Fixing Darren's lathe

[bogstandard]

Nick,

The original bearings are staying in there. Nothing on the jobsheet about doing that mod.

Darren should be quite capable of doing it, if and when needed.

But I do have high hopes for the machine as it is.


John

[Darren]

Already done the taper bearings some time ago. When the lathe was fairly new the plastic gears inside the headstock sheared. Did you notice they are now metal John? I hope they are still there 
I put them in hoping it may help to improve the finish I was getting. Didn't make a tad of difference...

Never noticed the head adjusting screws for lining the head back up? Newbie alert 

[bogstandard]

Darren,

Yes, the gears are still there

I am in fact a bit annoyed. I have done a parts count, and there is nothing left over except for the redundant gib strip bits.

I normally get a few left over extras to put in my parts boxes.

I have got the leadscrew working as good as it will ever get, it is slightly out of alignment and bent, I managed to get everything aligned so that just by hand turning the leadscrew the saddle was moving nicely. The whole saddle area has been built up and adjusted.

I feel like burning a bit of midnight oil, so I think I will go out and align the head up while it is all quiet. Then connect up the electric string, turn on the wiggly amps, and see what happens.

John

[Darren]

That's me awake for the night.....

[bogstandard]

You can go and get a bit of shuteye now Darren.

As usual, I have hit a last minute hitch. Why can't things go right for a change?


But this time, I caught it straight away. I had set everything up to clock up the spindle and at the end of the silver steel bar I got runout well over what my DTI could measure. A quick check showed the chuck was wobbling about like a drunken Scotsman.

So the chuck was unbolted and given a good dose of looking at and a service while it was stripped down, not much wrong there.

This pic shows the lathe with the electrics still hanging off, as it wasn't worth doing if the head casting had to be shimmed up.
This shows my DTI setup, by having it on the saddle, I can move it easily between the x and y axis.



So while the chuck was off, I wacked a new 3MT centre up the spout and dropped the DTI on it, to check the runout. 0.0002", not even worth bothering about, a film of oil or a speck of dirt up the spout could cause that.




So the DTI was switched to check the runout on the backplate. It found the problem straight away. 0.0025" runout, no wonder it was wobbling about at the end of the test rod. It was tried on other areas of the plate, with the same sort of results.



So I have now decided, first thing in the morning, I will get the electrics on  and skim the backplate level, and hope that the head is true, otherwise I will have to take the electrics off again if major movement is required. I think I might just wack in a saddle lock while I'm at it,  it will only take a couple of minutes, and will definitely be needed if I am skimming across the face of the backplate.

This lathe has to be finished tomorrow morning, as I have a private rush job waiting in the wings that will take a couple of days, and Ralph is calling tomorrow afternoon. Maybe I can get him to take a vid of the lathe in action.

So out comes the sledgehammer and angle grinder again. I have to use a bit of brute force to get the 6" nail hole thru the saddle for the lock.
 

Bogs

[bogstandard]

So this will finally be the last technical post about putting Darrens lathe to rights.

I left it last night with the backplate requiring skimming. Normally a dead easy job, but not on this type of lathe, it has no saddle lock, so the facing cut could end up any shape as the tool tip was pushed out of line by cutting forces.
So the first bit is how I cured the problem. I fitted an easy to do and use saddle lock.

After rooting thru my racks, I found the ideal bit to do the job, an 8mm steel bolt with a fitted brass tip. It isn't necessary to use a bolt the same as this, you could drop say a 6mm long slug of close fitting brass rod down the hole and screw a bolt down onto the top of it.




So I found a position for the lock bolt to go. About half way across the tailstock slide, and positioned so that the adjusting grub screws for the cross slide would miss the bolt head, no matter what position the bolt head would end up at. I chose this rail because I thought that the tailstock should never reach the area that this bolt will be working in.
So I just then put in a good centre, but make sure you don't break thru the saddle, you will end up drilling the bed.




After removing the leadscrew end support, I was able to slide the saddle so that it just overhung the back of the bed far enough so that I could drill right thru the saddle. The saddle was drilled and then tapped out to fit the bolt. You need to be careful that the hole is drilled truly vertical, if needs be, get someone to watch you while you are drilling and to tell you if you are going off square.




