ShopBot Standalone Indexer Tool
ShopBot is known for making high quality CNC tools at levels of complexity and cost that are approachable to individual users. These tools perform full 3 axis CNC machining operations on a wide range of sizes and types of material. Adding an indexing head, often called an indexer or 4th axis, increases these capabilities even further. With the indexer installed, the ShopBot can be set up for turnings, multisided operations, and full 4 axis machining. With these capabilities, the ShopBot can create parts that would have been time consuming, or even impossible with conventional 3 axis machining.
Often, when people first see an indexing head setup they think of it as a lathe. The indexer setup has two significant differences from a standard lathe. First, the spinning bit provides cutting force instead of the rotation of the work stock. With the bit performing the cutting action, the turning axis is freed to move at any rate needed. It can be programed to move in the reverse direction and stop at any defined point in its rotation.
The other improvement over a lathe is that the ShopBot is able to move in 3 directions relative to the turning axis. Because of this, standard 3 axis cutting operations can be performed on any side of a work piece.
A case study application
Recently, a customer came to ShopBot Production Support seeking help with setting up to cut custom rifle stocks. Rifle stocks are a great example of parts that can be made more quickly and simply with a 4 axis tool. They require cutting operations on at least three separate sides. On a standard tool each step would require careful tool and material setup. The piece would have to be picked up, rotated and, precisely repositioned after each cutting operation. This process takes time and invites error. With an indexer, a file can be made that performs all of these steps with no stops to reconfigure the workpiece.
While working to create a procedure for this specific application, we found that there was an opening in our lineup for an indexer specific version of a ShopBot. We developed this tool in parallel with the application project. We were able to identify many issues that the increased complexity of a fourth axis brings up. These lessons heavily influenced the development of the tool and future indexer applications.
Machining a rifle stock
Big capability, Small footprint
The intent of the Standalone Indexer Tool was to provide full 4 axis machining capability in a tool with a much smaller footprint than the conventional 96 by 48 inch setup. At first the plan was to build a CNC lathe with only three axes. These would be the turning axis, the longitudinal axis, and the vertical axis. This resulted in a machine with great turning ability but did not allow milling work to happen on any specific face.
Adding the fourth transverse axis allows an end mill to extend deep into a part and create precise 90 degree milled pockets, and important feature for inletting metal receivers into rifle stocks. The extra axis also allows the tool to be used for conventional 3 axes routing when an optional deck is installed.
Milled pocket
Low backlash gear head
Chucking up a large piece of stock revealed a limitation with the existing indexer gear head. The backlash in the head was 15 arc minutes. At 4 inches off center this movement resulted in approximately 0.020”. In continuous turning operations with pressure exerted in one direction, the backlash was not an issue. However, when doing two sided machining the slop created an issue with tolerance error.
Citing this issue, a low backlash gearhead was selected. This head reduced backlash to less than 3 arc minutes. The side to side movement reduced to below 0.005 inches. This change allows multi-sided and multi-direction machining.
In addition to the gear head we developed procedures to speed up the zeroing process. Zeroing the tool with a set routine allows fast and repeatable setup for production operations.
Indexer head and tail stocks
Custom tool configuration
The modular nature of ShopBot tools allows a great variety of customizable configurations. The Standalone Indexer is one example of this capability, and uses only a handful of specialized parts. If you have a need for a tool that doesn’t quite fit into our advertised lineup feel free to contact ShopBot. We will discuss your needs, offer some suggestions, and issue a quote on a tool that exactly meets your needs.
Specifications
Foot Print
L36” x W96” x H67”
Nominal Cutting area
L20”x W60” x H6”
Actual Full Motion Area
L21” x W62” x H8”
Maximum Turning Area
Maximum Radius 4.75”
Maximum Length 48”
Square Stock 6”x 6”