V-carving clear plastic

[Chuck Keysor]

Hello Shopbot friends:

I tried to V-carve a simple sign on some clear plastic someone had given me. I don't know what type of plastic it was, as the cover paper had been removed, and I have never cut clear plastic. (My guess is that it was something that would be purchased at a local hardware store for storm window replacements.) The plastic was 1/4" thick. I used a 60 degree "laser" bit, at 1.5IPS, and 12krpm.

The first letter turned out OK, but after that, most, if not all were ruined as follows: Plastic re-melted and stuck onto the point of the bit, forming a disk, that scrubbed and melted the surface of the plastic on both sides of the carved text.

When the bit would lift to make a move, I used a thin piece of wood to knock off the disk from the tip, but in a few seconds, a new plastic disk had formed on the tip, and it resumed scrubbing/melting the surface on each side of the V-groove. When I was done, I had maybe 20 little plastic disks laying on my machine bed, some as large as a quarter of an inch in diameter.

My first guess is that if the original protective sheet of paper had been in place, that none of this would have happened. But that is just my guess. Are there other issues here that would have condemned this experiment to failure?

I'll upload pictures later, but I hope my description is sufficient for some basic feedback.

Thanks, Chuck

[jerry_stanek]

If you spray it with some dish detergent before you cut that will help a lot

[Chuck Keysor]

Thanks Jerry! But what I forgot to mention,,,,, duh,,,, is that I have a second piece of this exact same material, so I don't want to mess THAT one up. And, it is exactly the same as the piece that I wrecked yesterday. Thanks, Chuck

[tlempicke]

There are lots of different kinds of plastic. Some cut pretty well and some not so good. Plexiglas can be either cast or extruded, and that makes a difference.
Don't be chicken with the cutting speeds. You have to be taking chips and moving right along to keep the bit cool.
One of the guys who shows up regularly at the Spring get together in Columbia SC has done some beautiful 3D carvings in plexi and edge lighted it with LED's. Really stunning work!

[Burkhardt]

Make sure you blow the chips off while cutting. If they accumulate in the grooves they are being re-cut while still warm and just melt on. The air stream may also cool the bit but I am not sure if that is substantial.
Maybe you can try some speed settings with the part that you already ruined. And make sure the v-bit is REALLY sharp.

[Chuck Keysor]

Thank you for your added input. I did move slowly, and did get small chips, which you can kind of see in the blurry photo (sorry, $40 digital cameras don't seem to work very well.......) But when originally experimenting with V-Carving, and reading posts, 1.5IPS is about as fast as I can go.

The blurry picture with the tape measure also shows some of the little disks which I kept flicking off of the tip of the V-bit.

The second picture shows the over-all sign, and ignoring all the chips and dust on the plastic, it shows how the disks scrubbed/melted the plastic on each side of the V-carving....

As I'm giving the sign away, I don't want to go buy the right material for this job........ However, what type of plastic SHOULD I be using?

Also note, I reverse cut this, IE, I cut it on the back side with reversed text.

Thanks, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29030&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29031&stc=1

[Chuck Keysor]

http://www.talkshopbot.com/forum/attachment.php?attachmentid=29032&stc=1

This is what I wanted the plaque to look like after painting. (Reverse carved on the back side, letters infilled, then the entire back side painted white.

Years ago, I had used a hand router to reverse carve letters on the back side of a piece of plexiglass (or something,,,, it too was free), and it carved well, and looked fantastic when viewed from the front side.

Chuck

[cnc_works]

I fairly confident that your issue is what tlempicke mentioned. You are describing classic problems with trying to cut extruded acrylic. I ran into this early on and learned fast to only cut cast acrylic. Good Luck!

[Tim Lucas]

Hello Shopbot friends:

I tried to V-carve a simple sign on some clear plastic someone had given me. I don't know what type of plastic it was, as the cover paper had been removed, and I have never cut clear plastic. (My guess is that it was something that would be purchased at a local hardware store for storm window replacements.) The plastic was 1/4" thick. I used a 60 degree "laser" bit, at 1.5IPS, and 12krpm.

The first letter turned out OK, but after that, most, if not all were ruined as follows: Plastic re-melted and stuck onto the point of the bit, forming a disk, that scrubbed and melted the surface of the plastic on both sides of the carved text.

