Finishing problems

[Darren]

Not sure where I should put this?

I have a problem with my 7x12 when using the carriage feed. Mainly when finishing a length of work it leaves a mirrored patten of the lead screw pitch on the surface.

This means I have to take the last cut with hand feed. This as you can imagine really spoils this little lathe and it would be great if it could be sorted.

But how? Suggestions most welcome...

Regards
Darren

[Bernd]

Darren,

How about a pic of the finish. Does it squeel, chatter, what?  That might help. Also make sure your speeds and feeds are correct. Sometimes to light a cut cand cause that. Make sure things are tight.

Bernd

[Darren]

Hi Bernd,

No nothing like that, it cuts really smoothly, just leaves a faint impression of the lead screw thread mirrored on the work.

I decided to have a better look today to see if I could improve things.
First I put a dial gauge on the bed and measured the carriageway as it was powered up and down the lathe.

To my horror I saw the carriage lifting up and down by 2 thou over it's whole length  

So off came the leadscrew and stuck it in the bigger lathe for further measuring



Between the leadscrew section and the bearing surface I measured 22 thou off center !! You could see it clearly going up and down as the lathe was turned by hand.
The tail end was fine, or at least better at 2 thou.

So what to do, buy another? Would that be just as bad............but then I thought what could I do with this one I already had? I mean, not much to loose was there.

So I attacked it and did this, pic's should explain, I had some sintered bearings from another project.


Truing the bearing area of the shaft and reducing it to fit some bearing I had.




Here I'm reducing the outside diameter of the bearing to fit into the mini lathes pillow block.



Installing the bearings, I had to use two, one at each end. I used a press as I wanted them tight fitting.



Fully home



Back on the lathe,
Looks good to me....





But did it work...?

Well the carriageway now only moves 1/4 of a thou, not perfect, but a lot better than it was. Certainly can't do any harm can it. Maybe I'll have another look at the tail end.

Will put it to the test shortly and see if the end result improves....

Regards
Darren

[Darren]

Tried a test to see if it was any better, it's improved a little but not good enough.

Here is an older piece that is worse than it looks, and it looks bad !! You can very easily feel this pattern.




In the chuck is a piece i've just tried after modifying the leadscrew, as you can see it's not much better. A little, but like I said, it's not good enough.



Regards
Darren

[Brass_Machine]

Darren,

I had a similar problem on my 7x lathe. Not quite as pronounced though. I fixed it by a combination of feed speed and using a HSS insert.

I know that isn't much help.

Eric

[Darren]

Ah, I wonder if others out there have similar probs with these small lathes?

Does anyone else on here use a 7x12 or similar?

I'm wondering if it's just down to the lightness of these machines, or at least the carriage.

Darren

I've threatened the missus that there may be a new addition after xmas, I'm toying with several possibilities.
A larger Smart and Brown, a Cardiff or a Colchester Student.  Be nice if I could see something larger in action to make further assessments.
Alas I don't know anyone locally with a lathe, let alone a bigger one. Or a workshop for that matter.

N Wales,

Here's some stuff I did a few years ago, http://homepage.ntlworld.com/darren.dean/index.htm

[bogstandard]

Darren,

I am not an expert on this sort of problem on a lathe, but have come across a similar situation on another type of machine.

Has it been like this ever since the machine was new, or is it a fault that has appeared over time?

It looks like the far side of the saddle is 'dragging', that is where the leadscrew is driving the one side, and the other side is lagging behind, then when the lag gets too much, it springs forwards to catch up, and then does the same thing over again. It only takes a few very difficult to see thous to cause a problem. It might not happen when using the handwheel because of the different moment forces involved.

I would try holding the leadscrew side rigid (or just engage the half nuts) and try to move the far side of the saddle backwards and forwards. If there is play there, you should be able to adjust up on the jibs to reduce the fwds/back play. But before doing all that, make sure you are not running dry on the far side, the lube should be on the top edge and the far side plus the far bottom of the slides.

