Griptru wil not ad just

[Chris Pearson 1Participant @chrispearson1]

Posted by ega on 02/04/2020 16:10:44:

It is apparent that the Griptru came in various forms.

I have recently acquired one, which has barely been used, if at all. Mine is the bespoke Myford one, so no backplate as such.

The adjustment is brought about by conical screws in the body bearing upon tabs which project forward internally from the base. If the body and base are clamped together tightly, it is difficult to see (i.e. IMHO impossible) how one could be moved over the other; but how tight is too tight?

On my particular chuck the screws which unite the body and base enter from the back, but with a separate baseplate, I imagine that they must enter from the front.

I have found that 1 Nm allows adjustment to be made with quite gentle force. 2 Nm makes the force a little more than I would like, but it is possible.

The next question is how tight do the screws need to be when turning? Possibly no more than 2 Nm. Remember that the manufacturers intend these chucks for grinding, so certainly not for roughing out. IMHO 5 Nm is plenty for a 4" chuck. The difference requires barely any movement of the screws.

If you don't have a torque driver, I would suggest that for adjustment, the screws be nipped up holding the short arm of a hex key between finger and thumb; afterwards just the normal good twist holding the long arm in the palm of the hand in the normal way.

HTH.

[Alan CrawleyParticipant @alancrawley27839]

My UK made Hardinge has one and the screws under the backplate so there is no way of adjusting on the run so to speak. If the instructions are followed and all taper screws are tight, as long as the mounting screws are tight enough to prevent endplay everything should be ok. No eccentric movement possible.

Edited By Alan Crawley on 19/10/2020 14:15:21

[SteviegtrParticipant @steviegtr]

Well it seems i have the same problem with chuck runout. I found this thread while mosing around, & wow. My blooming chuck is adjustable. I have had the machine a while now & have just worked around the fact that it has a 9thou runout.

Now thanks to this amazing forum & members i can adjust it (hopefully).

Steve.

[mechman48Participant @mechman48]

Would have been a better video if you had shown close up of movement if the dti pointer during adjustment.

George.

[Clive Brown 1Participant @clivebrown1]

I have a 4" Griptru which came ready mounted on a Boxford backplate. I can't say that I'm wildly impressed. It's tedious to adjust and only seems to hold its accuracy for diameters very close to the one it's adjusted to I use it basically as a general purpose chuck. I wouldn't buy another one.

[SteviegtrParticipant @steviegtr]

Well i have been i the workshop for a few hours , trying to adjust the chuck. I was having no luck at all. So i took it to pieces to see how it all worked. Gave it a good clean , although it was clean inside.

Put it back together & started to adjust. As someone said further up the thread , you need to loosen the backplate or it will not move. Once i did that away she went . I have gone from 9 thou runout to literaly zero. I have taken plenty of pics & video of doing it. I will compile it all tonight & hopefully get it uploaded either tonight or tomorrow.

I also turned a 1" stainless bar 8" long down to check for runout along the bed. Pretty much perfect all the way.

Once done i will post a link for anyone who has one & having trouble adjusting it.

Steve.

[SteviegtrParticipant @steviegtr]

I have uploaded a video for anyone having trouble with these chucks. Hope it is of some use.

Steve.

3 Jaw adjustable chuck

[Lee RogersParticipant @leerogers95060]

Perfect timing , I have one on the bench right now that came with an ETA lathe aquired earlier this year. Never seen so much swarf in a chuck before , preventing that is something I will address on reassembly.

I'm seeing 2 points in the previous posts and the PB instructions that are as I see it key to getting the desired result.

1. The correct fitting to the backplate is vital , Blindingly obvious ? No , not if you have no idea how the job was done in the first place so I'll give it a thorough once (or twice) over.

2. Damage is done to these chucks when adjusting if the first step in the sequence , slacken off all the adjusters , is ignored.

Finally. The idea is to take up a few thou not half a yard like a 4 jaw. There should be no need to slacken the retaining bolts.

I'll be back later to eat some humble pie when all my theories are blown out of the water.

[SteviegtrParticipant @steviegtr]

Posted by Lee Rogers on 20/10/2020 08:06:30:

Perfect timing ,

I'm seeing 2 points in the previous posts and the PB instructions that are as I see it key to getting the desired result.

Finally. The idea is to take up a few thou not half a yard like a 4 jaw. There should be no need to slacken the retaining bolts.

I'll be back later to eat some humble pie when all my theories are blown out of the water.

Have you not watched the video.

Steve.

[Alan CrawleyParticipant @alancrawley27839]

Lee has summed it up neatly.

I have watched a couple of videos about these chucks and have to wonder if the users have read the maker's instructions. It only claims to repeat accurately at the diameter set, and also that the chuck key should be used in the same hole every time. You have to forget the habit of checking all three. And the same number should be used to unloosen it.

