Machining Polycarbonate

[Tool-n-Around]

I just updated my previous post regarding the Super-PID info.

Here's a link to a wealth of information on the CNCZone forum concerning this, I'm a contributor as well:

https://www.cnczone.com/forums/diy-cnc-router-table-machines/112658-cnc-manufacturing-forum.html

Wow, that thread is 101 pages back to 2010. CNC zone is where I discovered S-PiD but I didnt see that one. I started at the end and read a few pages back. I've also read the manual and instruction. Think I'm sold. I have several older 6902 Porter Cable routers.  Although the are older they are virtually brand new. 10 amp 120vac, 1/2" collet capable. Not variable speed. I dont recall if they are soft start but if so no biggie to mod for that and rpm sensor.

I'll get some additional wire/cable length, knob, 5v fan, some other odds and ends. Can package myself. no problem. I may come back to you when it gets time for the CB interface. Will also need to check the gecko controller in my machine. Am I forgetting anything before I order?

Best,
Kelly

[Tool-n-Around]

Wonderful!  Thanks for checking in Airnocker.

That will add worlds of capabilities to your machine at not much cost.  You still must deal with the rigidity problems, but speed has been one of your major issues, and this will solve that.

Lloyd

As far as rigidity I actually think the gantry beams are ok, but the Z-axis definitely needs some attention. It's fairly stout for extruded aluminum rail. Here it is compared to open builds C-Channel.

Best,
Kelly

[airnocker]

Small world, eh?  I'm also "airnocker" on the CNCZone and have numerous posts in that topic.

I've always used parallel port break-out board (CNC4PC) going back to when I was using Windows XP.  I've been on Windows 7 Pro with my dedicated CNC PC for quite some time but still use a PC that has a parallel port.  My DIY PID enclosure just sits below my machine.  You probably don't need a cooling fan, just a good heatsink like mine.  See photo.

I'd search the Super-PID post or the Internet in general for using the Gecko controller with the Super-PID.  I just did and found this YT video: https://www.youtube.com/watch?v=x75SQLxLNv4.

So look for info on the Gecko model you are using.

You should wind up with 4 cables entering/exiting your Super-PID enclosure:
1. AC Power IN
2. AC Power to your router
3. Speed sensor signals to/from router
4. PID control signals to your machine's controller pins.  (I originally said Gecko controller pins, sorry)

Using the PID with CB is not different than using a spindle with speed control, the main setup will be with Mach3 or whatever machine control software you are using.

Best of luck.

[Bubba]

I use Super PID since v.1 with G540 controller and ESS.  All is working trouble free, would recommend it.     

[Tool-n-Around]

......Will also need to check the gecko controller in my machine.

I'm talking out my backside. My Mega V controller board has an Arduino mega2560.

https://store.arduino.cc/products/arduino-mega-2560-rev3?_gl=1*in7xq1*_ga*OTQxNzI0OTI1LjE2NDk2ODcxNDI.*_ga_NEXN8H46L5*MTY0OTY4NzE0Mi4xLjEuMTY0OTY4NzE0OC4w

The board is running grbl 1.1i or later, customized by MR for rotary axis enablement. I'll have to do some more investigation on router control and the pin outs. I did order the Super PiD and will start another thread when th etime comes to get it up and running.

Best,
Kelly

[airnocker]

Cool.  So one pin will be used as an digital INPUT from the Super-PID optical speed sensor positioned over the end of the router's motor shaft.  This signals one O/1 cycle per motor revolution.  Another pin with be defined as a digital OUTPUT that connects to the Super-PID for ON/OFF control.  Another pin will be defined as a PWM OUTPUT from your Arduino's control software that tells the Super-PID speed controller the router RPM defined by your G-Code.

[dave benson]

Kelly
1.1 is the latest version, in earlier versions the PWM frequency was 8 khz.
new versions have 1 khz because it was better for noise imunity.

I made my own pwm to analogue converter, but you can get them on ebay for 10 bucks.

This is a snippet from ElectronicsFourm.

Spectrum of the rectangular signal produced by the PWM is large and variable.
This can be a problem without appropriate filtering, construction and PCB layout.
Resistors, capacitors and operational amplifiers for filtering and buffering of PWM
signals should have appropriate characteristics.

It might pay to check if the SuperPID controller is expecting a true PWM input where the
mark\space ratio is measured not the voltage or whether it is an analogue voltage input only
(no input filtering) or whether it does expect a PWM signal and has the input filtering.

You can kinda get away with whacking a PWM signal into a true analogue input, but the
linearity may not be the best.
I watched a vid on utube where CNCnuts was trying out his new SuperPID cutting
mdf and acrylic, he made some cuts and videoed the spindle rpm while the cuts
were taking place, I stopped and started the video  and found the max and min deviation
in rpm, it dipped 200 rpm and then overshot 100 rpm before settling. Commanded at
12000 rpm. This represents 2.5% error and he was pretty happy with that and showed the
cut surface for the wood, which looked ok.

