Lathe speed and catches

[Rob Miller]

Is the likelihood of a catch reduced with faster lathe speed? How does speed affect the severity of a catch? I've been keeping my Craftsman bench lathe on the lowest speed or second lowest to reduce vibration at the start but wonder if I should be increasing the speed after the piece is balanced.

[Dennis Ford]

The likelihood of a catch is greater at low speed, the severity of a catch is greater at high speed.

[Dale Miner]

An increase in rpm will not lessen the likelyhood of a catch, but it will make the catch happen with more force.

When a catch happens, it is a good idea to shut the lathe off and present the tool exactly the same as just before the catch occurred. Rotate the lathe by hand and try to see what happened that caused the catch. With a gouge, the fault will usually be a presentation that allowed the bevel to not make contact. Sometimes just a few degrees of rotation or a slight change vertically causes the bevel to loose contact. With a scraper, the cause is usually trying to cut in a fashion that the force of the cut pulls the scraper downward into the wood. On the outside of a vessel or spindle this can occur when trying to use a scraper above center or pointing upwards, and on the inside of a bowl, from using the scraper at or below center.

Dull tools increase the likelyhood of a catch. The reason for this is that as a tool gets dull, the edge needs to be presented more aggressively to get cutting action. By aggressively, I mean rotating the edge just slightly off the bevel. When the edge does start cutting, it is then able to cut without any bevel support and cuts uncontrolled.



If

[robert baccus]

Darn good reason to go buy yet another tool yeah.

[Thom Sturgill]

I agree with Dennis, in part because of something Dale said. Dull tools contribute to the likelihood of catches. High speed lets the tool be more aggressive while not forcing the edge into the wood, if that makes sense. Also while turning pieces like square or winged bowls where you are 'cutting air' much of the time, if you turn slow there is more time for the tool tip to wander deeper into the plane of the cut before meeting wood again - instant catch! This is also where the difference between 'gliding along the bevel' and 'riding the bevel' comes into play. The latter implies pressure, however light, on the bevel forcing the tool into the wood.

[Dale Miner]

A catch occurs from improper tool presentation. Using high rpm's as a means to use improper presentation and 'get away with it' is a poor substitute for learning the correct technique, and perhaps will preclude ever learning good technique.

When turning square or natural edge pieces, the theory that more rpm's helps from reducing the time the cut is out of the wood ignores the other part of the process; the tool is also in the cut for a shorter period. A proper stance and light bevel contact (float not ride) and a steady hand with comfortable rpm's will produce the same results as high rpm's. Perhaps better results if the turner is not comfortable with the higher rpm's. The main benefit from more rpm's on interupted cuts from my viewpoint is the increased visibility of the 'shadow line' of the part.

I recall a statement that I think is attributed to John Jordan; "Yes, your tool needs sharpened."

A dull tool causes many problems and most tunrers starting out lack the experience to know when the tool is dull. During a demo I once had a 2 year turner ask me how often I sharpened my tools. When the answer was 'every five to fifteen minutes of turning', the reply was' Oh, I thought every couple of weeks'. This fellow would typically spin 10" to 12" blanks at about 1000 to 1500 rpm and with both hands on the tool handle stand back and poke the tool into the wood. I tried a few times to work with him, but the concept of bevel rubbing never sank in. When starting out, somewhere he had gotten the idea that high rpm's would help reduce catches. Eventually he did lower the rpm's somewhat and started using the carbide scraper type tools. I think he no longer turns.

When a tool gets dull, the usual reaction is to press harder on the tool both into the wood and the bevel against the wood. The result of pressing harder is a poor cut and difficulties with a smooth profile. The next change is rolling the bevel off the wood to make the tool cut, and that is when a catch is likely.

Going back to the question posed by the OP, my advice is do not increase your rpm's in an attempt to reduce catches. Instead work on tool presentation and technique at an rpm that you are comfortable with. Try to find a club or other turners in your area that can help with technique and tool presentation.

[Rob Miller]

Going back to the question posed by the OP, my advice is do not increase your rpm's in an attempt to reduce catches. Instead work on tool presentation and technique at an rpm that you are comfortable with. Try to find a club or other turners in your area that can help with technique and tool presentation.

