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Cutting foam sheets... with a needle!

Just when I think I am ready to cut out a new plane, I keep breaking needles. I have tried the needle keeper like Mobeast and the wire around the bearing like David and Jason. Each time I set my rpm to around 6000 rpms and let the machine just run without the needle even touching the foam board. Around 5 min of running the needle will break, so far I have tried different motors, motor mounts, esc's with no luck. Last night I think I found my problem, I think I have a faulty servo tester. Using my tach, I took constant readings that went from 12000 rpm's to the motor just bumping, without touching the dial. I then pecked the servo tester and the motor started again. The servo tester servo.jpg that I am using is a inexpensive one that I purchased from Amazon. Does anyone know of a better option or a more reliable servo tester or did I just get a dud.​
 
Just when I think I am ready to cut out a new plane, I keep breaking needles. I have tried the needle keeper like Mobeast and the wire around the bearing like David and Jason. Each time I set my rpm to around 6000 rpms and let the machine just run without the needle even touching the foam board. Around 5 min of running the needle will break, so far I have tried different motors, motor mounts, esc's with no luck. Last night I think I found my problem, I think I have a faulty servo tester. Using my tach, I took constant readings that went from 12000 rpm's to the motor just bumping, without touching the dial. I then pecked the servo tester and the motor started again. The servo tester View attachment 133468 that I am using is a inexpensive one that I purchased from Amazon. Does anyone know of a better option or a more reliable servo tester or did I just get a dud.​
Are you using a tach to get your rpms? Picture of your cutter and details about how it's set up would help... motor, voltage, etc. Also, 12000 rpm will almost always result in bad stuff happening. ESC are very non-linear... i.e. with a 1000kv motor and 12v, you should see 11k-12k rpms at full throttle (servo tester max on dial). BUT it will pass through 6000-8000 rpm before you get more then 1/4 or 1/3 on the servo tester dial. The dial is linear and is usually pretty accurate when exercising a servo... but as a motor control, not so. Stay near the lower end... and I highly recommend getting a digital laser tachometer if you don't already have one... this is the one I have.

Also, watch where I use the tach and adjust the servo tester in this video... I'm not rotating the knob very far at all to get 8000 rpm. Turn down the sound :eek:


-- David
 
Thanks, Rockyboy.

I've never heard about such a thing... so wasn't aware of it. While that would be neat, for this application, that's probably overkill IMHO. Once the proper/desired cutter rpms have been determined using the tach, it seems a pretty easy thing to simply mark/remember where on the servo tester's dial that setting is... and then simply go straight to it for successive runs. An exact RPM reading really isn't necessary (I shoot for ~8000 rpm, no load) and a couple hundred rpms either way isn't going to hurt... you simply want the lowest RPM setting that gives acceptable perforations/mm and cleanest cuts at an acceptable feed rate (in my experience, 10-15 perforations/mm for DTFB). That should also result in the least stress and longest life for the cutter/needle.

In the video I referenced, I took far longer to start the job as I was demonstrating a few things... in actuality, it takes less than a minute to switch on the vacuum, move the tool head to desired X/Y start, start the cutter and set speed to a mark on the dial, lower Z to material surface, and then start the job. My gcode always has a G92 X0 Y0 Z0 in the header so it sets in the current X/Y/Z settings at job start as the origin for all cuts. Not difficult at all...

-- David
 
Are you using a tach to get your rpms? Picture of your cutter and details about how it's set up would help... motor, voltage, etc. Also, 12000 rpm will almost always result in bad stuff happening. ESC are very non-linear... i.e. with a 1000kv motor and 12v, you should see 11k-12k rpms at full throttle (servo tester max on dial). BUT it will pass through 6000-8000 rpm before you get more then 1/4 or 1/3 on the servo tester dial. The dial is linear and is usually pretty accurate when exercising a servo... but as a motor control, not so. Stay near the lower end... and I highly recommend getting a digital laser tachometer if you don't already have one... this is the one I have.

Also, watch where I use the tach and adjust the servo tester in this video... I'm not rotating the knob very far at all to get 8000 rpm. Turn down the sound :eek:


-- David
Thanks for the help David, I swapped out the servo tester, ESC and motor. I am now getting consistent readings with my digital tachometer. I am not sure which was giving me the problem, but all seems well for now.
 
Guys, I first saw David's needle cutter on the RC Powers thread and have been following it on 3 forums since. I have been watching my yard carefully for a hairy goriila to come by so that I could offer him bananas in return for building me a CNC. Sadly they seem to be indigenous to TX. Since I have no CAD skills, no engineering skills and limited time due to business obligations I did the only thing that made sense and ordered the Lowrider2 hardware from Ryan at V1.

As I am now printing the 3D parts I was wondering if anyone was aware of a needle cutter mount design that was out there for the LR2. I am going to attempt use the CF2822 design that David has developed but am struggling to figure out how to adapt it to attach to the LR2 611 plate. If anyone is aware of a design for this mount please post where I can find it.

I want to keep the router option so in the future I can cut out wood to make some of the other cool machines you guys are doing, I am looking at you Moebeast.

So whether I ever get this machine working or not I have enjoyed watching the progress you all have shared with us! Thanks!

Tim
 
Guys, I first saw David's needle cutter on the RC Powers thread and have been following it on 3 forums since. I have been watching my yard carefully for a hairy goriila to come by so that I could offer him bananas in return for building me a CNC. Sadly they seem to be indigenous to TX. Since I have no CAD skills, no engineering skills and limited time due to business obligations I did the only thing that made sense and ordered the Lowrider2 hardware from Ryan at V1.

As I am now printing the 3D parts I was wondering if anyone was aware of a needle cutter mount design that was out there for the LR2. I am going to attempt use the CF2822 design that David has developed but am struggling to figure out how to adapt it to attach to the LR2 611 plate. If anyone is aware of a design for this mount please post where I can find it.

I want to keep the router option so in the future I can cut out wood to make some of the other cool machines you guys are doing, I am looking at you Moebeast.

So whether I ever get this machine working or not I have enjoyed watching the progress you all have shared with us! Thanks!

Tim
Thank you, Tim, for the kind words. I thought hairy gorillas were more widespread... but what do I know?

Look back to here... and the following posts for the collaboration between Rockyboy and Jason (jhitesma) on a 611 mount for a LR2 needle cutter. I THINK Rockyboy actually has one working and Jason's design is out on the Onshape site... 611 mount.

Hopefully, one, or both, will chime in to give better information.

Again, thanks for dropping in.... welcome!

-- David