Help Drilling Acrylics

[dankc908]

Yesterday I was drilling about 20 acrylic blanks for an order of razor handles. I noticed, on a few blanks, that the entry hole seemed to be bigger than the exit hole (definitely bigger than the tuble and/or drill bit). Any ideas what caused this? Any ideas how to solve the problem. Most of the blanks will, probably, work but I'd like to to be a bit better. I am drilling on the lathe.

Dan

 

[lorbay]

It is usually caused buy heat and it does not take that much. Just the heat in the cutting is enough to grap the surrounding plastic without the bit getting warm. Use a bit of water and you will notice quite a difference.

Lin.

 

[Robert111]

Maybe the bit wandered a little when you started drilling. Did you use a center drill?

 

[CKormann]

I agree with Robert about using a center drill. If you don't have one, you can always cut your blank a little longer than you normally would, and after drilling trim off the end with the wider hole.

Chris

 

[randyrls]

I have noticed that retracting and then extending the bit into the cut enlarges the entry point of the hole. I use a drill press, but I suspect the same problem can happen when using a lathe for drilling. So now I, Stop the drill press and clear the flutes, Insert the drill bit back into the blank, Start the drill press and continue with drilling.

 

[Haynie]

This stuff does not like heat period. I drill slow, back out often, and cool after it is backed off. I cool with water from a spray bottle right into the hole and it is cold water. I probably use too much but I don't get the bigger entery than exit nor oblong entries.

 

[ed4copies]

Hey Dan!

As everyone has said, heat is the major culprit. So, cooling the bit will help.

Second: the bit is "wandering" in the hole. So, sharpen the bit and it will overcome the resistance of the material more easily.

If you are making one-tube pens and drilling on the lathe, consider drilling all the way through (very seldom blows out when being held securely on the lathe) and use the exit side as your "good" side. Thus you cut or face off the widened hole. It seems to only widen for the first quarter inch or so.

Hope this helps!!

Ed

 

[raar25]

I have been making alot of bracelet helpers with acrylic and I have found out when the chips build up the is some chatter in the blank which sends the hole path slightly off center causing the entry point to wander and the hole goes oversize. Definately try center drilling and clearing cips frequently. There have been times if I dont clear the chips frequently that the friction causes the chips to melt and form a homogenous blob around the drill bit and the drill chatters around alot.

So use scary sharp drill (like a colt 5) and clear chips often.

 

[ed4copies]

IF you get it hot ENOUGH---it will GRAB your bit and not let go!!

(Of course, this is hearsay, I would NEVER be that impatient!!!!):biggrin::biggrin::biggrin:

 

[mbroberg]

IF you get it hot ENOUGH---it will GRAB your bit and not let go!!

(Of course, this is hearsay, I would NEVER be that impatient!!!!):biggrin::biggrin::biggrin:

I can verify the truth of this "Hearsay".

 

[alphageek]

I can verify the truth of this "Hearsay".

Me too.... But I have to say that my drill doctor has helped me not see this issue any more.

 

[dankc908]

I can verify the truth of this "Hearsay".

Me too.... But I have to say that my drill doctor has helped me not see this issue any more.

Will the drill doctor work on the Colt 5 Star drill bits? I've thought about getting one but I love the Colt bits.

 

[alphageek]

I can verify the truth of this "Hearsay".

Me too.... But I have to say that my drill doctor has helped me not see this issue any more.

Will the drill doctor work on the Colt 5 Star drill bits? I've thought about getting one but I love the Colt bits.

Nope - the colt bits have 4 cutters and unless one of the other models of drill doctor can handle them, I think not. The drill doctor (at least mine) is designed for 2 cutting surfaces.

 

[Jim Smith]

I guess this could be a version of the drill bit wandering, but the drill bit make be running true, but if your blank is not locked in place, it will wobble a bit. enlarging the hole as you drill.

Jim Smith

 

[PenMan1]

This is caused by the bit "wiggling" a bit before starting the hole. The cure is a simple as it can be. Buy another Jacobs chuck on Morse Taper (usually under $10 at HF). Keep this chuck loaded with a centering bit. Use this chuck to center the hole before drilling with the bit. I'll bet big dollars that will end your problems.

 

[dankc908]

Many thanks to all! I think I know what to do now!

Dan

 

[jzerger]

Although it sounds like this thread has run its course, here's a possibility that (due to impatience) can also cause oblong holes. I've been running into this as I've been drilling longer blanks on my lathe (those for the longer click pens; CEO Executive Clicker, Vertex click, etc.). Since my drill bits are usually not long enough to go all the way through (and also to try and get "clean" entry holes on both ends of the blanks; especially with tru-stone) I turn the blank around and drill from the other end also. Every once in awhile (usually with acrylic, sometimes with tru-stone) the holes are not aligned when they meet somewhere in the middle of the blank. I think there are two things, either of which causes frustration (at the least):

1) the blank may not have been square so when turned around the hole was not centered on the other end in the same place. I usually take care of this when gluing the tube in.

2) when turning the blank around and putting it in the blank-drilling chuck (I use the one from PSI (love it), the blank is a bit "soft" due to the heat from the initial drilling; it is very easy to tighten the blank in the chuck too much and end up with an "oblong" hole at the end you just drilled as the blank was "smushed" a tad. So it isn't enough to just have a "cool bit", you need a cool blank also.

 

[KenV]

John, any machinist will point out that a two flute drill bit always drills an oval hole. That is why they use a reamer to get a really round hole.

Most of the time there is a lot of oval tis the bit, or a really non-precise process.

A three flute bit gives a 3-lobe hole.

 

[Paul in OKC]

John, any machinist will point out that a two flute drill bit always drills an oval hole. That is why they use a reamer to get a really round hole.

Most of the time there is a lot of oval tis the bit, or a really non-precise process.

A three flute bit gives a 3-lobe hole.

Sorry to be a machinist that disagrees, Ken. It can be a bit oval at the top, once you get the full diameter in the hole a bit it is good. If the bit 'wanders' all the way thru, it can be a bit oval. Reamers are for getting a good finish and a dead on hole size.
I am on the side of the bit wandering at the start. Heat is an issue, but rarely the cause of this issue. A center drill (often called a combined drill and counter sink) will help give the bit a straight start.

 

[jzerger]

I use mostly Brad Point bits. Isn't the point on these considered a center-drill starter or is there something better?

 

[Jim Burr]

IF you get it hot ENOUGH---it will GRAB your bit and not let go!!

(Of course, this is hearsay, I would NEVER be that impatient!!!!):biggrin::biggrin::biggrin:

I can verify the truth of this "Hearsay".

I can categorically state this is complete and utter nonsense!!:tongue:
Where did I put that bar clamp?

 

[ed4copies]

IF you get it hot ENOUGH---it will GRAB your bit and not let go!!

(Of course, this is hearsay, I would NEVER be that impatient!!!!):biggrin::biggrin::biggrin:

I can verify the truth of this "Hearsay".

I can categorically state this is complete and utter nonsense!!:tongue:
Where did I put that bar clamp?

Well, I have been further informed that you can then put the bit and the piece of plastic into a 200 degree oven for 15 minutes or so. Be prepared, when you remove from oven!!! Put on an "oven mitt", on your left hand (assuming you are right handed), grab the blank with the "mitted hand" and grab the top of the bit with a locking plier. (Vicegrip)

Turn the locking plier counterclockwise, while attempting to pull it apart from the plastic piece.

This WILL work---not always on the first try!!!
(or so I am TOLD!!):biggrin::biggrin::biggrin: