South Bend 9 lathe still struggles with parting

ericc

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Thanks for the dimensions. My parting blade is 0.089", and the small grooving tool is 0.05". The grooving tool works much better on steel. I have a suspicion that the P-2 Empire T blade will be kind of challenging at 3/32" thickness. I'm almost there. It just looks like an issue of power, although there is some instability with the steel parting. I guess it is going to require a really steady hand for the 1.5" steel. I don't look forward to it.
 

mattthemuppet2

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at a pinch you can leave a bit more stock on the part, use a hacksaw to cut off the part and then flip it around to face the saw cut side.
 

vecair

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I have had a South Bend 9 lathe for a while, and I am still having difficulties with parting. I think I know what the problem is. Actually, there were lots of problems. The first one was too much rake on the parting tool. The cross slide has too much backlash and the tool gets sucked in, causing a crash. A lot of internet posts say that backlash does not matter as long as you wind it all out, but that is not quite correct. Also, tightening the gib screws for both cross slide and compound helps.

Another problem I had was not feeding aggressively enough. I developed a timid habit after reading an internet post that suggested increasing the feed rate at the first sign of chatter. This is true. Kind of. The first time I tried this, I snapped the tip off a parting blade. It seems that sometimes this is good advice and sometimes not. You have to listen to what the machine is telling you and "do the right thing." The second time I did this, I was using a homemade parting tool holder with a trimmed down blade that was for a larger lathe. This time, the blade had zero rake, due to previous bad experiences. The material was aluminum, and as soon as I touched the bar with the tool, there was a bunch of scary chatter. I doubled the feed rate and the chatter instantly stopped. Not only that, a beautiful curled ribbon chip was produced, and the tool sailed right through the bar. The finish was beautiful, and I saved the piece that I parted off.

So, the time came to part a larger steel bar (about 1.5"). Slow feed caused chatter, so time to crank it faster! This didn't work. The blade jammed, and in a scary way. Finally, the belt slipped. It appears that there wasn't enough torque, so I used the back gear. This gave plenty of torque, but the feed became very fiddly. I could only feed slowly, else the blade would catch and stall the lathe. I was afraid of breaking something! This problem was probably due to insufficient power. I could part by feeding very slowly with little crumb like chips. This was no good, but as soon as I tried feeding faster it would jam again. The job could be done this way, but it would take forever, and also be risky. I didn't want to damage anything.

This experience reminded me of a parting lesson that I saw at Techshop. The instructor told the students to part at minimum speed, which on the 14x40 lathe is pretty slow. Feed slowly and carefully, barely getting a chip. This took a long time to part, but at least he said it was safe. These 14x40 lathes had a lot of power, and parting was easy at almost full speed for the material, but this was an intriguing technique. It seems that it does have its place with an underpowered lathe.

Could my parting blade be too thick? I have a grooving tool which is thinner, and has no trouble with steel. The parting tool is 0.089", which is similar to the Empire P-2 blades which seem to be the correct size for a South Bend 9. I have a China-made HSS tool, but it looks and feels cheap, and I'm afraid to use it. It measures 0.053" thick on the top and 0.054" on the bottom. It has a slight taper like the old fashioned blades. My large 7/8" blades start at 0.125 on the top and are 0.090" in the middle and thinnest at the bottom. This Chinese tool is thicker at the bottom. But it is thinner, Could 3/32" (Empire size) be a little thick for the South Bend on steel? For aluminum, I think I have it down. Easy and smooth with the 0.089" blade.
I have a SB9 as well and have exactly the same problems. After some experimenting I think its just too light, too worn for really successful parting I have tried many combinations of blades, tools, adjustments and such. I notice the entire machine vibrates when parting. For mine I think a solid heavy base bolted to the floor would help but I can't do that here. I noticed that when I tighten the gibs and clamp down all moving parts except the cross slide it does better. Good reason to buy a bigger lathe :)
 

DavidR8

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[mention]ericc [/mention]
[mention]Nyala [/mention]
I just happened to check the motor on my lathe and it turns out that it’s only 1/2” hp after all.


Sent from my iPhone using Tapatalk
 

ericc

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After restoring the symmetry of the turnbuckle, the lathe does much better. Here is some work with the tool on 1.374" diameter steel. So, the belt tightening helped a lot. This was at the 235 rpm setting.

Hmm. Trouble with photos again. Will try later.
 

ericc

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Great. I think it worked. This is another compound spigot which will go into a tool block, one of the suggestions. But it requires a parting tool.
 

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M.T. Pockets

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I too have a SB9 model C and struggled with parting when I first got it. Let me first say I am not a noob at using a lathe, I just learned on much bigger machines. Your problem isnt HP or rigidity, it's technique. And yes, you can use a 1/8 bar, that's the size I use, even for cutting 2" of stainless.

1. Make sure the tools is sharp, sharpen it with a stone or diamond grinding wheel.
2. Make sure your geometry is dead on. The bar needs to parallel to your workpiece and the cutting tip needs to be right at center of axis of rotation.
3. Go slow. Use your slowest speed with the back gear engaged. Make sure your belt is also gripping enough and not slipping. I strongly recommend not using night spindle speeds. Parting by definition has high chip load which the south bend 9 can't handle at high speed.
4. Chip load, keep it at around 5 thou for aluminum. For steel, maybe drop it down to 2 or 3 thou.

Do this and you shouldn't have any issues. The sb9 will do the same things a much larger lathe will do, just slower and its also a lot less forgiving.
 

epanzella

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Eliminate the compound with a tool block. Makes your setup much more rigid and allows small machines to part like their big brothers. zDSC_0891.JPG
 

Tim9

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I have had very little success parting on my South Bend Lathes using the older hss tooling. I use 2mm carbide with the 10mm-shank parting tooling and the difference has been night and day.
I use lubricant and on deeper cuts I’ll sometimes back it off and then go back in to the side of the first cut to make the groove wider. Everything must be tight.
South Bends of the WW-2 vintage are 75 years old. So we’ve got wear. I tighten my set screws a little snug and lock the carriage.
 

ericc

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Eliminate the compound with a tool block. Makes your setup much more rigid and allows small machines to part like their big brothers.
On its way! I made the base and the spigot. Now to decide what kind of block to make.
 

ericc

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Eliminate the compound with a tool block. Makes your setup much more rigid and allows small machines to part like their big brothers.
On its way! I made the base and the spigot. Now to decide what kind of block to make.
 

ericc

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The tool block is finished. It is a lot more stable than the compound. Here it is parting with a 1" lathe tool which has a GTN3 insert. This is a big tool for a much bigger lathe. It worked, however there was still something loose somewhere since after some cutting, the tool would dive. I'm not sure where it was coming from, but it seemed the cross slide would get looser after a while, as would the carriage lock. The cut could be completed by remembering to tighten them periodically. Here is a picture. It worked better, but I wouldn't say it was great. It was probably not worth the effort, but it was interesting.
 

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epanzella

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If you use a tool that's too big for your lathe you undo the benefits of the tool block. Try using a parting tool the machine was designed for with the tool block.
 
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