Gidday . hearty good wishes to All.
This subject would probably hijack the gearbox identification thread so I need a seperate thread.. This is a thread about Commando gear teeth . Not shells, shafts or bearings. mainly focusing on interchangeability and strength and design changes..
I will endeavour to be as factual as my knowledge allows. By nature, the subjects of strength and durability will get reasonably technical. Cant avoid this. so I will try and keep the technical jargon to a minimum though this may sometimes be necessary to speak jargon.
it is also intended to inform and educate lay people who may have an interest in the technical side of gears.
My experience is at trade level only. So any qualified engineers and others are welcome to chime in and correct me where necessary. Please do. I do not know it all and it is inevitable that I will stuff up somewhere.
where technical terms are necessary, I will try and give a definition of these terms and what they mean. Another purpose is to provide factual information that is relevant and accurate.
claims will be justified as best I can. the onus of proof is always with the person making the claims.
Some of my claims may challenge "conventional wisdom".
just like the "conventional wisdom" that claims line boring was used in crank case production.
gear design changes can be similar to head porting. yes, changes can be easily made.
but a design change may have negative consequences as well. so not all changes have to have a positive effect.
Stephen Hill, this thread may answer your question about increased load carrying capacity of early and late changes and the consequences of such change. i agree with you that there is no signifiant strength changes between early and late. though it may get a bit convoluted.
So a bit of basics for those interested.
A pinion will be the driving gear. A gear will be the driven gear.
the teeth of the pinion and gear touch at special diameters, roughly in the middle of the tooth... these diameters are known as the pitch circle. If the teeth were removed from gear and pinion, the imaginery point of contact will be where the pitch circles touch.
the pitch circle is very important.it has a dimension and can be calculated.
for any 2 gears to mesh, the spacing of the teeth on both gears must be the same.
but because the teeth are at an angle to each other, and the pitch circles differ in diameter, measurement of the spacing must be at a particular point. So where do we measure the tooth spacing. At the outside of the tooth, the bottom of the tooth or somewhere in between. the answer is somewhere in between. the pitch circle.
The center distance between pinion and gear is the distance in inches between the centres of the pitch circles.
So the pitch circle circumference divided by the number of teeth will give whats known as the circular pitch. or tooth spacing.
this tooth spacing must be the same for any meshing driver and driven gear.
But there are other factors also, such as the tooth width and depth. these must also be the same for any pair of meshing gears.
So we need something like a standard tooth size. so the size of teeth like thread pitches is standardised.
this standardised sizes is known as DP, or Diameteral Pitch. it has no measureable dimension and basically refers to a certain tooth size. it is expressed as a number only.
the numbers mean a 20DP gear has a very small tooth, 5 DP has a lot larger tooth, 1 DP is a very large tooth.
The bigger the number the smaller the tooth. 1 DP is the biggest standard tooth.
The tooth size of all AMC boxes since 1956 including our Commando's and Dommies etc is 10 DP. before that I dont know and this thread is only relevant to Post 1956 boxes.
Bigger teeth than 1 DP use a different system entirely that is not relevant here.
if any gear or pinion is of the same DP, the circular pitch or tooth spacing is the same, tooth thickness is the same and depth of tooth is the same. and they will mesh.
A 20 DP tooth will not mesh with a 5 DP size tooth.
end of sermon. a bit more basics to come before we get down to the nitty gritty. i do reckon this basic stuff is very necessary to follow what is to come.
If some kind person would post a drawing of gear teeth terminology that shows this stuff, especially pitch circle and tooth spacing, addendum, dedendum etc, it would be appreciated.
It is easier to look at a drawing to understand this. More to come . best wishes Aussie bradley
This subject would probably hijack the gearbox identification thread so I need a seperate thread.. This is a thread about Commando gear teeth . Not shells, shafts or bearings. mainly focusing on interchangeability and strength and design changes..
I will endeavour to be as factual as my knowledge allows. By nature, the subjects of strength and durability will get reasonably technical. Cant avoid this. so I will try and keep the technical jargon to a minimum though this may sometimes be necessary to speak jargon.
it is also intended to inform and educate lay people who may have an interest in the technical side of gears.
My experience is at trade level only. So any qualified engineers and others are welcome to chime in and correct me where necessary. Please do. I do not know it all and it is inevitable that I will stuff up somewhere.
where technical terms are necessary, I will try and give a definition of these terms and what they mean. Another purpose is to provide factual information that is relevant and accurate.
claims will be justified as best I can. the onus of proof is always with the person making the claims.
Some of my claims may challenge "conventional wisdom".
just like the "conventional wisdom" that claims line boring was used in crank case production.
gear design changes can be similar to head porting. yes, changes can be easily made.
but a design change may have negative consequences as well. so not all changes have to have a positive effect.
Stephen Hill, this thread may answer your question about increased load carrying capacity of early and late changes and the consequences of such change. i agree with you that there is no signifiant strength changes between early and late. though it may get a bit convoluted.
So a bit of basics for those interested.
A pinion will be the driving gear. A gear will be the driven gear.
the teeth of the pinion and gear touch at special diameters, roughly in the middle of the tooth... these diameters are known as the pitch circle. If the teeth were removed from gear and pinion, the imaginery point of contact will be where the pitch circles touch.
the pitch circle is very important.it has a dimension and can be calculated.
for any 2 gears to mesh, the spacing of the teeth on both gears must be the same.
but because the teeth are at an angle to each other, and the pitch circles differ in diameter, measurement of the spacing must be at a particular point. So where do we measure the tooth spacing. At the outside of the tooth, the bottom of the tooth or somewhere in between. the answer is somewhere in between. the pitch circle.
The center distance between pinion and gear is the distance in inches between the centres of the pitch circles.
So the pitch circle circumference divided by the number of teeth will give whats known as the circular pitch. or tooth spacing.
this tooth spacing must be the same for any meshing driver and driven gear.
But there are other factors also, such as the tooth width and depth. these must also be the same for any pair of meshing gears.
So we need something like a standard tooth size. so the size of teeth like thread pitches is standardised.
this standardised sizes is known as DP, or Diameteral Pitch. it has no measureable dimension and basically refers to a certain tooth size. it is expressed as a number only.
the numbers mean a 20DP gear has a very small tooth, 5 DP has a lot larger tooth, 1 DP is a very large tooth.
The bigger the number the smaller the tooth. 1 DP is the biggest standard tooth.
The tooth size of all AMC boxes since 1956 including our Commando's and Dommies etc is 10 DP. before that I dont know and this thread is only relevant to Post 1956 boxes.
Bigger teeth than 1 DP use a different system entirely that is not relevant here.
if any gear or pinion is of the same DP, the circular pitch or tooth spacing is the same, tooth thickness is the same and depth of tooth is the same. and they will mesh.
A 20 DP tooth will not mesh with a 5 DP size tooth.
end of sermon. a bit more basics to come before we get down to the nitty gritty. i do reckon this basic stuff is very necessary to follow what is to come.
If some kind person would post a drawing of gear teeth terminology that shows this stuff, especially pitch circle and tooth spacing, addendum, dedendum etc, it would be appreciated.
It is easier to look at a drawing to understand this. More to come . best wishes Aussie bradley
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