Need enlightenment on the countershaft pulley.

[littlejack]

I sure hope you fellas don't get tired of all my questions. I'm lernin.
Regarding the two step countershaft pulley. The drive belt is on the smaller of the two v-grooves. I know that this will increase the
speed of the spindle, correct?
I was getting acquainted with the machine after I put the new link-belt on, and it looked like things were running pretty fast.
Question: What would "those" speeds be for as opposed to having the drive belt on the bigger of the two v-groove pulley's?
I did not get a manual with the lathe regarding the different speeds, and their purposes. Would it be better to run the machine on the larger
pulley (to slow things down) for all practical purposes? I want to practice cutting threads, and would like to start out at the right speed.

Jack

 

[pollardd]

Hi Jack,
The speed you want to use depends on multiple things.
Like the diameter you are turning, the type of material, the type of cutter (hss or carbide)
I'm not sure exactly what type of lathe you have but my Atlas has 16 speeds.
4 on the main spindle 2 on the counter shaft and 2 on the back gears.
4x2x2 = 16
The actual speed on the spindle depends on how fast your motor spins.

I asked a similar question when I first got my lathe.
http://www.hobby-machinist.com/showthread.php/18768-What-are-the-actual-spindle-speeds

Have a read and see if this helps with your question.

Tell us what you are turning as an example and we will help you calculate the optimum speed as a starting point. Because there are so many variables you will often need to adjust.

As a simple rule if it is screaming or your tool burns out your going too fast
if it sings your going ok. It is more critical if you are getting paid by the hour rather than a hobby.

Once you figure out your actual RPM of each belt position you can use a site like this one to calculate which one to use for your situation.
http://littlemachineshop.com/Reference/CuttingSpeeds.php#Turning

Hope this helps
David

 

[Dranreb]

I want to practice cutting threads, and would like to start out at the right speed.

Jack

To start out cutting threads you can't go wrong by using the slowest possible speed using your back gear, and a bit of ally or brass..

It'll take a while to get a feel for which speed and tool shape to use for a job, I turned my best finish ever only the other day, just got the combination of tool, speed, and metal perfectly.

Bernard

 

[Mondo]

I read your posts, you need a manual!

But just to get started, download these documents:
http://vintagemachinery.org/pubs/detail.aspx?id=6212
http://vintagemachinery.org/pubs/detail.aspx?id=6177
http://vintagemachinery.org/pubs/detail.aspx?id=3455
http://vintagemachinery.org/pubs/detail.aspx?id=3395

Then make a donation to vintagemachinery.org.

For the complete book search for "Manual of Lathe Operations and Machinist Tables"
There are dozens of sources for downloading in .pdf or for purchase on a CDROM, or in hard copy, both originals and reprints. Most download sites require membership, some free, others require a token fee to support maintaining the site.

 

[Terrywerm]

Jack: We will not get tired of your questions, not one bit. Remember that learning, sharing, asking questions, etc. is what this forum is all about. If you have a question, PLEASE do post it. You will get the answers you need, plus there might be someone else out there that will learn from it as well!

 

[littlejack]

I went out this afternoon to check things out, and figure my angle of attack to mount/level te beast.
I knew that the motor had been changed out, and is a Leesen 1725 rpm, 1/2 HP. The sheave on the motor shaft has been replaced as well.
It is a single groove taper-lock 3.25 diameter. It is driving the small pulley of the counter shaft. I have to break it loose (the motor
sheave) slide it to the right to drive the big pulley.
I will have to buy a new belt, but was going to replace the v-belt with a link-belt anyway.
I will keep my eye out on flea-bay for the proper motor pulley.
Again, thank you for all for your help.
Much appreciated.
Jack

 

[Hawkeye]

Jack, your best bet to learn the actual speeds that your lathe turns is to pick up an optical tach. They can be had quite cheaply at times. As you say, motors get changed, pulleys get changed. I've noticed quite a change in RPM after replacing a belt.

The more attention you pay to using the correct speeds for the material, tooling and diameter, the better your results will be. Not just the finish on the metal, but also in terms of damaged tooling. Experience talking. :whistle:

 

[pdentrem]

I can not remember which Atlas you have but the early 10 and 12" lathes have a 4" and 2 1/2" motor pulley. I ended up making one by using two pulleys of that size and turning them to fit together. This was in the days before online listings came about.
Pierre