FRC 95 The Grasshoppers 2019 Build Thread


#161

Are the guy wires used to support the elevator as a replacement for metal structure? Is the only benefit weight savings?


#162

Yes.

No. It allows for more clearance to adjacent mechanisms and wide mounting flexibility


#163

I just wanted to say that following this thread has been a blast, and we really enjoyed working with you guys last year at Fairfield. Hopefully we’ll see you guys at NECMP, good luck! - 7127


#165

Great progress today, although we’re not finished.

Skids, umbilical, cargo collector, jack guides, and other sundry mechanisms have all been added. We’ve tested the hand-off from ground collector to elevator for the hatch, seems to work nicely.

Another coach is going to send me some video from today, I hope have that posted soon.


#166

Have you guys tested the over-center linkage yet? Any video?


#167

We haven’t actuated them under air power yet, but as-mounted they both go just over-center and lock up nicely. I hope to have that sorted and tested on Monday. We likely need to arrange some spreaders for the guy wires to get everything cleared properly.


#168

#169

FYI - We are still doing our endmill giveaway.

Here is the product page.

JHH2500V is 99% of what we have to send out.

Here is a demo video (we have posted before) of using the mill in 6061T6 aluminum on a Tormach.

Shipping via flat-rate envelope is $7.50, so $8 via PayPal as goods/services covers it and accurately captures your shipping information. If you want to send a few more bucks for our Saturday donut fund that is always appreciated. Just shoot me a PM for my PayPal ID. I’ll send somewhere between 5 and 10 end mills with each order depending on demand. You can get mills more than once of course! This is an ongoing giveaway because these are cast-offs from my company. They have machined a little bit of carbon and are deflecting an extra 1-3µm now, so are worn out for our purposes. For FRC/metal purposes they’re basically new.


#170

Can these endmills be used on a CNC router? My team usually uses single flute endmills of similar size and I’m unsure what the extra flutes mean in terms of functionality for us.


#171

They can theoretically, depending on machine limitations. You should need to feed faster than a 1 flute I think. They are spec’d at .0005 to .0015ipt in aluminum.


#172

It might help to know what speeds and feeds you are running in that demo. Where can I find more information?


#173

The demo utilized HSM techniques. Something like 20-30ipm, 4800rpm, .7in doc, 20% step over.

@Andy_A has the details I think.


#174

It’d be really hard to do for most routers, cutting aluminum. It’s already pretty tricky with a mill.

The short and sweet version is that each flute on an endmill needs to take enough of a ‘bite’ out of the material to keep it cutting and not just rubbing. This is called chipload, and having too low of a chipload can break a tool just as fast as too high a chipload.

With a target chipload in mind, we can calculate a starting feed rate by multiplying the spindle RPM, the number of flutes and that target. The manufacturer data suggests .0005 to .0015". Take the middle value of .001"

A typical CNC router motor runs around 24000 RPM, this tool has five flutes and we’re targeting .001" per tooth.

24k * 5 * .001= 120 inches per minute.

That’s faster then the rapid moves on most routers! Rigidity and spindle power will make cuts at that speed pretty impossible for most cnc routers even if they can move that fast.

In addition to wonky feed rates, these sort of high flute count tools don’t leave a lot of room for the resulting chips to get out of the tool and away from the cut. Aluminum, in particular, has an affinity for the coating these tools use and will weld to it if they get hot enough. Clearing the chips, keeping the tool cool and lubricated requires either flood coolant or a pretty strong air or mist blast.

These tools are really meant for profiling hard machining materials, like stainless or tool steels. They can cut aluminum, but it requires a rigid machine, correct feeds and speeds, and good coolant delivery.

I keep them on hand, but generally avoid using them in aluminum for the aforementioned issues. I’ve gotten great results milling A1 tool steel and titanium with them, though, so they’re super handy to have around.


#175

I don’t have that model or CAM data handy, but that sounds about right except the stepover was probably lower. I know I adjusted the feed overrides a fair amount to get results that felt right, so the calculated values were really only a rough starting point. The exact values are going to depend a lot on the machine, coolant setup and geometry.

The best advice I could give for using these tools in aluminum is to avoid slotting, use flood coolant or an aggressive mist and keep that chip load up.


#176

Possibly silly question: Why not run the router at a lower RPM?


#177

If you can, that’s one possible solution. The issue is that most CNC routers use a literal router intended for wood working. They generally have very high RPM. They may have some level of speed control built in, or you can add it in the form of a VFD, but power can fall off quickly as you lower RPM. By the time you’ve slowed the spindle down to get feeds that work for the axis motors, the spindle motor is no longer producing enough power to complete the cut.


#178

This design is awesome. Reminds me of 3357 comets robot from the power up season combined with a gear floor pickup up from steamworks.


#179

Our students have been learning about meme heritage. Namely…

Leroy…

Jenkins.


#180

At least you have chicken grasshoppers


#181