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Ringo
07-22-2019, 07:52 PM
Here is the sainted Logan speed chart from the hallowed book:
whats wrong with this picture?

http://bbs.homeshopmachinist.net/attachment.php?attachmentid=5643&d=1563547126


Here is the speeds as I did the pulley math:
whats wrong with this picture?


http://bbs.homeshopmachinist.net/attachment.php?attachmentid=5694&d=1563839478

PStechPaul
07-22-2019, 08:50 PM
Maybe a picture of your lathe pulleys is what we need to look at. I bet they don't look much like the illustration.

nickel-city-fab
07-22-2019, 08:51 PM
It looks to me like pulleys numbered 4 and 5 have been swapped for something non standard

oxford
07-22-2019, 09:01 PM
It seems like it would be a whole lot easier if you just made your own speed chart and taped it to the lathe. If what you say is correct there is a typo in the book, not the first time this has happened.

A.K. Boomer
07-22-2019, 09:23 PM
can you tell us just where your discrepancy is and how you arrived to that conclusion?

Ringo
07-22-2019, 09:35 PM
can you tell us just where your discrepancy is and how you arrived to that conclusion?

this started with this post:
http://bbs.homeshopmachinist.net/threads/79402-Need-help-with-pullet-diameter-ratio-math-please

I kept asking why there is something wrong, my lathe is running too fast, etc., etc.
I grind tool bits and only get smoke and chatter, I couldnt figure it out,
The discrepancy is that the speeds in the chart are listed in sequence from left to right,
when actually,
they should be listed from top to bottom,
THAT is why I couldn't figger out how to grind a bit, nor run the machine,
Hells bells, if position 1-3 was fast, then 2-3 is totally out of the question, right?
WRONG!!
The Logan book was sending me in the wrong direction to get to the sequential speeds.

PStechPaul
07-22-2019, 09:41 PM
Or, use the lathe to make pulleys that match the chart?

RB211
07-22-2019, 09:49 PM
How about we just flip the bird to the book and charts, and we make the lathe do what you want? I suggest a 3phase motor and a VFD. Easier than making new pulleys, and more capability.

Sent from my SM-G950U1 using Tapatalk

A.K. Boomer
07-22-2019, 09:56 PM
this started with this post:
http://bbs.homeshopmachinist.net/threads/79402-Need-help-with-pullet-diameter-ratio-math-please

I kept asking why there is something wrong, my lathe is running too fast, etc., etc.
I grind tool bits and only get smoke and chatter, I couldnt figure it out,
The discrepancy is that the speeds in the chart are listed in sequence from left to right,
when actually,
they should be listed from top to bottom,
THAT is why I couldn't figger out how to grind a bit, nor run the machine,
Hells bells, if position 1-3 was fast, then 2-3 is totally out of the question, right?
WRONG!!
The Logan book was sending me in the wrong direction to get to the sequential speeds.

All I can tell you by the looks of the picture is that if 1-3 is fast then 2-3 IS a whole lot faster,,, that's what the picture shows...

Ringo
07-22-2019, 10:12 PM
How about we just flip the bird to the book and charts, and we make the lathe do what you want? I suggest a 3phase motor and a VFD. Easier than making new pulleys, and more capability.

Sent from my SM-G950U1 using Tapatalk

That is forthcoming,,,,
the original motor pulley crapped da' bed, spun on the shaft.
So, I been unhappy with this machine (or couldn't figger it out) for awhile,
so, new pulleys and ratios are forthcoming.
Stay tuned.

Ringo
07-22-2019, 10:14 PM
All I can tell you by the looks of the picture is that if 1-3 is fast then 2-3 IS a whole lot faster,,, that's what the picture shows...

NO, !!!
that is actually the next logical step.
Look at the second chart, that is the one I did the manual math on.
The Logan chart is all dorked up.

RB211
07-22-2019, 10:17 PM
So a new drive system is forthcoming, so what is this current discussion about? That something printed doesn't make sense? Or trying to make sense of it?

