Messages

61

CamBam help (General usage) / Re: Machining Polycarbonate - Progress

« on: November 28, 2022, 00:24:42 am »

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

Changes:

.25"D and .031"D End mills were polished O-flute.
I added spiral lead in moves to everything.
Everything was cut at 45 in/min except the logo which was 30 in/min
I used soapy water for the logo cut only chasing the cutter and clearing chips with a wet chip brush, everything else was cut dry.
I reduced DOC on the dish cuts to the filter gland so there was a light finish cut.
I reduced depth of cut on the .25D EM perimeter cuts to .1". I used a rouging cut at .35 width which was the longest of ops, then two full depth finish cuts removing .005" each time.
The stock was secured with six screws. The stock was warped .090" high in the middle over 21" of length.  The screws were able to pull it flat but not very happy with the stock flatness.
I removed the protective film for all machining.


General Impressions:

Significant improvement over previous attempt. Still some areas could be better. I uploaded a high(er) resolution photo.
The logo is crisp and I'm quite satisfied with how it cut.
The ornamental grooves are ok, had some minor burrs here and there on the surface edges that needed to be struck off with a razor, but a fair trade for me to be able to cut it dry.
The dish cut on the filter gland is much better......still some tool marks but much improved.
The perimeter cut is much better but still the most difficult for my machine and leaves greatest room for improvement.

I think I'm 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. It's just a hobby machine fellas. It just makes for a lot of cantilever leverage on the Z-axis and the it's not exceptionally rigid to begin with, coupled with the fact that it rides on extruded aluminum gantry this 44" in both X & Y. I think I can stiffen it up a bit and have a few things on my upgrade list. I'm sure cutting these ops with fluid would help. I'm just not set up adequately to do so, but could remedy that.

I can do a little hand work on the perimeter and this one and it will be passable. I think I may order some acrylic and make a couple for comparison. I'll post some completion photos when I get there.

Best,
Kelly

62

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 27, 2022, 16:41:21 pm »

What's a practical/economical waste board material?. When I surface the mdf wb, it's fuzzy and I dont think lacquer finish would be sufficient for bonding tape and using the tape/CA Glue method. Maybe just contact cement thin plastic sheet (like .125" acrylic) to the mdf? I'll need 24" x 16" waste board.

Best,
Kelly

63

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 27, 2022, 00:26:37 am »

Polycarbonate’s super power is impact resistance, scratch resistance not so much. There are formulations, where a thin glass hard like layer is applied during manufacture
to help this.

I may need to look at using acrylic. I thought the toughness trumped the scratching but pc scratches easily. Since they're just display pieces, durability may be more a matter of scratch than impact resistance. Not sure it will change the machining issues much though.

I don’t know if it’s my imagination or not, but looking at the tool marks at the bottom of the cuts (on the outer periphery) it looks like the tool is digging in at times, so the tool is porpoising along as it’s making the cut, It might pay to check the backlash in the Z axis, on your type of machine the Y axis can contribute to this as well, if you look at the wheels on the Y axis and they appear to have a white ring around them, then they have worn in a little and need a snug up.

I’ll check both. It may also be the stock getting lifted off the table by up shear. I’d probably need vacuum hold down if so. We’ll see how much pc I do in the future. I need to get through these two peices in the present.

The z-axis is just an acme screw with kind of a hokey backlash anti-device but it’s on linear rails. The wheels on the rest may very well may need tightening. That darn foam has quite a charge when cut and that which escapes vacuum collection clings to everything including the v-grooves for the wheels which compress the fluff with cycles into much harder interference. If I don’t wipe (especially the underside that I can’t see) it can build up enough to cause step loss. I was considering adding some air jets to keep/blow the fluff out of there, but I need to modify the machine for more Z-axis travel and when I do so, I’m giving serious consideration to upgrading everything to linear rails (versus wheels) and ball screws (versus rack and pinion). It would just be imported rails and screws, but I can do the whole machine for $350. The rails have wipers that will probably handle the foam dust fine, not sure about the ball screws. Re-engineering my cnc machine hardware for such would be no big deal for me. While I was at it, I would probably fill the aluminum extrusions for stiffness…….but maybe not the one on the moving gantry to keep it light. Even with the cheap imported linear motion stuff I bet it would be a significant improvement for the machine and probably good value for money.
 

