purpleheart

Jeff:

Purpleheart is really not one tree -- it is a bunch of related trees which look pretty much alike. Much 'purpleheart' has significant amounts of silica in it so is highly abrasive. Even if you grind well, it is possible with some purpleheart that the edge will not last more than a few seconds.

Much purpleheart is also very brittle. It starts out that way and if it is kiln dried poorly, it gets even more so.

Also, the purple color will become a muddy, ugly brown. A U/V inhibiting finish will slow down the color shift but you cannot stop it.

Sometimes a piece of wood will respond best to a scraper, sometimes to a shearing cut controlled by a rubbing bevel and sometimes to a shear scraper. When there is trouble, you try them all. And you regrind just before the finishing cuts.

In the end, though, life is too short to p*ss away a part of it turning purpleheart -- it just ain't worth it. Anyway, that is my feeling on the subject. And I used to sell the stuff and got it for free.

Bill

Jeff wrote:

you need sharp tools and lots of sanding- you can get brighter colors with heat and acid - I believe some of these tips are in the tips section of

In my experience, purpleheart can be splintery but not un-useably so. Are you sure you're cutting in the right direction for the grain orientation in relation to the spin? To my mind's eye, a 7/8" disk would likely have the grain running perpendicular to the lathe axis and should be cut from the side of the disk instead of on the edge.

A roughing gouge isn't the best tool for doing this but almost any other gouge would be. You want to approach the cut from the side of the disk and aim the tool tip toward the center of the 7/8" thickness. If you use a parting tool or scraper go at it from the same direction - your aim is to sever across the fibers. It sounds to me like you're tearing out chunks because you're hitting the endgrain as the disk spins while the cutting edge approaches the outermost edge of the disk.

Please post again if none of this makes sense. Perhaps others can explain more clearly - or perhaps I totally have the wrong impression as to what's happening.

The less you tug at the fiber, the better the surface will be. Or, more to the point, the better the area just below the surface will be. That's what gives us fits, the places where we've torn some out by the roots rather than cutting it at ground level.

Your final pass or two is always worth a sharpen or hone, and should be made across the fibers. If you disc is from a board, which I suspect it is, that means the edge of your tool should be as close to vertical as possible to maintain control and to allow the fibers to run down the edge and release themselves. It doesn't matter what the name of the tool is, you want a controlled edge in the right position. In this case, a big roughing gouge, which has nearly straight wings would act almost as a beading tool or skew without the control problems of those narrow tools . I'm a fan of long-radius (forged, or "Continental") gouges, because they give me more edge in a shallower cut.

A scraper is always going to tear some fibers unless it's on edge, being used as a cutter. A dull one can be a nightmare, a sharp one takes some preparation. This tool is worth honing, because it's presented broadside to the piece, and any grinding "teeth" will leave their mark. It should be honed and deburred, in my estimation, and then used either fresh from deburring or after a smooth burr has been turned with a burnisher. Even more critical here that you let the wood come to the edge, rather than taking the edge to the wood.

Purpleheart may be as cheap as pine to you, so maybe you can call it practice. Personally, as a novice, I'd be turning every lump of fir or pine I came across for the practice, even to the point of making a prototype of a piece I was going to make in something expensive.

The wood is your teacher. When you cut it, the shavings fall, not fly, and there's almost no pressure on your tool. When you hack it, both the wood and the tool fight you, and suffer the consequences, perhaps even to the point of flying at you.

It makes sense, Owen, and thanks. I essentially aimed the gouge at the center of the thickness, rubbing the side bevel and receding until the edge barely began to take shavings, and working from the sides toward the center. And it did fine until the disc was largely round (I started with an *almost* round disc cut on a bandsaw, mounted on a 3" faceplate) with no bandsaw marks visible. Then--wham--a chunk tore out all three times. Others have implied that those final cuts probably should have been preceded by a sharpening, and I think that's right, as the edge felt dulled. I think I'll take Bill R's recommendation and scrap the purpleheart idea. I've had similar edge-dulling problems turning silica-rich teak but without the tearout.

Thanks to all who offered their assistance. This learning process is lengthy and frustrating, but shortened somewhat by help from experienced turners. Your advice and comments are appreciated.

Jeff

Well my two cents worth might be of help or it might not. When I have turned purpleheart I have found that sharp tools are a must. I have also found that if you take lighter cuts there is less tear out. I have pictures of a few pieces that I have turned using purpleheart posted on my website.

Only partially correct.

This has been discussed repeatedly in rec.woodworking. What you say is true of some species of purpleheart. For others, though, the wood is a muddy, ugly brown when freshly cut, and exposure to UV produces a brilliant purple color.

I'm not sure that every timber is a good timber for turning or that we should try turning any and all available wood. I suppose that living in an area of plentiful and varied trees colors my view, but life is too short for some compromises. Cheap beer and purpleheart are two for me. :)

Purpleheart is an exotic name and when fresh, the color is eyecatching, but the kind of purpleheart I've wasted my turning time on reminds me of a pretty woman with a bad disposition: attractive but brittle and hard to deal with, can fly off the handle and is often dangerous, worsens over time and harms the things we use trying to improve them.

Turning time is short, the list of turning projects long; better timbers and good women are out there. I've been blessed with finding both.

