I loved this video, the back ground music, the static, the lines and hairs, you went to a lot of effort to make it. Your British humour is wonderful. My mother used a "modern labour saving device" the washing mangle. I am from a now "dire metrical" country but grew up with trig tables ("with fewer mistakes"!) and the imperial system. I very much appreciate the full calculations are given. Well done, bravo.
I have been machining parts for over 50 years I never cut a gear in my life a while back a friend brought a 50 to 1 gearbox that was damaged needed a new worm. So some quiet time with my machinery handbook I was not able to find a pitch in metric Or inch, looking for that box of change gears I've never used nothing, I have faced such dilemmas trying to cut multiple start threads when you're already at the maximum thread pitch provided on the machine. That's when I realized what that one lever I've never used in my life was for. "The Magic Lever" π (pi) and Mod (module) inch and metric worms yay. Sure wish I had known about that a long time ago. Never too old to learn. Also I wish to thank you for your latest video on building the controller that makes it all work. Did something similar like 40 some odd years ago with a digital read out on a manual Mill to make roots blower rotors so as I moved the table in the X axis it rotated the rotor to the correct position. A friend of mine and myself prototyped what became a PSI blower they work great with methanol not so good with nitromethane it tends to go off in the blower with catastrophic results. Unlike a Roots style blower a rotary screw compressor actually compresses the air inside the blower way more efficient than a Roots blower that just beats the air to death bringing atmospheric pressure air into a pressurized manifold. Turning one of those massive pumps at about 10,000 RPM or more things start to go wrong the slow Helix on a roots rotor looked at linearly it's going the speed of sound making it difficult to the right amount of fuel in the cylinders fuel blobs bouncing all through the manifold rotary screw compressor takes what little air and a massive amount of fuel and attempts to compress that leading to a massive explosion as there is way more fuel than air and the nitro explodes in the blower you have the same issue inside the engine as more nitro exists than air as it is being compressed fortunately you have two spark plugs firing roughly 65°, before top dead center that begins the decomposition of the nitromethane molecule while still compressing it that is why top fuel cars make so much horsepower you're turning a cylinder filled with liquid into hot gas. Heat pressure 44 amps of spark times two each cylinder makes a thousand horsepower. My land speed car uses 500 lb nitromethane in under a minute to go 4 miles under power.
My hat is off to you not only for a literate demonstration of the process but also for all the little details; this one hit me square in the sense of ha-ha and I am glad for it!
Someone has been watching Pathé Films. 😆 I have plans to make my steam engine build in a similar manner. Fantastic job on the editing, voice and soundtrack.
I have been laughing out loud through this whole video. Thank you! I needed the info, being a newbie, but in a more digestible form. Your humorous approach is perfect!
Fabulous, I just watched your metric video, and was about to ask for the calculations for DP gears, as I want to cut some for a 1" minnie traction engine. I'm so glad that I scrolled down a bit, before I did. This video is brilliant, had me laughing my socks off! I think I finally understand gear cutting now. Now just to get my head around trig and I'm all set 😄
This was absolutely delightful! I burst out laughing when I saw the subtitle on the cover of the book of trig tables. I am old enough to remember learning to use trig and logarithm tables -- shortly before inexpensive electronic calculators became available.
Oh mate....very very fine work. Not just the Hobbs but this is just brilliant buddy 🤪 maximum effort well delivered. 🤪 I'll be laughing about this for weeks but very few people I know will get it. Great stuff.
Andy, this was wonderful! ;D About the only thing you missed was showing a steam-engine-powered, overhead-line-shaft/leather-belt machine shop doing the work for the lathe & mill work. ;) (And _I_ live in the US too!)
A little sarcasm on imperial precision of things but what missing in this imperial version is that the compound slide should be set to 14.5 degrees when cutting the hob.
