Machining Polycarbonate

[lloydsp]

"... bumping into the limits of my machine rigidity greatly aggravated by my having the router fully extended and all things biased for maximum stroke and height under gantry."
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So. elevate the work with some plates beneath it.  Get it up closer to the gantry, so that the rigidity is not so challanged.

Lloyd

[Tool-n-Around]

"... bumping into the limits of my machine rigidity greatly aggravated by my having the router fully extended and all things biased for maximum stroke and height under gantry."
--------------
So. elevate the work with some plates beneath it.  Get it up closer to the gantry, so that the rigidity is not so challanged.

Lloyd

Yes, I'm actually going to raise the gantry further becasue I need more z travel for pattern work and a removable platform was the plan. I just havent been cutting much but foam so wasn't as obvious until I started cutting on the pc recently.

Best,
Kelly

[airnocker]

Lloyd beat me to the punch.  I wholly agree with what he said in raising your work holding to limit your z-axis travel.

[dave benson]

I’d be happy with the logo, it looks nice and crisp.
One thing I forgot to mention earlier, was that the longitudinal slots (on close inspection)
look a little wavy, you can improve on this by changing the machining strategy (toolpaths).
Joe Pie has an excellent video on the causes of this and the solution.
https://www.youtube.com/watch?v=QGHujqWlxtg

At 22 minutes in this video he’s milling Acrylic which is worth a look.
https://www.youtube.com/watch?v=6JH3frgVpGY&t=1282s

With the upgrades for your machine, the priority concern would be the Y axis, the present
carriage mechanism is wanting in many ways.
It works mainly because the wheels are compliant.

This young man is doing a mill, the procedure is not exactly the same as for a router but it
might give you a big picture view of how to go about the installation process and some of the
tools and techniques involved.
https://www.youtube.com/watch?v=wxRKSAuqZ2I&t=401s

I’ve included a pdf in the zip, It’s long and technical, so just skip over the stuff not of interest
It does have a good section on linear rails and another where they model a gantry machine as
a spring system.

Upgrades can be a rabbit hole, you upgrade one aspect of the router and this points out another
weak point.

There are many types of linear carriage and rail systems, but for the sake of discussion, two
common types are round rail and round and C section carriages, and rectangular section rail
and carriages.

1….Pom wheels → running directly on the extrusion.
Cheap quite, tolerant to misalignment. Slow, intolerant of debris not very accurate.

2….Round section rails bolted to a foot plate that’s bolted to the extrusion.
A step up in accuracy over the wheels, adds a bit of stiffness, because of the foot mount.
Less tolerant of misalignment than the wheels but more tolerant than the rectangular section
rails.

3…..Rectangular section rails are the most accurate, but require a prepared surface to run
smoothly, bolting them down to an unprepared extrusion would very likely cause binding issues.

In the pic there is an example of the tolerances you might expect to see in the extrusion.

Just some things to think about.
edit: I can't seem to upload the zip it keeps getting rejected, I'll keep trying.
Dave

[airnocker]

Dave, there is a problem with the YouTube links you supplied.

[dave benson]

I couldn't get the pdf to upload either, its 10mb zipped.
Dave

[Chip Owner]

I did some test cuts and used those learnings to cut another polycarbonate lid.


... I'm sure cutting these ops with fluid would help. I'm just not set up adequately to do so, but could remedy that.


Best,
Kelly

I'm in the school that with the right feeds & speeds and the right bit, fluid isn't needed. Having the same problem as you with the MDF bed and also not wanting anything else added to the atmosphere or my shop, it's used for other commercial activity.

I had exactly the same issue in the early days of researching cutting alu, everywhere I went talked about some kind of fluid and still see endless videos of people needlessly spraying lubricant in various guises. I was lucky enough to find a guy who had spent years working in the industry just setting up his own consultancy. All the videos from his previous employer showed clean cuts, little to no tool marks and zero fluid, even over large sheets.

I asked him how?

His response: With the variety of bits now availabe there are plenty of bits on the market designed to cut almost any material, even steel, without requiring lubricant. Yes it may shorten tool life on the really hard materials but they exist. In my case it was switching to DLC type single flutes.

There are videos on YT of people cutting PC, 6mm depth of cut, 5m per minute speed with 6mm bits on machines not disimilar to yours, getting nice clean cuts.

I would seriously look at the bits you use first and this may cure all your problems without you needing to create other solutions & solve the problems it may create. I appreciate not as cheap as a bit of washing up liquid or WD40 but will allow you to carry on cutting dry.

[Tool-n-Around]

.........I'm in the school that with the right feeds & speeds and the right bit, fluid isn't needed. Having the same problem as you with the MDF bed and also not wanting anything else added to the atmosphere or my shop, it's used for other commercial activity........There are videos on YT of people cutting PC, 6mm depth of cut, 5m per minute speed with 6mm bits on machines not disimilar to yours, getting nice clean cuts........I would seriously look at the bits you use first and this may cure all your problems without you needing to create other solutions & solve the problems it may create. I appreciate not as cheap as a bit of washing up liquid or WD40 but will allow you to carry on cutting dry.

