Polyresin question

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ed4copies

ed4copies

Local Chapter Manager
Joined
Mar 25, 2005
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24,638
Location
Racine, WI, USA.
Having "exotics" is really fun. People think I know all the answers, so I play along, usually, and give them good answers. This one I had no clue:

Customer: "I blew up four of your blanks, could they be defective?"

Further exploration and conversation gives the following facts:
1. The gentleman has turned our blanks successfully in the past.
2. They are "blowing up" on the drill press, where he is using a vice to hold them (limited vibration).
3. He is NOT trying to drill through, cuts off the end.
4. Making an emperor
5. Has brand new drill bits
6. Temperature in the shop is 40 degrees, fahrenheit.
7. Expects it may get to 30 degrees and still wants to work there and make pens.

What problems do you see and how would you overcome them?

No, he won't move his shop into the house.

All help and any experience would be appreciated. I would not be able to keep my hands working at 40 degrees, so I won't be likely to solve this one on my own.

BTW, the gentleman is VERY reasonable, so he will try any reasonable solution, I believe.

Thanks!!
 
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Can't help with that, I turn in the basement. I have had problems with turning PR but it had nothing to do with temperature. It was technique or lack of. Just don't ask me about sanding. I still can't get that right.
 
The possibility exists that the blanks are all bad, the probability is another thing. Are the blanks that blew up all from the same batch? Can the fact that the drilling generates heat cause blanks that are at 40 degrees to shatter from thermal expansion? Or is the tempature cold enough to make the blanks brittle and shatter upon drilling. I would suggest he takes the remaining blanks in the house and lets them warm up before drilling. this would give an indication if tempature is the cause.
 
Ed, try this: take a pr blank and get it down below forty degrees (try a freezer silly) and maybe a drill bit as well. Drill and turn like normal and see if you get the same results.
 
mredburn said:
The possibility exists that the blanks are all bad, the probability is another thing. Are the blanks that blew up all from the same batch?
No, they are different colors, therefore different batches--good question and one I asked.

Can the fact that the drilling generates heat cause blanks that are at 40 degrees to shatter from thermal expansion?
Don't know, I hope someone here will help answer that question.


Or is the tempature cold enough to make the blanks brittle and shatter upon drilling. I would suggest he takes the remaining blanks in the house and lets them warm up before drilling.
Careful, it appears we think alike. This is also what I suggested. (but, I have no idea if it will work!)


this would give an indication if tempature is the cause.
Click to expand...

Thanks for your reply!!
 
GOOD ANSWER (no, I am not trying out for Family Feud)

rjwolfe3 said:
Ed, try this: take a pr blank and get it down below forty degrees (try a freezer silly) and maybe a drill bit as well. Drill and turn like normal and see if you get the same results.
Click to expand...

Worth a shot!!!
 
There is a property of plastics that is called the glass transition temperature. Like a melting point, it involves a phase change in the material. Without getting too technical (google if you want more), below this temperature, the plastic is more brittle, and above it is more rubbery. Not rubbery to the point where it will flex, but definietly less brittle. I do not know the glass transition temperperature of PR which can vary some depending on the source and how much catalyst is used, but suspect this could contribute. Only 2 solutions I know are 1) wait until it gets warmer 2) order them predrilled (with a slight upcharge of course)
 
The pressure from the vise when drilling can cause the blank to blow out even if you have not drilled all of the way through. Have him try this: put a support block under the blank to raise it to the desired height (if needed) and use only enough pressue to keep the blank from turning. This is best done if the blank is square. The blank and drill should be warm. Cold temperatures will increase thermal stresses and probably increase the brittleness.
 
BRobbins629 said:
There is a property of plastics that is called the glass transition temperature. Like a melting point, it involves a phase change in the material. Without getting too technical (google if you want more), below this temperature, the plastic is more brittle, and above it is more rubbery. Not rubbery to the point where it will flex, but definietly less brittle. I do not know the glass transition temperperature of PR which can vary some depending on the source and how much catalyst is used, but suspect this could contribute. Only 2 solutions I know are 1) wait until it gets warmer 2) order them predrilled (with a slight upcharge of course)
Click to expand...

Thanks for you input, Bruce, I was hoping to hear from you.


I like your "revenue based thinking" Bruce!!!!

However, when he puts them on the lathe, won't he encounter the same difficulties in "shaving off" ribbons??
 
How were they drilled? Were chips evacuating normally?

