Our team has a CNC plasma cutter (PlasmaCam) laying around that I want to put to good use. I’m hoping to plasma cut our robot’s chassis next year but I’m not sure it has the accuracy to do it. We also have a CNC Mill but it has a smaller working area.
Has any team successfully plasma cut there robot’s chassis and/or parts? Any tips?
We’ve cut parts in steel using a plasma cutter. We haven’t had any problems with the parts - they were cut very accurately. Occasionally we have to drill a small hole out though because the plasma cutter doesn’t recognize it enough/give it enough power. I think that is due to our configuration of the device, some setting we need to change somewhere.
On a side note has anyone ever plasma-cut aluminum? We were planning on doing it sometime this week and could use some pointers.
Not sure what system you have, and there are a lot of variables at play here, but what we’ve found is that it’s better to run slower feed rates than suggested by the manufacturer, as this leads to less beveled edges. This will cause more dross buildup, so you will have to do some sanding/filing afterward.
While not quite the same thing, our chassis was laser cut from plywood. The machine works in the same way with a rail for each axis and is very accurate. As long as your plasma cutter is well calibrated, you shouldn’t have any problems.
The answer is yes, but there are some limitations which as others have pointed out have to do with the cut quality you can get from your machine. As a general example: Would I cut pockets and location holes with a plasma, yes. Would I build an integrated gearbox in a chassis, no.
The limitations I think it is important to be aware of are bending. It is extremely hard to bend accurate parts with a cheap break, and this can be as much as of a limitation as the cutting machine. The method I prefer when using a plasma is to cut location based features on the flat plates and add simple flanges for strength, which geometrically don’t need to be as accurate.
A cnc Plasma cutter is an extremely valuable tool for a team to have as it can significantly reduce time and increase accuracy, you just need to learn the limitations of which ever machine you get, and make sure to experiment before the build season to learn what those limitations are.
Thanks for all the help,
I’m hoping to design and build a chassis in the off season that we can modify for build season so I can learn how to use it. We do have some heavy duty brakes from the 50’s but I’m not sure how accurate they are.
Are table is a plasma cam with advanced height control and are cutter is a miller 375.
In 2012 Team1325 got our chassis conveyor and shooter cut with a plasma cutter and then gave it to a sponsor to bend. It worked out very well all in all. The cuts were not clean and took a lot of niners…i mean deburring. Also small holes (0.25 inch)did not work well so we ended up just drilling most of them in.
I forgot to mention…it was a sheetmetal chassis 0.09 5052 aluminum.
Small features like rivet holes are best drilled - although you can ‘mark’ their location with the plasma torch. Better are larger features, but the edge condition may not be as smooth as you prefer. It isn’t like milled, laser or waterjet surface finish.
With aluminum, beware the effects of heat on the material - aluminum expands as you torch it, and so when it cools everything gets a little smaller (and closer together…).
Don hit the nail on the head what we do to put holes in parts. We undersize and finish the holes on a drill press.
For bearing holes we precision ground a step drill to finsh the holes for a perfect press fit.
The thermal expansion is manageable by controlling feeds and knowing how much you can cut before pausing the cutter and letting things cool along with the order of the cuts. We do primary holes first (location critical items like bearings or interfaces) and then leave lightening holes and frame cutting for later with cooling down time allowed between the patterns.
Also the best way to clean the edges and remove the slag is a scotchbrite pad on a die-grinder. Deburring tools are a bad idea to try on the slag they skip off easily and don’t clean it well.
Set up is everything. It’s not just about drawing a hole and some lines that will make it work. You need your plasma cutting machine to be setup correctly for your material of choice. If you learn that, your cut and part quality will make it worth the effort.
I would not plasma cut small holes. You could “mark” by blasting the center, this doesn’t always work!
Plasma cutting aluminum is very doable. It does create lots of “slag” that sticks to the aluminum, more than steel slag does. On sheets you won’t notice it, but in tube or u-channel it will stick to the walls. I find that a twist lock scrotch pad will take that stuff off real easy. Otherwise it’s a pain.
We plasma cut a lot of parts for our robot this year. Normally we have use a waterjet for many of our sheetmetal parts, but our company’s waterjet machine broke in early Jan, and was down for the whole build season, so we had to make other plans.
This took a little trial and error, but we were able to make transmission plates, rivet holes and a lot of other fairly precise parts in Aluminum sheet as thin as 0.050" on a plasma cutter. The tolerencing is not nearly as good as a waterjet or laser (but it is good enough for FRC).
A few tips: Use big rivets, we use a lot of 1/4" rivets, so 0.010 tolerence or so on the holes doesn’t really matter. Make all bearing holes slighty undersized and ream to fit. Make more simple assembled parts rather than a few complex peices if you are going to form them.