Good points. Given the improvement I saw with the O-Flute cutters, I'm certainly interested in gains available with other cutters as well, but I can say having observed and experimented my machine, it's hard for me to see getting anywhere near the recommended feeds/speeds from the cutter manufacturer on my machine or those in that video. I need to assess/address the (prone) aspects of my Z axis as to how much contribution is there. Just keep in mind this is a relatively large work envelop machine  that is supported by an aluminum extrusion gantry........it has it's limitations in riigity but was still probably good value for money, is very light and works well for cutting foam at high speed. I just need to decide how much Polycarbonate (and/or hard material) machining I want to do in the future.

I just wanted to machine two PC air filter lids, but didn't appreciate it may present the need to reconfigure the machine, build a platform, add a fluid dispensing and collection system, and buy a set of dedicated cutting bits. 

However, I may be willing to account for such things if I decide to do future machine upgrades. It's a ball rolling down hill.

Best,
Kelly

[Tool-n-Around]

……..One thing I forgot to mention earlier, was that the longitudinal slots (on close inspection)
look a little wavy, you can improve on this by changing the machining strategy (toolpaths).
Joe Pie has an excellent video on the causes of this and the solution.

Thanks Dave I'll have a look at those.

With the upgrades for your machine, the priority concern would be the Y axis, the present carriage mechanism is wanting in many ways.

Completely agree. I’ll take in those videos too. Is there a way you can PM me a link so I can download the larger pdf document? For my machine I was thinking HGH style rails and SFU series ball screws to replace the wrack and pinion. You can probably tell I’m talking Taiwanese/Chinese stuff. Not real CNC grade stuff but the machine will never be that standard nor does it need to be. Though I’d likely pick up some positional accuracy, the other big motivation was debris tolerance and reduced maintenance/recalibrating. My future projects will have long run times and my machine needs to be able to run reliably unattended. The vast majority of use will be polystyrene lost foam casting patterns. I think it may be best for me to start a different thread on the machine upgrades in the machine section of the forum. As an odd coincidence, the manufacturer of my machine recently offered what they are calling the “pro” version of my machine. My linear rail strategy would be similar but with slightly better rails than they chose. They stuck with the rack and pinion drive but I’m eyeing ball screws. Here’s their link.

https://millrightcnc.com/product/mega-v-pro/

Upgrades can be a rabbit hole, you upgrade one aspect of the router and this points out another weak point.

You sure got that right. I’m looking at 2.2kw spindles as well. At some point there’s a decision to be taken on whether to upgrade or buy up.

Best,
Kelly

[lloydsp]

Of course, rigidity of the axes is the first thing you should 'fix', if they're repairable.

But then, as was mentioned earlier, consider adding a PID speed control.  They're not expensive, and you can get nearly full horsepower out of a brush motor, even at very low speeds.

Lloyd

[Tool-n-Around]

.......One thing I forgot to mention earlier, was that the longitudinal slots (on close inspection) look a little wavy, you can improve on this by changing the machining strategy (toolpaths).

You have a good eye. I had to go hold the part up and look down the grooves very closely and at first I thought it may have just been irregular deburring of the edge but looking closer, I think you are absolutely correct. Those are done with an engraving MOP. I don't get a lead in choice with that MOP but don't think that is the source.

Having watched the video, although the .188"D ball nose is 1" CL double spriral carbide, and BN isnt the best cutting profile, I don't think it's cutter flex based upon sound of cut. The cut depth is so light, it seems much more likely to be Z-axis flex. Having already tightened up the wheels, I just may need build a platform and reduce the router stick out as previously suggested, because if it's flexing that much on those light cuts, no wonder I get poor performance on those full (1/2") depth perimeter cuts, even shaving .005".

The acrylic machining video was eye opening. I did buy some acrylic to experiment with. We'll see how it goes with respect to blow outs and cratering.

Thanks for those vids.

Best,
Kelly

[Tool-n-Around]

Of course, rigidity of the axes is the first thing you should 'fix', if they're repairable.

But then, as was mentioned earlier, consider adding a PID speed control.  They're not expensive, and you can get nearly full horsepower out of a brush motor, even at very low speeds.

Lloyd

Thanks for that suggestion Lloyd. I did some searching found this offering. I'm sure there are others but this may be a very sensible alternative to an import spindle and VFD for me for many reasons such as posted in my machine upgrade thread. I won't get spindle perofrmance but may get similar level of control and good/better performance for a niversal brush motor, and I have many routers. If anyone is ware how has a favorite please let me know.

https://www.vhipe.com/product-private/SuperPID.htm
https://www.vhipe.com/product-private/SuperPID-v2_Instructions.pdf

But, ships from Australia. No worries about that except time and cost being a US based guy.

Has anyone here actually used this product with CamBam?

Best,
Kelly

[airnocker]

I have and have used this Super-PID since version 2 came out with CamBam and Mach3.  It is an excellent product.

Used it for 9 years and never had a problem.

NOTE: most conventional routers (Porter Cable, Dewalt, etc.) can usually be modified to incorporate the Super-PID controller. If you want to see if your router can be converted for use with Super-PID, post the make and model of your router.  I've posted step by step instructions on another CNC website on how I did the conversion on my Porter Cable 890 and can share with anyone interested.

[lloydsp]

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

[airnocker]

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