Maximum cut on a SBL 9A

Mrtechnologist2u · Feb 19, 2013

A different post got me to wondering what would be a heavy cut or even maximum cut in mild steel. (assuming a non-interupted cut)

Mine is a '42 vintage w/leatherbelt. I currently have a lantern style tool post and the option of using a solid steel tool post that fits in my dual tool SBL post 4 t-slot cross -slide, not shure if that will make a difference. ( I havent tried it out yet.) I have been conservative so far in my machining because it has been @#$%&*!! cold out in the shop this winter.

I already got frost bite on a finger on my right hand by handling a 3' section of 1" barstock when it was -40degrees (30 secs was all it took). It raised quite a blister! AND no I didnt have gloves on! I will next time.

If trial and error to determine do you just take deeper cuts till you get chatter or the belt slips or (something gives)

lenny baledge · Feb 19, 2013

I was just looking through my copy of HTRAL last night. I think it was 1/8" DOC for 1/4" total diameter. I wasn't actually looking for that information, I just saw it in passing so someone correct me if I'm wrong.

I've never been able to get close to max cut on any of my lathes, but I'm just a hobby guy and still learning. I have a two 13's and and a 16 and I usually don't even take that much with them. I didn't even have a smaller 9" SB until a few months ago & I ended up with four complete lathes. When it warms up, I'll clean one up and start playing with it.

Lenny

lenny baledge · Feb 19, 2013

I just confirmed in HTRAL.

Note: These are from the 1928 version & are all depth of cut (DOC). Total diameter reduction would be 2x.

9" 1/8
11" 3/16
13" 1/4
15" 5/16
16" 3/8
18" 7/16
21" 1/2
24" 9/16 <------- That's and 1-1/8" diameter reduction per pass!!!!

Lenny

macgyver · Feb 19, 2013

If you can keep the belt from slipping, they will take a heavy cut. On my 14.5 I finally got the belt just right and when I have a properly sharpened cutter, it can hog it off.

It is nice to hear the motor bog a little vs the spindle slowing down.

Haven't tried to max out the 18, you might need to do that Lenny,

Jason

lenny baledge · Feb 19, 2013

I'll be measuring the barn for that thing. I didn't get the pics of the shaper for you tonight. I've been hauling in wood getting ready for the ice. Looks like you guys are going to get some too.

Lenny

SteveM · Feb 19, 2013

My heavy 9 was listed as taking 3/16 cut in one pass. When I get the thing up and running, that's going to be a BIG improvement over talking 10 thou at a time with the Atlas.

Steve

vandis · Feb 20, 2013

I have to say I don't understand this fascination with the max depth of cut that one can take with the South Bend lathes. First, this is a hobby for most of us--something relaxing to do in the evening or perhaps all day long if you're retired. Most of us are unlikely to be using these lathes for any sort of money-making enterprise. So what's the rush? Maybe there's something "manly" about watching a red hot string of metal spill off the cutting tool? Heavy cuts mean heavy reaction forces on the spindle bearings and countershaft bearings from the resulting tool and belt loads. Heavy bearing forces mean an increased potential for bearing wear. Are we in a rush to wear out an irreplaceable piece of equipment?

Sure, your 9" workshop lathe can take 1/8" deep cut if the belts are in good shape but do you really want to do that to your lathe?

iwananew10K · Feb 20, 2013

just for discussion,i`ve read from a few sources that it is actually easier on the machine to take fewer,heavier cuts than a bunch of little ones.

i think HTRAL actually recommends " the heaviest cut the tool will allow" - or something like that.

for the record, i`m a heavy cut,low speed,high feed guy.

lenny baledge · Feb 20, 2013

Vandis,

I agree with you that most of us are hobby guys & I do like seeing the toolbit skim across the face of the steel with a small tiny curl developing. However, I'd like to see a pile of nice thick "6" shaped slabs piling up on the carriage sometime. For me, I think that will represent that I have reached some sort level of expertise & understanding.

How hard is it on the lathe? I don't know the complete answer, but it does put a tremendous strain on lots of components. If the lathe is well tuned with all tolerances close to spec, I would think we could take maximum cut each time we use it without any worry of shortening it's useful life for us. I say useful life for us because, as you pointed out, we're hobby guys. We don't use it every day, or even every week. Things would obviously be different if the spindle had 0.010" of slop, the crossfeed nut was trashed, the gibs were mal-adjusted, and we maxed it out all the time. That much stress, with that many pieces rattling around would surely takes it's toll.

