above or below center?

Re: above or below center?

George Balock

>DW,

The edge of your gouge should not be below the centerline of your turning. The tool rest can be slightly below center and sometimes slightly above center and sometimes at center, it depends on the cut. The only tools that "cut" below center line are scrapers, but that's not what you asked.

George

Re: above or below center?

DWFII

>George,

Thanks for taking the time to respond.

That's kind of what I thought and it *is* what I've been doing. But I ran across a remark somewhere that mentioned...you're right...scrapers being used below center.

Can you (or anyone) fill me in on why the scraper would be used differently? What's the logic/reason? (technical talk is OK, by me)

DW

Re: above or below center?

Rodney in Maypearl, TX

>When scrapping, you want the edge of the scrapper below center so that if (when)you get a catch the scrapper is simply "kicked out" slightly instead of digging in and knocking your teeth out. As a matter of fact, you won't really get a catch per se if you hold it this way -- it'll just grab a little.

Hold the scrapper very lightly and don't allow the entire edge of the scrapper be engaged at once.

Re: above or below center?

Keith Tompkins

>Hi Rodney, I am assuming you are scraping on the outside. On the inside, I would scrape above center for the same reason, the tool will encounter only air if it catches.

Re: above or below center?

MikeinCapeMay

>Right, in the event of a catch you don't want wood beneath the scraper, I position it a bit above center on the inside and a bit below on the outside. The scraper flat on the rest with the handle trailing down a bit. You certainly don't want the handle trailing high DAMHIKT.

why not gouges, too?

DWFII

>I live in an area where there is no woodturning group nor have I ever run across or heard of turning classes in my area. So I have to more or less teach myself. I am reading books and watching Bill's dvd and trying to learn from you folks. So even though I am doing my best to follow theose instructions I would also like to know basic principles.

For instance, I have now read that interior scraping should be done below center in several places, above center here, and now I'm wondering why interior *gouging* wouldn't adhere to the same principles of above or below center as scraping. ??!

I intend to rough out the interior of a black locust bowl today and I will watch Bill's video before I begin and read what Richard Raffin has to say as well. But, again, I am trying to understand the logic, not just ape the motions.

Thanks for taking the time, guys.

DW

One possible reason

Mike Schwing from Md.

>Or maybe more...

Hollow form scraping is generally done with restricted movement of the cutting tool. The position of the tool is limited by the opening of the vessel - usually right close to center of the diameter. This limits tool approach, and normal gouges (and tool approaches) must be altered in their use accordingly. If you were to try to use some excellent bowl gouges in this case, the bevel would get in the way of the cutting tool. You'd try to raise the cutting edge up like you do with a bowl, but then you'd be limited in your cutting range to an inch or so, because you can't adjust the tool approach - you're stuck with it at center. If you think about where you prefer to put the toolrest with a bowl, and where the tool axis lies - it is normally over near the rim of the bowl. Move that gouge to center and see how well you can use it.

Scrapers tend to work a bit better in this case - and most of them have the bevel ground away so it doesn't make contact with the work surface. Raising it up a bit above centerline assures that if it catches, it'll bite air on the way down and relieve the catch. Other tools have captured cutting edges so as to avoid too much edge making contact with the wood.

I do use my ellsworth grind gouge in the bottom of a hollow form, but you need a really long, heavy handle to remain in control with a toolrest so far away from the cutting edge, not to mention a really soft touch. I have had better luck with that than with the scraper at the bottoms - and I have the blow ups to prove it.

Hope this made at least a little sense.

Re: why not gouges, too?

Brad Vietje

>DW,

Just to clarify -- in case there is any confusion at all -- you do not EVER want a scraper to be used below center on the inside of a bowl or hollow form. You ALWAYS want the burr edge of a scraping tool to work below center on the outside of a rounded form (bowl, etc...) if you're using a tool rest (you could also use a cabinet scraper anywhere you want, but it would be angled away from the spinning wood, and without a rest). If you have been told otherwise, I wouldn't trust that source with your safety any longer.

The reasons have already been given -- if there is a catch, the tool bounces away into air, not deeper into the wood.

Here's what might be confusing: using the inside of a hollow form as an example, you want the cutting tip at or above center, but the handle, and sometimes the tool rest might be below center so you can aim the cutting tip properly. The cutting tip should angle downward a few degrees, to engage the burr edge, and allow the bevel to be kept AWAY from the wood. With curved, or swan-neck tools this usually means rotating them a few degrees CCW to get a shear scraping action.

