Acrylic cracks

[Irish Pat]

I have noticed that I get a very small crack on the end on my acrylics when I'm sanding them.What am I doing wrong,I sand with a dry sandpaper.

 

[Ambidex]

The only reason I can think of is heat. Too aggressive sanding could do that too I suppose. Slow and a light touch with the paper and stopping to erase the radial scratches may solve your problem. Otherwise I'd like to see some pictures of the kind and location of the cracks...could be the cracks are there from too aggressive turning and you don't see them till you sand to a certain grit..

 

[ed4copies]

I have noticed that I get a very small crack on the end on my acrylics when I'm sanding them.What am I doing wrong,I sand with a dry sandpaper.

Unlikely, Pat!!

More likely you are SEEING the crack when it gets sawdust in it.

Do you use a pen mill?
What KIND of acrylic? Be specific about the blank, this MATTERS!!

I have sanded with dry sandpaper for nearly 20 years, that is NOT the likely problem.

Happy to help, need more clues!!
Ed

 

[Dan Masshardt]

Unlikely, Pat!! More likely you are SEEING the crack when it gets sawdust in it. Do you use a pen mill? What KIND of acrylic? Be specific about the blank, this MATTERS!! I have sanded with dry sandpaper for nearly 20 years, that is NOT the likely problem. Happy to help, need more clues!! Ed

Maybe the cold you mentioned yesterday?

 

[1080Wayne]

As Ed says , but I rather doubt it will be sawdust . Acrylic dust , almost certainly . Cracks could also possibly be from drilling .

 

[Irish Pat]

I have noticed that I get a very small crack on the end on my acrylics when I'm sanding them.What am I doing wrong,I sand with a dry sandpaper.

Unlikely, Pat!!

More likely you are SEEING the crack when it gets sawdust in it.

Do you use a pen mill?
What KIND of acrylic? Be specific about the blank, this MATTERS!!

I have sanded with dry sandpaper for nearly 20 years, that is NOT the likely problem.

Happy to help, need more clues!!
Ed

Hi Ed,
I do use a pen mill.The acrylic in questain are just the basic ones with lines running through them(see photo) .I think myself it could be ME with all the sanding,I start with 180-12000,I do feel the heat,I think I need to stop between sanding grits or cool it down.I have done many acrylics before but this has happened a few times this week.

 

[rich gubbin]

Hi there, are you sure its a crack in the acrylic, run your fingernail across it to feel. It could be the paint crazing if you reverse paint. This happens to me when the temperature drops and the paint isnt drying enough between coats or hasnt cured enough before you gule the tubes in.

 

[ed4copies]

That should be a pretty easy material to work with!!

Are you making a pen style that leaves very little on the tube?? Churchill cap??

Sorry to agree, but yes, when that type of material develops cracks, it IS operator error (please understand I know this BECAUSE I have screwed up so many of them!!),
but I have never seen it crack in sanding. My guess would be that your pen mill is cracking it and the crack shows up when you sand and it gets dust in it. (BTW, conversely, if you clean the crack and drizzle a little thin CA on it, it will likely disappear!!)

What size hole and finished outside diameter are you attempting, please?

 

[Sabaharr]

If it is the heat you can beat that problem by running the lathe at its slowest setting and wet sanding, espically if you use micro mesh. MM works at its best when used wet.

 

[ed4copies]

I found another potential cause, yesterday.

I will show pics in a different thread, in the next few days, but the problem was I did not "face" the blank all the way to the brass tube (the material was a couple thousandths longer than the tube). So, as I neared the final "pen size", the bushing was pushing on the material and the thumbscrew tightened a little, cracking the end.

INTERESTING phenomenon: I'm sure I have done it before---but I now have time to study my mistakes----which I am REALLY enjoying!!