I am very new to CNC work. I have a number of wood blocks that I would like to use but they are a little irregular in size, definitely not perfect rectangular boxes. I would like to mill them to be a standard size so I can do some double sided machining.
Am I correct that the work flow in the CAM software would be something like:
Designate the model as the size block I want then…
Make the stock size in the program a little larger in all dimensions than the stock actually is
Run a roughing tool path
I understand this may be limited by the shaft length of the mill for machining flat sides that are longer than about an inch.
As long as the material is bigger then the finished work you could just draw a rectangle and cut them to size before machining the project. Depending on depth just do an outside contour and use the center as your origin. I like to use bottom of material because I dont cut through to the spoilboard or leave an onion skin. After getting the material to size then you can machine your double sided project. Most people seem to be using dowels to register the projects for the double sided machining. By having the project cut down to size it will be easier to register your material for the double sided machining. It seems that registration is very important in double sided machining.
Depending on the depth of your material you may need to get some longer bits to machine through the material. Cadance Manufacturing makes a 1/4" that can cut up to 2" thick. They relive the shank above the cutting flutes to allow you to cut deeper contours. If your material is 3/4" most of the 1/4" bits can handle that. One caution about longer bits. Longer bits exagerate router/spindle run out. So seat your bits deeper but not all the way up. When you start the router you should be able to judge if the router/spindle sounds different and you might need to reseat and retighten a long bit. Also longer bits tend to vibrate more. Pause the job periodically and check the tightness of the collet to keep the bit from slipping. I have a 4" OAL long 1/4" bit and I can hear it when starting if the bit is not right. Will Adams always recommends making your slot bigger then the bit diameter to make it easier for the operation. Cutting a 1/4" deep groove deeply causes a lot of stress on the bit and material so you could offset your outer perimeter about 3/8" around and cut that instead of just a 1/4" wide contour/pocket.
If your material is rough cut try surfacing one side first and shim it as necessary to take off the least amount of material. Then flip it over and surface the other side. You need your material to be a uniform thickness. I use wedges and hot glue to hold irregular shaped material. A little denatured aclohol will make the hot glue soft and you can take it off the material and/or spoilboard. Then after getting both sides flat you can find the approximate center and draw a rectangle to cut out before machining the project.
Even simpler is cutting the material size on a table saw if you have one. But you can do it on the CNC if that is your only option. Then you can surface it by making a rectangle bigger than the material to get all of the surface flat. I use a piece of plywood with a piece of t-track screwed down and run that through the table saw to get a zero clearance edge. Then clamp your material to that and get one straight edge. Then you can use the fence to get a second parallel side. Then just use a miter gauge to get the two other sides square to the first sides.
Thanks so much everyone. As I read and learn more these answers become more and more useful. I’d say you’ve even anticipated several of my future concerns.