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Thread: Two similar tools, one catches one doesn’t, why

  1. #1
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    Two similar tools, one catches one doesn’t, why

    I built two carbide cutter tools a while back. Both use a half inch carbide cutter. The difference is that one tool uses a 3/8” round rod and the other uses a 3/8” square rod. Both tools have about 10” of steel sticking out of the handle and about 4” in the handle.
    The square rod cannot touch the wood without catching, but the round rod can cut the same area fairly easily. My initial thoughts were that the round rod is able to flex a little allowing some forgiveness.
    Does anyone else have a theory about this?
    "Everything will be alright in the end.... If it isn't alright, then it isn't the end!"

  2. #2
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    The round one probably tilts slightly changing the angle of attack.

  3. #3
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    Ditto it's not the flex. Flat scrapers catch if you have the cutter is higher than the handle. Scrapers need to be level or slightly downhill to avoid a catch. Twisting them one way or the other which would be the main difference between a flat bar and round bar would simply change the shear angle that the wood crosses the cutter. It might actually increase the chances of a catch if the tool isn't perfectly level. The flat scrapers can be used as bevel rubbing tools if the nose of the bar holding the cutter is ground correctly. However if your not good with bevel rubbing tools then your looking for a really good catch. The fact that your building flat carbide scrapers suggests to me that this is the issue.

  4. #4
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    That makes alot of sense. As a relative newbie I have not accumulated alot of tools and therefore the experience level is not there as you said. But I should have clarified one thing. The catches are are occuring in the bottom of a deep semi-hollow form. Getting a bowl gouge in there is beyond my abilities right now.
    I can see where a slight variation in height of the cutter would change the angle of attack fron negative to positive and the round bar would be more forgiving as it allows the cutter to roll with the cut so to speak.
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  5. #5
    A lot of it can depend on how you are cutting. The square cutters are better for plunging more straight in while the rounded cutters are better at sweeping side to side. This is because of shape. If you are inside a hollow form, and sweep a square cutter from center to side, when you hit the side wall, you can end up with both the bottom and the side of the cutter in the wood at the same time, so you can double the cutting pressure in an instant. If you are aware of this, you can get away with it if you are just barely cutting wood. If you are roughing and taking heavy cuts, you can get over powered. Both cutters can work up on edge for shear scraping and cutting. The thing with the square bar stock is that it has a sharp edge and doesn't move across the tool rest as easily as bar stock that has the edges gently eased/rounded over. Round bar stock, or half round bar stock works great up on edge, but for flat scraping cuts, it can be a little tipsy.

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  6. #6
    Square corners seem to grab more on all tooling. Shapers to hand tools.

  7. #7
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    Reed, I am working on the wife for that weekend, we’ll see if I’m successful.
    Both the cutters are round cutters and that is what confounded me to begin with. But now with the discussion here I can see that the round bar may be able to ever so slightly roll with the punch where the square bar resists.
    Also, I was looking at a short video I took when I was roughing the blank and I may be holding the tool at too much of an angle.
    I will give it another try with a negative angle and see if it works.

  8. #8
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    It has to be where your cutting with the tools and possibly the shape of the bottom. If it's end grain you should be cutting from the middle out. The shape of the shaft should have little to do with the cut other than the round one may try to tilt on you and if your cutting near the sides and it tilts down it could be pulled deeper into the wood. Since your having the trouble with the square shaft still could be the same. I was watching a new turner the other day using the Hunter Viceroy which has a square shaft and he kept tilting the tool to the left lifting one side of the square shaft off the tool rest. Not a problem with that tool. You also haven't said what size your carbide cutters are. Large cutters can grab easier than small cutters. Try to keep the tool level and cut at the center. Take small cuts until you can feel how the wood is accepting the cuts, then get more aggressive if needed. If it's end grain cut from the center out and be careful when you approach the wall. The shape of the shaft should not have anything to do with it. Since you made the tools your self the mounting of the cutter might be different. Make sure they are the same and perfectly flat.

  9. #9
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    What Reed said... The only other variable I can think of is the height of the cutter on the bar. Most round cutters I would imagine are mounted in the center of the round bar. The square, need only be set down the thickness of the insert. This could mean the square bar cutter is just a bit higher than the round, causing the catch. Did that make any sense?

  10. #10
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    John, yes it is end grain and they are 1/2 " cutters. I have come to the conclusion is that because I am about 6 inches deep in the hollow form the support is iffy and my angle of attack is probably all over the place. Last night i couldn't even get the round bar to cut without grabbing. My next step is to either get a better bowl rest to support closer to the work, or get a hollowing system, and some better bowl gouges.
    As for the cutter placement on the bar, i do have the one on the round bar cut into the bar and the square bar on top. But I try to compensate for that in the tool rest.
    "Everything will be alright in the end.... If it isn't alright, then it isn't the end!"

  11. #11
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    Hanging any tool over the tool rest that far is hairy. Most people who hollow by hand use a smaller cutter. 3/16" HSS metal cutting bits are the most common. I use either those or the 6mm Hunter Carbide cutters mounted in a bar. Hand held is still trick at any depth. I built myself a copy of Lyle Jameison's captured bar hollowing system. What a huge change. No more white knuckle scared your going to blow the piece us moments. Just gently one handed relaxed removal of wood. I highly recommend one of the systems of captured bar hollowing if your going to do much of that. I'm fond of Lyle's because there aren't any moving parts to ever go wrong. Others like the Elbow tool or Trent Bosch hollowing system They all work so much better than hand hollowing.

  12. #12
    Quote Originally Posted by scott ward View Post
    But I should have clarified one thing. The catches are are occuring in the bottom of a deep semi-hollow form.
    One cause for a sudden catch at the bottom of a hollow form, vase, bowl or whatever could be because you are going to far and as you cross the center line you end up on the uphill side. That will cause your tool to rise off the tool rest and slam it back down.

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