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    Default Gear hobbing 101 required.

    I've bought a small hobbing machine which cuts spur gears only. It's a Mikron 112. The machine is complete and working, just needs cleaning and lubricating and a VFD fitted for the motor, I have a full set of change gears and a decent number of cutting hobs.

    What I don't have is much of a clue how to use it. I have cut a few gears using single-point and involute cutters. I understand the basic principles behind hobbing gears but what I am struggling with is to understand the basic considerations for setting up to cut your average spur gear and how to decide what feeds to use etc.

    This is the machine in question.I have the controls mostly figured out, they are pretty self-apparent. I'm looking for some decent clear instruction on the procedure for setting up this type of machine for cutting,

    hob5.jpg

    Also I'd like to know how to decipher the various numbers on the hobs themselves. Some have DP and MOD stamped on them, others just a number.

    Pete,

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    Quote Originally Posted by Peter. View Post
    I've bought a small hobbing machine which cuts spur gears only. It's a Mikron 112. The machine is complete and working, just needs cleaning and lubricating and a VFD fitted for the motor, I have a full set of change gears and a decent number of cutting hobs.

    What I don't have is much of a clue how to use it. I have cut a few gears using single-point and involute cutters. I understand the basic principles behind hobbing gears but what I am struggling with is to understand the basic considerations for setting up to cut your average spur gear and how to decide what feeds to use etc.

    This is the machine in question.I have the controls mostly figured out, they are pretty self-apparent. I'm looking for some decent clear instruction on the procedure for setting up this type of machine for cutting,

    hob5.jpg

    Also I'd like to know how to decipher the various numbers on the hobs themselves. Some have DP and MOD stamped on them, others just a number.

    Pete,
    Google finds several possible sources for help right in your own time-zone, Peter:

    Gear Hob Book??? - The Home Machinist!

    Info please: Mikron 112 Gear Hobber

    Dunno if Andrew ever got to where he needed that strait-jacket, but the device seems intricate enough to at least keep you out of pubs and brothels for a long, long while.


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    Thanks Bill.

    It's Andrew's machine I bought. He's been kind enough to give me all that he had with the machine along with some old setup cards and a scanned manual (In German) but info general info is fairly scarce it seems. There's no 'how to run a lathe' equivalent for hobbing machines that I can find.

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    Hi Peter, not sure where about in England you are but obviously within striking distance of Sussex if you got your hobber from Andrew.
    Reason for replying to your post is that I know that Steve Mooney in Burgess Hill has a largish stock of Mikron hobbers and I would suspect but don't know for sure that there will be parts and accessories for them too on the shelves. Might be worth giving them a call, I find them a really pleasant company to deal with.

    Homepage | Steven Mooney Machinery

    hope this is of use to you.


    Alan

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    Quote Originally Posted by Peter. View Post
    There's no 'how to run a lathe' equivalent for hobbing machines that I can find.
    Seems an accurate observation, as it would vary from one hobbing machine design to the next far more than it does for lathes. Or general-purpose mills.

    The crucial 10% or less unique to each in the several lineal FEET of books that other poster mentioned would have to be ferreted-out, then related to the one specific machine.

    Suspect you'd make more money, faster, with this old gal if you adapted it to grinding coffee beans ... or shelling candlenuts.


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    Write all the markings on the end of the hob down first. After it's mounted it's a pain to take it off because you forgot the whole depth or whatever. With all the numbers you will be keeping in your head you *will* forget.

    Markings on the end of the hob show the tooth size (DP or Mod), swivel angle and usually the whole depth. Sometimes this is "WD" and sometimes "D+F" (tooth depth plus clearance) which means the same. For spur gears, set the hob head at the swivel angle as marked. Right hand hob goes one way, left hand the other. What you are trying to achieve is a rack parallel to the face of the gear so a right-hand hob on yours would be tilted to the right, a left-hand hob to the left. Check me on this, sometimes my brain goes astray. Just look at it, you will see what's right. The teeth of the hob at the cut should be at a 90 to the blank. Or at 0 to the axis of the blank, however you want to think of it.

    While I'm here, for helicals same hand adds the hob angle to the gear helix angle to get the swivel angle, opposite hands subtract, e.g. RH hob and RH gear, add. RH hob and LH gear, subtract.

    Install your index gears according to the number of teeth you want. You will most likely be using single-start hobs so the index chart will work as-is but if you ever go to a double-start, remember to cut the index by half.

    Install your feed gears according to the feedrate. For each revolution of the part the feedrate will give you X advance of the tooth. For say 16 DP you might want to start with .025 feed, just to get the feel of it.

    Now choose the speed gears according to the material. Hobbing is generally slower than turning or milling, think HSS speeds and maybe drop back a little until you have a better feel for the machine. Unlike turning and milling, going too slow doesn't seem to hurt.