If that isn't the problem, try to only partially engage the half nuts, so that it is only just driving the saddle, and see if the fault is still there. If it disappears, that would point to your problem leadscrew, and you might get around it by adjusting the engagement force on the half nuts. Not an ideal situation, but if it gets rid of it, you are halfway there.

That is all I have, hope it helps with your problem.

John

BTW I am in fairly easy striking distance. Crewe, Cheshire. Plus you have Ralph in N. Wales.

[Darren]

Hi John,
Had another good look taking on board your comments. I've had this lathe about two years and it's always done it.

I've always thought there was a lot of movement in the carriage, up/down and rocking horizontally side to side. But then I've little to compare it to.
My S&B is a plain lathe and thus locks its carriage down hard to the bed. Movement is manual only.

On the 7x12 there are adjusters underneath, ie when tightened they pull the carriage down, no gibs as such, just some crude plain bars.
The thing is, the bed seems narrower at the tail than the headstock. If I adjust the "gibs" for mid point along the bed it becomes very slack at the tail and impossible to get near the headstock.

It could be dirt, I doubt it but I'll gunk it all down and give it a good clean and try again.

Will post here when that's done.

Yep, Crew is not too far, Ralph must be in between then.

I'm nr Porthmadog, well almost.....just think model trains that are put to work..... ;D

Regards
Darren

[Divided he ad]

Hi Darren, I've been reading your post and was thinking of play in the saddle too... Maybe undulations in the lead screw moving the whole saddle?

Well it's a thought. The tapered bed is a new one on me though!

I've also checked the distances involved.... A good trek!!

http://maps.google.co.uk/maps?f=d&saddr=mold&daddr=A494+to:52.987511,-3.390656+to:Porthmadog,+Gwynedd,+United+Kingdom&hl=en&geocode=%3BFbVWKQMdQo7M_w%3B%3B&mra=dpe&mrcr=0&mrsp=2&sz=10&via=1,2&sll=53.078353,-3.637848&sspn=0.52055,1.450195&ie=UTF8&z=10

(personally I'd grab and drag the blue line over to the 494 Road.... It will travel much faster than the winding roads, no matter what the computer says!)

Crewe works out at just shy of 2 1/2  hrs.

I've only got a 9x20 and John has the now super acurate beastie.... Not too sure of it's size and can't remember the name!!!  (the memory is getting worse with age!) it is a nice big fella with a gap bed and I'm sure 20+ inches between centres (I'm sure John will clarify?  ;D ) I'm sure visits could be sorted..... You'd have to be ready for a messy cramped workshop where two can barely fit at mine though!! It's only just over 6'6"  square! 


It'll be interesting to see your findings.


Ralph.

[bogstandard]

Darren,

The bed must have been machined that way, because when a bed wears, it always does it the opposite to what you have. It always tapers towards the head, and when you adjust, you have trouble getting it to the tailstock end.

Maybe after 20 to 30 years of hard use, it will wear itself parallel.

How long is the bed? Because if you really want to fix it well, it might fit onto my mill, and I know I can get it within a thou parallelism, which must be better than you have now.

This is my new 'beastie' as Ralph calls it.

http://www.chesteruk.net/store/crusader_lathe.htm

John

[Darren]

Hi John, Ralph,

I took some measurements of the 7x12 bed

Length
Total 25"
Front of headstock to tailstock end 20"

Width
Head just under chuck 82.74mm
Tail 82.53mm
Difference 0.21mm/8.19 thou


Bed thickness for carriageway
Head back 8.57mm
Tail back 8.23
Difference 0.34mm/13.26 thou

Head Front 13.53mm
Tail Front 13.38mm
Difference 0.15mm/5.85 thou

As  you can see, not too clever are they..

Ralph, small workshops, clutter, loosing things sounds familiar.

I have a mate in Holywell and often take the misus to Flint shopping.

