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Date: 08/15/00 at 11:17 AM
Posted by: Mazak George
E-mail: MazakGeorge@aol.com
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In Reply to: Tapping posted by Duane S. on 08/14/00 at 7:26 AM:
My name is George and I use to be an Applications Engineer for Mazak Machine Tools and Mori Seiki. Currently I am the District Sales Manager for the Inland Empire in Southern California.
Tapping has always been tedious. There are so many factors to consider.
First is what type of hole are you tapping. Is it a blind hole? Is it a through hole? How deep do you need to tap? What type of material are you tapping?
All these questions will affect the type of tap you use. There are many types of taps. Some taps pull the chips out of the hole others push them through. When you have answered the questions above then you can pick the appropriate tap form your local vendor.
Once you have addressed the part then you need to address the machine.
Does the machine have rigid tapping capabilities? I assume in this case your older machine does not. I recommend you use a tension and compression holder. I have used all types. They all work well provided you use them in the right application.
There are different tension and compression holders for different ranges of taps. If you use to large of a holder then the tension and compression ratio might be to stiff for the application that you have. This is one of the keys!
Most people try to purchase the one magic tool that does all applications. Some times this works, but most often you end up sacrificing. My suggestion is to use the holder that your tap size falls in the middle of the holder’s range.
The next important factor is the pre-drilled hole. What size do you drill the hole? There are many charts for finding out what size of drill should be used for pre-drilling a tapped hole. In considering this you must keep in mind the type of material you are drilling. Depending on the material, some holes shrink after they are drilled. If this occurs then the tap will have a hard time cutting the threads. In this situation I suggest you drill a bit oversized. Sometimes a couple of thousands does the trick.
Also the speed and feed that you used to drill the hole can make a difference. Some materials heat treat when drilled to fast or slow.
Coolant also effects the tapping process. If your coolant does not have the correct lubricity then there will be more friction when cutting the threads. My recommendation when tapping a troubled hole is to use tapping oil. Just place an optional stop in your program and swab the tap and the hole with oil. This normally gets you out of the jam.
Another solution can be the dwell that you programmed. In most cases the spindle is able to reverse in synchronization with the servomotors driving your axes. The reason you program a dwell at the end of the feed to depth is to allow the tension and compression mechanism in the holder to compensate for error in the lag time of the spindle and servomotors. If you have problems, increase the dwell time before you reverse the spindle.
I hope I have provided some clues to your mystery.
Sincerely,
George Pineda
District Sales Manager
Mazak Corporation