    Mount your work fixture.

    Pop the first part up, indicate it, whatever you are going to do to make sure it runs true. Gear blanks MUST have one face square to the bore. This is extremely important. You would be shocked by how easy it is to bend an arbor with out-of-parallel faces. Not permanently bend, just bend enough to make a crap gear. If you are going to stack them, then parallelism is even more important. When you make the blanks, keep it in mind which face is the one that's square to your bore and make sure to mount them that way. If you have a surface grinder, on fine pitch I wouldn't be ashamed to pop them up on the grinder and hit the face of the opposite side. As ITW used to say, "Good blanks make good gears."

    Back your hob out of the way and turn 'er on. Feed the hob in by hand until it just touches the blank. Set the infeed dial to 0. Grab your magic marker and mark one tooth witness mark, let the part go around a time or two until you can see witnesses all the way around.

    Count the number of marks. CHECK THE PRINT. Don't trust your memory on this, it's really really sad when you have a $500 blank with the wrong number of teeth. You don't want to be the first on your block with a $500 doorstop.

    Move the hob clear of the part on the infeed side, set your stop. Move the hob clear of the part on the exit side, set your stop.

    Move the hob clear on the infeed side, then move the hobslide (or the table, depending on which moves) in to .025 or .030 shy of the whole depth that you wrote down earlier.

    Trip the feed lever, turn on coolant and watch 'er feed through the blank.

    Measure.

    Adjust depth.

    Cut to size.

    Measure.

    Adjust again and measure again or run parts.

    Hope that gets you started ....

    btw, unless the hob swivel is very limited like some spur-only G&E's, you can cut helicals, too. From the photo, you should be able to. The change gears are a bit of a bitch but it can be done. It's even common on old Barber-Colman #3's.

    p.s. You shouldn't need a variable frequency thing. Just use the speed change gears. That's how it was designed.

    p.p.s. You can switch between climb or conventional cut by adding an idler to the feed train. Pfauter loves climb, other companies say conventional is better. Up to you, but if you are having a difficult time with a part, think about swapping direction. All the usual stuff applies - material and fixturing count as to which is better, bla bla bla.

    triple p.s. Does this have an infeed ? If so you can cut wormgears, too. Even if it doesn't, you can do small numbers of them by hand. Just set the hob in the middle of the blank and feed straight in. Looks like a nice little hobber.

    quadruple p.s. Once you have the correct depth set, don't monkey with it. Cut the teeth, remove the parts, move the hob slide back to the start point without inny-outting if possible, put on new blank and go. This is the easiest way. If you must move the hob in and out, then you can but use an indicator, not just the marks on the infeed dial. On fine pitch, small amounts add up. Also, for initial placement of the hob along its arbor, where it is doesn't matter. But if you are running a lot of pieces you will need to shift the hob as it dulls. So choose whatever place you want on where to orient the hob along the arbor and make that a habit. Then you can keep track of how dull the hob is as you swap jobs around. As the cutter dulls, you can just move it along its axis until you run out of teeth. Your machine will either have a mechanism to do this or you can swap out arbor spacers. It only takes three hob teeth to generate a gear tooth, so any three-tooth sharp area on the hob will be fine. Hope that's enough to get you going.

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    Quote Originally Posted by Peter. View Post
    I've bought a small hobbing machine which cuts spur gears only. It's a Mikron 112. The machine is complete and working, just needs cleaning and lubricating and a VFD fitted for the motor, I have a full set of change gears and a decent number of cutting hobs.

    What I don't have is much of a clue how to use it. I have cut a few gears using single-point and involute cutters. I understand the basic principles behind hobbing gears but what I am struggling with is to understand the basic considerations for setting up to cut your average spur gear and how to decide what feeds to use etc.

    This is the machine in question.I have the controls mostly figured out, they are pretty self-apparent. I'm looking for some decent clear instruction on the procedure for setting up this type of machine for cutting,

    hob5.jpg

    Also I'd like to know how to decipher the various numbers on the hobs themselves. Some have DP and MOD stamped on them, others just a number.

    Pete,
    .
    modern cnc gear cutting machines can be scary fast. then gears might need grinding and or lapping and inspection.
    .
    poorly cut gears can shake a machine to pieces at high rpm. many places the people running the gear making machines are highly paid specialist. many gear making machine manufacturers offer training courses. they are really designed for people who will full time just make gears

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    Thanks for the starter Seamoss, I appreciate you taking the time to type all that out.

    I gotta digest what you said and I'm busy translating the manual into English plus reviving the oily worn out setup cards then I guess I might have a few more questions.