So saddle run back up the bed, leadscrew support bracket fitted and adjusted and the bolt fitted into the hole.
It only takes a light nip up to get the saddle locked solid. Another successful job, time to carry on.




To cut a long story short, I got all the electrics in and then run the machine up. It was working very intermittently, sometime power, sometimes not. The problem was found just after Ralph arrived. A loose connection in the interlock block hanging at the back of the machine.
So I could then carry on. Saddle was locked up, and the face was blued up to show me what was going on while I cleaned it up. Ralph was looking over my shoulder, and he commented on how much it was out.
Ignore the blue ring in the middle, that is a recess. If you look at the left hand side, the face is nearly cleaned up, whilst opposite to it, there was hardly any removed. I carried on until I had a clean face all the way across.




So the face cleaned up, ready for the chuck to be remounted.




I couldn't wait, so chucked up a lump of 3/4" hex and in low gear ratio put a cut on of 0.100", speed 800, pushed down of the leadscrew feed and took a cut. I wasn't happy with the finish, so tried it again, same thing.
Then it clicked, this was a mini lathe, not mine, plus it was doing an interupted cut. So a cut on of 50 thou, and things started to improve. I eventually ended up at a 25 thou cut, and was almost happy with the finish.
The problems Darren had been having have now disappeared.




So I flipped the bar round in the chuck, locked up the saddle and hand fed across the end. Not too bad, and I am sure I could improve on it with a bit more use of the machine.




So I now thought I would have another go at improving the finish, so changed over to high ratio (this will give a finer feed).
Usual 50 thou for rough cuts, and a final of 5 thou.
Now happy with the results.




Now for the bad news. On checking over the chuck, it has a built in runout of about 2 thou. This is about normal for a generic chuck like this.




Not much I can do about it.




I have just one other issue, the machine is cutting slightly tapered, so tomorrow that will be fitted in during a private job I have to do, it just requires a small tweak on head alignment, a quickie tap with a sledgehammer might just do it.

So Darren, your lathe is ready to pick up after tomorrow.

Everyone else. If Darren hasn't contacted me in the next four weeks, I will have for sale a one user refurbished lathe.

I fly out tonight, to a secret location in the Bahamas for a five week holiday.


Very happy Bogs

[Divided he ad]

Ralph was looking over my shoulder, and he commented on how much it was out.

  He was....  and did!



Good to see that it now cuts pretty much the way it should 



Go easy with that sledge hammer John..... Maybe use the 2lb ball pein instead?   


Darren,

I can't quite remember how bad it was the first time I saw it there on Johns bench? (memory ain't what it used to be) But, the saddle runs as smooth as the proverbial baby bum! (Never quite understood that one?!) 


Your going to be happy with the end result   




Ralph.

[Stilldrillin]

"Very happy Bogs".

I`m not surprised!

What a crackin` posting this has been! 

Thanks John, for showing & telling....... I`ve thoroughly enjoyed every word & pic. 

David.

[Darren]

You have given us all a wonderful insight covering many aspects John. I'm sure that sincerely applies to all of us whether new to the game or not.
Each post has been very clear and informative keeping us riveted to the show for the following installment.

Sad to see it come to an end in a way, but of course I'm personally bouncing up and down...

I know "Pat's on Backs" are not allowed, been told off for it before,
Tough..!! That's a wicked result from a  . Who'd have thought it could have been so far out yet still usable. (well ok only just)

I'll make the arraignments, be good to have a chin wag again at the same time. Not quite the strangers this time....

[bogstandard]

Ralph,

But, the saddle runs as smooth as the proverbial baby bum! (Never quite understood that one?!)

Smooth as a baby's bum. Silky.
Opposite of most probably what yours is, that would be called 'rough ar**d'.

I did enjoy your visit though, it is nice to talk to someone who answers back in a legible language, rather than just 'woof, woof'.

Bandit is good, but is limited a bit on his vocabulary.


David,

I am very pleased you enjoyed the long post, and thank you for the comments.
I hope it has given an insight into how things can be achieved, and that little challenges can occur at every corner, and have to be put right before the journey can continue.

We got from A to B, but had to detour thru X,Y & Z to get there.

Darren,

Who'd have thought it could have been so far out yet still usable.

