Drill bits for plastics

[knoba]

Tip angle 60°, flat 4° rake, clearance angle 12°






Page link: https://knoba.wordpress.com/2015/04/...s-for-plastic/

Thanks Ken!

[kbalch]

Thanks knoba! I've added your Drill Bits for Plastics to our Miscellaneous category, as well as to your builder page: knoba's Homemade Tools. Your receipt:

Drill Bits for Plastics by knoba

tags: plastic, drill bit

[DIYer]

School me on this, please. Would the reprofiled bits prevent jagged edges? Cracking? I just use metal bits when I need to drill through plastic.

[kbalch]

Yes, those bits are used to avoid ("prevent" is probably overstating their efficacy) chipping and cracking. I used special plexiglass bits with similar profiles to drill the canopy on my airplane.

Ken

[knoba]

As Ken said.

You can use metal bits but it's wise to take some special precautions;
Use an undrilled area of a sacrificial backing piece (wood) for each hole.
Avoid using pilot holes if process permits.
Clamp the plastic down.
Use slower rpm speeds.
Slow feed pressure down on break-through.

hth

[Paul Jones]

I wish I had these for drilling Plexiglas parts. Have you also ground special drills for drilling brass?

[Altair]

I'm gonna give this one a try. Recently drilled a panel of plexi, lots of hairline cracks.

[knoba]

I wish I had these for drilling Plexiglas parts. Have you also ground special drills for drilling brass?

Hi Paul,

You do some very nice work, btw!

No I haven't reground a set for brass. Do you mean; once the bit grabs into brass it starts pulling itself through without much coercion from the operator?

I would have thought the best geometry for brass drill bits would be to back-off the "lip relief" shown in the following diagram as "x";



hth.

[Paul Jones]

Hi Knoba,

Thanks for the compliment. I have similar trait to Ken's toolmaker mentor concerning "finishing the areas that no one else will ever see".

For years I have been temped to reduce the lip relief for some larger nominal sized import drills I use for drilling brass with the tailstock in the lathe. A few times I had 3/4" drills pull the tailstock chuck out while drilling out brass or bronze round stock prior to boring. No serious accidents but something to avoid. I found rolling a small section of printer paper in between the chuck and tailstock Morse tapers seem to make it hold better but doesn't fix the root cause.

Thanks, Paul

[DIYer]

As Ken said.

You can use metal bits but it's wise to take some special precautions;
Use an undrilled area of a sacrificial backing piece (wood) for each hole.
Avoid using pilot holes if process permits.
Clamp the plastic down.
Use slower rpm speeds.
Slow feed pressure down on break-through.

hth

Great advice, knoba! Thanks!