Thanks -- I appreciate all of the contributions to this question. I am, in fact, staying on the bevel to the best of my capability. The places I'm getting catches are usually on the inside of an inwardly curved rim and on the outside of an outwardly curved rim, i.e. in the concavity of a curve, and also when trying to clean up the very edge of the rim where there isn't enough surface area to provide good bevel contact. I've learned that for the edge, a VERY light cut will help to square it up with VERY slow presentation. On the inside of the outside concavity, the problem again occurs right where the curve meets the rim of the vessel because one is either forced to cut uphill from the body of the vessel towards the rim or to cut downhill from a point where there is no support and/or little or no surface area to contact the bevel properly before presenting the edge to the workpiece.

[Reed Gray]

Yea, speed had nothing to do with catches. Speed will contribute to how spectacular the catch is, but it is not in any way the cause. Catches happpen for a couple of different reasons.

One is hanging out too far off the tool rest. There is a lever at work here, and no matter how long your handle is and how heavy duty your tool is, if you hang out too far, you will get over powered.

Another is biting off more than you can chew. One way for this to happen is when starting a piece, especially if it is not perfectly flat and round, you just plunge the tool into the wood rather than gently nibbling away to get it rounded out. If you have some belt slack, the piece will stop, and the belt will squeal. If not, the tool can get yanked out of your hand. Another way to get over powered, maybe more so with scrapers, is when sweeping through the transition area of the bowl. If you go from the bottom of the bowl to the side, you can suddenly end up with steel cutting both the bottom and side of the bowl at the same time. Again, the tool can get yanked out of your hand, or you can squeal the lathe belt.

The most common one is not having the tool balanced as you cut. I do talk about this a little bit on my video clip about using a spindle roughing gouge. If you have used a skew, or tried to use one, and experienced that catch that leaves a spiral cut in the wood, this is part of it, not just coming off the bevel. So, the part of your tool that is doing the cutting needs to be resting on the tool rest. With gouges, if you have the flutes straight up, and are trying to cut with the wing rather than the bottom of the flute, the gouge will roll into the cut, making a catch. This is why I always roll the flutes over about 45 or more degrees, and drop the handle. This is a bit easier to see on my clip about the fluteless gouge. If you drop the handle a bit, and roll the tool over, there is no way you can get the high side of the cutting edge into the wood. With scrapers, they sit flat on the tool rest, so no problem balancing them that way. With a shear scrape, you drop the handle and cut with the lower half of the tool.

I really need to do a separate clip on catches.

robo hippy

[Greg A Jones]

I really need to do a separate clip on catches.

robo hippy

You could use me as a model. I'm quite adept at doing them. :-/

[Reed Gray]

The tale I tell when demonstrating, is that when I began, I didn't know the difference between a gouge or scraper, and had no difficulty gouging equally big holes with either tool.

The tip about rolling gouges a bit on the side, and dropping the handle is pretty big. Some do cut with a bit of the wing on the up hill/wood side, and it can be done, especially if the bevel is rubbing, but come off the bevel even a tiny bit, and you catch because the tool instantly goes from a bevel rubbing cut to a scraping cut, and when scraping you need to have the handle raised a bit or level. If it is pointing up, you are sticking your finger into the fan in the wrong direction (I know I am not the only one to play with ceiling fans, in spite of warnings from my mom). If you find the spindle roughing gouge footage from Ian 'Robbo' Robertson from Australia, it is what happens when he gets his rather spectacular catch. Over extended, and comes off the bevel....

robo hippy

[Dale Miner]

Thanks -- I appreciate all of the contributions to this question. I am, in fact, staying on the bevel to the best of my capability. The places I'm getting catches are usually on the inside of an inwardly curved rim and on the outside of an outwardly curved rim, i.e. in the concavity of a curve, and also when trying to clean up the very edge of the rim where there isn't enough surface area to provide good bevel contact. I've learned that for the edge, a VERY light cut will help to square it up with VERY slow presentation. On the inside of the outside concavity, the problem again occurs right where the curve meets the rim of the vessel because one is either forced to cut uphill from the body of the vessel towards the rim or to cut downhill from a point where there is no support and/or little or no surface area to contact the bevel properly before presenting the edge to the workpiece.

