Fixing Darren's lathe

[Darren]

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


John

Well I wouldn't quite say easy, depends on who you are 


Ralph,
Expect this baby to be showing its talents quite soon as I have a small job just waiting for it's return.
But I'm sure many other projects will follow 

[Bernd]

Excellent as always John,

GRIZZLY LATHE, look out because here I come to rebuild you. 

Your an insperation John.

Bernd

[Twinsquirrel]

Hi All,

I thought I might revive this thread, 'cos it's so darn good AND because I have spent the afternoon measuring and skimming the underside of the ways on my mini-lathe which is the same as Darren's.

In my case I had a taper end to end of .24mm   which I have suspected for a long time. The good news for me is that I can't detect any sag or twist in the bed at all, the bad news is that I had to reset the bed on my milling table 6 times to skim the full length both sides because my mill is MUCH smaller than John's   but with a bit of jiggery-pockery I managed get the transitions between cuts just right with a nice finish using a Glanze form tool mounted upside down in  a flycutter with the mill in reverse.

I was feeling pretty pleased that I had managed to get the taper down to .07mm end-to-end with no lumps and bumps but now I'm having second thoughts........ What tolerance should I work to?

BTW I dont know what posessed me to start this, I am way out of my comfort zone here.  


David TS

[bogstandard]

David,

I would leave the main casting as it is now, because with your setup, I don't think you would be able to get it any closer. Besides, that is a very reasonable figure to have over such a length.

You will find any other tweaking much easier because everything is so much smaller.

If what you say is correct, you could stop at almost any point, and know that you have already made a significant improvement.

Well done indeed.

John

[Twinsquirrel]

Thanks John,

I had worked myself up into a bit of a lather about it but you have put my mind at rest, as you say certainly a significant improvement.

Looking at the weather forecast I cant see me doing much proper work tomorrow so I may have a go at your tapered gibs mod I can feel the symptoms of  creeping up on me 

David TS

[bogstandard]

David,

All I would do is wrap a bit of something like 240 or 400 W&D paper around a square edged flat bar and spend a few minutes just rubbing up and down each slideway, plenty of thin oil as well, where you have machined, just to blend together any transition machining marks. Other than that, you should be ready to go.

Before doing any machining on the saddle, make your carriers and tapered jibs first, leaving a little bit extra on the carriers height and width to give you something to fiddle with. Then if you do get into a pickle, you can always revert back to the old jibs.


John

[Twinsquirrel]

John,

Yup sounds like a good idea, the last thing I want to do is back myself into a corner and end up with a pile of scrap. I would say that I will take it slowly but I only have 2 speeds: dead slow and stop.

David TS

[Darren]

Bloomin ek David,

That's pretty good going considering you feel out of depth. In fact that's pretty good going all round.

0.07mm = 0.0027559" or 2.8 thou over 24"

Usable working area is 12", so that's 1.4 thou. And we are only talking about the gib tightness not ways to the spindle accuracy.
Besides, you need somewhere for the oil to sit.

 

[Mike K]

Excellent, David.  You've got me interested in trying this.

Got any pics of your work?  Did you happen to do this on a mini-mill?

Mike

[bogstandard]

If you are going to show any more, could I suggest that you raise a new topic. Then David will get all the recognition for it, rather than just being an add on to my post, where it will most probably get lost over time.


John

[Twinsquirrel]

New thread started, I really need a hug right now. Is it wrong to love a tool so much? as much as this little lathe is a bit wobbly and dare I say inaccurate I am extremely attached to it/her, she is my first you know 

Mike, nope not doing it on a Mini-mini mill this is a similar machine to mine



Darren

Thanks, I had to put on my brown trousers and bicycle clips when I started cutting but overall I'm pleased with progress so far.


David TS

[seanacais]

Joking aside, that lathe is looking like a pretty darn accurate machine now.

Darren:

I have gone through much of the same experience that you have with your machine.

My machine wasn't so much bulged in the middle as it had a 0.017" difference in bed thickness from HS end to TS end in the front and 0.014" thickness, in the other direction of course, in the back.

After fixing that, I found that the saddle gib mounting plates needed  adjustment by about  0.006" and the saddle/bed contact area was out as well.

