I’ve just tried to cut m12 x 1.75 but I’ve **Language** the thread up twiceZ looking at my data plate it doesn’t list 1.75 as being able to engage at any lines? Do I have to keep to a certain number?
You need to make sure you have the tight gearing, then don't disengage the half nuts until you are finished, cut, wind out tool, reverse back beyond start, wind in tool,, forward, repeat
Going by the chart you can't use the threading dial (unless you change the gear on the dial, then you might).
Had the exact same problem on my Colchester, 1.75mm pitch not listed with the standard gearbox. Apparently I'd have to set it to 2.5mm and introduce an intermediate 35/50 gear train. Even then you'd still have to keep the half nut engaged at all times. So I bought a die instead...
I basically got a double start thread then chipped the insert. I’ve got 1.75mm pitch on my gearbox and I’ve just successfully cut a M12 x 1.75 thread. Had to leave the half nuts engaged and turn the thread like an English thread. Lathe in forwards, stop, wind out, lathe in reverse, repeat etc. Looks like you can’t use the thread dial indicator on a Harrison 140 to cut 1.75mm threads. Must be some weird maths involved.
There IS a method you can use but the only real benefit of it is if you're threading to a shoulder. You still have to run carriage back with the motor.
Or you can start off a dead stop and engage in the same number at exactly the same bed position which is how I do metric on a imperial leadscrew. As Pete said the answer to your question was written on your lathe instruction plate
You may find Dr.Al's page useful on that www.cgtk.co.uk/metalwork/calculators/threaddialindicator I dont know what they were thinking when they put 48 teeth on my indicator gear, impossible to get the right number every time.
Right, I am probably going to make a pigs ear of this but here goes: Get yourself set up for the pitch you want, take your first cut noting EXACTLY where you started on the indicator. Then disengage the half nuts at the shoulder, stop the machine, put it in reverse and when the indicator is back exactly where it started re-engage the half nuts so it goes back towards the tailstock, when clear - Stop. Then wind it on a bit more and start again. If you follow me?
If you've got to reverse the lathe I don't see any point in disengaging the nuts and leaving yourself open to a cock up.
Leave the nuts in not to bad on a short thread My lathe has a clutch and a reverse on the motor This makes it much less painful
Same lathe John so not too much of an issue really leaving the half nuts engaged. I cut a thread about 60mm long in less than 10 minutes using this method.
This is the video, I remember it because I was looking at the Titanium turning, see if he had discovered a non dangerous technique (he hasn't) but he shows this forward-reverse way of using the thread indicator really well. It is about 161/2 minutes in:
That’s the painful method of having to put machine in reverse and gaffing I put the lathe bed stop at a comfortable start position so I get the same start position then use same number on thread dial indicator. I have to use this method as my monarch has a metric only box and imperial leadscrew and forward only on the clutch so machine motor would have to be restarted in reverse. Go broke like that Same for my big dsg have to select a reverse gear erghhrr My late dsg has a patent compensation thread dial indicator with two dials which can do nearly all metric pitches. My Holbrook has leadscrew single dog clutch reverse. My mastiff has reverse on the clutch so gets major abuse!!
Well I would agree with you, it is the hard way, but useful when you are in a situation where Brad is right now, or when turning Titanium, did I tell you I hate turning Titanium? This is why: But I would think you know that. It also knocks hell out of tooling AND machines. I do this for very few parts.
