What happened here? Acrylic blank problem.

[Dan_F]

Here is a pic of a blank I just finished turning.

Does anyone have a guess as to what caused the vertical marks that you see in the white areas. They actually show up through the blue too, but not so much in the pic. These marks are on the inside surface of the blank.

I painted the inside of the blank, two coats of white Testor's, and painted the tubes white as well. This is the barrel of a Ligero (El Grande). The cap turned out fine.

While the material on the cap is half again as thick as that of the barrel, the marks were visible well before it was turned to final dimension. My first guess was scoring from the drill bit (cap and barrel take different size bits), but now I'm not so sure. Any thoughts?

Dan

 

[el_d]

I use testors also and have seen this on my stuff.
My problem is "brush marks" from the Q-tip. Another coat of testors paint usually paints the interior of the tube completely so that there are no areas with thin coverage. I also paint the brass tube.

 

[Daniel]

My guess would be marks from the drill bit. I once asked around about being able to drill a clear acrylic rod so that it remained clear. I was told to use oil while drilling. it is a bit hard to do if you do not have oil flowing constantly as the drill bit carries it back out as fast as you put it in. I also polished the inside of a tube all way through Micro Mesh and that worked pretty good but real time consuming. be careful the MM melts real easy. at least sanding inside the tube woudl make the marks consistent.

 

[maxwell_smart007]

I was thinking that it's the paint not sticking to the tube properly...perhaps when you push it in it rubs off a bit...

 

[Paul Downes]

Could it be that you scraped off the paint from the high spots left by the drilling when you inserted the tube? Also, I wonder how well testors paint sticks to acrylic? I think it is an enamal paint which probably won't stick as well as other paints. paint some on the outside of the blank and see how hard it is to scrape off. I still sand the tubes and then spray paint them as well as the insides of the blank. Heck I've been using a white primer and black rustoleum and they work well.

 

[Dan_F]

At this point I'm leaning in the direction of drill scratches. I had considered maybe the tube caused the scratches going in, but there are just too many of them, and scattered all over the blank. I thought about them being Qtip marks (my "brush") too, but if it was either of these, I would expect to see a similar problem on the cap piece, and that one is fine.

Dan

 

[Nolan]

Drill got too hot and for a lack of a better term melted the blue into a swirl pattern on the inside. IMHO

 

[Blind_Squirrel]

To me it looks like air trapped between the blank and the tube. No matter how hard you try, you are going to get some air in with the glue.
- The white paint may not have been thick enough to be opaque.

How do you glue your blanks in?
- What type of glue do you use?
- Do you spin your tube?
- The glue you used may have melted or stripped some of the paint.

How tight did the tube feel when you glued it in?
- There may not have been enough room for the painted blank to fit in the hole. The tube may have scrapped off some of the paint.

 

[Dan_F]

Originally posted by n4631x

Drill got too hot and for a lack of a better term melted the blue into a swirl pattern on the inside. IMHO

I was wondering about the color, using my loupe, I can see both blueish and blackish marks, so whether it melted or just ground the dust into scratches, that seems to be what happened. I didn't think it got all that how, I took shallow bites and cleared often, but who knows what happens at that level?

This drill bit is a 135* split point from the Harbor Freight set, the cap was done without incident by a standard 118* bit. Would that have an effect on temperature while drilling?

Dan

 

[Dan_F]

Scott---Thanks for your interest. I don't think its air, I've done that too, and it looked different. I used two coats of Testors on the inside of the blank.

I use epoxy, coat the inside of the blank and the outside of tube, twist the tube as its going in. I don't remember feeling anything different as I was inserting the tube. I don't think that I twisted it enough to cause the scratch pattern seen.

I think Nolan nailed it, either dust or melted material filled in the scratches, and was sealed in by the paint, thus leaving mostly blue but a few black marks as well.

Dan

 

[Nolan]

Originally posted by Dan_F

Originally posted by n4631x

Drill got too hot and for a lack of a better term melted the blue into a swirl pattern on the inside. IMHO

I was wondering about the color, using my loupe, I can see both blueish and blackish marks, so whether it melted or just ground the dust into scratches, that seems to be what happened. I didn't think it got all that how, I took shallow bites and cleared often, but who knows what happens at that level?

This drill bit is a 135* split point from the Harbor Freight set, the cap was done without incident by a standard 118* bit. Would that have an effect on temperature while drilling?

Dan

118 and 135 are different in that a 135 is "typically" designed to drill harder material, self centering because of split point and less pressure need to drill cause of the 135 angle. 118 are an all around drill for use in wood and metal. Basically what controls temp as far as drill bits are concerned (speaking of the design of the bit not external issues like cutting fluids, drill speed and feed pressure) is the metallergy type and coating of the bit. I would think the difference is the quality of the two bits used, where did the 118 come from and is it a better quality bit than the HF bit? I grew up in a welding and machine shop and will tell you there is a huge difference in cuttting tools. IMHO HF stuff isnt worth the paper the receipt is printed on. If you have the money and you want a good bit buy Magnum series Norseman bits. http://www.norsemandrill.com

 

[Dan_F]

The bit comparison is interesting. The 135* is HF, the titanium coated HSS complete set (letter, number, and fractional) . They get pretty good reviews on this site, but maybe more for wood that acrylic. The entrance hole actually seems more accurate with this bit (as I'm drilling the bit seems to fit the hole better than with the other bit, which is a Triumph HSS). However, it does leave more scratches on the inside than the Triumph. This hasn't really been much of a factor until recently, as these are the first large acrylic pens I've done.

I have a few of the smaller Norseman bits, but mostly cheaper ones in the large sizes, where the Norseman's get spendy in a hurry. If they will spare me this sort of aggravation though, it would be worth it. I have a set through 1/2" or the Triumph HSS (uncoated), which I thought were a pretty high quality brand, I just used the HF because I thought I saw in thread somewhere here that 135* was preferable for acrylic.

Dan

 

[avbill]

If it is dust did you use compressed air to blow out the dust before painting the acrylic blank? just another thought.

bill

 

[CSue]

I've seen that in some of mine - and it was caused by the paint not sticking well enough to tube &/or acrylic. A few times I've felt the heat from the finish heat up the acrylic so much that the spin of the acrylic was slower than the tube causing some of the paint to come off. I'm still working out what kind of paint to use.

 

[Nolan]

Originally posted by Dan_F

because I thought I saw in thread somewhere here that 135* was preferable for acrylic.

Dan

IMHO 135 are best for what we are doing cause the split point keeps the bit from wandering and also breaks the chips as they go. So you get a better start and straighter hole plus the flutes clean good cause the chips are being broken and not coming out in a long curly tail. This all helps I feel to drill the biggest hole in the smallest blank without blank failure (wandering hole, too much heat, not clearing flutes out and causing the blank to blow out). With good bits a 7/8 blank isnt needed for making pens. Keep in mind these are just my opinions and everyone is free to disagree.

 

[Dan_F]

Originally posted by CSue

I've seen that in some of mine - and it was caused by the paint not sticking well enough to tube &/or acrylic. A few times I've felt the heat from the finish heat up the acrylic so much that the spin of the acrylic was slower than the tube causing some of the paint to come off. I'm still working out what kind of paint to use.

I wet sand then buff, blanks never get warm, let alone hot.

Dan

 

[MCSO5164]

I've had worse finishes, hope you get it figured out. Wish I knew the fix for you but I'm still a rookie. Good luck.