Author Topic: Newish from Old  (Read 10882 times)

Offline rotorhead

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Newish from Old
« on: November 12, 2012, 06:41:56 PM »
Hi Folks,

After seeing krv3000's mag chuck reformation, I thought I'd add my attempts at revitalizing a 250mm Griptru 6 jaw for my 6 1/2" Master.

I bought this for £125, but upon stripping, found it in a very sorry state, it was full of rust and gunge, most of the internals were quite badly pitted, and it was a sod to dismantle.

Starting with a much modified L0 backplate, (I'd tried making my own version of a Griptru, but failed miserably)...

Then to fitting it to the chuck back body, mounting on the spindle to true up faces, and reduce clearances to ones supplied by Pratt...

Chucked it all back together to test, and was pleasantly surprised at the accuracy so easily obtained...

Stripped it again to clean up the outside of the main body, made up a new dual purpose key, and hey presto looks quite good...

Not much clearance to the apron though, but look at the bore.....


Chris
Sunny Scunny,
North Lincolnshire.

Offline Jonny

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Re: Newish from Old
« Reply #1 on: November 13, 2012, 09:43:24 AM »
Been after one of those 6 jaw chucks for two years, at the right price.

Not using the other three jaws?

Offline rotorhead

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Re: Newish from Old
« Reply #2 on: November 13, 2012, 05:18:18 PM »
Hi Johnny,

I'd ordered a brand new 200 mm 3 Jaw Griptru @ £526 from Buck and Hickman last December, April this year with not even a likelihood of a delivery date, I got a refund.

Asked about at our local Autojumble (Normous Newark), and a tool stallholder said he had this 250 mm for £125, so I jumped at it, even though it only had the inside jaws.

No 6 jaw has the first scroll guide broken off, so I went for using just 3, apart from the likely ingress of swarf in the empty guide slots, the improved visibility far outweighs any perceived advantage of the 6 jaws.

On re-assembly as per advice given by a technician at Pratt, the 6 countersunk screws holding the body together, should only be hand tightened, I'm presuming with say a 'Tee' handled key.

I'm experiencing a slight juddering, (not previously noticed with my original 200 mm 3 jaw), whilst parting of at high speed, on materials such as En8M & En24T, so I'm wondering if the screws are tight enough, I'm thinking that some sort of torque setting would need to be applied, to give consistent sliding pressure to the movable body parts.

What size are you after? and what price range are you looking to pay, all the new ones I've Googled for, are as dear as a decent sized secondhand lathe, Jubilee Tools in Derby are listing an incomplete 200 mm 6 jaw Griptru for £475, I offered them £350 inc tax, but they said it would have to be with the tax, so I left it, I believe they still have it.

By incomplete I mean only the inside jaws and only 2 adjusting screws.

Sorry if I've waffled on, but can't seem to sleep since being made redundant a week and half ago....
Chris
Sunny Scunny,
North Lincolnshire.

Offline Jonny

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Re: Newish from Old
« Reply #3 on: November 13, 2012, 07:12:52 PM »
I only want a small 6" ish permanently left with the external clamping jaws in for gripping from 3 1/8" to 6" round. The 3 jaws seriously mark the job.
I have startup probs with bigger chucks, playing safe i always give it a push and the hit the lever start. The smaller i go the less tendency to flip the main consumer unit even at 540rpm. Spindle only might startup set on 2500rpm.
One reason i went for the M300 than a Triumpth.

Just a small 5 1/4" chuck with 5" round on previous scrapped 140 http://pic20.picturetrail.com/VOL15/728921/1252422/14582043.jpg

Missed out on a few English on the bay but would settle for a polish, soft jaws will be available.

You will be ok using number 6 jaw as long as the scroll makes contact with the second worm. Got first two off on number 1 on RT.

