Pressure angle of Schaublin change gears?
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  1. #1
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    Does anyone know the pressure angle and module of the change gears for the 102 threading attachment? I'd rather cut them than buy, Schaublin is mighty proud of their spares.

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    Hi ... I guess this is not what you'll probabily want to hear ... but I've been down the same road trying to get some 102VM gears and a replacement gear for the Schaublin 13 ...

    ... after some research from gear companies here in England I was advised that Schaublin use very "Non-standard" sizes to obviously stop people doing just going elsewhere. In the case of the Schaublin 13 gear it was going to cost me more than Schaublin's price, and that high enough!!

    I sincerely hope you can prove the above statement wrong ... and advise me of your findings.

    Best of luck

    John

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    Hi guys.

    I have had a look at the changewheels for a 102N-VM. They look like they are simply module1. A 60 tooth wheel has a diameter of 62 mm. A module 1 gear miller fits nicely between 2 teeth.

    Cheers
    Erik

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    Thanks guys- Just grabbed a gear and popped it on the projector, sure looks like a module 1 alright. Can't seem to find a calculation in my books to find the pressure angle though... maybe a call to Schaublin is in order. Will keep you posted.

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    Thanks guys for the info on gears.
    Can someone state how many gears are included with the 102N-vm, as i also need these (bought without) and i will make them in my own workshop. Alright thery are module 1, but sizes, no. of pieces and so on...
    Thanks!

    Vladimir

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    Vladimir ... Here's a complete list from my 102VM manual, that should get you going

    24T(2), 25T, 28T, 30T(2), 32T, 35T, 36T, 40T(2), 45T, 48T, 50T, 55T, 60T, 65T, 66T, 70T, 80T, 90T, 95T, 100T(2) 120T and 127T ... this should be 26 gears in total!

    Good luck ...

    John

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    Sorry John - the "N" model has another set.
    There are 31 total:

    30, 50, 55, 60, 64,
    72, 3x75, 2x80, 81, 83,
    84, 90, 92, 93, 96,
    98, 2x100, 101, 102, 104,
    108, 116, 2x120, 125, 126,
    127

    Hi Vladimir - you know why I am collecting this info.

    Cheers
    Erik

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    Hi Eric ... No problem, thanks for clearing that up

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    Thank you Erik and Milflyer!
    It will help me a lot! [img]smile.gif[/img]

    @Erik: Yes i know, i am working on it and hope to have some news in the next few days!

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    Hi Screwmachine, did you ever find out what the PA is and any other useful info as I am in the same position needing to make gears for the 102-VM. Thanks, Adam

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    If someone has some extras or is making them I'd be interested in purchasing a number of them since the set that came with mine is very limited.

    Thanks
    Andy

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    Hello,

    I have a lot of extra gears for the 102vm and the 120vm.
    If you are interested, let me know
    img_6240.jpgimg_6245.jpg

    Regards,
    Matthias

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    Stewart,

    Here is a link to a page that tells how to measure pressure angle of an unknown gear.

    How to Measure Pressure Angle of a Gear – Gear Pressure Angle, Gear Terminologies, Equations

    Probably the easiest way would be to draw it up in CAD and measure the angle.

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    Quote Originally Posted by SIP6A View Post
    Here is a link to a page that is full of shit.
    Fixed that for you

    For example : "Now measure the addendum ..."

    Get real. There is no way to do this. Period.

    " ...subtract the double addendum from the outer diameter and you will get the pitch circle diameter"

    More horseshit. Pitch diameter is an imaginary number, there is no way to measure it. You can calculate it from the number of teeth in the mating parts and the center distance, but you can't measure it.

    This page is crap.

    Probably the easiest way would be to draw it up in CAD and measure the angle.
    How the hell do you plan to do that ? Seriously ? Pressure angle is another mathematically derived number, it's not something you can meaure directly.

    Some potential methods in general use :

    Gear tooth gages. They come with both 20* and 14.5* racks. The one that rolls smoothly is the correct one. This is assuming it isn't something less common, like 17 1/2* or 22 1/2* or even something the manufacturer used specifically to thwart aftermarket guys.

    Wires. Calculate the m.o.w. for different size wires at two or three different diameters for both pressure angles. See which one is closest. This is probably the only truly accurate way to do this.

    Comparator. If you do have a program that will correctly draw involute curves, then you could try recreating the gears on paper either manually or with cad, then use an optical comparator to judge which is correct. But to do this, you're going to have to figure out a lot of other stuff as well. May as well just do the wires method and be finished.

    Me, I'd just go with 20* for starters cuz 14 1/2* metric gears are rare as hen's teeth. 25* teeth are more for heavily-loaded power transmission parts, so not as likely. Quick check, if you think they are 1 Mod is grab a one mod gear and see if it rolls smoothly. If it feels grinchy, then go to Step B.

    The other one to watch out for would be perhaps 22 1/2*. Twenty-two-anda-half rolls very smoothly, and if they were high-quality (Schaublin is, yes ?) and famous for making something "special", then this would be a possibility. Sometimes the mental guesswork is just as important as the "I'ma gonna measure this" detective work.

    1 Mod is pretty dinky. Better get out the magnifying glasses

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    Seamoss
    Don't change the wording of my post trying to make yourself look clever. It just makes.you look like a dick.

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    Thought about this last night, you are probably right about the dick thing but the complete explanation is long. Oh well, maybe I deserve this ...

    First off, that page's explanation of how to figure the DP is

    1) impossible. There is no way to "measure the addendum" so how are you expected to deduct two addendums from the o.d. ?

