Boring is a preferred method of producing accurate sized holes in manufacturing.
Boring offers distinct benefits over other hole making strategies such as reaming. Hole boring comes with a unique set of rules. This guide helps address those rules and will aid in maximising the cost benefits of your boring bar investment.
The general rule in boring is to keep the boring bars to a minimum length. At the early stages of any production planning, maximum effort must be put into a machining strategy that will keep boring bars as short as possible.
In new projects the only limiting factor should be the length of the bore.
Machine (spindle) choice and fixture design should be highly characterised by the impacts of boring tool length.
Stability is greatly increased with larger spindles.
Rigibore and the Rigibore global distributor network will directly support you with your installation of tooling. This guide should be used as a way of best directing questions to Rigibore so when technical support is required we can quickly help your application.
There are a number of factors that should be considered in the early stages of a manufacturing process that requires accurate hole production (boring).
The following is required to quote for a suitable boring bar:
Tools will be designed from the component print and machine specifications. Recommendations will be made with regard to the boring process.
In designing the tool the Rigibore team will use experienced knowledge to maximise tool efficiency while minimising deflection and vibration.
As a fundamental rule, tools will be kept as short as possible.
On packages, tools will be combined where possible to reduce the investment needed to perform the machining operation.
Decisions will be made that, where possible, will reduce negative impacts of cutting forces on the bar.
These including cutting geometry, component selection, balancing and in some cases recommendations may be made to change the process variable or cutting technologies, such as depth of cut to maximise the efficiency of the boring bar.
Once a tool is designed the cutting technologies can usually be adjusted to achieve optimum results for the tool.
In the quoting process a Rigibore applications engineer will design the tooling to the previously stated criteria. Each quote is given a reference number and all data relating to this quote request is securely stored against this reference.
Drawings are produced detailing the key dimensional characteristics of the tooling.
A quotation file breaking down the costing and options for individual tools and hardware will be sent along with the PDF drawings of the tools.
As with all bespoke tooling, Rigibore will expect to recieve a sign off print from the end user. As part of the sign off procedure end users should consider:
Delivery of special tools is often shorter than expected, but it's still a good idea to plan well in advance:
| Required | Consider | Notes | |
|---|---|---|---|
| 1.0 | Required PPE |
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Safety is a key priority (risk assessment) |
| 2.0 | Presetter | ||
| 2.1 | Correct spindle adaptor | Adaptors can change the usable length of a presetter. Enure that the presetter is long enough with the correct adaptor | |
| 3.0 | Tool drawings | RADS printout contains all the required information to set the tool | |
| 4.0 | Inserts | Correct size | |
| 4.1 | Correct grade | ||
| 4.2 | Correct geometry | ||
| 4.3 | Correct nose radius | ||
| 5.0 | Pull studs | Details of the correct pull stud can be found on the machine tool | |
| 6.0 | Coolant tubes | Some shanks like HSK require separate coolant tubes - Failure to fit can damage spindle seals | |
| 7.0 | Balluff chips | Tool ID chips used for storing unique IDs and setting data | |
| 8.0 | Adjusting tools | ||
| 9.0 | Blue tack | Used for cleaning cutting edges when using non-contact measurement to preset tooling | |
| 10.0 | Engineering blue |
All CNC tooling should be treated as a precision product. Extra care should be taken not to damage tapers, connecting surfaces or introduce contaminating dirt onto connection surfaces.
