How do I make my own gear hobs? (Gear cutting)

[@lorengrimes5293]

That was the clearest, most concise explanation of basic gear theory I have ever seen.

[@anthonybabiak8352]

Excellent! 25 years in a machine shop and I now know more about hobbling than ever.

[@markrainford1219]

A book's worth of knowledge in thirteen minutes. Thank you.

[@notamouse5630]

Thanks for going through the theory on gear design and gear standards, this is very helpful for understanding the engineering behind the standards.

[@mymechanics]

Awesome video, everthing was very well explained. Now I need to watch the other video about the build of the gear hobbing attachment.

[@MrCrankyface]

Thanks for going through all the calculations, makes the process even more interesting when you can get a better grip on it!

[@digital945]

You are a teacher more than a machinist ..thank you sir for sharing your knowledge.

[@euclidallglorytotheloglady5500]

Whelp... this is just the first of MANY times I'll be watching this.. So much valuable info here. Awesome work! Thank you!

[@jmtx.]

Goes to show how important mathematics truly is. Thanks for sharing such an awesome video!

[@Saand1338]

This was a great video! Prior to watching this and the two attachment videos I understood that hobbing existed but not what it entailed, and I've come away with a great appreciation for the mathematics, planning and applications of the process. I'm not a machinist, so it's always fascinating to learn about the techniques that are part of the manufacturing of precision components.

[@toxanbi]

I think you don't take into an account something. I would prefer to be wrong here, but... Consider making a spur-gear having PA = 20°. That means that the toothed rack complementary to such gear would have trapezoidal profile of tooth with also 20° angle between trapezium s sides and axis of symmetry. If you going to cur the gear using the rack as a cutter, no problem: you have to move cutting rack towards the gear in direction parallel to gear axis. With the hob things change: to compensate for helical "nature" of gear hob, you make an adjustment of milling machine axis and you mention that at 11:30. Now projection of the cutting edge (of its contour) of the hob to imaginary vertical plane will differ from its real contour - it will be compressed in by vertical axis by the factor of cos(helix_angle). If the scaling transformation has different scaling factors on X/Y axes, that transformation does not preserve angles. Thus you'll get slightly decreased PA on your gear. You probably don't notice that the gears you make have decreased PA because with helix angles as low as 5° or 10° the cosine of helix angle is ~ 0.99619 or ~ 0.98481 respectively, which means one-axis scaling to a factor of 99.6%/98.4%. So depth of the groove you cut isn't affected, but the width of the groove is about 1% less than required. Also, if you making two gears that should couple to each other, they will mate perfectly even if it's PA angle is unintentionally decreased. However, you are getting non-standard and modified profile of your gear teeth, so it won't mate perfectly with the gear manufactured somewhere else. However, all this considerations become not actual if at the stage of thread cutting (07:17) you tilt you cutter by the angle matching the helix angle of you thread. Which isn't the case as far as I can see.

[@AndysMachines]

That's a very astute observation and clear description of this effect! Yes, you are correct, the tilt of the hob does affect the pressure angle of the gear it generates. This is known as 'cosine error', though in this case the effects are so small that I've never felt it necessary to correct for them as they will likely be swamped by other errors that are beyond the accuracy I can achieve. This hob was tilted to an angle of 4°, commercial hobs are generally larger diameter than my home-made ones and are tilted to less of an angle, around 1-2°. The cosine of 4 is 0.9976 giving a pitch error of 0.24%. At 1° the pitch error is only 0.015%. A tilt of 4° would change the pressure angle from 20° to 19.96°. I don't think I can grind the cutter used to cut the hob to within 0.04° even if I do it on the lathe and set the compound slide very carefully with a dial indicator. Also when I screw cut the hob I am not able to reproduce the module thread with an accuracy better than 0.2% on my lathe due to limitations of the leadscrew and change wheels. Also as you say, if I cut mating gears with the same hob then they can actually have quite large deviations from the pressure angle I was aiming for and they will still be perfectly matched to each other. However it is still useful to know about this effect and good that you pointed it out, as for example I can try and make the cosine error of the hob and the screwcutting pitch error cancel each other out rather than both adding up in the same direction.

[@MarkATrombley]

I think I sprained a frontal lobe.

