Hello,
I am part of FTC Team 22105 and we are designing a telescopic arm. We are wondering if anyone knows any tips on where we get a boxtube pocketed, as most commercial retailers don’t appear to offer box tube cutting for cheap.
Does anyone know where we could get something like this done? Or if anyone would be willing to pocket a boxtube for us and ship it if we pay for shipping and materials.
Ps: We are mainly doing the pocketing for the aesthetics
Thanks!
Can you locate a nearby team (most likely FRC) which will let you use their CNC router?
Good. I’ve heard it described as “judge catnip” but even teams doing it to their tubes knew the more traditional play would be to plan the design around thinner tube without pockets.
Which I hope you’ll consider here as an alternative. 
Here me out:
We will try, thanks!
Yes, we are aware that pocketing boxtube loses a lot of strength to weight ratio that going thinner doesn’t. However, we are already doing pocketed 1/16in, which while it loses a decent amount of strength, is more than strong enough for FTC loads.
Ya your options to reduce weight are basically:
Cheap and non-functional pocketing are usually mutually exclusive, as pocketing thin tube requires a significant amount of machine time and is difficult to hold onto the parts. The most functional pocketing for boxtube is to slot it using a large endmill (1/2" slot for 1" boxtube) and isn’t particularly time consuming.
Actually one caveat, you can slot a boxtube normal to the direction the bending load is applied and not lose significant strength (aka if you are bending a boxtube down, you can slot the top and the bottom). This however is only the case if the significant bending loads are only applied in one direction, and there’s no significant torsion.
The reason this case works is that the two main reasons that pocketing boxtube is bad is that you are introducing stress risers, and splitting the boxtube into two significantly weaker beams in parallel. Slots with large radii don’t introduce significant stress risers and putting the slots normal to the applied bending load doesn’t split the boxtube in two.
In regards to the slotted pocketing, we are currently planning to do isogrid pocketing for the aesthetics it gives, similar to FRC 2910 in 2022.
An issue I can think of the slotted pocketing is that the bearings will no longer be facing a wall in the slot (for the bearings at the bottom of each stage on each of the 4 sides). Though I guess you could just push the bearings to the side rather than the middle.
Thanks for the FEA image! For now we will probably stick with Isogrid because it allows to keep our current design with bearings on the center at the bottom of the stage and looks very aesthetic to our team.
That is a pretty small isogrid to be cut with an endmill for the tube sizes commonly used in FTC.
What sizes/ wall thickness of tube are you thinking? A laser may be a better call than cnc router/mill operations.
No idea if these guys are good or not, but seem to have a similar send-cut-send or fabworks model to parts. Zero idea on afordability, leadtimes etc. (I have always wanted to design parts with a tube laser, let us know if you do somehow go this route, you could do some crazy aesthetic designs beyond isogrid)
What’s the size of the box tube? Aluminum?
I think you’re in San Diego. If you’d like to come up to Long Beach I’m happy to help on our CNC
Edit: IF our equipment is able to cut what you’re looking for
Yeah, we were thinking of some 1 foot square tubes of 0.5, 1, 1.5, and 2in side length, with the 0.5in being unpocketed.
The wall thickness in our CAD is 4/5mm, though the pocket radius is rather small (IIRC going to 1mm on the 1in tube).
Yeah, a Laser might be better, I talked with another team that ran a similar Isogrid pocketed boxtube and they used a laser cutter for the pockets and flipped it on its side 4 times.
I have checked on Xometry, and it is unfortunately well beyond our team’s finances.
What aesthetic designs do you have in mind other than isogrid?
Thank you so much for the offer! Here are the specs:
Box Tube Dimensions: A little under 1 foot for each one, 0.5, 1, 1.5, and 2in side lengths of the square
Material: Aluminum
I think this is probably a better option for FRC-scale parts than FTC, but we have used Osh Cut for this – if the stock sizes match what you need, it’s not totally out of bounds on price, though far from cheap. We used this for frame rails.
It can be very nice to be able to order what you have in CAD, particularly if you don’t have the option of doing anything with high tolerance in-house. We were pleased with the service, and the turn-around time was reasonable.
You may want to clean up the splatter that can be left on the inside of the tube (a wire brush on an extension on a drill might be a good way to go here). We just ran some wooden stock through to knock off the worst of it.
Their website, unfortunately, doesn’t appear to offer 1/16in tubes in all of our sizes (it doesn’t have 2in tubes in 1/16in thickness). Thanks for the link though!
Xometry is reputable and fast, I know a few ppl in the keyboard hobby that get one-offs or protos made there, and they also do surface treatments like anodizing, powder coating, and e-coating. Since it’s done in the US and with a quick turnaround, one-off parts are quite expensive
You should be doing this anyways, bearings in the middle of boxtube is really bad for the boxtube and will deform it under normal usage because you are loading the face in bending.
And really, slot and large holes are the only two boxtube pocketing patterns that don’t significantly weaken the structure, isogrid on small boxtube creates a bunch of small stress risers and is significantly more expensive due to requiring a bunch of machine time with a small endmill.
