# South Bend 9 lathe still struggles with parting



## ericc (Mar 25, 2020)

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.


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## MontanaLon (Mar 25, 2020)

I have noticed parting actually works better when I use higher spindle RPM than lower. The only thing I can figure is that at a higher spindle speed feed rates are reduced as a function of inches per revolution. If I slow down I have all sorts of issues but they seem to go away at higher speeds.

One thing I do notice at the higher speed is increased heat build up so it is important to lube well or you can fry a HSS parting tool in short order.


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## benmychree (Mar 25, 2020)

In my opinion, 1/8" is too wide for a small lathe, 3/32" is probably the best to use.  I can't imagine that a parting tool thicker at the bottom could possibly work, even it it was one thou thicker at the top, it would surely bind in the cut; the best type is the T type, such as the P-2 blade that you mention.  One thing that I have seen that makes for parting troubles is when a QC tool post is used and it is located on the compound so that it overhangs the parting tool to the left, over the edge of the cross slide, the tendency being to allow the tool to bind in the cut by leaning over due to any looseness in the slides.  This I found in a lathe that I bought some time back, a 9" Monarch in like new condition, now when I part on it, I move toe tool post to the right so that the tool is over the cross slide; problem goes away.   With my 19" Regal LeBlond, no problem to part.  You pointed out that some tools you used had back rake at the point; if they do, expect hogging in, they should have very little or no back rake.  Besides that, maybe its time to fix the backlash problem ----


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## benmychree (Mar 25, 2020)

MontanaLon said:


> I have noticed parting actually works better when I use higher spindle RPM than lower. The only thing I can figure is that at a higher spindle speed feed rates are reduced as a function of inches per revolution. If I slow down I have all sorts of issues but they seem to go away at higher speeds.
> 
> One thing I do notice at the higher speed is increased heat build up so it is important to lube well or you can fry a HSS parting tool in short order.


I quite agree with you in that parting is usually best done at higher speeds, and yes, lube is a necessity, whether it be coolant or cutting oil.  Of course the (higher) speed should be within recommended cutting speeds for the material being worked.


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## mickri (Mar 25, 2020)

I feel your pain when trying to part off.  I am parting challenged also.  I started this thread to help me out. https://www.hobby-machinist.com/threads/parting-geometry.79683/#post-683866.  The is some good info in there and possible solutions.


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## Markkjohnson (Mar 25, 2020)

ericc said:


> 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.
> 
> I Changed the cross feed nut on my sb9. Backlash went to zero and parting is easy. You can fine them on ebay mine was $39.00 and very easy to change.
> 
> ...


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## Mitch Alsup (Mar 25, 2020)

I guess I am the only lathe operator who has never had problems parting off. 

My philosophy is slower (RPMs) and more cutting oil with hand operated feed rate listening to the machine while I part-off. Slower with hand controlled feed rate allows one to take enough bite on the metal without over stressing the tool (face).

2-years into my 12×36 and I am still using the original sharp edge on my parting tool with hundreds if not thousands of part-off events.
My parting tool is HSS t-shaped and about 3/32" wide.
While I part mostly aluminum, the blade has also parted useful amounts of mild steel, some 304 stainless, and a couple of pieces of Titanium.


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## benmychree (Mar 25, 2020)

An old machinist friend told me that parting and threading were the two things that newbies struggled with, and with time threading got better, parting never did; perhaps an exaggeration, but there is some truth to it.


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## MontanaLon (Mar 25, 2020)

Also something I have found interesting and may point to the need for a new cross slide nut. 

If I turn the compound to 0* and use it instead of the cross slide to do the parting cut, it goes much better. When I had it apart when I got it the compound nut and screw were very tight fitting where the cross slide nut had noticeable play on the screw. Maybe I will take this time off to get another set and see if that helps.


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## mattthemuppet2 (Mar 25, 2020)

the fact that you said you then put it into back gear told me alot. You're parting too fast for the material and blade thickness. Start off at your slowest possible speed, use some thinner stock (1/2-1") and get a feel for things. If you get alot of chatter on first contact, you're going too fast.


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## mikey (Mar 25, 2020)

ericc said:


> The first one was too much rake on the parting tool. ... Also, tightening the gib screws for both cross slide and compound helps.



