In order to maintain consistently tight tolerances on Hardinge Super-Precision cnc lathes the machine must be at a stabilized temperature and the temperature must be maintained. This is especially important when live tooling and Y-axis features are used in production on a component and any warm up programs should incorporate these functions as well. When dealing with thermals, keep in mind that thermal time constants (ttc’s) should be taken into account. Slow ambient temperature changes have slow gradual effects on the machine due to the “ttc” of the machine base. These changes are oftentimes mixed with tool wear and at times are not singled out. With the live tooling and Y-axis features, heat is generated by the live tool system which may transfer into the Y-axis slide assembly. The Y-axis slide assembly has a very quick “ttc” rate and if the machine sits idle for short periods of time, thermal migration may occur.
Thermal Compensation
February 25, 2009
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Advantage of Left-hand Turning Tools
February 17, 2009Hardinge has taught the use of left-hand turning tools for heavy cuts on slant bed turning centers. By running “reverse spindle” (M4 direction), the left-hand stick tooling allows the cutting forces to be directed toward the bed of the machine. This allows the operator the advantage to push tools harder, reducing chatter and offering better tool life.
Machine tools that run “forward spindle” use right-hand tooling (M3 direction) in upside down position. This condition tends to lift the top plate upward and away from the machine bed. This is absolutely a less stiff scenario and can cause numerous problems.
Another big advantage to left-hand tooling is that the operator can see the insert and can easily check it for wear (rather than upside down tooling where the insert is hidden from view).
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The Importance of Tool Centerline
February 12, 2009Ask any operator about the importance of putting tools “on center” and many will say it’s important. Ask that same group how often they actually check for center and most will hesitate, and reply “not often”.
Keep in mind that standard tooling doesn’t guarantee centerline. Using the “flat” on a boring bar is only good to about +/- .005”. Square shank tools, especially with molded inserts, are good to about +/- .003”.
A typical comment echoed is “my parts are not high precision so centerline is not as important.”
Note that tools positioned above centerline wear excessively and inserts can become rather costly.
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Calculating RPMs for Lathes and Mills
February 3, 2009Determining the proper rpm for a rotating tool for milling or drilling, or the proper rpm for a chuck when turning on cnc lathes, is a question many new CNC programmers are often faced with. Before calculating the RPM of the tool or part, here are two basic things you need to know:
- Material (Aluminum, Brass, Steel, etc.)
- Cutting tool composition (HSS, Carbide, Ceramic, etc.)
All cutting tools have an ideal cutting speed based on the material. Brass or aluminum cuts easier than steel for example. Cutting tool manufacturers have this information available through catalogs, tech support phone numbers, or possibly websites. If no other information is available to you, the Machine Tools Handbook will have some basic guidelines in the chapter devoted to “Speeds and Feeds” – http://search.barnesandnoble.com/booksearch.
Let’s start with an example for milling applications. Say you have a high-speed cutter (HSS) and want to machine 6061T6 aluminum. You can look in the cutting tool manufacturer’s catalog and find that you can use 250 surface feet per minute when you have a ½” (.500”) diameter end mill.
Here’s a quick and easy way to calculate the answer. The formula is:
Multiply 12 times 250. (Answer is 3000.)
Multiply the diameter of the tool times π (pi) ( .5 * 3.1416 = 1.5708 )
Take 1.5708 and divide that into 3000. Your answer should be 1909.85485
The proper RPM is: 1909
Tip!
If you do this a lot, enter this formula into a programmable calculator or an Excel spreadsheet as follows:
In cell A1 type the text “Enter Surface Speed”; in cell A2, type the text “Enter Tool or Part Diameter” and in Cell A4, type the text “Calculated RPM”. In cell B1 type the number 250. In Cell B2, type .500
Cell B4 is going to contain your answer. So type the formula in the cell like this: =(12*b1)/(b2*3.1416) and press the ENTER key.
You can “right mouse click” on cell B4 and click on “Format Cells” and choose the “Number” tab and change the decimal places to “0” so your answer is in even numbers.
That’s it! Save the worksheet and you can easily calculate proper RPM’s for yourself.
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