Fixing Darren's lathe

[bogstandard]

Now to cheer up Darren.

The private project I am working on has come to a halt while more material and tooling is awaiting delivery. So I am slipping Darrens tiny job in while I have a little time to spare.

This is my first real project to be shown on here, but please bear in mind, my health is still a little fragile, so there might be slight gaps in the posting, and I am a little rusty in the humour department as well, but I will try to keep you entertained.

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                                                                             DARREN'S BENT LATHE



So now we start.

This is Darren's very poorly lathe, just as he delivered it to my hospital, and I have gathered around a few tools I will use to take it apart.

Just joking of course, the rasp at the front is way too small, I will use my angle grinder instead. The coffee is there to keep me awake.




Here is the bit I want for me to work on. It came apart in a couple of minutes, with only a few chunks knocked out of the casting, and a couple of snipped wires (how's your welding and soldering Darren?).




Don't want to get too frivolous here, so I will show you a bit of the technical side.

When Darren first mentioned this lathe, it was to do with the finish of cut he was achieving, it was very poor. It was mentioned that the saddle tightened up as it went along the bed, then slackened off at each end. This is a sure sign of something wrong with the bedway, and when it was delivered, this fact was confirmed with a little checking over with a mic.

So I need to get a more accurate layout of what is happening with the bed. So I duly used the great 24" rule that Ralph had bought me as a gift, and marked out every 3 inches using a paint stick. I then took a micrometer reading at each point and marked it down on the bed. These are thous, and definitely shows that there is a 'bulge' in the centre of the slideways.




A check down the reverse side confirmed the same sort of problem, a definite sagging belly, or a bulging top.

This now causes me a great deal of concern. When in the machining stage of this casting did the problem occur? If it was while the top of the bed was being ground, then there is nothing that can be done in my small workshop, my little surface grinder just couldn't cope with the bed length. But if it is as I suspect, and the top of the bed is flat, and it is the underside that is sagging, then there should be no real problems fixing it.




So the first job is to get it up onto a known flat surface, level it up, and run a few end to end checks on it.

This is the setup I am using on my mill at present, so that will be stripped down, and the whole lot cleaned off, to see if I can carry out surgery on this sorry little casting.



Maybe another posting today, maybe not. Just depends how my power nap goes.

Bogs

[sbwhart]

Hi John

Looking forwards to developments.

You can make a fortune fixing ''sagging bellies and bulging tops''

                     

Cheers

 

Stew

[Bernd]

Are you sure that the hammer is big enough? 

And what's mixed in with the coffee? 

You don't have to answer that Doctor Bogs untill after the patiant has died.

OK, now a bit more on serious side.

You know John I think that may be the problem with my Grizzly lathe. I'm going to have to check that some time. There are other problems with it too. So going to keep a close watch on this thread. May need the info for doing mine now that I can put it on the Bridgeport to do the milling if that's what it needs.

You take care of your health. I like it when you write up one of these threads with a bit of humour in them. Always entertaining and informative.   

Bernd

[Darren]

Now to cheer up Darren.



Bogs

Well I needed cheering up John and that's just the ticket....

You'll have one guaranteed member glued to the show paying full att to how this is done.....

[cedge]

John
You were remiss in not showing Darren the huge rosebud heating torch you'll be using to "adjust" the bed .

Steve

[bogstandard]

Steve,

I didn't show him that because of two reasons, the first, I didn't want to scare him too much, and the second, by showing it, would reveal that I really am a raggedy ar**d grease monkey.

Right, I said I might be back with a bit more, but a lot of you will find it totally boring. I spent two hours checking the casting over, just to see what exactly the problem was. Also you must excuse the pics, I can't quite hold steady enough nowadays, but I managed to get enough that weren't too out of focus or shaky to make up a bit of a post.

