Bad day in the shop yesterday.

[gundog]

I was running a toolpath to drill some .250" holes in some HDPE seaboard .5" thick drilling through with a 3 flute EM designed for plunging as it center cuts. The swarf would not clear off the bit and ruined the material by making huge swirl scratches in the textured finish of the material. $160 sheet of material ruined. I have ran this same bit many times using the same parameters of plunge speed and RPM never having a problem but this time it was a disaster.

I would have caught it sooner but I was running a 2nd CNC machine that required frequent tool changes and by the time I looked it had pretty much ruined the whole 4x8 sheet.

I am changing tools from here on out to a special drill bit designed for plastic the problem is it really tears up my spoilboard because it has such a long taper at the point I have to drill .250" into the spoilboard to get a hole through the .5" material.

I wonder why all the sudden this same tool path I have been using does not work. I tried a new bit and got the same results again. I have been doing it this way for over a year with great results. I am not really looking for an answer I am just venting.

Mike

[bleeth]

Sounds like they changed their plastic formula. Since you have scrap now (sorry) try lowering your spin speed or plunge speed. Or add pecking at .25 deep.

[bleeth]

Mike: I just read closer. 3 flutes seems like a lot for soft plastic. I like 1 or 2 max and will use an o-flute over an end mill every day.

[gundog]

Mike: I just read closer. 3 flutes seems like a lot for soft plastic. I like 1 or 2 max and will use an o-flute over an end mill every day.

I agree but my tool supplier said they were designed for aluminum and he thought they would work I was skeptical but they did work very well for many sheets and hundreds of the same holes until yesterday. I was using this for drilling holes.

I bought a special plastic drill bit a while back but after getting it and seeing how long the taper is on the bit I would have to drill through the part by .250" to get a full diameter hole that is why up until now I never used it. I hate drilling that deep in my spoil board.

I have used 2 flute up spiral bits before for this but after so many holes I had the same issue.

In the past I would watch as this tool path ran so I could stop it and clear the bit when the plastic started to build up so I could clear the bit and restart. I quit doing that after using these 3 flute bits because they had worked so well then this.

I never have the problem milling profiles or pockets just drilling. I sometimes run air on the bit to try and clear the swarf off but that did not work either this time. I will post some pictures of the damage.

I am thinking maybe the bit changed I did get a few new ones the other day and I may have changed out the original but they were bought from the same guy so maybe something changed I need to check. I use this same bit on my bed mill to machine aluminum so I had several in house.

Mike

[jerry_stanek]

Could the bit have been coated and the coating is now worn off.

[bleeth]

You can make a "plastic" drill bit by taking a standard drill bit and back-filing the end a bit, then it doesn't grab.

[gundog]

After thinking about the problem a little it occurs to me that the helix actually creates the problem if the flutes were straight they would not likely wrap around the bit and build up. I am going to experiment with some straight flute bits and see what happens. I may also go back to peck drilling but I hope not as it adds time to the tool paths especially if you are drilling 100 holes or more.

Mike

[Brady Watson]

All of the O-flute geometries I have seen are non-center cutting - meaning that they are not designed to be plunged straight in, nor are they to be used for drilling because there is no cutting edge there to cut. Drilling polycarb can be tricky - and I have run into the issue of birdsnesting and the nest 'engine turning' the face of the material - rending it scrap.

You have two choices - 1) If the holes size matches your collet, get a purpose made bit for drilling plastic. 2) Use a smaller spiral-O bit and do an inside profile with helical step down/ramp to make sure that non-center cutting tool is in fact routing.

Additionally, you can piggyback a drill that runs at an appropriate speed for drilling to your spindle (via air drill mount from SB) and chuck up whatever drill size you want in the proper 'pointy' tip for plastic.

-B

[feinddj]

I often throw a piece of 1/4 mdf on my table as a sacrificial board. Vac hold down goes right through and your spoil board doesn't get marked up.

D