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10th Oct 2020, 07:54 PM #181Golden Member
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30T m1.75 gives 10mm of meat between the thread and bore. I guess this is plenty.
I just tried the 74T m1.75 in position E and it doesn't quite fit but the 72T m1.75 should fit having a 3.5mm smaller radius.
80T m1.75 fits in position E and D & E will mesh.
Tomorrow I will try the templates for;
- (36/idler/127) * (60/72)
- (30/idler/127) * (80/80)
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10th Oct 2020, 07:59 PM #182Golden Member
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Def not stupid. I agree that it is possibly original. There is probably an idler missing from the top left position also. Anything could have happened after all these years and probably multiple owners. Happy to use the 63T m1.5 if we can make it all work. There are multiple conflicting issues - namely a set of ratios that work AND that fit in the case AND that mesh together!
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10th Oct 2020, 08:05 PM #183I break stuff...
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Wait, wha? Is the 74 not permanently attached to the 117 in some fashion? Or did you just offer it up to have a look, and CBF with removing the 72 to check that one?
If 80T m=1.5 (assume you typoed) fits, then logically 68T m=1.75 should also fit? And if you think that 72T m=1.75 might even fit now, then you can make D and E in m=1.75 anywhere from 68T to 72T as suits, save you needing to buy two cutters - providing of course you can make the (30/idler/127) work out.
I'd think 10mm is plenty of meat, but if worried about it make a long gear, and split it into multiples so you have spares!
Preferable to break an external change gear to anything else, but I doubt it will be an issue given how much more gearing is downstream anyway, and the typical loads in thread cutting (minus attempting to cut a thread through the face of the chuck of course, see point 1, lol).
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10th Oct 2020, 08:33 PM #184Golden Member
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Oh dear, the moose are laughing at me again.........
80T m1.75 would have definitely been a typo. And.......I tried the 72T m1.75 gear NOT the 74T. This means that the 72T m1.75 does not fit which stuffs up some things! The largest that will fit into position E will be 70T m1.75 or 82T m1.5 (126mm and 123mm respectively).
I agree with using m1.75 in positions D&E to minimise cutter purchases. I assume they are going to be horribly expensive!
36/127 55/66 works - will see if that fits as they are 9.625mm closer than the 50/60.
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10th Oct 2020, 08:41 PM #185I break stuff...
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Okay, if E can take 70T in m=1.75, and we're happy with 30T m=1.75 for bore diameter, then go for (30/idler/127) * (70/70), all in m=1.75.
That should allow you to get mesh between D and E, and if you can't get a whole tooth number on idler B with that configuration, take one tooth off both D and E at the same time (to maintain the 1:1 ratio there) and recheck. Rinse and repeat until you either lose mesh between D and E, or get a working idler.
If that fails, swap D and E to 82T m1.5, and repeat.
Hopefully SOMETHING in that range will work out!
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11th Oct 2020, 05:06 PM #186Golden Member
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Thanks for hanging in there J&H. I think Stu has gone Moose hunting.....
Good day in the shed. I got my new gears made!!
DummyGears2.jpgDummyGears1.jpg
These gears are the 30/idler/127 80/80 using 1.75/1.75/1.75 1.5/1.5. You can see that I have had to put the compound gear on backwards and will have to space the small and large gear on it apart by a gears width whereas the original one only had a 3mm gap. I will have to carefully measure the gear shapes then find a way to make them. That will be a great learning opportunity!
In case anybody is wondering why I have the gears touching, I have shaved each down by 1/2 the teeth depth. This means that if my wooden gears touch then the real ones will mesh teeth.
To keep everything the same mod I can change the 2 80T 1.5's for 70T 1.75 which is 3mm larger in diameter but will be damn tight in position E.
You can see I will need to make a do-dad to allow the idler to position correctly but this will just be some bar stock with a couple of holes.
I might go another step and design the gears in TurboCAD then 3D print them as an additional check that everything fits. I expect these gears will be an epic adventure for me so I want to get it right.
All this cos I wanted to cut an M20 screw thread so that I could make an arbour so that I could take 4mm off the OD of some wheel so that I could finish building my machine skates so that I can move some machines and organise the shed. One thing sure leads to another!!!!!!!!!!!!!!
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11th Oct 2020, 05:31 PM #187I break stuff...
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Looking good! Glad we found a combo that looks like it should work out.
Don't forget, in this config, the actual number of teeth on D and E is irrelevant - only matters that they're the same as each other. So whatever m=1.75 gear has the same OD as 80T, you can use that - eg 68/68, or 69/69. Just depends on what you can cut with your dividing plates. Hell, it just occurs to me, if you wanted to, you could grab a pair of timing chain gears off a car, or a couple of dirtbike sprockets, and make it chain drive from the back of the 127 to the input shaft!
The other good thing is that with two gears of the same tooth count and module, with a little planning you can actually cut both at the same time on a single piece, then split them! Efficiency!
I'd definitely 3d print a set. I was actually going to make this observation earlier, that if you had one you could actually print the gears, and they'll probably actually work for a decent while (and replacements are a low effort endeavour!). 127 might be an issue depending on your bed size is all.
So yep, print a set, and have a crack at cutting that 2.5mm thread on a test piece!
I expect a photo of said 2.5mm thread on my desk tomorrow morning.
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12th Oct 2020, 09:03 PM #188Most Valued Member
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Oh he is still around, its just that I am stuck halfway between you and franco. I agree with you regarding this gearbox not being built with "pretty damn close" in mind, but with franco about the 63 not being a ring in. Add to that "if the 117/74 isnt for imp/metric conversion, what is it for?". So I come back now and again to scratch my head for awhile lol
Could you give me some rough dimensions of the shaft splines please.
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13th Oct 2020, 06:05 PM #189Golden Member
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28mm OD and 23mm ID with 6 splines
I either need to find a way to cut these are buy a splined hub and mount a gear to it with an interference fit and key.
Cutters bought. Trying to design the gears on TurboCAD but it appears limited to 100 teeth using the easy method so will have to draw manually!
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13th Oct 2020, 06:38 PM #190Most Valued Member
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13th Oct 2020, 06:44 PM #191Most Valued Member
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While you are at it.
How about you work out how many teeth a gear with a 86.9mm dia would have?
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13th Oct 2020, 06:52 PM #192Golden Member
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13th Oct 2020, 07:19 PM #193Most Valued Member
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14th Oct 2020, 10:09 PM #194Golden Member
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I drew a gear.... 127T m1.75 30mm bore 17mm thick
Gear_127T_m1.75v3.JPG
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3rd Nov 2020, 07:39 PM #195Golden Member
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Test gears 3D printed. Will mount on the weekend and see if they fit correctly....
20201103_190637.jpg
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