Page 1 of 3 123 LastLast
Results 1 to 10 of 30

Thread: Cutting Circles

  1. #1

    Cutting Circles

    Cutting Circles, an Illustrated Tutorial by TJ Mobile Audio. Basic yes, but essential.

    Part One: Methods & Tools
    Part Two: Advantages and Disadvantages
    Part Three: End Notes
    Experiments should be repeatable: they should fail the same way every time.

  2. #2
    Part One: Methods & Tools.

    There are several methods for cutting circles. For this tutorial, I will assume your material is wood, a wood product, or a workable plastic. For metals, stone, and other products you will need to adapt the methods presented.

    Method One:
    (This method requires a jig saw, a drill, an accurately drawn circle, and patience.)

    One common method is using a jig saw, and cutting freehand. Before undertaking this method, be sure you have a fresh blade suitable to the material you are cutting, and set the speed of the saw accordingly. In this method, you must have a way to draw accurate circles. A compass like this works fine:



    (Not my image)

    If you don't have a compass, you can use a piece of non-stretchy string. Tie the ends in loops and make sure it is the appropriate length. Drive a nail or screw in the center of your circle, pull the string tight, and use it as a guide for your pencil.

    One final method for getting an accurate circle is to draw a circle in any drawing or photo editing program, print the page, and adhere it to your work surface with spray adhesive, or a glue stick.

    Note: If you have not used a jig saw before, practice on some cheap OSB. Suspend it above the floor (or above your work bench) using spacers and clamps, draw a line with gradual curves and bends, then follow the line as accurately as you can. Once you are comfortable with the saw, move on to circles.

    Additional not: Some people prefer to cut while pushing the saw forward, others prefer to drag the saw toward them. As far as I am concerned, both are safe enough to be considered "correct". Try both blade orientations, and see which one works best for you.

    Now that you have an accurate circle drawn as a guide, drill a hole on the edge of the circle large enough for your jig saw blade to start. Cut slowly, or at least slowly enough that the blade does not jump and break. If you start getting off of your line, make a gradual correction. Too sharp of a turn will put additional stress on the motor and blade.


    Method Two:
    (This method requires a plunge router, or a fixed base router and a drill. It also requires a large drill bit, or hole saw, and store-bought or DIY circle jig.)

    This is the method I almost always use. I will start by explaining DIY circle jigs. You can skip the blue section if you want to use a store-bought circle jig.

    For a DIY circle jig, you need a scrap of plywood or MDF long enough to easily span the largest hole you will ever cut. This is an important safety concern, too small of a jig could allow the router to drop into the hole you just cut, breaking the bit (which is spinning at or near 30,000 RPMs) and shooting tungsten carbide shrapnel toward all parts of your body. Consider yourself warned.

    Name:  CIMG1077.jpg
Views: 218
Size:  95.3 KB

    Using method 3, cut a hole with plenty of clearance for your bit.

    Name:  CIMG1078.jpg
Views: 198
Size:  93.3 KB

    Optionally, you can use a roundover bit or detail sander to smooth the edges. This helps prevent snagging as the jig rotates.

    Name:  CIMG1079.jpg
Views: 205
Size:  93.9 KB

    You will need to remove the router's base plate, and use the same screws to affix your router. Be sure to counter-sink the holes deep enough for the screws to attach securely. Now measure the appropriate distance from the outside edge of the router bit to some point along the jig. This will be the radius (not diameter) of your hole. Drill a small hole there, and insert a dowel, nail, or pin for your pivot point.


    Now that your jig is ready, practice cutting holes on scrap material. (Note, with a fixed base router you will need to pre-drill a starting hole.) Be sure your bit is inserted as far into the collet as it can go, and tighten it securely with a wrench. Refer to the safety warning above if you feel like leaving the bit loose. If your router starts to make excess noise or vibrations, double-check the collet for tightness.

    You can cut a test hole at about 1/16" depth before committing to the final hole. This allows you to measure the actual diameter, and serves as a good guide for drilling the starting hole. It also results in a cleaner finish edge by scoring the workpiece:



    Next, drill the starting hole. Note that this step is not necessary for plunge-base routers:



    Cut clockwise for holes, and counter-clockwise for circular discs (outside edge of mounting rings, for instance). Refer to this dude's book for more details: The New Router Handbook - Google Books

    When you finish the hole, it will leave little un-cut part like this:



    Do not attempt to hold the router free-hand to smooth this over. The best method is to use a Dremel or detail sander:



    Now your hole is done, you can cut as many identical holes as you would like with only minimal thought. Obviously pay attention to router speed, and do not try to force the router through the material. If your cuts are difficult, such as when cutting thick material, do it in multiple passes. Be sure to blow out the sawdust in between passes.

    Method Three:
    (This method requires a powerful drill, and a hole cutting saw of the proper diameter.)

    Insert the hole saw tightly in the drill's chuck, and begin cutting. It can sometimes help to pre-drill a small hole to keep the pilot bit from traveling.
    Last edited by TJ Mobile Audio; 10-24-2010 at 10:27 PM.
    Experiments should be repeatable: they should fail the same way every time.

  3. #3
    Part Two: Advantages and Disadvantages.

