ATC and Tool Magazines: Types, Specifications and What to Check
A machining centre can mill, drill and tap in one setup because of its automatic tool changer. When buying a machine, magazine type and capacity are often treated as secondary specifications — but they set the tool change time and the largest tool you can carry. This article covers the common magazine types, how to read the specification, and what to watch in selection and maintenance.
1. What the ATC Does
ATC stands for Automatic Tool Changer, and its job is to let the spindle load the next tool on a program command, without stopping the machine for someone to change it by hand.
That capability is what gives a machining centre its value: milling, drilling, tapping and boring can all be completed in one setup, and what you save is not only the changeover time but the location error that comes with every re-clamping.
2. How Magazine Types Divide
| Type | Characteristics | Typical use |
|---|---|---|
| Carousel | Whole disc moves under the spindle to change; simple structure | Entry-level and small vertical machines |
| Disc type | Uses a tool arm to swap; faster | Mainstream on vertical machining centres |
| Umbrella type | Tool pockets arranged in an umbrella form | Small and mid capacity machines |
| Chain type | Pockets hang on a chain; capacity can be extended | Machines needing a large tool count |
| Hydraulic tool arm | Tool arm driven hydraulically | Large or heavy-duty machines |
⚠ Catalogues also call the chain type a chain magazine or a chain-driven magazine — the same arrangement under different names.
3. Reading the Specification
The magazine line on a quotation usually carries three numbers:
Spindle taper size — commonly 40 or 50 (for example BT40 and BT50). This fixes the holder interface, and indirectly how heavy and how large a tool you can carry. On the differences between taper systems see Spindle Taper Systems Overview.
Tool capacity — how many tools the magazine holds. Maker manuals list configurations such as "24 tools" (maker example; varies by model). Too little capacity forces a manual tool change mid-job, which defeats the point of having an ATC.
Tool change time — maker manuals quote roughly 2 to 3 seconds (maker example value; varies with model and tool weight). In volume production, a few hundred changes a day makes that difference add up.
One specification that is easy to miss: left-hand or right-hand magazine. Which side of the machine the magazine sits on affects the operator's working path and the space available for service — confirm it first when the floor layout is tight.
4. Selection and Maintenance
Large diameter tool management: a large tool such as a face mill cutter body encroaches on the neighbouring pockets when it sits in the magazine. Most controllers can reserve the adjacent pockets through a PLC setting so nothing is loaded there and the tools do not interfere during a change. Confirm this function when buying — not every model supports it.
Chip protection: the most common source of magazine faults is chips and coolant getting into the pockets. A fully enclosed design cuts these problems substantially and is worth prioritising in the options list.
Tool pockets are consumables: the spring clips that grip the holder fatigue, and once slack a tool can drop during a change. This belongs on the periodic inspection list, not in the repair-when-broken category.
5. Frequently Asked Questions (FAQ)
Q: What does ATC stand for?
Automatic Tool Changer. It lets the spindle change tools automatically on a program command, with no machine stop for manual changing.
Q: What is the difference between a carousel and a disc type magazine?
A carousel moves the whole disc under the spindle to change tools and is mechanically simple; a disc type uses a tool arm, changes faster, and is mainstream on vertical machining centres.
Q: How do I choose between a 40 and a 50 taper magazine?
It follows the spindle taper. Size 50 takes larger tools and heavier cuts; size 40 is lighter and changes faster. Decide by the kind of work you run.
Q: Will a large diameter tool fit in the magazine?
Yes, but it encroaches on the neighbouring pockets. The controller's large diameter tool management function must reserve those pockets, and since not every model supports it, confirm this before buying.
This article is part of CNC Machining Fundamentals: The Complete Guide - Know the Machine and Shop, Then Read the Drawing; that guide shows how the whole topic fits together.