So near enough I'd say.... ;D

[bogstandard]

Goodness me Darren, that isn't a lathe, it's a banana.

It is no wonder you are having trouble with it. That needs some serious work to get it to be a precision machine, but nothing should be discarded until all hope is lost. Getting the bed casting sorted should be a fairly straightforwards job. The hard bit is getting all the other bits to fit correctly afterwards. You will most probably find that the saddle, head and tailstock castings will be in the same sort of ballpark.

They were most probably assembled by having a large number of each casting, and were swapped about until you got something that almost worked. Then it was stuck in a box, and sold.

If you need assistance, don't be afraid to ask. It is most probably only a good days machining worth to get it something like.

John

[Darren]

Yes John, I didn't think it was too clever!

I sorta gave up with it, perhaps understandably you might think, and bought a Smart and Brown 3ph Model L lathe about a year ago.

This is a capstan lathe that came with a 6 position semi auto turret and a twin tool cut off slide. Great for small production work if you want to make many identical small parts. At the time it was just what I needed and did it's job admirably. 100 small parts in a hour is easily achievable once it's been set up which can sometimes take a while.
Since then I've bought quite a bit of tooling for the capstan so that job is now much easier thankfully.
Anyway, the important bit is that it has paid for itself easily.

Then I bought another S&B L lathe just for a compound slide and tailstock. Ever since then the mini lathe has seen almost no use. The compound slide looks ropey to say the least, but it is nice and tight and cuts superbly accurately.

Alas it's basically just a plain lathe, so no feed and no screw cutting facilities. It can also only make small length parts, max about 3" long up to 9" diameter.

It was only the other day I had my first go at cutting a thread on a lathe. For some reason I'd been putting this off thinking it would be a bit difficult. I was so wrong, the little lathe does this just fine with a nice finish too. I look at it sometimes and think what a nice dinky little thing the 7x is . If only it was a little better built.
I'm not knocking it, I think they are great and also think I was just unlucky with the build accuracy of mine. Others manage well with theirs, for a long time I just thought is was me.

Anyway, back to the issue at hand, yes it would be great to have an accurate mini lathe. If it was I'd never part with it. Ever !
As for needing help, I am not the one to put it right. I simply don't have the skills or tools needed.

One day maybe, but not for a while yet !!!

But, I have one question. I certainly don't expect anyone to spend a day machining out of sheer kindness, and I suspect you may fall into that category John.
So, as I am hankering for another larger lathe, ambitious? maybe...gotta push forward eh..would I be better off putting efforts towards that end or is a super accurate mini lathe worth having as well?
Genuine question as I do not know the answer to that.

Regards
Darren

[bogstandard]

Darren,

As a lot of model engineers find out when they come to me, I happily help out, with no charges at all, except for the coffee, that comes at £20 a mug. Just joking of course, it is in fact £25.

Any lathe, no matter how big or small is worth putting time into. I have restored a few lathes, and my last one was a prewar Atlas, which I had used up until a few months ago as my only lathe, it kept me going for 15 years, and when I sold it, it was machining better than if it was new.

To me, your little lathe would always be a machining asset, and would really be worth keeping if it was put on the right side of good. I don't mind putting a few hours into it, F.O.C. If you could leave it with me, I could just plod along on it as and when I have some time spare. It takes up no room, so it could go into my back metal prep shop. The offer is there if you want it. I would suggest you have a private word with Ralph to find out my 'rules'.

Choosing a good second hand lathe is like walking into a minefield blindfolded.

In the UK, you can't go far wrong with one of the UD boxford range, preferably the AUD. They were the ones that were installed in schools and other educational departments, and if you can get one of those, they had hardly ever been used. They can be picked up fairly reasonably, and they are almost bombproof. It is a fairly easy motor swap to convert from 3 to single phase, but it is always worth considering putting a converter on them to run 3 phase from single. Imperial machines are the easier of the machines to get cheap spares for.

http://www.lathes.co.uk/boxford/index.html

John

[Darren]

John,

I can see you are a man with a passion/obsession for tools. How can I say no to your offer !!

