Threading Angle for some Austrian lathes and Taiwanese/Chinese clones

[MikeA]

Hello all,

Just thought I would post a brief note about something I learned last night while reading 'The Shop Wisdom of Rudy Kouhoupt', volume three. He had a brief sidebar in his article on how to make one's own lathe collets that commented, " I have encountered lathes from Austria and Taiwan that are calibrated to indicate the angle between the compound slide and the longitudinal axis of the lathe. If you are working on a lathe calibrated this way, you will have to set your compound slide to the complementary angle of 61° in order to have the compound slide in the correct position."

Kaching! It struck me immediately why I've been struggling to cut decent single point threads on my Maximat V10P in spite of doing everything imaginable to get good threads including buying several purpose-built tools specifically for threading - I've been setting the compound over to 29°, assuming it was the same angle I used on my Atlas lathe. One reads 29° and figures I'm smack on target. I've been trying darn near everything I could think of to make decent, clean threads and every time they would be torn and terrible, necessitating a less-than-satisfactory 'clean-up' with a die.

Went into the shop this morning to make sure and it's as plain as the nose on my face - when the protractor on the compound is set to '0°' the compound is parallel to the ways rather than 90° to the ways as it is with the Atlas.

My understanding is many of the older Emco Maier clones from Taiwan were basically copies of the Maximat and it's possible others may run into the same problem so I thought I should pass it along

All the best,
Mike

[BillTodd]

Just imagine extending the V of the thread outwards ; your top-slide should be set a degree or less inside or outside of this V (there are good arguments for 1/2°, 1°, inside or outside)

The top-slide & tool should point and move in the direction of the cut so:

External RH = \
Internal RH = /
External LH = /
Internal LH = \


Bill

[75Plus]

Mike, on my Chinese 12 X 36 lathe there are two index marks on the carriage 90 degrees apart. Due to the way the scale is attached I have to use the mark that is on the center line of the lathe when setting up for single point threading.

Joe

[MikeA]

Hello Bill,

Thanks for the input - I am aware of the correct (or perhaps I should say, several recommended angles) and have been successful with my last lathe, indeed, that was a big part of my frustration. I thought I was doing a 'perfect' setup, actually shooting for 29 1/2° but due to the difference in the way the protractor was marked, I actually was setting it at 60 1/2° relative to the workpiece.

Evidently there are very few lathes that use this uncommon method of marking the protractor and I never thought about it.

Best,
Mike

[BillTodd]

Evidently there are very few lathes that use this uncommon method of marking the protractor and I never thought about it.

My Hardinge is the same; They recommend setting at 59° (for a standard 60° thread)

[MikeA]

Hello Bill,

Good to hear I'm in good company with your Hardinge! Thanks for the information.

Best,
Mike

[Ned Ludd]

Hi Guys,
Why bother moving the top slide from its position parallel to the lathe axis, it really is not necessary when cutting threads. Just use the cross slide for in-feed and save all this faffing about.
Ned

[doubleboost]

It is possible to cut threads this way but the load on the tool with a big deep thread is massive
Using the top slide for the feed makes life much easier on deep threads

[Ned Ludd]

This is a myth, when thread cutting, but would be the case if one were to cut a single vee groove. When the tool is cutting the thread do you think the work piece knows which way the tool moved inwards? It only knows the tool to be moving sideways.
Ned

[philf]

It is possible to cut threads this way but the load on the tool with a big deep thread is massive
Using the top slide for the feed makes life much easier on deep threads

Hi Doubleboost,

Just an observation - in your demo the topslide is set at 29.5 degrees from parallel with the workpiece. It should be set at 29.5 degrees from perpendicular to the workpiece! (Or 60.5 degrees on your topslide scale.) For small pitch threads like a 1.5 mm pitch I don't usually bother and feed in just from the cross-slide and I don't have a problem. On bigger pitch screws I was taught to leave the topslide parallel to the workpiece and to advance the topslide 1/2 the amount of the cross-slide infeed (which has the same effect as setting the topslide).

Cheers.

Phil.

[BillTodd]

Hi Guys,
Why bother moving the top slide from its position parallel to the lathe axis,...

Well, On my machine it enables the use of the quick retract top-slide

On more conventional machines it, allows one to use the cross-slide as the quick retract with less 'faffing' when resetting its position.

But otherwise I agree with you, One can cut perfectly good threads either way.