[@aunabreslingaming3279]

Yea

[@rneal63]

That's awesome! I have an old CNC lathe that the control didn't work and used LinuxCNC on it. It's really great at threading and can cut any thread, inch, metric or anything else. I'm thinking that it would be great for making hobs with the odd spacing on hobs for DP gears. I love it that one hob can replace a whole set of gear cutters. It would even be possible to put a hobbing attachment directly on the CNC lathe and synchronize with the spindle that is already encoded.

[@jonminer9891]

Hello, Andy. I enjoy your relaxed and careful videos. Thanks for sharing! Stay Healthy!

[@satipsrl5207]

Nicest explanation,thank you my teacher,....this trick is for my retire,if my wife will permits to take my my mill and lathe in garage

[@jimsvideos7201]

Brilliant work in After Effects; you've cleared up some long-standing uncertainty for me.

[@rockyrodriguez2351]

Now I learned the basic of gear making, thanks for sharing this video…

[@kevinbritt8427]

I like your funny words magic man. But seriously, as a plumber who will never have to touch a lathe or mill to make a gear in my life this was cool

[@mrfxm55]

Thank you and Greetings from Florida USA 🇺🇲😎

[@MrLaTEchno]

...................now this is the way to help ourselves in the '' real World'' my friend. Knowledge shared is a treasure we need to grow as a whole, Humanity must have people like you. [ good heart and mind ] ready to learn others what to do...many thanks for this little gem. Let it flow, so others can grow. Greetings from Holland.

[@franz_k6000]

man this video is an example of QUALITY content please keep making these Grüße aus dem Oberallgäu

[@irish-simon]

fantastic video I been cutting gears 30+ years in work and I learnt something from it Thank you keep up the geat work

[@dianamccandless7094]

Best video ever. I'm not kidding. Thank you for ALL the details!

[@MachiningandMicrowaves]

Very good explanation and demonstration.

[@adrianfernandez1806]

WHEN YOU KNOW YOU KNOW > You are an expert on this feild

[@JoseSilveira-newhandleforYT]

Probably the best video on hobbing I've seen. Thanks!

[@ralphf8951]

Wonderful explanation. Lots of time and energy went into this one!

[@karroome]

You, sir are an excellent instructor. I was so focused during the math bit, I think I fainted for a second or two🤯🤣

[@timmienorrie]

Well done, Sir. Well done. A veritable masterclass.

[@abhishekkuksal5700]

You are actually good in metrology as well!

[@AmalgmousProxy]

This is BEAUTIFUL! What a wealth of useful information without the nonsense. Thank you for this! Subscribed!

[@michaelrosenlof1084]

Very nicely done, Andy, very enjoyable-thank you very much ✅👍

[@ebrewste]

Just watched the imperial version :) It makes me appreciate this video even more.

[@northernmetalworker]

Thank you for this video. I haven't been able to find anything on KZbin. I'm needing to make a batch of 3 DP 67 tooth gears for my work. This helped me immensely.

[@AndysMachines]

Wow! Those are pretty big gears!

[@elanjacobs1]

If you need to make proper gears, buy a proper cutter. As impressive as this is, it's nowhere near good enough for a commercial product.

[@AndysMachines]

@@elanjacobs1 I'm not claiming my home-made hobs are as good as commercial cutters, and I'll always use a commercial one if I have the right size. But it is possible to make DIY cutters like this that produce results plenty good enough for most applications and at a fraction of the cost. I don't know what a 3DP gear hob would cost, but it's not going to be cheap!

[@northernmetalworker]

@@AndysMachines it's a small batch of maybe 5 or 6. I'm going to try and get a hold of some 6" diameter o1 tool steel for making the hob. Should work well enough if I take things slow.

[@zebdeming]

Fantastic video and a great explanation of how to measure and figure out gear math!

[@TheMadMagician87]

Thanks, a lot of knowledge wrapped up in this video - very helpful!

[@richardmoffatt6606]

Geezus F*CK that was more than I anticipated. Well, it appears I'll be purchasing my own hobs because for my application, I certainly don't have the necessary tools nor the precision mathematical abilities to do so. WOW my friend, you have garnered my complete respect, and also, admiration in the time you spent in creating this video. I applaud you.

[@shigatsuningen]

Geee whiz what did I just look at. Got to love it because I think I just nailed the national standards test for the 2nd year mathematics of senior high school again, this time in one single 13,14 min sitting.

[@faroironandcustoms6577]

WOW!!! New subscriber here. I understand almost none of what I just watched. But I really wish I did.