    Here are some of the many hobs I got. The ones in the pic have only the one number on them. Some have M stamped on the opposite face, the rest in the pic have nothing.Is there a way to identify what type of cutter they are just from the single number or must I measure them? I have a couple of gear tooth calipers with the machine.

    hobs1.jpg

    Pete.

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    Quote Originally Posted by Peter. View Post
    Here are some of the many hobs I got. The ones in the pic have only the one number on them. Some have M stamped on the opposite face, the rest in the pic have nothing.Is there a way to identify what type of cutter they are just from the single number or must I measure them? I have a couple of gear tooth calipers with the machine.
    Eek. No fun

    For starters you could get a set of rack gages ... Browning used to sell them, I've seen them on fleabay, don't know if you have distributors in England ? They are not too expensive. That'd get you close, then you could verify with your tooth verniers, then figure the lead and get the setting angle from that ... no fun at all. And they aren't necessarily anything standard. Lots of hobs are el-weirdo for specific jobs. 12.937 DP 17 1/2* PA, that kind of thing. To actually determine what you have is a lot of work. Optical comparator maybe ?

    I hate to say it but if those were in a box at auction, people would pay maybe $1 apiece for them because of the lack of markings. The guy who sold them to you might know ? Or at least tell you where they came from, which might give you a clue ?

    What's the arbor size ? New small hobs from China are around $100 apiece. They are accurate but the steel is questionable so life isn't up to Pfauter-Maag levels. Still, for a small shop they are a good deal. Some guy is selling direct on fleabay.

    btw, I think I got the swivel angle for helicals wrong. I think opposites add, same subtract. But my math sucks, have to look at the setup in real life to remind myself. You're not ready to do helicals yet tho, so not a problem

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    A notevfor buying hobs. A lot of ebay sellers are clueless. They claim new or light used when they are sharpened so thin that they are of questionable use. And ask way too much anyway. Example, Gleason Gear Hob Cutter 3" OAL 1/2 DP 3deg PA 1.25" ARB (214-4-22-1PGC3-9) | eBay

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    Quote Originally Posted by Mebfab View Post
    A lot of ebay sellers are clueless.
    Clueless doesn't begin to describe it ! Is this guy insane ? $ 750 ?!?! It's worth about $15 delivered by a really cute girl, and only if she promises to have lunch with you ! What a stupid shit !

    The good part is, blow up the photo and you can see how they should be marked on the end.

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    Pete I seem to remember that the number only hobs are marked with Mikron part numbers

    Relatively easybtonidentify the hobs as their profile is the same as the eqivilent rack

    I used to mount them on an arbor and Vee blocks and squint at them with a centering scope mounted in the Bridgeport and use it as a Travelling microscope. Once you accurately have the pitch it usually is fairly obvious what the hob is unless it is a special.

    You should find I marked up quite a few using a sharpie pen

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    Good Morning Pete and Andrew, I see were on about same time. I still experiencing jet lag and have the damn cough. went to Doc Friday...nothing wrong he said, did xrays, blood, etc....but I come home and cough. Have to sit in my Lazy Boy to sleep... Maybe I need fresh air, some farm smells again and need to tickle Doris ?..:-) That was one crazy fun time...thanks for inviting me. Rich

    PS: I know a guy in Springfield VT who runs and rebuild those machines. If Seamoss's great advice doesn't help email me and i'll give you his info. He used to work at Fellows Gear Company as a service tech and he also is hosting our May class.
    Maybe easier to call him too.

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    Peter
    I have been through your problems when I bought my first hobber I was lucky to get some advice from some now retired experts.
    I think your Mikron will do spur and helicals up to about 5" dia, you could do with a copy of the manual in English, if you can't find one PM me and I will give you some possible contacts.
    Peter

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    Thanks Peter,

    Yes I understand that 5" is the limit as far as diameter is concerned. I've successfully translated the manual, I'll post it up when I've checked a few things on it. There's a discrepancy between the German and English setup cards which I can't check until it's running, currently it's about 50% there with cleaning and oiling.

    There's no mention of how to set up for helical cutting in the manual. I'll leave that as a question for anther day.

    Pete.

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    Quote Originally Posted by Peter. View Post
    Is there a way to identify what type of cutter they are just from the single number or must I measure them? I have a couple of gear tooth calipers with the machine.
    I just realized it's not the fifteenth century anymore ...

    CAD program, depth mics, gear tooth verniers :

    Open the CAD program, start new file. Put a line along the X axis, maybe 2" long.

    Measure the depth from the tip to the root on your hob. Can't get it really accurate this way but it's not critical.

    Make a line parallel to the first at the measured distance.

    Now take two measurements of tooth thickness at any convenient depth, say .050 and .125

    Make two lines through those point symmetric about the Y axis. You now have one tooth.

    Now measure over two teeth at any convenient depth, same depth as before or not, doesn't matter.

    Draw line through new points, this would give the flank of tooth B.

