CNC

You are not logged in. [ Login ] Why log in
(NOTE: Login is not required to post)

Design for CNC - tips for 18mm Baltic Birch

5/9/20       
Jeff Member

I'm designing some furniture that will be cut on an CNC machine out of 18mm Baltic birch plywood. After I get a pre-production prototype I'm happy with I plan to kickstart it with a minimum initial batch of 50.
I've already had one prototype made on a CNC machine, and I learned a lot. But I have questions for the next prototype.
I plan to design it to be assembled by gluing pieces face to face with 5/16" diameter wood dowel pins, 1” long, giving me a 36mm thick slab with features on both sides. This worked well on the first prototype. That said, I only used the pins for location, and screwed the parts together.

Question 1: Will I need to chamfer or otherwise relieve the edges of the holes in case the glue swells the grain around the hole?

Question 2: How accurate can I expect things to be on the Z axis? I thought +/- .010” was reasonable… but this shop was way off. It worked for the prototype, but it wouldn’t work on production runs. Am I asking too much of CNC? I don’t think they had a vacuum hold down system.

Question 3: Due to the number of holes (3 different sizes), I know I will need to send this to a shop with a tool changer. Should I strive to make sure the majority of the non-hole features can be cut by a 3/8” bit instead of a 1/4” bit?

Question 4: I’m plan to do my own nesting, primarily to make sure I can keep my materials cost down. If I am cutting two parts next to each other, I assume I should keep the parts farther than one tool diameter apart so you don’t cut both edges (one climb, one conventional cut) at the same time? So that both parts can be cut climb or conventional as fits the bit / material?

Question 5: Any face to face joining techniques I should look at other than dowel pins? I am worried about glue squeeze out.

Question 6: Other than making parts self-align and making it easy to assemble by keeping part count and confusion down, what else can I do to make this cheaper and easier to manufacture? I’m planning on a clear polyurethane finish.

Thanks for any help you can give!

-Jeff

5/10/20       #2: Design for CNC - tips for 18mm Balt ...
Tom Gardiner

My thoughts are:
1. No need to chamber the dowel holes more on that later.
2. I strongly recommend finding a shop with vacuum holding. You cannot depend on Baltic birch to lie flat on the table otherwise and even sometimes with vacuum it will have enough warp to lift off the table. Another slow method would be to use the cnc to drill pilot holes in the the sheet to hold down.
Once you have reliable holding the cnc will have a Z axis accuracy of < .005" easily.
3. A tool changer will be much faster as the drill routine is quicker per hole, however, a 1/4" bit can route holes of any size larger by using a spiral plunge cut. Bet on 2-3 seconds per hole.
Using a down shear will reduce the fur around the holes but can cause excessive heat build and possibly fires with the chips being forced down into the holes.
Tool size is a variable that will determine the feed speed of the router. Each router can handle feeds and depth of cut differently depending on the rigidity and power of the machine. Talk with the machine operator to find out what his/her machine can handle. My router is a light industrial 4 x 8 and is happy routing 18 mm BB in a single pass with a 5/16" compression bit. A 1/4" bit would take two passes.
4. By all means do your own nesting. My software doesn't offer the option of using a common line to cut parts. I offset my parts by ~.010" when nesting. You may want to include a last pass tolerance into the toolpath to achieve the best finish so you will have to allow for it in nesting. Once again work with the cnc operator to get the best results for that machine and the operator's preferences. I know I am more likely to give a favourable quote to a job when I am confident in the way it will run ( ie it's the way I have cut before)
5. Glue squeeze out can be controlled by how much and how glue is applied. A random bead of glue squeezed liberally around is a recipe for messy glue ups and patches of unglued material. I have a hopper glue roller to apply a consistent film to the entire surface but a paint roller will be sufficient for little investment. If you are screwing together your parts I suggest you drill clearance holes for the screws with the cnc. I like to see well placed screws if they must be used.
6. Sanding and finishing will likely be the largest labour cost in any furniture job done with plywood. Choose the best ply you can. All BB is not created equally - some have large voids that show in the edges. Top sheet sanding can be brutally bad and requires heavy sanding to be acceptable for a finish. Take the time to test the cnc footpaths for best finish possible. Don't be going after the fastest run times only to face hours of edge sanding.
Birch plywood furniture looks great on paper /screen but the proof of its lasting appeal will be in it's finishing details. How does the edge feel? Is the top lustrous or show sanding marks? If you must see screws are they part of the appeal or do the distract or seem to be randomly placed and driven poorly.
Make use of the cnc's ability to do repeatable tasks quickly. Don't think that you can do an operation later faster /better.
Surface sand your material before cnc at least up to the second last grit. Even better find a shop with a wide belt sander.
Spray the finish! It will be tougher, look better and take a tenth of the time.
That is it for now.
Tom

