Author Topic: Micro lathe refurb  (Read 23213 times)

Offline Allen Smithee

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Re: Micro lathe refurb
« Reply #15 on: August 31, 2014, 04:07:40 PM »
What sort of power are you looking for, and at what (motor spindle) rpm? I would say it's crying out for a small brushless motor, and if you're only looking for 200watts it would be dirt-cheap to do, as well as giving you full speed-control (and the intriguing possibility of being able to run from a car battery!)

If you're interested I can help you choose the components...

AS
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Offline ths

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Re: Micro lathe refurb
« Reply #16 on: September 01, 2014, 01:22:21 PM »


Hugh, I would like to see those photographs,  I got the original (I think) layshaft with mine which I understand is uncommon.

Hope this is OK with you Rod.

I purchased this about 4years ago via an eBay auction. It came from the estate of an O gauge modeller in the northern suburbs of Sydney. I don't know if he was the original owner, but it is little used, and in wonderful nick. What can I say? It came with all the accessories that were available for it, and the only one that might be expected to be here (travelling steady), was not, but I don't think Flexispeed made one. I have the manual that came with it, and it is not listed.



Here we have the lathe, mounted on the Flexispeed recommended (it's in the manual) drawer in cupboard. I have the drawer, but it's not in the shot. The motor is a Parvalux 1/4 HP, sprayed in the same Hammerite blue as the lathe. The countershaft is different to John Hill's, being a Picador product, as is the motor pulley. The drip tray is a piece of galvanised quad guttering, cut down and soft soldered to fit the purpose. An outlet, soldered in, may be discerned to the bottom left of the tray. A 12"/300mm ruler acts as a scale.

From left to right, backish row, gear cover with threading chart, swivelling vertical slide, change gears, 3 jaw chuck, 4 jaw chuck (I made the key), vise for the vertical slides, fixed vertical slide, fixed steady, faceplate, angle plate, headstock pulley cover.

At the front are a few things I've made for it, soft centre, 3/16" endmill holder, a revolving centre modified from one sold for the Seig C0, a holder for 13/16" dies, and an ER16 collet holder, which takes up to 10mm.



This shot shows the motorising side a bit better, as well as the change gears and the fine feed mechanism (but not very well). The fine feed is lovely, a double worm and wheel system that the makers say gives .0015" travel per revolution of the headstock spindle, and is separate from the change wheel system. Here I have the gears arranged to cut a 40tpi thread, but I'll be buggered if I can arrange it to cut anything but a very nice left hand thread. I wonder if I'll have to make a third banjo stud, given that for the required gears to mesh, an idler is necessary, which reverses the usual right hand cutting direction.

I've never done much with it, but have made an Elmers wobbler on it. Great on brass, struggles a bit on steel, but more to be found out. It's a baby, but a sweet one.

How fast could you run the spindle? Mild (I think) steel in cast iron.  I have a 24 v DC motor, ex mobility device, a power supply, and have ordered a couple of speed controllers...

Hugh.

Offline ths

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Re: Micro lathe refurb
« Reply #17 on: September 01, 2014, 01:46:26 PM »
I forgot to say, the manual has been scanned, PM for a copy. Hugh.

Offline tangler

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Re: Micro lathe refurb
« Reply #18 on: September 01, 2014, 04:44:24 PM »
Hugh,

Thank you very much indeed for sharing the photos.  My, that takes me back:  the very first lathe I ever used was exactly that model.  It sat at the back of the lab where I first worked.  I guess that's why I've been attracted to my Flexispeed, which is, I think, a generation earlier. I have PM'd you. 

I've had a couple of setbacks over the weekend.

With the paint dry (mostly - I'm a bit impatient) I've put the lathe together with a temporary motor system to work out what speeds and power I really need.



 I've made a couple of changes:  The handwheels had been modified to have rotating handles.  I don't like these so I hand turned a couple of new ones in stainless.  I' also made a Drummond type tool holder to fit directly on the cross slide in the hope that it gives me a more rigid option than the topslide.

