[polyfractal]

https://youtu.be/qiM20-woEOk

Hey all, thought this might be of interest to folks here. I purchased a Benchtop Pro 2x3 and wired it up with a CNCDepot S30C spindle and Fogbuster to do some aluminum milling. Finally got everything in a state that it could make chips (although still have a lot of work to do) and filmed some tests to work out speeds/feeds. If you want to skip ahead to the cuts, here are the timecodes: Straight cuts (2:24), Puzzle attempt #1 (11:22), Puzzle attempt #2 (16:37).

Overall I'm super happy with how it is performing. Hit ~8in² MRR without bogging down the spindle too much. Main limiting factor seems to be the sheer weight of the machine; at high feeds the acceleration/deceleration throws the whole table and machine around, which will affect tolerances. The machine itself weighs a few hundred pounds - maybe 400ish after adding vise and spindle? - and the table is a welded frame I knocked together, so probably another 100-200lb. So not a lot of mass in general to damp fast accelerations.

But at slower feeds (<80ipm) it cooks along nicely with HSM toolpaths. Only tested with 1/4" end mills so far, planning on trying some larger end mills, flycutter, etc in the near future. Also going to try my luck with mild steel and see how it goes.

I was debating between the BP2x3 and "proper" mini VMCs like a Syil/Skyfire/Tormach or even Haas MiniMill. Ended up with the Avid system for a few reasons. I'm still in a prototype'y phase for things that I'm working on, and some parts may end up being plastic, so the larger work envelope was very appealing (really didn't want to get a VMC and then find out it was too small for the parts I need). The lower cost was certainly a plus, and by adding an ATC high speed spindle I felt I manage most tool paths even if they had to go a bit slower. Still need to do some tolerance checks but I think the BP2x3 will hold tolerances that I need at a reasonable feed rate.

We'll see if the choice pans out, but so far I'm pretty happy with how it's looking.


For fun, I did a little bit of spectrographic chatter analysis. More examples in the video, but here are some annotated charts from a prior run. By analyzing the audio spectrum, you can identify the harmonics of the spindle and the end mill flutes:

Attachment 434668

And if you look at the spectrum over time you can identify various events, find examples of new chatter frequencies that show up when entering a cut, and even see the motor bogging down a little from the cut (because the main spindle frequencies decrease slightly when it enters the cut, which directly correlates to the rotational speed):

Attachment 434666


Still a lot of work left to do on the router:

• Enclosure to contain chips, and reduce sound
• Zero-speed ATC interlock wiring
• Low-pressure fault sensor wiring
• Tool rack and ATC macros
• Flattening work table, and/or large fixture plate
• Bolting down to the welded table to increase overall mass of machine
• Toolsetter and wireless touch probe setup

[HuguesP]

thanks for the video, very interesting, i am waiting for my 2x2 benchtop pro myself. its been a month or so, so i should get it soon.

[polyfractal]

Have fun! Mine assembled very easily, the instruction manual and assembly video were super clear. Think I had mine fully assembled over two or three evenings