A.K. Boomer
07-22-2019, 10:18 PM
don't care about the math just yet - im telling you that if 1-3 is fast then 2-3 is a whole lot faster, and according to the logan chart they do show that...

A.K. Boomer
07-22-2019, 10:21 PM
in fact - just eye balling the motors pully size it is your math that is way way off,,, again and i reiterate - if 1-3 is fast then 2-3 IS A WHOLE LOT FASTER --- and way way more than what your math is showing...

RB211
07-22-2019, 10:30 PM
Please post a picture of your drive

Sent from my SM-G950U1 using Tapatalk

PStechPaul
07-22-2019, 10:33 PM
Here is some more information on the Logan lathe pulleys. The following mentions motor pulley sizes of 2.31" and 4.28", or roughly a 2:1 ratio for high/low speed range.

https://www.hobby-machinist.com/threads/logan-200-pulley-size.16925/

The following spec sheet shows speeds of 179, 334, 420, 620, 780, 1450:

http://www.lathe.com/catalogs/210.pdf

General info:

http://www.lathes.co.uk/latheparts/page3.html

Pulleys available on eBay:

https://www.ebay.com/sch/i.html?_nkw=logan+lathe+pulley

A.K. Boomer
07-22-2019, 10:33 PM
The logan chart is right on the money - maybe he has his motors pulleys flipped along with his countershaft and is just going by 1 and 2 like in the logan chart,,,

but make no mistake - the logan chart is correct in everything stated - that's just eyeballing the ratio's but im good at that and they match up with the specs...

754
07-22-2019, 11:00 PM
How about this, did it to my Southbend.
Mearsure speed, I used mechanical Starrett tach. Then write them on the pully guard or the wall..
Is there any other way ?

A.K. Boomer
07-22-2019, 11:09 PM
they also make those RPM guns - you stick a piece of reflective tape on the pulley or whatever and then just point and read,,, i think their pretty cheap now...

J Tiers
07-22-2019, 11:32 PM
The logan chart is right on the money - maybe he has his motors pulleys flipped along with his countershaft and is just going by 1 and 2 like in the logan chart,,,

but make no mistake - the logan chart is correct in everything stated - that's just eyeballing the ratio's but im good at that and they match up with the specs...

it looks so far as if that is not so.... to get the speeds, you actually have to alternate between range 1 and range 2.... each alternate speed in the range is in the opposite chart portion from what is shown, even though the speeds are all there.

The ratios in the chart disagree with each other as well, the ratio between 4 & 5 does not seem to agree between range 1 and range 2. that may be due to the screwed up position of the speeds.

Now, I don't think that is so horrible, the ranges are only approximate, with a built-in error of at least 6% just due to the motor slowing under load.

A.K. Boomer
07-22-2019, 11:43 PM
it looks so far as if that is not so.... to get the speeds, you actually have to alternate between range 1 and range 2.... each alternate speed in the range is in the opposite chart portion from what is shown, even though the speeds are all there.

The ratios in the chart disagree with each other as well, the ratio between 4 & 5 does not seem to agree between range 1 and range 2. that may be due to the screwed up position of the speeds.

Now, I don't think that is so horrible, the ranges are only approximate, with a built-in error of at least 6% just due to the motor slowing under load.

JT - it's box stock simple and A-typical,,,

You keep it in low (or 1) on the motor side and then use the finer increments of 3-4-5 on the spindle countershaft part --- when you want the next ratio higher then you drop it into high (or 2) on the motor and then again walk your way up from 3-4-5 again on the spindle side... that's what both the chart shows and I might add what the pulleys ratio's show...

A.K. Boomer
07-22-2019, 11:49 PM
and I might add - there's no "alteration" between range 1 and 2 as if you had to do it every other time or whatever, you have 6 speeds - and you only have to alternate between the 1-2 range once to get to them all from 1st speed to 6th speed...

really no big whoop.

