Drilling into solid PVC plastic

Bodankie · Sep 27, 2016

I am trying to drill a .750" hole into a solid PVC rod on a lathe. Total part length is just under 4" so I'm going at this from 2 sides. I can't seem to keep the plastic from melting. I've tried multiple feed and speed variations, coolant, and pecking and each run gives the same result. Every hole looks just as bad as the one before. Any advice or tips would be greatly appreciated.

DavidScott · Sep 27, 2016

Use a new drill??? Plastic doesn't like tools that have cut metal. Slow the spindle down, increase the feed rate to .01"-.02" chip load, and use lots of coolant.

John Welden · Sep 27, 2016

what kind of rpm you running?

Gray PVC?

Bodankie · Sep 27, 2016

Yes it is gray PVC. I started out at 1000 rpm, then slowed to 750, 500, and then 350.

John Welden · Sep 27, 2016

Bodankie said:
Yes it is gray PVC. I started out at 1000 rpm, then slowed to 750, 500, and then 350.

I might try drilling on the mill so the coolant fills the hole up. Maybe try even less RPM and higher feed. Peck a lot.

KilrB · Sep 27, 2016

What diameter rod?

How's the grind on your drill?

You want plenty of clearance, hone the cutting edges and thin the web.

How are the lands and flutes?

You want wide, deep flutes and narrow lands for drilling plastic.

Some drills just aren't made for drilling plastic ...

Prototyper · Sep 27, 2016

Drill undersize then bore to size?

Guest · Sep 27, 2016

Parabolic flute drill or a drill like post#6 described.

MK Proto · Sep 27, 2016

You need to buy one of these drills. Tip geometry is made for plastic. Series 7-5 | 4 (.29) High Speed Steel Two Flute Wire Drill for Plastic (Item 7-633) | Item Detail | LMT Onsrud

DavidScott · Sep 27, 2016

If the drill is sharp 500 rpm is plenty slow with .1"-.4", or more, pecks on the lathe. You not only need the lips of the drill to be sharp but the margins as well. PVC is about as easy as it gets for plastic. If your still having problems at 350 rpms I would guess that your margins are too dull.

How many holes do you need to drill? Unless you need to drill a few hundred I would just go with whatever drill is easiest to get. You really don't need anything special unless you are doing a few hundred holes or more. As long as you can hold onto the part you can really push a standard drill. How hard? Keep going until you notice some issues then back off a little. .02" feed per tooth is just getting started.

Limy Sami · Sep 27, 2016

Or got really cheap and use one of these DeWalt Flat Wood Bit 28mm | Flat Wood Bits & Sets | Screwfix.com at say 18mm then bore to finish, I use em all the time.

DO NOT use the self feeding screw type of flatbit, and shut that speed right down

doug925 · Sep 27, 2016

I started machining PVC when I was 16 y/o. Now I'm 44, and still machine it weekly.
Run your drill with a LOT of coolant. Through coolant, if you can.
A sharp drill and coolant will yield great results!

Feed it HARD. Maybe 0.02-0.03" per rev.
Keep your RPM down around 300 if no coolant through, or up to 1000 RPM if you can supply enough coolant down hole.

The shavings will expand greatly, so a parabolic drill, or spade is best. The shavings are causing the melting.
Get rid of those, and you should run through the parts fast.

Doug.

SteveBausch · Sep 27, 2016

Yep, as others have said, some sort of spade or "paddle" bit. Perhaps a pilot hole....

What's your tolerance?

I'd say PVC is just grey wood with no grain, but wood doesn't have a pronounced coefficient of expansion, and wood shavings don't wrap around the drill.

Metalcutter · Sep 27, 2016

Get a nice piece of general steel and make a nice cut. Then with that setup drill the plastic.

Stanley Dornfeld

regards.

cyanidekid · Sep 27, 2016

yep, pilot it

SteveBausch said:
Yep, as others have said, some sort of spade or "paddle" bit. Perhaps a pilot hole....