A P-type parting tool is flat on top so it has zero rake. Are you using a different tool in the above statement or are you talking about the relief angle, the angle under the tool tip? Also, are you using a QCTP with the tool holder that holds the blade at an upward angle? If so, that gives you positive rake and can definitely dig in if the lathe is not rigid.



ericc said:


> Another problem I had was not feeding aggressively enough.  ... You have to listen to what the machine is telling you and "do the right thing."



The feed when parting manually is actually about feel rather than sound. You want to feel a slight resistance to the feed. When you get it right you have to maintain it all the way in. This applies to all materials. The resistance is lighter at higher speeds and harder at lower speeds. 



ericc said:


> 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.



You should be able to part most materials at 1/2 - 2/3 turning speed. For your 1.5" bar, that would be between 125-200 rpm or so. As I mentioned, feed gets easier at higher speeds. My Super 11 will part mild steel at 200 rpm with no issues, and my little Sherline lathe with a rear mounted parting tool will part a 1" mild steel bar at about 1200 rpm. The speed helps.



ericc said:


> Could my parting blade be too thick?



All else being good, a P2 blade should part most materials on a 9" lathe. Parting tools are form tools; the wider they are, the more resistance you will have and the more power and rigidity the tool will require to function for any given material. In my opinion, it is best to use the narrowest blade that will work with your machine. I use a P1-N blade (0.040" wide)on my Sherline to part almost anything that fits in the lathe and have no problems parting at speeds that are usually 2-3 times normal turning speeds, and that includes steel up to about 1.25" OD. 

I do not like the tool holders that angle the tool upwards. In my opinion, a horizontal tool holder is better because it allows the tool to perform like what it is - a form tool with zero rake. 

I suspect the issues you're having may be due to multiple factors. The gibs and fits of the cross slide and compound are always suspect. This is why guys with plinths have fewer issues when parting - no gibs, just solid material under the tool post. Getting the tip of the tool exactly on center is important; not close but dead on. The tool aligned perpendicular to the work is important, too. What is not as critical is overhang; a P-type blade can stick out and still maintain rigidity if all other factors are good. 

I would look really hard at movement at the tool due to movement of the cross slide and compound. Put a turning tool in your tool post and lock it down. Put a dial indicator on top of the tool bit and try moving the cross slide and compound up and down with your hands to see how much movement there is. If it is excessive, like more than a thou, then you have some issues to sort out.


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## Mitch Alsup (Mar 25, 2020)

MontanaLon said:


> Also something I have found interesting and may point to the need for a new cross slide nut.
> 
> If I turn the compound to 0* and use it instead of the cross slide to do the parting cut, it goes much better. When I had it apart when I got it the compound nut and screw were very tight fitting where the cross slide nut had noticeable play on the screw. Maybe I will take this time off to get another set and see if that helps.



Do you lock down the compound when just using the cross slide. This may be where your lack of stiffness lies.


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## Dorn (Mar 26, 2020)

I had trouble using a parting off tool until I made a special holder for my QCTP that holds the cutoff blade upside down.  Then I run the lathe in reverse.  Because this forces the tip of the tool to flex away from the work when under load it completely gets rid of the problem of digging in.

I don't worry about the chuck unscrewing when working on small stuff.  When I'm holding bigger diameter stuff in the 3 Jaw I use a T-shaped "nut" that slips inside the chuck.  The crossbar of the T bears against the backplate and the base is screwed into the collet drawbar.  Because the thread pitches of the drawbar and spindle nose are different, there is no way the chuck can unscrew.


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## Nyala (Mar 26, 2020)

I too own a SB 9" lathe, a Model C.  It is powered by a 1/2 HP motor, which I attribute most problems to.

I recently parted off a piece of 1.5" aluminum.  It took 20 minutes, using a 3/32" parting tool.  Any attempt to adjust the feed resulted in bringing the lathe to a complete stop.  It didn't matter if I adjusted the RPM higher or lower.  I had to use a feed of about .004" and wait for it to complete the cut before feeding in another .004", all the while flooding it with oil.

I rarely knurl anything, but when I try, I use my clamp-on knurling tool and I can bring the lathe to a complete stop, if not careful.  The best knurl that I usually get is basically a roughed up surface.  Try to do more and the lathe stops.  Flooding with oil doesn't help.   