J Tiers
07-23-2019, 01:28 AM
JT - it's box stock simple and A-typical,,,

You keep it in low (or 1) on the motor side and then use the finer increments of 3-4-5 on the spindle countershaft part --- when you want the next ratio higher then you drop it into high (or 2) on the motor and then again walk your way up from 3-4-5 again on the spindle side... that's what both the chart shows and I might add what the pulleys ratio's show...

Well a stone hammer simple look at the pulley sizes suggests that what you wrote is flat wrong.... care to show your work?

PStechPaul
07-23-2019, 02:45 AM
The spindle pulley seems to be specified as 2.88", 4", and 5":

https://i.ebayimg.com/images/g/7CMAAOSwQwZagoG4/s-l1600.jpg

The motor pulley is supposed to be 2.5" and 5.25", for about 2:1 hi/lo ratio, and meant for a V-belt:
https://i.ebayimg.com/images/g/t~8AAOSwSCRc99O9/s-l1600.jpg

It looks like the spindle pulleys are for flat belts:
https://i.ebayimg.com/images/g/2BYAAOSwRChcydB7/s-l1600.jpg

I'm pretty sure the lathe must have been modified at some point, or it is a different model from that shown in the manual. No point arguing - the OP's lathe runs at the speeds determined by the installed pulleys, and the only way to make it otherwise is to replace the pulleys and/or install a variable speed drive.

I'm only guessing, however. It would help to see an image of the OP's lathe in question. Some other possible pulleys:

https://i.ebayimg.com/images/g/zQkAAOSwX3FaPDzM/s-l1600.jpg

https://i.ebayimg.com/images/g/zUUAAOSw3gJZNMGs/s-l1600.jpg

Richard P Wilson
07-23-2019, 03:09 AM
From PSTechPaul's photos, the OP's motor pulley is wrong, which is what I said in one of his other threads on this topic.

A.K. Boomer
07-23-2019, 08:16 AM
Well a stone hammer simple look at the pulley sizes suggests that what you wrote is flat wrong.... care to show your work?

Here's all you need to know, the change of 1&2 are greater than any other combination you can come up with on 3-4&5 and that includes skipping from 3 and going directly to 5

so "first speed" is obviously 1-3 combo, second is 1-4 third is 1-5

to get 4th speed you go to 2nd and back down to 3, fifth is 2-4 and 6th is 2-5

because the difference between 1-2 is greater than any other change it means it overshoots enough to make 4th speed greater than third even though your using the least amount of increase on the spindle side increments, again due to the more drastic increase from 1-2 which i will add the pulleys DO show exactly that

again - there is nothing "wrong" with the logan diagram and in fact it's "spot on" I cannot speak for exact RPM's and such as i don't even know the motor speed,,, I can however eyeball the pulley sizes and tell you they correspond to the ratio increases in the sequence they are describing them...

Ringo
07-23-2019, 09:02 AM
Here's all you need to know, the change of 1&2 are greater than any other combination you can come up with on 3-4&5 and that includes skipping from 3 and going directly to 5

so "first speed" is obviously 1-3 combo, second is 1-4 third is 1-5

to get 4th speed you go to 2nd and back down to 3, fifth is 2-4 and 6th is 2-5

because the difference between 1-2 is greater than any other change it means it overshoots enough to make 4th speed greater than third even though your using the least amount of increase on the spindle side increments, again due to the more drastic increase from 1-2 which i will add the pulleys DO show exactly that

again - there is nothing "wrong" with the logan diagram and in fact it's "spot on" I cannot speak for exact RPM's and such as i don't even know the motor speed,,, I can however eyeball the pulley sizes and tell you they correspond to the ratio increases in the sequence they are describing them...