True! I actually just reused footage from the metric version, I hardly ever cut DP gears myself, but nowadays they are mostly cut to 20° like metric ones rather than 14.5°
Enjoyed the tongue-in-check approach but in your earlier videos on building the Dividing Head "Gear Hobbilng Attachment" parts 1 & 2. You show the dimensions for the raw material but I'd really appreciate a set of dimensioned drawings. I am trying to work them out by watching the videos again and pulling screen shots and scaling them but a set of plans would make it a whole bunch easier. Keep up the good work.
Thanks! The dimensions are not really critical, you can build it any size to suit your needs. If you want it to tilt all the way to 90° you just need to allow enough space between the supports and height above the base for it to rotate all the way. I only did rough drawings myself when building this, but when I get time I will upload some dimensioned drawings to Patreon.
I guess you had as much fun making this as I had watching it. Very well done all round. You demonstrated that neither a ruler nor a thumb can measure the cutter width (which by itself makes this whole process cutting edge technology), but surely these old imperial geezers would have done it with cigarette papers, they seem to use those for nearly everything that needs measuring? Do you think there will ever come a day when a woman could make an imperial gear hob?
Quite good! Open questions: (Before having "rewatched" metric version :-) ) Did you grind relief on the teeth, or can you get away without it? How many teeth/gashes are you suggesting? Is a special assymetric relief for the cutter advisable to account for the helix angle? Do you mark the hob helix angle, pressure angle and pitch on the hob to remember all this?
I don't actually put any relief on the sides of the hob teeth and I keep them quite short because of this. It is possible to add this relief but it's a lot of extra work and doesn't seem to affect the cutting at least at the slow feedrates used in hobbing. I usually cut as many teeth as I can fit using one endmill to cut both the face of the teeth and the back relief of the next row of teeth at the same time. I find it easier to store small cutters in plastic bags with the information written on rather than try and put it on the cutter itself.
Really enjoyed the explanation - having just made a hob successfully for cutting worm wheels. I am a bit fuzzy on setting the helix angle of the hob relative to the worm wheel blank as the worm gear in use is smaller in diameter than the hob (both worm gear and hob were screw-cut at 12 t.p.i. with the same tool). The helix angle of the worm gear is 6.8degrees and that of the hob is 3.7degrees, so the hob was set relative to the worm wheel for hobbing at 3.1degrees, being the difference. The gears mesh well - but is this the correct way to do it?
If the hob is bigger than the worm I would probably do the same as you did and tilt it to make up the difference in the angles. Strictly speaking this will introduce a cosine error which will affect the cut, but at ~3° it will only be around 0.15% pitch error which is probably negligible. Obviously the worm won't make full contact with the teeth of the wheel, but probably not a problem, I have seen worms run with straight cut helical gears many times.
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?
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.
Next could you explain knerling and how rubbing against the piece in the lathe cuts the pattern. To me it just looks like the tool is pressing into the metal.
Question: When using the "New Fangled Ball Bearing Trick": I'm guessing the cutter has no rake angle and is raised half the ball diameter on a 0.125 gauge block so the helix clearance angle does not affect the new fangled measurement? How do we calculate the helix clearance angle for any given hob diameter? Thanks again
At the helical angle of it's spiral cut teeth so that they cut in the horizontal plane (the direction of feed). There's more detail about this in my other videos on building the hobbing attachment.
For a 16DP gear the pitch is pi/16, =0.1963" or 4.987mm, but yes close enough that you could get away with using 5mm, the total pitch error along the length of the hob would only be around 50 microns.
I'm not a specialist of english language nor a good english speaker for sure .. But am i right, that you are trying to sound much less birtish than normally, of course to fit those chevrolet educational documetaries?
I am disappointed! I bought that same bench grinder to try to follow this tutorial but they sent me a metric one and does not work for grinding imperial.😔 All jokes aside this video is funny as heck.
That's actually correct. Since 1959 the inch has been defined in mm. Before that there were different sized inches sometimes in use at the same time, such as the bigger Scottish Inch. Even today there is still the US Survey Inch which is fractionally different to the 'regular' inch (1/8" per mile difference), but it's being phased out in 2023.
