Need help with scaper

[Paul Rains]

:confused: ok, I am doing well with my bowls for most part, but that dang scraper can screw a nice bowl in the blink of the eye. How about 3 or 4 must have tips to keep from chunking a good looking bowl with the scraping process? I am doing NE bowls at present time.

thanks in advance

[Bernie Weishapl]

Paul I don't use scrapers on bowls at all. I use shear cuts with gouges. One thing I do remember from a demo is don't leave the scarper flat on the tool rest. Turn it up to about a 45 deg angle for a shear cut. I just don't use scrapers much. I am sure others that use scrapers will chime in.

[willis martin]

Paul, I'm no expert but i've found that raising the tool rest slightly above center then make sure the cutting edge is slightly pointed dowmward gives me the best results .At the same time do'nt get too agressive. Hope that helps Willis Martin Tyler Texas

[Richard Madison]

Ditto what Bernie said. Not sure how it came about, but all my scraping is done with a bowl gouge. Most of it is shear scraping to some greater or lesser degree. Used to get bad catches with scrapers. Think I found what Willis said - down angle and tool rest almost touching the work.

[Steve Schlumpf]

Paul - I use a heavy duty round scraper to finish off the inside bottom of bowls. Like Willis said, tool rest slightly above center so you can present a downward angle when cutting. Make sure you have a nice burr on the scraper, take very light cuts and keep the scraper moving from the outside of the bowl towards the center! Everyone has their own style of doing things - that one works for me.

[Paul Rains]

I have been using a bowl scraper on inside and having problems, I sheer cut on outside.

[Curt Fuller]

Paul, I'm wondering if your problem might be related to how far the tool is hanging over the tool rest. On the inside of bowls if you don't have a curved tool rest then sometimes you get to where you're tool is too far over the rest. Then that little bit of extra leverage the bowl puts on the tool causes the scraper to catch and pull itself into the bowl. Then you have a big old gouge taken out of what was just starting to be a real nice bowl. If you don't have a curved rest you just have to keep moving the rest to keep close to the coutour of the bowl. It's tempting to try to make one long pass over the entire inside curve but I know from experience that that's when it'll grap and screw up a nice bowl.

[Paul Rains]

I was maxing out my Jet Midi lathe with a NE bowl probably right at 10 inches, and 5 deep, I couldn't get my tool rest very deep and near bottom of bowl at all. I think getting it up higher and downward angle will help too, I am sure I was lacking there also. I kinda figured my toolrest was my problem.

[Don Carter]

Paul:
I use a big thick scraper from PSI to finish the inside of bowls and smaller boxes. You have gotten great advice.

I do approach the wood with the scraper sitting at almost a 45 degree angle so that only a small portion of scraper is actually touching. I don't have a very aggressive burr on the scraper but I do sharpen it often. I must say that

I am no expert at using a scraper. This just works for me.

What kind of angle are you sharpening the scraper?

All the best.

Don

[Ken Fitzgerald]

Paul,

I use a scraper if I need to clean up the inside of the bowl. You have gotten some pretty sage advice IMHO. Tool rest slightly above center...the scraper presented in a downward angle. I use a Robert Sorby extra heavy duty scraper. It's 1" wide and 3/8" thick. This thing has some meat to it. No vibration. It works well but.....think extremely light cuts....and keep it moving.

[alex carey]

good advice so far.

http://www.pennstateind.com/store/LX130.html

I recently bought this guy for finishing cuts on bowls. It has worked quite well. You might consider this. Because of it's size it can hang over a tool rest quite far.

[ROY DICK]

Paul,

I feel your pain. Guess I'll try what the others have suggested.
If I get it to work I'll be looking for a different paper weight
Thanks to everyone for the tips.

Roy.

[Bob Bergstrom]

Putting a negative grind on the scraper will help with catching. To put a negative grind 2 to 3 degrees on the scraper, flip it over and grind the top face on a belt sander back about 1/4 to 1/3 inch. This negative grind will make the scraper less grabby. Much more manageable tool.