Turn to Safety, Arch Fortiter

Bill, I should have read your post before repeating the gist of it. Sorry, but at least we agree. A.

(three things to consider, but verify: the printed word, the expert's answer and the unexamined anecdote.)

Turn to Safety, Arch Fortiter

Hi Jeff

You have gotten a lot and good info already, I want to add one thing that might help you some, yes purpleheart does splinter easy and as such tearout happens, if tool, angle and approach are not perfect, but if you use CA glue on the endgrain it becomes less prone to tearout, problem of course is the CA use does show and if that is not acceptable than this is no help.

Have fun and take care Leo Van Der Loo

Jeff wrote:

Never heard so much badmouthing of a pretty wood. I've never had a tearout problem. I use a round nosed scraper (I scrape everything). The final scrapes are very, very light at the higher speeds. I glue a 3/8" plywood piece to the bottom and screw the faceplate into this. I use purpleheart all the time in laminated bowls and lamps. I'm looking at some now that are over

============================================ Only ever tried to turn one piece, And that was enough (I wondered wh it was so cheap for such a large blank !

This just brought up another question: is tearout more common at slower speeds? I generally turn at the lower end of the speed scale. Could this be part of my problem?

Jeff

Hi James

I was not badmouthing purpleheart, just stating a fact that purpleheart splinters easily, which it does, I have turned purpleheart without tearout but I am very careful on how I approach it, it is not a very forgiving wood to work with, and yes when sanded and finished it is a beautiful wood, if it was not, I don't think people would put up with it, however after a year or so you start to lose the color, the same as what happens with most/many woods be it bloodwood, yellowheart, padauk, cherry, walnut, afzelia, rosewood, teak, etc., just that some color changes are liked and others are not.

Have fun and take care Leo Vaan Der Loo

James R. Shields wrote:

Some of this has got to be personal preference - I can't stand turning American Elm but I know of several folks who rave about the stuff. The finished wood is usually very pretty but I don't like its characteristics when turning. I've only turned a little purpleheart and none in bowl orientation so probably can't offer it much defense.

But also like with some pretty women, the rewards for putting up with all that crap can be oooohhhhhhsoooooo rewarding.

If the tool is sharp and the controlling force in the cut direction is appropriate then lathe speed wouldn't matter. If you try to push the tool into the wood instead of letting it easily advance as it cuts then yes you can tear out portions more easily at slow speeds than high. It's more a function of the turner's speed rather than the lathe's.

When the tool is dull - or not as sharp as it might need to be - then that can play a role in tearout. In effect the cutting edge is acting as a wedge and levering out the wood. This will rear it's ugly head when one encounters a section of grain that might be at a different angle than the section that was just traversed. Many of the tropicals are more susceptible to this as they're generally more brittle than the more flexible northern hemisphere hardwoods. Domestically, Red Oak gives some of us grief in this regard.

Now that I reread what I wrote above, I see that in both paragraphs the situation is caused by the wood being levered out - either by operator force or by an edge that acts as a wedge instead of a knife.

After yours and others' posts I've concluded that tool sharpness is the culprit here. I have a Oneway Wolverine system on an 8" VS Delta grinder, so it's not as if I couldn't take an extra minute to tune up the edge of my tool before making final cuts. I think laziness interceded here and I paid for it. I will try again, following the good advice I've gotten here, if only as an exercise in learning. Despite the criticism of purpleheart, I do like the color and texture of the wood, and envision doing some more interesting turnings in the future.

Thanks for your help.

Jeff

Jeff,

I love purpleheart, personally, and have turned miles of it. I use it in pens, bowls, boxes, goblets,etc., and the only time I have problems with it is if I try to approach it with a less-than-sharp tool of any kind, or try to rush turning it. As has been noted, it is a somewhat splintery wood, and can be brittle, but not as brittle as saaaay, pink ivory, and I don't know too many guys (or gals) would would gripe about turning a hunk of that.

Anyhow, the color loss problem is easily solved by the simple expedient of keeping it out of the sun! My SIL has a piece that I turned for her almost 4 years ago now, and it is a rich, deep purple, not unlike grape Nehi. I don't recall the finish I used on it, but since it was early in my turning career, it was probably something like a poly. She keeps it in her dining room, sitting on a buffet and the color is fine.

If you want to avoid tear-out, keep scrapers away from it in facelate orientation, unless you are doing the inside of a steep-sided bowl. Increase the bevel angle on your bowl gouge and learn to use that properly, rather than a roughing gouge or a scraper and you should have few problems. I might recommend practicing on a cheaper, easier wood, though. It's tempting to just plunge right into the exotics when you start turning (I did the same thing!), but there's much to be said for practicing techniques on firewood.

Have fun, above all, and don't let someone else's prejudices, (in either direction) dictate what you'll be willing to turn or to like.

Thanks for the advice, Chuck. I turned another disc of purpleheart today with success. But I kept my bowl gouge (not the roughing gouge this time) extremely sharp. It has a David Ellsworth-like grind. I should have used it from the get-go.

I also started a piece of Jatoba for a small platter. That was most enjoyable to turn, if somewhat hard and dense. But for an exotic the price is very low. I do turn pieces of firewood and some bowl blanks that I've cut from recently-felled trees around here. I don't always know what the wood is, and most of it is rather plain and uninteresting, but it is useful for the learning experience.

Jeff