Maximum DOC on smithy 1220 lathe

[mac1911]

As I work with my smithy and play around Im finding frustrating areas.
Im very new to machining and speeds and feeds are still a bit of a blur.
Partly because of the differences between full production models and these smaller limitted hobby type machines.

What im a bit lost on is the different gear speeds
I have it set per from factory by Smithy tech and the info he emailed to me. Its working ok but Im not sure how I manipulate the gears say to do a rough cut say a speed of .015 .020” ?
So far things are improving.
I have been able to machine parts for the lathe and finally made a replacement handle missing from my bearing/seal driver

 

[Ulma Doctor]

Tool profile is going to dictate doc and spindle speed.
If you stick to 50 to 70 SFM range on steels
150-200 SFM for a lot of non-ferrous metals
The DOC’s can be quite deep .025”to .030” or more (depending on tool)

I don’t have a smitty, but the above should hold true

 

[markba633csi]

You don't have to use power feed; I often make parts feeding mostly or entirely by hand. Also, it's a good way to get a feel for what the machine
likes and how far you can push it before it starts to complain. It also gives valuable feedback about the sharpness of your cutting tool. When it's cutting well the feeling is unmistakable- you can recognize it easily

 

[mac1911]

Tool profile is going to dictate doc and spindle speed.
If you stick to 50 to 70 SFM range on steels
150-200 SFM for a lot of non-ferrous metals
The DOC’s can be quite deep .025”to .030” or more (depending on tool)

I don’t have a smitty, but the above should hold true

Right

You don't have to use power feed; I often make parts feeding mostly or entirely by hand. Also, it's a good way to get a feel for what the machine
likes and how far you can push it before it starts to complain. It also gives valuable feedback about the sharpness of your cutting tool. When it's cutting well the feeling is unmistakable- you can recognize it easily

im going to need a bigger wheel , feeding by hand on this thing is a pita

 

[Jake M]

As I work with my smithy and play around Im finding frustrating areas.
Im very new to machining and speeds and feeds are still a bit of a blur.

That's kind of how it goes. It's a lot to wrap your head around all at once. Hang in there though, it'll come together soon enough.

Partly because of the differences between full production models and these smaller limitted hobby type machines.

This is, and will always be real. I'm gonna second Ulma Doctor's starting points, if the charts aren't getting you where you need to be. Sometimes it's easier to start slower and work up, as he suggests, than it is to start with the charts and work down.

What im a bit lost on is the different gear speeds
I have it set per from factory by Smithy tech and the info he emailed to me. Its working ok but Im not sure how I manipulate the gears say to do a rough cut say a speed of .015 .020” ?

I don't think you want that. The carriage feed on a light lathe will rarely be that heavy, unless you're threading something. Your depth of cut, the cross feed dial, can easily be that and more, depending what you're doing. The power feed/change gears though... I have a South Bend 9 inch, which has a LOT of feed options compared to yours. To the point that I seldom am actually looking for a "number", but rather reacting to "this is going well, I can bump it up some", or "this is laboring too hard, I'm gonna back it off some". But even without numbers, I can tell you that that 0.006 per rev, on my lathe is the higest speed on the "second row", I don't get anywhere beyond that unless I'm threading. My experience says that you make more time by being more aggressive on the depth of cut on the cross slide than you do by being more aggressive on the feed per rev.

Just for reference, maybe perspective... You tossed out 0.015 per rev, or 0.020 per rev as a target. If you use the 0.020 number, that's a 50 thread per inch machine screw. Probably doable sometimes, in some materials, but generally a little bit overwhelming for a small lathe. On your gear chart, it looks like after 0.006 per rev, your next option is 30 threads per inch, which is about 0.033 per rev. I don't think you're going to do much with that besides threading.