I have used one professionally for a good number of years without problems. The retaining screws are never touched. And I believe I may have stated earlier, if ham-fisted users strain them so they are bell-mouthed the jaws can be corrected carefully on a surface grinder. No need to grind the bore and make the jaw face concave.

[Tony Pratt 1Participant @tonypratt1]

Plus one for Alan's comments, good bit of kit if used correctly.

Tony

[SillyOldDufferModerator @sillyoldduffer]

My take for what it's worth!

Whether or not the fixing screws need to be slackened to adjust the chuck has been argued since they first appeared. Myford didn't know, and it took a long time to get a statement out of Bernerd. Their view is repeated as a correction to the article posted by ega earlier in this thread:

So the maker says the fixing bolts should not be touched. Yet the suggestion they need to be slackened pops up in Model Engineering as regularly as Xmas. Owners don't believe Bernerd.

I think the answer to the paradox lies in the question: "What could possibly go wrong?"

Several things!

First, the range of adjustment is tiny, perhaps smaller than common-sense suggests is reasonable. A Griptru might be forced bending one or more of the wedging screws.

Second, Pratt Bernerd's instructions (also in ega's post) make it clear that the adjusters are worked in a particular way. If the chuck is operated by the sort of optimist who never reads instructions, then he might well work the adjusters in opposition, jambing the device. If he also has gorilla instincts, the adjusters could be forced. Maybe many times in the hands of a persistently heavy-handed owner.

Third, some people can't stop themselves dismantling their toys, even though they don't know how to put how to put them back together! Or after several years service a chuck is taken apart for a clean. My guess is the fixing screws are tightened to a particular torque in the factory, and some amateurs tighten them excessively. Some Lads believe tighter is better and ensure it by whacking their spanner extender with a big hammer. Ignorance is bliss.

Fourth, years of corrosion and gunge is likely to gradually increase friction between the chuck body and backplate causing the mechanism to stiffen up. Again, some owners will force the adjusters, maybe causing damage.

If the fixing screws are too loose, the chuck will rotate slightly independent of the adjusters, again with risk of damage.

The answer? I suggest the fixing screws are torqued to a specification such that friction between chuck and backplate is somewhat lower than wedging screw force. As a screw-driven wedge is an excellent force multiplier, I'd expect the fixing screws to be more than finger-tight, perhaps another turn or so, but not vigorously tight. I'd experiment until as Bernerd say "no great force is needed to operate the adjusting screws".

Although the mechanism is solidly built, make sure the wedge screws haven't been bent by an enthusiast. If bent the mechanism won't work properly. Otherwise I suggest there's no need to touch the fixing screws provided they've been tightened correctly and the moving surfaces are clean.

Dave

[SteviegtrParticipant @steviegtr]

Well SOD i bought my lathe with the extra's supplied so i cannot comment on the tightness of the rear backplate fixings. I only know what i had would not move. After stripping it & seeing how it operated it seems i was turning the wrong side. I did 1st take the tension off the 3 adjusters so no binding could occur.

However the body was solid to the backplate , hence stripping it too. I can only say that yes the instructions maybe correct for a new or untouched chuck. When one is very old & probably passed through many owners then who knows what has been done.

I just wonder how many you have found to be hard to adjust.

Not sure about the dig of people taking things apart & cannot put them back together. Surely it cannot have been at me.!!!.

I just hope the guys who have a go at adjustment find their screws not so tight or stuck up.

Try following a Haynes manual.

Steve.

Edited By Steviegtr on 20/10/2020 16:26:09

[Lee RogersParticipant @leerogers95060]

It's back together on the bench. I previously mentioned that it was choked with swarf there was even some in the bottom of the backplate retaining bolt holes. That leads me to concur with SOD Dave on the points he makes.

I'm now at the trial and error stage with the torque. I should add that mine is mounted on the adaptor plate mentioned in the PB instructions and no slackening or adjustment is possible once it's mounted on the lathe.

No 3 jaw is a mighty clamping tool (some seem to think they are&nbsp and this one I see as a light duty chuck with the benefit of being able to clock it in like a 4 jaw for every job.

[SteviegtrParticipant @steviegtr]

I have read this complete thread over twice now. Conclusion right or wrong is.

There are 2 types of this chuck. The main one is a chuck mounted to a back plate by long screws from the front face of the chuck approx 2" long. These go through clearanced holes the full thickness of the chuck to threaded holes in the mounting plate. The Myford one which i have has a dedicated backplate & is bolted directly to the rear of the chuck by means of threaded holes flush with the rear of the chuck.

I think logically that the front entry bolted type would be much easier to adjust without any slackening of the said bolts. C on the diagram further up this thread.

On the Myford type i can see why it would be much harder to push the chuck sideways when boited directly with short bolts , straight into a threaded entry. No flex The front mounted type has around 1 5/8" of free shank to be able to deflect.

Waiting for the gunfire.

Steve.

[Lee RogersParticipant @leerogers95060]

Posted by Steviegtr on 20/10/2020 17:43:24:

I have read this complete thread over twice now. Conclusion right or wrong is.

