Cracking Acrylics

[Jyd]

Ok guys and gals I just don't know what I am doing wrong. I posted awhile back about pieces of my wood or acrylic blanks chiping out at the end of the blank, after reading all the replies I got new Gorilla glue epoxy and started turning again.

Now I am getting a crack length wise about 3/8" long in the end of the 2 acrylic blanks I have tried to do. I have tried to make sure they are glued down well, I even push the tube out the other end and apply epoxy on it and work it back in. It always happens as I am getting the blank thinned down and near to size and always on the tailstock end.

One was a PSI Apollo Infinity and the one today was a slimline from Berea Hardwoods so I am sure it is nothing to do with the kits and all to do with me and my experience. They were left overnight to cure and squared using the jig that I got from a member of this group, and by the way it works fantastic. The Apollo was turned on my mandrel using a mandrel saver, the slimline was tbc.

Could I have the tailstock to tight? I await your comments and go back to turning only wood for now.

Randy

 

[TonyL]

Tagging along. Thanks for posting. I haven't had the experience YET

 

[lyonsacc]

My daughter had a similar problem with that. She was tightening the tail stock too much (turning between centers) and was actually expanding the end of the brass tube.

 

[Charlie_W]

Lyonsacc may have the answer. You only need the tailstock tight enough to prevent the blank from slipping.
You said you were squaring the ends of the blank. Are they trimmed flush to the end of the tube or just square. If they are cut long, the pressure from the tailstock could cause the cracking as the blank gets thinner. Just a thought. Also, make sure your tailstock lines up with the head stock.
Hope this helps.

 

[Jyd]

Lyonsacc may have the answer. You only need the tailstock tight enough to prevent the blank from slipping.
You said you were squaring the ends of the blank. Are they trimmed flush to the end of the tube or just square. If they are cut long, the pressure from the tailstock could cause the cracking as the blank gets thinner. Just a thought. Also, make sure your tailstock lines up with the head stock.
Hope this helps.

They are trimmed to the brass tube, I think I need to back off on the pressure once the blank is rounded and see what happens I just hope this is the cure as it is getting pretty expensive throwing away blanks. :at-wits-end:

Thanks to all
Jyd

 

[Charlie_W]

They are trimmed to the brass tube, I think I need to back off on the pressure once the blank is rounded and see what happens I just hope this is the cure as it is getting pretty expensive throwing away blanks. :at-wits-end:

Thanks to all
Jyd[/QUOTE]

Don't throw them away. Turn off the bad end down to the tube, drill a piece of something else, add glue and slide the new piece on the end. Trim and get back to turning. You might want to do both ends for appearance.

 

[Jim Burr]

I couldn't tell when this is happening Randy. Is it just turning or assembly?

 

[kwmay]

A few thoughts from my experience with acrylic.

First, your blank may not actually be acrylic. In fact, if you cast your own pen blanks it is darn hard to find acrylic resin in craft stores due to the hardener toxicity. Sometimes the blank may be cast from polyester resin. There are different grades for any of the plastics but you won't see that when you are ordering from online. How hard the blank is to work with, i.e. cracking, has a lot to do with how much hardener is added. The only way for you to know is to remember which blank's are harder to work with.

Second, I echo what others are saying about not over-tightening the tailstock. Just tight enough to keep the blank from stopping as you carve. Of course, that tends to happen as you first start on the blank before it is round.

Third, do not be aggressive with acrylic, especially as you start rounding. Take your time and be patient.

Finally, I have 3 words about your carving tools - SHARP, SHARP and SHARP. And don't scrimp on the cost of the tool. It makes all the difference. Acrylic can be rough on the tools. I generally end up sharpening after every other acrylic pen.

Hope this helps.

 

[WriteON]

Finally, I have 3 words about your carving tools - SHARP, SHARP and SHARP. And don't scrimp on the cost of the tool. It makes all the difference. Acrylic can be rough on the tools. I generally end up sharpening after every other acrylic pen.

Hope this helps.

