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Thread: Hollow grind question

  1. #1
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    Hollow grind question

    I’m finally set up to be able to put a hollow grind on my edge tools. Slow speed grinder and 80 grit CBN. Here’s a picture of one of my first grinds (60 1/2 block plane).

    91260E79-B130-4365-ADC0-E407D8363CA3.jpg
    I know I need to work a little more on the micro-bevel. Question is, the 80 grit scratch pattern...it’s ok as long as the micro bevel has no scratches right? Being used to polished bevels, the scratches kind of bother me...but is there a reason it should? Do I need a higher grit CBN to smooth it out some?

    Thanks!

  2. #2
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    I’ve recently gotten set up to hollow grind bevels and have left the primary bevel as it is off the wheel. Between hollow grinding and stepping up to some good quality 3m lapping papers from wet/dry stuff I’ve gotten far sharper edges than I had previously been getting. That being said, your scratch pattern looks a bit more aggressive than what mine seem to end up with. Could just be how close the blade is to the lens though!

  3. #3
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    I would hone the bevel smooth and put a micro bevel on the edge. Google micro bevel.

  4. #4
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    Phil; I purchased the #80 and #120 grit cbn wheels over 12 months ago.

    The #120 cbn supplies a finer scratch pattern that's better suited to follow up work on the honing stones.

  5. #5
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    Thanks all. Appreciate the input on the 120 grit, Stewie. Sounds like a good use for the $ sitting in my paypal account.

  6. #6
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    Quote Originally Posted by Phil Mueller View Post
    I’m finally set up to be able to put a hollow grind on my edge tools. Slow speed grinder and 80 grit CBN. Here’s a picture of one of my first grinds (60 1/2 block plane).

    91260E79-B130-4365-ADC0-E407D8363CA3.jpg
    I know I need to work a little more on the micro-bevel. Question is, the 80 grit scratch pattern...it’s ok as long as the micro bevel has no scratches right? Being used to polished bevels, the scratches kind of bother me...but is there a reason it should? Do I need a higher grit CBN to smooth it out some?

    Thanks!

    The way I do it is to grind the hollow until all defects are removed then it all gets done on the stone(s) after that. I usually make the first stone 1000, place the blade on the stone and feel for the heel and toe touching then slightly lift the heel and start honing until the grind marks are gone and the bevel has been established, being very small this does not take long. Rinse and repeat for each stone you want to use. I do not worry about angles, just a small lift and the more you practise the better the muscle memory. Lock your arms to your side to prevent any change of angle caused by arm movement and then move your whole body back and forth to move the blade along the stone.
    Chris

    Everything I like is either illegal, immoral or fattening

  7. #7
    Leaving the scratch marks in the hollow grind works just fine. In fact, you will have less surface to remove when you need to re-sharpen this way. If you are lucky you will not need to grind again and just use your stones.

  8. #8
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    Ignore the scratch marks in the hollow, you can't do anything about them with a flat stone and if you want a blemish free full bevel hollow grinding is the wrong method to be using as the primary bevel has to be flat for that to happen. The beauty of the hollow grind is the speed it can be done at, five minutes and you have a sharp blade from go to whoa.
    Chris

    Everything I like is either illegal, immoral or fattening

  9. #9
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    Quote Originally Posted by Phil Mueller View Post
    I’m finally set up to be able to put a hollow grind on my edge tools. Slow speed grinder and 80 grit CBN. Here’s a picture of one of my first grinds (60 1/2 block plane).

    91260E79-B130-4365-ADC0-E407D8363CA3.jpg
    I know I need to work a little more on the micro-bevel. Question is, the 80 grit scratch pattern...it’s ok as long as the micro bevel has no scratches right? Being used to polished bevels, the scratches kind of bother me...but is there a reason it should? Do I need a higher grit CBN to smooth it out some?

    Thanks!
    Hi Phil

    Scratches on the hollow are expected. Scratches on the secondary or micro bevel are not.

    I recommend that you get a 180 grit CBN wheel for refreshing the hollow. 80 grit is too coarse to allow for one to quickly remove scratches. 120 grit is too close to 80 grit.

    I wrote about this a few years back: http://www.inthewoodshop.com/Woodwor...ningSetUp.html

    180 grit CBN and honed ..



    Regards from Perth

    Derek

  10. #10
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    Phil; Derek's correct. I went and checked the finer grit rating on my CBN set up. (The 180 grit CBN wheel is on the right hand side of the grinder.) My apologies for the confusion.

    Stewie;

    Last edited by Stewie Simpson; 08-16-2018 at 9:23 AM.

  11. #11
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    Thank you both. No apologies for confusion necessary. Actually, Woodturners Wonders does not have 120 grit, so I made a wild assumption that it probably was 180. Order sent and looking forward to using it.

  12. #12
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    Quote Originally Posted by Phil Mueller View Post
    Thanks all. Appreciate the input on the 120 grit, Stewie. Sounds like a good use for the $ sitting in my paypal account.
    Why stop at 120? At the moment I use 80, 220, and 600 grit CBN wheels on 1/2-speed bench grinders and a 1200 grit CBN on a Tormek. I like the edge I get with the 1200, great for my lathe spindle gouges with a minimal amount of honing. I use the 600 for scrapers and some other tools.

  13. #13
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    180 grit is for bench chisels. Lathe chisels are different since one may use them off a grinder.

    Regards from Perth

    Derek
    Last edited by Derek Cohen; 08-16-2018 at 11:31 AM.

  14. #14
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    Quote Originally Posted by Derek Cohen View Post
    Lathe chisels are different since one may use them off a grinder.
    That's certainly true for some, especially those turning bowls green wood. I prefer to turn hard, dry wood so I hone/strop nearly all lathe tools from the grinder, some lightly with the leather wheel of the Tormek, some with polishing compound rubbed on a piece of resawn MDF, and some with very fine diamond and/or a ceramic stone.

    Turners often use scrapers and rely on the burr directly from a coarse grinding wheel. I prefer use a finer wheel, hone away the grinder burr, and raise a burr with a carbide burnisher.

    I'm not as experienced with sharpening bench chisels and plane irons. After reading some of the sharpening threads here I'm sometimes amazed that I can get an edge as sharp as I do with my crude techniques!

    JKJ

  15. #15
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    I​t just occurred to me that I’ve spent another $200 on sharpening, and based on another post where Derek mentioned a medium Spyderco may just add a bit more to that. When does this slippery slope end!
    Last edited by Phil Mueller; 08-19-2018 at 8:48 AM.

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