Drilling acrylics

[Chaz]

Lets see if I can explain.

Drilling a pen blank. Let's say 8mm. Acrylic of some sort. You drill in to a certain depth - say 1" or greater.
When you pull the drill bit out to clear it, built-up shavings expand out of the flute. They are under pressure.

I'm drilling .75–1" at a time.

I'm wondering if these shavings, building up, generating both heat (via friction) and pressure (shavings can't escape), can erode the outside of the hole being drilled, so you end up with a wider hole near the bottom. Not a lot - say .0001, give or take.

Ideas, or did I have way too much fun in the 70s?

 

[carlmorrell]

In the immortal words of Henny Youngman "If it hurts when you do that, don't do that". At least I think it was him. Heat is your enemy when drilling acrylics. I never go 1" without evacuating. At most, I go 1/2". Also, what speed do you drill? I never go over 1500rpm, closer to 1000. After I drill, perhaps 1/2", I check the temperature on the drill bit. You will be surprised how hot it can get. Actually, what I do is I count to 10 or 15 before I pull the bit and check it's heat. I don't know about other people, and perhaps there are many ways to get this done. But when I am drilling acrylics, It may take as long as 5 minutes to drill it. Most time is waiting for the bit to cool. I don't like spraying water, everything ends up rusty. But I do keep a vacuum on it and the moving air helps cool the bit

 

[its_virgil]

Drill shallower and clear the swarf more often....maybe 1/2 inch then exit and clear the swarf. You will find that different resin blanks will drill differently. When I first started I had a few resin blanks split in half while drilling because of the swarf buildup, heat, and possibly a little pressure build up.

Acrylic is a specific type of resin. The word acrylic is often (incorrectly) used as a generic term for any and all resins...much like kleneex is used for all tissue brands.

Do a good turn daily!
Don

 

[Woodchipper]

Yep, drill slowly, withdraw the bit, clean it and let it cool. Drill an inch or two at a time. As mentioned, different synthetics will behave differently. Once...I drilled too fast on the drill press. The blank stuck to the bit. Do I have to tell how much fun it was to cut off the blank from the bit?

 

[Chaz]

Acrylic is a specific type of resin. The word acrylic is often (incorrectly) used as a generic term for any and all resins...much like kleneex is used for all tissue brands.

Yes, I know, but until I can find a better term that everyone recognizes, I'm gonna keep using the word acrylic. You knew what I was talking about right way, didn't you?

It's like gun folks who insist on using terms like suppressor and magazine, when the rest of us mere mortals use silencer and clip and communicate just fine.

 

[Chaz]

I'm asking because I've recently started using Rick Herrel's pin chucks. They are very sensitive to tube diameter. A bare, 8mm tube works great, but stick that into one of my blanks and it's way different.

I think .....

The hole I drilled (with a quality brad-point bit) is slightly bigger than optimal (friction and heat), and there is a tiny space between the tube and the blank. When I turn the blank to lock in the pin, it rolls is instead of catching, and with the force applied in twisting, the tube expands. The expansion may be minute but enough to prevent the pin chuck from functioning correctly.

 

[Chaz]

Most time is waiting for the bit to cool. I don't like spraying water, everything ends up rusty. But I do keep a vacuum on it and the moving air helps cool the bit

Yes, that's a problem, when you have a dozen or more sticks to drill. A couple of years ago, I experimented with aerosol brake cleaner, for cooling drill bits. It works really well, quickly, but at the time I wasn't seeing what I am now, so I didn't continue. The fumes are also kinda toxic, but I have the best ventilated shop you've ever seen.

I need some acetone for other things, so I'll grab some brake cleaner while I'm out.

 

[egnald]

All good recommendations. Most inexpensive drill bits are actually manufactured to the low side of their tolerance because it is assumed that the final hole will be slightly larger due to concentricity and runout (TIR) of the drilling equipment and process which not only includes the drill bit itself but also the drill chuck, and the characteristics of the material being drilled along with the holding mechanism being used for the material. For precision machining we drill a hole slightly undersized so that we can use a more precision tool, a reamer, to finish the job to the tolerance we are after.

Even though most drill bits themselves are manufactured to the low end of the tolerance, the holes that they produce are almost always oversized because of these factors. Drilling a softer, more resilient material on a well aligned lathe using precise tools such as a four jaw chuck to hold the work and collet chuck to hold the drill bit instead of a Jacobs chuck, can provide a hole that is closer to the actual drill bit diameter than using a drill press or other method.

I also use a dry lubricant, BladeCote (used to be called DriCote) to help dissipate heat and to help the swarf eject up the flutes. As has already been suggested, peck drilling is highly recommended. The rule of thumb we used in the machine shop was to retract the drill for clearing and cooling was to not exceed 3 times the drill bit diameter for each peck (although my personal rule was 2 times the diameter). As suggested, for an 8mm drill try pecking at about 1/2-inch intervals.