[@brendanaengenheister5351]

very impressive but with all those calculations I can understand why some people prefer to save up and buy a commercially produced one.

[@cooperised]

Surely not! The maths takes a fraction of the time that the machining takes. Buying cutters is a good idea if you're "cash rich and time poor", but if you have the time to make them, don't let the maths put you off. :-)

[@AndysMachines]

Well said,@@cooperised The maths and theory behind it isn't actually that hard once you start looking into it, but I think a lot of people are put off by the very idea. It's also good to know this stuff if you never even make your own cutters as it's gives you a better understanding of how commercial ones work.

[@death_parade]

LOL. I am at the opposite spectrum. The math doesn't scare me but actually trying to machine it does.

[@LikeFactoryMade]

I wish I could like this more than once!

[@velcro8299]

Thanks Andy, Learning a ton

[@TheEvertw]

Thank you for an excellent explanation! Shows how useful math can be...

[@mehdiocquerre4409]

Love it. Thank you so much for sharing this

[@jimviau327]

Great learning content. Thanks. 11:40 - Wished you talked a bit about the technique utilized to synchronize both rotation.

[@AndysMachines]

Thanks! I talk a lot more about this in my other videos on building the gear hobbing attachment and the controller for it. Here's a playlist of my gear related content: kzbin.info/aero/PL7T9LOrvm0qLMHvxnMJsi_gqrfyUoaeCp&si=lIYIPAcKikYL8jvz

[@MrCharliebbarkin]

Great video, probably the best reference on the subject

[@николайгрушичев-в1ж]

Спасибо Вам, буржуи! Теперь будем делать червячные фрезы по науке!

[@PorkBarrel.]

Great reference video we're saving for future use thank you.

[@MurrayCann]

I agree with the chap below, however I still have a question. You made the hob in a spiral thread, I was lead to believe that doesn't have to be so and you can cut using a dial guage to measure the different positions for you cutter, especially for a spur gear. Is this so?

[@AndysMachines]

Not sure who the chap below is at it depends on how the comments are ordered. But if it's actual hobbing with the gear blank rotating as the teeth are cut then yes, the hob needs to have a helical tooth arrangement. It's also possible to use a hob that looks like a stack of #8 gear cutters (rack profile) without any helix and index each tooth, or for more accuracy index the blank by a fraction of a tooth and move the 'hob' up or down a corresponding amount. This type of 'hob' will cut any number of teeth just like a real hob and it's how I used to do it before I developed proper rotating hobbing methods.

[@stanley6602]

Very easy to understand gear calculation tutorial. Nice video👍

[@ebrewste]

I think this was the best hobbing video I’ve seen. Nice work!

[@YooProjects]

Super professional video!! Thank you very much dear man. Waiting for your next video

[@Cornpop1234]

How would you calculate the flat distance for grinding a hss tool for making a worm wheel hob? Also when cutting the hob the OD should be bigger than the worm gear for clearance how much bigger? When making a hob to a cut worm wheel wouldn't the hob match many dimensions of the worm gear. There for the hob is only used to cut worm wheels for that specific worm gear. If the worm gear is 2 start would the hob have to be 2 start or would single start hob work?

[@AndysMachines]

You would do it in a very similar way. Yes, the worm hob should be similar to the worm except that the addendum and dedendum are swapped over, so the OD of the hob is greater than that of the worm (by 0.5-0.8 x module). People often make two identical worms, cut teeth into one and use that as a hob to make the worm wheel, though this does work it is not technically correct as there will be no clearance. I actually made a worm, matching hob and then cut a worm wheel with it recently. I took video footage of the process and this will most likely be in an upcoming video where I'll try and explain the whole process.

[@KW-ei3pi]

Interesting and very well presented. You have and amazing amount of knowledge. Thank you

[@jamescopeland5358]

Great video

[@sibalogh]

This is a sound presentation. I have just learned the concepts of the module, addendum, dedendum, angle of pressure, the tip of width, and how to work them out.

[@kenshelhamer9816]

Would it be possible to plunge straight into the hob with a single point form tool at every pitch increment, and not generating a helical formed hob, then not tilting the spindle axis as the teeth would be perpendicular to the gear's axis? thanks for producing great information. subscribed.

