hy rico, just rereading the thread. all gears work on a sliding action thats how the pinion moves them. as the pinion revolves, the tooth thats been pushing on the big gear slides of, the next tooth thats engaged should just be starting to push. with a pinion of 5.5mm dia and different tooth counts,, look at the profile of the teeth. you go from a v shape on the 8t to a waisted profile with a little flatted ball on top in the 10t pinion, for clearance. this allows many different teeth sizes in a given diameter. im talking about inline motors, but the same applies, to a [fixed pinion and gear centres] on an anglewinder and sidewinder. down to the reason i was leading upto. gears are cut on a hob with the cutter set at a right angle to the centre of the gear so if you want a 1/8 offset you just move the cutter down 1/8 and cut the gears. this will give a perfect gearmesh if set up correctly at the 1/8 offset. it wont work if you try to set it it up in a straight line. the 1mm offset on slot it gears are a bit of a fudge up, it just happens that a slot it gear[inline] thats been cut on the centreline will work nearly as well if its been set up with a 1mm offset, if you tried to offset it anymore than 1mm you,d run into trouble pretty fast. end of my one finger typing marathon. john
same ratio dfferent gears
hy would some one like to explain the different combo,s, and why. take a 3-1 ratio, the standard is 9-27. going to extremes, what about 7-21 or 11-33 there must be a difference and i,d like to know. a euro sport runs 6-1 6-36 why. john
61 - 65 of 65 Posts
re: "all gears work on a sliding action thats how the pinion moves them"
with respect, that's not true...and that's one of the points I was trying to make earlier on. Any gear that's designed with the classic Involute profile (such as a sidewinder with pinion and spur,
as well as properly shaped contrates on inline setups) are specifically shaped to eliminate frictional losses from sliding contact. That's the whole point of the profile...it's by definition, the shape
which allows only "normal" reaction forces at all points of contact. You might think of it as "rolling" contact at all times.
That's why I'm saying that weight (inertia) is one problem...but going too small to save weight and sacrificing a well-formed gear profile isn't good either. There's a balance
that involves lightness, quality of profile and material stiffness for optimum performance. Sorry to repeat, but something like a thin, Aluminum, precise slot-it gear is a good example.
John
with respect, that's not true...and that's one of the points I was trying to make earlier on. Any gear that's designed with the classic Involute profile (such as a sidewinder with pinion and spur,
as well as properly shaped contrates on inline setups) are specifically shaped to eliminate frictional losses from sliding contact. That's the whole point of the profile...it's by definition, the shape
which allows only "normal" reaction forces at all points of contact. You might think of it as "rolling" contact at all times.
That's why I'm saying that weight (inertia) is one problem...but going too small to save weight and sacrificing a well-formed gear profile isn't good either. There's a balance
that involves lightness, quality of profile and material stiffness for optimum performance. Sorry to repeat, but something like a thin, Aluminum, precise slot-it gear is a good example.
John
QUOTE (John Cahill @ 20 May 2012, 23:44) <{POST_SNAPBACK}>re: "all gears work on a sliding action thats how the pinion moves them"
with respect, that's not true...and that's one of the points I was trying to make earlier on. Any gear that's designed with the classic Involute profile (such as a sidewinder with pinion and spur,
as well as properly shaped contrates on inline setups) are specifically shaped to eliminate frictional losses from sliding contact. That's the whole point of the profile...it's by definition, the shape
which allows only "normal" reaction forces at all points of contact. You might think of it as "rolling" contact at all times.
That's why I'm saying that weight (inertia) is one problem...but going too small to save weight and sacrificing a well-formed gear profile isn't good either. There's a balance
that involves lightness, quality of profile and material stiffness for optimum performance. Sorry to repeat, but something like a thin, Aluminum, precise slot-it gear is a good example.
John
Which leads into the concept that a 3:1 ratio (ie 27/8 = 3) is only the average mechanical advantage over a complete revolution. At any point in time the actual advantage may be less than 3:1 or more than 3:1. This is due to the fact that the pinion does not slide against the spur. The "rolling" action sees the point of contact of the pinion on the spur move from the land of the spur down towards the base. This effectively changes the mechanical advantage. Then as that tooth disengages the following tooth engages and the whole process starts again.
cheers
rick1776
with respect, that's not true...and that's one of the points I was trying to make earlier on. Any gear that's designed with the classic Involute profile (such as a sidewinder with pinion and spur,
as well as properly shaped contrates on inline setups) are specifically shaped to eliminate frictional losses from sliding contact. That's the whole point of the profile...it's by definition, the shape
which allows only "normal" reaction forces at all points of contact. You might think of it as "rolling" contact at all times.
That's why I'm saying that weight (inertia) is one problem...but going too small to save weight and sacrificing a well-formed gear profile isn't good either. There's a balance
that involves lightness, quality of profile and material stiffness for optimum performance. Sorry to repeat, but something like a thin, Aluminum, precise slot-it gear is a good example.
John
Which leads into the concept that a 3:1 ratio (ie 27/8 = 3) is only the average mechanical advantage over a complete revolution. At any point in time the actual advantage may be less than 3:1 or more than 3:1. This is due to the fact that the pinion does not slide against the spur. The "rolling" action sees the point of contact of the pinion on the spur move from the land of the spur down towards the base. This effectively changes the mechanical advantage. Then as that tooth disengages the following tooth engages and the whole process starts again.
cheers
rick1776
27-9 is a 3-1 ratio, which is neither here or there. you,ve got the concept upside down. the very tip of the pinion does all the work and the mechanical advantage does change as you said. take it that that the pinion is fully engaged on the centre line, as the pinion revolves, the tip only, slides along the land of the driven gear pushing it downward till it disengages and the next spline of the pinion slots in. at no time should the back of the pinion spline touch the rear land of the driven gear. hence all the funny tooth shapes, which are found on different teeth counts with the same dia pinion. idealy the top of a pinion tooth would be ball shaped, to minimize friction and noise as it rolls-slides down the land of the gear thats being driven. john
61 - 65 of 65 Posts
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