Truing up chucks

[SillyOldDufferModerator @sillyoldduffer]

Posted by Andrew Tinsley on 07/05/2017 11:36:45:

Ha,

The above is an interesting way of thinking about ME. I started off building steam locos and the kit was merely an ends to a means. Now however, I am more interested in making kit not models! There is always the opposite viewpoint.

…

Andrew.

Very true Andrew. I tend to forget about restoring and fixing stuff even though I enjoy doing it. Model Engineering is a broad church and I think it all has good value.

Dave

[egaParticipant @ega]

Neil Lickfold:

I have just checked my Griptru, bought new in late 80s, and there is no washer under the heads of the three 6mm capscrews securing the backplate to the body, nor is there any mention of washers in the instructions.

There is an informative passage about the use of the Griptru in GHT's ME's Workshop Manual.

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Everyone,

I finally got the job finished and checked out. I used 4 adjusting screws as advised. I have set the screws for the best average run out on diameters from approx. 0.5 to 2.0 inches in diameter. I am very pleased that I have beaten my hoped for improvement of average run out. It is now around 3 thou. This from the above range of diameters and repeating the rechecking operation several times.

So the old Cushman chuck can deal with the rough old turning jobs with improved accuracy. In my case it took about 3 hours to do the job and much longer to assess the run outs before and after the mod, I kept getting interrupted by the grandchildren! Certainly worth a try if you have a similar chuck that is in the same sort of condition.

Andrew.

[SillyOldDufferModerator @sillyoldduffer]

Result!

[Michael GilliganParticipant @michaelgilligan61133]

Further to the exchange between 'Hopper' and 'not done it yet'

I don't have figures to hand, but it is self-evident that the Griptru arrangement cannot be as robust as a spigotted fixing … 600UK gives tacit acknowledgement of this by stating:

Griptru chucks are often used in grinding operations and the 6 jaw Griptru allows the gripping of thin walled components with minimum distortion. A proven micro adjustment device on both 3 and 6 jaw chucks permits concentricity to be adjusted to within 0.005mm TIR.

**LINK**

http://www.600uk.com/products/pratt-burnerd-manual-chucks/

Yes you can modify your 3-jaw chuck to approximate Griptru performance; but it might be unrealistic to then expect it to also handle rough or heavy turning as reliably as it did before.

MichaelG.

[Neil WyattModerator @neilwyatt]

Posted by Andrew Tinsley on 07/05/2017 11:36:45:

The Cushman chuck is definitely not a worn out heap of manure, in fact it isn't in bad nick as far as I can tell, The jaws are a good fit with no appreciable rock detectable and the scroll looks to be in good condition. Well worth an hour or twos punt, to see if it can be improved.

Try cleaning it first. When my chucks have apparently lost their accuracy it's amazing how much they improve if you take them apart, clean and re-assemble, it isn't just visible swarf on the scroll that causes problems, you only need a thou of swarf somewhere to put the TIR two-thou out.

Neil

[Andrew TinsleyParticipant @andrewtinsley63637]

Hello Neil,

Disassembly and cleaning was the first thing I tried on the old Cushman chuck, No problems were encountered with swarf or other debris, just oil that seems to have got there when using an oil can for lubricating metal while turning. No improvement in accuracy was found on reassembly. I do agree that this should be the first port of call if a chuck starts to run out suddenly.

I suppose my reference to grip true chucks was a bit tongue in cheek. I never expected the modification to produce that sort of accuracy! You certainly can reduce the run out to near zero for a particular job. After all, the modified chuck is a crude 4 jaw in effect (having 4 adjusters at 90 degrees to each other) . But no one in their right mind would do this if they had a 4 jaw to hand!

To repeat my findings, the average run out was approx 3 thou, for chucked pieces from 0.5 to 2.0 inches in diameter. So I certainly achieved my hoped for run out on the old chuck. It worked for me and was not a big job, highly recommended for chucks that are getting a bit tired in the run out department!

Andrew.

Edited By Andrew Tinsley on 09/05/2017 12:06:03

[Neil LickfoldParticipant @neillickfold44316]

I pulled apart my newer Griptru chuck. I was surprised to find it had bellville washers under the std washer under the capscrew. I knew the old one had the bellville washers under the capscrews. Anyway, I put it back together without the mini spring washers, and did not like it at all. So I put them back in, but left out the regular washers.

The grease in the chuck had gone to a very thick gunky wax like substance. New thing for me is to make stripping and cleaning more often than 20 years. I was pleased that there was no swarf in the back. Maybe the gunky waxy grease is like that for a reason. In the mean time, I just used Lithium EP grease.