[@AndysMachines]

Yes, you can do that and I have done it that way in the past. What you end up with is not technically a hob, but a stack of disc gear cutters. You still need to index the blank for each tooth, but like a hob the tooth profile is generated from multiple cuts so you can use it to cut any number of teeth, though the profile is more approximate, especially for low tooth counts which don't intersect with as many teeth of the 'hob'. (You can improve on this by indexing the gear a fraction of a tooth and raising/lowering the 'hob' by an appropriate amount)

[@ChristophLehner]

Very very informative video. Thanks for sharing

[@TinkerInTheShop]

Thanks, After watching this video I've decided to purchase all gears instead ;-) Great info here.

[@zachary3777]

When you tilt the head of mill, doesn't that slightly distort the shape of the teeth, compared to your cutter?

[@AndysMachines]

Good observation! Yes it does, it introduces what is called 'cosine error' however if the tilt of the head is only a few degrees then it's so small that it's not worth worrying about (the cosine error produced by a 3° angle is something like 0.001). You could account for this when making the hob if it has very large teeth relative to it's diameter by adding the error on to the pitch so it gets cancelled out. I've no idea if commercial hobs account for this error, they usually have a smaller tilt, only a single degree or so. They may be ground in such a way that the error is cancelled out automatically by the process.

[@zachary3777]

@@AndysMachines Thanks for the reply! I knew the error would be small, but i asked because i was going through it in my and wasn't sure if that got cancelled out somehow. To take it another step further, i believe theoretically the helix angle at the root of the cutter is greater than at the tip. I guess the only way to get a perfect tooth is to generate it from a rack, or single point cutter.

[@AndysMachines]

@@zachary3777 Yes, the helix angle does change with the radius, but I suppose that's also true when the hob is made, so perhaps the effects of this cancel out. Another reason commercial hobs are usually quite large diameter in comparison to the size of the teeth (at least compared to my home-made ones).

[@bikefarmtaiwan1800]

Super interesting! Well done - excellent work

[@davelowe1977]

Man, that was GOOD!

[@jirvin4505]

Having difficulty understanding why the single point hob cutter needs the tip flattened? I followed the ~3:30 graphics but cannot see how the flat bottom created on the hob by the flattened cutter is involved in cutting the gear teeth? Only way I see the flat bottom of the hob teeth come into play is if the hob is driven too deep into the gear blank…. Help

[@AndysMachines]

You are right, the flat at the bottom of the hob (top of the tooth) is not absolutely necessary, but most gear hobs are the 'topping' type which means they will cut the tops of the teeth if the blank is oversize (or not concentric). When cutting the hob with a single-point cutter the most important thing is to get the depth of cut correct to produce teeth of the correct width, having a precise location for the flat makes this easier and the top of the tooth is the obvious place. You could use a cutter with a sharp point and base the calculations on that, but the point would be very weak, probably break off, and the hob teeth would be cut deeper than necessary which would make them weaker. A third way is to put a radius on the single point cutter some way beyond where the flat would be, this would produce a 'non-topping' gear hob

[@tirumaltradingtirumalatr-wn2kl]

Great job

[@JesseSchoch]

sweet, thanks for showing the cutter flat calculation!!! Not sure if you've checked out my video on cnc gear cutting without a gear cutter but I was hoping to find this calculation and now I can update my simulator!

[@AndysMachines]

Yes, I did see your video in the past. That's actually a very accurate way to generate gears as you are taking a large number of individual cuts to generate the involute profile. I used to do something similar using a 'hob' with no helix, like a series of stacked discs with a rack-like tooth profile and cutting on the side of the blank, indexing by one tooth at a time produced fairly good profile, and then you can take additional cuts with the 'hob' at different heights.

[@mr.ranyhomemade2466]

You so amazing about your diy tools

[@richardmoffatt6606]

I must ask, do you possess the ability to calculate the number of teeth required for parts to rotate at a correct speed? For example, rotating one gear one rotation would spin the adjoining gear 365.25 times? 1:365.25? Also, I'm a welder and metallurgy specialist, so the thickness and composition of the gears would be determined by the force required to sustain the loads on the teeth - are there particular addendum and deddendum angles and depths that are what could be called typical for usage? I understand that's weighted more for engineering, however the terms of different teeth would be helpful to know for my own research.. are you aware of any terminology with respect to teeth? Thanks for your video, it's wonderful to have you share your knowledge, where, in typical industry, skilled individuals hate to share their knowledge because it makes them less valuable to their company they work for. I have come across this hundreds of time in my industry

