# What Is The Biggest Diameter Of Steel You May Cut?



## A. Fig Lee (Jun 30, 2015)

Hello guys,
I'm deciding on whether to improve my 7x12 metalworker or sell it and buy South Bend.
So far was impressed by SB - some people claim up to 7" diameter of steel successfully cut on it.

I only capable to do 1/2" of steel. 1" of steel very hard to cut off, though just a regular turning doable with 
0.5 mm or 0.02" (diameter) for each pass.

Anyone had a luck to turning/cut off 3" steel?

P.S. I have 30206 bearings, have not installed it yet. To install I need a tool. Which is silly to buy since I have lathe and may make it. But lathe is not capable of making that diameter. Secondly, you need working lathe to cut spacer width.. 
Anyone in Toronto/GTA area wants to upgrade bearings? We may use each other lathe and do both.
Thank you


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## RJSakowski (Jun 30, 2015)

The maximum diameter which you can practically cut is going to be limited by the available torque, the lowest spindle speed, and the size of your chuck.  As the diameter increases, more torque is required to make a cut. Small lathes don't have a lot of torque to spare.  Also, as diameter increases, the surface speed increases, requiring running at a lower spindle speed.  Finally, small lathes  have small chucks which have shallow jaws.  The ability to safely hold a large diameter workpiece is diminished.  Using a center in the tailstock would, IMO, be an absolute on a workpiece approaching the swing of the lathe.

You mention cut on in the first paragraph and cut off in the second and third.  If you are referring to parting when you say cut off, that is another issue.  Parting is not the easiest operation on a lathe as can be attested to by multiple posts on this site. Small lathes have small parting tools and extending the parting blade  enough to part even a 3" diameter in steel is a challenge.  I would saw the piece with a band saw or (ugh) a hack saw and face the piece on the lathe to finish.


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## brino (Jun 30, 2015)

Parting off on a lathe can be a totally different beast than regular turning......the relatively wide tool face, the extended tool overhang, the changing sfpm all make parting more difficult. It really seems to exaggerate any slop/flex in the entire lathe; ways, cross-slide and tool post. Chatter and noise are common, but so is the tool getting jammed in the cut and the work piece trying to climb up the parting tool.

There are some very good threads here dealing with most of the issues:

http://www.hobby-machinist.com/threads/parting-for-idiots.32938/
http://www.hobby-machinist.com/threads/help-parting-on-a-curve.36268/#post-310396
http://www.hobby-machinist.com/threads/rear-tool-post-parting-tool-holder.36455/#post-310961

With my current setup (Southbend 9x54" lathe and AXA-style quick change tool post) I would not attempt to part-off anything over about 2 inches. However, I am considering a back tool post just for parting.....that should help.

-brino


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## brino (Jun 30, 2015)

As Bob mentions it's not clear if you mean simple surface turning or parting (cut-off).

To be very clear:

Do not part-off (cut-off) on a lathe while using a tailstock centre!
The cut off part needs a place to go otherwise it will pinch the cut-off tool and bad things happen.

-brino


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## T Bredehoft (Jun 30, 2015)

I worked in one tool room or another for almost 30 years, never parted off anything over 1 1/2 inches.  We had horizontal and vertical band saws for that.


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## A. Fig Lee (Jun 30, 2015)

Thank you all.
Indeed.. I used to work 3 years as a lathe operator, but it was back 30 years ago and lathe we had was 10 kVA motor, 5000-10000 pounds ..
So, never had a problem with anything. But do not remember parting big diameter. I think anything bigger then 1" was pre cut.
That solves one problem. I may leave with it. Cut it with saw.

But what a practical diameter for turning (not parting) of steel? 
Would it make on 3" diameter?
I saw examples SB could turn even 7". 

P.S. Yes, I do understand cutting speed etc..


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## royesses (Jun 30, 2015)

I've turned 3" steel and aluminum on my 7x10 HF mini. I do have angular contact bearings and a reduction pulley set installed. The angular contact bearings don't require any changes, they are a direct replacement. If you look up the approximated spacer difference you could cut one now and later use a belt sander to get it to the dimension you need for the tapered roller bearings. I believe the spacer modification is to get correct alignment of the gears?


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## A. Fig Lee (Jun 30, 2015)

Bingo, *royesses, *that what I wanted to know. So, I may stay with mini lathe. Just improve it a little bit. I have 30206 bearings, and if I remember correctly, they altogether wider something like 1.5 mm then original. Problem is, I do not know dimension of the spacer until I remove original bearings and get access to the spacer. Besides, I was told to replace the spacer with a metal one. But not sure which one was mentioned, that one, or other, which sits close to double nut on left side.

Edit: spacer in question is white one on picture 6 in   http://www.arceurotrade.co.uk/machineguides/Mini-Lathe-Angular-Contact-Bearing-Change-Guide.pdf
But make a metallic one I think was on pic 3, black one. Same URL


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## mikey (Jun 30, 2015)

A. Fig Lee said:


> I only capable to do 1/2" of steel. 1" of steel very hard to cut off, though just a regular turning doable with0.5 mm or 0.02" (diameter) for each pass.
> 
> Anyone had a luck to turning/cut off 3" steel?



Something is off - a 7X12 should be capable of much more than this. I own a Sherline lathe and have turned a 3" steel work piece up close to the faceplate and regularly turn steel up to 1.5"OD over the cross slide. I regularly take a 0.05" roughing depth of cut in mild steel and part easily with a rear mounted parting tool in every material I've mounted on the lathe. A 7X12 is a much larger lathe in comparison so I'm curious to know why you can't do it.