How do you sharpen and what are the best tools. Thanks, Frank

 

[rblakemore]

I usually use the EZ tools square scrapers for my pen turning. After ruining too many blanks, I started watching my scraper. I had a tendency to turn it on the tool rest that resulted in one corner of the scraper hitting the acrylic, digging in and shattering the blank. When I paid greater attention and kept my scraper firmly on the tool rest only taking off small shavings at a time I had better success. Also that some colors of blanks are much more brittle than others. I find dark blues and greens much harder than the others. The blanks that are embedded in clear acrylic such as woodcrafts circuit board pens are so bad that I sand them down most of the way with the electric sander then mount on the mandrel and start at 150 and go up. I no longer use a skew on them at all. Right now in lace acrylester is kicking my butt. I tired of using 2 blanks to make 1 pen so for the next one -nothing but sandpaper.

 

[TonyL]

Sharp tools

A few thoughts from my experience with acrylic.

First, your blank may not actually be acrylic. In fact, if you cast your own pen blanks it is darn hard to find acrylic resin in craft stores due to the hardener toxicity. Sometimes the blank may be cast from polyester resin. There are different grades for any of the plastics but you won't see that when you are ordering from online. How hard the blank is to work with, i.e. cracking, has a lot to do with how much hardener is added. The only way for you to know is to remember which blank's are harder to work with.

Second, I echo what others are saying about not over-tightening the tailstock. Just tight enough to keep the blank from stopping as you carve. Of course, that tends to happen as you first start on the blank before it is round.

Third, do not be aggressive with acrylic, especially as you start rounding. Take your time and be patient.

Finally, I have 3 words about your carving tools - SHARP, SHARP and SHARP. And don't scrimp on the cost of the tool. It makes all the difference. Acrylic can be rough on the tools. I generally end up sharpening after every other acrylic pen.

Hope this helps.

I am just a beginner and use Easy Wood Tools (carbide) for acrylic pen turning and I sharpen mine after every two pens. OldMan5050 (Dave N. taught me how).

 

[thewishman]

Tools don't need to be expensive to do the job. Harbor Freight and Benjamin's Best tools make pens just as nice as expensive tools. Any tool works better when it is sharp.

Randy, with the lathe off, can you scrape a ribbon off of the acrylic blank with your tool? If not, you should sharpen it. I started with the tools I mentioned, sharpened with a $3 whetstone. When tools are not sharp, we tend to press harder into the blank to make the tool work, and that leads to cranking down the tailstock keep the blank moving.

 

[johncrane]

You could be overheating the blank when drilling, causing fine hairline cracks in the center core which you won't see till the blank is turned down. use DNA in a spray bottle and squirt the drill bit and squirt inside the hole, this will kill the heat dead.and won't cause rust.

 

[kwmay]

Finally, I have 3 words about your carving tools - SHARP, SHARP and SHARP. And don't scrimp on the cost of the tool. It makes all the difference. Acrylic can be rough on the tools. I generally end up sharpening after every other acrylic pen.

Hope this helps.

How do you sharpen and what are the best tools. Thanks, Frank

+++++++
I use Benjamin's Best from Penn State Industries, but I would also consider Sorby's tools found at Woodcraft. For sharpening I use the Work Sharp WS3000.

 

[plano_harry]

I am going with John on the drilling. If you can't hold onto the bit when you pull it out of the hole, you are drilling too fast and overheating. Assuming you are drilling from the center to the tail, another suggestion is to leave the blank long to avoid drill stress at the exit. After you drill, cut the blank to length and the problem may go away. If not, you are over tightening.

 

[low_48]

I use a technique that I came up with when I learned to turn corn cobs. I would never turn from the center of the blank to the ends. I always turn from the ends to the middle. If you are pushing a chip towards the ends, it puts extra forces on the material, and it becomes unsupported as you finish the cut. It's very easy to get chips and maybe cracks this way. We didn't have them fancy carbide cutters in them days, and I'm still not a fan of them for turning thin walled materials like pens. I still say the skew is the tool to use. Nothing cuts as gentle. Carbide scraper guys always wonder how to turn coffee bean blanks and not loose beans. I have never lost a single bean using a skew.