Offline rotorhead

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Re: Newish from Old
« Reply #4 on: November 14, 2012, 09:00:40 AM »

I think you will only get a Pratt Burnerd made Griptru, I have made several and numerous searches through the net, but sadly found nothing readily available, those that were, are too expensive and or incomplete.

How about adapting some soft jaws, with wider attachments, skimmed out to your desired gripping sizes?

Funny you should mention startup problems though, I have to pull the clutch lever up very carefully on the Master, whatever speed setting I'm in.

Using a 4Hp VFD with a 3Ph 3Hp 3000rpm motor trips the overload protection in the VFD, if started a bit vigorously, anyway I'm of the mind that starting steadily is far better.

This is the case for both the Master and the Elliott Miller, with the miller I wind the speed up from 0 to 60Hz on the potentiometer, as there is a lot of drag through the gears.
Chris
Sunny Scunny,
North Lincolnshire.

Offline awemawson

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Re: Newish from Old
« Reply #5 on: November 14, 2012, 02:15:53 PM »
There are 'soft starters' available for three phase motors that would cure your problem. Most nowadays are electronic varying the phase angle that a triac is triggered at, but a simple one can be made with a time delay relay and three high power resistors. The resistors go in series with the three phases of the motor feed (or one phase of a single phase motor) and the relay contacts short the resistor out a pre-determined time after start up.

Andrew Mawson
East Sussex

Offline rotorhead

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Re: Newish from Old
« Reply #6 on: November 14, 2012, 04:41:40 PM »
Hi awemawson,

Not being altogether very electronically savvy, but managed to wire up the remote for it to work as intentioned, as the vender whom sold it to me, did include a very simplified wiring diagram, I don't have the requisite skill to go down the route you have kindly suggested.

I'm not really sure soft starting is the problem, as this VFD does start up slowly even with the variable switch set at full Hz, on the lathe it's the sudden inertial loading of spinning up the heavy chuck mass, that can cause the trip out, then it's just a case of switching off the power, to, I presume let it reset itself and then restart it.

On the miller, with such a large and heavy gear train (It's a big machine, the original motor was 10Hp if I remember rightly, I'm now driving it with a 3Hp albeit with twice the revs, to theoretically get the torque requirement, and driving it on the lowest input speed pulley), if I don't take care to set the Hz to zero, it also sometimes trips out from a cold start.

Chris
Sunny Scunny,
North Lincolnshire.

Offline philf

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Re: Newish from Old
« Reply #7 on: November 14, 2012, 05:33:41 PM »
Hi awemawson,

Not being altogether very electronically savvy, but managed to wire up the remote for it to work as intentioned, as the vender whom sold it to me, did include a very simplified wiring diagram, I don't have the requisite skill to go down the route you have kindly suggested.

I'm not really sure soft starting is the problem, as this VFD does start up slowly even with the variable switch set at full Hz, on the lathe it's the sudden inertial loading of spinning up the heavy chuck mass, that can cause the trip out, then it's just a case of switching off the power, to, I presume let it reset itself and then restart it.

On the miller, with such a large and heavy gear train (It's a big machine, the original motor was 10Hp if I remember rightly, I'm now driving it with a 3Hp albeit with twice the revs, to theoretically get the torque requirement, and driving it on the lowest input speed pulley), if I don't take care to set the Hz to zero, it also sometimes trips out from a cold start.

From this and your previous post I'd say that you should avoid using the clutch altogether to start the lathe - use the controls on the VFD (or remote controls) to start and stop it - it's the only way that the 'soft-start' on the VFD will do any good. It should be easy to adjust the acceleration/decelleration times to avoid tripping the VFD providing it's of adequate capacity.
Phil Fern
Location: Marple, Cheshire

Offline rotorhead

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Re: Newish from Old
« Reply #8 on: November 15, 2012, 05:29:49 AM »
Hi Philf,

Thanks for that, I have to admit I hadn't even given that any consideration, a very good pointer, the VFD is a 4Hp one, powering 3Hp motors(not at the same time).

