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Thread: Skew chisel spiral grooves--not the good kind

  1. #1
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    Skew chisel spiral grooves--not the good kind

    Hey all

    I sometimes get spiral grooves when attempting a planing cut with my skew.

    I found an old thread here which was quite helpful but I feel like it didn't quite get to the bottom of it.

    I'm wondering if a hollow grind has anything to do with it. I typically grind on a 220 CBN using whatever the skew setting on the angle jig that came with the Wolverine tool rest system. It says 20-40* or something like that.

    I then hone on a 600/1200 dmt plate as needed.

    Any theories on whether a hollow ground skew will keep the bevel from having a adequate riding surface and result in a skipped cut? The resulting cut is very clean, it's just bumpy as all get out.

    I'm using a standard 3/4" Ashley Iles skew if it matters.

    I'm turning more and more furniture legs and would like to remove the sanding step until after assembly.

  2. #2
    Generally it comes from too much pressure on the bevel when cutting. From some unknown skew master, "The bevel should rub the wood, but the wood shouldn't know it." This is probably the most difficult thing to learn about any bevel rubbing cut, and that is how little pressure is needed, which is pretty much none. Also, if you are turning long and thin, this extra pressure can cause the spindle to flex, which can cause and/or add to that decorative spiral.

    Best skew video I have seen is Allan Batty, which is up on You Tube. Richard Raffen also has one that he did for Fine Woodworking some time back. He starts it off with a major catch that still makes me jump even after all the times I have watched it...

    robo hippy

  3. #3
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    As Reed said, too much pressure.

    Also, keep the heel of the bevel off the wood or touching very lightly. If the back of the bevel rides on the wood, especially with pressure, the heel will rise with some small imperfection in the cut. This causes the cutting edge to cut deeper and can start to make a spiral that gets worse and worse with each pass! This is avoided with all the contact on the cutting edge and the heel of the bevel off the wood.

    To get rid of the spiral I use a technique not generally recommended with the skew: cut directly with the short point. This turns up the fibers and can leave a horrible surface but it will take off the spirals and the surface can be cleaned up with the next pass.

    I grind all my skews with a 8" 600grit CBN wheel which leaves a shallow hollow grind. I don't touch it with the diamond hone unless touching up the edge between sharpenings - the slight hollow grind makes this simple (I use the hand-held Eze-Lap paddle hones, extra fine).

    For a razor edge after sharpening on the wheel I strop with polishing compound to remove the grinder burr. I used to do this with polishing compound on a piece of hard leather on a flat surface but now I touch it to the Tormek honing wheel to remove the burr. Then my secret weapon: a hard strop made from MDF. I resaw a piece of MDF (about 4"x6" or so) on the bandsaw to give a roughened surface. Then I rub polishing compound into that surface. I sometimes use the Tormek honing paste but usually just rub it with a green or yellow stick to apply the compound. To strop the skew before use (and to renew the sharp edge several times before touching up with the diamond hone or regrinding), I put the piece of MDF on the bench, place the bevel of the skew flat on the surface, raise the heel of the bevel ever so slightly, and pull the skew straight back while pressing down hard. You can see how well this works since the compound on the hard MDF surface instantly starts turning black! Testing the edge by shaving arm hair confirms the sharpness. I wish I had pictures of all this.

    BTW, the skew is the first tool I put in their hands of first-time students. I mount a cylinder (soft maple, cherry, or poplar, about 1.5" in diameter or so) that I've already turned round and smooth. I leave the lathe turned off. I show them how to stand and hold the tool then rotate the lathe by hand while they experiment with the tool until they can make it cut. I watch carefully and verbally correct presentation, angles and movement as needed. After a bit of practice they get the feel of the tool and can make beautiful shavings. I then turn the lathe on very slow and we practice planing cuts. (I may turn the lathe on and resmooth the cylinder myself as needed - I want them to concentrate on controlling the tool without having to deal with irregularities in the wood at the same time.) I gradually turn the speed up until it's wide open! I have done this many, many times and have never had a student get a catch. After mastering planing cuts we go to v-grooves then start on the spindle gouge. Before long most are ready to make a spindle project to take home.