Rigibore tools are preset before shipping with gauge inserts. However, you will need to fit inserts and adjust preset dimensions prior to first use.
| Action | Notes | |
|---|---|---|
| 11.0 | Setup presetter | |
| 11.1 | Clean all connecting adaptor faces and assemble presetter components | |
| 11.2 | Calibrate presetter | Calibration hardware/software supplied by the presetter manufacturer |
| 12.0 | Unpack the tool | Required adjustment tools may be fastened to the outside of the packaging |
| 12.1 | Keep any reusable packaging for future storage of the tooling | |
| 12.2 | Fit required pull stud or coolant tube | Correct torques must be applied to pull studs, over tightening can deform tapers causing performance problems or damaging spindles |
| 12.3 | Clean the tool taper and insert into presetter adaptor | |
| 12.4 | Ensure the correct adaptor program is selected on the presetter | |
| 12.5 | Clamp tool into presetter ensuring for good connection | |
| 13.0 | Starting with the tool furthest from the taper carefully remove the insert screw with the correct torx key and fit the insert to the pocket | Ensure correct radius of insert |
| 13.1 | Visually inspect for good seating | Ensure there are no gaps between the pocket and the insert base. If unsure use a piece of shim to check for any clearances, if you cannot seat the insert, check for debris in the pocket or on the base of the insert, clean and repeat check |
| 13.2 | Tighten the insert screw | Ensure for an element of pull back roughly 1/4 turn on the insert screw |
| 13.3 | Clean cutting edge using blue tack | This removes any contamination that may affect non contact measurement systems on most modern presetters |
| 13.4 | Using the presetter, measure the position of the cutting edge and course adjust | Make course adjustment > ±0.1mm, if required, to length first then the diameter |
| 13.5 | Repeat items 13.0 to 13.5 until rough setting is complete on all edges of tool | |
| 14.0 | Establish critical component or reference dimensions for tooling | Combination tools may contain a number of cutting edges, some of these edges may have critical relationships such as two blind holes. Other features may be relative but not critical to these features, for example a chamfer |
| 14.1 | Starting with the critical or reference edge, adjust to finish size. Continue to adjust all edges to finish size | |
| 15.0 | Make a note of all edge positions and note and double check tool offset dimensions required for the machine | |
| 15.1 | Clearly label tool as set |
The most important part of this phase is the planning and pre assessment of the expected results.
As with all machining processes the entire process must be monitored and controlled to achieve tight tolerances and good process stability or a high CPK.
Besides the tooling there are many factors that impact the performance of hole boring processes.
| Criteria | Details | Notes |
|---|---|---|
| Material variation | Material variance has a huge impact on boring bars | Hardness, inclusions, chemical composition |
| Core shift | For boring processes the start process is usually a pre-formed hole. This may be pre-cast or pre-forged or it may be pre-drilled | |
| Fixture/component positioning | ||
| Fixture/component clamping forces | ||
| Program datum positioning | ||
| Coolant supply |
| Details | Notes | ||
|---|---|---|---|
| 16.0 | Required PPE |
|
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| 17.0 | Machine tool access | Access to a guarded machine tool with all required safety features fitted including interlocks and guards | |
| 18.0 | Parts | Access to test parts | |
| 19.0 | Programs | Pre written programs, verified with correct offset requirements, required spindle orientations and clearance distances | |
| 20.0 | Offsets | Tool length offset measurements | |
| 21.0 | Measurement equipment | Manual methods of measuring tool cutting results | |
| 22.0 | Start point speeds and feeds | Estimated speeds and feeds for the tool based on standard industry prerequisites | See specific section on speeds and feeds |
To calculate a starting point for speeds and feeds you need specific information about the tool.
Start points for speeds and feeds are calculated but are only a starting figure. They are based on the surface speed and the feed rate, outlined below.
Speeds & Feeds Calculator ToolSurface speed is the speed that the material moves past the cutting edge of the tool. So in boring operations the diameter is theoretically unwound. A constant RPM is applied based on a known surface speed which will give a technically established starting point.
| Material | Surface Speed m/min (carbide) |
|---|---|
| Steel | 150 |
| Stainless steel | 100 |
| Cast iron | 250 |
| Nodular cast iron | 100 |
| Aluminum | 1000 |
Calculate the RPM using the following equation:
The feed rate is the axial speed at which the boring bar is fed through the component. This feed rate will have an impact on surface finish.
Starting point feed rate for all boring operations is between 0.1 - 0.2mm per revolution.
