Hercus 9" parallel turning accuracy

**cba_melbourne** · 12th October 2011, 07:54 PM

Originally Posted by Matt McLeod;1385565[FONT=Courier New

Now, Harold says I should be aiming for 0.002mm over 100mm length. I'm hoping that is a publishing typo and should be 0.02mm because I can't measure to 2 microns.[/FONT]

Matt, the bed alignment is usually done with an engineer's precision level. Only if it is known that the headstock-to-bed alignment has not been disturbed, then a shortcut method using a test bar sitting directly in the headstock taper can be used. This test bar is normally 300mm long (12"). In either case, the final verification is by taking a test cut as you describe.

The tolerance for parallelism of the spindle center line to the longitudinal motion of the carriage (both vertically and horizontally) is typically +/- 0.02mm measured over 200mm along the test bar. This tolerance was set out before WW2 by a professor Schlesinger in the USA. He created a set of tests called after him the Sclhesinger inspection record. The intention was to protect lathe buyers from inferior quality by setting a minimum standard. Ever since, all lathe makers have been using this inspection record during final assembly of their lathes. Of course, 0.02mm is a rather rough figure for an average production lathe. An expensive toolroom class lathe like a Hardinge or a Schaublin will be many times better.

Now to give you a practical figure for a lathe very similar to yours, I did look up such an accuracy test report for a Soth Bend 10K lathe. Every 10K came with such a report, giving both the allowable error and the actual error for the one particular lathe id was filled in for The cutting test as you did it, specifies a maximum permissible diameter error of 0.0003" (0.0076mm). A typical result would be 0.0002" or about 0.005mm. This should be achievable by properly levelling or shimming the lathe bed.

Levelling is simply the quickest and easiest way to align a lathe. Of course a lathe that is not level can also be shimmed into alignment - the best example are lathes used on ships. But it takes a lot more time, as you are currently finding out.

Chris

**4-6-4** · 13th October 2011, 08:21 PM

I have been told by a Hercus owner the only way to get the Hercus late true and parallel to to go by the instructions in the Hercus manual. He explained them to me and they are not easy. But my friend tells me his cuts true and parrallel after following the instructions
4-6-4

**morrisman** · 13th October 2011, 08:35 PM

Originally Posted by 4-6-4

I have been told by a Hercus owner the only way to get the Hercus late true and parallel to to go by the instructions in the Hercus manual. He explained them to me and they are not easy. But my friend tells me his cuts true and parrallel after following the instructions
4-6-4

Can you tell us where to get a copy of the manual

**pipeclay** · 13th October 2011, 09:00 PM

Do you have a copy of the text book of turning,the answers you require should be found there.

**morrisman** · 13th October 2011, 10:47 PM

This may be of some help
Setting a metalworking lathe to turn parallel 01

**Matt McLeod** · 14th October 2011, 08:37 AM

Hi Stu,
Thanks for your input.

Yes "tailstock spindle" not headstock spindle.

Yes it was seven times I took the measurements, but I used light cuts (no more than three thou on the crossfeed dial) before I put a mic on it.

Set up the belts for highest spindle speed, powerfeed, lowest feed/in on the box (whatever that is...maybe I should put a computer in the shed), carbide tipped cutting tools.

Shims went under the *bed* mounting bolts, front side of the lathe, *tailstock end* of the bed....just like my version of TBoT says, Chapter 1, pages 5-6.

Thanks for your input so far fellas, I will spend some more time over the weekend seeing if I can tune it up a little more and ask more stupid questions on Sunday arvo.

Cheers
Matt

**4-6-4** · 14th October 2011, 10:28 PM

Greetings chaps, The next time I go down to my mates place I will get pics of this Hercus. I will also try and find out where there is a copy of the Hercus Instructions. This is possibly the best equipped Hercus around. It has a clutch so that the motor runs at all times, just like a real lathe, Also it has an extended crosslide a rear tool post. a quick change tool holder with 30 holders. So you keep a tool in its own holder, no more packing. A taper turning attachment is also a feature. All of these features are made in the mates workshop. All castings were made and cast in the RMIT Foundry by the owner. I must admit that I have a bit of a chuckle when I see Hercus attached to a wooden bench.
Tootle Pip for now.

**.RC.** · 15th October 2011, 08:47 AM

Originally Posted by Matt McLeod

carbide tipped cutting tools.

carbide takes more force to make a cut then HSS... It has greater potential to push the work away..

To do this test you want a very sharp HSS cutter with no approach angle on the tool..

Also the talk of 0.002mm over 100mm is purely hypothetical and near impossible to measure consistently for the average home user..

Go by the spec sheets of what the lathe was designed for..

Acceptable tolerances should be around 0.02mm over 200mm maximum...

**dle147** · 15th October 2011, 10:52 PM

Matt,

Whoops - sorry Matt, posted this before I realised yours is a 9" lathe and I don't know how to delete the post. My comments relate to the 260 .... but if the mounting is similar ...

If you are shimming between the bed and the tray, at each of the 4 attachment bolt locations that mount the bed pedestals to the tray, there is a hex head threaded insert screwed into the cast pedestal. ie each attachment bolt goes through the centre of the threaded insert. Loosen each bolt where you think you need a shim and then screw the threaded insert clockwise to increase or c/clockwise to reduce the gap between the bed and the tray - that'll obviate the need for shimming. When the lathe is first set up, they protrude the threaded insert about 1mm below the pedestal base, and I know with mine, that leaves plenty of insert thread left for adjustment.

Hope this helps.

David.

**4-6-4** · 16th October 2011, 08:59 PM

Greetings chaps, I have found out more about the Hercus Hand bool It is called Text book of Turning and it was printed by Hercus. It is said that Hercus lifted the publication from South Bend in America. Not surprising since the Hercus was copied from a South Bend. I was at a Model Engineers in Melbourne once and heard a talk given bu one of the sons of Hercus. He told a story about a trip his father made to the USA. He went to south bend and was being shown around. It took the south Bend people a while to realize who their visitor was. They then showed him the door. I am going on a pilgrimage to my mates place and will have pics of how to level a Hercus. The Hercus book is available on the internet I will try and find it. 4-6-4

**4-6-4** · 16th October 2011, 09:10 PM

I have found the Hercus book on line. I Googled Text book of machining and the Practical Machinist site came up and there in the first post was a link to a copy of the book. It is a 1970 edition and is the full edition. 4-6-4

**4-6-4** · 17th October 2011, 09:49 PM

Greetings chaps, I have finally managed to visit the mates workshop and here are thje Picks I promised. His machine is mounted on legs bur the principal is as described in the Hercus Book.

**4-6-4** · 17th October 2011, 09:50 PM

damn the pics did not load Will try again 4-6-4

**.RC.** · 20th November 2011, 11:05 PM

This may interest some people here

http://www.wswells.com/data/howto/H-3.pdf

I had a problem today with a Hercus 260 I am sorting out.... Did a test cut and unsupported the workpiece was tapered by 0.1mm over 100mm.. Removed the headstock, wiped down the seating area thinking the problem was there..... Same result..

Found that instruction there on page 20 of the linked pdf and blow me down if adjusting one side of the tailstock did not get rid of the taper... I thought they would have been more rigid then that.... Ended up with a 0.01mm over 100mm taper...

**jack620** · 21st November 2011, 07:53 AM

Thanks for the pdf Ray. The technique described on page 20 is exactly the same technique as described in the Hercus Textbook of Turning.
Chris

PS. can anybody see any reason why you couldn't use aluminium bar for this test?

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