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rotorhead:
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.....

Jonny:
Been after one of those 6 jaw chucks for two years, at the right price.

Not using the other three jaws?

rotorhead:
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....

Jonny:
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.

rotorhead:

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.

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