Love to see your work, always puts a smile on my dial.

Me too, I really enjoy it. I’m working on a couple projects now that will be my most complex and best work so far. Right now it’s being paced by my CAD learning curve to model the projects, not cut them, but I’m getting there. Th efoam patterns should be some pretty impressive (at least for me) 3D machining work. When I do, I’'ll stop back and share. Heck, I'll probably be back for help. I still have great appreciation for all the help and patience this forum provided to me when I was just starting out.

Best,
Kelly

64

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 26, 2022, 15:37:36 pm »

I forgot one important detail. I machined that previous lid with the protective film in place. Not so on the most recent effort. The film adhesive seems to be waxy feeling. I did it to prevent scratching while handling because that is how the professional friend of mine I previously mentioned did it. May it have served as cutting lube? What do you think?

Best,
Kelly

65

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 26, 2022, 15:24:38 pm »

.......I did everything wrong to make an acceptable cut.....Wrong speeds and feeds........Crappy work holding (sitting on parallels in the vice) so no support at all......Wrong type of endmill (it was a well-used one for cutting AL, four flute).......No air blast. Short of spinning the endmill in reverse, I could not think of anything else to do wrong.

The only thing I did was lubricate the cut with straight dish washing liquid at
the start of the cut with my finger......Tooling marks aside, the piece came out optically clear, I can see straight through it
(40 mm) to the woodgrain of the table.

Wow! I must say, I went back and looked at the pics of one of the other polycarb lids I did. Ignorance was bliss. I paid no particular attention to anything and just cut it at an arbitrarily lower speed than I was cutting polystyrene casting patterns foam. The logo had some burrs stuck to it but they came off with a wooden pick. Those were the cut speeds I started with on this filter, however, the cutters may not be the same....cant be sure on that. Attached a picture of the resulting air filter assembly with both aluminum and pc lid.

I’m not suggesting that you use the dish washing liquid, just that if you are still struggling to get an optically clear surface to your satisfaction, after taking all of the above advice (which is good) then it’s well worth considering. Dave

Well if not suggesting it's sure making a strong case for it! I have not gotten back to experimenting with it because I had family visit and they stayed....so will be back at it when they depart.

Best,
Kelly

66

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 25, 2022, 02:38:38 am »

There is a vid on Utube where the people from carbide create cut out some polycarbonate
and give the feeds and speeds for various tool diameters.

I always forget YouTube. Upon quick search I see there’s tons there.

He does lament that his software doesn’t have a spiral lead in’s, CB does though.
This is important is can help a lot, is for example in your Logo where you are using a
ball end endmill, it’s a good idea to use the leadins as plunging straight down into the material
is not a ball end mill’s superpower, (typically the plunge feed rate is less than a center cutting endmill) and as this is the start of the cut and if you get chip welding it’s hard to recover from.

My palm is on my forehead. In fact I could see this happening upon the plunge. I will incorporate lead ins.

I always use dish washing detergent for polycarbonate\Acrylic.

Will do so after some more (dry) experimentation.

Without the cutting surface speed for the material or the chipload from the endmills manufacturer data sheet your feed and speeds cannot be calculated, so it’s a guesstimate at best.

Well, I searched my memory, poked around, and low and behold found the O-Flute data. The feederate for the ¼”D bit is making my eyes pop a bit. My router is only 1.25HP and at lowest speed, will be a fraction of that. Will need modest DOC for what the chart suggests. See attached.

When I machine polycarbonate, I always use single flute endmill (have better success with HS .25"EM vs carbide. Use lots of compressed air directed where endmill engages piece. Because I have PID spindle control, run the spindle at 9000 rpm, and high feedrate, and .25 deep. The feedrate most often is set at 45 ipm. Hopefully this will give you idea. Get scrap piece, set the rpm's to low end and make cuts varying the feed rate. When cuts the best it sound/feel like the endmill will break any moment. That where you will see nice cut. Good luck.