5/10/20       #4: Design for CNC - tips for 18mm Balt ...
Jeff Member

Thanks Tom!

All the parts will be cut "good side down" and then get glued together to show the good sides on the outside.

-Jeff

5/12/20       #5: Design for CNC - tips for 18mm Balt ...
Dropout Member

90% of what we cut is baltic birch.

Any design that needs a tolerance of 0.010 Z using wood needs a rethink - too many factors involved.

The quickest way to the best finish is a 1/2 compression spiral chipbreaker as a 0.020 oversize first pass and a 1/2 downspiral finish pass. We run the first at 750 or 800 IPM and the finish (if needed) at 500 to 600.

I leave 13mm between parts on a nest.

You don't mention the size of your parts, but we do many small parts. We cut these 16.5mm deep and then separate on a trim router. We use an upspiral flush trim bit for best edge finish.

Nesting yourself sounds like a good idea, but if the shop you deal with has decent nesting software don't waste your time. They can do it better and quicker than you can.

Hourly rate is a bad way to have people quote. I charge $140.00 per hour and am usually lowest cost per part when compared to people in the $100.00 per hour range.

Where I am 5X5 BB is less cost per square foot than 4X8 so look for 5X10 table. Load/unload and tool change time divided by 50 square feet instead of 32. Over time it's a big deal.

5/13/20       #6: Design for CNC - tips for 18mm Balt ...
John Meachen Member

If you are using full sheets it might be more efficient to use vacuum bagging to bond them together unless you have a press.All you need is a plastic sheet and a flat surface.A piece of breather cloth is handy too and the stack can be as many sheets as you like.Even clamping pressure and much greater force to minimise the glue line thickness and glue usage.You can use masking tape to align the edges or 2 small pins per sheet.I have found online nesting available for rectangular shapes and you set the parameters to match your needs.

5/20/20       #8: Design for CNC - tips for 18mm Balt ...
Jamie

Only thing I can contribute to what others have said is to consider gluing your sheet goods together before the cnc. We do this on a regular basis, just apply glue to both pieces, align them and place them in the press. CNC time will be slightly decreased over-all due to only handling half the number of parts, even though the actual spindle run time may be exactly the same. I also find that two pieces glued together seem to stay a little flatter on the vacuum table than a single sheet.

6/1/20       #9: Design for CNC - tips for 18mm Balt ...
Jeff Member

Thanks everyone!


Post a Response
  • Notify me of responses to this thread
  • Subscribe to email updates on this Forum
  • To receive email notification of additions to this forum thread,
    enter your name and email address, and then click the
    "Keep Me Posted" button below.

    Please Note: If you have posted a message or response,
    do not submit this request ... you are already signed up
    to receive notification!