    Each method has it's share of advantages and disadvantages. Choose the one that works best for you, but consider the following:

    Method One (jig saw) has probably the lowest equipment cost. You can most likely pick up a brand new jig saw at your local Harbor Freight for under $30, or a used one at a pawn shop for $10 to $20. Buying good blades, and most importantly blades appropriate for your workpiece, will save you a lot of frustration. Method one is the least precise of the three methods, and is not particularly quick, so consequently it requires the most patience and skill. However, I recommend method one if you only plan to cut one hole every few years, and a fairly large one (for a subwoofer, for instance).

    Method Two has the highest equipment cost, but will give you professional results. If you like your power tools, use option two. Once you get your router, you will find a myriad of other uses for it. Cheap routers can be had for $50 to $80, while nicer models can be anywhere up to several hundred dollars. Buy one that suits your needs, no more, no less. Plan ahead, yes, but don't spend so much that you can't afford speakers! Router bits can be pricey as well, so only buy them as you need them.

    Method Three gives professional results as well, but there are a few drawbacks. First, you will need a new hole saw for each circle size. Second, you are limited in hole size by the saws available. Third, much larger than a 3" or 4" hole and even the hardiest drill will be getting a workout. Be sure you only use sharp saws, and take breaks intermittently so the wood does not burn. If you have access to both sides of the workpiece, once the pilot hole is all the way through you may switch sides to ensure a clean edge.
    Last edited by TJ Mobile Audio; 06-20-2011 at 10:38 PM.
    Experiments should be repeatable: they should fail the same way every time.

  4. #4
    Part Three: End Notes (will be edited on an ongoing basis).

    Have fun cutting holes! If you have any suggestions for how I can improve this tutorial, feel free to chime in. Thanks for looking!

    One safety consideration mentioned by MVM, be sure your workpiece is secured so it can't fly away. Remember most routers spin 20k to 30k RPMs, and the edge of your bit exerts considerable force as it cuts. This consideration is increasingly important as the size of your workpiece decreases.

    Jay suggested that the center piece be secured relative to the outside, which can help eliminate the little nub seen in the pictures above. This can be accomplished with brad nails and a brace (or sacrificial piece of plywood). On boxes, this method may require cutting the speaker hole before securing the baffle. In cases where this would make the material on the edge of the baffle too thin to be readily secured, consider tacking a brace on the inside before assembling the box.

    As stated earlier I use a jig that spans the entire hole, so the center drops into the box. I have never had problems with this method but agree with Jay's sentiment.
    Last edited by TJ Mobile Audio; 06-21-2011 at 01:52 PM.
    Experiments should be repeatable: they should fail the same way every time.

  5. #5
    Junior Member
    Join Date
    May 2011
    Location
    Flushing, MI
    Posts
    7
    TJ,

    One suggestion I use...When I am cutting circles (rings specifically) I've found that using a brad nailer to hold things in place works very well.
    I usually pop 2 brads in ring area and a couple in the center piece (that you won't use). Once you make the circle with the router, it eliminates the the little nub. Then I pry it up with a screwdriver or something and cut the excess brad off. You can tap them into the wood and make them flush with a small hammer. I use a 1/4" upspiral bit to make rings with a plunge router.

    Jay

  6. #6
    Senior Member cvjoint's Avatar
    Join Date
    Mar 2011
    Location
    Northern California
    Posts
    801
    Real Name
    George
    Nice! A wealth of information.

  7. #7
    Quote Originally Posted by JayinMI View Post
    TJ,

    One suggestion I use...When I am cutting circles (rings specifically) I've found that using a brad nailer to hold things in place works very well.
    I usually pop 2 brads in ring area and a couple in the center piece (that you won't use). Once you make the circle with the router, it eliminates the the little nub. Then I pry it up with a screwdriver or something and cut the excess brad off. You can tap them into the wood and make them flush with a small hammer. I use a 1/4" upspiral bit to make rings with a plunge router.

    Jay
    Jay, that's a good idea. So are you suggesting to brad nail a small cross piece on the inside side of your baffle before cutting the hole? This would take some forethought on an enclosure but would definitely improve the results. For mission-critical holes, I have occasionally attached the piece being cut to a sacrificial board in a similar manner.

    Mission-critical as in this:

    Name:  CIMG0297.jpg
Views: 854
Size:  86.0 KB
    Experiments should be repeatable: they should fail the same way every time.

  8. #8
    Devil's Advocate Adam_MSS's Avatar
    Join Date
    Aug 2010
    Posts
    1,578
    Real Name
    Adam
    Quote Originally Posted by TJ Mobile Audio View Post
    J For mission-critical holes, I have occasionally attached the piece being cut to a sacrificial board in a similar manner.
    That's what I typically do. Downside for me is that I then have to deal with all the sawdust coming at me as it precludes the use of spiral downcut bit (with pilot hole), but hey, that's what vac systems are for.
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg



  9. #9
    I always used the jigsaw method. Works but as stated not really precise. Just bought a $60 skil router at Walmart and made a circle jig for it last night. Works for the three or so rings I need to cut a year.

  10. #10
    Administrator
    Join Date
    Aug 2010
    Posts
    249
    Something you forgot to mention. Seems like common sense, but I've found common sense is anything but.

    If you're working with a router, the piece of material you're working with MUST be secured so that it can't move. Doesn't move isn't good enough. CAN'T move is what you want. No wobbly base structure either. Stout base structure, with the material you're working with securely fastened to. THEN proceed with routing.

    I've had MDF rings flying around my garage like Tron disks
    Just because you don't understand the data doesn't mean it's not relevant.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •