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posted on 19/1/22 at 10:18 PM
Don't you just hate it when...
Don't you just hate it when someone comes up with an excellent solution to something you've wanted to fix for years... and then you find
out what it costs...
I have the exact same lathe as shown in the following video - sold in the 1940's, it works very well within its limits, but was originally
designed to be belt driven either by treadle or by a motor mounted underneath. Neither is very convenient! I have a motor and pulley mounted behind,
but the flat belt pulleys only have 3 steps that, together with the back gear, gives me 6 speeds. It's a real faff to alter things.
I saw this video and thought that was exactly what I needed.
Then I looked up the cost of the major parts: the control unit works out to around £200, which I thought was not unreasonable. Then I looked up the
cost of the 3-phase motor - somewhere around £1200, if you can even find one for sale to non-industrial buyers!
Sadly, I don't think I'll bother (unless I can find a cheaper solution). Shame, as it looked so neat.
I did not buy from this seller, the last seller now wants over £100 when I only paid £59
You will find the model I have advertised from about £70 to over £100.
What I try to do is find the cheapest listed making sure the Seller has over 97% feedback.
I have a Model: AT1-2200X 2.2KW version running a 1.1kw motor, I always try to overate the contoller a little.
Just watch out for the Ebay sellers Power ratings quoted.
I have seen untis advertized as 2.2kw when the model shows Model: AT1-1500X (1.5kw) and not Model: AT1-2200X
The Model: AT1-1500X may well be more than enough for your lathe.
Note you will need a 240vac three phase motor.
Some can be rewired from 380v to 240v.
And with this VFD controller you and set up Start speed, Braking speed and forward or reverse.
If you do get one, feel free to ask any questions.
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Building: It is an ex-Locost - it has gone to the IOW!
posted on 20/1/22 at 01:57 PM
Yes - I think that motor has some form of feedback mechanism to let the controller know the current shaft rpm. I think that setup is more
sophisticated than it appears at first glance!
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Building: It is an ex-Locost - it has gone to the IOW!
posted on 22/1/22 at 03:45 PM
One last question: What sort of torque could I expect with a VFD controller and a normal 3-phase motor, if I turn the speed right down?
Currently, with the lathe's belt at the highest reduction ratio, and the back gear engaged, the chuck spins at 42rpm (useful for cast iron).
Assuming a motor capable of around 1500rpm, a max lathe shaft speed of 1000rpm, this means a basic reduction ratio of 1.5:1 to ensure that the lathe
doesn't over-rev at max output. If I want a minimum shaft speed of 50rpm (for the sake of easy maths) then I would have to run the motor at
75rpm - will the motor have any torque at this speed, and is it likely to overheat* (because its cooling fan isn't running sufficient fast)?
This is based on the idea of taking away the back-gear as in the video - if I leave it in place (which would be a PITA) then I need only run the motor
at around 450 - 500 rpm minimum.
Note that this a small lathe that currently runs very, very easily on an 0.75kW single-phase motor - the flat belt slips before I overload the motor -
and I don't do heavy work. It was originally designed for treadle drive! I've been looking at a few YouTube tutorials about VFDs and it
seems like the target is somewhere around 150% of max load capability for variable torque applications. Considering that I never overload my current
motor then I'm sure that a 0.75kW 3-phase motor would have more than sufficient power, especially as it doesn't have the starting torque
problems that single-phase motors have.
Watch out running standard induction motors at low speeds. Too low and the inbuilt cooling fan may not give enough air-flow. It is probably not going
to be a problem for the speeds you will require and the length of time that it runs for, but it could be. If so, fitting a separately powered fan,
with its own motor would solve the problem.
Or go the whole hog and use your lathe to build a variator like on the Raglan lathes
I doubt my motor setup would lack the tourqe I need the belts slip way to much for load speed turning with out the backgear.
So on my setup I have not change the belt speeds since the VDF
I know only use two drive speeds, normal and backgear.
Mine is now controlled by a simple CNC system. Which if setup better can change the spindle speed relative to the diameter.
Ther VDU has made a big improvement on mine, and very shortly after upgraded my mill the same way.
I was also luck finding a nice second hand motor for £40.
Also do not for get a 4 pole 1400rpm motor can be over driven. In therory to 11200rpm. I limit mine to 50% over at 2100rpm.
This mean a higher ratio is needed but will give more spindle torque.
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Building: It is an ex-Locost - it has gone to the IOW!
posted on 22/1/22 at 04:48 PM
It really is a PITA to keep the back gear!
Its driving gear links to a part of the casting for the flat belt, which I want to get rid of (the belt slips far too easily). To do that I would
have to find another lathe that could be used to remove the flat belt pulleys neatly, and then I'd have to devise some means of duplicating the
engagement mechanism (the back gear drive wheel couples to the flat belt pulleys via a spring-loaded pin). The idea of using a toothed belt as shown
in that video appeals greatly
wiki states the grason lathe I had was made from the '20s to the '50s.
If the drive is the same, could you not replace the flat belt pully for a toothed pully and machine the end drive plate to match the old one
so the the back gear drive pin can still be used.
I sure I did this makein my own pully.
I do under stand the pain ugrading your lathe having to use the lathe being upgraded.
I went through this pain upgrading my mill to cnc. I must have stripped it down and rebuilt it five times just to make bits for it.
Have you considerd treadmill dc motors. I saw a hold 2hp treadmill sell locally for a £1.
Being a dc motor it would have good low speed torque.
I guess these would need some decent electrical/electronic know how to use them.
One other option , could you not bore out a toothed pully to fit over the small or middle flat belt pully
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posted on 16/2/22 at 10:21 PM
Just to regurgitate this topic...
I've decided to get an 0.75kw (1hp) 3-phase motor, plus a Chinese 240v single-phase to 3-phase VFD to match, and I will keep the back gear -
although it means that I will have to remove the spindle and the back-gear shaft when I fit the belt. I think that I will be able to mount the motor
so that the belt stays clear of both shafts.
I have one question - and this is my reason for posting - I know that it's a 3-phase motor, the windings have to either be 220/240v or can be
wired as such (delta configuration), and in my case I need a 4-pole motor to get the speed I want. Anything else I need to know?
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posted on 17/2/22 at 03:08 AM
Overnight musings... I have a cunning plan...
This is a picture of the Headstock on my kind of lathe:
You can see the three-step flat belt pulley - I am wondering whether I can get hold of a toothed belt pulley big enough to slide over one of the
steps, bored out as necessary to fit. It would have to be fastened somehow, but that's not a major issue.
This would result in a nonslip drive belt that wouldn't require any mods to the lathe, apart from fixing the pulley on.
Another option would to use a CAM timing belt pully.
And this the perfect forum to ask for old car parts.
I would try to use the center one on your flat pully. I do have some old timing pullies that may fit, if you can measure the diameter.
This is looking to be the best solution. It also means that I can do all of the machining before stripping down the lathe. Unfortunately I have zero
knowledge of toothed drive belt technology, apart from the skinny little GT2 belts on my 3D printers. Basically, I don't know what a sensible
size belt would be in this application.
Diam of the centre pulley is 83.5mm, and I have about 15mm to play with between the pulley and the headstock casting (it's actually more than
that, but it's good to have a bit of spare space). This means that the maximum outer diameter of the toothed pulley is 98.5mm (let's call
it 100mm). There's no clearance limit in all other directions, apart from downwards to the headstock. I am limited to 25mm with on each step
of the old pulley.
I might have to get creative and make a stepped hole so that the new pulley's boss can sit on the smallest step of the old pulley, otherwise
I'll have to machine the boss right off and fix the resulting toothed ring onto the old pulley using something like Loctite, which would worry
me (although I did fix the wheels of a 5" steam loco onto their axles, and later pulled more than 10 big blokes around a track!).
Note: Diam of the smallest pulley is just under 64mm, with similar clearance.
Ideally I could do with a toothed pulley like the one seen in the video I posted originally - no boss.
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posted on 17/2/22 at 04:14 PM
Thanks for your detailed input!
I'm starting to think that 15mm will be fine for this lathe - and I'm not even sure that I need a 0.75kW motor either as I reckon a 0.55kW
will be sufficient (but I'll probably get a 075kW anyway). I might use a 25mm width pulley and use a 15mm belt (assuming that the pitch and
tooth shape is the same) as that looks similar to what they used in the original video. Whatever - I might fit a 25mm belt, even though it's
overkill!
I'll probably use a 1.5kW or 2.2kW VFD, to allow a little bit of reserve capacity - there's not much difference in cost.
My first task is to get the lathe pulley sorted - once that's done I can think about the motor, VFD and remote. The motor pulley should be easy
enough, as I'm only looking for something like a 3:2 reduction ratio (1400 in, 1000 at the spindle, speed controlled by the VFD).
The current plan is to fit a tachometer to the lathe spindle as well - there's plenty of identical cheap digital ones with a Hall effect sensor
on eBay these days.
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posted on 19/2/22 at 03:50 PM
Well, the shopping has begun...
My little Zyto lathe is as near as dammit the same as the old Myford ML1 - ML4 range of lathes, although probably not as well made. The motor
originally fitted to those was 1/4HP, and the favourite user modification was to upgrade to 1/3HP. Because of this I decided to go for a 1/3HP motor
(0.25kW) as I was starting to think that my original plan for 1HP was excessive. It's not a heavily-built lathe, having only plain bronze
bearings, etc.
This also means that the new VFD and motor are quire a bit cheaper!
I have also located an ideal 48-5M-25 toothed pulley, ready to machining to fit onto the smallest flat-belt pulley - I will get loads of clearance for
the belt under this one. It is unflanged (which is ideal) but I will fit a flanged pulley to the motor. Various bits of guidance I've seen
suggests that it is OK to have one pulley without a flange, as long as the belt run isn't too long. It's a 25mm pulley, but I may well
use a 15mm motor pulley and belt - assuming that the 15mm and 25mm belts have the same tooth form. This should prevent the smaller belt from drifting
off the wider pulley.
Currently the lathe's motor has a countershaft driven by a v-belt, but I hope to get rid of that... we shall see.
My aim is to get a spindle speed of 950 - 1000 rpm, so a motor pulley driving directly shouldn't be too small (32 - 34 teeth). At least the VFD
gives some scope for adjusting the motor speed to suit the spindle, using the max frequency setting.
Ive fitted a few VFD's , mostly Chinese ones onto mills/lathes/drills etc
The VFD controller box can be programmed to show spindle speed so no need for a separate box unless you want to change gears/belts.
I put a 750w 3 ph motor on a pillar drill and to be honest its too low on torque at the lower speeds if I want to keep the 1800rpm top speed ( i
fitted the 3ph motor so I don't have to change belts as its a pain in the hoop)
I have a 2.2kw motor on my milling machine and that has plenty torque for pretty much everything i do . I'd prob go bigger than you think you
need , cheap VFd's just are'nt that efficient at lower speeds. Not sure i would like to have a toothed belt tho when things go wrong id
rather something slipped, a new belt and any of the spray on anti-slip chemicals work wonders.
Good place for VFD's is Bangood , they have a sale every so often and usually get a 2.2 kw one for 60 quid , and that will power pretty much any
motor up to 2.2kw. comes from china so a 2 week wait but customer service is reasonable and way better than fleabay.
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posted on 19/2/22 at 10:26 PM
The thing to remember with my old lathe is that it was originally designed to be powered by foot treadle! I'm keeping the back gear, so
I'll still have low-speed power when required.
Belt slip is the biggest problem for me - the flat belts run between the headstock bearings and inevitably get oily. The bearings are in pretty good
nick, but oil does dribble out. I haven't got room for a v-belt, and I think even that would slip eventually.
quote:Originally posted by David Jenkins
The thing to remember with my old lathe is that it was originally designed to be powered by foot treadle! I'm keeping the back gear, so
I'll still have low-speed power when required.
Belt slip is the biggest problem for me - the flat belts run between the headstock bearings and inevitably get oily. The bearings are in pretty good
nick, but oil does dribble out. I haven't got room for a v-belt, and I think even that would slip eventually.
A multi-V belt would be flatter and have more grip maybe?
quote:Originally posted by David Jenkins
Thanks for your detailed input!
I'm starting to think that 15mm will be fine for this lathe - and I'm not even sure that I need a 0.75kW motor either as I reckon a 0.55kW
will be sufficient (but I'll probably get a 075kW anyway). I might use a 25mm width pulley and use a 15mm belt (assuming that the pitch and
tooth shape is the same) as that looks similar to what they used in the original video. Whatever - I might fit a 25mm belt, even though it's
overkill!
I'll probably use a 1.5kW or 2.2kW VFD, to allow a little bit of reserve capacity - there's not much difference in cost.
It's worth doing a little more research. From what I have heard, the VFD should be reasonably closely matched to the motor. Oversizing it may
have negative consequences, but I've not looked into it myself.