Rob,

If I understand what you are describing and where you are having your catches, it sounds like you are turning with the flute nearly straight up. If so, then it is almost impossible to make initial contact with a piece on the rim without the gouge skating or worse. When making initial contact where there is nothing to support the bevel until the cut has progressed a ways, the flute needs to be rolled over (like the letter V or U on it's side). If the gouge is ground correctly, then the part of the edge that makes initial contact will be vertical or parallel with rotation. When the edge is presented in that orientation, the gouge has little tendency to skate or roll over into a catch. Once the cut has progressed a short ways, the gouge can be rotated slowly back to about a 45 degree upwards orientation to allow for faster/heavier cutting. Another help in starting a cut at the rim is to cut a small 45 degree bevel on the rim first, and then start the cut in the bevel in the direction wanted. The small beveled cut allows for the gouge to find a place to register against without removing much material.

If you are having catches in the concavity of a curve, then the bevel is coming off the wood. With a fingernail ground with a jig, the bevel becomes more acute as the edge moves along the wing. If you are cutting with the flute nearly vertical, it is very easy as the curve is made for the gouge to start cutting farther away from the tip of the gouge in the more acute area. When this happens the bevel loses contact and a catch occurs. Usually a rather nasty catch.

When cuttin those concavities if you are not already, try to develop a technique that uses the gouge with the flute at about a 45 degree angle i.e. 10:30 or 2:30. This will be making the cut with the lower wing of the gouge and keep the upper wing well away from the wood. On the outside of a bowl or vessel, the handle can be dropped and the gouge pulled through the curve. This is a cut that takes some practice, but is one that is very worthwhile to master.

[Greg A Jones]

Rob,

Another help in starting a cut at the rim is to cut a small 45 degree bevel on the rim first, and then start the cut in the bevel in the direction wanted. The small beveled cut allows for the gouge to find a place to register against without removing much material.


This is the method taught in a book I've been studying. Cut the notch and then make the finishing cut off that with the flute straight up. I've done it a couple of times but it's pretty nerve wracking for a beginner like me. One little twist counterclockwise and the resulting blowout can be fairly spectacular. I'm much more comfortable with the gouge being rolled over clockwise and easing into the cut through manipulation of the handle with my right hand while watching the part of the flute that is engaging the wood.

[Rob Miller]

Rob,



When cutting those concavities if you are not already, try to develop a technique that uses the gouge with the flute at about a 45 degree angle i.e. 10:30 or 2:30. This will be making the cut with the lower wing of the gouge and keep the upper wing well away from the wood. On the outside of a bowl or vessel, the handle can be dropped and the gouge pulled through the curve. This is a cut that takes some practice, but is one that is very worthwhile to master.

So, from what I think you're saying, I should be making a pull-cut on the inside concavity, starting with an angle of about 90 degrees and rotating the bottom wing in to start the cut?

[Reed Gray]

Rob,
Watch my You Tube clips (type in robo hippy), and come see me at the Symposium. I will be next to Doug Thompson in the vendor area.

robo hippy

[Dale Miner]

So, from what I think you're saying, I should be making a pull-cut on the inside concavity, starting with an angle of about 90 degrees and rotating the bottom wing in to start the cut?
Rob,
The first two sentences you quoted are discussing a push cut with the handle horizontal. The flute should be at either 3:00 or 9:00 depending the cut being made. This provides a safe start to the cut, but does not allow for a much stock removal. After the cut is started, rotating the flute more open allows for better stock removal, but the flute should never be rotated straight up as that is when catches occur. Try starting a cut by holding the gouge against the wood and rotating the lathe by hand. The safe or neutral flute position will be apparent that way.

The last two sentences refer to a pull cut that is done with the handle down on the outside of a bowl or vessel. This cut is often usefull when a push cut can not be used due to the headstock or tailstock being in the way or the profile being cut makes a push cut impractical..

Take Reed up on his offer. Five or ten minutes in person will make a huge difference. If you can, take your gouge with you and get his advice on the profile of your grind.