Author Topic: How do I solve this? (Read 9917 times)

Anzaniste · « **on:** January 21, 2012, 05:38:43 PM »

I was squaring up a block in my Centec Mill following the standard procedure described in several places using a piece of bar on the moving jaw to stop lifting. The work piece came out tapered. ( I had checked the tram and it was fine). The way it was tapered suggested the vice jaw was not truly perpendicular
Mystified I eventually ran a dti up and down the face of the fixed jaw on the vice and it was not vertical by a couple of thou! A square against this face with a light behind gave no indication that the jaw was not square to the vice.

Puzzled I wondered what to try next. I bolted a 1-2-3 block to the bed as below................

DSCN0321 by Anzaniste, on Flickr

And ran the knee up and down. From top to bottom of the block it was out by 5 thou, the bottom of the block being furthest away from the column. Suspecting the block I tried it all different ways end for ending etc. and got the same result.

If I grab hold of the knee and lift it the dti deflects about 5 thou however I cant imagine how this can be the same as running the knee up and down on the dovetail slide.

Can any one offer any advice, explanation or remedy?

Jonny · « **Reply #1 on:** January 21, 2012, 05:51:50 PM »

Play or wear in the vertical dovetails or not locked down.
Does the knee get tight at either end or sloppy in the middle?

krv3000 · « **Reply #2 on:** January 21, 2012, 05:53:52 PM »

HI just my thought on this if you can move the knee up and dawn as you describe have you tried to a gust the Gib to see if that improves it

Fergus OMore · « **Reply #3 on:** January 21, 2012, 06:17:52 PM »

Go into 'Advance Machine Work' by Robert H. Smith. It's a freebee on the net

Basically it is pages 14 -14 to 16 but there is a lot more general alignment information surrounding this.

Cheers

N

Anzaniste · « **Reply #4 on:** January 22, 2012, 08:14:14 PM »

Thanks for your comments. Got distracted by London Model Engineering Exhibition this weekend so have not been in the shed.
I had considered the possibility of gib tightening and that will be my first move.

FOM. Thanks for pointing me to the book, I've actually got a copy on mt book shelves and hah forgotten how much of that kind of info was in it.

I'll have to stop my self from being distracted by my new toy, a Leinen Jig Borer, and sort out the Centec.

Davo J · « **Reply #5 on:** January 23, 2012, 03:14:34 AM »

If your measurements are right that means the block is leaning back toward the column at the top, so is not caused by sag as it would be the other way. Bridgeport's make the knee high from factory but that is only around a thou, but your seems to be much more.

If you Y axis is not worn much you could try winding the table forward and placing the block directly on the Y axis way and start from there up.
Do as suggested and make sure your gib is snug, but it's a case of starting at the bottom and working your way up to see where the fault is.
Something that can throw thing out is swarf caught under the saddle as well so you really need to take things apart and give it all a good clean up and go from there.

Dave

Fergus OMore · « **Reply #6 on:** January 23, 2012, 04:35:03 AM »

Quote from: Anzaniste on January 22, 2012, 08:14:14 PM

FOM. Thanks for pointing me to the book, I've actually got a copy on my book shelves and hah forgotten how much of that kind of info was in it.

There's a lot there! Two more sets- one is that great tome called Machine Tool Reconditioning by Connelly. Bloody expensive, appallingly heavy but you could possibly borrow one from a public library. Your nearest- perhaps is Gateshead! There was a copy there.
Again, you want a copy of Holzapffel. I think that it is a freebie.

As I can't count, here is a third. It is Georg Schlesinger's book on Machine Tool testing.
Newcastle upon Tyne HAD a copy.

Maybe a fourth? Well, why not? Ned Westbury as Editor of Model Engineer wrote as Geometer and I do recall some of his writings still appear about alignments- they were on the net.

However, I think that the result of the obvious examinations should be recorded. As two planes on sliding bits of machine tools wear, have you removed the gib and checked the parallelism or what is left by two cylinders and J Blocks or what you have as substitutes?
One side, that is the side that the gib was fitted should be unmarked but what about the working side? Again, turning to the gib itself- have you miked it for parallelism?

To be sure, there is a lot to do. Maybe there is a time to refresh skills such as blueing and scraping slides.

cheers

Anzaniste · « **Reply #7 on:** January 23, 2012, 09:23:39 AM »

I've obviously got a lot more serious measuring to do but I will have a go at the gib strips first.

I am at a loss to find out what a J hook is.

As highlighted by FOM I obviously am lazy at turning to to my own reference library so I have made use of my bookshelf and looked in Connelly, Robert H Smith, Machinery's Hand Book, three books I have on metrology a couple of different Engineers Hand Books even an ancient Herbrt's tools catalogue, nowhere can I find reference to a J-Hook.

Googling has produced no answer!!

What is a J-Hook??

I'm off to the shed now to fiddle with my gib strip!!

DMIOM · « **Reply #8 on:** January 23, 2012, 10:19:21 AM »

Quote from: Anzaniste on January 23, 2012, 09:23:39 AM

.....
I am at a loss to find out what a J hook is.
......What is a J-Hook??
.....

I don't know what a J-hook is in this context - neither to be honest do I know what the "J-block" FOM referred to is either!

Dave

Fergus OMore · « **Reply #9 on:** January 23, 2012, 10:29:30 AM »

Ah, a J Hook? I've suddenly had a bit of the Aurora Borealis( yep, it's supposed to be over Newcastle tonight again)
I reckon it is not a 'push scraper' but a pull scraper- beloved of Ian Bradley and Norman Hallows- writing as Duplex.

Of course, since Connelly, there is such a thing as epoxies and fillings of metal. You could fart about with a bit of Devcon to find if there are 'hollows' not Hallows. I used a bit of Loctite 660 for some job on a leaky Myford Super 7 early oiler.

