3/8" Versus 1/2" Compression Bits

      The smaller-diameter bits reduce waste, but may deflect in thick material. September 30, 2010

I've been using a 1/2" compression bit for outline cutting on mostly 3/4" pine core 2-sided melamine. Recently I ran a 3/8" compression bit and liked the results. What are the advantages and disadvantages of using a 3/8" compression bit versus a 1/2" compression bit?

Forum Responses
(CNC Forum)
From contributor H:
The disadvantage I've encountered when cutting size-critical slots is that the 3/8" bit will deflect when it enters and exits the board, forming a small nib there. A rule of thumb I found is that the diameter of the tool should not be less than half of the depth of cut. A 3/8" tool is on the borderline for a 3/4" cut. If you're producing acceptable cuts with 3/8" tools, then there's no disadvantage that I know of.

From Brian Personett, forum technical advisor:
I started out using 1/2", but switched to 3/8" for cutting 3/4 and even 1" material years ago and have never looked back.

From contributor G:
Less dust with the 3/8.

From contributor M:

25% less dust.

25% less waste... The difference in normally nested sheets of casework on 4 by 8 melamine can amount to more than one full sheet of material per lift, on average. That is a real yield, and it is not in the dust collector.

25% less expensive tool. See Vortex.com for a typical example.


I have found that 1/2 inch tools last a little longer, but not 25% longer.

My experience is that 1/2 inch tools cut a little nicer as they begin to get dull in VC plywood, perhaps due to rake angles, perhaps for other reasons. The difference is not huge here either.

Yes, there is less deflection, but it is very important to distinguish bit deflection from machine deflection. Often these two effects get confused. You may find that machine deflection occurs in both cases, negating much of a difference. It is an unusual machine that has no deflection at all.

Larger and heavier ones usually have less machine deflection; small, light machines have more.

Contributor H's method is best. Try the 3/8 and see if it is a problem, then try the 1/2. If the problem goes away, it is bit; if not, it is machine.

You can usually run 1/2 inch tools a little faster due to a larger gullet that takes a larger chip. Part of this difference, though, is negated by cutting a larger kerf and thus having more chip to remove. My experience is that 1/2 inch bits can run faster by a few percent, all other factors being equal, though a strict interpretation of chip loads often says 1/2 inch should run slower.

For all of these reasons, I normally run 3/8 for both compression and mortise compression. I do use a 1/2 inch corrugated hogging bit for rough cutting MDF and plywood.

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 © 1996-2016 - 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