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Building a 4 Spindle/3 Axis CNC Machine Router

Having recently lost my mother...

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For all woodworkers, the day comes that you are asked to make something that you have either never made before, or, the thought of making it sends chills up your spine.

My day and my never made before project came about a month after my mother passed away.

A former employee came to our shop and asked us if we could make a cremation urn. His father had passed away the day before and he wanted us to make the urn rather than buying one from somewhere else.

The only requirements for the urn were it had to be 220 cubic inches in volume to hold the remains, and he wanted us to make it. Design, wood, finish, these choices were all mine.

I went to work on the urn immediately. I decided that since my turning skills were limited, I would only use the lathe for finish detail that you would normally find on a lathe turned piece. The hollowing of the urn, the rough turning and the carving detail, I would entrust to my design skills, my computer and my CNC machines.

The first step was to design the urn in the computer. After designing the urn, I calculated the inside volume and then scaled the model to ensure that I had at least 220 cubic inches.

The next step was to split the computer model in half and position it in a bounding box. The bounding box was equal in size to the piece of 16/4 maple that I had another person prep while I was working on the model. The position of any 3D model in relation to the stock you are working with, will dictate the success or failure on any CNC project. This is especially true when you have to move the stock from one machine to another.

After completion of the tool paths, it was time to get the wood mounted to the machine and get the code loaded for cutting.

Getting-Started.jpg
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After the stock is positioned and mounted correctly, meaning in relation to the Work Piece Home Position, the program is loaded and the chips start to fly.

Roughing-the-Halves.jpg
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This project is a good example of one that you do not make a test piece for. Of course it was not without problems. You either know it is going to work because of your experience and the knowledge of your machines and your software, or you waste a lot of wood trying to figure it out.

Fortunately, I only had one problem while making the urn. A dull bit was the culprit on this particular project. High spindle speed, 16,000 RPM's combined with long lag times in the direction changes caused burning on the inside walls of the urn. I could have stopped the program, changed the settings and resumed, I simply opted to let the program run since the rough out process had chewed up 20 minutes of machine time already. I also knew the burn marks could be sanded out so I was not concerned.

Finished-Halves.jpg
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A bad joke needs to be inserted at this point so here it goes. "BURN MARKS!!! He's not gonna see em. Especially with the lid on!!!"

Actually, there were many other jokes that day and in the days that followed. Most of them made by me. The jokes were a defense mechanism that kept me from tearing up as every hour spent on this project kept reminding me of my own mother and her recent passing.

Anyway, I will try to bring some civility back to this blog.

After the infamous burn marks were sanded the stock was cut in half. Each half of the urn had four, 1/8 inch holes drilled during the CNC carving. These holes are symmetrically positioned in what would become the bottom rim and the lid of the urn.

Halfs-Ready-for-glue.jpg
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The holes act as registration marks to align the two halves for glue up. 1/8 inch dowels are inserted prior to glue up. When the two halves go together. the inside walls match up to become virtually seamless. You can get an idea of just how good these holes work later on in the blog when the lid comes off.

With the halves glued up and the glue cured, the urn is ready for the outside carving detail on our 10 spindle machine.

Setting-Up-CNC-Carving.jpg
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The majority of the work now takes place on the 4th Axis of the CNC machine. Roughing out the large hollow block of wood is expedited with a 3/4 inch ball mill.

CNC-3-Quarter-Roughing-1.jpg
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In just under 10 minutes, the 3/4 inch ball mill removes enough material to allow for the next bit change. With the removal of most of the wood that does not look like a cremation urn, a cremation urn starts to emerge.

CNC-3-Quarter-Roughing.jpg
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With 1/2 inch ball mill cleaning up the urn, the final shape and the detail of the urn start to come through. The fluting is starting to show and some of the carving detail is emerging. There is still an eighth of an inch of material that needs to be removed with the smaller bits that are still to come.

CNC-Half-Inch-Carving.jpg
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The 1/2 inch ball operation took less then 20 minutes to complete. After completing the 1/2 inch ball mill carving, the urn is finished with a 1/4 inch ball mill. The small prismatic diamond band is completed using a 1/16 inch ball mill.

More to follow...

Updated 10-16-2009 at 10:40 PM by Guy Mathews

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