This is a central, and critical difference between scraping tools and bevel-supported cutting tools: with scrapers, you do not want the bevel to touch the wood, while with cutting tools (gouges, skews, etc...) you need bevel support for control and to avoid serious catches.

I would advise you practice on an open bowl anything you intend to do inside a hollow form if you're not certain what will happen -- you will be much better able to see how the cut works, especially if you rotate the lathe by hand to see the dynamics of what's happening. That's much better than picking chunks of wood out of your walls, ceilings, or forehead !

Safe spinning,

Brad Vietje

Thetford, VT

Re: why not gouges, too?

Wally Dickerman at Green Valley, Az.

>Well put Brad. I would add one more thing. All scrapers should be used with the handle pointing up a little. (Except in shear scraping) For the same reasons, when scraping inside a vessel with a hollowing tool, the cutting or scraping tip should be angled down for best results. Position the tool rest so that with the tool angled down, you're still working above center. Not all hollowing tools allow you to do this. One of the reasons why I still like my Stewart tool after all these years.

Wally

Did I miss something here?

DWFII

>Didn't Brad say NEVER scrape below centerline inside a bowl and then Wally said the tip should be angled downward??!!

Is there a contradiction? Or Is the scraper supposed be above centerline and also angled down?

Thanks

Re: why not gouges, too?

MikeinCapeMay

>Interesting. With a scraper I've always trailed the handle down a bit ala Raffin. Whether below or above the center line. Trailing up, even when above center it seems would invite a problem in the event of a catch, throwing the tool downward.

Re: Did I miss something here?

Wally Dickerman at Green Valley, Az.

>Set the toolrest so that with the CUTTER tipped downward, it's still not below center. Not the angle of the tool itself, just roll it a little to the left.

Wally

Re: why not gouges, too?

Wally Dickerman at Green Valley, Az.

>Perhaps we're not talking about the same thing here. I've watched Raffan using a scraper, and he uses it level or pointing slightly down. To point it up, the wood is coming into the edge. Pointing it down, the wood is going away from it. When I use my Stewart tool, if I have the cutter point up, it's more apt to catch than it it's pointing down.

Wally

Re: why not gouges, too?

Wally Dickerman at Green Valley, Az.

>I should add that in shear scraping, the handle is pointing down.

I got curious, so I checked out Raffan's book on bowls. On page 95, his instructions on using a scraper are to use it with the tool pointing slightly down.

Wally

Re: why not gouges, too?

MikeinCapeMay

>I think we have different editions, mine is from '98 and for me it's on page 83. I think we may be reading the same thing and interpreting it differently. However, you're much more accomplished and experienced than me and I certainly defer.

Re: Did I miss something here?

Brad Vietje

>Thanks, Wally for clarifing this... I agree -- with a straight scraper, like the common half-round or side profile scraper, the handle would have to be higher than the tip, and the tip still above center for safety. That often requires a larger opening than I prefer, so I most often use angled (a la Ellsworth) or curved-neck scraping tools. When I mentioned the handle downward I was thinking of curved neck scraping tools working through a small opening, so there would not be enough room to get the rest and handle above center -- the tool is rotated CCW (sometimes quite a bit) so the tip is trailing downward, and yet still cutting above center.

Sorry DW for the confusion -- if you play around inside a bowl, you'll see all truths revealed, despite my fumbling with the English language :)

Safe spinning,

Brad Vietje

Thetford, VT

Re: above or below center?

Bill Grumbine, Kutztown PA

>Good morning all

The scraper is an exciting tool to use when it catches. In the video, and in my classes, I have people use the scraper dead on center when on the inside of the bowl, and the handle as flat as flat can be, or just a hair raised so that the tip is trailing just a bit. The key is to have the tip on center so that the direction of travel of the wood is straight down and forcing the tool against the tool rest. If the scraper gets above or below this position, the wood is not pushing it at an angle and is "closing around it" because of the arc of the inside curve. This increases the likelihood of a catch. With the handle raised just a bit, the tip will trail so that a catch is minimized, but if it is raised too high, it will catch just as if the tool had been lowered overall. Dropping the handle is to live on the ragged edge of disaster, and the wood will explain that better than I ever could in short order. ;-)

Bill