Question on gear change to slow feed rate.

[GreggC]

I'm guessing that you have a G4000 or clone. If you run the 60 tooth gear in place of the 120 tooth gear and the 80 tooth gear in the b position, you should get down to .00176"/rev. You may be close to hitting the bushing behind the 80 tooth gear with the 127 tooth gear. If you have interference, swap the 120 tooth gear for the 127tooth gear and you should be good. That would increase the feed rate to .00186/rev.

Excellent,
Thank you !!

 

[savarin]

Does the 120 hang below the lathe and hit the bench ??

Not any more, I raised my lathe onto blocks for a better height for me.

I also cut out a section of the cover for clearance.

I removed the hinge bolt and replaced it with a ring pin for easy removal.

 

[GreggC]

Not any more, I raised my lathe onto blocks for a better height for me.
View attachment 261221
I also cut out a section of the cover for clearance.
View attachment 261222
I removed the hinge bolt and replaced it with a ring pin for easy removal.

I was just thinking about having to cutout the cover,
Whether I swap the 120 and the 60 or take RJ's suggestion at least I now know Ill be able to substantially
reduce the feed rate from the original .0047 to somewhere around .0018.
Looking forward to working with that.
Thanks guys !!

 

[Tozguy]

Way easier to change the "B" gear,
In fact the parts list shows may lathe came with a stack of gears and one is a 80 tooth
Item 123, Im gonna try it when I get off work.

View attachment 261140

Just curious about why it is easier for you to change gear B than change gear A. On my lathe the spare change gears will fit equally well on shaft A or B.

 

[GreggC]

Just curious about why it is easier for you to change gear B than change gear A. On my lathe the spare change gears will fit equally well on shaft A or B.

That comment was in reference to post #2,
Before any suggestions were made on swapping gears,
rgray commented " That or A gear smaller"
The "A" gear is a 28 tooth gear, going smaller
would mean having a custom gear made.
So in my mind its was easier to purchase the 80 tooth.

 

[Tozguy]

OK, I see, thanks.
If the spare change gears start at 28T, is the 'standard' gear that was already installed even smaller? On my lathe (12x36) the 'OEM' gear in position A is a 24T and feed can be set as low as .002''. Are you sure that a 28T gear is the smallest available to purchase for your lathe?
It seems a shame to have to start cutting covers or blocking up the lathe to fit a larger than intended gear on B if it can be avoided.

 

[GreggC]

OK, I see, thanks.
If the spare change gears start at 28T, is the 'standard' gear that was already installed even smaller? On my lathe (12x36) the 'OEM' gear in position A is a 24T and feed can be set as low as .002''. Are you sure that a 28T gear is the smallest available to purchase for your lathe?
It seems a shame to have to start cutting covers or blocking up the lathe to fit a larger than intended gear on B if it can be avoided.

I just had a chance to check the included gears with my lathe,
28t installed in "A"
Two 30T's
36T
42T
45t
60T installed in "B"
I just ordered a 80T

Im going to go with RJ's suggestion,
I will run the 60 tooth gear in place of the 120 tooth gear and the just now ordered 80 tooth gear in the b position,
As per RJ that will get down to .00176"/rev,
Going from .00476 to .00176, that should be perfect.

 

[GreggC]

I'm guessing that you have a G4000 or clone. If you run the 60 tooth gear in place of the 120 tooth gear and the 80 tooth gear in the b position, you should get down to .00176"/rev. You may be close to hitting the bushing behind the 80 tooth gear with the 127 tooth gear. If you have interference, swap the 120 tooth gear for the 127tooth gear and you should be good. That would increase the feed rate to .00186/rev.

RJ,
How do you calculate the feed rate with gear selection ??

 

[RJSakowski]

I kind of cheated. I used the published feed rate for the lathe and just did ratios. The 60 tooth gear replaced the 120 tooth gear which reduced the feed rate by 60/120 or .5. The 80 tooth b gear was replaced by the 120 tooth gear which reduced the feed rate further by a factor of 80/120 or .75. The overall reduction is .5 x .75 or .375. that reduction applied to your slowest stock feed rate would take it from .00476 to .00176.

The calculation can be done from scratch but to do so, You would have to know what the gearing gear box and in the carriage is.
edit: As pointed out by Tozguy, 80/120 = .6667. That ratio times .5 equals .3333 and the feed rate would be .0159"/rev. Thanks Toz!

 

[Tozguy]

The overall ratio through the 28T-127T/120T-80T drive is .33.
The overall ratio through the 28T-127T/60T-120T drive is .11.
So the change of ratio from one configuration to the other will cut the feed rate TO one third of whatever you start with (.11/.33)
Basically I agree with RJ's approach but there might be a math correction to consider.
(RJ please note that 80/120 = .6667 and not .75)