People can adapt and make use of even the most feeble and badly adjusted machines, and produce some outstanding work.
The word 'adapt' is crucial. If a machine can be made to allow the user to not have to adapt to it's little foibles, and having to fight with it to produce what is needed, then a more relaxed and happier experience can be achieved.

Not quite the strangers this time....

I never class anyone as a stranger, just someone I have never met in person before. That little belief has got me in and out of a few sticky situations at times, from looking down the barrel of an Arabian muzzle loader, to being towed across the desert in a landrover by a pair of camels. But hey!, you only pass this way once, so make the best use of it.

I will look forwards to our next meeting.


Was it all worth it?

To me, yes.

It got me back up and running again after a long layoff, and I enjoyed every minute of the challenges.

It is after all only a mini lathe, and only so much can be done to it to make it a more precise machine. It will never compete with much more expensive and larger machines. But it is now performing to it's maximum potential, just by doing a couple of mods, and a lot of hacking and tweaking.

Accept what it is, and take it from there.


John


Sorry lads, looks like the lathe auction is off. Darren still wants it.

[Bernd]

Very nice thread John. I've grown a set of brass monkies now that I see how easy it is to get one of these sows ear lathes turned into a silk purse. The Grizzly is definatley going to get a rebuild, the question is "when".

Agin thanks for a very wonderful and informative thread. It's encouraged me to try the same on my lathe.

Oh, and Ralph if your reading this, that link to the guys lathe was a great inspiration too. Thanks.

Bernd

[bogstandard]

Bernd,

Glad you enjoyed it, and hope that it has encouraged a few people to try out a few of the things.

The saddle lock especially, that only took about half an hour, and totally transforms the way the machine can face off.

Don't worry, one day you will find you don't have anything to do, then you can try doing a few of the fixes on your Grizzly.

I have dozens of projects in the pipeline, just hope I have the time and will to carry them all out.

John

[SPiN Racing]

Excellent thread John!!

Thanks for sharing the work with us.. it has been enlightening.

Can I suggest we sticky this? SO its something of a reference? SO many start with a less expensive lathe.. and some of the things you discovered, and repaired may help others wandering through the forum.

[Twinsquirrel]

Superb thread as usual John! I now have another page of modifications to do to my mini!!

Re: The chuck runout, I saw this article about grinding the chuck jaws when I first bought my lathe http://mini-lathe.org.uk/true_the_chuck.shtml.

What are the pro's and con's of doing this, is it worth my while as I have about the same run out on my machine.

Great to see you firing on all cylinders again

David

[NickG]

Excellent read John.

Just realised last night that my cheapo chinese mill has tapered gib strips on all axis too ... probably made wrongly mind you  but it's still pretty smooth!

Nick

[bogstandard]

David,

The general consensus amongst 'people in the know' is NOT to grind chuck jaws as it only puts it right in the position that the jaws are in at the time of the grind.

On much larger chucks, growing runout doesn't rear it's ugly head due to them having a lot more 'meat'. The scolls are much larger on a larger chuck and don't 'bend' as much when tightening down hard. A small chuck can be easily bent internally if the jaws are overtightened. It isn't the jaws that are out, it is usually the scroll or the followers on the back of the jaws that have come to grief.

In fact, if you think about it, if you do grind the jaws, when they are moved to a different position, they just might be worse than they were in the first place.

I do grind independant four jaws, but they are removed from the chuck first and each one is reground to be perfectly square on the gripping face, this is because they do distort and wear over time, as unlike a three jaw, you can get immense differences in holding pressures applied on each jaw due to the way things are held and adjusted.

BTW still only firing on two cylinders of a V8, but the gearbox is OK.


Nick,

Now the far eastern makers are getting their act together, things like tapered gibs are starting to become standard on a lot of the new models now. In a few more years, they will have everything perfected, and the quality will shoot up. We are actually starting to see it the the quality of tooling, a few years ago you wouldn't have touched it. Now you can buy with the confidence of knowing that it will do a very acceptable job. The machines are going the same way.

Look what happened to Japan, cheap tat to begin with, now world leaders in quality. At the moment Taiwan seems to be the leader of the up and coming pack, with China and India coming a very close second. In fact on larger and more expensive machine tools, they are already up with the best of them. What we see and buy is only in the bottom 10%.

