It is hard to believe that it was only seven years ago I witnessed a CNC router in action for the very first time. I was fascinated and simply had to have one! Although I had been in the creative end of the three dimensional sign business for most of my life I didn't really know what I would do with one - but I just knew it could do fantastic stuff.

Through extensive research I quickly found out that with the relative simplicity of EnRoute, CNC routers were capable of just about anything imaginable. This journal will chronicle that journey to date and continue each week with two or three entries as we continue to explore just what is possible with this wonderful software... -dan

Friday, February 17, 2012

Routing times with textures

A question that often pops up in our email box and at workshops is about routing times. Folks want to know how long it will take to run these kinds of files. The reality is there is no simple answer. Mostly it depends on the router you own.

My new MultiCam is significantly faster than my old router. I've been told this is because of more powerful servo motors and larger spur gears on the drives. I just know it is faster and quieter than my old one by far.

There is also the matter of how the router is set up or tuned for lack of a better word. When a router goes from horizontal travel to vertical travel it literally stops as it changes direction. This effect can be dampened somewhat by changing the driver parameters to have the router cut the corner a teeny bit, meaning it can be taken faster. My MultiCam tech tuned my last router for me and in the process sped it up by half before the quality of the cuts changed enough to notice. I'd love to have him come back and play with my current machine and in the process make the cuts a little smoother and have the machine speed up significantly. I can only imagine the speed we would get out of it then.

Servo motors can be pushed a lot harder than the old stepper motors, meaning these types of machines will cut down on the router times by a whole bunch. But all this costs money too and we have to decide where the wallet stops and the patience kicks in.

The files that take the longest are the ones with the most texture... with the detailed woodgrain files taking the longest.  But they do look mighty fine when they are done. I come from the days when we did things the old way... applying the heavy sandblasting mask, pounding it down, then drawing out the design and patiently hand cutting the frisket, peeling out the parts not needed and then sandblasting the sign. That job is right up there with cleaning an oven (the old fashioned way). I can think of a thousand things I'd rather do.

Now I build the file in my studio, looking up occasionally at the gorgeous views I enjoy. Then I lay down a sheet of Precision Board. start the router and go do something fun.

Today I did a file that was a good one to analyze. It was a detailed sandblasted woodgrain that would push the capabilities to the max. It also has some flat bits so we could see how much the router sped up on those areas. The sign measured 44" tall by 28" wide meaning it was about 8.5 square feet in area. The file was programmed at 300 inches per minute horizontally (X and Y axis) and 150 inches per minute in the Z axis. It had an 80% overlap on the final pass using a 1/8" ball nose bit. The rough pass was done using a 3/8" ball nose bit and an 50% overlap and a 0.10" offset.  I timed both cuts and also shot some stills and video.

Here's a shot of the rough pass in progress. The sole purpose of this pass is to remove material. In doing so it eases strain on the 1/8" tapered ball nose bit I use for the final pass. The roughing pass took 35 minutes from start to finish.

The automatic tool changer changed bits while I was answering my email this morning. I can fairly hear it from my office. The noise pitch of the small bit is slightly higher. This finish file took just under six and a half hours to route from start to finish or 45 minutes per square foot. Not bad in my book, and certainly a whole lot after than doing it by hand!

Here's the video of the finish pass. I programmed this file at 300 per minute but in the one minute of the video the router only travels 108 inches - one third of the speed I actually programmed it.  The reason is the texture, slowing down the forward speed with the up and down movement. If you watch the movie all the way through you will notice the router speed up significantly on the bottom triangle and on the top part of the sign - both smooth areas. Obviously routing times will increase as detail is increased. 

With texture being so important to the work we do in our shop I have to calculate these increased routing times into the project budget.

The thing to remember however is not to solely determine the cost of the project by routing times. If you do you are selling yourself short - especially if you have a fast router. If my hourly rate is the same as someone else's with a slower router and I price by time and materials alone, then the sign becomes cheaper - simply because I can do it faster. Personally I'd like to be rewarded for investing in a faster machine and stick the extra cash in my pocket!