The following instructions should be carried out for each of the tools used in the operation.
This could be a rough boring bar, semi finishing boring bar or just a finish boring bar.
See section below on establishing a preset size.
| Action | Notes | |
|---|---|---|
| 23.0 | Load part to machine fixture | |
| 23.1 | Check fixture clamping | |
| 23.2 | Check bore location to program datum | |
| 24.0 | Pre-check program with tool removed from machine | |
| 25.0 | Load tool to machine |
Clean taper before inserting into machine. It's also worth double checking the following:
|
| 26.1 | Run cycle | |
| 27.0 | Measure part | |
| 28.0 | Adjust tool | See notes (below) on established preset size for finish tooling |
Because of the impact of deflection on boring bars they will not ultimately cut the size that they are set to. For this reason it is necessary to establish a preset size.
Establishing a preset size is relatively simple but many factors have a dramatic influence on the deflection.
| Criteria | Details | Notes |
|---|---|---|
| Depth of cut | Depth of cut affects the loading on the cutting edge which will ultimately affect push off and affect the cut size | It's important to maintain a reasonable depth of cut for all operations |
| Insert wear | Flank wear is the natural wearing of insert due to the abrasive wear mechanism | Cutting times are estimated at around 15 minutes of contact for cutting edges. This can be affected by insert grades, coatings and applications. |
| Semi finish or rough bore size | Semi finishers and roughers play an important part in maintaining a reasonable depth of cut for the finishing operation | If the semi finish or rough size is dramatically changed this will increase the depth of cut on the finishing tool |
| Coolant supply | Coolant supply - helps evacuate chips, helps prevent insert problems and removes heat from the workpiece. It also aids in cooling chips helping to fracture swarf into manageable chips |
The most effective way to set a finish tool is to take half the stock off at a time.
Typically a finishing operation should be maximum of between 0.1 - 0.2mm depth of cut on radius.
Finishing tools are generally single point so that there is one effective cutting edge that can be used to hold size, this can have a negative impact on push off as the cutting edge is not supported.
| Action | Notes | |
|---|---|---|
| 30.0 | Measure the semi pre finished bore size to establish the depth of cut for the finishing operation | |
| 31.0 | Use engineering blue to mark the pre bore sides | |
| 32.0 | Preset the finishing tool to only clean up the pre finished bore | |
| 33.0 | Run tool through program making small adjustments until the pre finished hole is cleaned up by undersized | |
| 34.0 | Measure the bored hole | |
| 35.0 | Adjust the tool to remove the remaining stock | |
| 36.0 | Adjust the tool to remove the remaining stock | |
| 37.0 | Load a new part to machine | |
| 38.0 | Run cycle | |
| 39.0 | Measure result | |
| 40.0 | Adjust tool to achieve finished size |
| Problem | Possible Cause | Solution |
|---|---|---|
| Poor sizing/difficulty holding tolerance | Cleanliness | Clean tool holder and spindle mounting faces |
| Insert mounting (sufficient pullback) | Check for pull back on insert | |
| Unit or cartridge rigidity |
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| Material variance | ||
| Roughing setup - depth of cut | ||
| Core shift | ||
| Datum offsets | ||
| Coolant supply | ||
| Swarf nesting | Insert geometry (chip breakers) | |
| Feed rate too low | Increase feed rate | |
| Chatter/vibration | Cleanliness | |
| Length diameter ratio | ||
| Poor finish | Feed rate too high | Decrease feed rate |
| Cleanliness | ||
| Chip evacuation | ||
| Balancing | ||
| Ovality | Fixture clamping | |
| Balancing | ||
| Roughing tool setup | ||
| Excessive insert wear | Excessive flank wear |
|
| Crater wear | Select insert with more positive geometry | |
| Plastic deformation | ||
| Built up edge | ||
| Broken inserts | Excessive load |
|
| Grade too brittle | ||
| Geometry too weak | ||
| Insert too small | ||
| Feed too high | ||
| Speed too high |
