Plastic drilling tips?

[FF]

Been a long time, but I have to drill some 3/8 holes in 1/4 inch Lexan.


Seem to remember there are special bits to not crack the plastic , or drilling in reverse as a quick solution.


Any advice?

 

[timb]

use a dull bit .very little pressure . reverse may work .if it grabs it will try to screw in and break the material .good luck

 

[jleonard]

I always use painter's tape to completely cover the area. Top and bottom.
And light drilling pressure.

 

[Duvie]

Look up how to sharpen a drill bit for plastic on the internet. It is very easy to do. The way you sharpen it makes it scrape the plastic and does not cut it. Mcmaster Carr should have bits for plastic if you want to go that route.

On another note if the material you are drilling is Lexan it will not crack. I have bent 1/4 inch thick Lexan 90 degrees in a vice on a cold day using a hammer.

My father was in the plastics business and he called polycarbonate (Lexan) "mailable".

 

[Portage_Bay]

A fabricator I know who has worked a lot with plexiglass used WD-40 as the lube when drilling.

 

[cool beans]

I've had success with finer divisioned step-drill bits. Also flipping the part over and finishing the other half of the hole from the back side.

 

[bayview]

Sharp corners and edges cause stress and lead to cracking after a while.

Chamfering the holes may relieve the stress caused by sharp corners of a cut hole.

Got to thinking and wondered if a hot iron melting the sharp edge might be a good stress reliving idea.
any polycarbonate experts here?

 

[Comodave]

I have some bits that specify they are for drilling plexiglass. They seem to work fine, go slow without much pressure.

 

[SoWhat]

Grind off the outside corner of the cutting edges. Make it more of a point than an angle. Drill at slow speed, light pressure. Or buy a special plastic bit. $5 on Amazon.

 

[RT Firefly]

Greetings,
Mr. b. "...hot iron melting the sharp edge might be a good stress reliving idea." In a previous life I was working in the midst of a machine shop. They got a job machining a fairly complex item in plastic. NO idea what the plastic was BUT they wanted the finished product to be stress and strain free.


The method to relieve strain in glassware (borosilicate/pyrex) is to anneal it @ 540C for one hour. Tried heat treating the plastic with numerous variations of temperature and time and was completely unable to change any strain patterns as observed by polariscope.



What I did learn is that as soon as you put a tool to plastic, you impart stress/strain. Fire polishing edges doesn't help and in some cases makes matters worse. Radiusing (sp?) edges may help...

 

[DDW]

Lexan (polycarbonate) you should be able to just use ordinary twist drills without problems. They may self feed aggressively which can be remedied by a very small flat ground freehand on the cutting lips (rake = 0 deg). It should not crack in any case. Plexiglass (acrylic) on the other hand will crack easily. The same trick works, but plastic specific bits are best.

 

[bayview]

Thanks RT

 

[BigTime]

For a hole that large I would try a new spade bit with light pressure while keeping lexan backed by a piece of wood.

 

[KnotYet]

Been a long time, but I have to drill some 3/8 holes in 1/4 inch Lexan.

Seem to remember there are special bits to not crack the plastic , or drilling in reverse as a quick solution.

Any advice?

Lexan is pretty forgiving and a step drill should work well.
Use light pressure to keep it from heating up.

 

[Xlantic]

When I drill or use a jigsaw to cut plastic (or stainless steel), I have an assistant direct a stream of water from a hose to the cutting area to keep the temperature down: the plastic does not melt and the SS doesn't harden.

 

[FF]

I have a Drill Doctor to resharpen the bit after dulling it , so I will try low pressure and hand job to flat grind the bit.

Thanks , folks.

 

[Skeeter]

Just grind a flat on the cutting edge of the drill (negative rake angle)and clamp a block of wood on the opposite side

 

[Mike H]

Run down to Home Depot or Lowes and buy a piece of Lexan to practice on.

 

[legemar]

Agree with SoWhat: grind the edges to make the drill pointed. Use slow speed, light pressure. This advice given me by plastics fabricators in Annapolis. Works every time.

 

[Brooksie]

If indeed you are using Lexan (polycarbonate) no special drilling tips are needed as it is almost impossible to crack. If you are putting bolts or screws through these holes, leave more clearance than you would with wood, metal. or fiberglass.
Acrylic (plexiglass) does crack easily and needs care when drilling.

 

[z1nonlyone]

Grind small flats on cutting edge so as to eliminate the "hook" that might otherwise "screw" into the plastic.

 

[psneeld]

Thought I read somewhere masonary bits work well. No twist to grab and pull.