Making Bolt Hole Chamfers with an End Mill on your CNC.

I spent the last 10 years using CNCs without a tool changer. Whenever the job required a bit change normally I thought about how I might be able to do the job using just one bit and some creative use of the CNC software I was using. This is one example.

Projects that needed perimeter or internal chamfers were done most efficiently with a bit change to a V bit.  I have a project that is put together with flat head bolts. The need to chamfer the bolt holes could have been done using a drill press after the CNC was done. Figuring out how to chamfer a hole with the same end mill I used for all the other cuts turned a 2 process job into one CNC  job with no bit changes. 

Vectric.com's Aspire and VCarve programs have a fluting toolpath.  Fluting takes a vector and ramps the bit down or down then up with the bit being centered on the vector. A circular array of 9 (or more) short vectors centered over the bolt hole, using a bit no larger than the diameter of the hole, can effectively chamfer the perimeter of the hole from the bolt head diameter down to the hole edge.  Using a small bit (1/8" or 1/16") may require a greater number of vectors to result in a relatively smooth chamfered edge. The chamfers in this image were made with a 1/4" diameter end mill. 

2 x 2 Hole Array

The slope of the chamfer and the diameter can be easily changed.  Aspire/VCarve also have a circular array layout tool that will use one vector that spans the hole and make any number you specify of rotated copies around the same center. Using an odd number of vectors results in a circle of lines with alternating start points.  Alternating the start points reduces the travel time needed move to each successive vector.  

Vectors Used

The center of the bit used is what follows the line. The depth the bit will slope down is set when creating the fluting toolpath.  In the image above the shaded area is a shadow of the area the 1/4" straight bit travelled over.  The short vectors used are shown in red. The center circle was the hole for the 1/4" bolt shaft. Depth of the fluting chamfer cuts was 1/8".

I made the vectors for one bolt hole, then simply copied them to all the other bolt locations. 

You can find downloadable  .CRV3d and .CRV file of the sample above on Vectric's user forum: Vectric.com

Questions or comments are encouraged!

4D

 

CNC cut Radiused Corners for Furniture Projects

I would occasionally have students design a cabinet box with radiused corners.  Before we had CNCs to use we might run the corner board across the table saw blade at an angle to cut the inside cove. Optionally we might use a cove bit or large ball end bit on the router table. Follow with a few angled table saw slices to remove much of the outside surface.  Then plane/scrape/sand away to smooth out the outer surface of the corner. 

Using a 3-axis CNC and Aspire software, and the job set up as a 2-sided job, both the inside and outside faces of the corner curve can be cut. 

The goal is to remove the red shaded areas from the rectangular starting block. 

Top and Bottom cut Areas

As the whole top area of both sides is being cut, an extra inch was added on both ends for a place to clamp it down.  The moulding toolpath in Aspire software using vector drawings of the section views makes easy work of removing the waste areas to leave a perfect curved corner. The 1" ends can then be trimmed off. 

Inside Surface

Outside Surface

Care must be taken to align the board when flipping to do the second side. The material used and grain direction of the board should also be considered when cutting the adjoining flat side of the cabinet box. Plywood could be used with corners with grain running as shown in the renders above.  The grain direction of hardwood sides must match the grain direction of the corners. Front to back for the examples shown, Use Biscuits or Dominos to join the curved corners to the flat sides. Cutting a slot for a spline between adjacent parts could also work. 

This same strategy can be used to make corner sections that aren't 90 degree. I had a student from another class request how to make radiused corners to attach angled wings for a chair seat.   With the potential load on the wings of the chair seat being fairly great he eventually attached them with metal brackets.  Wood corners might split in such cases. 

A hexagon box with radiused corner would be a great application for CNC cut corners. Just draw up the inside and outside vectors of a 120 degree corner section. A few other drafting tricks might be needed.  :)

4D

Comments or Questions welcomed and appreciated!

  

Using a CNC to solve unusual woodworking challenges.

Do a search for what a 3-axis CNC is capable of, and generally you'll find people cutting flat work on their CNC bed. Some have a radial 4th axis to do simple or complex cylindrically confined projects. Most come with limits describing the width, length, and vertical cutting range projects should be confined to.  Many CNCs are capable of solving far more woodworking challenges, but you'll need to literally think outside that cutting limits box.

In 2004 or so purchase my own 3-axis CNC Shark. I cut flat parts for student furniture designs in my garage for the next few years. Bumping into the area limits of this small CNC, I purchase a larger Probotix CNC for my home shop. A desire to cut tenons on the ends of long stretchers led me to open up one end of my Probotix CNC for vertical access down to the floor. Once opened up, I realized with some jigging I could clamp parts at angles other than 90 degrees. Four or five revisions/updates of my compound angle clamping jig have led me to what I know can be done today.  What a CNC can do doesn't stop at the spoil board plane. 

Opportunities arise when you think about using more than just the flat bed of a CNC to clamp your parts to.   Many come with 2 motors pushing/pulling the gantry, which may mean there is nothing running under the bed.  Once you consider using the space under the bed, the next step is to make access to it. In my case I initially left open the front 1/4 of my CNC's bed, and mounted the CNC on an open frame with no top on it.  I now have access to all the vertical space between the bed of my CNC and the floor.

With access, the next step is to come up with a way to clamp parts under/inside the frame to hold them rigidly where the CNC can reach the areas that need to be cut.  

If you clamp your parts or jigs to one of the frame rails, make sure the rails are securely mounted and can't be rotated or racked or bent or flexed when under load. I made a jig that clamps to the front rail as I knew it couldn't rotate the way the frame is assembled: My Jig 

Bridges that span the frame, clamping jigs, accessory rails, and even the frame rails themselves can contribute to the potential woodworking challenges you can solve with a CNC. Bridge support.

T-slots, either in track strips you can buy or the frame member extrusions themselves come in very handy for attaching jigs/bridges/cross rails to.  One example is my bridges that screw into t-nuts in the frame rails and themselves have t-track down their middle to use for clamps that hold your project boards down. Another is my advanced compound angle clamping jig that bolts into the inner face and top slots of the front frame rail.  Sections of t-track could be installed on such a jig, but my current version has holes for c-clamps to hold project boards and reference edges/stops to. 

It is below the bed where opportunities for creative CNC cut solutions live.  To take advantage you'll need creative jigging to clamp your project parts down there.

4D

Comments and questions encouraged and appreciated!