I'll try it out now I've completed another mod to my VFD/socket arrangement.

I was fed up changing over plugs from the lathe to the miller, so now I've installed a changeover switch, to have both motors plugged in, but just turn the switch.

Chris
Sunny Scunny,
North Lincolnshire.

Offline awemawson

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Re: Newish from Old
« Reply #9 on: November 15, 2012, 06:20:36 AM »
You can kill the output devices on a VFD by switching it's output. I'm sure you only swap plugs when everything is off, but your arrangement would allow 'hot swapping' which would likely result in the VFD dying.
Andrew Mawson
East Sussex

Offline rotorhead

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Re: Newish from Old
« Reply #10 on: November 15, 2012, 06:51:54 AM »


I do let the Hz drop to zero before either swapping plugs(before mod), or switching over, as I thought there might be a conflict with the VFD.

But do I actually need to switch the power off to the VFD?

All and any input/info is very welcome, as I don't want to b*ll*cks anything up, funds are a bit tight now.
Chris
Sunny Scunny,
North Lincolnshire.

Offline philf

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Re: Newish from Old
« Reply #11 on: November 15, 2012, 08:11:00 AM »


I do let the Hz drop to zero before either swapping plugs(before mod), or switching over, as I thought there might be a conflict with the VFD.

But do I actually need to switch the power off to the VFD?

All and any input/info is very welcome, as I don't want to b*ll*cks anything up, funds are a bit tight now.

Hi rotorhead,

Yes, I would turn the power off to the VFD before switching from one machine to another. Better be safe than be sorry.

Just thinking that, if you use the VFD to stop the lathe, you made need to set a long decelleration time or connect a braking resistor to the VFD to dissipate the energy stored in the lathe.

Cheers.

Phil.
« Last Edit: November 15, 2012, 08:57:25 AM by philf »
Phil Fern
Location: Marple, Cheshire

Offline rotorhead

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Re: Newish from Old
« Reply #12 on: November 15, 2012, 09:33:08 AM »
Hi Philf,

As I'll be trying the soft start method now, that'll mean engaging the clutch before starting the VFD.

To stop, I can release the clutch, then switch off or turn the down Hz, thereby protecting both.

It's starting to get a little more complicated to achieve a more satisfactory result, but better safe than sorry, eh?

Having thought about this a bit more through the comments in this thread, am I using a realistic combination of 3Hp motor and 4Hp VFD as is, or do they need some sort of synchronizing?

I initially used a 3Hp IMO, but that was for a 1/2Hp motor on my Clarkson Mk1, seeing how well things went with that, I converted my lathe and miller to 3Ph aswell, using 3Hp 3000 rpm motors, and utilising a plug in system to use whichever.

Whilst not actually having any problems with that setup, I did think a bit more on the VFD size side might make things more tolerant.

Chris
Sunny Scunny,
North Lincolnshire.

Offline philf

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Re: Newish from Old
« Reply #13 on: November 15, 2012, 10:53:26 AM »
Hi Philf,

As I'll be trying the soft start method now, that'll mean engaging the clutch before starting the VFD.

To stop, I can release the clutch, then switch off or turn the down Hz, thereby protecting both.

It's starting to get a little more complicated to achieve a more satisfactory result, but better safe than sorry, eh?

Having thought about this a bit more through the comments in this thread, am I using a realistic combination of 3Hp motor and 4Hp VFD as is, or do they need some sort of synchronizing?

I initially used a 3Hp IMO, but that was for a 1/2Hp motor on my Clarkson Mk1, seeing how well things went with that, I converted my lathe and miller to 3Ph aswell, using 3Hp 3000 rpm motors, and utilising a plug in system to use whichever.

Whilst not actually having any problems with that setup, I did think a bit more on the VFD size side might make things more tolerant.