My standard feed cuts are basically .010, and maybe .015 if I'm lucky, otherwise I can bring the lathe to another full stop.  I recently turned a piece of 2" steel to a major diameter of 1.75" for about 1/2" and a minor diameter of 1/4" for a 1/4-20 thread for about 1/2".  It took about 2 hours.

I've thought about moving up to a 1HP motor but I'm not sure that the bearings would hold up to more power, so I just suffer through.


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## savarin (Mar 26, 2020)

Made a solid plinth for my 9x20 and all my parting woes vanished.








						Plinth For Qctp On 9 X 20 Lathe
					

In my never ceasing search for more rigidity in my lathe I decided to make a plinth for the qctp. In its normal configuration I can often see the complete top slide assembly flex slightly. (I think I punish my lathe a bit) After seeing Bill G's plinth I felt it was time to go. I forgot to take...




					www.hobby-machinist.com
				



Also this solved the chatter when it reappeared








						stopping parting chatter
					

Attempting to part off the end plates for the possible steam engine produced the most horrendous screaming chatter I have ever heard.:bawling: I really thought I had solved all these problems by using the solid plinth for the tool post.  I tried everything to try to solve it but nothing worked...




					www.hobby-machinist.com
				



check out post 29








						I think I have a parting problem........
					

I think I have a real problem with parting on the lathe. When I got my fist lathe I bought a HHS parting blade and installed it into the holder that came with my QCTP. I started with a thinner parting blade, around .087" thick I think, and watched a bunch of video's before attempting to actually...




					www.hobby-machinist.com
				



Rigidity is the key.


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## DavidR8 (Mar 26, 2020)

Nyala said:


> I too own a SB 9" lathe, a Model C. It is powered by a 1/2 HP motor, which I attribute most problems to.
> 
> I recently parted off a piece of 1.5" aluminum. It took 20 minutes, using a 3/32" parting tool. Any attempt to adjust the feed resulted in bringing the lathe to a complete stop. It didn't matter if I adjusted the RPM higher or lower. I had to use a feed of about .004" and wait for it to complete the cut before feeding in another .004", all the while flooding it with oil.
> 
> ...



@Nyala I have a South Bend 10K with a 3/4 hp motor and have no problem with a .020 DoC in 1018 steel using a sharp HSS tool.
Are you using carbide or HSS?


Sent from my iPhone using Tapatalk


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## Janderso (Mar 26, 2020)

+1 on rigidity.


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## ericc (Mar 26, 2020)

MontanaLon said:


> Also something I have found interesting and may point to the need for a new cross slide nut.
> 
> If I turn the compound to 0* and use it instead of the cross slide to do the parting cut, it goes much better. When I had it apart when I got it the compound nut and screw were very tight fitting where the cross slide nut had noticeable play on the screw. Maybe I will take this time off to get another set and see if that helps.



This is indeed interesting.  I'll have to give this a try.  It may give me the impetus to replace the cross feed nut.  Although I am afraid that this may not be enough, since the screw is also pretty worn.  The compound is pretty tight, though.


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## ericc (Mar 26, 2020)

mattthemuppet2 said:


> the fact that you said you then put it into back gear told me alot. You're parting too fast for the material and blade thickness. Start off at your slowest possible speed, use some thinner stock (1/2-1") and get a feel for things. If you get alot of chatter on first contact, you're going too fast.


 
That is not completely true.  I experienced the "chatter at normal speed but too slow of feed".  I would suspect that no less than 1/2 recommended speed is appropriate for parting.  The problem with too slow is that feed becomes tricky, even with nerves of steel.  Higher speeds give you more leeway in the feed rate.  As I recall, I was parting aluminum (3/4" at 750RPM).  I got a lot of chatter until I increased the feed rate.  The noise changed to a smooth hiss, ribbons started flying off, and the finish was excellent, even to a professional machinist who I showed this to.  But timidity does have its advantages.  I am pretty smooth, and I can smoothly force the parting tool into the part until the lathe crashes.  I only did this once, though.  Ok, twice.  So "feed faster" is not a hard and fast rule.


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## ericc (Mar 26, 2020)

Dorn said:


> I had trouble using a parting off tool until I made a special holder for my QCTP that holds the cutoff blade upside down.  Then I run the lathe in reverse.  Because this forces the tip of the tool to flex away from the work when under load it completely gets rid of the problem of digging in.
> 
> I don't worry about the chuck unscrewing when working on small stuff.  When I'm holding bigger diameter stuff in the 3 Jaw I use a T-shaped "nut" that slips inside the chuck.  The crossbar of the T bears against the backplate and the base is screwed into the collet drawbar.  Because the thread pitches of the drawbar and spindle nose are different, there is no way the chuck can unscrew.



