Post By cypherp
Post By David Merrill
Making a threading dial (thread chasing dial) for a METRIC lead screw?
As mentioned in my previous post I guess I'll have to make some threading dials for my lathe...
it's a DeVallieré H-130 set up for metric stuff (Page Title)
I know that with a lathe set up for imperial threads / american stuff the gear's Tooth Count of the threading dial would have to be a multiple (4x) of the TPI count of the Lead screw....
I also know that for a metric lead screw to cover the whole range one needs several gears...
But how to calculate how many teeth the gears must have... ???
my lathe can cut threads with a mm pitch from 0,45mm to 4mm (so it's quite a broad range)....
I mean there must be some equivalent type of calculation I can do to figure out what gears I must cut...
Do a bit of research, all you ask is on the web.
Metric thread dials aren't simple animals even with metric lead screws. There will be multiple worm wheels to cover your range of threads and the divisions on the dial won't be evenly spaced.
That's probably why your lathe was produced without a thread dial. They're not easy to use and expensive to make.
Imperial wins this battle, big time.
not truly wanting to be sarcastic - but all I have to do then is to go back to be doing what I did for the last few hours, that is, asking google??
honestly - It's not like it's an everyday question that has been answered a thousand times... OK - I might not be a Google-Master ...
if you know anything specific, please let me know I truly would appreciate some specifics.
I know that it will take me at least three maybe even up to five gears (no problem, I've been making gears for a while, I'm just not in on the whole math of calculating them properly... I can take a drawing or any specs and produce it though).
As mentioned, I am aware that on an imperial lead screw it takes just one single 12T or 24T gear (usually) to get a dial...
but alas, I rarely need to do imperial gear stuff, so that's why a metric lathe....
So - if there's any hard info on how to calculate the gears for a metric lead screw's thread chaser, I appreciate any info, link, math...
May be if you stopped slagging people helping you off they would be more inclined to help. Equally if you engaged your brain, assuming you done what would be primary school maths over here you would realise its simply a case of how the pitch your cutting divides into your lead screw. If yours is 4mm, doing 1mm, 2mm and 4mm is as easy as it is with imperial.
Gets progressively harder for all the other silly metric pitches.
Won't work worth a dam cutting imperial threads at all!! That requires a metric to imperial conversion on the gear drive to the dial (yep some manufacturers done it, you can find out who on google)
A far better effort is to make a quick retracting threading tool. Makes it far faster winding it back all the time.
Equally look into some die heads. Can't beat one pass threading :-)
Just an idea. One gear metric thread dial, with encoder, micro controller and LCD readout. One button to power on/off, one to cycle thread pitch, one to zero.
That is an extremely good idea. Should not be too hard to do, but packaging would be the key - get it small, self contained and oil-tight. The encoder would probably have to be a fairly high count per rev? Excellent idea for a project.
here's what I calculated so far....
my lead-screw has a 4mm pitch....
Thread pitch - Gear - Segment on dial (to engage in)
0,45 - 27 - Segment 3
0,5 - 20 - Segment 4
0,6 - 27 - Segment 3
0,75 - 27 - Segment 3
0,9 - 27 - Segment 3
1 - 20 - Segment 4
1,2 - 27 - Segment 3
1,25 - 20 - Segment 4
1,5 - 27 - Segment 3
1,75 - 21 - Segment 3
2 - 20 - Segment 4
2,5 - 20 - Segment 4
3 - 27 - Segment 3
3,5 - 21 - Segment 3
4 - 20 - Segment 4
So that means I would need a 20, 21 and 27 Tooth gear to get all the thread pitches my lathe allows for....
can anyone confirm this?? before I probably make some crap
I have 3 gears on the stem of my metric thread cutting dial and they are 28, 30 and 32 teeth. Those give you the prime numbers 2,3,5 & 7, which combined with a few different gears will give you all the metric thread pitches you will need. Not quite as straightforward as cutting TPI on an imperial lathe, but 95% of the world's machinists cope. I can take a photo of my thread chasing chart, ie dial teeth v pitch, if that will help.