The Logan book chart is in fact dorked up. The smallest speed changes is in 1 & 2. spindle pulleys are much bigger steps.
position 1 is pulleys 6 3/8" - 2 3/4" or 2.3:1 and that 750rpm
position 2 is pulley 6" - 2 1/4" or 2.6:1 and that 673rpm
there is only 75 rpm difference in the 1-2 position of driving countershaft

A.K. Boomer
07-23-2019, 09:10 AM
Then you have different size pulleys on your lathe in comparison to the illustrations - the logan chart is not "dorked up"

it's spot on...

take a pic of your drivetrain and post it - or if you already have please direct me to it....

Ringo
07-23-2019, 09:17 AM
go to post 32
http://bbs.homeshopmachinist.net/threads/79383-Tell-me-about-V-belt-lathe-speeds/page4

A.K. Boomer
07-23-2019, 09:29 AM
WOW that's drastically different and definitely matches YOUR specs not logans,,, all i can say is, the logan illustration matches what they are stating for ratio changes

and your re-calibrated diagnoses matches what your showing for pulley's and config's

I was going to say that for what your talking about your 1-2 pulley size would almost have to be identical and they are --- not very much difference - now take a look at the logan pic and it's radical and is the largest difference,

your 3-4-5 increments are also more radical

I can see exactly what your saying and why your having problems... I don't know if they changed things and re-designed it and your looking at an older illustration or what...

Ringo
07-23-2019, 09:43 AM
I just got off the phone with Scott Logan, my pulleys are in fact correct diameters.
The book photos are correct also. I got the exact book for my 9B-17.
It is the book speed chart that is wrong, the numbers are there but in the wrong positions in the chart
Scott also admit that the other Logan lathes have a larger pulley steps on the motors.
My pulley steps on motor are very close to each other in size, which makes the smallest incremental speed changes on the motor

A.K. Boomer
07-23-2019, 09:51 AM
Scott also admit that the other Logan lathes have a larger pulley steps on the motors.
My pulley steps on motor are very close to each other in size, which makes the smallest incremental speed changes on the motor

It all makes sense - but with this last sentence it tells me your just looking at the illustration for "the other logan lathes"

the illustration does match the ratio specs and seeing as they actually DO build lathes with more radical pulley size difference on the motor's side then everything makes sense... that's what this illustration is for.

there could be one alternative and that's that they got to lazy and just used this illustration for ALL lathes --- in which case it does not make the illustration wrong itself - it's the application of it that's off...

the illustration in your O.P. is spot on...

your diagnoses of what you have is also spot on, they are two totally different systems and with yours you do have to change back and forth with your 1-2 as you try to increase speeds incrementally...

J Tiers
07-23-2019, 10:00 AM
What we end up with is a bit of a tempest in a teapot. The speeds listed are , yes, all available , but you need to bop back and forth on the motor side pulley set to go through them in sequence.

BTW, what I found was that in motor position 1, the sequence is 364, 607, 1007, while in position 2 it is 465, 776, and 1288. Those are all assuming the nominal motor speed, which would be taking a heavy cut. At no load, the speeds would be a few percent faster; the top speed, for instance, would be about 1365 rpm, and the slowest available speed would be about 380 rpm (without using back gear).

The differences are presumably du to rounding, and using OD instead of effective pulley pitch, and may also be due to actual errors in the table, since the table is clearly wrong as far as what belt positions you use for each spindle speed.

Ringo
07-23-2019, 10:06 AM
yes, and that is probably why so many responses were indicating my math is wrong. When actually their 'similar' lathe is pulleyed different than mine.
Add to that the fact my book speed chart is flat out wrong, that is why I was getting smoke & chatter all the time, I could not find correct speed per the book, and could not grind a HSS bit to work. (frustrating)
The original pulleys are no longer available from Logan, so, I am on my own to create a pulley drive. I now have no reservations to create a Frankenlathe because Scott already told me no pulleys are to be had.
Here is a good pic of the similar size of countershaft pulley
the spoked single groove is what I did as to make some repair parts for now


http://bbs.homeshopmachinist.net/attachment.php?attachmentid=5695&d=1563890036

A.K. Boomer
07-23-2019, 10:28 AM
Ringo - is this the original book that came with the lathe? my guess is it's not or if it is they just got lazy,