    Your Name:
    E-Mail Address:
    Enter the correct numbers into the field below:
     

    Date of your Birth:



    Return to top of page

    Buy & Sell Exchanges | Forums | Galleries | Site Map

    FORUM GUIDELINES: Please review the guidelines below before posting at WOODWEB's Interactive Message Boards (return to top)

  • WOODWEB is a professional industrial woodworking site. Hobbyist and homeowner woodworking questions are inappropriate.
  • Messages should be kept reasonably short and on topic, relating to the focus of the forum. Responses should relate to the original question.
  • A valid email return address must be included with each message.
  • Advertising is inappropriate. The only exceptions are the Classified Ads Exchange, Machinery Exchange, Lumber Exchange, and Job Opportunities and Services Exchange. When posting listings in these areas, review the posting instructions carefully.
  • Subject lines may be edited for length and clarity.
  • "Cross posting" is not permitted. Choose the best forum for your question, and post your question at one forum only.
  • Messages requesting private responses will be removed - Forums are designed to provide information and assistance for all of our visitors. Private response requests are appropriate at WOODWEB's Exchanges and Job Opportunities and Services.
  • Messages that accuse businesses or individuals of alleged negative actions or behavior are inappropriate since WOODWEB is unable to verify or substantiate the claims.
  • Posts with the intent of soliciting answers to surveys are not appropriate. Contact WOODWEB for more information on initiating a survey.
  • Excessive forum participation by an individual upsets the balance of a healthy forum atmosphere. Individuals who excessively post responses containing marginal content will be considered repeat forum abusers.
  • Responses that initiate or support inappropriate and off-topic discussion of general politics detract from the professional woodworking focus of WOODWEB, and will be removed.
  • Participants are encouraged to use their real name when posting. Intentionally using another persons name is prohibited, and posts of this nature will be removed at WOODWEB's discretion.
  • Comments, questions, or criticisms regarding Forum policies should be directed to WOODWEB's Systems Administrator
    (return to top).

    Carefully review your message before clicking on the "Send Message" button - you will not be able to revise the message once it has been sent.

    You will be notified of responses to the message(s) you posted via email. Be sure to enter your email address correctly.

    WOODWEB's forums are a highly regarded resource for professional woodworkers. Messages and responses that are crafted in a professional and civil manner strengthen this resource. Messages that do not reflect a professional tone reduce the value of our forums.

    Messages are inappropriate when their content: is deemed libelous in nature or is based on rumor, fails to meet basic standards of decorum, contains blatant advertising or inappropriate emphasis on self promotion (return to top).

    Libel:   Posts which defame an individual or organization, or employ a tone which can be viewed as malicious in nature. Words, pictures, or cartoons which expose a person or organization to public hatred, shame, disgrace, or ridicule, or induce an ill opinion of a person or organization, are libelous.

    Improper Decorum:   Posts which are profane, inciting, disrespectful or uncivil in tone, or maliciously worded. This also includes the venting of unsubstantiated opinions. Such messages do little to illuminate a given topic, and often have the opposite effect. Constructive criticism is acceptable (return to top).

    Advertising:   The purpose of WOODWEB Forums is to provide answers, not an advertising venue. Companies participating in a Forum discussion should provide specific answers to posted questions. WOODWEB suggests that businesses include an appropriately crafted signature in order to identify their company. A well meaning post that seems to be on-topic but contains a product reference may do your business more harm than good in the Forum environment. Forum users may perceive your references to specific products as unsolicited advertising (spam) and consciously avoid your web site or services. A well-crafted signature is an appropriate way to advertise your services that will not offend potential customers. Signatures should be limited to 4-6 lines, and may contain information that identifies the type of business you're in, your URL and email address (return to top).

    Repeated Forum Abuse: Forum participants who repeatedly fail to follow WOODWEB's Forum Guidelines may encounter difficulty when attempting to post messages.

    There are often situations when the original message asks for opinions: "What is the best widget for my type of shop?". To a certain extent, the person posting the message is responsible for including specific questions within the message. An open ended question (like the one above) invites responses that may read as sales pitches. WOODWEB suggests that companies responding to such a question provide detailed and substantive replies rather than responses that read as a one-sided product promotion. It has been WOODWEB's experience that substantive responses are held in higher regard by our readers (return to top).

