Double Tracking means that the knurling wheels are not tracking properly. In this situation, the knurling wheels will create a different pattern than the original design and may overlap or "double die"
There are two main causes of a knurling tool double tracking:
Dorian Tool has developed a “Knurling Calculator Spreadsheet” that can calculate all of the parameters to avoid double tracking.
If you would like to request an electronic copy send us a note in the comments section below or, for faster results, in the form you get when you click the button below. We'll quickly get a spreadsheet sent over to you!
Hannibal Carbide has assembled a very nice overview of some common problems associated with carbide reamers and how to avoid them.
Make sure you are using the correct flute style and tool type.
HANNIBAL recommends 2-3% of the reamer diameter as a starting point for stock removal. 2% for steels and tough alloys, 3% for non-ferrous materials and cast irons. Solid carbide & carbide tipped reamers must have adequate stock to remove or they will rub in the hole and generate excessive heat, which leads to premature tool wear.
Improper Speeds & Feeds
The right combination of speeds and feeds is critical to tool life and consistent size and finish. Getting the correct starting points is a key element. Reaming is a finishing operation and proper speeds and feeds must be run to achieve size, straightness and finish.
If the fixturing cannot hold the piece securely and in line with the spindle, then producing a good finish will be very difficult. A reamed hole is only going to be as good as the machine and fixturing used to machine and hold the part.
Excessing Runout (spindle or tool holder)
Runout leads to poor finishes, oversized, tapered, and bellmouth holes, as well as poor tool life. Floating holders or bushings can sometimes be used to compensate for runout, but the best solution is to fix the problem.
Make sure the coolant you are using is recommended for reaming your particular materials. Many coolants will prove effective for reaming if the concentration level is maintained with specifications. Take the time to check the levels on a regular basis.
Improper Sharpening or Geometry
If a new tool works fine, but fails to perform after resharpening, the problem is obvious. However, depending on the hardness and condition of the material you are reaming, the tool geometry may need to be altered to get optimum performance and tool life. Geometries most often changed are the circular margins, radial rake, and the primary chamfer clearance.
Material Changes (hardness and/or condition)
Castings lead the way in inconsistency. Hard spots, free carbides, and scale can all lead to inconsistent results when reaming. A heat treatment that varies just a few points from part to part can cause problems.
Hannibal Carbide has assembled some basic technical guidelines for optimizing reamers. Following these guidelines will increase your productivity. Ream it right the first time with Hannibal Carbide.
Most reamer manufacturers will provide you with a starting point for speeds and feeds. Here's some things to keep in mind:
As you seek the optimum speed and feed for your application, look and listen for signs or sounds that could save you time.
Listen for the reamer squealing upon entry—this means speed or feed is too high or alignment is poor.
Examine the chip for size and color. Examine the finish for signs of chatter.
Here's a short guide on understanding Cut Tap Chamfers. This is an excerpt from Allen Benjamin's Technical Tap Guide Engineering Data.
A tap chamfer is the tapering of the threads to distribute cutting action over several teeth. The type of hole to be tapped has much to do with the chamfer style of that tap that’s best suited.
Some holes go all the way through. Some, while not through-holes, are relatively deep. Some are quite shallow (a little deeper than diameter).
Each of these three kinds of holes - through, deep-bottoming blind, and shallow bottoming - has a tap chamfer best suited to specific threading requirements.
This style, with a 7-10 thread chamfer, has the longest chamfer of the three to distribute action over the maximum number of teeth; and the taper also acts as a guide in starting the cutting action in the hole. Taper style taps start the thread square with the workpiece. Taper taps are commonly used in through holes and in materials where a tapered guide is necessary.
This style, with a 3-5 thread chamfer, is most widely used in through holes and where there is sufficient room at the bottom in blind holes.
Semi (or Modified) Bottoming Taps
This style, with a 2 to 2.5 thread chamfer, should be used when-ever possible in difficult material applications in blind holes, when threads are not required to the bottom of the hole
This style, designed with a 1 to 2 thread chamfer, is made with just enough chamfer for starting in the hole; as the name implies, it is designed to thread blind holes to the bottom.
PLEASE NOTE: Taper, plug and bottoming taps as a set, in a given size (for example: 1/4-20 NC) are identical as to size, length and vi-tal measurements; the difference is in the chamfered threaded portion at the point. As a rule, such taps when used by hand are furnished in sets of three of a given size...namely, taper, plug and bottoming (and should be used in that order)
Tech Tips: Dorian Tool
Installing a turret can give a real productivity boost for shops. With a CNC turret, more tools can be carried at one time.
The lathe is one of the oldest and most versatile machine tools. Few shops can do without the processing capability offered by the CNC lathe. Long before automatic toolchangers were applied to milling machines, the lathe had a multiple-tool configuration. The tool post gave lathe users the ability to select from several mounted tools and index them as needed during a turning cycle.
Many CNC lathes are still offered with the manual tool post design. Shops can generally purchase these machines at very reasonable prices. Some shops have found a need to increase the flexibility of these lathes by adding an indexable turret in place of the manual tool post.