since we know they made a lathe that fits the description of the speed chart and pulley diagram in this OP im thinking it's most likely a progressive illustration, anotherwords your model lathe was the earlier one, it gave the identical speeds but with more hassle, then as progress goes an engineer said "hey - why don't we just overshoot the half way point with the 1-2 change and make the spindle side cluster shorter ratio" walla, now you get to use 1 for the first three speeds and 2 for the last three... they simplified it and I would think that came latter as there's no advantage to doing things the other way... you have an earlier lathe then what's shown in your OP illustration...

mattthemuppet
07-23-2019, 10:44 AM
as JT said, tempest in a teacup. Use the speed that works for the material (size, type, cutters) that you're turning. If you get smoke and chatter, use the next lowest speed. Rinse and repeat until you find one that works, scribble it on a piece of paper tacked to the wall above the lathe and use that combination in future. It really doesn't make the blindest bit of difference what chart is right or wrong. In fact you dont even need a speed chart - simply go by what the lathe is telling you. The more you use it, the better you'll get.

Then get a 3ph motor and VFD as RB211 suggested. Or a treadmill motor and controller (less money, more work).

A.K. Boomer
07-23-2019, 11:25 AM
I disagree - there's nothing like knowing as to "why" and also learning theory of operation - it's what separates guys like Ringo from the rest of the crowd and also will help you with all kinds of other things if you make it a pattern in your life rather than relying on things you may very well know "work" but don't know exactly as to "why"

kudos to you Ringo...

J Tiers
07-23-2019, 11:52 AM
Eh?

We KNOW why..... he got problems because he believed the book. When it was investigated, the reason became obvious.

But there is no reason to avoid listening and watching to see what the machine is doing. If what you see is wrong, there is no need to complain that "it should work", you do what you need to, and then later you can cut up the corpse and find out why, if you can.

Nobody is advocating being ignorant of problems and just accepting them passively. But there is a time and place for observation and adapting, vs stopping and going into full 'crime scene exploration" mode.

Not only that, but often THAT is the way you find out what is actually wrong.... if the "fix" you find makes no sense according to what "should happen", now you have another clue as to the problem.

BCRider
07-23-2019, 11:56 AM
The bigger added on pulley is a nice fix. But then so would be proper sized motor pulleys.... I assume those are coming and then you can use all three pulleys on the motor side?

I mentioned in the other post when I learned that you were trying to turn 2" 4140 that this would be a back gear job in any event. At least with the stock pulleys regardless of mistakes in the speed chart for your lathe.

Looking up recommended cutting speed for alloy steel like 4140 I find numbers like 40-60 SFM And for 2" diameter this turns out to be 76 to 114 rpm. And on a lighter lathe like the Logan I'd want to be closer to the 70 to 76 RPM side of things. As I understand it you were trying to do this with the lower direct drive speed. And since it appears that you'd be trying to run it at around 5 times too fast. So no wonder your HSS tool was chattering and burning up. And even with your new bigger pulley I'm going to guess that your new lowest speed is still up around 200 RPM so at least two to three times faster than you want to run a piece of such size.

There's no doubt that your findings show that the book's chart is messed up. But perhaps there was a model that matched that book chart but it's not YOUR lathe. As it happens looking at your calculated chart the same speeds are all there. But not in the same order. The motor side is needed to do the minor step and the cone steps provide a the shift to the next pair which you then use the motor pulley to select.

Of course now you'll have a new option for lower side speeds with the big pulley in place and not need to use the back gear. The possible downside being that with a lower and higher torque direct drive speed you might find any big resistance jobs cause the belts to slip where with back gear the gearing that lowers the speed would bull through the cut. So keep the idea of the back gear as an option for such cases.

