Planer vs. spiral insert heads -- for planers

      Which provides the best finish--a planer type or a spiral insert knife head? January 16, 2001

Question
What difference in finish can be expected from a planer type head (such as Terminus) versus a spiral insert knife head (such as DML Spiral Pro)?

Forum Responses
A Terminus head uses a series of single knives that go the entire width of the head. The DML Spiral Pro uses small inserts that are staggered in a spiral around the head.

Both heads are excellent for roughing wood. The spiral design is quieter. The carbide used in a spiral head is normally C2 grade, while the Terminus or Great Lakes carbide is C4 grade. The C2 does not last as long as the C4. This means that the C2 inserts must be flipped more often. For a normal 9" width head, the spiral head has about 64 inserts while the straight head has no more than 4 knives. The time to flip inserts differs from 5 minutes to 1 hour.

For most woods, the C4 carbides run longer that the C2. The finish quality for roughing is not much different. The finish quality for a finished surface varies depending on the insert used. The straight design produces a very clean full width cut. The spiral design can use two different inserts. The first insert is straight across and can cause minor lines in the wood surface. The second insert is slightly rounded at the edges. This allows the overlap between the inserts to blend well. If the inserts are installed correctly, there is generally no blend line.

Dave Rankin, forum technical advisor



Carbide or diamond knives start out much duller than HSS. As dulling of HSS occurs, a fresh joint brings back the finish quality. While HSS is capable of crowding 20-26 knife marks into an inch in hardwood because of its keen edge, carbide or diamond is capable of 12 at most. So high speed steel straight knives win every time for finish quality.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
I think it should be noted that if your wood has a lot of knots or dried glue, then the C-2 grade will be more forgiving than the C-4 as it has a more shock resistance with 6% cobalt versus the 3% cobalt found in a typical C-4. However, not all manufacturers’ C-2 and C-4s are the same. I am basing this on the C-2 and C-4 grades that I manufacture.



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: Primary Processing: General

  • KnowledgeBase: Solid Wood Machining

  • KnowledgeBase: Solid Wood Machining: Setup and Maintenance

  • KnowledgeBase: Solid Wood Machining: Tooling

  • KnowledgeBase: Woodworking Miscellaneous

  • KnowledgeBase: Woodworking Miscellaneous: Woodworking

  • KnowledgeBase: Knowledge Base


    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 © 1996-2016 - 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