Carbide end mill too aggressive for PR?

[jbswearingen]

This evening I tried milling two blanks from PR that I cast and the ends shattered. I was trying to do it by hand, with the mill in my hand drill. I then tried it on the DP (a third attempt) and it seemed to work a bit better, no shattering, but it didn't seem happy.

I've only used the steel mills before, but figured that the longer life of the carbide blades would make the price worth it.

Thoughts or advice?

 

[BRobbins629]

Turn the cutter upside down, mount some 120 grit adhesive backed sand paper and you will now have a sanding mill, much gentler on all blanks.

 

[jbswearingen]

I've tried that. WAY too dang slow.

 

[reiddog1]

Brad,
I haven't used a pen mill in a long time. I think that they are too aggressive and a PITA. Take a look at Ed's video (ed4copies) and make yourself a sanding mill. I personally have a scrap piece of wood screwed to a faceplate that I use self adhesive sandpaper with, and a jacobs chuck with the HF punch set to dress the ends of my blank. On one of Curtis' alumilite videos, he shows his set up that is very similar to mine. Hope this helps.

Dave

 

[reiddog1]

Turn the pen barrel down most of the way and then use the sandpaper method. Goes much faster!!

 

[jbswearingen]

Yup, I made a sanding mill for my lathe, using a milled flat on a shaft to glue the paper to. It clogs up quickly and must be moved around too much. It's too slow, too. I've never had a problem with end mills before; they've worked perfectly for me. But they were all steel.

 

[pensbydesign]

need more speed, i am not sure a hand drill can get enough speed

 

[SerenityWoodWorks]

Fast speed on the DP and very slow and light cuts works great for me. I also take the blank to the disc sander to get it close to the brass prior to using the mill as to not try and take too much off with the mill.

 

[chrisk]

The first endmills I used were steel mills. I also tried a sanding mill...
My conclusion: a good carbide mill is the way to go. Till now I only had one approaching that perfection, allowing me to even clean my blanks after CA finishing them. And this mill is the one I purchased two years ago from Nolan.
This mill was honed twice by professionals and I still use it now.
Last summer, in order to anticipate my mill's end of life, I purchased two custom made carbide mills from a factory in Greece. While they do the job, they are some miles behind Nolan's mill, and certainly some issues have to be fixed before I use them like my Nolan's mill. Not sure though that this factory will fix these issues.

Anyway, some months ago, a member here wrote that the US firm Whiteside was about to commercialize a carbide pen mill. Has anyone ever heard about that?

 

[jttheclockman]

I use a carbide mill all the time and mine too was Nolan's. The number of cutters makes a difference. The more the better. The sharper the better. Light pressure is needed. Get close then sand.

 

[jbswearingen]

Okay, I'll check out Nolan's mill. Anyone have a link to see it?

 

[chrisk]

Okay, I'll check out Nolan's mill. Anyone have a link to see it?

Brad, unfortunately, Nolan stopped selling through the forum. As for the carbide pen mills, a member here, Mike Kennedy (a.k.a. "IPD Mr") has been in touch with Nolan for this purpose but he was told that the machinist who modified steel mills to carbide ones has closed his shop.

Brad, how many cutters on your mill?

 

[longbeard]

Bench sander with a disc works for me, then when im close to final size demension, i do as Ed describes in his video, only i've been using sandpaper with the sticky back instead of glue.

 

[randyrls]

This evening I tried milling two blanks from PR that I cast and the ends shattered. I was trying to do it by hand, with the mill in my hand drill. I then tried it on the DP (a third attempt) and it seemed to work a bit better, no shattering, but it didn't seem happy.

Brad; Any cutting tool puts "point stress" on the material being cut at the point of contact between the material and the cutter point. PR tends to be brittle and using excessive catalyst may make it more brittle. Because I don't want that point stress on any delicate or fragile blanks, I always use a sanding jig. I cut long, drill short, trim the end on a saw, and then square up the blank with a sanding jig.

Hope this helps.

 

[jbswearingen]

I don't think I could make it any less brittle with the hardener--I only use four drops per ounce, and an oven to speed the reaction along. I'll try higher speeds and a lighter cut and see what that does.

 

[Sylvanite]

What's really important is the speed of the reaction. The amount of hardener is only part of the equation. Other variables include ambient temperature, resin temperature, thickness of the pour, and any additives (including promoters mixed in by the manufacturer, thinners and thickeners such as styrene and silica, and especially colorants).

There is a minimum amount of hardener (e.g. MEKP) needed. It supplies the oxygen atoms needed to crosslink the polyester chains for a strong crystal. Beyond that, additional hardener accelerates the reaction. MEKP is typically added to PR at 1%-2% by volume. For our casts, 1% is a good starting point.

The resin is meant to be used at around 70 Degrees Farenheit. Above 80 degrees, the reaction will happen more quickly. Below 60, the reaction rate will be retarded. The curing process is exothermic, so it will generate heat as it goes. The thicker the cast, the more heat it will retain, and the faster the reaction will proceed.