That does work.  I tried this on a lathe with a camlock chuck, and it worked great.  But I am afraid of unscrewing my chuck.  I have seen several "experts" post that beginners are overly afraid of the chuck unscrewing and that it never happens.  It happened to me once, however, and it was extremely scary.  It looked like the chuck was moving in slow motion, but there was nothing I could do to stop it.  I couldn't even manage to reach the switch.  I was lucky that I didn't lose any teeth, and realize that I can't believe everything I read on the web.


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## ericc (Mar 26, 2020)

DavidR8 said:


> I have a South Bend 10K with a 3/4 hp motor and have no problem with a .020 DoC in 1018 steel using a sharp HSS tool.
> Are you using carbide or HSS?



I am using HSS.  Cleveland Mo-max.  I don't think my motor is 3/4 HP.  I cannot see any markings.  I'll have to get under the table and check.  My lathe will do 0.020" DoC in mild steel.


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## mickri (Mar 26, 2020)

Dorn said:


> I don't worry about the chuck unscrewing when working on small stuff. When I'm holding bigger diameter stuff in the 3 Jaw I use a T-shaped "nut" that slips inside the chuck. The crossbar of the T bears against the backplate and the base is screwed into the collet drawbar. Because the thread pitches of the drawbar and spindle nose are different, there is no way the chuck can unscrew.


This is very interesting to me because I am parting challenged and I would love to be able to part in reverse.  My thought is to use a LH thread drawbar.  That way the T-shaped nut would tighten against the chuck if the chuck tried to unscrew.


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## DavidR8 (Mar 26, 2020)

ericc said:


> I am using HSS.  Cleveland Mo-max.  I don't think my motor is 3/4 HP.  I cannot see any markings.  I'll have to get under the table and check.  My lathe will do 0.020" DoC in mild steel.


Sorry I hijacked your thread a bit replying to @Nyala as they were saying that they can barely part because of a 1/2hp motor.


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## Winegrower (Mar 26, 2020)

I had tons of parting issues with my 10" Logan, until I got the blade type carbide insert tool.   This solved most problems, and the rest pretty much went away when I got the 14" Takisawa lathe.   Wow, now I can part off 3" steel rounds without too much fear...set the speed where the cut temperature looks under control, lots of cutting fluid, not too aggressive a feed, around 0.003" per revolution, and it generally works.   Occasionally I mess up by failing to get an exactly perpendicular blade on a deep cut and I have broken a couple of inserts like this.   I count this as a user error.

I buy the cheap blades with 10 inserts of unknown quality.   They work OK.   Someday, maybe with my virus check, I'll get a brand name tool and inserts, and compare.   Maybe.  Or buy food, have to see.


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## Dorn (Mar 26, 2020)

mickri said:


> This is very interesting to me because I am parting challenged and I would love to be able to part in reverse.  My thought is to use a LH thread drawbar.  That way the T-shaped nut would tighten against the chuck if the chuck tried to unscrew.


Don't worry about using a left hand thread.  Just as long as the two threads are of different pitch and the finer pitch is on the drawbar.  If the chuck tries to unscrew it just tightens the T nut against the backplate and presto chango the unscrewing doesn't happen.


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## mickri (Mar 26, 2020)

I have two RH thread drawbars for the spindle on my lathe for holding 3C collets.  One is a 3/8 external thread.  I'll have to measure the TPI.  The other has a very fine internal thread.  I'll make a T nut for the 3/8 drawbar.  Be a good learning experience.  I will make the nut with a MT3 taper to fit the spindle and with a collar to fit the bore on my chucks.


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## macardoso (Mar 26, 2020)

Mitch Alsup said:


> I guess I am the only lathe operator who has never had problems parting off.
> 
> My philosophy is slower (RPMs) and more cutting oil with hand operated feed rate listening to the machine while I part-off. Slower with hand controlled feed rate allows one to take enough bite on the metal without over stressing the tool (face).
> 
> ...