I popped the casting onto the mill table, and immediately noticed that the whole casting had a twist in it. It was 'rocking' on the machined bases, I measured it and there was roughly a 0.010" (0.25mm) gap under one edge. So I got a 3-2-1 block, put it onto the top faces and checked for rock on there. Sure enough, the block rocked (just like madmodders). The decision now had to be taken whether to carry on or give up and call it a day. So to give it another chance of life, I decided to clamp it down and see what happened.




Once clamped down, all rock disappeared on the top faces. So I have decided to give it a reprieve and machine it up, if everything else checks out. This will mean Darren will have to bolt the lathe to a flat section of either 4" thick walled square tube or a length of u-shaped girder. Just to keep the twist under control. Unless of course he can come up with a nice piece of thick Welsh slate to bolt it to.
I suspect that during it's life it has been resting on an uneven surface, and because there is no strength in the drip tray it was bolted to, and only supported on four rubber feet, it has taken on a permanent twist.




So out came the trusty Verdict DTI and the casting was set up to 0-0 at either end of the run (my first mistake). I then did a run along the edge and noticed it had a 3 thou dip in the middle. Oh! s**t I thought, it has got an end to end bend in it as well.
So I sat back in my chair, feeling all dejected.  After a while a little light appeared above my head, "you stupid bugger Bogs, that isn't a datum face", so can be almost any shape, there are four running datum faces on the casting, and I was measuring the wrong one.




So anyway, I decided to check the back face to see if it mirrored the front, but not so, nice and straight (within a thou).
Confidence boosted, I decided to check the main datum running faces.




I checked the runout on both angled faces, 0-0.





Then the first top face, again 0-0.




And the last top face, 0-0. So that proves my initial suspicion, a sagging belly, not a bulging top.
Feeling a lot more confident now. It is fixable.




Now I need to see if my original readings with a mic were true. So set the DTI to read the under face at a place that was about 6 thou under the centre reading.




Moved to the centre, and sure enough, a six thou sag (you can just make it out on the dial). Now a very happy bogs, theory proved right.




So now comes a major decision, machine it on the spot and hope that the casting hasn't been hardened underneath where the jibs run, or mount it onto angle plates and machine it with a known cutter that I know will hack the material off.

I can use the side and face cutter, hoping the material isn't too hard and do it in situ, or use the solid carbide which is guaranteed to work, but will require two more precision setups using angle plates.



Decisions, decisions.

My brain hurts (in a Monty Python voice).

Bogs

[Baldrocker]

Humour? Joking? Bugger it I just went out and bought
the biggest sledge hammer I could find!

[bogstandard]

Paul,

It is always better to smile than frown, and once you get to know my (our) quirky little ways, you will soon find out that I (we) always try to make light of a lot of things. Sometimes a little misunderstood, but never too much.

Humour is understood worldwide, and in these times, we need as much as we can get.

Rather than reams of technical jargon, it helps to put a bit of humanity into a post. So I tend to do it as though I am writing a personal account of what I get up to (complete with talking to myself or Bandit).

I think that is why we all get on so well on this site, as long as you don't go over the top and become downright vulgar and abusive, almost anything goes.

Bogs

[Darren]

Hi John,

That casting does sound to be in bad shape, even to a novice like me.
It's always sat on a good solid surface, but, under the oil pan it has rubber feet.

So it could have twisted to any shape it liked really I guess.

Best I take the feet off then. I would order another bed, but it's likely to be no different from what a couple of peeps have said on here.
That is, it seems I'm not alone with this finish problem.....

[bogstandard]

Darren,

By the time this has had a few hours spent on it, and if you can get it onto something rigid, it should be a first class machine. Well worth keeping and using.

A new casting would be of no use at all, it would most probably still require reworking to get it something like.

Now that the problem has been found, it will take no time at all to machine up, and I am thoroughly enjoying this little project.

Trust me

Bogs

[Darren]

Darren,
I am thoroughly enjoying this little project.

Trust me

Bogs

It's a challenge thing init Bogs.......great when you can conqueror.....

[SPiN Racing]

Cool Post!


(I see another tool I think I may need to buy when the paycheck arrives Thursday... <note> add one of those dial indicators that measures sideways..)