    The staff of WOODWEB assume no responsibility for the accuracy, content, or outcome of any posting transmitted at WOODWEB's Message Boards. Participants should undertake the use of machinery, materials and methods discussed at WOODWEB's Message Boards after considerate evaluation, and at their own risk. WOODWEB reserves the right to delete any messages it deems inappropriate. (return to top)


  • Forum Posting Help
    Your Name The name you enter in this field will be the name that appears with your post or response (return to form).
    Your Website Personal or business website links must point to the author's website. Inappropriate links will be removed without notice, and at WOODWEB's sole discretion. WOODWEB reserves the right to delete any messages with links it deems inappropriate. (return to form)
    E-Mail Address Your e-mail address will not be publicly viewable. Forum participants will be able to contact you using a contact link (included with your post) that is substituted for your actual address. You must include a valid email address in this field. (return to form)
    Subject Subject may be edited for length and clarity. Subject lines should provide an indication of the content of your post. (return to form)
    Thread Related Link and Image Guidelines Thread Related Links posted at WOODWEB's Forums and Exchanges should point to locations that provide supporting information for the topic being discussed in the current message thread. The purpose of WOODWEB Forums is to provide answers, not to serve as an advertising venue. A Thread Related Link that directs visitors to an area with inappropriate content will be removed. WOODWEB reserves the right to delete any messages with links or images it deems inappropriate. (return to form)
    Thread Related File Uploads Thread Related Files posted at WOODWEB's Forums and Exchanges should provide supporting information for the topic being discussed in the current message thread. Video Files: acceptable video formats are: .MOV .AVI .WMV .MPEG .MPG .MP4 (Image Upload Tips)   If you encounter any difficulty when uploading video files, E-mail WOODWEB for assistance. The purpose of WOODWEB Forums is to provide answers, not to serve as an advertising venue. A Thread Related File that contains inappropriate content will be removed, and uploaded files that are not directly related to the message thread will be removed. WOODWEB reserves the right to delete any messages with links, files, or images it deems inappropriate. (return to form)
    Onsrud Cutter Vortex Tool Company T-Tool USA
    Sponsors
    • W. Moore Profiles, Ltd.
      Supplying Knives and Cutters to the Woodworking Industry - Standard and Custom Profiles Available
    • T-Tool USA LLC
      Quality Tool-Holders, Tooling Supplies and Accessories for Numerous Cutting and Grinding Applications
    • Industrial CNC
      Affordable, Easy, Industrial Grade CNC Routers for Woodworking and Cabinetmaking - Free Lifetime Support
    • American National Knife
      Manufacturer of HSS and Carbide Tipped Woodworking Knife Sets for Planers, Jointers, Molders, Shapers
    • Carter Products
      Band Saw Guides, Blades, Wheels, Tires, Line Lasers and 2D Projectors, Wide Belt Sanding Accessories, Vacuum Holding Systems and More
    • Thermwood Corporation
      Computer Numerical Control (CNC) Routers and Accessories
    • MachineryMax
      New and Used Machinery for the Professional Woodworker
    • Country Saw & Knife
      Complete Sharpening Services for Wood and Metal Saw Blades, Jointer Knives, and Bandsaw Blades
    • Rangate
      Woodworking Machinery, Supplies and Knowledge
    • Tooling on the Web
      Tooling and Tooling Accessories - Free Re-Sharpening for Qualifying Tools
    • MARTIN Woodworking Machines Corp.
      Quality Woodworking Machinery Engineered and Manufactured in Germany
    • Shop Gear Inc.
      Distributor of Co-matic Power Feeders, Le-matic Portable Edgebanders, and Supplier of Woodworking Machinery, Tooling and Accessories in North America
    • Weinig Group-USA
      Wood Moulders and Knife Grinding Equipment

    Become a Sponsor today!