I'm in the same boat. Set lathe to 100 rpm and I like using the power cross feed. Drip a bit of oil and let the machine do its job. 3/32 parting blades held in a cheap AXA parting holder. Works fine for steel, aluminum, stainless, etc. I only have issues on poorly supported or thin and hollow parts.


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## mattthemuppet2 (Mar 26, 2020)

ericc said:


> That is not completely true.  I experienced the "chatter at normal speed but too slow of feed".  I would suspect that no less than 1/2 recommended speed is appropriate for parting.  The problem with too slow is that feed becomes tricky, even with nerves of steel.  Higher speeds give you more leeway in the feed rate.  As I recall, I was parting aluminum (3/4" at 750RPM).  I got a lot of chatter until I increased the feed rate.  The noise changed to a smooth hiss, ribbons started flying off, and the finish was excellent, even to a professional machinist who I showed this to.  But timidity does have its advantages.  I am pretty smooth, and I can smoothly force the parting tool into the part until the lathe crashes.  I only did this once, though.  Ok, twice.  So "feed faster" is not a hard and fast rule.



the opposite actually - the slower you go, the slower you need to feed. Seriously mate, I'm working with a lathe that makes yours look like an American Pacemaker. 1/2 of normal turning feed is too fast. I can happily turn 1" steel at 6-700rpm, but I have to drop down to 100-120rpm for parting. Works beautifully, nice little curls, never snapped a blade. You can get away with an awful lot when working with aluminium that you can't when you're working with steel.


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## ericc (Mar 26, 2020)

mattthemuppet2 said:


> the opposite actually - the slower you go, the slower you need to feed. Seriously mate, I'm working with a lathe that makes yours look like an American Pacemaker. 1/2 of normal turning feed is too fast. I can happily turn 1" steel at 6-700rpm, but I have to drop down to 100-120rpm for parting. Works beautifully, nice little curls, never snapped a blade. You can get away with an awful lot when working with aluminium that you can't when you're working with steel.



Maybe you are right, Matt.  I just put a 5/8" mild steel bar into the chuck and tried it at 250 RPM.  It parted just fine with no chatter.  lBut, it was slow going and no curled ribbon chips.  The lathe was noticeably struggling and it sounded like the blade might catch if I pushed it too hard.  I estimated about 0.001 per rev.  But the piece was clean, and no drama.

I have a strong feeling that the lathe is underpowered.  I looked at the motor, and it is 1 HP.  Should be enough.  I puled out the underdrive belt tensioner and found that the turnbuckle was tightened as far as it would go *on one side*.  That means that it was bottomed out.  Also, the cotter key was missing.  I made a new one and centered the turnbuckle.  It seems that I am getting more tension on the flat belt now.  I put a torque wrench in the chuck and it showed about 5 foot pounds before the fix and 10 foot pounds after.  10 foot pounds at 250 RPM is 0.47 HP, so that should be enough.  I still feel it is marginal.

How wide (thick) is your parting tool?


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## mattthemuppet2 (Mar 26, 2020)

it's a little counterintuitive, but if you think about it in terms of chip load per rev it makes more sense. If the rpm is low, the feed is slower or the chip load would be too high, conversely it allows you to keep the chip load high enough to avoid rubbing or chatter. Also gives you more margin for error - it's easier to speed up or slow down feed speed in response to cutting conditions when you're not turning the handle as fast as you can.

I typically use a 0.04" T-type blade for small stuff and the next size up (it's about twice as wide, around 2mm) for large stuff as it can tolerate greater stick out without flexing. Both from Shars many many moons ago. The thicker one has to run slower as the amount of metal removed per rev is higher.


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## ericc (Mar 26, 2020)

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.


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## mattthemuppet2 (Mar 27, 2020)

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.


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## vecair (Mar 28, 2020)

ericc said:


> 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.
> 
> ...



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


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## DavidR8 (Mar 28, 2020)

[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. 


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## ericc (Mar 29, 2020)

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.


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## ericc (Mar 29, 2020)

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 (Mar 29, 2020)

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.


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## epanzella (Mar 29, 2020)

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


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## Tim9 (Mar 29, 2020)

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.


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## ericc (Mar 31, 2020)

epanzella said:


> 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.


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## ericc (Mar 31, 2020)

epanzella said:


> 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.


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## ericc (Apr 4, 2020)

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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## ericc (Apr 4, 2020)

Here's the result..


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## epanzella (Apr 4, 2020)

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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