Ringo
07-23-2019, 12:18 PM
Guys,
this is the proper book, and proper pulleys, I've proven its all here.
this is one of the later model machines, did you notice it is NOT a flat belt machine?
Its just that the numbers in the speed chart on page 6 are listed in wrong positions.
While my crude math numbers arent quite the same, when I found out the smallest speed increment is on 1-2 position, thats when it all fell into place as far as speed increments.

No, the 2" 4140 didnt chatter, it was doing ok until the materiel walked out of the 3jaw and wrecked the facing cut, facing cut slows down as it turns in, correct?

nickel-city-fab
07-23-2019, 12:26 PM
Yep, facing cut slows down as it turns in. My very small lathe likes to have razor sharp tools for jobs like that, it takes the load off the rest of the machine

A.K. Boomer
07-23-2019, 12:42 PM
Its just that the numbers in the speed chart on page 6 are listed in wrong positions.
actually their not - again their spot on for the illustration, it's the entire illustration that DOES NOT BELONG TO YOUR PARTICULAR LATHE ---- BUT is verified by the logan rep that it DOES INDEED belong to another logan lathe WITH more of a gap between 1&2 pulley...



While my crude math numbers arent quite the same, when I found out the smallest speed increment is on 1-2 position, thats when it all fell into place as far as speed increments. yes and again bravo --- but again the illustration is not showing that - therefor you cannot use the illustration for your lathe - its not that they jacked up the speed chart again ITS SPOT ON for that illustration --- it's the fact that your trying to use the wrong illustration for your lathe...

A.K. Boomer
07-23-2019, 12:51 PM
But there is a time and place for observation and adapting, vs stopping and going into full 'crime scene exploration" mode.




LOL --- learning the most basic fundamentals of how a system works is hardly going into "full crime scene exploration mode" lol

it's simply getting your act together first hand instead of blindly trying to bump into everything along the way like Mr. Magoo... lol

It also allows guys like me who look at theory of operation first to make the proper assessment right off, instead of guys like you who are quoted to saying "the illustration is wrong"

Ringo
07-23-2019, 01:08 PM
OK guys,
I am re-pulleying my machine.
Everybody chime in and tell me the optimum speeds to buy pulleys and diameters.
This much I know.:
factory step pulleys are not available, so thats not an option.
My local supplier has some pulleys he letting go at cheap prices, this is a very good option.
1. buy a 2groove 2.55" dia (no steps) for $4.24 and mount that on the motor, this is not a step pulley therefore would require a extra belt on hand for 'quick change'
run this 2.55 dia on the new 9" ($6.74) in the picture above, and run the old large 6 3/8" as in the picture above
2. run the same 2groove 2.55 on motor, and have large/small single pulleys of 10.5 and 9" (with the extra belt)

here is a proposed speed chart showing the original Logan chart corrected, and proposed option 1
notice pulley dia noted in far right


http://bbs.homeshopmachinist.net/attachment.php?attachmentid=5702&d=1563901517

who, and how many of you think I need to go slower in direct drive?

BCRider
07-23-2019, 01:56 PM
Don't rely on your 4140 experience to drive the whole decision. You're keen as blazes for the lower speed side of things just now due to that one tool steel job you are having trouble with. But one day you'll find yourself working with aluminium, brass or plastic that gives a better finish when using a higher speed and you'll be wishing for a 1500'ish RPM option.

My lathe's lowest direct speed is 370. I find that for turning 1.5 and up to 3" mild steel with HSS that this is just fine. And for tough alloy from 1" and under with HSS it's fine too. For other special cases I'll switch to carbide and coolant or use back gear as needed. So all in all I'm not seeing why you feel you need to make any changes. Mostly what I see is that you just need to double check the SFM speeds for the material you're using and convert that to a suitable RPM and use back gear when needed. Which for your 4140 job from the other thread that brought all this to a head would still be required. 297 RPM is still about 4 times what it should be and you'd need to be using a lower back gear speed to get down around 70 to 80 RPM. At least for the periphery of that slug of metal.

