Griptru wil not ad just

[richard 2Participant @richard2]

Hi Everyone

Like many of us I have a Griptru chuck on my S7B.

It came (2nd-hand) from one of our most respected advertisers many moons ago.

Yes, I have G.T's book and the relevant pages have been copied and sit on the bench near the lathe.

I am totally unable to get any adjustment of the chuck following the text!

But – I can relatively easily adjust the chuck using light taps on the body with a plastic-headed hammer.

So, please advise – I have never taken a chuck to pieces – I'm 84 so I think very carefully before getting into something I do not really understand.

Many years ago I had a similar Griptru and adjusted this almost every time I used it with no problem at all.

For various reasons I now have a replacement workshop and tools.

But this problem really baffles me.

Please, can someone help.

Many thanks in advance.

Richard.

[richard 2Participant @richard2]

[Tony SimonsParticipant @tonysimons69671]

The screws fastening the chuck body to the backplate are too tight, they need to be just snugged up.

[John ReeseParticipant @johnreese12848]

Are there pads between the adjusting screws and the pilot on the backplate? If there are and one or more pads are missing it may be impossible to adjust the chuck. My Yuasa was set up that way. Also I discovered that the pads have a shoulder. If the pilot on the backplate is made too small (Don't ask how I know) the shoulders on the pads bottom inside the hole and will not reach the pilot.

As to the adjustment: if there are four adjusting screws the adjustment is identical to centering work in a 4 jaw. If it has 3 adjusting screws like my Yuasa, I don't know a straightforward procedure. I just fiddled with the adjustments until I got it running true.

[richard 2Participant @richard2]

Many thanks.

I will take off the back-plate and have a look at the inside.

Does anyone know if there is a picture anywhere of the inside

of a Griptru so that i can compare?

Richard.

[Michael GilliganParticipant @michaelgilligan61133]

Richard,

It's not very detailed, but there's a useful scan on this page: **LINK**

http://www.practicalmachinist.com/vb/general/pratt-burnerd-chuck-help-141755/

MichaelG.

[Tony Pratt 1Participant @tonypratt1]

Richard,

I have personally taken these chucks apart a few times now although it was some time ago, first completely undo & remove the 3 adjusting screws then take out the 3 screws in the chuck back.

I think it should come apart then.

Tony

[Alan CrawleyParticipant @alancrawley27839]

I have read numerous times about the tightness of the screws in the backplate. These are nothing to do with the adjustment and they must be full tightened.

In simple terms the chuck is in two parts, the back 'slice' is fixed to the normal backplate and the front part is adjusted on the back part. The screws that connect the two parts of the chuck proper are not even accessible without taking the backplate off.

I have read of someone who advises loosening/retightening the screws in the backplate every setting.

I hope this is clear

[egaParticipant @ega]

Posted by Alan Crawley on 02/04/2020 12:51:26:

I have read numerous times about the tightness of the screws in the backplate. These are nothing to do with the adjustment and they must be full tightened.

In simple terms the chuck is in two parts, the back 'slice' is fixed to the normal backplate and the front part is adjusted on the back part. The screws that connect the two parts of the chuck proper are not even accessible without taking the backplate off.

I have read of someone who advises loosening/retightening the screws in the backplate every setting.

I hope this is clear

That someone (or one of them) was GHT who corresponded with PB about the correct way to use the adjustment feature.

I have the BP Griptru leaflet somewhere and shall be looking at it again with a wet towel over my head; have I been doing it wrong all these years?

[Nick Clarke 3Participant @nickclarke3]

There was a short (1 page) article in ME when these were introduced (Sept 1954).

Basically slack off the screws in the front (jaw) side of the chuck slightly to enable it to be adjusted. If the chuck is fitted to a back plate do not touch those holding the chuck to the backplate. If it screws direct onto the lathe mandrel the screws on the front only connect the two halves of the chuck together, they are not part of the fitting to the lathe.

If you like PM me and I'll dig it out and scan the page.

Edited By Nick Clarke 3 on 02/04/2020 14:08:23

[egaParticipant @ega]

Nick Clarke:

Many thanks for the offer; I will see if I have this myself but if not will certainly PM you.

I suppose it might be a public service to post the article on the forum.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ega on 02/04/2020 14:22:27:

Nick Clarke:

Many thanks for the offer; I will see if I have this myself but if not will certainly PM you.

I suppose it might be a public service to post the article on the forum.

.

… and if the scan is tiff, pdf, or whatever: I can probably convert it to jpg for the forum’s benefit.

MichaelG.

[egaParticipant @ega]

MichaelG:

A very timely offer as I have just been vainly trying to upload the results of my researches in PDF!