The motor I hoped to use was this one:



It's a brushed Parvalux, rated at 1/10 Hp and 3,500 rpm.  I bought it second hand and it has had some work done on it with an NVR switch.  On no load it ran at 17,000 rpm and with countershaft system the slowest speed of the lathe spindle was 7,000   :o .  Presumably the torque was minimal.  Perhaps I'll make toolpost grinder someday.

This is a1,400 rpm 1/6HP induction motor which I use to drive the overhead gear on the Myford.



The starting capacitor, reverse and on/off switch live in a separate box which can be seen in the 2nd photo, so not really the compact system I'd hoped for.  I made an ally pulley for the countershaft to match the lathe pulleys which appear to be for an M size belt.  The countershaft itself was from an old home made power hacksaw I was given (and have since dismantled).  The drive belt is 6mm hollow urethane which is a) too small and b) old and brittle - it keeps breaking.  The pulley on the motor was the existing one.  The system worked well enough for a trial.



This system gave a maximum speed of 2,100 at the lathe spindle which I think is about right.  I can make a 2 speed pulley system for the lathe and countershaft to give me some more speeds.

I tried some trial cuts.  The lathe stalled very easily as the belt slipped on the lathe pulley.  Worse however, was the appalling chatter  :( .  I mentioned early on in this restoration that there was sufficient take up in the bearings to cope with the wear in the spindle.  I think I was wrong  :-[ .  I used the 1/2" ground silver steel and some blue to check the headstock bearings and they appear to be good.  The spindle was less so, with poor contact near the flange and the rear bearing only appeared to contact over half the diameter.   In this design, the end float can only be taken up by adjusting the pulley against the rear of the front bearing - which is strange because this need to be slackened off to engage the back gear (and is why, presumably, the pulley is cast iron,  to run on the spindle).  The large back gear pulley is fixed to the spindle by a grub screw.  As a test to see if the spindle was really the problem I mounted a length of 1/2" precision ground mid steel (the un-bent half for those kind souls who have been following this saga) in the headstock with the pulley and back gear.  These were fastened to the shaft with their grubs screws, the back gear taking up the end float.  It was very noticeable that the spindle needed a quarter turn of the adjusting screws to bring any pressure on the spindle while the PGMS needed barely a nip (it will be remembered that spindle measured 2 thou undersize).  I was also somewhat surprised that I need to ream both pulley and the back gear to get them to slide onto the shaft.  Perhaps the design was deliberately 2 thou under 1/2".



A trial cut was taken. 



Smooth as you like.  Something of a relief really but it does mean that I have to make a new spindle.  I've been trying to work out a way of using the PGMS but that means attaching the flange somehow.  I think I'm going to have to turn the whole thing and use an external lap to bring it to size.  I will also need to try and replicate the worm on the end - never done that and do I copy the wear?

Apart from that, the issues that still need sorting are:

 a)  the drive belts.  I'd ordered some cogged ZX belt which I'd hoped would be more flexible than the standard M size belt but my ebay supplier has failed to deliver.  Today I've ordered some 8mm urethane belt from GLR Kennions so I'll see if that does the job.  I'd like to keep the pulley centres small if I can to have a rather more compact set up than I've used for the trials.  Elastic belt would have the advantage that I would not need a tensioning device to change speed.

b) the motor.  I'd rather not use the induction motor since it has another life so, AS, I am interested in finding a compact motor with good torque and variable speed.  What can we do for 200W and a lathe spindle speed of 2,000 rpm?

Sorry about all the text,

Rod

Edited for nonsense

« Last Edit: September 01, 2014, 05:49:25 PM by tangler »

Offline Allen Smithee

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Re: Micro lathe refurb
« Reply #19 on: September 01, 2014, 04:58:46 PM »
Rod - what's the current reduction ratio (both with the pulleys you have there via the countershaft and/or if you were driving the countershaft directly)? 200-300w is no problem at all - I just need to know the motor speeds you're after.