Wonderful, the "dinky" may stay with me yet,

Think I'd better I'll 'ave a little chat with Ralph about these "rules" of yours..

Darren

[Brass_Machine]

Darren,

You are a lucky man. Bogs is one of the nicest guys in my hobby circle. I would love to live close by to go for a visit and coffee. Alas, I have an ocean to cross first. However, the day will come when he and Ralph will have to put up with me coming for a visit.

Take him up on his offer!

Eric

[Darren]

Darren,

Bogs is one of the nicest guys in my hobby circle.
Eric

I'm starting to realise this, and I suspect many others here fall into a similar category.

I went to my local scrappy to see if I could find any suitable material for lathe work, I was told by the owner  "sure have a good look around and take what you want mate"

My world has suddenly become a nicer place !!

Darren

[CrewCab]

In the UK, you can't go far wrong with one of the UD boxford range, preferably the AUD.

Funnily enough John and I had a similar conversation a few months back ................. and .........  lo and behold ...........  look what followed me home ........... 



Before that I was using a Chester 9" x 20" which is a nice little machine, but to be fair the Boxford does have an edge, mainly due to build quality and mass, it treats CRS like the 9 x 20 deals with aluminium.

Dave .............. aka .............. CC 

[Darren]

That looks good Dave, a lot of people really favor these Boxfords from what I can tell.

Alas I have an ambitious project in mind for the future in that I wish to turn a new 12" or even 13" platter for my record player.
On those lines I'm thinking a Colchester Student for example, I also wish to turn 30mm S bars up to around 300 or 400mm long and drill and tap the ends.
I can do the last bit on my S&B if the new lathe isn't able.

I know from experience, that I want the next lathe purchase to be my last, famous last words.


Thanks John, I will speak to Ralph hopefully face to face sometime. I have been playing with metal for a long time.
It's the machining/engineering that's new to me...loving it though.

Did you see the link to my now very old web site? http://homepage.ntlworld.com/darren.dean/index.htm

[Brass_Machine]

Darren,

Both the GSXR and the locost fit in well here (yes I have the build a sportscar book...). I am very heavily into bikes and cars as well. Look about the forum and you will see my CF stands. Both projects will fit in here, do up some posts!

Eric

[Darren]

Hi Eric,

Those were some time ago now. I spent 4 years working on that bike, every nut and bolt etc. The engine was bored, gas flowed, dyna jetted etc and was a stonker.
160 two up no problem.... There was very little of the original bike by the end, I'd fettled with just about everything. Gearbox, clutch, suspension frame bodywork and painted it more than a few times !!

The Locost was never finished, sadly due to personal circumstances I had to put all my belongings onto storage for a year or so until
some lowlife emptied the lot, my whole life...gone in one stroke....bike, car, tools the lot.

Anyway, life moves on dunit, that was a while ago now and after a long absence I'm slowly putting a workshop back together.
Different goals, same lunatic at the wheel.... ;D

[Brass_Machine]

Locosts are pretty cool. I am working on a locost inspired 3 wheeler powered by a sporting V-twin. Right now it is in the very early phases. Only exists in my head and a few bits here and there in my CAD software. I will probably start it next summer as long as I find a new job and get my finances straight first.

Sorry to here about the low life. Thieves should be hung.

Eric

[Divided he ad]

Thieves should be hung......

Edit.... You missed "Drawn and Quartered" !! I fully concur!


 (IMO)


Ralph.

[CrewCab]

Can I add "needle at birth", just a personal opinion of course

CC  >

[bogstandard]

You lot would make it to easy for them.

Meathook thru the dangly bits, then a brick hung on the end, 3" above the ground.

Oh, I forgot, public branding on the forehead with a big letter T as well.

That is a bit better than sending them on safari.