    JKJ

  4. #4
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    Could be one of 3 things, or all of them. Long small diameter wood can whip or get in a resonance as it gets thinner. Too much tail stock pressure. Too much pressure on the bevel. Flat or hollow grind makes no difference for me. Once you get that started, it takes work to cut it off. I find that beginners grip the skew with a death grip. Relax your grip, and relax your body. It works for me.
    Last edited by Richard Coers; 05-30-2021 at 5:14 PM.

  5. #5
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    Awesome. Thanks guys. Iím headed to the shop in a bit to turn stretchers. Iíll keep all this in mind.

    I do tend to grip the skew for dear life, but there was a time a few years ago when I made a batch of rolling pins and had the light grip down by cradling the piece while apply light pressure with the thumb of the same hand. I lost it somewhere along the way.

    Good to know a hollow grind shouldnít be the issue.

    Ill evaluate tailstock pressure more closely.

  6. #6
    Good reading

  7. #7
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    Quote Originally Posted by chuck van dyck View Post
    ...Ill evaluate tailstock pressure more closely.
    In my experience the tailstock pressure and the vibration from the wood flexing (whirl) is primarily a problem with relatively thin spindles. I guess it could apply to your table legs if they were long. However, I personally have never experienced the spiral problem you mentioned with thin spindles. For me, vibration and flexing result in a different effect.

    I do agree with the advice to relax. I've had students with the death grip and even tense up their back, shoulders, and legs. I had to tell one guy a dozen times to relax!

    For thin spindles I also often use my left thumb to help guide the skew (or spindle gouge, Hunter tool, etc) for delicate cuts, with fingers supporting the back of the spindle. This prevents flexing and gives far better control at the cut. I call it the "left hand steady rest". In one of his books Richard Raffan said this method will also let you know if you are using too much pressure with the tool - the supporting fingers will start to get hot!

    This works for planing (or detailing with a spindle gouge) in either direction:

    D02_thinner_IMG_5030.jpg E01_reverse_IMG_5036.jpg

    When I do demos on thin spindles I mention that it's the length vs the diameter that makes the spindle thin, not just the diameter. I consider this Hickory hoe handle a thin spindle since it's long and had to use the same methods to control vibration - left hand support and attention to tailstock pressure. (I have a bed extension but for this I still had both the headstock and tailstock hanging off the ends of the lathe as much as possible!)

    handle_shuffle_hoe_comp.jpg

    BTW, if I start to get flexing with thin spindles sometimes less tailstock pressure helps, sometimes more. A higher speed may also help. I usually turn thin spindles wide open, over 3000 rpm on my lathes. I find this makes smooth cuts easier. Another thing that really helps control flexing is holding one end of the wood firmly in a chuck or collet or something rather than between centers. (I didn't use a chuck on the hoe handle since it would have taken a little away from the handle length.)

    JKJ

  8. #8
    I recently turned a walking stick around 36" and had to be careful about too much vibration. Tailstock pressure I think was a factor in why the first one fractured and decided to leave the lathe on wings. The second one I was much more careful about pressure and taking lighter, controlled passes. I got lots of skew practice. I dealt with the spirals a couple times and made adjustments. Now I understand more of the 'why' after reading this thread.

    I was asked if I used a "steady rest", which I don't own, and wonder after seeing the above hoe handle picture if you should use one or not?

    Here is what I made:20210605_175657.jpg20210606_193903.jpg

  9. #9
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    Spindles without steady rests.

    Quote Originally Posted by Allen Mattsen View Post
    I... recently turned a walking stick around 36" and had to be careful about too much vibration. Tailstock pressure I think was a factor in why the first one fractured and decided to leave the lathe ...
    Nice walking stick!

    Sometimes the wood will split at the tailstock due to too much pressure, especially on thin spindles made from hard exotics, brittle, or figured wood.

    To help with this I do several things:

    - Look for straight grain blanks without significant wild figure or cross grain, especially at the tailstock end. Burled wood is especially difficult and can be more flexible along the length too.

