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Unread 05-12-2017, 04:34 AM
RoboChair's Avatar
RoboChair RoboChair is offline
He who fixes with hammers #tsimfd
AKA: Devin Castellucci
FRC #1678 (Citrus Circuits and 5458 Digital Minds)
Team Role: Mentor
 
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Rookie Year: 2005
Location: Davis, CA
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CNC Routers for FRC Robotics

This post isn't going to machine itself. Let's begin.

The topic of this thread is CNC routers and all associated topic content. The intent of this thread is to create a highly comprehensive discussion about CNC routers and how teams use and abuse them. This is to provide an easy reference to any and all interested teams who want to do the same.

Let me start this off with saying that a CNC router is one of the most powerful tools for FRC teams that money can buy. If I had to sell all of my equipment except for one machine, that one machine would be our CNC router. Every team would benefit from a CNC router. Regardless of what you currently have (even if you have a shop full of VMC’s), CNC routers will still add some serious productivity boosts. This is my personal opinion and it is fine if yours differs from mine.

Why is a CNC router such a powerful FRC tool?
--Rapid prototyping with a 4'x4' bed to work with allows quick development of mechanisms with very accurate dimensions that can be changed and redone quickly.
--Machine any square or rectangular tubing reliably, repeatedly, and rapidly. Includes bearing holes and rivet patterns.
--Fantastically easy sheet machining in polycarbonate.
--Easy machining of sheet aluminum(with appropriate CNC) for parts such as the following, bellypans(lightened), gussets, thin gearbox plates, and sent sheet metal component flat patterns.
--Machining of plate aluminum(3/16"+) is not hard at all(with the right machine set up) allowing you to make the following parts, drivetrain side plates, drivetrain gearboxes and similar, chain sprockets, certain types of gears, and much more.

Every CNC router is a different machine and behaves differently than any other model. Unfortunately this means that it can be very hard to find good advice about feeds and speeds for a given machine without tracking down someone using a similar setup and tooling. Unfortunately this also mean that the only machine I can give that kind of advice for is the VeloxCNC routers, mostly the 50x50 model. I'm going to leave a lot of the specifics of feeds and speeds out because it would be a lot of work to put it all up here and you will get more benefit from my CNC router video series.

What machine should you look at buying if you are interested in owning a CNC router?
This is going to depend on a few factors that will be team specific.

How much space can you make?
We all have limited room for equipment and it can be hard to find a place for a large CNC router. Our VeloxCNC takes up about 8 foot squared and it is a large chunk of space. I suggest you buy the biggest machine you can support within your space. It is worth the sacrifice you make for the space and you could very easily work a storage system into the stand/table your router sits on so the space is used effectively. For FRC type work there is not much benefit to a 4'x8' bed size because almost nothing we build requires any part with a dimension over 4 feet long. If you have plenty of room, go for it. DO NOT get a machine with less than 4 feet in at least one dimension as it will seriously hobble the utility of the machine. 4'x4' machines are a perfect fit for the work we do and allows us to machine half sheets of whatever material we want.

How big is your budget?
This is the hard part of giving advice for what machine you should look at. With any major piece of shop equipment it is worth spending as much as you can reasonably handle on it. Every additional dollar gets you more machine than the previous. It is always better to plan to save up to get the bigger or better machine than to get a cheaper machine now. Pick the machine you want and need, then find the money to make it happen. It's a lot easier to convince sponsors to give you additional funds when you have a very specific plan for what you are going to do with them.

What are the important points for a CNC router that will be cutting metal?
Rigidity! You want a solid machine that can both drill and mill. To accomplish this you need a rigid gantry design and minimal cantilevered loads on the machine. Raw motor speed and power are not as important, but you do need a spindle that can handle the loads.

What machine do I recommend and are there any others I would want to avoid?
Begin personally biased opinions here-> I LOVE our VeloxCNC. It is solidly built and handles everything I throw at it admirably. The gantry on our 50x50 is built like a tank with thick plating and doesn't budge easy and the 2 acme screws it uses on the Y axis make it really easy to maintain square. Furthermore, Velox is the only company I’ve seen that shows their machine tackling a serious block of aluminum in their demo videos. As for machines I would say to avoid, stay away from the desktop models as they are rarely stiff enough to even machine aluminum.