Thanks Bubba, wont be able to get quite that low rpm but have been in that 45 ipm range. Only carbide at the moment, but anxious to try the single O-Flute. The chart I posted seems to suggest 150-200ipm…..dont know that I’ll have the courage.

My router also originally came with its own "dial" speed control in a similar rpm range like yours and could not go below 14K rpm either.  With this PID controller it can now go down far further, like 5K rpm, under complete control by Mach3.  My acrylic milling/engraving speeds are usually in the 10-12K range, feeds in the 30-45 ips range. .......Their website is https://www.precisebits.com/.

Thanks for that airnocker and for the source. Similar to other feedrates mentioned but cant quite dial that low rpm. May need a little more feedrate and less DOC.

Thanks for replies guys.

Best,
Kelly

67

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 24, 2022, 21:57:04 pm »

Would a variable duty-cycle motor driver perhaps permit you to run that router more slowly? Lloyd

Well, the router already has a dial that varies speed from 14krpm-24krpm, which was kind of handy for experimenting because I can change speed as it cuts and observe the chip and general quality of cuts. I'm not sure what it uses for control, probably PWM or maybe just rheostat given its a brush motor. Not sure I could get away with another such device in series, and they do lose power at lower Rs......not a problem for the small bit bit likely so for the .25D 2-sided cuts.

Best,
Kelly

68

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 24, 2022, 21:46:54 pm »

Why is coolant not an option?  It's fairly inexpensive and simple to implement. Lloyd

Well perhaps not an option is too strong, but at least not a good option for me since most all of my work is dry cutting softer materials and with an mdf bed and waste board, I’d suppose I could just make a collection pan. Would still be a heck of a mess along with the wet chip ejection and prevent vacuum chip collection. If need be and I do enough with polycarb in the future, I probably have a spindle purchase in my future for reasons other than just this, instead of the cheap router, which should afford a bigger speed range if needed. Not yet certain it’s needed…..I thought my sample cut on the logo looked good, but that long stringy burr got woulnd up on the cutter which did not happen on the sample. I have a few things to try. I think it may benefit from more feedrate too but with that small of a pattern the direction changes can get inertially violent.

One possible reason liquid cooling may not be an option is that not everyone's machine is waterproof or even water splatter-proof.

That is the case with me at the moment but could probably be managed.

I know you said coolant was not an option and it's the same for me, but, I get far better cutting with a little washing up liquid in water just dribbled on top.

A little puddle or squirt bottle applied spritz would be a possibility on the logo. It’s small so not much of a mess to deal with but enough to handle the perimeter cuts would be a lot more to deal with.

I'm no expert but have done a lot of polycarbonate engraving and milling, relatively speaking.

If welding is occurring then that is an indication of high friction and heat.  You're on the right path to increase your feed rate if you cannot decrease your spindle rpm.  Also, large diameter mill bits will have a higher angular velocity than a much smaller bit for a given rpm.

What cutters and speed did you use?

The .25D cute was a low helix angle spiral which according to the manufacturer is designed for hard plastics, which may be the case but even though its upcut, probably doesn’t eject chips as well, especially on the two sided cut. I have a single O-flute cutter in that .25D which is supposed to be better, and thinking with a little shallower depth increment and more federate may do the trick dry.
The .031 cutter I was using to cut the logo is actually a single O-flute not round nose. I had to look at that thing under high magnification to confirm such.

I’ll do some experimenting tomorrow and report back.

Thanks for the replies and Happy Thanksgiving to the US guys.

Best,
Kelly

69

CamBam help (General usage) / Re: Machining Polycarbonate

« on: November 24, 2022, 15:05:30 pm »

I couldnt find any information of cutting speeds for PC....probably not looking in the right place.

Just thinking this through a little bit, if I'm melting the polycarbonate, I'm dwelling and/or not ejecting chips. Since I can't go any lower in rpm, I may need to increase feed rate. If the router cant handle that, then take smaller depth of cut. Also, I have a .25" O-flute carbide bit that is supposed to be for harder plastics. Being single flute seems that it will also help. I can buy 1/32 O-flute flat bottom bits inexpensively.....may do that too just to have them if the .25D O-flute performs well.