When you drill PR, it tends to bunch up a lot to the point where when you back out the drill bit you get a jack in the box effect where the swarf pops out and expands.

My thinking is that the sudden temperature change caused by drilling heat makes these swarf pieces extra expandable?
 
I turn in very cold temperatures, Ed, as my Canadian shop is rather cold! :) IBut I don't turn when it gets rather cold...perhaps the issue is the drill...an emperor is a rather large bit, and creates heat...if the bit is not entirely sharp, and the blank is cold, thermal shock might be the culprit as much as drilling out of the bottom...

I'd recommend that he keep the drills and blanks in his house until he's ready to drill them, and have him avoid drilling through...cut to size later...if that solves the problem, all the better. If not, we'll have to try something else.
 
It will be equally brittle when turning. I have turned PR in the very cold with very sharp tools and very small bites. Risk is increased but it can be done. Maybe you should make the pen for him/her?
 
BRobbins629 said:
It will be equally brittle when turning. I have turned PR in the very cold with very sharp tools and very small bites. Risk is increased but it can be done. Maybe you should make the pen for him/her?
Click to expand...

It is a "he". And he has turned quite a few of our blanks successfully. So, he believed me when I hypothesized that the temperature could be an issue. BUT, I wanted the kind of feedback we are getting here to give me some assurance that I COULD be correct.

And, anything I learn may be helpful in the NEXT call I receive!!!
 
1.Brand new drill bits don't mean sharp drill bits.
2.The temperature is going to change drastically when the drill bit starts to spin in the blank.
3.The holes being drilled are large and should be predrilled with smaller bits.
 
Another thing. Most of the drillbits I have been receiving have had a sticky coating on them. If you don't take that off they can grab and tear a chunk out of a perfectly good blank. DAMHIKT!
 
wolftat said:
1.Brand new drill bits don't mean sharp drill bits.
2.The temperature is going to change drastically when the drill bit starts to spin in the blank.
3.The holes being drilled are large and should be predrilled with smaller bits.
Click to expand...

1. On the other hand, the brand new drill bits could be TOO sharp for brittle and cold plastic.
2. Sorry can't agree on this as the temperature rise is going to be the same irrespective of the ambient temperature. If the act of drilling causes a temperature rise of say 30 deg C then it will do the same for any ambient temp.
3. I know that some people do this but I have blown more blanks by predrilling and now just use a centre drill, then the correct size.

My money is on the blanks being a bit more brittle because of the cold added to the brand new bits:wink:
 
skiprat said:
1. On the other hand, the brand new drill bits could be TOO sharp for brittle and cold plastic.
2. Sorry can't agree on this as the temperature rise is going to be the same irrespective of the ambient temperature. If the act of drilling causes a temperature rise of say 30 deg C then it will do the same for any ambient temp.
3. I know that some people do this but I have blown more blanks by predrilling and now just use a centre drill, then the correct size.

My money is on the blanks being a bit more brittle because of the cold added to the brand new bits:wink:
Click to expand...
I agree that it is most likely a temperature issue, but the temperature of the blank is going to change a lot quicker than the temperature of the drill bit due to friction of the cutting. Either way, the temperature is going to be an issue here. Final solution would be to heat the shop.
 
I would suggest he warm the bit and the blank at room temp first. To help with the heat, since its resin, maybe have him pour some water over it during drilling to keep the blank and drillbit cool. I have a small water bottle I poked a nailhole in the top for things like this or when I want to do any small wet sanding.
 
mywoodshopca said:
I would suggest he warm the bit and the blank at room temp first. To help with the heat, since its resin, maybe have him pour some water over it during drilling to keep the blank and drillbit cool. I have a small water bottle I poked a nailhole in the top for things like this or when I want to do any small wet sanding.
Click to expand...


And that was my final recommendation.

At which point he mentioned that he tried to mark the center by "tapping" a nail into it. This also broke the blank.

I have done the same, trying to tap my spur drive into PR blanks--if you want a "start" point, revolve the nail, don't hit it. (Not relevant to your statement, just free advice!!)
 
I also think the cold blank with the warming bit from cutting is causing it to blow out. Like suggested I would warm blanks to house temps, take out when ready to drill and use water as a lube/coolant see if this will help the process...now turning them cold may do the same thing. Heat the shop or store blanks inside when not working them.
 