There are 2 types of this chuck. The main one is a chuck mounted to a back plate by long screws from the front face of the chuck approx 2" long. These go through clearanced holes the full thickness of the chuck to threaded holes in the mounting plate. The Myford one which i have has a dedicated backplate & is bolted directly to the rear of the chuck by means of threaded holes flush with the rear of the chuck.

I think logically that the front entry bolted type would be much easier to adjust without any slackening of the said bolts. C on the diagram further up this thread.

On the Myford type i can see why it would be much harder to push the chuck sideways when boited directly with short bolts , straight into a threaded entry. No flex The front mounted type has around 1 5/8" of free shank to be able to deflect.

Waiting for the gunfire.

Steve.

Mine has the adjustable backplate , this then has an adaptor backplate secured from the rear so that it covers up the disputed loosen or not bolts , so it is clear that they are not intended to be loosened.

I have it on a non running lathe now and I have it to a half thou. The bolts have been taken up to a light torque on the short side of a normal allen key. This light touch is a bit counter intuative untill you remember that it is the adjustment cones that are keeping things together.

As for the adjustment procedure it's easy once you get the routine in your head. Loosen opposite before you tighten and numbers on the chuck help too.

[Alan CrawleyParticipant @alancrawley27839]

The only slight thing that is wrong with your last post Lee is the word "disputed". The bolts are nipped up and left alone, indisputable.

And the other poster's idea of bending the bolts to effect adjustment is horrifying. One part slides across the face of the other.

As you say, the ultimate tightening of the three conical screws holds it all in place.

[Lee RogersParticipant @leerogers95060]

Posted by Alan Crawley on 20/10/2020 19:43:26:

The only slight thing that is wrong with your last post Lee is the word "disputed". The bolts are nipped up and left alone, indisputable.

Not disputed by me , I'm just refering to the run of the thread and a video.

It's a cracking little chuck and I have a small aluminium piston to make for a Walther LP3 target pistol , Just the sort of light work it was made for, very pleased with it.

[Neil LickfoldParticipant @neillickfold44316]

I have 2 grip true chucks, and both of mine have bellville washers under the screw heads for the backplate to the chuck. One was second hand, and the other was New in box.

[SteviegtrParticipant @steviegtr]

Twisted words again. I said that the longer screws of the front mounted bolt chucks would be easier to adjust because of the flex in the bolts.

I love this forum but there are so many negative comments from some who have never even tried to do this job. The ones that have, have half agreed that it is necessary to loosen the bolts a wee bit the rest do not. Again i say that after being made in i believe 1977 my bolts were probably tightened up a tad too much .

I will soon be doing a video of my F-type jaguar v8 doing 0- 60 in under 3 seconds. With an expected speed of over 200 mph I bet some will have a view that this cannot be done. After changing the pistons for 8.2.1 super forged or acrolite & bringing the supercharger up to the Eaton rated max , giving over 700 bhp. How many will comment saying you cannot do that or it is impossible. Even after showing it being done , some will still post negative comments. I love this forum.

I was having a conversation with a group of very intelligent people tonight about this forum. Some suggested that with old age comes a,,,,, i cannot be wrong , i have done this all my life.

One guy a professor asked me a question which was,,

If you have, drilled a wall & fitted rawlplugs all your working life & fitted screws into them. I came up to you & told you of a better way of doing this what would be your reply.

I said no way i have always done it this way even when i was an apprentice drilling the holes with a rawldrill & hammer, & chewing the rawlplugs that were made from horse crap. He said , there you go Human beings will never admit to being wrong., Stat.

Point being some folk are so set in there ways , they can see no further than the end of there fingers.

Don't forget only 66 days till Chrimbo.

Steve.

Edited By Steviegtr on 21/10/2020 02:59:01

[derek hall 1Participant @derekhall1]

I think my chuck looks like yours Steve, however I have not stripped it down to check, or clean. The chuck is probably as old as the lathe circa 1963.

However I treat it as a standard 3 jaw chuck and I dont bother with the griptru function. As long as I do all machining operations at the same time it's fine for me. If i need to rechuck a previous machined component i will use a independent 4 jaw and a "clock"…..not sure if that's quicker than twiddling the adjusting screws on the the griptru or not……perhaps I should try!

The late great Tubal Cain who I have always regarded as one of my virtual mentors, said "there is always more than one solution to an engineering problem"….

66 days to chrimbo????……you have ruined my day!!!!

Best wishes

Derek

[Dave WoottonParticipant @davewootton]

Steve

Not going to comment on the griptrue, but please post a link to the video of the Jaguar when you've done it, I'll look forward to that, love the sound of a V8. Or any other engine really!

Sorry to go off topic.

Dave

[John Hall 7Participant @johnhall7]

Please can anyone tell me what edition of ME contained the details of the Griptru chuck by Nick Clarke

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