    If you trust your measuring, just copy the other flank from tooth A to tooth B at the same distance. If you want to double-check yourself, measure the second tooth thickness at that depth and draw the other flank through those points.

    Trim all the overlapping stuff.

    Now you've got the rack. Measure the hob o.d., you've got the lead from your rack, calculate the helix angle. Setting angle on a hobber is not very critical, you can be as much as 1/2 degree off without hurting anything so do a good job but no need to freak out.

    Sometimes this computer stuff is okay The only thing that will be iffy is the whole depth, since unless it's a topping hob there will be clearance at the bottom of the tooth. But whole depth isn't super-critical sicne it's not the end number you need anyhow. It's just convenient for getting close to size. So you can calculate standard numbers and it won't matter. 2.157/DP in general should do ya.

    You've now got every bit of information you need to determine what the hob is. MARK IT ! Some day someone else may want to use it.

    For marking, don't use an engraver. The sides of hobs really need to be smooth and parallel and perfect. So one of those cheap edm marking kits is nice. In fact, with fine pitch hobs they often have indicating bands on the hob, at the ends. Unless the bore or the arbor is really worn out you can't tap them in but you'd be surprised what rotating the hob on the arbor can accomplish. Sometimes. The stuff is all supposed to be concentric and a tight fit, right ? Well ....

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    Quote Originally Posted by Peter. View Post

    There's no mention of how to set up for helical cutting in the manual. I'll leave that as a question for anther day.

    Pete.
    I once saw mentioned on a gear forum that there are Barber-Coleman machine manuals that explain that well, and that there are reprints available on Ebay. I haven't looked for the info myself, just want to pass this along.

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    Quote Originally Posted by Mud View Post
    I once saw mentioned on a gear forum that there are Barber-Coleman machine manuals that explain that well, and that there are reprints available on Ebay. I haven't looked for the info myself, just want to pass this along.
    The principle is pretty simple : on a straightforward simple gear hobber like a #3 Barber, the table is geared to make one tooth space for every revolution of the hob. If you are cutting a 20 tooth gear, then for every 20 revolutions of the hob the part will make one turn. Now feed the hob along the axis of the blank and we get spur teeth.

    So you have two sets of gear ratios ; the index gears and the feed gears. They are independent. Normally when you turn on a hobber the hob and the part rotate. The slide can be sitting anywhere but the cutter and part will always rotate in a timed relationship to each other. After the tooth spaces are cut you can run the hob back and forth through the gear no problem, everything stays in time. Feed doesn't matter. Kinda freaky the first time you do it but after a while, it's second nature. Which can be a problem ...

    On an antique, to cut a helical first you lie to the index. Then you create a relationship between the index and the feed. If you are cutting, say, a 20 tooth gear with a feed of .1" and a lead of 20", then you would gear the index to cut 20.1 teeth. So for every ten revolutions of the part you would gain one tooth space. Then to get the full lead you would have to go around (200)x (.1) = 20". Obviously you don't have to go around 200 times, that just gives you the correct gearing for an example. And I probably blew it cuz I can't even multiply by two in my head anymore. Dang calculators.

    It's pretty easy actually however it's tricky because after you run a hobber for a while certain things become automatic - like kicking the feed out at the end of travel or even any time you feel like it. When cutting a helical without a diff, you cannot ever disengage the feed after you have once engaged it. That means at the end of a pass you must turn off the machine, put the motor in reverse, and back the thing up to the beginning to take a second cut. Imagine running a lathe like that, you'd have to slap your hand about twenty times a minute to keep it from grabbing the feed lever.

    Pain in the ass but if you don't have a diff, it's better than not being able to cut a helical at all.

    The differential came later - it's another set of gears between the index and feed gears that does this for you automatically. With a diff you can disengage the feed again any old time because the differential sets a ratio between the index and feed, so as you move the hob slide the diff will speed up or slow down the table relative to the position of the hob.

    You can do another stunt with this trick too - if you want a prime gear that you don't have a change gear for, you can cheat the machine by telling it to cut a gear one bigger than what you want. Then lie to the index gears and make them cut a part one tooth fewer than what you want. It'll come out even, making a spur gear of the number of teeth you don't have.

    With an nc hobber the electronics do all this. But nc hobbers be purty expensive.

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    Thank you - nice explanation ! I'm looking into this as I need to start making timing belt pulleys. I'm tired buying rubbish. It seems I might be able to make a milling machine pretend to be a hobber.

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    The late John Stevenson did exactly that using a universal (ie swivle table) horizontal, an encoder on the shaft and some 'gearing' electronics between the encoder and a 4th axis for the work blank.

    Sadly a quick look at his old site implies the files have gone

    http://www.practicalmachinist.com/vb...-hobber-83916/

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