Ringo
07-23-2019, 02:11 PM
the original motor drive pulley stripped out is the driver in this.............
the desire to slow it down a bit is the outcome of the need for new motor pulley.
and, decifering the book speed chart
I have never ever turned it all the way up to the highest step........not in 25years
I'm looking for 6 useable speeds, not just 3 or 4
But, I see you are happy with pulley speed 370,

nickel-city-fab
07-23-2019, 02:20 PM
Hrm, I would call your proposal good -- no real big jumps in in speed, or "gaps" until get up to the top 3 speeds. It looks good for most work.

BCRider
07-23-2019, 03:33 PM
the original motor drive pulley stripped out is the driver in this.............
the desire to slow it down a bit is the outcome of the need for new motor pulley.
and, decifering the book speed chart
I have never ever turned it all the way up to the highest step........not in 25years
I'm looking for 6 useable speeds, not just 3 or 4
But, I see you are happy with pulley speed 370,

To be fair your plan is to drop from around 350 to 300. Not a bad plan overall. And if it will give you access to a broader usable range then great.

For my part I've used the very top speed a few times for small diameter "pins" and smaller plastic parts where the higher SFM speeds do provide a better surface finish. But I freely admit that it's very rare that I use the two highest speeds. Like you I find myself wishing for a slightly lower direct speed. Just not as often as you're clearly aiming for. So your plan fits your needs more closely. And that's not a bad thing at all. And for the most part I'm OK with the 370 and don't mind using back gear when it's appropriate.

Ringo
07-23-2019, 03:43 PM
Thanks,
I heard a couple others mention the low direct speed in the 250ish range, I am awaiting to hear from them as well.

MattiJ
07-23-2019, 04:21 PM
Thanks,
I heard a couple others mention the low direct speed in the 250ish range, I am awaiting to hear from them as well.

IMO slowing down the direct drive from 350 to 300 is not worth a hassle, hardly noticeable difference.
Slowing from 350 to 170 would make actual difference in many cases but you might find the top speed lacking in that case.

PStechPaul
07-23-2019, 04:23 PM
My HF 9x20 lathe has a wide range of speeds, from 120 RPM to 2000 RPM, but for a long time after I got it, I only used the lowest speed. I found even that, 120 RPM, was a bit too fast for some threading operations (3/4"-8 LH square), so I made a spindle crank to do it by hand. I still don't usually use recommended RPM for the SFM called for. I just use what feels comfortable and mostly much slower than spec - it's fine for HSS tooling and I find it more relaxing to use slower speeds - and the speed recommended in charts is usually pretty much a maximum determined by optimum cost in terms of speed as well as longevity of tooling. That is more for commercial shops where time is money.

My 9x20 lathe uses an interesting method for speed change. There is a 3 groove pulley on the motor and another 3 groove pulley on a countershaft that spins about 3.3 times slower than the motor. A third 3-groove pulley, with diameters of 1.2-3.0-6.0 units, on the spindle, is then connected with a long belt to either the motor pulley or the countershaft. Thus the speeds of 120, 300, and 600 in low range, and 400, 1000, and 2000 in high range. I've considered installing a bull gear, but would probably be better to use a VFD. The machine has plenty of torque at 120 RPM. Note the use of an idler pulley that makes belt changes easy, and it also allows for starting the machine with the belt loose to avoid start-up stress (belt breakage). I sometimes even run it with the belt loose as a safety clutch.

http://enginuitysystems.com/pix/tools/9x20_Lathe_Spindle_Speed.PNG

http://enginuitysystems.com/pix/tools/9x20_Lathe_Spindle_Belt.PNG

So if you will be installing a new set of pulleys, it might be worthwhile to think about how to get a wider range of speeds, as well as a much lower minimum speed without using the bull gear (unless you already have that).

J Tiers
07-23-2019, 04:37 PM
If he starts at 250 rpm, and uses a pulley ratio of 1.4, he should get 250, 350, 490, 686, 960, and 1350. Back gear at a ratio of 6:1 would then give 41, 58, 81, 114, 160, and 225 rpm. That seems like a useful set of speeds.

