V-Grooving for a Miter-Fold on a CNC

      Cutting a V-groove with a CNC's rotary bit has inherent limitations because of bit speed. But there are solutions. March 25, 2007

I am trying to make open faced (5 sided) mitre folded boxes. The components are Baltic birch 3/4" ply. My test run worked fine with MDF, but when I run the Baltic birch, the mitres are no longer 45, but around 46 degrees, and the cut edge is kind of lumpy. The edges are also coming out with some excess fuzz, making it so that I have to go and carefully sand the outside edges before glue up. Can anyone offer advice? My MDF run was perfect. My Baltic birch BB/BB is a disaster.

Forum Responses
(CNC Forum)
From contributor D:
Don't mean to state the obvious, but would it be because the plywood is cutting rough versus the MDF cutting smooth? I would expect the plies of the Baltic to be inconsistently cut - this is typical when you use a router bit to cut it. The fibers sort of push out of the way rather than cut clean. When you fold it up, the cross grain is probably holding the joint open. Are you using a vertical router to cut the joint or a horizontal blade? Perhaps the tool people can suggest the best way to attempt this? I wouldn't expect it to work very well in a plywood.

From contributor P:
It sounds like the main problem you have is that the material is not being held down completely flat to the spoil board and there is movement.

From the original questioner:
Thank you for your responses. Am I wrong to think that this is a pretty routine job? Has anyone successfully made nice mitre folds with this material? By the way, the material is Baltic birch b/bb 3/4". I am thinking I should CNC the panels and then cut the mitres on a panel saw.

From contributor U:
If you consider the geometry of a V-bit which is used for V-grooving on a CNC machine, there is one major drawback - the tip of the bit has absolutely no rim speed. As rim speed is critical for quality machining, you might say that the tip of the V-bit is literally bludgeoning the material. The optimum method for V-grooving with a CNC machine is to use a single sided right angle aggregate head with a V-grooving cutterhead. We (Benz Inc.) can offer you a specially designed head which is equipped with a gear reduction system. This allows your operator to program the motor spindle to run at 9,000 RPM to 10,000 RPM, which is necessary in order to achieve maximum torque and horse power from your spindle motor with an output speed to the tool of right around 5,000 RPM to 6,000 RPM. This is typically the ideal speed for the V-grooving cutterhead.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Computerization

  • KnowledgeBase: Computerization: CNC Machinery and Techniques

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2019 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article