Rotorhead,

A 4hp VFD will be more than man enough for a 3hp motor. There is usually a motor current setting on the VFD so you could probably set it for a 1/4hp if you wanted. There is always a factor of safety built in so it would, for some minutes, cope with in excess of 4hp. I guess you've already discovered this for yourself with your Clarkson with a 3hp VFD and a 1/2hp motor. You could probably make a few bob by selling the 3hp VFD and buying a cheap 1/2hp one for that!

Phil.
Phil Fern
Location: Marple, Cheshire

Offline rotorhead

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Re: Newish from Old
« Reply #14 on: November 15, 2012, 08:08:30 PM »
Hi Philf,

I'll need to keep the 3Hp IMO especially for the Clarkson, as it's at the other end of my garage/workshop, the boss would have me sell it all, just to keep the swarf out of the house, dare say it would keep us both comfortable for a few months.

But then then I'd be under her feet, It'd be me to go next, even less expense for her.

Anyway thanks for the replies lads, you've all given me things to consider and mull over.
Chris
Sunny Scunny,
North Lincolnshire.

Offline Jonny

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Re: Newish from Old
« Reply #15 on: November 16, 2012, 03:56:31 PM »
Thats assuming his motors dual voltage regarding VFD.

Mines not and a 5.5hp 400V 3ph wont run a 3hp motor without a helping hand. Even a Transawave 5hp convertor mines like no tomorrow when putting a minor cut on.

I have to run my 3hp 400V motor from a single phase 240V supply to 400V 3ph output, best part of £1100.

Rather defeating the object not using the Master clutch, its the best part of the lathe like Harrison 11"/140. Motors permanently running, so real easy to convert.

Offline philf

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Re: Newish from Old
« Reply #16 on: November 16, 2012, 04:55:19 PM »
Rather defeating the object not using the Master clutch, its the best part of the lathe like Harrison 11"/140. Motors permanently running, so real easy to convert.

Hi Jonny,

The problem is that the instantaneous current when dropping the clutch in is going to be huge and thus the VFD trips - not a problem when you let the VFD accelerate the load.

I didn't consider that the motor may not be wired Delta for 230v but if it wasn't I don't think it would trip the VFD - it just wouldn't have any torque if it was a 230V inverter.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline rotorhead

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Re: Newish from Old
« Reply #17 on: November 16, 2012, 05:11:47 PM »
Luckily all my motors are dual voltage, I certainly now like the ability to raise or lower the frequency/speed of the motor, since assembling the remote control box.

I don't use that feature with the Clarkson, I usually run it at just 50Hz, that seems plenty fast enough with the pulley gearing.

It's only since fitting the 250 mm/10" Griptru that I've experienced the startup overloading, but it IS far larger/heavier even that the 10" 4 jaw.

Also I'll tighten the rear body countersunk screws, to see if that eliminates the juddering whilst parting off.

Time will tell, I'll give the suggestions a tryout this next week or so, and give an update of what I find to be best for myself and equipment.

Once it's running, taking a 50-75 thou cut on a 75mm dia 24T bar, with an 08 tip I have no problems.

I received a warning whilst posting this reply, it appears Phil had posted more or less at the same time.

After reading Phil's message, I'll mention that the motor voltages are 220/230 /380/440, and the VFD is 220/230v 3Ph out
« Last Edit: November 17, 2012, 12:27:35 PM by rotorhead »
Chris
Sunny Scunny,
North Lincolnshire.

Offline mattinker

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Re: Newish from Old
« Reply #18 on: November 17, 2012, 03:39:07 AM »


I don't use that feature with the Clarkson, I usually run it at just 50Hz, that seems plenty fast enough with the pulley gearing.



Just a thought, the MKI Clarkson runs at 4000rpm, the MKII has two speeds, 4000 and 6000rpm, the latter being used for smaller diameter wheels, running at up 75hertz might be worthwhile. Without off course over-speeding the wheel.

Regards, Matthew

Offline krv3000

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Re: Newish from Old
« Reply #19 on: November 24, 2012, 05:54:07 PM »
well dun