A little mishap

So, I have to replace two knobs on an antique desk. I couldn't find exactly what I wanted on Ebay, so I bought a couple of stock Cherry knobs from a place. The originals are Mahogany by the way. Anyway, the knobs came in and I wanted to make them more like the shape of the originals, so I chucked up one of the new knobs on the lathe. I'm not a lathe pro - actually a complete newbie. I was using what I would describe as a 3/8" wide roughing gouge. It was the smallest of the cup-shaped tools I had. Well, I chewed out the bottom base part of the knob without issue. Getting braver, I moved the tool more into the center gully part of the knob.... WHACK!:eek:

The knob, now in two pieces lay there silently, lifelessly on my floor atop a small pile of cherry shavings. The tool, also now in two pieces, taking its final bow. The handle still in my right hand, the tool end, making peace with it's demise, lay lifelessly next to the two knob pieces on the floor - atop the shavings.

The good news is that this lathe is a piece of junk, and probably so were the tools. The bad news is that this probably would not have happened to one of you. So now I'm asking what horrible mistake did my bravery cause?

In order from left to right - A new, untouched knob, the original, my work of art
https://i.imgur.com/6jEd3dQ.jpg?1

To actually break the tool, you must have had one hell of a catch! I hope you didn't suffer any physical damage.

If I were to guess, it would be that when you were trying to cut what is essentially a cove, you lost bevel support and the now-unsupported edge caught and everything went downhill from there. There will be other, much more experienced people join this discussion, I'm sure, and they will likely be able to offer better insights into this mishap.

Glad you weren't hurt! I am guessing that a number of things happened to cause the mishap. First, you didn't say how high or how far away from the wood you had the tool rest positioned. Having the tool hang out over the rest unsupported will make any catch worse. Next thing, seeing as how the wood is really chewed up, I would take a guess that you were turning 'uphill', meaning you were turning starting at the smallest diameter and moving towards the larger diameter. When you do that, can almost guaranty a catch! A photo of the broken tool might also help us in understanding what happened.

Off, I have limited experience turning and that is the sort of thing, I would have mounted on the drill press and reduced using sand paper wrapped around a block and then wrapped around a dowel. The grain shows it should have been turned with a bowl gouge. You might have used a small spindle gouge with a narrow shaft into the handle. They will snap. They will also catch terribly on a cross grain. I have an ancient AMT spindle gouge that came in a box of old lathe chisels. It is twisted around almost an 1/4 turn from what it should be. Probably from a similar bad catch.

Roughing gouges tend to be ground square across the flutes of the gouge, and 3/8 is a really small one. Bowl gouges tend to be more round nose, and detail gouges are more pointy. I would guess that you were using one of them. The catch looks to me more like you caught the point rather than the wing. For that type of cove cut, most would use a detail type gouge, and you cut with a little bit of the nose, and more of the wing if that makes any sense. Start by rubbing the bevel, then roll over into the cove till it starts to cut. If you just stuck the point into that piece, that would give a catch similar to that one.

As for breaking the tool, no idea here. On a piece with that small diameter, it would take a combination of a really bad/weak tool, warp factor 10 speed, and hanging out way too far off of the tool rest.

robo hippy

Quote:

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Originally Posted by Mike Dowell

...I'm not a lathe pro - actually a complete newbie. I was using what I would describe as a 3/8" wide roughing gouge. It was the smallest of the cup-shaped tools I had. Well, I chewed out the bottom base part of the knob without issue. Getting braver, I moved the tool more into the center gully part of the knob.... WHACK!:eek:
The knob, now in two pieces lay there silently, lifelessly on my floor atop a small pile of cherry shavings. The tool, also now in two pieces, taking its final bow. The handle still in my right hand, the tool end, making peace with it's demise, lay lifelessly next to the two knob pieces on the floor - atop the shavings.
The good news is that this lathe is a piece of junk, and probably so were the tools. The bad news is that this probably would not have happened to one of you. So now I'm asking what horrible mistake did my bravery cause?
In order from left to right - A new, untouched knob, the original, my work of art

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Mike,

At least we got to enjoy your wonderful prose!

Without a picture of the cup-shaped "what I would describe as a 3/8" wide roughing gouge" it's hard to tell what tool it actually is, how it was ground, and whether it was appropriate for a relatively deep cove like that. If it was in fact a roughing gouge it was not appropriate for that cut. There are a number of things that could go wrong (and all of them in an eyeblink!) even with the proper tool. It helps if the tool is ground and sharpened appropriately but the most important thing is how it is used. A spindle gouge is typically used for such cuts.