For the kind of work, you propose to do it will be fine.

If you could invent a method, device or incantation to reduce or eliminate
the noise these things make, you could retire on the proceeds.

Dave

Install and Test of Super-PID 2048 - CNCnutz Episode 19 - YouTube

[airnocker]

Interesting info Dave.  I've cut aluminum, acrylic, polycarb, 3/4" plywood, 3" oak and never saw any significant change is router speed...using Mach 3 Mill.  Nor have I seen any noise that affects anything in or around the PID, BOB, computer, computer display, etc..  I will watch the video with interest.  You make some great precautionary points.

Update: I've watched the video and to be fair, his sensor painting and detector installation was kind of sloppy, and his router was a very old one with aging issues.

The Super-PID expects a Mach3 type of PWM signal (a true PWM) and uses it to control a Triac duty cycle for motor speed control.

Here is this PID's Version 2 instruction PDF.

[Tool-n-Around]

I'm gonna call this one complete.

I made the second PC lid and I'd say it's improved over the previous but the perimeter cut although better is still poorer than it should be even though I reduced the full hieght finish cuts from .5" to .25" by cutting the chamfer before the finish cuts. I don't have more PC machining in the immediate future so maybe I can make some machine upgrades that add some rigidty and broader/better router speed control before the next go. Thanks for all the helpful suggestions fellas.

Best,
Kelly

[pixelmaker]

Hello Kelly
I think for such an application cast PMMA is the better choice. Inside the air filter the material is cooled, outside it gets very hot in the engine area.

PC does not withstand these temperatures and fluctuations as well as PMMA. PC will turn yellow quite quickly. PMMA does not have this problem. I have driven  radiator mounts from PMMA in my car for many years without the material changing visually.

ralf

[Tool-n-Around]

That's interesting Ralf,

I've seen conflicting information on chemical compatability of both PC and PMMA. I originally selected PC (perhaps 20 years ago) because of what was reported to be superior chemical resistance, primarily to gasoline and oils, and stablility at higher operating temperatures.

If you search the subject "Chemical Compatabilty of Polycarbonate", specifically with respect to gasoline/petroleum, the vast majority of references classify it as good to excellent. A few say unacceptable but referrence no standard or source for the rating. The source I buy my PC from rates it as "good" but not excellent.

If I do the same search for PMMA, most will say moderate to poor, and many (more than PC) will say not suitable. The same source I buy the PC stock from rates it as moderate to poor.

As far as operating temperature, PC has a glass transition temp of 147C while PMMA is 105C so I think that pretty clearly favors PC.

As far as aging and optical clarity, I think Ultraviolet is the primary culprit of diminished optical clarity for PC. Under the bonnet/hood, it's well shielded from sunlight.

Use and practice on actual operating engines over the years seems to bare out PC is indeed resistant to attack from gasoline, however they tend to get foggy deposits on the inside (oil vapor) of the filter and dust on the outside, both of which can be wiped off and cleaned with mild detergent, but it takes great care because the PC scratches so easily. I dont have the same history/experience with PMMA so can't comment other than I'm confident it would be much more scratch resistant.

I did buy some PMMA to compare machinability on the same part and MOPs but haven't done so yet.

Best,
Kelly

[pixelmaker]

https://www.neolab.de/media/wysiwyg/content/laborwissen/wissenswertes/Chemikalienbestaendigkeit-von-Kunststoffen.pdf
looking in this list I have a better resistance for gasoline with PMMA than with PC.
For diesel oil and petroleum I have a good resistance (0) for PMMA, a low resistance (-) for PC.
Only with ethyl and methyl alcohol does PC do a little better, but if it is a cast PMMA and it is well tempered the durability is just as good as with PC.

PMMA is often used on cars, for lamp glasses, for coverings and trim parts, but PC is not used. The headlight lenses of the Mercedes Benz W203 C were made of polycarbonate and after 5 years they had yellowed and get stress corrosion cracking. Replacement lenses were then made from impact-resistant PMMA .

ralf

[Tool-n-Around]

Like I said, you'll find conflicting information. Back when I originally selected PC, I just placed a piece an a jar with gasoline and watched how it aged. There was no visual degradation or obvious change to hardness after 6 months.

Best,
Kelly

[pixelmaker]

It is the constant temperature changes in the engine room that cause the PC to yellow and age.
I think gasoline is not a problem there at the air filter.
Oil fingers have no reason to be there either.
Otherwise, PC has a much softer surface and is more sensitive to scratches than PMMA.

ralf