What flow process does 1678 use to make their CNC parts?
Once we have the CAD of a given part we convert the faces to be machined to .DXF format to use with our CAM software. Occasionally we have a part with a lot of features that is difficult to generate effective toolpaths for with our usual software and we instead generate the toolpaths in SolidWorks with a CAM plugin called HSMxpress(the free version). Our default CAM software is Vectric Cut2D Pro and I highly recommend it for a number of reasons. Mainly, it is a very straightforward program that is dirt simple to learn and use: I like to describe it as the MSPaint of CAM software: easy to use and easy to do all the basics but lacking many of the complex features of more expensive software. That said, you don't need PhotoShop to make a picture of a circle. It's most powerful feature is definitely it's best: the auto nesting feature. Drop a few dozen parts into the program and hit “Nest” and it does all the work of nesting your parts with minimal material waste. Afterwards, we generate our G-code for all the parts we are going to run. We’ve developed a tool library that is segregated by material type where our cutters have all of their settings tuned for that specific type of material to make tool selection easy for our students. Then the G-code is loaded to a cloud storage location and our operators can download the new code and run the machine.

Running our machine
Our machine can be broken down into 2 main areas of use: the sacrifice table and our tube jig. Most of our work is done by using the 2 layer particle board “sacrifice” to hold down stock with screws and machine the majority of our parts. We also machine the whole thing flat so we can get good depth control on 3D parts.
At work I use PVC foam instead of wood and run a water based oil emulsion coolant, it is a lot more expensive but ambient humidity was enough to mess with the flatness of the wood. Off to the side in the second image you can see our tubing jig which uses a number of toolmakers vises we got from Shars.com to support up to 4 inches of tubing in width.



The tubing jig has a set work offset in our controller software for the router (Mach3), so all we need to do is load a tube already cut to length and run program.
We run an air line to the router from our compressor and we use a mister nozzle that runs WD-40 when we run aluminum to keep the cutter lubricated and cool while clearing the chips it makes from the cut path. We also run a shop vac with an extended line and a Loc-Line nozzle down to our work area to suck up the excess chips. At a minimum you should run air, but coolant of some kind is highly recommended.

Cutters
When running aluminum it is important to use end mills with fewer flutes to maximize chip clearing. We prefer to use single flute cutters, but 2 flute also work well. Please save yourself the hassle and buy good quality end mills and drill bits. For drill bits you want split-point 135 degree short length bits. Chisel tip drill bits take much more force to drill with and your spindle and Z-axis will thank you for using split-point drill bits. We don't make our router drill any larger than a #11 drill bit for 2 reasons. The first is that it is easier on the machine and second is it improves the accuracy of your drilling by minimizing spindle deflection from the plunge forces.

CNC Router Video Series
Please look forward to seeing some more videos by me and 1678 popping up over the summer! I am going to be making them for a couple of reasons. One is to make it easier to train my students how to use our machine. Second is to enable the FIRST community to have a technical resource to learn the various methods we use to make our router easy to use for our operators and not have to learn it via trial and error. I'm really looking forward to doing this and having a bunch of videos with various topics related to running a router for FRC. Please let me know if there are any specific topics you would like to see covered.

Part examples run on our VeloxCNC
This is a 3/16" thick gearbox plate we used for one of our shooter designs this year machined out of 6061-T6 aluminum.


This is a belly pan machined out of 0.090" 6061-T6 aluminum.


This is a battery pan made out of 0.063 5052 aluminum.


If you have a CNC router please write a post about your experience with it, any troubles you've had, your recommendations, and any particular praise you have for your machine. I want to see lots of input from teams of all walks about their experience with CNC routers.

Best Regards,
Devin Castellucci
Team 1678
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12 Years and counting! Over a third of my life has been spent with FRC.
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