Threadcutting on Myford ML7 question

Just tried my first bit of threadcutting on my ML7 this evening, making a drawbar for my Sturdimill, 5/8" UNC thread. I originally intended to use the
setover method as recommended by Chris Heapy, amongst others, but I discovered that I cannot set the topslide to 30 degrees (what would be 60 degrees as the zero is with the topslide at 90 degrees to the crosslide). Am I missing something with this method or is it a limitation with the ML7? I ended up going in at 90 degrees using the crosslide and taking small cuts (.010" at first, finishing with .002") and ended up with a good finish, but it looks very aggressive doing it this way. Martin.
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Martin Whybrow wrote:

i cant answesr your question regarding screw cutting on a myford, but i can say, screw cutting is agressive, you think you are only taking a 0.002" cut, so you are expecting a small curl of swarf, but, using the plunge method (90 in) you are in truth taking a large surface area of material (0.0002" at the tip, but at a guess 0.006" on the sides) off because of the cross section of the tool used.
if you can get the half angle (set over as you call it) method to work, you will get a much better thread finish, and there is 50 less force on the tool. the only thing to remember is that you need to wind the cut with to topslide, and that, as you are working on an angle that you need to do some simple trig to work out your depth of cut.
I am impressed that you managed to get a thread, i have engineers with HND's under me at work, and they wouldnt know where to start cutting a thread on a lathe.... very very sad state of affairs if you ask me, and the question must be raised... what the hell did they learn at college?????
HTH
dont get me started on engineering......... you will never shut me up, I am an engineer...... therefor i live!
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dont get me started on engineering......... you will never shut me up, I am
an engineer...... therefor i live!
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On Wed, 01 Dec 2004 23:05:14 +0000, Tim Bird wrote:

Which buttons to press to get the CAC system to do it for them?
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Ken Parkes wrote:

probaly more truth in that than i dare to admit..... glad to know there are still some REAL engineers in the world
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Visit my updated website @ www.timbird.net
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There is a distinct difference between "Engineers" and "Craftsmen" but of course a little overlap is possible.......
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There is a limitation : the Super 7 has a better design that fixes this, and there are mods you can do to improve it but you can get to 30 degrees from the cross-slide (Bradley's book claims 63 degrees from the centre position, which could well be correct).
I puzzled over this for a while as the scale marks stop at 45 degrees and that's also where the vernier hits the corner of the cross-slide. Yet all the ML7-specific books (Sparey, Bradley ..) show the same layout as Chris Heapy's photo. Then I had one of those d'oh moments and wound the topslide back another inch or so until it cleared the corner :-). So you only get about 2" of topslide travel once you're past 45 degrees from the centre line.
-adrian
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wrote:

a
the
60
crosslide). Am

I
I too have had a d'oh moment; I had left the T bolts on their original positions with the front one at the right end of its slot limiting the movement to less than the 60 degrees I needed; I've no idea why I didn't realise this earlier as I only moved them for another job 3 days previously! I will move them to the opposite ends of the slots before I do the next threading job. BTW, try threading at bottom speed without backgear (I have to, I need to replace the bullwheel and backgear due to the last owner's carelessness), it really tests your reactions! I'm very glad that my ML7 has a clutch making it easy to stop the spindle quickly :-) Martin.
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I don't have a clutch but I do have a VFD : this makes it easy to have a selection of run modes (I think the latest Super 7 does something similar).
I have it wired to provide slow-forward and slow-reverse options where the on/off buttons are non-latching, i.e. the motor stops as soon as I release the green button. This makes it much easier to make short 'jog' runs.
The speed control range is also reduced in these modes so that the control knob only allows about a quarter of the normal maximum. I do have a working backgear but hardly ever use it.
-adrian
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It is possible to set the top-slide over at 60 (well it is on mine) but you go beyond the standard engraved markings.
What I did was set the top-slide at 30 and make another mark on the top of the cross-slide where the Zero Degrees line rested then simply move the top-slide again so that the 30 mark aligned with the new 'scratch'.
Where I had difficulty was setting it to cut an Acme thread (14 - 75) even more important that this is done due to the much larger tool contact. I had to remove the standard clamping bolts and use straps bolted through the rear tee-slots - not entirely satisfactory but it worked. A further problem is that the top-slide is only engraved to 45 and to get the 75 you need to align the new 'scratch' with 45. What I did in fact was to make another mark on the cross-slide where the 24 is when the top-slide was at 30, finally aligning the 40 engraving with the second 'scratch'. By now of course the feed handle of the top-slide is likely to interfere with the cross-slide dial, so making sure there is sufficient travel in the top-slide is another issue.
I haven't yet had the courage to drill and tap the Cross-slide to make clamping easier - but I will soon as I need to cut another two acme lead-screws.
JG
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I can identify with you on your problem also having just done my first threads, internal & external , not without some hair pulling &manual reference into the early hours and some reruns!
I have an S7b but the ML& should allow the deflection of the topslide to 30 deg. The point is where does the 30deg measure from? In my ignorance & inexperience I moved the top slide round to 30deg mark, it is indexed on the S7. Then gaily cut away using about 40rpm. I advanced at about .002" , this seemed OK and didnt tear too much. I got to thread depth & offered up the part to fit - NO!! Looking at the cut thread it was laid over to one side , I had an angle effectively of 60deg on the right hand side plus 30 deg on the left. I had to reposition the topslide to 60deg on the index and all was well. This is all to say and I suppose it is obvious really that the 30deg or 27.5 deg is off the line of the crossslide travel. I just looked at the index marks and assumed it would be right
Another experience I had was with the poor thread profile I cut initially. This was down to me using the tumbler gears to reverse the saddle and not the motor . In the end I didnt disengage the half nuts at all, even on the Whit threads and all was well. The use of the tumbler gears to reverse put the tool out of sync with the work each time. My threads cut were 20x1.00 metric external and 9/16 x 26 internal
I suppose we all learn by our mistakes
Mike
Just tried my first bit of threadcutting on my ML7 this evening, making a drawbar for my Sturdimill, 5/8" UNC thread. I originally intended to use the setover method as recommended by Chris Heapy, amongst others, but I discovered that I cannot set the topslide to 30 degrees (what would be 60 degrees as the zero is with the topslide at 90 degrees to the crosslide). Am I missing something with this method or is it a limitation with the ML7? I ended up going in at 90 degrees using the crosslide and taking small cuts (.010" at first, finishing with .002") and ended up with a good finish, but it looks very aggressive doing it this way. Martin.
--
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