South Bend Swarf

Around about the time I bought my first lathe as a boy in the mid 70s (a Portass Model S), I found a book about lathe operation in the local library that wasn't written or published by the South Bend Lathe Co but had many photos that were attributed to them. A constant theme that struck me was the continuous, spiralled swarf that came off the tool, something you don't see these days. There was clearly nothing unique about their machines that would cause this effect so it was evidently down to common practice at the time. Recently I bought a copy of South Bend's "How To Run A Lathe" which is still readily available to buy or download off the internet. Most of the content dates from the war years give or take a couple of decades. What are often described these days as "clever" techniques like the use of the cross slide to draw the tool in and out while screwcutting with the topslide at 29 degrees are simply stated as the way it should be done - and this before most of us were born.

In the photos, that evocative swarf is there in abundance. It got me thinking...and experimenting.

With some consideration, a few things seemed clear:

· Cutting speeds must have been pretty modest, otherwise these spirals would have been lethal. Also, coolant was generally applied by brush (lard oil etc!), so heat generation must have been low. It all points to slow RPMs.

· Feed per turn must have been fairly modest too, otherwise the power and rigidity required would have been significant.

· The angle and offset of the cutting edge relative to the work piece are critical. It's got to be presented at a significant angle to the radial direction to generate a continuous spiralled swarf. This is achieved by angling the toolbit at about 30 degrees to the horizontal and where possible gaining another 5 degrees by deliberately raising the tip of the toolbit above the centreline. It’s rather like planing a piece of wood with the plane at an angle to the direction of travel.

I managed to buy an Indian or Chinese copy of one of those "American" toolbit holders after a bit of searching (they are out of fashion these days), cut and welded it to better follow the angles shown in the SB book and ground up a couple of 5/16" HSS bits as recommended therein.

I did some trials on my Bantam using a piece of scrap 1" dia mild steel. With 120RPM, 2.4''' per rev and 6mm width of cut, I was soon making some fine spirals. Lowering the tool tip reduces the pitch of the spiral (bunching it up), while raising it increases the pitch as you might expect. Raising the speed to 180rpm caused chattering despite tailstock support and coolant. I tried a second bit with a longer cutting edge and managed to get a ~10mm width of cut but of course I couldn't generate a decent vertical offset with this tool turning a 1" dia workpiece, so the swarf had a very short pitch - I'd drilled a 1/4" dia pilot hole for it to work into. I'd need a 2" or so diameter piece to allow me to raise the tip of tool enough to lengthen the spiral pitch to the point where it is flexible enough to clear the tool holder and flow from the work cleanly.

That's it. Probably nothing of any great practical value but an interesting experiment to me at least. The feed rates are a lot lower than we tend to use these days with the prevalence of carbide tools, pumped coolant and high power high speed machinery. Note that I had to fit a larger 60t gear on my Bantam geabox to get the feedrate low enough.

Hope you find this interesting!

Muzzer

Very interesting. We used to grind a chipbreaker groove on the top face of the tool, just behind the cutting edge, so it would break those spirals up. As you said, they can be quite dangerous! I think the modern carbide inserts all have an integral chipbreaker groove.

Lots easier to clean up the swarf doing it your way though!

Interesting indeed Muzzer, your spiral swarf looks as good as those in the book. Book is downloaded, now I have to find time to read it.

Regards

Thor

Edited By Thor on 30/04/2013 05:49:55

Very nice spirals - you can cut them up for Christmas tree decorations - German woodturners do the same, though obviously with wood.

Or use them as razor wire!

Going back to the days when Myford had proper Open Days at Beeston, you could see in the swarf bins, and they always had strings of swarf like this.

Very interesting, thank you.

Phil

Edited By Robbo on 30/04/2013 09:34:41

Get a bit of 316 stainless, and you'll end up with spirals of swarf by the mile, I find that a pair of side cutters, and a glove on the hand takes care of most of the swarf. A non free cutting steel can also cause long strings of swarf, but I find it breaks up easier than stainless. Ian S C

I have a 1949 South Bend model 9a lathe. I also have a reprint of their "How to run a lathe" book.

