by George Bulliss
Having a CNC mill and a CAD/CAM system allows the user to cut a wide variety of shapes that would be difficult, if not impossible, on manual equipment. If you can draw it or import it into your CAM system, chances are you can create a toolpath. But can you actually cut the part?
The odd shapes that can be created in CNC can get you into trouble when working on parts that require multiple setups. After cutting those pretty curves on the top of your part, you may be stumped when it comes to securing the workpiece for operations on other sides. Standard workholding methods may not work when faced with complex curves.
One answer to this problem that I have used many times in the past has been double-sided tape and an appropriately-shaped fixture. There are many brands of tape out there; some are better than others. I always used the standard “masking tape” variety; others have had good luck with the thicker carpet tapes.
In order for the tape to work, the surfaces must be absolutely clean. Use a solvent, such as alcohol, and make sure it is completely removed before applying the tape. The solvent can also be used to loosen the part for removal.
The surfaces of the fixture that will be in contact with the taped area of the part must match perfectly. The best way to ensure that they do is to use the same surfaces for writing the fixture cutter path as you did for cutting the part. Simply rotate the geometry and cut the “back side” of the appropriate surfaces. Make sure to offset the cuts by the thickness of the tape (.007″ for the tape I used). This offset can be done with CAM system commands or by lying about the cutter size and length when programming and setting the tool. Make sure to clear any corners in the fixture, and you should have a perfect fitting nest to tape your part to.
You will be surprised by how strong the tape is when you take the time to do the correct set up. I have cut numerous plastic and aluminum parts this way and even a few steel parts.
Please do us a tremendous favor and forward this e-mail on to your machining friends!
Are you not a subscriber to DIGITAL MACHINIST? Visit us at www.digitalmachinist.net and request a no-obligation issue, or call and request it at 1-800-447-7367. Tell them you received an e-mail from a friend!
And don’t forget to check out Digital Machinist’s page on Facebook and our Twitter feed!
Your friend thinks you’ll enjoy DM, or you wouldn’t have this e-mail!
We hope you enjoyed this e-mail tip, brought to you by your friends at Digital Machinist.
Get Involved!
Do you enjoy our e-mail tips? Has one of them ever “knocked something loose” in your head? Your tip could be a future e-mail blast from your favorite magazine. Just send your tips to george.bulliss@VPDemandCreation.com. If we use your tip, we will extend your subscription by an issue. We like to see 200 to 300 words, plus an image, if available. Thanks!
We hope you enjoyed this e-mail tip, brought to you by your friends at Digital Machinist, dedicated to precision metalworking.