What's your tolerance?

I'd say PVC is just grey wood with no grain, but wood doesn't have a pronounced coefficient of expansion, and wood shavings don't wrap around the drill.

you didn't mention drilling a pilot hole. if you are using a .750 twist drill without a split point, and without drilling a pilot hole, you are heating up the plastic rubbing the "wedge point" of the web into it. once it heats there it just sets things off on the wrong path.

Limy Sami · Sep 27, 2016

SteveBausch said:
Yep, as others have said, some sort of spade or "paddle" bit. Perhaps a pilot hole....

What's your tolerance?

I'd say PVC is just grey wood with no grain, but wood doesn't have a pronounced coefficient of expansion, and wood shavings don't wrap around the drill.

IME with wood flat bits you don't need a pilot hole - just push it through!

What you do need with any drill with plastics is SHARP, with plenty of clearance on the cutting edge, (like 15 deg) and back taper on the drill to prevent flutes rubbing and causing heat.

Bobw · Sep 27, 2016

I'm machining some PVC right now too... ***** WARNING **** total cluster fuckaroo of a setup pic below.

Once a year or so I have a repeat job with the gray stuff. Its an easy one to work with. Its not quite Delrin :cloud9:

But its not Teflon or UHMW :angry:

... This white hardware store pipe seems quite a bit harder than the gray stuff I've worked with.

doug925 said:
Feed it HARD. Maybe 0.02-0.03" per rev.

THAT ^^^^^

Though I would honestly suggest feeding HARDER.. I've fed .060 a rev with a 5/16 in UHMW :mad5:

(I HATE that stuff) and
I'm running some HDPE in the mill right now and feeding .040 a rev on a 1". And I KNOW I can go harder... Give me a sec....

At 250sfm (1000rpms).. She's fine at .100 a rev... Parts done. I'm going to try .150 a rev.. Going through 1" thick, no
peck..

.150 was FINE... Hang on again...

.200".. It did it, but it pushed up some burrs. I'm pretty sure I over ran the relief angle of the drill..

Here is .200 a rev, kind of ugly, its actually tossing a burr.

And here is my cluster fuckaroo... Parting off hardware store PVC pipe. Shooting for as few burrs as possible.
5/8" spacers. Running 7 at a whack, takes about a minute. Running dry so I don't have to wash 'em.

Back to the OP.. Just PUNCH IT.. Take what you would feed the same drill in a mild steel and multiply X 10.
Slow SPeed, and pile drive it. Just don't out run the relief.

adama · Sep 28, 2016

cyanidekid said:
you didn't mention drilling a pilot hole. if you are using a .750 twist drill without a split point, and without drilling a pilot hole, you are heating up the plastic rubbing the "wedge point" of the web into it. once it heats there it just sets things off on the wrong path.

IMHO thats not a issue, the bit that gets warm from the point is so small - removed so fast its just not a issue in plastic. The heat never gets to conduct into the part as its simply cut away too fast!

adama · Sep 28, 2016

Hard ware store pipe parting? You using a Alu style - sharpness insert? Can really help, also helps to use on with some angle on the end, but you need more than the regular 7 degrees to see any benefit. Biggest problem i had when doing similar with 3" down pipe was the wall thickness is all over the place!

Bobw · Sep 28, 2016

adama said:
Hard ware store pipe parting? You using a Alu style - sharpness insert? Can really help, also helps to use on with some angle on the end, but you need more than the regular 7 degrees to see any benefit. Biggest problem i had when doing similar with 3" down pipe was the wall thickness is all over the place!

Just took a regular old part off insert I had in the drawer to the grinder.. Added a bunch of top rake and made it dead sharp.

Wall thickness and ID to OD is NOT concentric and the pipes are not straight. The only thing that mattered on these is thickness, and
that didn't even matter, they just had to all be the same.. Tolerance of "whatever", as long as it works. Not a bad little job, but it
looks like it snowed in here.

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