Think I just may need to experiment a bit on some test plaques.

Best,
Kelly

70

CamBam help (General usage) / Machining Polycarbonate

« on: November 23, 2022, 23:48:26 pm »

Hi all. Been a while but I’ve been busy with cb. I haven’t had to pay very close attention to feed/speed machining foam patterns but not the case here.

Looking for a little feed and speed guidance for machining polycarbonate. I previously made a post about another polycarbonate lid I made, but I’ll be darned if I can find it. Before I post the cb file, thought I’d just start with the piece I machined, and describe some of the issues I had, and see if I can get a nudge in the right direction.

The part is a display lid for an automotive air filter. The stock size is 21”L x 8”w x .5”t.

I’m seeing a lot of chip welding. I don’t have cut data for the bits, but in general they are carbide woodworking bits unless I say otherwise.

First op was the logo. I had machined it before on a previous project (also polycarbonate) with pretty good results. I set the lowest speed on my router (about 14krpm). It’s a single flute .031” ball nose cutter so it can fit through the narrowest regions of the letter pockets. The feed rates are 15in/min. The depth of cut was .020” and final depth .031. I cut a test plaque and thought it looked good. When I cut the logo on the actual part the chips melted/welded around the bit and scarred the surface around the ellipse. I’m thinking I need to back off to a smaller depth increment to help clear the chips and keep compressed air on the cut. The problem is the darn chips tend to hang on the surface edge like a stringy burr so they can’t always be cleared. Not sure which direction I need to go on feed/speed. I’m at low rpm limit. Coolant/mist is not really option.

The ornamental grooves cut pretty well.

The perimeter chamfer (.5”D double flute 90 degree vee). Depth increment was .15” and final depth .2”, 16krpm. It was a total mess with chip welding on the conventional cut side only. I did a .005” clean up climb cut and the chip welding switched to the waste side, and the part finish looked OK.

The filter gland is cut with a .5”D dish cutter. I didnt post a picture and it has some tool marks in part from the piece being inadequately secured (a screw in each corner and two in centrally in the part). I’m not too concerned about this because the gland turns visbly black when the filter element is installed and I'll never achieve optical clarity on my machine or without polishing.

The .25”D double flute spiral end mill perimeter cuts were a mess. The feed rate 60in/min, depth increment was .25”, and .35” cut width, 16krpm, which for sure was too aggressive for my router and probably so for my hobby cnc machine, especially in the initial two-sided plunge cut. I had a final .5" full depth finish cut of .010” which after observing the chamfer cut, I chose to climb cut. I didn’t post pictures because probably same issue here. The perimeter finish is not so great but why does climb cutting seem to be producing a better result?

I can post additional info as needed, but had to break the cb file up for tool changes and made in-process mods to those files so will need to update the consolidated file before I do so. I can probably salvage this part with some elbow grease but looking to do much better on next pieces.

Best,
Kelly

71

CamBam help (General usage) / Re: Some Qs on Imported CAD Files

« on: September 25, 2022, 15:39:02 pm »

I was off gallavanting about England for a week but back on the pitch now!

...For what you want to do it’s not worth the effort to use step files...........The STL format is old but it’s it’s an open standard, newer programs are transitioning to AMF (the 3D printing crowd are all over it) which is better in every way.

Will check that out.

I don’t know about Alibre, It has a somewhat checkered history, that software has been bought and sold a few times,.....

Old stuff I read said it was it could be a bit buggy bit buggy. I have several friend that use it and recommended it. I tried the demos of a few others and it seemed pretty good to me and has a pretty good user forum. As a hobbyist and less frequent user the perpetual license and (lower) cost of ownership ownership made it look like a good value for me comparedto packages that were $1000s to buy and maintain.

In short use a stl and dig around in Alibre to find the working with mesh’s doc. Some programs like Prusa slicer (free) will automatically on loading the file repair it and on occasions I’ve had a stl file that I could not fix and running through the slicer it was repaired. Alibre may already do this, I don’t know. It’ll be a matter of trial-and-error finding what works best for you, just reduce the stl triangle count until it’s not usable in CB .....