AS
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Offline tangler

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Re: Micro lathe refurb
« Reply #20 on: September 01, 2014, 05:45:42 PM »
Hi AS,

According to my laser tacho the motor is running at 1470, the countershaft at 1142 and the lathe spindle speeds are 655, 1237 and 2170.  Clearly I didn't get my home made countershaft stepped pulley quite right since the middle pulleys are supposed to be the same size and should give the countershaft speed.

So, motor to countershaft is a reduction of  1.29 :1

Countershaft to lathe are 1.9 :1,  1:1 (approx  :-[)  and .55 : 1

The countershaft speed is about right so I guess it's how we connect the the motor to the countershaft.  If we have a variable speed motor then a single pulley, perhaps with a timing belt, would be fine so we could have quite a significant speed reduction if necessary.

Thinking out loud now:  The worm gear gives a very fine (I think .5 thou per rev) feed. A separate small variable speed motor driving this would obviate the need to cut a worm and thereby enable a proper end float adjustment outboard of the rear spindle bearing.  If we've already got a 12v supply.....

Cheers,

Rod

Offline Allen Smithee

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Re: Micro lathe refurb
« Reply #21 on: September 01, 2014, 06:10:59 PM »
So essentially if you want a maximum chuck speed of (say) 2500rpm you're looking for something that will drive the countershaft at roughly 1300rpm. If it was a staright DC motor operating from a 12v supply then (allowing for some sag) you' be looking for a motor of around 140rpm/v to drive the countershaft directly - this can be done, but it's an expensive solution. There are cheap brushless motors available with Kv ratings of 400-500rpm/v, so could you produce (say) a 3:1 reduction with a new motor-to-countershaft pulley? If so then the resulting motor would have loads of "headroom" (being rated for well over 40A continuous rather than the required 20ish) and would have continuously variable speed control. You may still want the gearing options in the countershaft pulley to increase the available torque when being used at lower speeds, although the torque at part-throttle should still be pretty good.

I'm fixated on 12v because it's very easy and cheap to get a 12v PSU rated for >50A, and that would just seem to simplfy things!

AS
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Online Jo

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Re: Micro lathe refurb
« Reply #22 on: September 01, 2014, 06:17:44 PM »
Rod only the later high speed Cowells go up to 2100 rpm, it has an uprated lubrication system to cope and they also redesigned the headstock bearings to make them much more substantial. I put a second pulley on my earlier one to enable her to do the higher speed but I must be honest I prefer not to push her that high and normally run her at 800 rpm (same as C2).

Jo
« Last Edit: September 01, 2014, 06:26:07 PM by Jo »
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Offline tangler

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Re: Micro lathe refurb
« Reply #23 on: September 01, 2014, 07:52:37 PM »
Jo,

Thanks for that.  I was under the impression that the high speed version (4,000 rpm) used a hard spindle in bronze bearings but that the standard (2100rpm) used a soft spindle in cast iron.  I'll bear your comment in mind but I think I'd like the capability, at least, to go to 2000.  Lubrication needs to be good though.  ETW recommends that the split in this sort of bearing be filled with something elastic to stop the oil spilling out sideways, while still allowing some adjustability.

Cheers,

Rod

Offline tangler

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Re: Micro lathe refurb
« Reply #24 on: September 01, 2014, 08:12:59 PM »
AS, 

What are we looking at, bearing in mind that my experience of electric flight began and ended with a 540 motor and 7.2V nicads (with a Mole charger - remember them?). 

Something like this?

http://www.hobbyking.co.uk/hobbyking/store/__18178__Turnigy_Aerodrive_SK3_6354_245kv_Brushless_Outrunner_Motor.html

or are there bigger, torquier, slower, cheaper ones about?

So, if I understand correctly 12v x 245 gives  2940 rpm.  3:1 reduction should be doable.  What would I be looking for in terms of a PSU and speed controller?