Most dyes and pigments made for PR will either not affect reaction rate, or will retard it. More hardener, higher temperature, or more time will be needed to cure.

Generally speaking, if the cure is fast or the temperature is high, then the cast will be more brittle. Also, if the temperature is high, you'll get more shrinkage when the cast cools.

4 drops of MEKP per ounce of Silmar 41 is a reasonable amount and shouldn't lead to brittle blanks. If, however, you heat the resin or put it in an oven to cure, that might.

I hope that helps,
Eric

 

[18111]

I had exactly the same experience you had and stop using it for a while until my steel mill dulled. I re-tried again recently and it works ok now. I use 5/8" trimmer on the hand drill. Slow speed and light cut, even lighter cut when caught, pull back and feed slower and cut as little materials as possible until bumps are removed then resume normal feed speed. I found slow speed for the plastics and high speed for the woods works better. Don't forget to wear leather gloves to protect your hand and release immediately when caught on the drill. It's painful if you don't. Need little practice but works. I still prefer to use steel mill though. The problem might be it has only two cutters. It might work better if four cutters are used like a steel one. Here is a little video I did. Hope it helps. Yoshi

 

[sbwertz]

Carbide is simply not as sharp as steel. It wears better and doesn't dull as fast, but isn't as sharp to begin with. Found that out with carbide drill bits. good article here.

http://www.woodweb.com/knowledge_base/Sharpness_of_High_Speed_Steel_Versus_Carbide.html

 

[ed4copies]

I've tried that. WAY too dang slow.

Hi Brad!!!

When I made pens for shows, I was extremely FAST!! Everything I did was FAST!! Blowups??? SURE!! Drilling, facing, turning---cracking the blank while assembling!!! Yes, all of these were "expected" parts of making a LOT of pens!!

Now I make far fewer pens! BUT, I have almost NO pen blanks that get damaged while becoming a pen.

Do what you want, but remember the TV "Highway" ad slogan: Speed kills!!

You can make fewer pens and be MORE profitable, if you use your brain to reduce waste.

 

[philipff]

I mount my barrels in a 4jaw (loosely), bring up the 60d. tail to make sure all is centered, tighten the jaws and remove the tailstock so that the open end is exposed to my spindle gouge. A few thousands of an inch come off at each pass until I see brass shining. Stop and reverse. - -- works perfect for me every time. philip

 

[Lenny]

I have never been able to find a Whiteside carbide pen mill trimmer other than the 2 cutter one here Whiteside Pen Mills

I am leary of this one as it only has two cutting wings.

As Sharon pointed out carbide can't be sharpened as sharp as steel, it's advantage is it doesn't get dull as fast.

I do use a homemade sanding shaft to dress the pen blank before assembly but it would be painfully slow to try to use it in place of a pen mill. A sander, either a stand alone disc sander or a makeshift one using your lathe and a faceplate with sandpaper attached (or some other method) is the way to go IMO. Using a drill chuck in the tailstock to hold a suitable sized punch Transfer Punch Set - 28 Piece will keep the pen blank nice and square to the sander.

 

[HamTurns]

This used to happen to me too ...

This used to happen to me too. I tried different speeds and different ways to hold one and turn the other.

What I found that made the biggest improvement was to use a 4 blade cutter.

The way I always use it now is to chuck up the trimming bit in the jacobs chuck, put that in the spindle and turn it about 1200 rpm. I then hold the blank with a pliers and put it onto the trimmer and push a little until it cuts enough to show a shine on the tube.

That way has been working well for me.

But I like the idea of making the backside of the cutter a sander, that's a great idea that I'm going to use.

Tom

 

[jbswearingen]

I think I've figured out how to make it work, but if it blows out again, I'll likely just buy another steel 4-cutter model and replace it more often.

Ed--

I hear ya on that (speed), but my time in the shop is very limited due to family, work, and school. I have to find ways to save time so that I'm productive.

 

[its_virgil]

Don't just replace them....sharpen then when needed. I don't like the two cutter mills nor do I like the 6 cutter ones. I mill my snake skin blanks with either a carbide or steel pen mill and have no problems with either. This may help in learning how to sharpen a pen mill.
http://www.penmakersguild.com/articles/penmillsharpening1.pdf

Do a good turn daily!
Don

I think I've figured out how to make it work, but if it blows out again, I'll likely just buy another steel 4-cutter model and replace it more often.

 

[edman2]

I've used nothing but carbide pen mills for more than five years on many pens both wood and acrylic. I have never had a shattered blank. I even use the two blade PSI carbide mills. The smaller one is sharper than the larger one but I have turned hundreds of pens and have yet to sharpen the mills. They both cut very well. I use a fast speed on my dp, hold the blank in my pen vise and use a very light touch. The light touch may be the most important.

I'm not sure what to suggest to you other than the extremely light pressure. I wish you the best.