The bad news is that it may take a bit of instruction and practice to make useful replicas of the knob. The good news is that once you get the practice it will get easier and easier and you soon will be a pro. The bad news is once you fall into the "vortex" of turning you will find yourself on a slippery slope of buying tools/lathes/wood, and refocusing your life. :) The good news is that life is so rewarding!

The deep cove is a common cut and like my piano teacher always said, "everything's easy once you know how!" If you lived near here I'd say bring some knobs over and we could work on some techinques - I'll bet you could do this with a little practice with the right tool. (Hey, road trip - come visit! I'll supply the lathe, instruction, and wood! I drove to your neck-o-the-woods to bring back the lathe I use now.) Is there a woodturning club near you? If so, I can almost promise that someone there would be glad to spend a few hours and get you on the path to success.

The knobs you started with were made by machine and the grain is running sideways, across the face. Unfortunately, cutting a deep cove like that can be difficult especially when beginning to learn, at least to make it smooth. For the best cut you need to start at the bottom of the cove and work up, very, very difficult! Far easier is to start at the top and work down to the middle from both sides, coordinating the tool swing, rotation, and thrust - get one of these wrong and bam!

If I were making these knobs I'd start with some mahogany pieces with the grain oriented to run from bottom to top instead from side to side (in your photo.) This is easier to turn into a shape like your knob since you won't be cutting across end grain on every revolution and the "proper" cut that gives the best surface will be downhill towards the bottom of the cove. In addition, using mahogany can make the knobs more like the originals.

What some would do is put the gouges to the side and use a round carbide cutter or a round-nose scraper. A cheap carbide cutter works like a crude scraper - it will certainly work but can leave the surface very rough with lots of tearout. (May be OK if you fill the torn grain and dye them dark to match the original.) A well-sharpened scraper can work better but the surface can still be left rough with tearout, depending on the wood and the orientation. Far better are the extremely sharp carbide bits used in the Hunter tools. The Hercules would be my first choice: http://huntertoolsystems.com/product-category/hercules/ The Hunter tools are wonderful but they are not cheap. Turner John Lucas teaches a beginner's class who use only a Hunter tool for the entire class! These can be used as scrapers, pushed straight into the wood, or used as a gouge for nearly glass-smooth surfaces.

JKJ

Maybe a better idea would be to not use chisels till the learning curve improves a tad, but use a file while the knob is turning (lathe or drill press, etc) to get rid of the ridge and shape the cove, and then sand the top a little flatter.
This may solve the immediate problem, then have fun learning how to use the tools later!

Here are some more pictures. So, I'm not ashed to accept that I have no clue what I'm doing. I like the idea of using a file and sand paper. Funny thing is, I actually turned a replacement spindle for a windsor chair not too long ago, and it came out great! That shows that a spindle is very different than a knob.
https://i.imgur.com/gEoOfjA.jpg
https://i.imgur.com/L02W5ix.jpg

Looks like your tool could have ended up hitting the drive spur. Is one of the points of the drive spur bent or deformed?

Also, you need to spend some time with a file and clean up the top surface of the tool rest. Use care and don’t get the surface too uneven.

Joe

A better thought re the tool rest. Take it to a machine shop and have it ground flat on a large disk sander.
You can smooth it up later with a file or emery cloth or sandpaper.

I`m thinking you got an uphill catch with a dull tool. No one anywhere has ever done that.https://www.sawmillcreek.org/clients...lies/smile.gif Dont give up, way more fun awaits you !

what I was thinking you might want to try is a round block screwed and centered to the knob where the attaching screw hole is anyway and use a 4 jaw chuck and use a live threaded end with wood cone to apply pressure on the piece into the chuck jaws to prevent escape of the piece.

Mike, hope this one helps:

https://www.youtube.com/watch?v=RoA1dMimSN8

I am guessing that the corner on the gouge caught. Notice here how I roll the gouge over so the wings don't catch...

robo hippy

That does indeed look somewhat like a 3/8 spindle roughing gouge (SRG), I would guess it is a "Continental" or "German" spindle gouge - they are typically forged tools (like a SRG) with flat tangs instead of ground from round stock. May have been carbon steel instead of HSS? There is a bit of a learning curve with the tool including how to properly grind it. Better to get a "normal" spindle gouge and some hands on training.