To the OP, 3 thou on an old 3jaw that may have been abused is not too bad really. Considering that a lot of parts are essentially made in 1 operation and the 2nd op is just a facing operation after, it will be fine.

Neil

[Roderick JenkinsParticipant @roderickjenkins93242]

Pratt Burnerd claim that their super precision chucks exceed the ISO 3089:1991 (E) class I standard and that the standard accuracy chucks exceed ISO 3089:1991 (E) class II. Does any body know what this means in terms of TIR and repeatibility?

Rod

[Neil LickfoldParticipant @neillickfold44316]

Rod, you can buy the ISO standard for chucks, but no where did I find it free to read. Only references to it. Did find that the 1991 is replaced with 2005. In saying that, class 1 is more accurate than class 2 , I did find a TIR for chucks to 300mm being 35um. I also found that super precision chucks have a repeatibilty to 0.013mm( 1/2 thou I assume) and an adjustment to 0.005mm. These were from the Pratt site about Griptru chucks. In realty if the spindle bearings are very good and the right gear, you can get a Griptru down to less than 2um. It won't repeat to that, so once the part has been removed, it will need dialing in again.

From what I have seem, the repeatibility and the TIR seem to go hand in hand. On chucks over 300mm the TIR goes to 75um so 3 thou in real measurements.

Neil

[Neil LickfoldParticipant @neillickfold44316]

So I did a minor referb on my old grip tru chuck. I added a grease point that puts grease into the area between the scroll and the chuck body, (main scroll location) and also puts grease into the main body under 1 of the pinions. Time will tell if it is a good idea or not. The other option was to turn off some from the body on the inner loaction and press onto there a sleeve, then retrim and recut the inner of the scroll as well. Here are the pics of the grease fitting and the position of the hole into the body and scroll.

Neil

 

 

 

So I made one of those rings that I had in my album with 3 holes to clamp the jaws with. I was not happy with the result from that method. So then got some jarrah from the left over spa pool surround, and cut it into piece 18mm wide and 5 mm thick. I put these in between the jaws, and turned it all out. Very happy with the result.

Neil

 

Edited By Neil Lickfold on 17/05/2017 12:04:44

[egaParticipant @ega]

Neil Lickfold:

I'm intrigued by your seemingly low-tech solution. Presumably, there is some spring and/or give in the timber for this to work?

The ring you mention seems not to be in your album now.

[Neil LickfoldParticipant @neillickfold44316]

Yes I deleted it from my album, as I did not want something there that was not effective. The wood can crush quite easily . I tightened the chuck to about the same as holding a part . Then rebored the inner of the jaws and trued the front face.

This is the picture I had in my album. It is a link to http://lathe.com/tips/chuck-jaw.htm

Neil

[PeteParticipant @pete41194]

Fwiw, my named by Emco high precision "heavy duty" Compact 5 three jaw is very specific in the instructions that came with it about returning each scroll pinion back to the same location they came out of in the chuck body after cleaning a chuck. Especially the one marked with the 0 postion on these chucks since that was the one they used to grind both sets of chuck jaws. Maybe something to keep in mind when cleaning and servicing a chuck, or when regrinding the jaws back true to the chucks body. Suburban Tool on Youtube has a very good video about how to properly regrind the jaws in a scroll chuck with some impressive results for runout. If anyone needs good dependable and accurate chucks I'd think they would. The jaws are just slightly ground with a recessed area at the very rear and a ring is used at that location to load the jaws by tightening against that ring. That preloads the jaws in the normal working direction then there ground. Preloading the jaws on the outside tips will tilt them very slightly outwards due to the minute but still important slot to jaw clearance. But the video explains the how and why far better than I can. The last set of chuck jaws I ground I wasn't seeing the improvement I thought I should. Not using the method Suburban does may be why but I can't say for sure yet.

Neils 100% correct about how important it is for a chuck to be properly cleaned. But something a thou or two in size can be fairly tough to spot at times. I've found a lot of improvement can sometimes be made if a sharp scriber is used to loosen any swarf in the corners of the scroll and jaw teeth. It's surprising just how much will still come out of a chuck you thought was spotless. Through drilling and boring tends to be what causes the most swarf to enter a chuck through the jaw slots. Whenever I can on shorter work pieces that need that through drilling or boring I'll usualy wedge a paper towel or small rag into the chucks through hole and just behind where the work will sit before tightening the workpiece in the chuck. Chucks still need cleaning every so often and the paper or rag just prolongs that job for a bit longer.