Cheers,

Rod

Online Jo

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Re: Micro lathe refurb
« Reply #25 on: September 01, 2014, 08:52:43 PM »
I was under the impression that the high speed version (4,000 rpm) used a hard spindle in bronze bearings but that the standard (2100rpm) used a soft spindle in cast iron.

 :facepalm: Another Cowells again: the CW, high speed watch makers lathe. Yes different bearings, nose spindle, variable speed control etc.

Mine are both the ME version but the later one was modded to allow for the higher 2100 RPM and less prone to break the headstock if you get heavy handed ;)

Jo
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Offline tangler

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Re: Micro lathe refurb
« Reply #26 on: September 01, 2014, 09:24:41 PM »
Hugh has very kindly sent me a copy of the manual for his Flexispeed.  "A long life can be expected form the spindle/bearings if the speed is kept below 1000 rpm".   In the configuration I got the lathe in the motor was connected directly to the lathe spindle.  Probably explains the chatter.

Thanks guys (and gal),

Rod

Offline ths

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Re: Micro lathe refurb
« Reply #27 on: September 01, 2014, 09:25:46 PM »


Mine are both the ME version but the later one was modded to allow for the higher 2100 RPM and less prone to break the headstock if you get heavy handed ;)

Jo

Jo, didn't you make headstock oilers for one of yours? Was that the high speed mod you refer to?

In regards to the PM Rod, I had another look at your photos on this thread, and  I can now see that it is an earlier incarnation, but later than Johns. His has the polished bronze reduction worm carrier, whereas yours has the painted casting, as has mine. Yours shares with Johns the brass/bronze apron plate, whereas mine is painted steel.

Hugh.

Offline tangler

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Re: Micro lathe refurb
« Reply #28 on: September 01, 2014, 09:43:35 PM »
My apron says "Flexispeed Sheffield", so before the Southampton concern..  I'm not convinced that the paint on mine was original.  It's satin bronze finish now though.  No point trying to get paint to stick to bronze when you don't need to.  The rest of the lathe is now is now Myford grey since I've had a tin of touch up enamel and never used it.  Must be 35 years old but was in perfect condition.

I have this even earlier one, missing the apron and lead screw.



Every thing is just that little bit smaller, much more like an Adept really.

Cheers,

Rod

Offline Allen Smithee

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Re: Micro lathe refurb
« Reply #29 on: September 01, 2014, 11:56:50 PM »
AS, 

What are we looking at, bearing in mind that my experience of electric flight began and ended with a 540 motor and 7.2V nicads (with a Mole charger - remember them?). 

One of the things I found when working on my garage/workshop clearance yesterday was a Mole cobalt 540 motor... :old:

Quote


Something like this?

http://www.hobbyking.co.uk/hobbyking/store/__18178__Turnigy_Aerodrive_SK3_6354_245kv_Brushless_Outrunner_Motor.html

or are there bigger, torquier, slower, cheaper ones about?

So, if I understand correctly 12v x 245 gives  2940 rpm.  3:1 reduction should be doable.

I will admit that when I first suggested this I hadn't appreciated quite how low the revs would be (at the motor) - I was assuming that the belt-drives would have an overall reduction ratio of around 6:1 or more! If that had been the case there would have been a range of suitable 28-36mm 40Aish outrunners around the 1000rpm/v mark costing from around 10. By the time you get down to below 500rpm/v things get bigger and more expensive! could you knock up another intermediate shaft in a pair of ball races with a toothed belt or gear reduction of 6:1?  That would certainly make things smaller and simpler!

Quote
What would I be looking for in terms of a PSU and speed controller?

For a speed controller I'd just look for a cheap one (but not an "opto" one) rated at anything over about 50A - that gives it the headroom to run with little cooling, and you don't need the bells & whistles of the more expensive ones. This would be controlled with a "servo tester" like this, which has a knice large knob on the front.

As for a power supply, I was going to suggest doing what I talk about in this article, which is cheap and reliable.

AS
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