[@AndysMachines]

1:365.25? That must be for a telescope or astronomical clock, right? That can be done with a train of gears, but you start to run into problems with prime numbers, for example you could do something like 365.25 =(1x3)/4x487. But 487 being prime does not divide down further so you would have to have a gear with 487 (or a multiple of) teeth. I believe clockmakers sometimes do things like this using differential gears to obtain fractional ratios with smaller gears. Addendums/dedendums and pressure angles are all fairly standard. Sometimes the pressure angle is increased (by only 5° or so) for high torque applications but the usual way is just to make the teeth an appropriate size for the force required. Do a search for the "Lewis equation," this will tell you based on the Young's modulus of the material and dimensions of the teeth, how much force they can withstand. For general gear terminology I have another video on identifying gears that might be helpful.

[@aaronholland2772]

Well, know I know what those module and dp charts are for on the lathes. Neat.

[@dougwood6186]

My brain hurts lol no seriously you a genius love you videos , don’t think i will get to that level but it all helps me understand the process before i attempt my first gear thanks

[@gillywild]

Absolutely superb presentation. Thank you :)

[@tylerkrug7719]

You are a friggin genius!!!

[@cristianpopescu78]

Great,amazing Video!

[@recurvestickerdragon]

ToT needs to try these

[@RixtronixLAB]

Vote up, nice video, thanks for sharing :)

[@davidtaylor6124]

Great video, really interesting!

[@NitroTom91]

If you'd tell us how you built the control box for the stepper motor that would be the last thing to get me started. Not because I'm lazy to work it out myself, but because I'm only getting started in electronics and I don't know where to start. Building it is no problem for me, but coming up with a layout for a circuit or using an arduino is beyond my abilities with not knowing what to look for.. Thank you for you huge effort to make these videos as good as they are, anyway.

[@AndysMachines]

A lot of people have asked for this and I'm working on an updated version of the controller with more modern components that will be simple to put together (arduino based). There will be a video on this in due course.

[@timstevens3361]

Hey Andy Great video ! im a cnc mill guy 25 yrs you diy a cnc mach too ?

[@AndysMachines]

Yes, I've converted a small manual milling machine to CNC and also added (very basic) CNC to my lathe. Over the years I've built a number of other CNC machines, mostly gantry router type.

[@timstevens3361]

@@AndysMachines im gona do that soon. i met a tobaco/ginseng farmer few yrs ago. i told him im a cnc mill guy, he told me alot of his friends build and run rc cars n copters. he also told me, some of his buds spend few $k/month on custom cnc machd parts. you could prbly mach parts like that. no crazy dims r tols.

[@AmalgmousProxy]

I'm returning to this video after an adventure in cutting gears with decent success to ask a question. What are your feelings about letting the hob drive the material? Came across a video where a tap was used as a hob and the material freewheeled. Haven't tried it myself.

[@AndysMachines]

It can work, but it is hit and miss and you can end up with a different number of teeth to that expected, or just a complete mess. It's critical to set the hob at the correct angle and best to cut to full depth in one pass. I would recommend gashing the blank with the correct number of slots to start with to give the hob something to locate on, but that kind of defeats the simple freehobbing approach.

[@michaelguzzi1]

Excellent, highly informative video!

[@igorkononov4249]

Очень полезное видео.Всё показано детально и доходчиво.Большое спасибо.

[@mountainsprings3303]

What a great tutorial, I learnt a lot, thanks

[@FinalFront]

How do they cut helical type gears like what manual transmissions in cars use?

[@AndysMachines]

You can do that with a gear hob, check out my other videos on the hobbing attachment.

[@johnsushchyk7933]

Very interesting Thank you Impressive work 👍🎄

[@patrickfischer2264]

What's with the helical shaped cutter, are you going to make internal gears

[@AndysMachines]

Yes, it was a small skiving cutter for making an internal ring gear.

[@nunomiguelrodriguessilva3028]

Great video👌thank you for sharing

[@ianbertenshaw4350]

Excellent video !

[@FedeGiannetti]

Good morning. I've seen the video, but I have problems with English :) In the video You tilted the milling head by the degrees of the hob helix, to put hob angle and table parallel. Quite right ? And then you tilted the divider towards the tray, why? What about straight teeth?

