- Thread starter Pete.
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julianthegypsy
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Amazing!
Pete.
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That has taxed my brain just reading all the machines needs to cut the gear...what an addition to the sheds arsenal that is
To be honest, it SEEMS really complicated, and learning it is a trial without the benefit of a solid maths education or machinist's apprenticeship but once you've got over the concept it's just a matter of applying the numbers correctly. It's daunting to begin with but once you have it figured out it's not so bad you just got to be careful with the steps. That's why I've taken the time to write it out here, because someone is going to come along one day in the same situation and hopefully my thread will help it to 'click' for them.
pressbrake1
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I can’t even remember my phone number these days so mighty impressive!
Hat very much off sir!Now that we have the index and feed gears set up, if we were cutting a spur gear we would be done. For a helical gear though we have to use the differential. This is exactly what it says, a differential set indide the machine that can add a percentage of turn to the index wheel to increase or decrease it according to the tooth pitch and helix angle being cut. This uses a 4-gear train and has to be calculated to a minimum of 5 decimal places for accurate gear cutting. To work out the gears you need the following:
Gear tooth pitch (also known as normal pitch) - I chose 1 module as it is a smallish tooth so puts a low stress on the machine and also makes the calculations a little bit simpler.
Helix angle - I chose 10 degrees just because
Machine constant - this is a number given by the manufacturer for the purpose of these caculations. It's specific to the model of machine and for my hobber the machine constant is 0.6366. Not having this number makes life VERY difficult so any machine which it is not known for it all but useless unless you put a lot of work into discovering it.
The manual gives a table of change gears for DP pitch gears and common helix angles but I am cutting a module gear so I have to use the formula given:
View attachment 427583
So the formula is 1.616964 x the sine of my helix (10deg) dividied by the module (1). Luckily you can get a full set of natural sine tables by downloading old gear cutting books. I got mine from Brown & Sharpe's book on milling operations published about 100years ago. The table gives the natural sine for 10 degrees as 0.17365.
View attachment 427595
So my decimal ratio for figuring out the 4 gear train is 1.61694 x 0.17365 (Divided by 1 which does nothing here) = 0.2807857986
Now there is a way of figuring out 4 gear trains from a decimal, and there are books with hundreds of pages of tables to look them up, but I don't need to use these as there is a clever guy who has written a program to do the job and shared it for free. It's called decimal to change gear. You put in the decimal, tick the boxes for all of the gears you have available and it will give you as many combinations of change gears as it can generate. I have all gears from 22T to 80T so I tick all those and put in my number and get the following result:
View attachment 427584
So now I have my 4 gear train: 29 driving 76 coupled to 39 driving 53. I try to set this up on my machine and find that the 39 won't reach the 53. No problem because on any gear train, any driver can be swapped with any other driver and any driven can be swapped with any other drive without changing the overall ratio. So I swap the 76 with the 53 and it all fits.
View attachment 427585
So, now I have spent hours reading and understanding, watching youtube videos, scouring old forum posts, downloading books and doing research. I spent an hour getting the 3 gear trains set and the blank mounted, the hob fitted and head angle set just right. It was time to hit the power lever.
It starts cutting and the tooth spacing looks good:
View attachment 427588
I watch it carefully and it does look like it's cutting the gear properly. If it was set wrong in any way it would be very apparent by now.
View attachment 427587
And then in just about 4 minutes it's done and the gear is cut. A bit of an anti-climax in the end which is how it should be. Gear hobbing is all stup then a few minutes cutting.
View attachment 427589
Anyway here it is, my first gear cut n this machine ad my first properly-cut helical gear. I shall keep it as a trophy
View attachment 427590
Windy Miller
Semi-Professional Potterer!
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There’s something quite hypnotic about that!
What cutting fluid does it use @Pete.Now that we have the index and feed gears set up, if we were cutting a spur gear we would be done. For a helical gear though we have to use the differential. This is exactly what it says, a differential set indide the machine that can add a percentage of turn to the index wheel to increase or decrease it according to the tooth pitch and helix angle being cut. This uses a 4-gear train and has to be calculated to a minimum of 5 decimal places for accurate gear cutting. To work out the gears you need the following:
Gear tooth pitch (also known as normal pitch) - I chose 1 module as it is a smallish tooth so puts a low stress on the machine and also makes the calculations a little bit simpler.
Helix angle - I chose 10 degrees just because
Machine constant - this is a number given by the manufacturer for the purpose of these caculations. It's specific to the model of machine and for my hobber the machine constant is 0.6366. Not having this number makes life VERY difficult so any machine which it is not known for it all but useless unless you put a lot of work into discovering it.
The manual gives a table of change gears for DP pitch gears and common helix angles but I am cutting a module gear so I have to use the formula given:
View attachment 427583
So the formula is 1.616964 x the sine of my helix (10deg) dividied by the module (1). Luckily you can get a full set of natural sine tables by downloading old gear cutting books. I got mine from Brown & Sharpe's book on milling operations published about 100years ago. The table gives the natural sine for 10 degrees as 0.17365.
View attachment 427595
So my decimal ratio for figuring out the 4 gear train is 1.61694 x 0.17365 (Divided by 1 which does nothing here) = 0.2807857986
Now there is a way of figuring out 4 gear trains from a decimal, and there are books with hundreds of pages of tables to look them up, but I don't need to use these as there is a clever guy who has written a program to do the job and shared it for free. It's called decimal to change gear. You put in the decimal, tick the boxes for all of the gears you have available and it will give you as many combinations of change gears as it can generate. I have all gears from 22T to 80T so I tick all those and put in my number and get the following result:
View attachment 427584
So now I have my 4 gear train: 29 driving 76 coupled to 39 driving 53. I try to set this up on my machine and find that the 39 won't reach the 53. No problem because on any gear train, any driver can be swapped with any other driver and any driven can be swapped with any other drive without changing the overall ratio. So I swap the 76 with the 53 and it all fits.
View attachment 427585
So, now I have spent hours reading and understanding, watching youtube videos, scouring old forum posts, downloading books and doing research. I spent an hour getting the 3 gear trains set and the blank mounted, the hob fitted and head angle set just right. It was time to hit the power lever.
It starts cutting and the tooth spacing looks good:
View attachment 427588
I watch it carefully and it does look like it's cutting the gear properly. If it was set wrong in any way it would be very apparent by now.
View attachment 427587
And then in just about 4 minutes it's done and the gear is cut. A bit of an anti-climax in the end which is how it should be. Gear hobbing is all stup then a few minutes cutting.
View attachment 427589
Anyway here it is, my first gear cut n this machine ad my first properly-cut helical gear. I shall keep it as a trophy
View attachment 427590
Onoff
In the land of the unfinished project I am King!
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You do yourself a disservice. We know you can though!
Sergei Slovenija
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can you share a link to this resource? Thank you
Pete.
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E T
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Pete already did. Post #86 in this thread.