If the problem is with the lathe then you can decide to upgrade it or move to another lathe but it could also be adjustments (gibs, headstock bearing preload, etc) or perhaps something about your cutting tools or whatever. It might allow us to be more helpful if you posted a pic of your set up so we can see what's going on. Something is just not right here.


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## Billh50 (Jun 30, 2015)

I have parted off up to 1 inch steel stock on my HF 7x12 with no problem. I have also parted off up to 3/4" Stainless in it.


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## royesses (Jun 30, 2015)

A. Fig Lee said:


> Bingo, *royesses, *that what I wanted to know. So, I may stay with mini lathe. Just improve it a little bit. I have 30206 bearings, and if I remember correctly, they altogether wider something like 1.5 mm then original. Problem is, I do not know dimension of the spacer until I remove original bearings and get access to the spacer. Besides, I was told to replace the spacer with a metal one. But not sure which one was mentioned, that one, or other, which sits close to double nut on left side.
> 
> Edit: spacer in question is white one on picture 6 in   http://www.arceurotrade.co.uk/machineguides/Mini-Lathe-Angular-Contact-Bearing-Change-Guide.pdf
> But make a metallic one I think was on pic 3, black one. Same URL



I don't know if you can order from littlemachineshop.com will they ship to you?, but you could order the oem spacer from them and make it out of any material you'd like. Also you could take it apart first and measure what is in yours. Your bearings are each 1.25mm thicker than the original bearings. So you would need to cut the spacer 2.5mm. I've had mine apart numerous times and don't even need to remove the headstock from the lathe to replace the bearings. I do use a blind bearing puller to remove the bearing from the housing. LMS may actually give you the dimensions over the phone. Worth a try.  I may put the 30206 bearings in mine if the angulars don't pan out. So far so good though.  Also the reduction pulley kit claims a 65% increase in torque. I have uploaded the arc-euro roller bearing upgrade instructions in pdf. Don't know if they will help you or not.
Roy

If you have a c2 7x12 just the rear spacer needs .010 or 2.5 mm cut off the length according to LMS.  From LMS:
This spacer goes on the spindle shaft behind the rear bearing.
This plastic spacer is 40 mm OD, 28 mm ID, and 32 mm long.

This is a tapered roller bearing that can be used to replace the spindle bearings on the mini lathe. It requires two of these bearings to update a mini lathe spindle.
These bearings are slightly wider than the standard bearings so the rear spacer must be shortened about 0.10" to use them.


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## T Bredehoft (Jun 30, 2015)

Oh, speaking of largest diameter turned, My 6 x 24 has handled 4.5 in cast iron, I turned the backing plate down to match my 4" 3 jaw chuck. Could have handled larger, I guess.


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## A. Fig Lee (Jul 1, 2015)

royesses said:


> I don't know if you can order from littlemachineshop.com will they ship to you?, but you could order the oem spacer from them and make it out of any material you'd like. ...



Yes, great idea, thank you


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## A. Fig Lee (Jul 3, 2015)

Now, idea is to make a stop inside the spindle, so I may insert piece of metal in chuck up to certain depth and make many pieces pre cut
to the same length. We used to have it on old german lathe. It was a threaded bar which we screw in the spindle.
So, to do that I need to make a piece with internal thread M27x1.5 and set it on spindle right behind double nut.
That piece would also have let say 1/4-20 thread for a bar to screw in.

Now, to make internal M27x1.5 thread I would have no problems on mini lathe or that is a good excuse to buy G9972Z on sale and prepare for hard talks with wife?


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## RJSakowski (Jul 3, 2015)

A. Fig Lee said:


> Now, idea is to make a stop inside the spindle, so I may insert piece of metal in chuck up to certain depth and make many pieces pre cut
> to the same length. We used to have it on old german lathe. It was a threaded bar which we screw in the spindle.
> So, to do that I need to make a piece with internal thread M27x1.5 and set it on spindle right behind double nut.
> That piece would also have let say 1/4-20 thread for a bar to screw in.
> ...


I have made work stops for the head stocks on my Atlas 6" and my Grizzly 10 x 22.  Here is the link for the one  that I made for my G0602:  http://www.hobby-machinist.com/threads/lathe-headstock-work-stop-g0602.32809/ 

I found a suitable tap on eBay for about $15 and cut the external threads for the adapter on the lathe.

For a bore your size, I would use a larger diameter stop rod.  I used 3/8-16 rod.   1/4-20 is rather spindly. 
You will find a number of other designs on the website as well.


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## Sk8ter (Jun 9, 2016)

for testing I have turned 8620 3" dia in my 7x16 either with the tail stock support or not I only can do about 20thou per pass ....and the lathe is more then powerful enough plus i use either my 6 3/8" dia chuck or the 4 jaw...but the 4 jaw is way out of balance 

anyways...my hendey lathe which i just sold is a flat belt conehead and can turn about 50thou per pass so not too bad for the little lathe


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## cascao (Jun 9, 2016)

On my BV20L-1 I have turned steel on 6 inches. No problem at 140 rpm (the minimum it has)
I can remove 1mm on diameter easily.


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## 4GSR (Jun 16, 2016)

Not to brag, I've faced off a piece of 12" OD aluminum plate on my 20" Lodge & Shipley lathe taking a 1/4" depth of cut at about .015" feed rate. The was around 500 RPM.  The 10 HP motor didn't even groan.


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