ALL pulleys would step at 1.4x per step (the actual is 1.42x, if you care about the details). The two motor pulley steps would be that ratio to each other, and the steps for the spindle/countershaft would also be that. The motor pulley would start at a ratio that gives 350 rpm direct from the motor on the slow speed step, which would be a ratio of 5.

Exact pulley sizes would be as needed, I am just suggesting the ratios. In that way, the speeds would be a continuous range starting from the lowest back gear and going sequentially to the highest speed with no overlaps.

If he uses the 1.42 more exact ratio (fifth root of 1450/250), then he ends up at the 1450 top speed based on the loaded nominal speed..

We can get into specific sizes at some point if desired.


.......

I mentioned in the other post when I learned that you were trying to turn 2" 4140 that this would be a back gear job in any event. At least with the stock pulleys regardless of mistakes in the speed chart for your lathe.

Looking up recommended cutting speed for alloy steel like 4140 I find numbers like 40-60 SFM And for 2" diameter this turns out to be 76 to 114 rpm. And on a lighter lathe like the Logan I'd want to be closer to the 70 to 76 RPM side of things. .....

if I had to run 4140 PH in back gear, I'd pack up the lathe and sell it to a pen maker.

I run 4140 in the lowest speed in normal drive, which is around 240 rpm on mine. I get nice blue chips and a reasonable stock reduction capability. HSS lasts about 2 or 3 passes before needing to be sharpened, but brazed carbide, which I have lots of, and which consequently I use for rough turning, lasts several passes at least. I've finished up all the rough turning without sharpening on arbors before. I save the better inserts for finish turning.

The real issue the OP has is that there is a sweet spot for 9" and 10" lathes around the 250 rpm area, and that is right where he's got nuthin....

OK, the 9" has a narrower bed than the 10" by almost an inch, but it is still a good machine, capable of reasonably hard work.

Ringo
07-23-2019, 04:48 PM
my 3 spindle steps are:
1.66:1 - 1:1 - .6:1

I can rather easily come up with this if I get a 10 1/2 pulley siamesed to the 9"
250 415 691
295 490 816

RB211
07-23-2019, 05:48 PM
I'd keep your pulley setup and get a 3phase motor and VFD. No reason to spend money on a fix that will be superseded.

Sent from my SM-G950U1 using Tapatalk

A.K. Boomer
07-23-2019, 06:07 PM
I'd keep your pulley setup and get a 3phase motor and VFD. No reason to spend money on a fix that will be superseded.

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That's kinda where im at with my step pulley mill, it really is all i need but might be nice to go VFD at sometime and that would mean I could still keep the step pulleys not only for the "sweet spot" but to also gear down once in awhile to oh say yank a tooth out of my head --- or what every machine operator dreams of --- exceeding my spindle RPM recommendations X-5

Ringo
07-23-2019, 06:34 PM
3phase + VFD = a lot more money than I want to spend to do this.

J Tiers
07-23-2019, 06:37 PM
my 3 spindle steps are:
1.66:1 - 1:1 - .6:1

....

Yes it is, and that is the bulk of your problem. That part needs fixed, and it should not be hard to do. Pulleys are plain turning. You have a little more to do because you will have sintered bronze inside one (the spindle pulley), but it is an easy sort of task, No need for exotic material, and just copy the profile of the most similar existing pulley step.

The disadvantage of the VFD is that you lose out on torque as you slow down.

Before someone solemnly assures me that a VFD maintains torque, I will mention that pulleys MULTIPLY torque, so that a 6:1 speed reduction gets you a 6x torque increase (less a bit of friction loss).

The VFD does not and cannot do that unless you play some funny games with the motor design. And even then, you do not get the multiplication, you just ue a motor that gives what you need at low speed, and tolerate the fact that it can do many times better than you need at other speeds.

So you will be using most of the pulley steps anyway even with the VFD.