Griptru wil not ad just

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.

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

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.

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.

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.

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

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?

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

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.

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.

This video may be helpful:

**LINK**

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

Well done, Sir

MichaelG.

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.

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!

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

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