[@AndysMachines]

Yes, the hob is tilted so that the teeth are parallel to the table. To cut a helical gear you then tilt the hobbing spindle to the helical angle. For a straight toothed spur gear you leave this spindle horizontal.

[@FedeGiannetti]

@@AndysMachines thanks

[@pcka12]

After the delights of the imperial version I was hoping for the Harold Wilson ‘white heat of technology’ version with shots of Concorde & V bombers plus ‘Arold’ & his pipe & Mac!

[@M.Fogaca]

hello, how are you? I'm Brazilian and I'm learning...can you tell me which thread pitch is similar to the diametral pitch 18....the gears of my lathe and this module and I would like to manufacture the same as you did but I don't know if it is possible to do the same as you did

[@AndysMachines]

Pitch=π/18 =0.175" (5.73 tpi) =4.43mm Or as close to that as you can get!

[@M.Fogaca]

@@AndysMachines so I'll try to do it with the step of 4 .5 and see the result....thanks a lot

[@ganeshlakade5753]

Gear profile good explain ⚙️⚙️⚙️

[@JesseSchoch]

is the cutter you made in the last shot for skiving?

[@AndysMachines]

Yes, It was my latest attempt to make a skiving cutter for internal gears. It was an improvement over previous ones but still not perfect. I'm beginning to think a shaper would be a better option. Skiving is great for industrial use where you want to produce hundreds of identical gears, but there's really a lot of work and calculations involved in making the cutters, which then are only suited to one size and tooth count of gear as the way they generate the profile is different.

[@JesseSchoch]

@@AndysMachines they do seem magical though

[@alexsancho9638]

Thank you vey much excellent explanation!

[@danielosornio8484]

You got the controller box or you made it, if so, you could make a video explaining how it works. Thank you very much and greetings.

[@PisTTasha]

Just amazing ! You really explained the whole thing better then a 1000 pages book ;) , Just curious where did you learn all o this ?

[@luciangv3252]

In books hahaha but i recomend u the handbook, there a lot of table, tecniques and standards knowledge.

[@leandromelton4191]

Supreme Mathematics!

[@Hossein_Ash]

Wow, Excellent. Thank you.

[@noneofabove5586]

What did you make with the cutter at the end ? An internal gear? Where did you find out how to calculate the gear cutting angles? Not just the spur gears but the spiral cuts also. Thanks great video.

[@AndysMachines]

That was a cutter for making an internal straight-toothed spur gear via a gear skiving method, though I didn't get the geometry quite right and although the gear worked it wasn't perfect.

[@emilgabor88]

Nice and weary interesting video. Thank you

[@ledfootlou2540]

Great video!!

[@gregwmanning]

At 5:31 the cutter has an obvious helix angle, at 5:36 the cutter used to for measurement has no helix angle. Do you cut with helixed cutter and filmed with the straight one? At 11:30 you say the hob is set in the milling machine at the helical angle of its teeth, is this exactly the same as cutting the hob on the lathe with parallel grooves and setting this hob in the mill square? Since your hob has short teeth, can it be used to cut helical gears with high helix angles say 45deg? Thanks Andy for the very detailed video(s)

[@AndysMachines]

That's actually the same cutter (it has a small mark on it which you can see in both shots) Though it's possible I might have reground it between these shots as it does look different, or it might be the camera angle. We are looking at the bottom of the cutter here and since this cutter is used for (right hand) screwcutting I have ground more relief on the left hand edge, I just do this by eye so it's probably more relief than is actually needed which is why it looks so asymmetrical from the bottom. What's important is that the top edge which has no rake and is symmetrical, is raised up on the parallel to exactly the centre height of the balls so that I am measuring across the cutting edges. I guess you could call the cutter 'helixed' It's really just ground to clear the helix of the screw. re. hob with parallel grooves set square in the mill. Yes, you can also do it that way. if you look at the hobs I made at 0:41 the hob with large teeth at the top of the picture is made this way (because otherwise with such large teeth on a small dia. hob it would have a very large helix angle). Yes this is effectively the same as a helical hob tilted at an angle, but since the angle is zero the blank cannot rotate during the cut in the normal way, so you have to index each tooth one at a time. It still generates the tooth profile in the same way a hob does though. Helical gears of even greater than 45° can be cut and the relief on the hob is not an issue since the hob is always cutting parallel to the teeth, not at an angle such as when screwcutting on a lathe where you have the helical angle of the screw yet top face of the cutter is usually horizontal.