When the bit would lift to make a move, I used a thin piece of wood to knock off the disk from the tip, but in a few seconds, a new plastic disk had formed on the tip, and it resumed scrubbing/melting the surface on each side of the V-groove. When I was done, I had maybe 20 little plastic disks laying on my machine bed, some as large as a quarter of an inch in diameter.

My first guess is that if the original protective sheet of paper had been in place, that none of this would have happened. But that is just my guess. Are there other issues here that would have condemned this experiment to failure?

I'll upload pictures later, but I hope my description is sufficient for some basic feedback.

Thanks, Chuck

Hello Chuck

I am not familiar with a laser bit - is it for cutting plastic? I have not cut much plastic but I did purchase a good quality bit just for plastic and that made all the difference.


Tim

[steve_g]

http://www.ebay.com/itm/like/122151762564?lpid=82&chn=ps&ul_noapp=true

CMT makes a 3 flute 60° bit that comes to a true point and market it as a laser point bit. IMHO, it’s the best V-Carving bit made!
On the down side, however, I haven’t found anyone who can sharpen them to original glory…
SG

[Chuck Keysor]

Thanks for the added feedback! Yes, I am using a CMT "Laser" bit. I have two, one which I save for extra-fine/light work, and that is the one I used. So I believe it is very sharp.

Last night I thought of a new approach, which might allow me to use what is apparently extruded acrylic plastic. Instead of doing regular "V-carving", I will switch to an outline font. This will allow me (with the font and size I need) to only need to carve grooves that are .03" wide. With such shallow lines, I shouldn't have all the remelt problems previously encountered.

When I go to paint, well, I'll wipe on the paint, wipe it off leaving it in the narrow grooves, then go and paint in the letters by hand. Maybe a bit tedious, but I it is a small sign. I'll post results when I have some...... Thanks, Chuck http://www.talkshopbot.com/forum/attachment.php?attachmentid=29043&stc=1

[Chuck Keysor]

This is the type of painting I would do, except the border and fill would be the same color.

I use outlining when I have material I don't want to have to cut too deeply, so that is where the idea came from for this plastic sign. http://www.talkshopbot.com/forum/attachment.php?attachmentid=29044&stc=1

[Xray]

May well be working with difficult acrylic, hard to tell. If it has a tint it is probably lexan, which is for sure not suited to rotary engraving.

When using a rotary bit on plexi you want to minimize heat buildup which causes the rewelded blobs, so you want to use as low RPM and as fast feed as possible. Since your goal seems to be an etch, you don't need much of a bite, and it looks like you are shallow enough [I go as shallow as .011 for a scratch, this demands a perfectly level surface & accurate Z, else you'll end up cutting air at some places, maybe too deep in others].

I prefer using engraving bits for work like this, drag bit [non rotary] often better yet, no chance of blobs with those as they generate no heat. But if you don't have those handy, the above is about all you can do, though some guys go so far as to mist as it cuts. Leaving paper on would have had no effect, except maybe make things a bit messier looking.

Here is an older thread with some good info about machining plexi - Though its focus is 3D, same general dynamics at play.

http://www.talkshopbot.com/forum/showthread.php?18228-Plexi-3D

[Chuck Keysor]

Thanks Doug! I just got up, and haven't read the link you supplied, as I have to out in a few minutes.

But I also thought I could use a simpler font (Helvetica) and then do a profile on line cut with a 1/8th diameter bit, cutting down just 1/16th of an inch. The simulation looks good. I have set it up to cut half of the file at 1.5IPS, and the other half at 3IPS.

I figured this would be easier to paint (wipe on/wipe off like V-carving). Any comments? I'll read your link when I get back, and before I actually cut anything.

Thanks again, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29082&stc=1

[Xray]

Not sure if your plan will look nice or not, I use a drag bit or engrave for fine details.
1/8 sounds a bit much to me, are you referring to a ballnose ? Alot would depend on size too, couldn't hurt to try but I am seeing the lines very close together, possibly jumbled, with very little to paint.

I paint plexi quite a bit, all lettering like yours would be doable but extremely tedious to paint by hand. Plexi does take paint well, never had any problems with that. Can be prone to streaking, solution is a good wipedown to remove any contaminants and use of quality brushes and paint.