[Kyle Iwamoto]

I got the PSI pair of scrapers, they work good for me. I use them a lot. Same advice, they have to be sharp. I burnish mine after the Tormek. I also have the Jet mini and turned a bowl about that big. Higher speed may help too. Yeah, it's scary on a small lathe. I want a bigger lathe. Someday......

[Reed Gray]

Paul,
I love scrapers, and use them as my primary roughing tool for bowls, and they do an excellent job on finish cuts as well. Several things here.

One, there are two different cuts you can do with the scraper (and just about any other turning tool): One is a scraping cut, and the other is a shear cut.

A scraping cut with a scraper is when the tool is held flat on the tool rest, and the cutting edge is 90 degrees to the spinning wood. This is a good roughing cut for fast stock removal, but not a good cut for finish work as it tends to 'pull' at the wood fiber more, and you get more tear out (you know those fuzzy spots on opposite sides of the bowl that you just can's sand out.

A shear cut is when you have the scraper (or gouge) on its edge at a 45 or so degree angle to the spinning wood. This is a finish cut, and not good for stock removal, but excellent for clean up work. You have to take several passes to clean up those ripples and bumps, but it leaves a much nicer finish than a scraping cut.

There are almost never any problems when turning the outside of a bowl. You have a big solid chunk of wood. However, when you start the inside of the bowl, as you remove wood, the walls of the bowl are no longer solid, and can flex with even slight pressure. A scraping cut creates more pressure, a gentle shear cut yields little pressure. The thinner you go, the more flexing you can get. The closer to the rim, the more flexing you will get (have you noticed that you have almost no problems on the bottom of the bowl, but a lot near the rim?). The bigger diameter the bowl, the more flexing you can get. A scraping cut on the rim of a bowl can make it explode, the vibration can cause the took to dig in much deeper. If this isn't making sence to you, think of a soap bubble. Left to itself, it stays pretty round, but small wind gusts can do all sorts of deforming. You have two choices here. Turn to final thickness, and start from the rim all the way down to the center of the bowl for a finish cut. This is very difficult because the wood moves as you remove the mass on the inside, and the end grain and flat grain cut differently, and the bowl, no matter how dry it is, will move slightly. It can be done, but as I said is difficult (again more so on bigger bowls). You can use a bowl steady rest to help this, but as a production turner, this takes too much time for me. You can use your hand as a steady rest on the outside of a bowl. Gentle pressure only: if your hand is getting hot, you are pressing too hard. If you press hard to prevent the vibrating, you can actually make the bowl vibrate more. This is a practiced skill you can learn. (Caution note: round over the rim of the bowl, if the edge is left square, it is like a small razor saw and will cut your hand!!!!!!!!!!). The other choice is to turn out the inside of the bowl in stages. Turn down the inside of the bowl an inch or two, then do any finish/touchup cuts. Then go down another inch or so, and repeat. You may have to do a little blending where you start the next stage, but this process gets you away from a lot of the vibration. This is my prefered method for larger bowls. I will turn smaller bowls (8 to 10 inch diameter) with one finish cut from rim to bottom.

When doing a finish cut with a scraper on the inside of the bowl, it is always a pull cut. I know this is backwards, but I can't seem to find a way to angle it so that I can come from the rim down. VERY gentle pull cuts work fine and are easier for me to control. A round nose, or swept back grind to the left. You want to have the cutting part at or below the center line (width wise) of your scraper. Of course, a freshly sharpened tool. I have found the negative rake scrapers to work better on harder woods, and a burr fresh from the grinder best for most woods. Never liked the burnished burrs. I prefer to hone the top surface to remove the old burr before you grind the fresh burr. You can sharpen the face and then hone the top, then hone the face and get a nice dainty burr that does a pretty good job (see the last AAW mag), but for most instances, it doesn't seem to be worth the trouble to me.

robo hippy

[Paul Rains]

thanks, great info!!