Both excellent value and exactly as advertised, and much more. South Bend are very tough, versatile, and capable machines. Far cheaper even today than many others and will do good work even if badly beaten up and abused as mine was before I bought it.

There is a USA based firm who have purchased the SB name and are now offering new lathes branded SB but these are Chinese/Taiwanese made machines. If you are looking for a SB I recommend only the pre-1980 old ones, definitely not the new ones.

JD

And for beginners.......do not try to remove swarf with your hand if the lathe is running.....Gloved or not. Some ribbons are very strong and seriously sharp. If they don't pull your arm in they can cut straight through a glove. If i must remove the stuff while the machine is running I use a thin wooden stick (that will break easily), But overall I hate doing it. I still remember a thin thread like bit that tried to circumcise my finger. And that was with the lathe stopped, I was just cleaning up.

Cheers

John

Edited By John McNamara on 30/04/2013 13:15:29

That has got to be one of the best free downloads i have been shown. Thanks for sharing that with us and you experimenting.

I have just printed it off and worth every page.

Bri

HI Muzzer,

Not as wide as your swarf, but I think my record with stainless steel was over 8 feet long when strectched out (but less than 1mm wide).

When boring silver steel at the weekend, the swarf was feeding itself down the mandrel and coming out of the back of the lathe!

Neil

Boiler Bri,

Can you say from where you downloaded the South Bend book? I've tried and failed to find it through an internet search.

John

This I like:

As well as the picture on the cover!

Neil

John H: google "wewilliams.net" The current edition (1966) is well worth buying if you can find it, as it is more comprehensive. It's freely available near me but then again I am currently living in Canada.....

Note the article on screwcutting too. Just good, common sense stuff, albeit with a distinct US flavour!

Muzzer

Muzzer,

Thanks for the heads-up. Have now downloaded said publication. Looks like an interesting read.

John

Seeing swarf like that always makes me wonder how those stainless steel pan scourers are made lovely long spirals of swarf with no sharp edges...how are they made?

Ian

When I got my lathe, two of the books that I bought were "How To Run A Lathe" 40th edition 1941, and number 36A "How To Cut Screw Threads In The Lathe, dated 1938, another book that I have not been able to find is no., 35 "How TO Grind Tool Cutter Bits", Those last two books were Price 10 cents, post paid to any address, coin or stamps of any country accepted.

I believe that the Boxford in England, and the Hercus in Austrailia trace their ancestry back to South Bend. Ian S C

Hi Murray,

Impressive stuff; I'm sure you could flog the swarf as art to some unsuspecting tourists. Now all you need is a decent milling machine.

Regards,

Andrew

Murray,

Spirals like those are what you aim for when using HS tools, sharp and leaving a good finish. Chipbreakers were designed to not produce spirals as when high speed machining the spirals would wrap around the spindle...... I don't need to elaborate. Spent many hours unravelling chucks in my day, mostly aluminium, after dodging the flying swarf.

the longest spiral I have seen was as an apprentice we had one supported in tubes the length of the bay some 50yards - only stopped as the tool was about to bury itself in the chuck.....

Trevor

Hi Guys,

Some years ago I was demonstrating a Myford at the Ascot ME exhibition and some chap asked if he could have the nice long spirals of swarf, as he had never seen the like?????

Thinking of the South bend book, early ones make no mention of setting the top slide at half the thread angle but the later ones do, clearly it is a new fangled war time thing.

chriStephens

PS, and on the length of swarf thing, I was turning down some nylon and got a length of swarf in excess of 140 yards, I know 'coz I measured it. I know little things please little minds, guilty!

Chris, by 1938, in the book "How to cut screw threads in the Lathe, they had got round to turning the compound rest to half thread angle. Ian S C

Half thread angle screwcutting goes further back than 1938

I have Machinery Encyclopedia out of Industrial Press and printed in 1917 with a clear illustration and description of the set up

The same book also describes thread milling so I guess there are not many really new ideas after all

Bob D