Can I Retrofit My Existing CAT40 or CAT50 Taper Spindles to Big Plus?
In the ever-evolving world of CNC machining, maximizing rigidity, accuracy, and tool life is always top of mind. One of the most significant upgrades machine shops consider is transitioning from standard CAT taper spindles to the BIG-PLUS® dual-contact spindle system. But a common question arises:
Can I retrofit my existing CAT40 or CAT50 taper spindle to accept BIG-PLUS tool holders?
Let Motor City Spindle Repair break down the answer and explain everything you need to know before making the leap.
What Is BIG-PLUS?
BIG-PLUS is a proprietary spindle system developed by BIG Daishowa (formerly BIG Kaiser) that allows simultaneous dual-contact between the taper and the flange face of the tool holder and the spindle. This dual contact drastically improves:
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Rigidity
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Vibration dampening
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Tool life
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Surface finish
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Repeatability
Standard CAT40 and CAT50 holders only contact on the taper, leaving a microscopic gap between the flange and spindle face. BIG-PLUS eliminates that.
Can You Retrofit a Standard CAT Spindle to BIG-PLUS?
Short answer: Not easily — and not officially.
While it is technically possible to machine a spindle to meet BIG-PLUS dimensions, BIG Daishowa does not license the retrofit process to third-party service providers or allow retrofits outside their authorized factory standards.
Here’s why:
1. Tight Tolerances
The BIG-PLUS interface requires micron-level tolerances (within ±1 µm) between the taper and flange face. Retrofitting requires ultra-precise grinding, inspection, and alignment — not just simple machining. Very few facilities are capable of meeting these standards, and even fewer are authorized.
2. Risk of Poor Performance
Improperly retrofitted spindles may not achieve full dual contact, which can result in:
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Excessive wear
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Poor runout
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Tool holder damage
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Reduced machining accuracy
3. No Warranty or Certification
Unauthorized retrofits void warranties and are not backed by BIG Daishowa. You may think you’re getting the BIG-PLUS benefits — but without certified performance, you could be worse off than before.
What’s the Recommended Path?
If you’re committed to adopting the BIG-PLUS system, the safest and most effective approach is:
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Factory replacement of the spindle with a certified BIG-PLUS-compatible unit from your machine tool builder or OEM.
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Purchase of BIG-PLUS tool holders to match the new spindle.
Many machine tool builders today offer BIG-PLUS-compatible machines as standard or as an upgrade option.
Final Verdict
Retrofitting a standard CAT40 or CAT50 spindle to BIG-PLUS is not recommended.
While it may be possible in theory, the risk to spindle integrity, tool life, and part quality makes it a gamble.
If you want the benefits of dual-contact performance, it’s best to consult with your machine tool OEM or BIG Daishowa directly and explore certified upgrade paths.
Bonus Tip: Check Your Machine!
Some machines (especially those from Japanese or European builders) may already have BIG-PLUS-compatible spindles even if you’re using standard CAT holders. Ask your builder or inspect your spindle face and tool holder wear pattern — you might already be halfway there.
Need help figuring out if BIG-PLUS is right for your shop?
Reach out to a Motor City Spindle Repair expert to evaluate your current setup and help plan the smartest next steps.
Need a FREE QUOTE on a CNC spindle repair? sales@motorcityrepair.com
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