Corian is worth a thought too for work like this if you can get ahold of some, holds details very well and no melting issues. Of course, totally different effect as its not transparent. Lettering is simple, just spray paint the whole thing, scrape off majority, when dry sand it down until only the black etch shows.

[Chuck Keysor]

Hello Doug, (you have nice looking signs by the way!).....

Now that my cut file is suddenly working, I did my test cut using "on-the-line" profile cutting of my sign with Helvetica font, and it cut great.

My bit is a 1/8th inch Amana O-spiral, and running at 1.5IPS, and 3IPS (I had it change speed mid file, maybe the text never got to full speed, but the boarder must have). It cut very nicely, producing nice chips, with no re-melting of any kind. (I couldn't tell any difference in the chip size when the speed doubled.)

I may not have mentioned, that the sign is 12" wide, and 16" tall, so the letters are formed with single passes of the 1/8" bit. So that is why I was able to use such a big bit. Not as slick as Times New Roman, but street signs (this is kind of a street sign) don't ever seem to use such nice font anyway.

I'll reverse my font, and proceed to cut this on my remaining good piece of plastic. I'll post a picture after I have painted it.

Thanks, Chuck

[Chuck Keysor]

http://www.talkshopbot.com/forum/attachment.php?attachmentid=29090&stc=1I had success cutting the sign on the other identical piece of plastic, using a 1/8" dia. O-spiral bit, single line font, Helvetica, with a profile on-the-line cut. The letters and boarder are the same size as the previous V-carved sign.

I didn't have any re-melting, and I cut at 3IPS and 10krpm. The only flaw is that tightly spaced semi-circular arc machining marks, are on the bottoms of all the machined letters. But I am assuming, that for this type of sign, that will be OK when I infill the machined letters with black paint.

I tried to take pictures of the machine marks on the bottoms of all the profile letter cuts, but my camera couldn't focus that close. Is there some type of bit that would reduced those marks? Or is there a practical way to clean them up? (For future reference.)

Thanks, Chuck

[Xray]

Letters themselves look nice shape wise, appears to be alot of chatter in them, something ain't right. Or maybe you didn't clean/blow it off yet ?

I use an old junk rotary toothbrush to clean up plexi cuts, but yours looks far beyond that [unless its lighting/angle]. If the chatter won't brush out, only option to clean would be flame polish [propane torch], but again, this looks a little far gone for that but might be worth a try for future reference. Just keep the flame moving like spray painting, plexi will flash and burn quick once it reaches a certain temp. Blows out quick enough but charring/warping will ruin a piece.

I would recommend getting some known good plexi [which you might not be able to find at a box store], and some dedicated engraving bits from precisebits.com if you plan on getting into plexi, and a diamond drag bit too.

Paint IMO will not hide the machining flaws, might actually highlight them. But it can be hard to judge a piece not in hand - Don't know what method you are planning for paint but I think a paint pen would be better than a brush.

[tlempicke]

I use a 1/8 O spiral bit for a lot of stuff. Here is a link to some really cheap bits that you can use once or twice and throw away.


I know that the purists on here are going to cry heresy, but I just carved a piece out of walnut and this bit did a great job. Almost no cleanup.
http://www.ebay.com/itm/10PCS-Durable-Carbide-CNC-1-8-0-87-inch-Single-Flute-Spiral-Router-Bits-/181989344371?hash=item2a5f690473:g:vUUAAOSwbsBXkzQ 0

[Chuck Keysor]

Thanks for the replies. Again sorry I just could not get a clear close up picture. And I had not cleaned off all the cutting chips. Perhaps I was in too much of a rush to post a reply.

For the bit, I used a brand new Amana bit #51471, spiral O flute bit.

The side walls of the letters cut beautifully, without any chatter, which when cutting wood, is where my chatter marks show up. All of the machining marks are on the bottom channel of the groove. (By bottom, I am of course talking about as the plastic was oriented while being machined.) On straight runs, like the boarders, the machining marks are perfectly spaced arcs. And the same marks are on the bottoms of all the letters, just not as evenly spaced.

If this shows through the paint, I'll live with it considering that it goes on a post on the edge of a field. But IF I had another piece of this plastic, I would not reverse carve it. If carved on the front side of the plastic, then all the machine marks would of course be under the paint.........