Installing such a turret can give a real productivity boost for shops running on Colchester, Harrison, Nardini, Bridgeport, Southwest Industries and other popular combination CNC lathes. With a CNC turret, more tools can be carried at one time. Programming the turret brings the right tool into the cut at the right time automatically. No stopping the machine to index a manually operated tool post is needed so cycle times are reduced for applications that use more than one tool.
For many turning applications a manual tool post has sufficient capacity. But any shop that is looking for a through-put gain in their turning operation without a major investment in new machine tools, can benefit by considering installation of a CNC turret.
The issue is more about processing efficiency than tool capacity, says lathe accessory maker, Dorian Tool (East Bernard, Texas). A turret configuration allows the machine tool to carry tools mounted in operation sequence. Sometimes turret tool capacity is sufficient for more than one job to run without a tooling setup in between. But significant production time is saved by the ability to automatically index the tool turret as part of the lathe's part processing program.
The turret offered by Dorian Tool is a bi-directional unit. Indexing therefore takes the shortest part from one tool station to another. It's operated by a three-phase 220/380 volt 50/60 hertz electric motor through an anti-backlash gear drive. Tool position is controlled by an absolute encoder which tracks actual position of the tool station. The working position of the turret can be right or left hand depending on the unit location ahead of or behind the lathe's spindle axis.
A proximity switch detects tool position and verifies turret lockup before a go signal is sent to the CNC. A three-piece Hirth-type coupling is used to hold the clamped turret radially. The turret indexes, station-to-station under one second. Fast index is achieved by not lifting the turret face. The entire indexing mechanism is housed in a Meehanite grade casting that helps damp cutting induced vibrations.
Four standard sizes of turrets are available. They are 100, 120, 160 and 200 mm respectively. Toolholding capacities of eight or 12 stations are available in ID, OD or combined tooling configurations.
Tool capacities range from 12 to 32 mm (1/2 to 1-1/4 inches). A VDI turret disk is available. Both turret disks have an integral coolant delivery system.
Simple electrical and coolant connections easily interface with the lathe. If an indexable turret is the difference between a CNC lathe and a CNC turning center, then this accessory is a cost effective way to up-grade your lathes.
Tech Tip: Dorian Tool
Double Tracking means that the knurling wheels are not tracking properly.
In this situation, the wheels will create a different pattern than what the design was originally made for. There are two main causes of this scenario:
Dorian Tool Developed a “Knurling Calculator Spreadsheet” that can calculate all of the parameters to avoid double tracking. Request an electronic copy by emailing us at: firstname.lastname@example.org
Tech Tip: Hannibal Carbide
Hannibal Carbide has compiled this guide to inform you of some basic technical knowledge regarding reamers. Following these guidelines will reduce overall set-up time, while increasing productivity.
Selecting the right tool, proper stock removal and correct speeds and feeds are all important and covered here in the Hannibal Carbide Reamer Guide.
"Ream it right the first time with Hannibal"
Best suited for non-chip forming materials, i.e. cast iron, bronze and free cutting brass. Preferred hole condition would be a thru hole.
Right Hand Spiral
Designed to pull the chip out of the hole in a blind hole application.Due to aggressive flute geometry, a right hand spiral may cut slightly oversized.Effective in bridging interruptions, such as keyways, cross-holes, etc.Excellent in highly ductile materials.
Left Hand Spiral
Excellent in thru holes, as the flutes tend to push the chips out ahead of the reamer.Effective in bridging interruptions, such as keyways, cross-holes, etc.Good for reaming hard materials.Should provide the very best size and finish.
Designed for high production runs in abrasive materials, when size or finish can be rapidly lost.Expand the diameter by turning the screw clockwise.The tool is now ready to be reground back to its original diameter and resharpened.This process should produce like new tool performance.
Center Fed Coolant (axial)
Center fed coolant design is used for blind hole reaming.Combine center fed coolant with right hand spiral for maximum chip clearing ability in highlyductile material.
Flute Fed Coolant (radial)
Flute fed coolant design is used for thru hole reaming.Effective in a cavity large enough for chip clearance.Flute fed coolant will flush the chips ahead of the reamer, providing the best hole size and finish.
OPTIMUM OPERATING CONDITIONS
While developing optimum conditions will require some investment in time, it will be beneficial by reducing cycle times and getting the best possible tool life. There are several elements to evaluate in this section. These elements are key to maximizing tool efficiency
Tech Tips: Decatur Diamond
CVD coated diamond tools are a perfect match for machining carbon fiber composites (CFC) such as carbon fiber reinforced polymer (CFRP). The very abrasive characteristics of composite materials severely limit the life of both carbide and PCD diamond tools. Tools with diamond on the surface wear longer and have a lower coefficient of friction. These characteristics provide substantial benefit to machining operations.
