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After doing a lot of playing around with calculations and spread sheets I have pretty much determined that the 127/120 transition is about the only good way to go on the 13" South Bend. I certainly have not come up with a combination which works. 127/120 = 1.058 and 62/59 = 1.0508. I am not sure if that is close enough. In any case I think that I would need an idler gear in the mix to make up the span between the spur gear and the shaft gear. I have not checked that yet. Probably just purchase the 3D printed gear set from eBay for $199. My printer will not print something that big. Probably not going to happen because I do not need metric threads very often.
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You might not need metric threads very often, but like a lot of things, when you need it, you need it, often NOW----.'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' KindelbergerComment
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Those numbers end up with an error of 0.75%. You'd be much closer with one of the other combinations such as 47/37. That would give less than 1/10 the error of the 62/59 combination.Originally posted by GordonL View Post
CNC machines only go through the motions.
Ideas expressed may be mine, or from anyone else in the universe.
Not responsible for clerical errors. Or those made by lay people either.
Number formats and units may be chosen at random depending on what day it is.
I reserve the right to use a number system with any integer base without prior notice.
Generalizations are understood to be "often" true, but not true in every case.Comment
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The problem is that it must match the 127/120 ratio not the 127/100 ratio. The 13" SB has a 6TPI leadscrew and the others have a 8TPI leadscrew so that means the that the input ratio must be different.Originally posted by J Tiers View PostComment
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It seems that is true only if the gears have to do "double duty".
The ratio set up in the idler train to the gearbox should already fix the ratio. Then you should be able to use the 127/100 combination.
Only if you need one set of gears to do both the metric conversion and the 6tpi ratio conversion should you need to have the other ratio. You can split the conversions between two combinations, which just means adding the metric conversion to the gear train that already correctly creates inch threads.CNC machines only go through the motions.
Ideas expressed may be mine, or from anyone else in the universe.
Not responsible for clerical errors. Or those made by lay people either.
Number formats and units may be chosen at random depending on what day it is.
I reserve the right to use a number system with any integer base without prior notice.
Generalizations are understood to be "often" true, but not true in every case.Comment
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I will have to play around with that. The existing gear train gives an input of 1 to .375 of spindle to screw gear so if I add a combo gear in that ratio I should be able to use the 100/127 or equivalent. There is already an 80 tooth gear in the train so adding a 30 tooth combo should accomplish that. I will have to do some playing around with CAD to see how things fit.Originally posted by J Tiers View PostLast edited by GordonL; 03-18-2023, 09:39 AM.Comment
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Can you use the 91/86 gears like in my lathe? Its ratio is very close to 127/120.Originally posted by GordonL View PostComment
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I think the reason for not using 91/86 is that it's a lot of teeth so going to cost more than one of the other versions. Also most of the time you can make do with a 50 instead of the 100 (or 60 for the 120) and put in a 2:1 in the gearbox thus using a cheap common gear. If you can't fit a 127 on your printer at those prices it is better to buy a bigger printer; an Ender 3 will print 8 ins.Comment
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