Yes it's likely correct that cutting the backplates step 1/32nd undersize so set screws can be used as a cheap alternative to a Grip Tru would cause it to be less resistant to movement when hogging great amounts of material off. I'm doubtful many M.E.'s really push there lathes that hard. But the coefficent of friction with the backplates bolts torqued up properly has to be quite high so you'd really have to be working a machine hard before I'd worry too much about it. Prof. Chaddock and GHT were two who really knew and practiced what they were talking about. Out of everything GHT wrote about the only single thing I can think of that I disagreed with was him stamping the numerials into a replacement shop made dial while it was still screwed to the lathes spindle nose. I suspect that Super 7 may have had sleeve type bearings? But it's still not a practice I'd subject a good chuck to. He did know far more than I ever will so I'd not really want to argue he was totaly and absolutely wrong either.

[IanTParticipant @iant]

All of the backplates I've machined have been "loose" – the first one because (frankly) I screwed it up but then because I found it simpler to do and then just "adjust" the chuck true at a mid-range hold. I don't think that the absolute accuracy/repeatable three jaw thing is particularly important to me. I've always assumed that my three jaws don't run true and can't be used for second operation work. Where accuracy is important is where my ER32 chucks are concerned, which I clocked true with a (ground) 12mm test piece. I do check them from time to time and I've not seen any change in setting on them.

However, I do understand why the register would be need to be exact in industry, where tools will be pushed harder and some workers might not be as careful as others. My chucks haven't moved but they might do if abused…

I do have a GripTrue 3J (with damage to one 'adjuster' – but it can still be used as a conventional 3J) and I've never bothered trying to fix it. If I need to do repetition work, then the ER32 collets cover the range I generally use and will be inherently more accurate I feel.

I must admit, I haven't cleaned my scrolls for a while – so this thread has generated a small twinge of guilt. Another thing added to the 'TUIT' list…

Regards,

IanT

[Tony Pratt 1Participant @tonypratt1]

Ian,

Yes in my humble opinions 'normal' 3 jaw chucks are not the best option for 2nd OP work as generally they don't hold work to a high level of concentricity but sometimes you can strike lucky.

Obviously if you have some sort of 'Griptru' chuck you can adjust the previously machined part to run true.

Tony

[Ex contributorParticipant @mgnbuk]

I presume what lathe manufacturers did (or maybe still do) was to temporarily fix the tailstock and head stock body together and bore/ machine all the mating surfaces at the same time. so that everything lines up on the bed.

You presume incorrectly, Michael.

Parts are made indvidually to tolerances & then "adjusted" on assembly to the required accuracy – that is what machine tool fitters are for !

Nigel B

[Danny M2ZParticipant @dannym2z]

To bore a nice concentic hole or turn truly, nobody seems to have mentioned 'soft jaws'.

They can make the worst chuck into an angel.

More details should follow (hopefully from people whom may know more)!

* Danny M *

[MWParticipant @mw27036]

Posted by Nigel B on 18/05/2017 12:53:45:

I presume what lathe manufacturers did (or maybe still do) was to temporarily fix the tailstock and head stock body together and bore/ machine all the mating surfaces at the same time. so that everything lines up on the bed.

You presume incorrectly, Michael.

Parts are made indvidually to tolerances & then "adjusted" on assembly to the required accuracy – that is what machine tool fitters are for !

Nigel B

Well thank you for enlightening me, all I knew was that something else had to be going on rather than every component being made individually to nominal drawing dimensions and then miraculously hoping you would get a finished machine from this alone when you fitted them altogether!

Michael W

Edited By Michael-w on 18/05/2017 14:29:40

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael-w on 18/05/2017 14:29:13:

Posted by Nigel B on 18/05/2017 12:53:45:

I presume what lathe manufacturers did (or maybe still do) was to temporarily fix the tailstock and head stock body together and bore/ machine all the mating surfaces at the same time. so that everything lines up on the bed.

You presume incorrectly, Michael.

Parts are made individually to tolerances & then "adjusted" on assembly to the required accuracy – that is what machine tool fitters are for !

Nigel B

… all I knew was that something else had to be going on rather than every component being made individually to nominal drawing dimensions and then miraculously hoping you would get a finished machine from this alone when you fitted them altogether!

Michael W

Actually that's exactly how most things are made these days isn't it? Parts are toleranced to be fully interchangeable, with minimal need for adjustments, ideally none at all.

