Drill bits for plastics

Tip angle 60°, flat 4° rake, clearance angle 12°
https://knoba.files.wordpress.com/20...plastic-02.jpg

https://knoba.files.wordpress.com/20...plastic-01.jpg

https://knoba.files.wordpress.com/2014/11/img_2920.jpg

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

Thanks Ken! :bow:

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:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="/drill-bits-for-plastics"><img src="/uploads/114526/drill-bits-for-plastics.jpeg" alt="Drill Bits for Plastics" /></a> </div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="/drill-bits-for-plastics">Drill Bits for Plastics</a> <span> by <a href="/builder/knoba_2">knoba</a></span> </div> <div class="tags"> tags: <a href="/tag/plastic">plastic</a>, <a href="/tag/drill-bit">drill bit</a> </div> </div> </div> </div>

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.

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

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

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

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

Quote:

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Originally Posted by Paul Jones

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

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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";

http://www.nouvaltools.com/sitebuild...g1-620x342.jpg

hth.

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

Quote:

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Originally Posted by 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

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Great advice, knoba! Thanks! :)

Quote:

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Originally Posted by 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

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I had similar issues with an old Hardinge lathe, it was remedied by skimming out the tail-stock quill socket with a morse taper reamer and then making sure the tail-stock ejector mechanism was working as it should. If I knew I was going to be hogging out a lot of meat and/or the material was soft I would give the morse taper insert a sharp, but gentle, tap on the end with a soft face mallet. I've not had any 'moments' with it since...

That's a pretty cool & interesting technique you mentioned, I'm not sure I've heard it before and I won't forget it. Thanks for passing it on!

Knoba,

Last month I bought a fine cut No. 3 Morse Taper to do exactly what you described for the skimming out the tailstock. I have been waiting for an opportunity to change out my 4-jaw chuck so I can insert a MT5 dead center into the headstock for accurately centering the reamer. I normally use a 3-jaw chuck but lately a lot of my projects require offset turning with the 4-jaw.

Thanks for confirming the technique.

Paul

Sounds like you're well ahead of the curve. If you get the chance to document the process, Paul, I think it's definitely worthwhile publishing for others to see!