Because CVD diamond tools last 10-50 times longer than carbide tools, and 3-4 times PCD diamond tools they:
The low friction of CVD diamond tools permit using speeds higher than both carbide and PCD – again contributing to higher productivity – with no degradation of the surface quality or tool life. The consistently sharp edge and lower friction allows delicate, thin wall sections to be machined quickly and precisely.
The sharp and long wearing edge also puts lower stresses on the part, fixturing, and equipment. Since CVD diamond has no cobalt binder to break down or abrade away they offer the longest possible tool life.
Carbon fiber composites can be machined successfully with diamond coated endmills if resin melting and chip evacuation are carefully controlled. Observance of the following guidelines should yield tool lifetimes of approximately 10 times the equivalent carbide tool.
Speeds and feeds must be adjusted to avoid melting or softening the resin in composite materials. This means that feeds must be 0.001” ipt or greater with larger diameters and speeds should be kept at 400-500 sfm for most types of materials.
As the depth of cut increases the cutting speeds should be reduced to below 400 to minimize heat buildup in the chips. For shallow depths of cut, feeds can be up to 0.010” ipt for 1/2” diameter tools. Maximum feed rates are a function of the depth of cut and limited by the tool strength for a given diameter.
For slot depths exceeding more than 1/2 the diameter of the endmill the evacuations of chips from the slot becomes extremely important. Failure to adequately remove chips can cause breakage of the carbide under the diamond film on the flute edge and subsequent catastrophic failure of the tool.
The use of 2-flute tools and moderate-to-high feed rates is highly recommended to insure good chip flow. Air flow into the cut and vacuum evacuation of chips from the cutting area are also recommended. Additional life improvements can be obtained by using a corner radius or ball end tool for the initial cut and then following up with a square end tool with a much shallower cut to achieve the final dimensions.
For side cutting applications there is also an issue with chip evacuation if the radial depth of cut exceeds 1/4 of the tool diameter for a 4-flute tool or 2/3 the diameter for a 3-flute tool. Maximum tool life and production rates are generally achieved with 2-flute tools operated at high feed rates for most side cutting applications.
Sidecutting Machining Parameters:
Recommended parameters for sidecutting are listed in the following chart for various flute configurations. Recommendations are based on a cutting speed of 400-500 sfm and a diameter of the tool greater than or equal to the material thickness. Larger radial depth of cuts are possible if the material is substantially thinner than the tool diameter.
Slotting Machining Parameters:
The recommended parameters for slotting are listed in the following chart for various flute configurations. Recommendations are based on a cutting speed of 400-500 sfm and a full width slot which does not penetrate the full thickness of the material thickness.
See the sidecutting chart above for slots which penetrate the full material thickness.
Note: VDOC’s greater than 100% of the tool diameter are listed for informational purposes only and are not recommended for normal operation.
Tech Tips: Hannibal Carbide
If you are ordering a special drill, here is the nomenclature you should be familiar with when preparing to write your specifications.
Modern CNC machines feature high-capacity tool changers that automatically swap toolholders in and out of the spindle as needed, by means of a high speed swing arm or a rotary carousel. Periodically, toolholders should be examined for wear and if necessary replaced to maintain cutting performance.
New operators should be taught how to properly evaluate toolholders so they can recognize when toolholders need to be replaced to prevent premature cutting tool failure, or even expensive damage to the spindle.
Many operators do not know why it is necessary to replace their tooling, or have the experience to tell when it is time to do so.
Determining if toolholder components need to be replaced is not a difficult task, but does require that the operator knows what to look for.
A worn out holder will not provide good accuracy and will quickly wear out your cutting tools. Worn tooling causes poor surface finish, and may damage your spindle.
This article will discuss the following types of causes and types of wear.
Checking For Spindle Mouth Wear
A worn spindle can cause runout issues that affect tool-holder accuracy and reduce cutting quality and productivity. This is a condition known as bell mouthing. If toolholder issues can be eliminated by bench checking T.I.R., then the source of the problem is often a worn out spindle mouth. A trained professional will be required to check and repair bell mouthing.
Taper Wear / Fretting
Check the taper for signs of wear or damage where it contacts the spindle mouth. Any problems with the taper will have a direct effect on machining accuracy. If there are any imperfections on the taper, the toolholder should not be used. If noticeable marking is evident on the taper a condition called fretting may be occurring.
Fretting happens when two steel parts (holder and spindle mouth) are rubbing against one another.
Once a toolholder is fretted it can pass the fretting to other spindles. A spindle with fretting can pass the fretting to other toolholders. Fretting in this sense if akin to sexually transmitted diseases and it should be considered just a seriously.
Fretting is believed to be caused by imperfect mating between tooholder taper and spindle, creating vibration and heat which develops the fretting. It is visible as small copper colored pits or marks on the taper. This is evidence that the toolholder is becoming worn. Fret-ting is easily mistaken for rust, but it is not. Once noticeable fretting develops the toolholder should be replaced. New toolholders that quickly develop fretting, or toolholders that stick in the spindle, may indicate a spindle that needs to be reground.
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