Lenny

Mrtechnologist2u · Feb 20, 2013

Thanks for the feedback. I was just curious.

I am a laid back sort of guy, just getting to know my lathe, and have been happy taking 20 thou off at a time. The lathe is old and so am I, so I just wanted to confirm my assumptions. (I should have looked it up in HTRL just didnt even think of it!) I dont like working that hard any more and I figure it was true for the lathe as well!

Thanks all!

SteveM · Feb 20, 2013

I think that if South Bend said it can take 1/8" off, then that's within the limits of the lathe. Even if I only do half that, I'm still way ahead of the Atlas.

While I do this for a hobby, trying to take 1/2" off 10 thou at a time is not a good use of my time.

The art/science/skill to all this is getting a part that is correct to the thou or tenth, as required. There are no awards for the most number of passes to get there.

My $0.02.

Steve

Rick_B · Feb 20, 2013

Chad - just for discussion purposes - you said you were a heavy cut/low speed/high feed guy. Do you modify that approach to light cut/high speed/low feed for finish cuts/improved surface finish?

Thanks
Rick

iwananew10K · Feb 20, 2013

yes.
for me the fun is in making the metal go away, so i`ll hog( in a SB9" sense!) as much as i can as as quick as i can(backgears) and then finish with something like a .010 pass at .003"/rev

if it ain`t smokin`- you gotta be jokin!

Rick_B · Feb 20, 2013

Thanks Chad - just wanted to make sure I understood what I THINK I know

Rick

bradjacob · Feb 20, 2013

iwananew10K said:
yes.
for me the fun is in making the metal go away, so i`ll hog( in a SB9" sense!) as much as i can as as quick as i can(backgears) and then finish with something like a .010 pass at .003"/rev

if it ain`t smokin`- you gotta be jokin!

Chad, I'd love to see some of that slow speed, high feed cutting in action. Can you post a video? I too have to admit that I want to get the most out of a cut, so the science of dialing that in, is of particular interest to me. At least to the specs that South Bend has laid out in HTRAL.

iwananew10K · Feb 21, 2013

just let `er rip!

it`s too cold for me -might freeze my pinky. that and the big iron guys might wet theirselves seeing a SB9 "hogging"
wouldn`t want that.

Conrad Hoffman · Feb 21, 2013

Remember that the tool grind has a huge effect on maximum DOC. Use a flat carbide tool like a modern shop would use and the machine will be in agony. use a knife-like tool for steel and it can cut like butter. There's a photo on one of the SB brochures or catalogs showing what I consider a huge cut on a steel round and the secret is the tool grind. And oil- don't forget oil!

Rick_B · Feb 21, 2013

That's a good point Conrad - I'm wondering when oil is appropriate - every sindle pass regardless of depth of cut, only heavier cuts, only cuts requiring a better finish, or some combination of this?

Rick

promacjoe · Feb 21, 2013

The maximum depth of cut is really kind of misleading. It is intended to be used as a measure between different machines. They specify a maximum depth the cut with most of the other variables being equal. RPM, feed rate, tool geometry. With the correct tool geometry, feed rate, RPM and a serpentine belt, you can get a greater depth of cut than advertised. I have a nine workshop and just as an experiment to see what the lathe would do, I have reduced the diameter of the work by as much as 3/8 of an inch, without chatter. But I do not recommend doing it very often. With a greater depth of cut you get greater amounts of heat. This heat has to go somewhere. Much of it comes off with the chip. Some of it goes to the cutting tool But a lot of it stays with the part. In some cases it will swell the part and cause a taper to be cut as it heats up. Depending on how hot you let your part get, The heat will reduce the final diameter of the cooled part.

Just something to consider when taking heavy rough cuts. And let your part cool before you take the final finish cut.

Joe.

72bwhite · Feb 22, 2013

watch the chips as they come off sometime on a deep cut at low rpm they come off gray and then turn straw or blue.
Old machines were intended to run low speed and hss tool.

Maximum cut on a SBL 9A

Aluminum

Cast Iron

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Stainless

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Diamond

Aluminum

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Cast Iron

Aluminum

Diamond

Stainless

Diamond

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Titanium

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Titanium

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