Our team recently was given access to a cnc shark hd4 which seems like it was geared more towards cuttting wood. Obviously this isnt very useful in frc so I was wondering what the steps would be to cut some metal on it. Probably just 8th inch (Im guessing thats all it can handle anyways). I have only a little experience with cnc’s in general. I am pretty experienced with 3d printers (assembly, wiring, repairs, gcode etc.) but I’m not sure how much of this knowledge will transfer. I know we will need to buy some metal bits and some cutting oil of some sort. What else? would we need to have a constant drip or spray of the oil while cutting?
Coolant is always good, but you probably don’t need a constant drip (although that is helpful). The CNC Shark may work for aluminum but it’s not going to be as good as a purpose-designed machine. You’ll just need to try it and see how it goes, but you should be able to cut metal pretty easily it seems like.
Your first step should be to purchase some quality metal cutting endmills. The West Coast Products 4mm endmills are good, as are the Onsrud O-flute Upcut single-flute endmills for aluminum. 1/8" diameter should work fine for your application, as a smaller endmill will have less force on it (and thus less force on the machine) making for an easier cut.
Start with a cutting speed of 15ipm at your maximum RPM, and try for a 1/32" deep cut in some aluminum. Make sure your aluminum is clamped down tight. If that succeeds (using the correct endmills!) then try and cut your circles and things to see how accurate it is.
I have been running a cnc router for several years cutting aluminum. Typical setup is .020 depth of cut at 20 inches per minute. Plunging at 0.5 ipm. I have cut up to 1/2" thick material so far. I recently switched to a 1/4" single flute up cut bit with better results than the router bit I was using. I have also used 1/8" diameter bits. Biggest issue is removal of chips as the vacuum system on the machine is marginal. Hand vacuuming helps. I also use a wax lube (acculube) that I apply to every other pass to a short portion of the cut, usually when the cutter is farthest away from me. The lube is not messy and keeps the aluminum from sticking to the cutter.
This can be slow compared to a standard milling machine but it works.
I totally reject your premise that wood isn’t useful for FRC.
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LOL. Looking for the “Like” button! 
We found that you could press bearings into 1/2" Baltic Birch very nicely… I think we used our CNC router to cut the holes about .005" undersize. We built several mechanisms (and a few drivetrains, and one whole robot) out of baltic birch.
If you examine the specific stiffness of wood vs. aluminum you’ll find that for solid cross sections that wood actually outperforms most materials in stiffness/weight ratio.
But yeah, you can do nice aluminum work with a CNC router once you get your settings worked out… no coolant required.
Jason
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You should be able to cut plastic (polycarbonate) as well, which is very useful for FRC.
Can I use the same bit as I do for aluminum on the polycarb?
For programming toolpaths, what CAD software are you using? SolidWorks has the HSMWorks plugin and Inventor HSM are both available on the Autodesk site. Fusion 360 is also an option.
As far as cutting the material, I’d recommend getting a cheap endmill first to learn with and work your way up to a more expensive option. Your first cuts won’t be ideal, but you won’t be breaking a $40 endmill on the first shot.
for cad we are using solidworks and the cnc came with its own software. I forget what it is. Can I get an hsm plugin for free through first? or does it come on the student edition.
You can email Solidworks (I think) and get free licenses of HSMworks. They also have SolidCAM which is pretty new, and I haven’t had a chance to look at it yet.
HSMWorks is owned by Autodesk now, so you can just go to the students site and grab it! All the Autodesk software on the student/education site is available for free to FIRST.
Yes. No coolant for polycarbonate is necessary.
A helical router bit will tend to lift the polycarbonate up off of the table. A router bit with straight flutes works better.
A few pointers that are more generic router tips, as I’ve never used the model you have access to.
- Pretty much the only bit you will ever need is the 4mm from WCP. At a price of $15, you can’t beat it. They have the same quality of Onsrud, but at 1/2 to 1/3 of the price.