Fitting delays production and the Fitters themselves are an expensive overhead (that is once you can manage without them!).

Eliminating fitters isn't miraculous, just the result of solid engineering improvements made over the last century and more. Your computer printer is probably the most accurate tool you own and it is highly unlikely that it was fettled in any way. The parts were assembled, like as not by robots, and it just worked off the end of a production line.

Of course there must be many exceptions, but to me the need for a fitter either indicates small-run production or a firm vulnerable to competition.

I'd suggest that fitting may in part explain the sad demise of Myford. The cause wasn't that Myford kit was in any way inferior, just that it couldn't be made down to a price that made a profit. Too many costly people making too many costly adjustments in the factory before the lathes were sold, by which time the product was expensive.

Also, it must have been hard to make a living selling lathes that owners cosset for 80 years. It's ironic to think that the original Myford may have been killed by fans keeping old lathes going rather than supporting their preferred company by buying a new one.

Dave

[MWParticipant @mw27036]

Posted by SillyOldDuffer on 18/05/2017 16:09:33:

Also, it must have been hard to make a living selling lathes that owners cosset for 80 years. It's ironic to think that the original Myford may have been killed by fans keeping old lathes going rather than supporting their preferred company by buying a new one.

Dave

I agree with the tolerances to an extent, the assembled individual item has to be tested and the reason why is because of the fear that when all the bits go together it wont do as it should. If they had that much faith in the lathe components they wouldn't do it.

The myford's were a victim of their own branding, they wanted good old fashioned solid quality yet as time moved on it's become increasingly harder to give that at a low price.

What they could've done is adapt to the changing market and start offering machines that ordinary people can afford, it may not be the best quality but it would be true to how they started.

Cut a few corners on the rear housing, using welded plate steel rather than iron castings for everything. Even they started making, or modding a far eastern type machine, yet beefed up a bit, they'd still be in business like warco.

By growing too snobbish they effectively cut off any hope of connecting with their core audience, mr average who wants a decent YET AFFORDABLE!!! british lathe and isn't too fussed over a few burrs here and there! It isn't rocket science.

Michael W

[Ex contributorParticipant @mgnbuk]

Of course there must be many exceptions, but to me the need for a fitter either indicates small-run production or a firm vulnerable to competition.

I would put many machine tool builders in the "small run" category. Machine tools are not consumer durables like printers in terms of volumes produced & the market is too small to justify the substantial investment required to produce say, a mini lathe or mill in a robotised factory. If Joe Public bought a new mini lathe at Currys every couple of years like they do printers, things may be different !

My former employer was of the opinion that fitters should be unnecessary if the machine shop did their job properly – but also complained about the cost of having parts precision machined. I understand that some volume builders ( Haas springs to mind) do machine to tolerances that require the machines to be "assembled" to the required accuracies from a kit or parts, rather than being "fitted". They do this by using linear guides that bolt-on, rather than require precision fitting like plain bearing machines – which is fine if a linear guide machine does what you want. If it doesn't, then it's back to a "hand fitted" plain bearing machine. They have also invested very heavily in the plant to produce the parts to the required standards.

Michael, fabrications where you suggest would probably cost more than a casting. The 7 series lathes were designed to be mass produced & (initially) sold at a competitive price. I guess that as their volumes declined, they started to believe the hype about the "higher quality than an import" & adjusted the pricing accordingly, rather than investing in more modern methods to produce the same (or better) quality product cheaper. An affordable British lathe – rough edges or not – is not likely anytime soon, I think. Though if you know why it isn't rocket science to do so, please demonstrate how !

Nigel B

[Neil LickfoldParticipant @neillickfold44316]

Getting back to chucks, I tried 3 methods to get the jaws correct on a worn bodied chuck. The video link of grinding a reference through a sleeve and then clamping down onto a spider or plug works for chucks that have a body in good order. The body of this chuck is worn. When I put the jaws from the new chuck into the old one, it would still clamp tighter on the back of the jaws and be loose on the front. When I used the ring with 3 holes in it for the jaws, the end result was the jaws were cut too much on the front. So when I clamped down on my test piece, the front was very tight with the back being loose. So then trimmed with the wood bits and it worked the best on this chuck. The wood is a physically hard wood and is clamped across the grain, not on the end grain. When I bored the jaws, in each case I used a boring bar with an insert capable of hard turning with a 0.2mm nose radius only taking small cuts each time to get a minimum clean up.

Hopefully this may help others who have worn chucks and would like to improve the chucks condition without too much effort with an more than acceptable outcome.

Neil

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