Dave

 

[Todd in PA]

I generally drill around 600-700. I don't know that's right, but my thought is slower means less friction heat. I peck 4-8 rotations of the quill. I think one rotation is a 1/16. I cool the bit between pecks cupping my hands over the shop vac nozzle and bit until it doesn't feel hot to my fingers.

I've sometimes noticed chipping chatter on the inside of the hole. On some plastics, it's visible through the pen exterior, even after painting. If I get chattering in the hole, I'm forced to use black paint. The chipping tends to be toward the hole entry, with the exit hole cleaner.

I've melted one blank into the bit. I hope never to repeat that.

 

[Curly]

I have a couple suggestions Chaz.

Firstly drill slower and lubricate the hole frequently. A few drops of dish washing liquid in a cup of water is about right. Doesn't cost diddly and doesn't pollute the air around you. Protect the bed of your lathe. I found a piece of a puppy pee pad is perfect. My other reason for using water and soap is some solvents can cause some plastics to craze. Small surface cracks that resemble cracked windshields. Sometimes right away and other times it can take months before showing.

Secondly use a standard drill bit (118º tip) and not a brad point. Brad points work great drilling into the side grain of wood but make more heat than a regular twist drill in plastics.

 

[KenB259]

All good advice , but it's unrealistic to try and hold holes to a tolerance of .0001

 

[Woodchipper]

I put an old towel on the lathe bed anytime I use water for wet sanding or cooling a drill bit. I wipe the drill bit to dry it.
Story: Used to have a customer, a large manufacturer who drilled about 80 holes in a truck frame. Had a DIY drill that mounted to the frame and advanced by hand. Told one of the guys, " I know a way that is faster." "What's that?" "Buy the holes and weld them on."

 

[randyrls]

I put an old towel on the lathe bed anytime I use water for wet sanding or cooling a drill bit. I wipe the drill bit to dry it.

John; Good Story!

Instead use a piece of thick shelf liner or craft foam. These won't let water soak through.

Chaz; As others have said don't use a brad point bit for synthetics. The bits heat up much too fast and it is difficult to sharpen them. For synthetic blanks use the "cut long, drill short, trim" method. Cut the blanks about 1/4 or 3/8" (8 ? mm) longer than the brass tube. Mark the drill bit and drill into the blank until the mark disappears into the blank. Add about a 1/16" (2mm) to the drilled depth. Now trim off the un-drilled end to exact length plus 1/32" (1mm). This avoids breaking the blank when the drill bit breaks through the end of the blank.

 

[jttheclockman]

This topic comes up all here and basically the same advice is given which is all good advise because we all been there done that. The one thing I just do not like reading is bnrad point bits used in any of the pen blanks we use. If used in wood that bit drilling into long grain woods can have a mind of its own. as far as size of hole. All bits will leave a hole larger that any bit. It is acceptable and we all work around it. If out of round or over sized hole at other end of blank happens then other problems are occuring. Peck drilling is the key along with speeds around 600 to 700rpm. I always cool my bits with DNA. No problems if it drips on bed. No rust and it cools bit quickly. It does become a rhythm when drill blanks but after a few you learn the do's and dont's pretty quickly. Good luck.

 

[Woodchipper]

"Mark the drill bit" is easily done with a piece of masking tape to indicate the stopping point.

 

[Chaz]

"Mark the drill bit" is easily done with a piece of masking tape to indicate the stopping point.

90% of my blank drilling goes to a certain depth - 2.5". I have a couple drill bits that I keep stop collars on, all the time

 

[Chaz]

John; Good Story!

Instead use a piece of thick shelf liner or craft foam. These won't let water soak through.

Chaz; As others have said don't use a brad point bit for synthetics. The bits heat up much too fast and it is difficult to sharpen them.

and I just bought 2 new BP's for this work - dammit!

Why do brad points heat up faster?

 

[egnald]

Brad-Point drill bits also known as Spur-Point Bits or Doweling-Bits are often promoted as the best drill bit for drilling wood. It is true that they do an outstanding job of creating clean bores on entry and during the cut across the grain, but they are not very good at drilling end grain -- which is the kind of wood drilling done by penturners. There are actually two different types of Brad-Point drill bits, one for softwoods and one for hardwoods, Bits for softwoods have less pointy and more rounded spurs. The spurs in the most common, hardwood bit, drag in end grain which can cause the bit to deflect. This should be less problematic when drilling plastics as there are no fibers involved, however, there are better choices for drilling end grain and plastics.

For the pen maker, general purpose twist drill bits are perhaps the most suitable choice; however they also come in a variety of designs depending on the specifics of the material to be drilled. General Purpose are usually ground with Point Angles of 118-degrees or a flatter 135-degrees. They work well for general-purpose drilling through wood, plastic, and light metals.

