- Longer tool life
Designs
Steep taper tool holders
similar to ISO 7388-1 (formerly DIN 69871)
with flat contact surface / taper face
[DUAL Contact]
Available with IS40 taper
Steep taper tool holders
similar to ISO 7388-2 (formerly JIS B 6339 MAS 403 BT)
with flat contact / taper face
[DUAL Contact]
Available with BT30 and BT40 taper
FAQ (Frequently Asked Questions)
Face holders must remain in contact with the spindle surface to ensure accuracy and the correct interface between the tool holder shank and the tool spindle taper.
When using standard tapered tools in a double-contact spindle, chips and debris can accumulate on the face if face contact is not maintained.
This contamination can then lead to damage to the spindle surface and/or the double-contact tool holder.
We therefore do not recommend using standard steep taper holders and double contact tool holders in the same machine spindle.
If the machine has a double contact spindle and is to be used with double contact tool holders, all tool holders should be double contact. Even if mixed use is possible in principle.
Tool holders with a dual contact steep taper system are available on the market under various different names, but are technically identical.
- Double contact steep taper system
- Double contact spindle system
- Dual contact spindle system
- Two-contact system
- Steep taper with flat contact surface
- Monoblock toolholder
- Monoblock adaptors
BBT is the designation used by Big Daishowa and BIG KAISER Precision Tools AG for the BIG‑PLUS® BT taper, and BDV is the designation for the BIG‑PLUS® ISO69871 taper. The BIG‑PLUS® CAT taper is designated BCV.