    2) mentally retarded. Do this instead

    Count the number of teeth and measure the o.d. Add two to the number of teeth and the o.d. of the part will be the pitch diameter of the +2 part. For example, if there are 30 teeth and the o.d. is 3.200, then the pitch diameter of a 32 tooth gear with the same size teeth is 3.2" therefore the DP is 10. (32/x=3.2, x=10)

    Easy and the normal way to guess at the DP of a tooth. No idea where they picked up that weird-ass plan.

    However ....

    The basic flaw in all of these discussions is a misunderstanding about gear engineering. All of the calculations in charts are a myth. Like eastern religions, the numbers we talk about are pointers to a concept, not the thing itself. I have never even seen this correctly explained in gear books, since engineers are seldom mystics. They just gloss over the discrepancies with words like "operating pitch diameter" and so on. But just like religion, it's all wrong and all lies if you take it literally.

    For example : imagine that you want a 3:1 ratio on 8" centers. Shafts are exactly 8" apart and you place a friction-driving disc on each one in 1:3 proportions. Now you have a 4" diameter disc on the driving shaft and a 12" diameter disc on the driven shaft. These are your pitch diameters. The REAL pitch diameters. This is the fiction upon which all gear engineering is based.

    Is there perfection in real life (tm) ? Of course not. It's a hot day in Phoenix and an aluminum housing in the sun. Expand the shaft distance a tiny bit, say .005" Do the friction discs touch ? No power transmission. The real pitch diameters MOVE with circumstances.

    It is not possible for a gear to have a pitch diameter or a pressure angle by itself. It only has these features in relation with another gear at a real distance.

    Since we cannot have perfect teeth on perfect center distances with absolute stiffness and no backlash, it is impossible for these "standard" numbers to ever be the truth. So when we say that a 10 DP gear with 32 teeth has a 3.2" pitch diameter, that's a convenience. And it works well enough 90% of the time. But if you depend on this when trying to back-calculate a gear, you can get into big trouble by expecting it to be reality.

    It gets worse. Lets take our 3:1 ratio example and put it into practice. I want to transmit 15 hp with this thing, so I'll choose 8 DP teeth. I have tinnitus and appreciate quiet, let's use 14 1/2* pressure angle. Standard sizes, people will have cutters, can transmit that much power no problem. 8" is huge, let's use 4" centers. It's only 15 hp, we don't need a box big enough for the Enterprise. Numbers of teeth will be 16 on the pinion and 48 on the gear. Perfect.

    Oops. Maybe not perfect. I'm going to get undercut on the pinion making it weak and at 16 teeth to 48 teeth, it will wear much faster than the gear. I can make it harder than the gear to help with wear but how about the undercut ?

    Take the 16 tooth blank and cut 15 teeth on it. You can do this quite easily with off-the-shelf hobs or shaper cutters. It works great, it's common and the slang term is "drop-tooth gear" but if you go to reverse engineer this thing with charts off a website, you're going to be in deep poo. Using the simple formulas nothing is going to calculate out correctly. We say it's 8 pitch because it rolls with an 8 pitch rack but it isn't really 8 pitch.

    Due to the generosity of the involute curve, different chart pitches and pressure angles will roll correctly together if the base pitch is the same. All the standard formulae are more of a guideline or a shorthand than they are factual, in many real world applications.

    Another very common situation is in automotive use. The maker is stuck with some arbitrary center distance but he wants to achieve a specific ratio. The gear designer will drop a tooth here or add a tooth there to change the ratio. In many cases you can do this with off-the-shelf "standard" cutters. But the teeth themselves are nowhere near "standard" anymore. Try to reverse engineer it strictly from charts and you're going to be up shit creek.

    Another common case would be replacements. Real world example, Ducati gearboxes were not up to snuff. Metric center distances. I made replacements, DP teeth. Even worse, to make it all fit I used stub tooth cutters and then for reasons related to dog diameters, interfering shafts in the enclosure, wear and strength desires and so on, all the teeth on both shafts were non-"standard." Reverse calculate that from simple charts and see where you end up.

    Let's do another because I like this one. Rear end gears. One drawback to hypoids is the massive amount of sliding they incur. Sliding = friction, friction = heat, heat = bad. With involute teeth there are three basic zones - approach action, where the teeth are sliding against each other, the middle mostly rolling area, then recess action where the teeth are sliding away from each other. Approach is obviously the worst from the standpoint of friction. So the people designing rear ends modified the teeth to have mostly recess action. This is why backing up is way noisier than going forward. Try to reverse engineer these teeth off a chart.

    There is more but I will stop I hope you can see that this isn't just "being a dick." The fictions about pitch, pitch diameter, pressure angle and so on are useful. In many cases they are close to the truth. But it is not realistic to assume that they are always going to be the truth and you can just insert measurements into a chart to reverse engineer a gear.

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  18. #17
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    If these are change gears pitch diameters are adjustable
    If in doubt I would replace all the gears with new stock gears
    These are cheap to get
    For example I pay for a M1 Z=20 €2.54 Z=50 €6.68 Z= 110 €15.96 Z=127 €19.49

    Peter

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    Peter is dead on the money!
    If these are change gears , just make a complete set and use off the shelf gears...Don't need to know the pressure angle...Now if only one is needed, then that is another story....

    Cheers Ross

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    Quote Originally Posted by AlfaGTA View Post
    If these are change gears , just make a complete set and use off the shelf gears...
    Been there, done that It seemed like every time I did anything I needed a gear that wasn't in the catalog. Usually a prime

    I'd first just buy one and see if it rolled. If they roll smoothly, that's all that counts.

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    Hi, do you still have those gears up for sale?


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