Fortunately the cross-slide was perpendicular so that wasn't an issue but this thread doesn't mention if  you had any trouble aligning the tailstock. 

I cannot get my tailstock aligned well to the spindle and there seems to be some problems with trying to adjust it.  http://www.robobits.com/realbull/tailstock.html has some pictures.  There are no pictures of your tailstock in the thread.  Is yours the same design as mine?

I'm curious if you had  any additional problems? 
 
I'm also wondering what the serial number stamped in your lathe is?  Our lathes appear identical and are about the same vintage.  The number stamped on mine is 033.  I'm wondering if perhaps you and I were the lucky receipients of the first  few machines that came off a fairly new assembly line in the Far East.

Kevin

[D_Harris]

I just finished reading this entire thread and it was inspirational.(Now to take mine mini out of the box). 

I'm assuming that there are no further updates to Darren's lathe.(?).

Darren Harris
Staten Island, New York.

[Darren]

I broke a tooth on a change wheel trying to cut a 6tpi thread ..... does that count as an upgrade 

No, no further upgrades were found necessary, congrats on your new joy toy 

[swarfmaker.com]

I just finished reading this entire thread.  Very good information.  I happen to have... three of these beasties... don't ask me why.  So, whatever fixes there are, I get to multiply by three.

I've been looking into this carriage gib problem for some time.  I started gathering materials to make the tapered gibs, but after reading about gibs in Machine Tool Reconditioning, I thought I had a simpler solution.  It's not as elegant as the tapered gib, but it might do the job while being quicker.

Has anyone investigate making loose-fitting gibs?  This is where the gib bracket is fixed to the carriage, and a series of adjusting screws press the gibs against the underside of the ways.  This design would automatically compensate for any angle of the carriage at the mounting point, and the relative angle of the underside of the ways.  I'm thinking of using 1/4 brass for the gibs ('cause I have it) and making the gib brackets out of standard size steel stock and shims, stacked up and drilled to create the proper form.  Unfortunately, to adjust the front gibs, the apron would have to be removed.  Once fitted and worn in a bit, they probably wouldn't have to be adjusted for years.

Any thoughts?

[Mike K]

Simpler still, I use shims and haven't looked back.

[simp]

Shims work!    But if the lathe is not flat on the bottom of the ways.  Your carriage is going to be loose in spots.   You can scrape  and fit the tappered gibs and its a whole lot better!   Unless bogs is your neighbor.             Also some lathes are pretty straight from the factory.

[madjackghengis]

With regard to "loose gibs", I've made and fit two extra cross slides to one of my lathes, a ten inch Logan lathe of 1948 vintage.  The cross slides were for using the lathe to mill, were castings bought from Metal Lathe accessories, and were machined mostly on a bench mill, with the second one machined on the lathe its self.  They were designed to use a gib with half a dozen gib screws to adjust it, and I used eighth by half inch hot rolled steel, clamped in the dovetail of the cross slides with small C-clamps to machine the angle on each edge, and a light sanding on both sides with some 320 wet or dry paper, to remove the mill scale.  They are about fifteen or more years old, haven't been adjusted since the first few months of wear, and are slick moving, with no play, and no discernable wear at all, on a lathe used daily for every kind of work repairing old machinery and engines.
    I've rebuilt a few mills and lathes with tapered gibs, and while the concept is "better engineering", in the big picture, it has little real value over "loose gibs" for the home shop, in my opinion.  The last time I refit a tapered gib, it was on a milling table that weighed about two tons, was about twelve feet long and three wide, and I rolled it over with a fork lift.  The workers had long used up the designed in usable adjustment of the x-axis gib, but kept going for more, and managed to get enough more that the table pulled the gib over its adjusting screw shoulder, lock the table to the knee, and required a come along to pull the table back out, free the gib, and allow the table to be removed.  I got a week's pay for repairing that gib, the table, and putting a new notch in the gib, and making a new gib screw, after scraping both the table dovetail flat and straight, and the tapered gib flat and straight.  They'd have saved half the cost if they had brought it to me before they jammed it, and had the machine back in service in a day or two instead of over a week.  Unless I'm replacing a tapered gib already in place and working, I always go with the "loose gib" and get good service out of it, completely satisfactory in all regards. mad jack