Carbide Hob Grinding - Feeds and Speeds Questions
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    Default Carbide Hob Grinding - Feeds and Speeds Questions

    The shop I work at recently picked up an Anca FX3 to grind our HSS and carbide hobs. I am new to grinding and looking for information on grinding carbide.

    I have read that carbide hobs are sharpened in one pass at full depth with a slow feed rate. However, this information is out of a shop book that is older than I am and much of the information is outdated.

    I have had semi-good finishes using the same program I use for HSS hobs, but with a diamond wheel. The tolerances for AA ground hobs are tight, so I am seeking any information to improve my process.

    Thanks in advance.

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    Hopefully Carbide Bob will chime in here, but I would call your grinding wheel manufacturer and speak with them. Everything I have read about carbide hob sharpening is that's its better to sharpen more often and remove less material than to wait for the hob to wear excessively and then have to remove a lot of material. Interested in what you find out. Welcome to PM!

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    Was going to say the biggest biggest MOST IMPORTANT thing when sharpening hobs is to make sure the face of the teeth is exactly radial (unless the hob is marked as having a hook, so always check.) ITW had charts showing what happens to the involute when you get the cutter face off radially, and it ain't pretty. That's even more important than finish or index spacing.

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    The programs used with these hobs has hob shift after every part and sharpened after one full pass across. The wear is minimal for carbide.
    I have been experimenting with the amount of removal, removing less and less. The finish and grind quality is noticeably better with a lower material removal

    Thanks for the advice.

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    Quote Originally Posted by EmanuelGoldstein View Post
    Was going to say the biggest biggest MOST IMPORTANT thing when sharpening hobs is to make sure the face of the teeth is exactly radial (unless the hob is marked as having a hook, so always check.) ITW had charts showing what happens to the involute when you get the cutter face off radially, and it ain't pretty. That's even more important than finish or index spacing.
    Thanks for the advice. The Anca I use does a pretty good job of probing the flute face. Flute rake is < 5 microns.

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    Just curious- how much are you hob shifting after each part in relation to the circular pitch? Have you seen any difference shifting after, say 10 parts? thanks in advance.

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    Quote Originally Posted by rhadfield View Post
    The programs used with these hobs has hob shift after every part and sharpened after one full pass across. The wear is minimal for carbide.
    I have been experimenting with the amount of removal, removing less and less. The finish and grind quality is noticeably better with a lower material removal

    Thanks for the advice.
    I've only minor experience sharpening carbide Hobs, but a bit more sharpening Carbide Shaper Cutters since we started making them ourselves. My experience agrees with this completely. I've found that sharpening more often, and removing surprisingly little translates directly to greatly improved life and quality of cut. We now only take a few tenths off to retain performance. This also has the benefit of preventing some of the more spectacular failures. You might find that your coolant medium will have more impact now that you've gotten to this point. Carbide Bob will have much good information in that area, too. Good luck.

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    Quote Originally Posted by Zahnrad Kopf View Post
    You might find that your coolant medium will have more impact now that you've gotten to this point.
    Coolant ? you're still running coolant ? I thought all you advanced guys had gone to dry cutting now !

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    Quote Originally Posted by EmanuelGoldstein View Post
    Coolant ? you're still running coolant ? I thought all you advanced guys had gone to dry cutting now !
    LOL. I am referring to the grinding coolant.

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    Quote Originally Posted by Zahnrad Kopf View Post
    LOL. I am referring to the grinding coolant.
    Kinda intersting that hob sharpening is generally dry, while shaper sharpening is generally wet. Never wondered about why before ... you gotta answer ?

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    Update

    After some trial and error, I have found parameters that yield very good results.

    Rough - 0.002" stock removal, 6 in/min at 4000 RPM
    Semi-Finish - .0006" stock removal, 10 in/min at 5000 RPM
    Finish - .0002" stock removal, 20 in/min at 5500 RPM with a spring pass

    I am also grinding wet.

    The resulting hob rake, lead, and flute spacing are all well within AA standards. Often, rake and flute spacing are < 1 micron.

    I believe the semi-finish is not required, but the best results are with the extra pass. We only grind a hand full of hobs per week, so the extra 5 minutes is not a problem.

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