Thread: Gear ratios

Hi Mike,
What is the Leadscrew pitch, and the gears driving the QC box, plus the threads you can get with the 36 speeds on the box?

If the input into the box is going the same speed as the spindle, this makes things a bit easier. You should find your A,B,C will be 1:1, 1:2, 1:4 so for instance A1 might give you 2tpi, B1 will give you 4 and C1 will give you 8tpi. the other 7 gears should give you the pitches in between. A pic of the plaque would help a lot.

I know i have just given you imperial, but hopefully you get the idea.

Hi Ewan

What I am really asking is : Do I work out the 1st gearbox ratios ( 3 combinations ) , then work out the main QC gearbox ratios ( 12 combinations ) , so how I can then work out the overall ratios X 36 combinations

How do I work out the overall output ratio , knowing the 2 ratios that are involved x 36 times

Mike

PS if you can imagine a car with 2 gearboxes , one in front of the other ..how do you work out the overall ratio of each gear combination.......... eg ratio gearbox 1 input - gearbox 2 output

Mike

Originally Posted by morrisman

Hi Ewan

What I am really asking is : Do I work out the 1st gearbox ratios ( 3 combinations ) , then work out the main QC gearbox ratios ( 12 combinations ) , so how I can then work out the overall ratios X 36 combinations

How do I work out the overall output ratio , knowing the 2 ratios that are involved x 36 times

Mike

Mike

Yes, i would work out the 3 combo's first, then the 8. it doesn't really matter which way round you put them the answer is still the same.

It could just be that you don’t have to worry about the Quick Change gearbox. I’m aware of that gear calculating software you might have down loaded. I haven’t, but wouldn’t that be more to do with direct ratios, between the spindle and the lead screw? Like old school were you didn’t have a Q.C.

In that case you would just set the QCc to the lead of the screw, and let gear ranges do the magic.

Phil.

Thanks for the replies

this diagram will help explain things. I have a 12" lathe with a 4mm pitch leadscrew

The diagram is for a imperial version , the metric version ( mine ) has different teeth numbers

I'd like to be able to do imperial threads .

Mike

Hi Mike,
Just to add to what i have already said, when i was working out the ratio's for the box i want to make, i tried to make it a metric box (as i have a 3.5mm leadscrew) that i could then use change gears to cut imperial. I soon found however, that it was far easier to use change gears to "trick" the box into thinking it was an imperial leadscrew and make an imperial box that could cut a full range of metric threads with only 4 different change gear combinations. You may find you need quite a few change gears to get imperial threads out of a metric box, at least i did find this. Imperial is way easier to work around for ratio's!
Could you take a pic of the plaque on the box for me?

A few pics Ewan

There is a 127 change gear among the change gears that came with the lathe

Martin Cleeve mentions you can trick a lathe with a 4mm lead screw into thinking it has a imperial 8tpi lead screw . But he doesnt use the QC gearbox at all.

The 40 tooth gear in pic 2 has a gear behind it with a different DP .... odd isnt it

MIKE

Originally Posted by morrisman

A few pics Ewan

There is a 127 change gear among the change gears that came with the lathe

Martin Cleeve mentions you can trick a lathe with a 4mm lead screw into thinking it has a imperial 8tpi lead screw . But he doesnt use the QC gearbox at all.

The 40 tooth gear in pic 2 has a gear behind it with a different DP .... odd isnt it

MIKE

Hi Mike,
I'm guessing its an 80t that the 40t is driving.....if not i've stuffed this all up. I've called the 12 speed box A thru L to avoid confusion.

Ratio's are final drive ratio's thru both halves of the box.

.....A......B......C......D......E......F......G......H......I......J......K......L
1 .375--.35 -.325--.3 ---.275--.25 --.225---.2 -.175-.15- .125 -.1
2 1.875-1.75-1.625-1.5-1.375 -1.25 1.125 --1---.875-.75--.625 - .5
3 7.5----7----6.5--6----5.5----5----4.5----4----3.5---3---2.5---2

I'm pretty sure thats right.

Originally Posted by Ueee

Hi Mike,
I'm guessing its an 80t that the 40t is driving.....if not i've stuffed this all up. I've called the 12 speed box A thru L to avoid confusion.

Ratio's are final drive ratio's thru both halves of the box.

.....A......B......C......D......E......F......G......H......I......J......K......L
1 .375--.35 -.325--.3 ---.275--.25 --.225---.2 -.175-.15- .125 -.1
2 1.875-1.75-1.625-1.5-1.375 -1.25 1.125 --1---.875-.75--.625 - .5
3 7.5----7----6.5--6----5.5----5----4.5----4----3.5----3----2.5---2

I'm pretty sure thats right.

Hi Ewan

yes it is a 80 tooth gear driven by the 40

Your a maths genius

I dunno about maths genius....i have been chasing numbers round my head for the last few months thinking about my gearbox and i think i've finally got it all worked out......

I must say though, i find maths easier than dealing with some people.......maths works within a fixed set of rules and boundaries, where as people sometimes.........

Originally Posted by Ueee

I dunno about maths genius....i have been chasing numbers round my head for the last few months thinking about my gearbox and i think i've finally got it all worked out......

I must say though, i find maths easier than dealing with some people.......maths works within a fixed set of rules and boundaries, where as people sometimes.........

Out of interest , these are the change gears that camw with the lathe

14.5 PA

40 X 3

56

64

65

66

70

72

75

80 X 4

85

91

105

108

110

112

127 ..this gear is damaged , gouged and missing teeth

Originally Posted by morrisman

Out of interest , these are the change gears that camw with the lathe

14.5 PA

40 X 3

56

64

65

66

70

72

75

80 X 4

85

91

105

108

110

112

127 ..this gear is damaged , gouged and missing teeth

Wow, thats a good range of gears, have you punched them into the program yet? Shame about the 127, thats the one you'll need the most. I guess it shows that it was used a lot for imperial threads.

If you put the 127 in tandem with the 80 that the 40t drives and drive the box off that you will have a pseudo 8tpi screw.

With the box it looks like this in even tpi, (from smallest to largest)

80, 64, 40, 32, Thats the 1st gear,
16, 8, Thats it for the 2nd gear
4, 2, and thats all for no 3!

yes

I typed in the ratios and change gears

I tried 12 tpi as a test

It came out with many gear combinations ...

But, I am assuming the input gear to the 3 speed gearbox is 80 teeth , it looks that way on the lathe .

If it is a 80 teeth input gear ( gear D ) , the software gives quite a few combinations with that gear

It looks great . I will go down to the library and print out the various tpi and gear combinations. I will load the software into their computer , and uninstall it when I'm finished
Thanks .... for the help
MIKE

Mike, how badly damaged is that 127t gear? Can you throw up a picture?
If it's only one tooth missing I'm wondering whether you can put a pin or two in it and then build up with a metal epoxy mix. I once had a skilled welder braze a tooth back on a CI gear for me - it was such a good job I always keep a small lump of CI around the place in case I need to do it again.

Michael