Common sense dictates that colder temperature makes for brittle plastic. Just take one of them thin pliable plastic binders and toss it outside right now. Tomorrow you pick it up and try and bend it and I guarantee it snaps right off. I see the temp of the bit not making any difference, and plastic does not transfer heat fast enough for a drill bit to warm the freezing blank up by the time the bit gets through it. I say leave the blanks in the house. If it was me, I'd bring the drill press and the blanks into the basement. You won't make too much of a mess just drilling. Then run out, spin a blank and immediately bring it back inside. This way you drill, spin and assemble a room temp blank. If you spin half a dozen and then bring them inside, wait a few hours before assembly. Bring the press in the house..it's not messy assembling a pen..you can do it at the kitchen table.
 
I can tell you that when I WANT to shatter blanks (to put into poured resin
for color/texture) I put them in the freezer. Then they pretty much shatter
no matter what tool I touch to them.

Polyester resins are less elastic when cold. Drilling generates heat, which causes
the resin to expand. But .. it can't expand as quickly when it is cold .
PR usually has a glass transition that is above room temp, so it's really only elastic
when it is warm to the touch. Below that, it is brittle.

That's my guess. What do I win?
 
I had the same problem when I tried to work in the unheated barn last year but i think I was so damn cold that i was going too fast. I suspect the statement " ...using brand new bits..." may have something to do with it. I do not know why but a couple years ago I had real trouble blowing up all sorts of PR blanks with a new bit, not sure why so I tossed it and have used the old bit since
 
Vise pressure for sure. Ask what does he mean by blowout. For a long time I tried drilling plexiglass and holding it with a regular small mobile vise. The two points of pressure would crack the blank every time. Would drill fine as long as it was abouve the vise. Once the hole is drilled the plastic has a place to move and especially with the drilling heat and cold materials it will probably crack like a frozen melon. Best results come from rounding blanks and going to collet which will hold from all sides and drill on lathe in small sessions.
 
This might have been said already, but I had this problem in the past. I always place a piece of wood under the blank so when I drill through the bottom there is enough support and no open hole to allow a breakout. I also keep all of my acrylic blanks up stairs in 70 degree temps and try to work them before they get cold.
 
He might want to try the new parabolic bits from COLT as well. The bits are made with a better grind on the bits for the plastics we use in penmaking. I have used them, and have just about replaced all of my "old" bits with the parabolic bit equivalents. I highly recommend them, and have done a product appraisal for them.

One other small thing to check is the table of his drill press. As others have stated here, the drill size for the kit he is drilling is fairly large in size. If the table is off a little from being level, the action of the drill in cold weather could certainly apply enough side pressure with a brad point bit to create the result he is getting. I suspect he has created a "perfect storm" with the cold and some other factor.......
 
I would also suspect a temp problem. I have seen other plastics become brittle when cold so would expect PR to do the same at some point. also even if the bit and plastic both start out at the same temp they will not stay that way, and they will not warm up evenly. The bit will get hot faster and hotter than the plastic. and the plastic will be warmer near the bit than at it's outside surface. all of this could cause cracking breaking and such. I would at least suggest he bring blanks indoors or warm them in some manner before drilling and see if that solves the problem.
 
papaturner said:
Too much pressure on the blanks in the vise?DAMHIKT:biggrin:
Click to expand...


I wondered that too.

With Emperor pens, I use several drills to get to the final size. I try using at least a 1 inch blank for them. That size drill scares me. :tongue:
 
papaturner said:
Too much pressure on the blanks in the vise?DAMHIKT:biggrin:
Click to expand...

I regularly use a vise to drill. But when I drill PR and such, I've made 90 degree "V" in two small pieces of wood. I put them in the vise and then insert the PR/Acrylic blank within the "<>" space between the two pieces of wood. It allows more "give" for the PR while supporting the length of the blank to be drilled. It also guarantees the blank is straight up and down.

I would imagine it would help maintain warmer PR temperature he would have keeping PR and bit indoors before drilling. Not having the PR come in contact with the metal vise would help reduce temperature problems.

Of course, living in So California, I would have to resort to the refrigerator experiment to know for sure.
 
For what its worth i had one of Ed's cat blanks ,glued up and waiting in the shop. The temp was pretty cold and had been for days.Decided to just knock the corners off in preperation for turning the blank the next day off. The blank started chipping really badly so i quit and brought it in the house. After a couple of days when everything warmed up, took it back out to the shop(which was warm now) and it turned like butter. I think the cold has a lot to do with it.
 
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