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Thread: why cant I cut this thread?
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13th Oct 2018, 11:19 PM #31Senior Member
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Hi Alf. To convert imperial to metric we multiply by 25.4 which is 25.4/1. To get whole numbers multiply by 5/5 = 127/5
If you had a 4mm leadscrew you would have to stop rotation, open half nut and rack carriage back 508mm and close half nut again for your 16tpi. Waste of time. Half nut must be left closed and spindle reversed. Hope that explains it ok.
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14th Oct 2018, 09:30 AM #32Most Valued Member
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How about this for a sanity check ( if I haven't botched my calc/logic)....
With a 4mm leadscrew it needs to rotate just over 6 turns to move an inch.
If you are wanting 16tpi then the chuck needs to rotate 16 turns in the same time the leadscrew does those ~6 turns.
16:6 is the same ratio as 8:3 so to save us having to turn the chuck 16 times to test, just turn it 8 and expect just over 3 turns on the leadscrew.
So put a mark on the chuck and leadscrew (no need to engage the half-nuts), then turn the chuck 8 turns and count the number of turns the leadscrew does.
If its not roughly 3 then there's definitely an issue in the change gear/gearbox side of things - so faff with the settings on the gearbox a bit test again and see what changes.
Steve
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15th Oct 2018, 10:38 PM #33Senior Member
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Just a thought Alf. Is there another lever somewhere there which indicates imperial or metric. All we have showing is the abc lever and the 123etc. The Mazak lathe which I had a bit to do with had another lever which brought in the conversion gear to change the selected lead to the required lead. Can you provide a pic of the gear train when the gear cover is removed?
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17th Oct 2018, 12:09 AM #34Senior Member
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O.K. guys,
thanks so much for your input, I have now got it figured out by googling how to cut an imperial thread on a metric lathe- apparently a 127 tooth change gear would be helpful but I don't have one - however if you divide 25.4 by 16 you get 1.58 and the closest metric thread is 1.5
so today I will cut a 1.5 metric thread over 14 mm. and see how close this will get me to my 16TPI - as I intend finishing the thread with a stock and die I'm not sure how close this will be (.47 threads over 14 mm.) my only concern is that I am cutting head studs for a flat head V8
suggest you all look up the above on google - where would we be without it ?
Regards Alf
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17th Oct 2018, 08:07 AM #35Most Valued Member
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17th Oct 2018, 09:09 AM #36Most Valued Member
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That's not going to work well, certainly not for head studs.
You need to do some more reading - there are a few other gear combinations that will get you closer than what you're planning even if not the perfect conversion that a 127T gear gives. Or find a 127T gear - there are a few people who could make one for you if they were willing.
Or borrow time on a lathe with an inch leadscrew.
Stuff like this is why I have a metric lathe and an inch lathe. Mostly it makes no difference - until thread cutting.....
PDW
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17th Oct 2018, 09:53 AM #37Most Valued Member
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Seems strange that the manufacturer gives you a thread chart and change gear settings but requires the end user to either set up their gear train differently to what they display or use gears either not displayed or provided.
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17th Oct 2018, 10:23 AM #38Most Valued Member
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Second hand lathe - who knows if the gear was originally provided or was an accessory. Could have gotten separated.
Pretty sure I don't have a 127T gear for my Chipmaster but it's never been a problem seeing as I cut metric threads on the Emco Maximat - which in fact does have that gear along with a bunch of others for setting up oddball pitches.
PDW
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17th Oct 2018, 10:25 AM #39Most Valued Member
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And is that displayed on a change gear chart or is it for the operator to ponder.
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17th Oct 2018, 11:10 AM #40Senior Member
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If you want a completely bastardised gearbox, buy an early model Nuttall lathe ex NSW TAFE. When things got metricated in the early 1970s they changed the 1/4" leadscrew for a 6mm one. There were only a few standard leads which could be cut on those ones.
Alf, it is a pitty you are too far north as you could have borrowed my Herbert die head and 3/8" bsw chasers. Life would have been simple for you.
For those who don't know, the other conversion gear is a 63 tooth using (for metric lathes) 1600/63 . Only 5 thou error in 1 metre. For imperial lathes it is 63/1600. Metric lathe to cut imperial it is a follower and for imperial lathes cutting metric it is a driver. I guess that most on this forum knows that bit of trivia though.
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17th Oct 2018, 12:21 PM #41Most Valued Member
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Yeah - I remember. It's one of the reasons I always tried to get the Yamazaki lathe.
FWIW I have one of the old leadscrews, half nuts and threading dial indicator. Never found a use for those bits. I even (currently) know where all those bits are. Happy to donate them to someone with one of the early conversions but they either have to come & get it or wait until next June when I drive north. If I do next year - possibility I'll take the boat instead (if the crane & low-loader people ever turn up to plan its removal from my shed that is.....)
PDW
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17th Oct 2018, 02:08 PM #42Golden Member
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Implied in the use of 127 is another gear of 100 or 135 but may not be needed depending upon what other gears you have.
There are other easier gear ratios, ie 47/37 = 1.27027027(repeats forever) not too difficult to cut if you have a mill or a friend with a mill or on your lathe if you have a milling attachment - see Xynudu videos on youtube.
Discussion here focussed on going the other way ie imperial to metric but still may be worth a read ....... Metric Threading along with a spreadsheet containing different gears with 1.27 ratio.
Bill
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17th Oct 2018, 08:04 PM #43Senior Member
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It is now 11 days and we aren't sure if Alf has got to cut that 16tpi thread. Most of us have some way of solving the problem, some through spreadsheets to find that odd gear which most haven't got and maybe no way of cutting the odd teeth gears whether it be the machinery or the right cutters. Some here have multiple machines which makes life rather easy so I thought it was time to add a POS machine that I won on fleabay a few years ago whilst wasting time on the computer to make that second machine a reality. It literally did fall off the back of a truck down Woolongong way when moving workshops. Yes, it is one of those POS Myford ML7 lathes which got restored and leans against the wall for decoration in the workshop. Everything on it is "Mickey Mouse" even down to the leadscrew with absolutely no wear. Other than a few small washers over the years and last week a couple of 2 start 8mm OD 4mm lead x 25 long trapezoidal nuts for a mates POS engraver from China where the original nuts in the kit were 2mm lead single start. How easy is it to go back to basics to set the gears to cut even metric on these simple lathes. Yes I could have done it on the larger Dashin but couldn't be bothered changing the gears to do the metric thread.
Sometimes it is worthwhile picking up that POS if there is room for it. for $450 with near a full set of gears, both steadies and unused vertical slide (which incidentally will never get used but is still a nice bit of bling on the shelf for more useless decor along the wall)!!
Don't write those small machines off as they can come in handy at times. A mate was making M12 bolts for a special project using his 1970s vintage ML10. The Coventry die head on that thing had it sorted with nice threads on 4140 in a flash.
Rusty
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20th Oct 2018, 07:53 PM #44Senior Member
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Thanks guys for all your input - I have given up trying to cut this thread and have given it to a local engineering shop to complete - the threads were actually UNC (should have known as they were head studs for a Ford) If I get this problem in future I will try to source a 127 T gear to suit my lathe which will apparently allow me to cut this thread - when I see photos of lathes such as Rustys above I feel ashamed that mine can't be eaten off but do they ever do any work?
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20th Oct 2018, 08:47 PM #45Pink 10EE owner
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Why do you want a 127 tooth, when the thread chart does not say it is needed?
Gold, the colour of choice for the discerning person.
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