I won't trouble you unless I have to as I can probably re-scan to JPG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ega on 02/04/2020 15:38:45:

MichaelG:

A very timely offer as I have just been vainly trying to upload the results of my researches in PDF!

I won't trouble you unless I have to as I can probably re-scan to JPG.

.

No trouble at all …

I will PM you my eMail address

MichaelG.

[old martParticipant @oldmart]

This video may be helpful:

**LINK**

[egaParticipant @ega]

Nick Clarke's ME article:

Plus correction:

PB leaflet drawing:

PB leaflet instructions:

My immediate reaction to the ME article was that my Griptru, which I think must be the Myford/Burnerd direct mount type, doesn't have the "tie-bolts C" referred to but does have three cap screws in the back of the chuck; these are the screws that I slacken slightly and then re-tighten after using the adjustment feature.

The ME correction, of course, retracts the advice to loosen screws "C".

The instructions which came with my chuck say nothing that I can see about loosening and re-tightening, a practice which I have adopted in light of GHT's advice.

It is apparent that the Griptru came in various forms.

Time to do some more experiments on the hardware!

PS I have yet to look at old mart's video.

Edited By ega on 02/04/2020 16:11:39

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Sir

MichaelG.

[egaParticipant @ega]

Well, I have viewed old mart's video, looked at MichaelG's link to the thread on the PM site (well worth reading in full) and re-read GHT's advice and conclude:

1. Slight loosening and final re-tightening of the retaining screws is unlikely to do any harm and may avoid straining the chuck through heavy-handed use of the adjusting screws.

2. The man in the video, who did not loosen/re-tighten, seemed to make rather slow and heavy weather of the process.

3. I have no immediate suggested answer to the OP's question beyond that already given by Tony Simons (over-tight retaining screws) unless the chuck is actually defective or damaged.

4. I need to do some experiments.

[Bob StevensonParticipant @bobstevenson13909]

This is brilliant!……I want to make up the bits to convert a Chinese 3-jaw into an adjustable chuck so I shall ponder over these posts later…..Thanks for posting ega!

[Brian HParticipant @brianh50089]

I'm glad this came up as I have an elderly Grip-Tru. Mine has suffered in the past from being adjusted whilst the screws holding the two parts of the chuck together had been overtightened . Following this piece in the M.E. I have dismantled the chuck, cleaned everything and reassembled it taking car not to overtighten any of the screws. It now works much better although the number of times it is used to get metal running dead true is very limited.

Brian

[old martParticipant @oldmart]

I have heard that the griptru with only three adjusting screws is much harder to adjust than other makers using four screws.

[Joseph Noci 1Participant @josephnoci1]

Richard said:

But – I can relatively easily adjust the chuck using light taps on the body with a plastic-headed hammer.

So TonySimmonds comment :

The screws fastening the chuck body to the backplate are too tight, they need to be just snugged up.

is invalid – the chuck is not 'stuck' due to the mentioned 'screws'

In fact , is is quite clear in the Grip-True and in the ROHM ZS Hi-True ( works in the same way as the Grip-True) documentation that the bolts fastening the chuck body to the spindle backplate are NOT to be loosened whilst adjusting the chuck concentricity.

Per the ROHM Manual:

Adjusting the chuck for concentric gripping

No mounting screws to be loosened for this adjustment

1. Chuck a workpiece or test mandrel and determine the
maximum indicator reading.
2. Depending on the position of the eccentricity, loosen one
or two of the adjusting screw spindles located opposite
the point of the maximum indicator reading.
3. The retighten the remaining one or two screw spindles
until the gripping centre has been corrected by an
amount corresponding to half the indicator reading.
4. Check radial run-out again and repeat the adjusting procedure
if necessary.
5. Lightly retighten the previously loosened

Richard, do the adjustment screws rotate easily? Can you loosen all three up completely, and lightly tap the body over in the direction of one of the adjusters, as far as it will go, then gently screw in that adjuster as far as it will go and observe if the body moves away from the screw?

Joe

[jacques maurelParticipant @jacquesmaurel42310]

Hello

Read my article in MEW issue 292 about adjustable chucks, more will be said in the following issue about the tightening screws.

J Maurel

[egaParticipant @ega]

Posted by jacques maurel on 03/04/2020 10:21:15:

Hello

Read my article in MEW issue 292 about adjustable chucks, more will be said in the following issue about the tightening screws.

J Maurel

I'm looking forward to the solution to this "great mystery"!

[egaParticipant @ega]

One small mystery I can solve is the disconnect between the text on MEW 292 pages 67 and 68: on close examination, the first line on 68 has been near-obliterated by the red line under the pull quote at top left, which has been repeated on page 70.

Edited By ega on 03/04/2020 13:59:55

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