    - I use a Steb center in the tailstock. These have spring-loaded points so they can't apply too much pressure even when tightened. They also have a serrated ring which grips the wood and can help prevent splitting. I keep these in a variety of sizes.

    drivecenters.jpg

    - A small hole drilled into the end of the blank can center the point making it easier/quicker to mount by feel and also can help prevent a center point from prying apart weak wood. (If using a center without a spring-loaded point I would make a much larger hole.) I keep a gimlet hanging by a magnet on the lathe for small holes. (The original "cordless" drill!)

    Gimlet1-300x158.jpg

    - To mount with the least amount of stress I put one end loosely in the chuck then put the Steb center point in the hole on the other end to keep it aligned while I tighten the chuck. I prefer to use a chuck on the drive end if there is room since it keeps that end of the blank stiff and minimizes vibration. For small/thin spindles I hold the drive end securely with a short morse taper turned on one end. Besides helping with the vibration it allows the piece to be taken off the lathe then remounted with perfect registration.

    morse_taper_IMG_5054 - Copy.jpg wands_bowl_P7203947cs.jpg

    With this method I've turned thin spindles over 2' long tapered from 1/2" down to about 1/16" (with no steady rest), these from shelving pine from Home Depot and walnut.

    pointers_B_IMG_20140311_113.jpg

    A longer, thicker spindle like the hoe handle (and several shovel handles I made) can be challenging, especially when roughing. I still use the left hand to stabilize the wood when taking it from square to round (I rough it with a large skew) but it requires a light touch!

    I don't have a steady rest but I imagine it could be handy when turning bigger things such as large vases. I use my hand to stabilize smaller pieces like that when they get thin but a steady rest might be easier or even necessary. This is what David Marks used when he turned is large vase a few years ago.

    david_marks_vessel_3.jpg david_marks_vessel.jpg

    JKJ

  10. #10
    Thanks John!

    Steb center is a good idea. I did first one w/ cup/stock live center and second one w/ cone center.

  11. #11
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    Quote Originally Posted by Allen Mattsen View Post
    Thanks John!

    Steb center is a good idea. I did first one w/ cup/stock live center and second one w/ cone center.
    For others reading I see the photo I posted of the Steb centers was one with two drive centers. The 1/2" Steb "revolving" (live) center is what I use in the tailstock for small, thin spindles like the wands. This photo has both the drive and live centers.

    Steb_Sorby.jpg

    Unfortunately, these are expensive and the larger ones are sometimes difficult to find.
    https://www.robert-sorby.co.uk/lrcst...ing-stebcentre

    I quit using the cone centers for spindle work although I sometimes use it to steady things with holes in the ends. Although I'd hate to turn spindles without the Steb centers, for things with holes I generally make a wooden piece to fit with a short 2MT to fit into the Nova live center. The Nova is one of my favorites because of it's versatility.

    live_center_MT2_IMG_7914.jpg

    JKJ
    Last edited by John K Jordan; 06-10-2021 at 5:57 PM. Reason: clarification of "revolving" plus fixed photos

  12. #12
    By revolving center you're referring to a 'safety center' that will stop your spindle if too much pressure applied (or a catch)?

    Yes, in general I've noticed Steb centers and similar are strangely expensive!

    I didn't have any luck bringing up the attachments...

  13. #13
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    Quote Originally Posted by Allen Mattsen View Post
    By revolving center you're referring to a 'safety center' that will stop your spindle if too much pressure applied (or a catch)?
    Yes, in general I've noticed Steb centers and similar are strangely expensive!
    I didn't have any luck bringing up the attachments...

    No, "Revolving" is apparently Sorby's term for "Live" center, with bearings. The Steb drive centers will in general give and spin if overstressed, somewhat like what is sometimes called a safety center, but with the teeth they hold much better than a smooth cup.

    Sorry about the attachments - I got distracted and the photos I uploaded must have timed out. I fixed them. The first picture has a Steb drive center and a Steb live (revolving) center.

    JKJ

  14. #14
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    I didn't see this in the other responses.
    Stuart Batty has some good videos on Vimeo,
    This one concerns spirals.... adjust your lathe rpm or your feed rate.
    https://vimeo.com/54043311
    "I became insane, with long intervals of horrible sanity." - Edgar Allan Poe

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