I'll experiment.

Thanks again.

Best,
Kelly

72

CamBam help (General usage) / Re: Some Qs on Imported CAD Files

« on: September 16, 2022, 15:13:21 pm »

An STL model surface is made up of  many small triangles, more triangles give a more faithful representation, however they make for large files.

Part of the question was rather STL was the best import format. I only selected it because I had used them before with success and I dont know any better. It doesnt seem like 15MB is excessive when the smart phone pictures these days are 5MB . Would you consider 75MB large for a CB program on a part that size with three scanline 3D MOPs.........one roughing and two finish? Other than being able to post the file here, it's not that big of a deal but if it can be 10x smaller, why not? Doesnt seem like the CB file is ever going to get smaller than the STL file it contains.

There are programs out there like Meshlab that you can use use to simplify the mesh (decimation is one methods) but not the only one, there are many more. You may already have the tools in Alibre, the surface deviation doesn’t need to be that small.  Typically, you can reduce the file size by many times.

The only Alibre tools I'm aware of are the STL parameters described at the link in the previous post.

You don’t need a stl file to have a resolution any greater than the resolution you can achieve with the tools (the diameters) you have selected.

I guess I'm just going to have to scratch my head a little more to see if I can decipher what that may mean to the three settings for the STL export and experiment a bit. I suspect it was excessive but cant say.

Great job on the Willy’s by the way.

Thanks Dave. It was a fun project.

Best,
Kelly

73

CamBam help (General usage) / Some Qs on Imported CAD Files

« on: September 15, 2022, 19:49:28 pm »

Hi fellas. It's been a while. I've been happily motoring along with CB and more recently bought some CAD software (Alibre Design) to solid model my projects. As you may recall, I primarily use CB to machine polystyrene foam patterns for lost foam casting, primarily automotive parts.

Attached is a Camotics simulation picture of my first CAD modeled part. It’s an automotive intake manifold flange. I saved the solid model as an STL file for use in CB and that file is 15MB. When I import it into CB and set up several scanline 3D Mops to machine it, it becomes a 75MB CB file so I assume too large to upload here. The actual part is roughly 20”L x 3.5”W x 1.25”H. I simulated in Camotics and it looks ok. I haven’t tried to optimize the run time. This model is not filleted. The filleted version is even larger but I figured it wasn’t necessary since I use a 1/4D ball end mill as the cutter and it happens naturally without the filleted model.

To date I’ve done most of my CAD within CB and not imported objects. What is the preferred type of CAD file to import and use within CB? For the STL file, I have a bunch of options about the faceting parameters, surface deviation, and coordinate system as described here in the Alibre documentation. I have no idea what is necessary/adequate for my use in CB and probably chose excessive parameters. Any rules of thumb or advice in this regard?

https://help.alibre.com/articles/#!alibre-help-v25/stl-export-settings

Ultimately, it seems this part would run much faster as a 2.5D part excluding the angled bosses, followed by some 3D MOPS for those bosses, but even with the run time, just running it as one surface would be quite attractive. Run time isn't me-time when you’re only making one or two parts :-)

Best,
Kelly

74

CamBam help (General usage) / Re: Bit pulling out arggg!

« on: April 27, 2022, 14:09:55 pm »

4. wrong size collet (e.g. metric instead of inch)

+1

Almost always caused by a bit advertised as inch that is actually nearest metric size.

I presume the shank on the bit is 1/2" and you are using a PC collet not an aftermarket 3/8" PC colllet. If not, where did you get the collet? A lot of aftermarket collets for PC Routers are total junk. Especially the ones sourced on eBay and Amazon.

Best,
Kelly

75

How to's and tutorials / Re: 4 axis machining with CamBam V1.0

« on: April 18, 2022, 14:41:45 pm »

That's great David, looks like a lot of work. Thank youso much. I think I have just the project for it. No Mach 3 though but I think I can do it with just positioning and a combination of 2D, 3D, and wrapping. I will revive the post when I get back on it.

https://cambamcnc.com/forum/index.php?topic=9402.msg73431#msg73431

Best,
Kelly