- Get yourself some Baltic birch, we’ve used it in some aspect of the final robot since 2012. General plywood is great for quickly testing concepts and iterating.
- Polycarbonate/lexan cuts like a dream
- If you want to learn with low risk of tool failure try cutting some insulation foam. It’s cheap and tool won’t care.
- Coolant, while a mess, is recommended to help with tool life and help if you don’t have the speeds/feeds perfect.
We got a CNC Router Parts 4848pro about this time last year, and primarily learned it during build season. We used it last year to great success for lots of concept testing, competition robot, practice robot, and numerous iterations as the season went on. We fabricated all flat stock and box tubing in house. It can be a bit of a learning curve, it was for us.
When you say your “team recently was given access”, does it mean you have exclusive access or do you share it with people using it for cutting wood? If you are sharing it with people cutting wood, you may want to verify that they know you are thinking of cutting metal on it. A friend had a cabinet making shop with some large CNC routers. When I asked him about using them for FRC work he declined because it leaves behind metal dust that makes it impossible to get a good finish on wood that is cut on the machine afterward.
+1
There have been quite a few teams that have used wood very effectively in FRC robots, even at the Championship level. It is all about understanding your materials and your manufacturing processes. DiscoBots used an entirely wood upper structure to support their electronics and bumpers in 2016. It’s manufacture used different tools so it’s construction was able to proceed in parallel with the construction of the aluminum tube chassis. It took a lot of abuse. The only damage occurred when the driver attempted to get air (again) while going through the Portcullis and hit it at the wrong angle with the wedge in front, cracking the joints between the front plate and the side plates. Using some cyanoacrylic glue and clamps, we had it repaired in about 15 minutes.
yes we will be sharing it with the woodshop teacher. (our team operates out of a woodshop and all metal tools are bought by us). The teacher knows next to nothing about cncing and pristine finish on the wood is not neccesary. He hasnt used it much in the 3 months he’s had it and has no objections if we use it for metal, provided we take good care of it.
we use wood for our bumpers of course, and our electronics board, but other than that, we’ve mostly found it to be too weak or too flexible for many other applications.
we also have a vacuum attachment, is that preferred or is it better to make it a blower?
Use the vacuum. And I say that regardless of wood or metal.
If you use a blower, you have chips/sawdust/aluminum dust all over the place downstream of the blower. If you use nothing, it’s all over the place period.
But if you use a vacuum that’s sized for what you’re doing, all that stuff gets pulled into a container, from which it can be easily removed to the trash can. Much cleaner and safer. Also you can disconnect the vacuum and use it to clean up the stuff that does escape.
I once had to help make a vacuum system for a piece of machining equipment. Once it was set up, cleanup was minimal if the containment shroud was properly placed relative to the workpiece. The alternative was lots of sweeping.
As stated before, one has to understand the material in order to get the most out of it. Most of your houses and the furniture in them are made from wood.
There are many grades of wood, just like there are many grades of metal. In general, a piece of plywood with more layers (plys) will be made to a higher quality level, have fewer defects (knotholes, splits, etc.), will be made from hgher quality wood, will have a smoother finish, will retain fasteners (screws) better and will be stronger. The highest strength plywoods compare favorably with sheet aluminum for strength and durability and is often easier to work with, especially for low-resource teams. The following are links to different types of commonly available plywood sorted by their relative strength.
3-ply sheathing, weakest, cheapest, do not use
5-ply B/C sanded, moderate strength, inexpensive, okay for prototypes
9-ply both sides sanded, high strength, moderate cost, best material for bumpers
13-ply baltic birch, highest strength, higher cost
Unavailable at Sierra Vista
Life in small town America.
we used to be able to get a nice selection of Baltic Birch at a local store, but it closed a few years ago.
Wood is good stuff. But so is metal. Figuring out what to use for which parts of the robot, is a great deign exercise.