Twist drills designed specifically for plastics are usually ground with Point Angles of either 60-degrees or 90-degrees. These shallower Point Angles allow the bits to be less aggressive and to more gradually enter and exit the material. Since they are less aggressive, or less "grabby", using them significantly reduces the potential for the material to crack or "blow out" especially when the bit punches through and exits the material. The point design also reduces friction and therefore aids in reducing heat buildup in both the material and in the drill bit.

Of course there are also lots of drill bit materials such as High Speed Steel, High Carbon steel, Cobalt steel, and Carbide Tipped or solid Carbide. The material has more to do with how long the bit stays sharp drilling into hard materials.

Although most drills will get the job done, for anyone planning to drill lots of plastic materials, I highly recommend the extra cost for 60-degree or 90-degree bits designed for drilling plastic.

Dave

 

[jrista]

Yes, I know, but until I can find a better term that everyone recognizes, I'm gonna keep using the word acrylic. You knew what I was talking about right way, didn't you?

It's like gun folks who insist on using terms like suppressor and magazine, when the rest of us mere mortals use silencer and clip and communicate just fine.

Resin is a good word, if you are curious. All plastics, acrylics, and other synthetic polymers that we turn are resins of one kind or another.

Regarding the drilling aspect. A tangential tought could also be that the drill isn't 100% perfectly strait. It doesn't take much (fraction of a degree to a degree) to result in the hole being slightly larger at the bottom than at the top, even if you frequently clear the swarf.

It could also potentially be drift of the bit through the wood (some think this is possible with a bradpoint bit...I'm not sure myslf, once the whole bit is in the material, I don't know how easily the bradpoint is going to drag the whole bit off track).

Another possibility is vibration, which will often increase the deeper you drill, and could lead to a larger exit hole.

Some of these things can be tuned. You can work on improving the straitness of your bit in the chuck, for example (i.e. make sure there isn't any junk built up on the jaws, etc.) You can work on minimizing vibration by finding the optimal rotational speed (either on the lathe or on a press). Stuff like that.

And, of course, clear the swarf frequently.

 

[KMCloonan]

For what it's worth, I typically drill at about 250 RPM for both resin and wood. I'm not (usually) in a hurry, and slower RPM = lower heat. I do back out the drill bit as I feel it getting harder to advance, to clear the chips - maybe 4-5 times on a typical blank.

 

[duncsuss]

Although most drills will get the job done, for anyone planning to drill lots of plastic materials, I highly recommend the extra cost for 60-degree or 90-degree bits designed for drilling plastic.

Dave

It was disappointing that the Drill Doctor sharpener doesn't allow me to set 90 degrees, I was thinking of re-grinding a few drill bits to compare the results to the more common 118 degrees. I might investigate to find out if there's a way to extend the range of angles.

 

[egnald]

It was disappointing that the Drill Doctor sharpener doesn't allow me to set 90 degrees, I was thinking of re-grinding a few drill bits to compare the results to the more common 118 degrees. I might investigate to find out if there's a way to extend the range of angles.

That's the only reason I never bought a Drill Doctor. I have thought about it many times though. - Dave

 

[leehljp]

While it took a number of posts to get to the type of bit needed for acrylics and David brought up the 90° bit point, Norseman and others have bits expressly for acrylics. I bought a couple of bits years ago when I lived in Japan and they were light years ahead of normal bits for drilling acrylic resin blanks. They are expensive as compared to normal bits, but worth it:

Example:

Amazon.com

 

[NJturner]

Yes, I know, but until I can find a better term that everyone recognizes, I'm gonna keep using the word acrylic. You knew what I was talking about right way, didn't you?

It's like gun folks who insist on using terms like suppressor and magazine, when the rest of us mere mortals use silencer and clip and communicate just fine.

I'm going to disagree with you on this one, not to be a pain but I think accuracy here is helpful vs generalization. We all turn some type of resin - be it acrylic, urethane (alumilite), Silmar (polyester), or the tons of other possibilities. With each of these they all have similar properties but enough dis-similar properties that I think it is important to be as accurate as possible because they need to be treated differently as we process them. Generically, I find the term resin to be acceptable when talking about a non-wood blank, but not a specific type like calling all of them acrylic.

 

[RunnerVince]

Generically, I find the term resin to be acceptable when talking about a non-wood blank, but not a specific type like calling all of them acrylic.

I like the word "synthetic" because the word "resin" is also so loaded these days.

 

[Woodchipper]

Acrylic? Synthetic? Different materials, different characteristics. Same goal...drill a hole in it. Worst I found was arbor vita...like drilling tool steel!

 

[Chaz]

I love the off-topic turn the commentary has taken. Not.