Yeah but what is the threads pitch on your lead screw Bob? That's the key bit of info to making it compatible with another lathe.
Ferrum i don't think the idea of engaging on the third works on all the ratios you have shown. Put simply once the lead screw has rotated once, its no longer going to be engaged on 3 but on 2, ie 3/4+3/4= 1 1/2 But your on the right track.
A lot of the other pitches could be engaged in a lot more places on the dial. But the ratio of screw to dial must be of complete revolutions to the pitch or its going to go out of sinc.
You folks might investigate how hardinge makes a lathe that cuts both inch
and metric threads, with no thread dial at all.
This would be the way to go I think.
Try these search strings in Google:
metric thread dial gear site:practicalmachinist.com
metric thread dial gear site:homeshopmachinist.net
The Google search strategy tends to put the hits on ALL the search terms near the head of the list - more sophisticated than most of the built-in forum searchs.
This is not a trivial problem, unlike the imperial case. If you really want to calculate things best to get a sight of Martin Cleeve's book Screwcutting In The Lathe which tells all you wanted to know (and a whole lot more) about gearing and thread pick up issues.
Frankly its best to copy an existing set-up. There are at least three common approaches depending on how many divisions are on the dial, whether the divisions are evenly spaced and whether there is more than one set of divisions. Casual inspection suggests that there are at least 6 adequately sane ways of going about things, especially if only a limited range of threads is to be covered.
For what its worth my Smart & Brown 1024 VSL has a 4 mm pitch lead screw with 12 evenly spaced divisions on the dial. There are 4 interchangeable drive gears of 12, 14, 15 and 18 teeth respectively and a spiffy little plate telling you how many divisions you need between engagements for 19 thread pitches. So even that isn't comprehensive. You couldn't pay me enough to use it in anger. But there are worse. I believe one breed of lathe sports a dial around 3 inches in diameter with 3 (or maybe 4?) independent sets of unevenly spaced divisions!!
Best answer is either a proper third lever fast return system which keeps the half nut engaged or a single tooth dog clutch as used by Holbrook, Pratt & Whitney and some other high class machines. Oh and Hardinge too. The mechanics of a single tooth clutch may be hard to install retrospectively but electronic operation should be feasible. A car door lock actuator seems a relatively inexpensive source for a hefty actuator.
I have a metric thread dial for sale. It is for a South Bend Lathe with a 4mm pitch leadscrew. Complete with Chart ( not pictured). It is new old stock with a little surface rust...$300
Shipping to Switzerland would be about $50
Thanks everyone so far!
Clive: I just ordered the book off amazon... cheap and should be at my place soon enough... thanks .- I always appreciate a good book
David: this is pure genius... didn't know... thx.
adama, thanks for the heads up on the dial thing...
Ted: I might be interested if my own project fails...
I love to make my own tools... but I can't dedicate too much time besides regular work to it... so if it gets too time consuming I'll pick you up on the offer...
btw. what's the diameter of the Southbends lead screw for which the thread dial thing was made for? (mine's roughly 24mm)
(btw. I used to own a SB9 lather couple of years ago... loved it...)
I'll get some brass rods during the next few days and will make a few gears and see where I'll get from there...
btw. here's a photo of the De Valliere H130:
( I know... it deserves a new paint job...)
and an ER32 Collet holder for my Aciera F3 Mill (with a W20 Spindle) I've made on the H130...
Hope you find Martin Cleeves book useful. Probably only a couple of chapters directly relevant to you but its the only readily available source I know of dealing with the pick up, thread dial and related issues from first principles and pretty comprehensively. Ton of stuff on change gears which is fairly wasted for most of us.
Heck I bought the book for two chapters and found the rest interesting, albeit in an intellectual way. Which wasn't too bad. Got a couple or three around where what I wanted works out at around £3 a page!
Ah I bet there are some useful infos in that book - and it was quite cheaply available...
guess it will make a good addition to my shop's library