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Turning Acrylic Pens - Blanks Blow Out!!

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Forum topic by mrjello posted 03-10-2010 08:40 PM 7334 views 0 times favorited 8 replies Add to Favorites Watch
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mrjello

28 posts in 1809 days


03-10-2010 08:40 PM

Topic tags/keywords: pen acrylic turning plastic lathe acrylic blank pen blanks pen turning question tip busted exploded help turning help

I’m new to turning, brand new.
Just bought my 1st lathe about 3 weeks ago.
I have a Chuck for the tail stock to do my drilling with ( I don’t have a drill press )
I’ve turned out 6 pens total ( including 1 acrylic ).

Now, I’m trying to turn another Acrylic and the blank busted out when I drilled the blank.
Thankfullly I had cut the blank a little long.

Got the tube glue in and the barrel trimmed up nice.

Went to turn the blank and was able to get it in round.
Then, I proceeded to shape it and the blank just exploded on the end.

I would really appreciate some insight on this ( as there is wisdom in a multitude of counselors )

Questions I have:
- How fast should I be drilliing Acrylic blanks ?
- How fast should I be turning Acrylic ?
- Are there any “tricks” that would help to prevent this “blowout” ?


8 replies so far

View lew's profile

lew

10155 posts in 2503 days


#1 posted 03-10-2010 08:59 PM

I’m no expert.

I have read that you need to use both slow speed and feed to prevent the problems you encountered. I also read that you should not drill completely through the blank in one direction. Using a brad point bit, drill until the tip just breaks thru then invert the blank and drill from the other end. This is supposed to prevent chip out on the ends of the blank

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View grub32's profile

grub32

210 posts in 1796 days


#2 posted 03-10-2010 09:04 PM

well…drill slow….heat is generated through drilling and it can brake the plastic. I use epoxy to glue in acrylics tubes. I think its better to prevent blow outs.

I also turn at high speed. I think it is more important to have really sharp tools tha worry bout speed. I just like how nice it shaves at high speed.

Ohhh…sharp enough to shave hair off your arm… scary sharp.

I have done lots of pens both ac and wood…check out penturners.org for tutorials and the pen masters…many LJ’s are members there to.

Grub

-- Science Teacher by Day, Wood Butcher by Night!!

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grub32

210 posts in 1796 days


#3 posted 03-10-2010 09:09 PM

in regard to drill depth…you can prevent blow outs also by not dilling all the way and then cut the end of to expose the hole on the edge…that works to on very brittle material.

best of luck,

Grub

-- Science Teacher by Day, Wood Butcher by Night!!

View michelletwo's profile

michelletwo

2290 posts in 1764 days


#4 posted 03-10-2010 09:25 PM

This is a very common problem Go to pen sites and they have libraires filled with info on drilling The Pen Shop., International assoc of penturners and one in Australia. Tons of folks there who know pens in & out. Drill for short distance, with a sharp, sharp, sharp bit, get swarf out, and drill again. Keep blank cool and as the above folks said, keep blank a tad long and drill short.

-- We call the destruction of replaceable human made items vandalism, while the destruction of irreplaceable natural resources is called development.

View Planeman's profile

Planeman

97 posts in 2325 days


#5 posted 03-11-2010 07:16 AM

Acrylic can be brittle. For long bores you need to do like is good practice for boring long holes on a metal lathe. Start with a small diameter drill like 18” dia. for the first bore, then progressively enlarge the hole with larger drill sizes in about 1/16” increments. Most drills in home workshops are “jobber’s” drills which are probably too short in the smaller sizes to make it through the hole. You will have to use “aircraft” drills which have long shanks. Probably a mail order item although I found a few at Lowe’s. When boring, make sure you use a sharp drill and take it easy. Withdraw the drill frequently to clear the chaff.

Rufus

-- Always remember half of the people in this country are below average.

View tooldad's profile

tooldad

658 posts in 2463 days


#6 posted 03-11-2010 08:31 AM

I teach woodshop and the pen bug has bit my students big time. My students are having some of the same problems. I can’t always be there to watch there every move since I have 17 doing different things at one time. I might take the suggestion of cutting a little long and not drilling through, then cut off the excess.

The comments about the sharp tools are a must. I was told at Rockler to make light cuts also. It takes 2-3x as long to turn an acrylic for me than it does a wood pen.

The chisel I have resorted to is the carbide tipped cutter from Craft Supplies. It is an $88 chisel, but I don’t have to constantly sharpen tools for my students. Going to get 2 more for next year. They are currently using my personal one that I bought at the wood show. There are replacement tips for about $18 each. Little steep in the beginning, but worth it in the long run.

View Sawdust2's profile

Sawdust2

1467 posts in 2836 days


#7 posted 04-07-2010 04:46 AM

If you have or get a collett chuck (little pricey) you can drill the blanks on your lathe. A far superior way to drill as it is less likely to blowout the end and will be exactly centered the length of the piece.
Else the best alternative is to cut the blank a little long. The little extra wasted is cheap compared to the value of the entire blank.
Then there are just 2 rules – make sure your skew is scary sharp (do not use a gouge) and that you make light cuts.
If you are fortunate enough to have a carbide chisel you can get to the skew stage a lot faster.
You can also turn your blanks round before you drill them. That will ease the jarring of trying to round the blank with the tube in it which can weaken a poor glue job.

Just a few pointers.

Lee

-- No piece is cut too short. It was meant for a smaller project.

View Brad-Scott's profile

Brad-Scott

11 posts in 653 days


#8 posted 07-07-2014 11:58 PM

I turn a lot of pens; and use a “Colt” bit available from all the pen pushers.
Get a bulk pack of Slimline pens and turn wooden blanks until you have the 7 mm pens down. Get an extra pack or two of brass tubes and turn them down to the bushings, no pen kit involved. Move on to Euro pens in wood surprisingly nice pens, also 7 mm and affordable. Get your finish up to luster in wood, you will find the same finishes in acrylic. I use white auto polishing compound, found in your garage, followed by clear coat polish, found in your garage. Wood is easy start with dewaxed Shellac, “Zinser” Clear at Lowe’s of HD. Add finish from there.
A Micro mesh sanding kit lasts just about forever. $18 bucks.
When you move on to acrylic it’s plastic. Plastic melts at moderately high temperatures. Drill slowly withdraw the bit frequently. Use the lathe as your drill press, it’s far more accurate and easier.
Learn to sharpen and use your skew. If you do not learn the use of the skew to not buy acrylic blanks. Anyone can learn the skew on any chunk of wood lying around. Keep at it. The plastic is pretty and diverse and Expensive.
Join IAP – Penturners.org it’s free. Look at the Pen turners Guild gallery, no don’t do that. It’s too far out.
Good luck!
Woodcraft has pen blank grab bags they are wood and cheap!

-- Brad~Scott

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