I would very much recommend practicing and using both the .003 and .006 options that you have to achieve your desired finish (and horsepower limits, depending what you're cutting), and use the cross slide to speed up the cut until you "burn up" any extra horsepower you have. While only two useful power feed speeds at first seems very limiting, I think you'll find that they are quite useful speeds, and you won't really be limited much by them. For example, I would SUSPECT that you might find with steel and it's alloys, that both roughing AND finishing happen at the 0.003 feed, with deeper passes for moving material faster, and shallower passes for better finish and final dimensions.

So far things are improving.
I have been able to machine parts for the lathe and finally made a replacement handle missing from my bearing/seal driver

That's awesome. It's cool to use stuff you have made.

 

[Alcap]

If I’m understanding your question, there are only 2 positions for turning on this machine .003 & .006 “ per revolution. The other gear positions are for threading

 

[markba633csi]

Good advice there from Jake

 

[mac1911]

If I’m understanding your question, there are only 2 positions for turning on this machine .003 & .006 “ per revolution. The other gear positions are for threading

Looks that what and my lead screw dial is small and at the right hand end of the lead screw , not on the apron. Makes for some annoying mannual work.

 

[mac1911]

That's kind of how it goes. It's a lot to wrap your head around all at once. Hang in there though, it'll come together soon enough.



This is, and will always be real. I'm gonna second Ulma Doctor's starting points, if the charts aren't getting you where you need to be. Sometimes it's easier to start slower and work up, as he suggests, than it is to start with the charts and work down.



I don't think you want that. The carriage feed on a light lathe will rarely be that heavy, unless you're threading something. Your depth of cut, the cross feed dial, can easily be that and more, depending what you're doing. The power feed/change gears though... I have a South Bend 9 inch, which has a LOT of feed options compared to yours. To the point that I seldom am actually looking for a "number", but rather reacting to "this is going well, I can bump it up some", or "this is laboring too hard, I'm gonna back it off some". But even without numbers, I can tell you that that 0.006 per rev, on my lathe is the higest speed on the "second row", I don't get anywhere beyond that unless I'm threading. My experience says that you make more time by being more aggressive on the depth of cut on the cross slide than you do by being more aggressive on the feed per rev.

Just for reference, maybe perspective... You tossed out 0.015 per rev, or 0.020 per rev as a target. If you use the 0.020 number, that's a 50 thread per inch machine screw. Probably doable sometimes, in some materials, but generally a little bit overwhelming for a small lathe. On your gear chart, it looks like after 0.006 per rev, your next option is 30 threads per inch, which is about 0.033 per rev. I don't think you're going to do much with that besides threading.

I would very much recommend practicing and using both the .003 and .006 options that you have to achieve your desired finish (and horsepower limits, depending what you're cutting), and use the cross slide to speed up the cut until you "burn up" any extra horsepower you have. While only two useful power feed speeds at first seems very limiting, I think you'll find that they are quite useful speeds, and you won't really be limited much by them. For example, I would SUSPECT that you might find with steel and it's alloys, that both roughing AND finishing happen at the 0.003 feed, with deeper passes for moving material faster, and shallower passes for better finish and final dimensions.


That's awesome. It's cool to use stuff you have made.

I got the machine for the price of hauling out of former owners garage. As a auto mechanic I could tell right away that mechanically it was in need of some help.
Turns out just about every nut and bolt where loose. Even the 2 set screws for the gear head. Which was not terrible as it made itveasier to realign the head with the ways.
It had a horrible taper cut when I first got it , im down to .002” over 12” which I think the tail shaft alignment now.
Getting there more and more.
Heck ny measuring skills are probably not up to .00X accuracy, lol
Posted some of my adventures here on the forum

Every time I use I learn something , find something and correct something.

I was having a heck of a time getting a decent finish the other day when I finally noticed the compound slightly moving.
So a wuick gib adjustment and locked it down. Back to good finish.

 

[markba633csi]

I see that the 1220 XL doesn't have a carriage feed wheel on the apron like most lathes so that would make hand feeding more difficult
It's a different bird all right