I'll post a picture after I have painted this. Thanks again, Chuck

[steve_g]

Chuck...
The swirls on the bottom of the cut are exactly what you should expect with this bit… it’s not a bottom cutting bit! A better finish can be had with a “FEM” style bit, flat across the bottom… at least in wood, not sure about plastic.
SG

[Chuck Keysor]

Thanks Steve! It is good to know that the cutting marks I got are not from some defect in my machine.

I used that bit because I had purchased it after seeing that it was recommended for cutting aluminum. But I hadn't gotten around to cutting the aluminum yet, so I knew the bit was sharp.

The bad news is that the on the aluminum that I plan to cut, I need to have a clean bottom cut! (Not to digress from my own thread, but should I plan to cut my aluminum with the Amana O-flute bit, and then clean it up with a different bit OR cut the aluminum with a different bit that will leave a smooth cut on the bottom?)

Thanks again, Chuck

[Chuck Keysor]

Hello Shopbot friends. I finally installed the carved plastic sign which I had discussed earlier in this thread. I tried to get some up-close pictures, but this camera's macro function is shot/junk.

Even though there were lots of machine marks on the bottoms of the grooves, (cut with a fish-tail end-mill, doing a profile cut "on-the-line"), as soon as I filled the grooves with black oil based paint, the machine marks disappeared! I got lucky for once. But there are machining irregularities on the sidewalls of the cuts, which in places make it so that all of the straight lines of the letters, are not as straight as they should be......

After filling in the grooves with black paint, and then letting that dry, I painted the back with white paint. When I held it up to the light to inspect the final work, I was chagrinned to see light shining through. So to fix that, I put on two heavy coats of grey paint on top of the white paint. It actually turned out OK, considering it was made from plastic I got out of the dumpster. But by the time I was done, I think I spent about 5 hours in total.... which is a bit disappointing.

Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29232&stc=1

[Xray]

Hey you spelled Property wrong !

No just kidding, looks nice.
I learned early on that light will shine through in spots that the eyeballs cannot detect so I always overcoat, usually once one way, when dry another coat cross wise, then a 3rd coat for good measure.

Choppy lines, outside of whacked nodes, can be caused by either a dull cutter, too high feed speeds or both.
Improper holddown and machine flex can also be factors.

[Chuck Keysor]

Yikes! You really had me fooled there on the property spelling! I am one of the worst spellers, so I could have easily spelled something wrong. But my reflexes instantly passed the buck, as I sent the text to the fire fighter's union steward to get his OK before I cut anything. Then I read the next line, and saw your just kidding line.

Thank you Doug for your kind words, and the good laugh!

I may have had some hold down issues, as I don't have a vacuum hold-down, and the plastic, though held down securely on the perimeter by mechanical clamps, had some crowning in the middle, and I was too lazy to take the part out and flip it over, figuring it would just give me varying depths of my on-line profile cut. But since I couldn't get a good close-up, I have forgotten exactly what the cutting irregularities actually looked like.

It was funny, as just the other day on the Aspire forum, someone complained that when he tried V-carving plastic, he got little plastic globs. Someone else had already replied that an on-line profile cut with an endmill would provide more satisfactory results.

Thanks, Chuck

[8Ball]

For a sign like that, i probably would have used color core since there isn't any painting required or as suggested, Corian. Corian is inexpensive for smaller pieces and is very easy to work with. I make plaques and signs similar to yours and it only takes an hour at most, total time for the sign using Corian.

[Chuck Keysor]

Thanks 8Ball. Other than wood, I do my experimenting with junk/scrap free stuff.

I do however, have some nice white Corian. But it has a glue-up to double the thickness on the edge for a big bullnose, and a lot of particle board glued onto the bottom. It seemed like a lot to clean it up to use for a free sign, so I chose the clear plastic figuring it would be more direct......... I guess I was wrong!

But there is something nice about the clear plastic with the engraving on the back side. The smooth exposed front looks good, and the fact that the letters seem to float inside the plastic is also appealing.

And I learned that V-carving low-grade clear plastic is not likely to work. Also, this was my first time doing on-the-line profile cutting for lettering, as I had always just done V-carving for lettering before. So I learned something there too.

Thanks, Chuck