John

[Twinsquirrel]

Thanks for that John, I had a feeling that article wasn't telling the whole story, I'm glad I held off from doing it now


David

[bogstandard]

I just couldn't stop playing with the damned thing, and rather than leaving the post in a bit of limbo, plus my conscience had got to me, saying that I couldn't really do anything with the chuck.

At the end of this post is a little vid, please read the text first before playing, as it will make a lot more sense.

I had already got the head sorted, but because of doing this next bit, I redid the head, and I will show what I got up to.


First off, the chuck. It had around 2 thou runout, which really is about normal for this sort of chuck. But I thought I should be able to reduce that to a more acceptable level, just by using a technique I have shown you before.
A bit of rough bar was mounted into the collet chuck. Even though this chuck has no detectable runout, I still turned the bar down to make it truly concentric.




The suspect lathe chuck was mounted onto the new arbor and the back face checked for runout. It was a fair bit out, so it was as usual, blued up.




The chuck was then cleaned up on the back face until the blue was all gone.




Everything was cleaned down and the chuck refitted on the lathe. The runout was checked, then the chuck was remounted into the next set of holes. The check and change was carried out on all three possible mounting combinations. I then chose the best reading and mounted the chuck in that position. The backplate and chuck were both pop marked, so if the chuck is ever removed, it can be remounted back in the same position.
The first part of the vid relates to the results obtained.




This part now covers my realigning of the head. Because I had redone the chuck, the head settings were now no longer valid.
So the first thing I did was to change the two rear head holdown cap screws for a pair of hex head bolts. When I had set it up before, the motor had to be removed each time so that the cap screws could be slackened, so taking about 15mins to reshim each time. Having to do that half a dozen times is no joke. Now the cap screws have been replaced, that time drops to 5mins, because the motor can be left in position.

The lathe was cutting tapered, getting larger the further away from the chuck, not a lot, more of an annoyance. If you turned a long bar between centres, it would become an issue

So using cooking foil (0.001" thickness) folded over to make a shim pack, I inserted one pack onto the rear face of the prism bed.




And another onto the front face. This effectively kicks the head over in the direction I want to go. After four attempts, using different shim packs, I had it rather good.




Outboard end.




Inboard end. Spot on, no taper at all.




If you now watch the vid, it will show the results.

So that really is it.

Bogs

[Darren]

I'd better get round yours pretty quick John.....


Otherwise It'll be CNC'd next and you'll get nothing else done !!! 

Yes, you did show us how to center a chuck before, but I'd never have made the connection and done it on a full sized chuck.

Oh don't laugh, I can just hear you from here, yes, yes it's only a piddly  lil' diddy chuck 

Joking aside, that lathe is looking like a pretty darn accurate machine now.
I'd better stop using it for grinding and polishing  That was about where it had been resigned to for a while.

Good job I have a polishing machine, must do a post on that sometime.

[bogstandard]

Darren,

It is actually a nice little lathe. Never having used one before, I can now see why it is so popular.

As long as people realise its limitations as to size and weight it will cut, then it does the job admirably.

Don't worry, that is now definitely it. I will clean it down (including my bench, which is covered in brass swarf) and get the covers back on and it will be ready for you.

Leave yourself a couple of hours free, and we can have a look at doing a bit of machining.


John

[Brass_Machine]

Very nice. I see what I am doing this summer. Thanks for the tips and inspiration John!

Eric

[Divided he ad]

A good rest (making stuff!) well earned I think John.


Good to see it is all running sweetly.


Darren you lucky ......  We'd better see some well turned work from you and this little beauty soon (well the next 6-8 months anyway) 



Ralph.

[Stilldrillin]

This posting just got even better.   

THANK YOU John...... 

David.

[bogstandard]

David,

Some of the purists would scream if they saw what I had done in this last part. The shimming should have gone a lot deeper and setting nose up/down as well, and they would burst into flames with rage at the way I treated the chuck.

It all depends what you want out of a lathe. With a LOT more time and effort, it really could be made absolutely perfect.

But what I have done is made the lathe cut as accurate as possible, by just a couple of easy to do things.

I haven't even played with the tailstock, that will be up to Darren to put back on centre. A fairly easy job if he wants to do it.

I have already shown how that is done somewhere else.

Just remember, this is the way I do things, it might not be right, but it gets the job done.

John

[sbwhart]

Nice one John 

Wounderful bit of work.     

Cheers
 
Stew