 

[gawdelpus]

I use a technique that I came up with when I learned to turn corn cobs. I would never turn from the center of the blank to the ends. I always turn from the ends to the middle. If you are pushing a chip towards the ends, it puts extra forces on the material, and it becomes unsupported as you finish the cut. It's very easy to get chips and maybe cracks this way. We didn't have them fancy carbide cutters in them days, and I'm still not a fan of them for turning thin walled materials like pens. I still say the skew is the tool to use. Nothing cuts as gentle. Carbide scraper guys always wonder how to turn coffee bean blanks and not loose beans. I have never lost a single bean using a skew.

Have to agree on the skew as the best tool for most materials when used properly. One thing I always do with either wood or acrylics is to turn the ends down first almost to the bushes , I do a fairly steep angle at about 45 degrees. both ends then I turn the blank to size either straight or with a curved body , I also use my skew as a scraper ,in fact for about a year it was only ever used as a scraper ,till some one showed me the way to use a skew, well worth the trouble to master as you can do much finer and controlled cuts with it . But in the end "sandpaper is a cutting tool" hehe, cheers ~ John

 

[lwalper]

Ditto all the above ...

• Too much heat/pressure when drilling
• Dull tools
• Excessive pressure on the tailstock
• Glue in the bore of the tube
• Burrs/deformation on the inside edge of the tube

Solutions:

• Cool/low pressure drilling
• Sharp tools and light cuts at high RPMs
• Clear the junk out of the tube

I think my problems with blank splitting are usually introduced at assembly--some also in production, but generally in assembly. In order for the pen to stay together the manufacturer depends on tube deformation. As a consequence, by design, the parts are a smidge larger than the inner diameter of the tube. When you press the parts together the tube deforms/stretches to match the size of the part. Unfortunately, on some of these hard, brittle plastics, the material will not stretch and you get a crack. Get a round file--a chainsaw sharpening file works well, or pick up a set of tool and die files--and file out a bit of the brass so that the parts have a snug finger press fit. You can always use a dab of CA glue to hold the parts in place once you have everything fitting well.

 

[lwalper]

That said, be careful with that file. You don't want to bugger up the rest of the inside of the tube, especially if you're making a twist pen where the tube slides over the twist mechanism. You want to leave the inside of the tube as smooth as possible. Roughed-up brass is like sliding the twist mechanism over sandpaper -- not a good mix, and almost impossible to assemble/disassemble for filler replacement. Trust me, I've done it, and destroyed a pen or two in the process!:frown:

 

[Jyd]

Update on Cracking Acrylics

Ok guys and gals I just don't know what I am doing wrong. I posted awhile back about pieces of my wood or acrylic blanks chiping out at the end of the blank, after reading all the replies I got new Gorilla glue epoxy and started turning again.

Now I am getting a crack length wise about 3/8" long in the end of the 2 acrylic blanks I have tried to do. I have tried to make sure they are glued down well, I even push the tube out the other end and apply epoxy on it and work it back in. It always happens as I am getting the blank thinned down and near to size and always on the tailstock end.

One was a PSI Apollo Infinity and the one today was a slimline from Berea Hardwoods so I am sure it is nothing to do with the kits and all to do with me and my experience. They were left overnight to cure and squared using the jig that I got from a member of this group, and by the way it works fantastic. The Apollo was turned on my mandrel using a mandrel saver, the slimline was tbc.

Could I have the tailstock to tight? I await your comments and go back to turning only wood for now.

Randy

Ok today I finally finished the "Demonized" Apollo pen kit that used up 4 blanks.

I paid close attention to the tail stock pressure which I am sure is what was causing the problem.

Thanks to all!

Randy

 

[Cmiles1985]

Having read your previous post, I would recommend finding some cheap acrylic blanks (from someone here or ePay) and some brass tubes (pretty cheap too) and practice practice practice!