Do I take the prize but what I had for today's breakfast I've forgotten.

Oh, and a J Block is a Johannsen gauge block

Anzaniste · « **Reply #10 on:** January 23, 2012, 02:38:40 PM »

Oh bugger a few more of the brain cells have gone awol, it must be reading Connelly which is comprehensive to say the least.

I've tightened up the gib s on the knee and it looks as if that was what was causing the dti funny reading against the upright. I shant know if it has solved the original problem for a bit as I have taken all the other bits to pieces!!

Hmmmm!

krv3000 · « **Reply #11 on:** January 24, 2012, 02:51:35 AM »

HI glad to see you may have sorted the problem

Anzaniste · « **Reply #12 on:** January 24, 2012, 05:22:35 AM »

KRV thanks for your kind thought,however, I dont know if I've solved the problem. So far I have shown the the gib strip on the vertical slide needed adjusting. I shall do all the others plus a bit of deep cleaning before I actually cut metal. Then I will know if I have solved the problem. I always was a pessimist.

Oh, and a J Block is a Johannsen gauge block - Aa :palm:haaa a slip gauge

Fergus OMore · « **Reply #13 on:** January 24, 2012, 06:11:45 AM »

Assume the side where the gib fits is straight
You should have scrape marks indicating this
Turn to the other side and look for the scraper's marks.
If there is a continuous evidence of scraping, there is very little wrong.
The only two problems left on that are the gib itself which should be blued in against a known 'reference'
At a push you try to insert feeler gauges or cigarette paper.
Then you should check the mating edges on the machine the same way.

Yonks back in the mists of time, I did the square shears on a Myford with nothing more than a bit of oversize rectangular bar which had been scraped and blued against the newly Blancharded bed of the lathe. It's as simple or as difficult as that.
If you find that there is the abilty to pull out a single bit of cigarette paper or your thinnest feeler gauge or see daylight between the two, you have wear ---and there is nowt that you can do until some form of remedial work is carried out.

I sincerely hope that it is all down to poor adjustments but that is the way that one goes.

Anzaniste · « **Reply #14 on:** February 09, 2012, 10:18:39 AM »

I haven't been ignoring every body but have been busy with other projects and have also been on holiday.

I have now stripped down the various slides (except the knee) and reset the gib strips which has sorted the problem of he dti wandering off the 1-2-3 block.
However.........

The standing jaw still leans a bit and a new phenomenon has reared its ugly head. I gripped in the machine vice a piece of ground stock sticking above the vice jaw by a couple of inches to emphasize the amount of lean in the standing jaw. Whilst I was setting this up I noticed that as I tightened the vice it leant more

!! As the vice overhung the table I moved it so that he standing jaw was fully supported this reduced the effect considerably. I'm still a bit disappointed in the vice but at least I know what to do.

As it was my birthday t'other day she whose name shall be spoken in hushed and reverent tones very kindly offered to buy me a nice new shiny tool

. Bless her I am now the proud possessor of one of those fancy tramming tools. (I was planning to build one a la Bogs but you can't turn down a gold plated offer)

Trammed in X axis a treat but horror of horrors the Y axis was way out. I'm now flummoxed 'cos there is no obvious method of adjusting this error. Funnily I have never trammed in this direction in the past because the head is not adjustable in this direction so I never saw the need to do it. With the new gadget its dead easy and quick so I just did it 'cos it was easy.

Can any body offer suggestions how I can put this right.

The mill is a CENTEC 2A. The error of .010" across the table which seems quite a lot to me.

Fergus OMore · « **Reply #15 on:** February 09, 2012, 10:58:02 AM »

Frankly, I cannot see why the reference to the vise/vice is relevant. To me, the vice is just an additional problem to solve.

Again, you should check the knee alignments before addressing what the table is up to. OK, I've never 'done' a Centec but you may have to put parallels or round rods over the guides to do the clocking. If these are OK and only if they are, move on to the table checks.

All that I am doing is finding where the possible fault or faults is.

As a sort of daft after thought, are you conducting all this with the Centec levelled up with decent spirit levels?

Anzaniste · « **Reply #16 on:** February 09, 2012, 03:53:00 PM »

The vice is mentioned because that is where this saga started.
I must be being really thick, I can't see what is meant by "round rods over the guides" Which guides?
The problem seems to me to be that dove tail slide that the knee runs up and down on is not in line with the spindle of the vertical head. I have got it in line in the x axis and now I need to get in line in the y axis where there is no obvious adjustment.

Fergus OMore · « **Reply #17 on:** February 09, 2012, 06:02:38 PM »

Putting precision rods at the outside of vee ways is pretty standard stuff - it makes it easier to measure as it goes over the top of perhaps worn ways. Again, putting rods in the vee ways is a check of parallelism.

If you think about it, you have no idea whatsover of the wear or distortion that has taken place. Creating some level as a reference becomes vitally important.
For instance, I have a bloody big bow micrometer which will bridge across ways. It look like a heap of ****** but it becomes a bridge comparator. If you follow 'the book' others have humpbacked straight edges to check.

You have to check the machine's geometry in each part.
You might only have to scrape or replace gibs.

What you always have to remember is machine ways have two sides. One side is metal to metal whilst the other will be unworn- but the gib filling the gap is the metal which slides on the fixed part of the machine.

Fergus OMore · « **Reply #18 on:** February 10, 2012, 04:54:48 AM »

I have a note of some techniques in lathe alignment and restoration which you might find useful.
I had to scrap most of it when the new owners of Model Engineer got tough. Anyway, it is immeiately prior to December 1988 in Model Engineer.

You may find the full articles by the late David Lammas worth reading.

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Author Topic: How do I solve this? (Read 9917 times)