PS: I already have a normal? Dial Indicator with a base, for measuring runout and thnigs on Rotary engines when I build them...

PPS: Nice to see I have SOME of the tools I need :P I just was using them for other things. (Vernier Calipers for measuring Thickness of Apex Seals)

[Brass_Machine]

That's our Bogs   

I learned a lot form this man from reading his informative posts.


Eric

[bogstandard]

Darren,

Yes it is the challenge that does it.

But I am no super machinist. I just look at the job logically and take my time to find a solution. That is why I show what I do.
It is easy saying do it this way, do it that way, but showing the working out to get the result, is how people learn things.

The machining of the item is the easy part.

Spin,

I have had that DTI for more years than I care to remember, and I use it more than any other tool in my workshop, it has got me out of a lot of little scrapes, where I needed to get in and measure something in an awkward place.

Eric,

Thank you, it is nice to know my little posts help people along their journey.


Bogs

[sbwhart]

Hi John

Very interesting  . I'm interested on seeing how you machine it straight. I wonder if the twist is due to the casting not beong left long enough to weather, before it was machined, they probibly knock these thing out as quickly as they can.

The casting process leaves residual stresses in the casting that need time to even themselves out, the term weathering comes from the good old days they just left the casting sitting in the foundry yard for a good few months or even years before they used them.

Those 100 year old shash weights you sowed me wouldn't have the same problem they were done moving years ago.


Have Fun

Stew

PS if you need help moving the casting about you know where I am just give me a call.

Stew

[bogstandard]

Stew,

That was the reason I got it bolted down to the table, to get it in the same position the bedways were originally machined in. If I can do my bit with it in that position, when it eventually gets taken off, and bolted to something substantial, everything should be spot on. The machining bit is the easy part, getting it into the stable situation it is now in was the worst. I am hoping I can get it to under 0.001" tolerance. The oil film on the bedways should be able to level it out within 0.002", so by going under that, I hope to have good success. The original max difference from my measurements was 0.011" (on the back side of the bed), so anything better than that is a step in the right direction.

Gone are the days when castings are left to 'weather' for up to years at a time, progress is so fast nowadays, three months is a long time, the machine would be well out of 'cutting edge design' before they even started to clean the castings down. They try to use heat to relieve stresses, but that is just like kiln dried wood, crap compared to the old methods of drying out naturally.

The twist could have been caused by almost anything, even the hardening of the slideways could have induced it, we will never know for definite, we can only assume.

I am also hoping that by me taking off a bit of the 'skin', some of the stresses might be relieved, and it may sit a little better when it is free standing.

PS if you need help moving the casting about you know where I am just give me a call

Thanks for the offer, but Mal (SWMBO) is getting rather good at moving things now, just get her into the yoke and chains and she can move mountains.

Thank goodness she doesn't read my posts, she would kill me.

John

[bogstandard]

After giving it a long thinking through, I decided that I would give the side/face cutter a go at it, then if that didn't work, I would take the difficult route.

First the problem.
I don't have enough movement on the x axis to do the job in one hit, so two shots will need to be done. But because I am working off the feet bottoms as a datum, if I do a good cleanup between operations and make sure everything is clean, I should be able to keep within my self imposed tolerance of 0.001".
I have decided to go with a slightly smaller cutter to help keep everything a little more rigid.

I also decided, because the rear side had up to 0.011" variation, to actually put cut on of 0.015" (0.4mm) and hope the area can be cleaned up in one quick swipe.
Once the cut was set for height, both z axis' were locked up rigid, and the DRO set to zero. From now until the end of the job, all areas will be cut at this setting.

This pic shows the start of the exercise, and to my great delight, the underside wasn't hard skinned, and gave a nice steady, smooth cut.




A shot from the top on the steady creep along the casting.




And this is what it looks like from the underside whilst cutting, notice how nice the surface is after being given the treatment by the cutter.




You can just about make out the spindle speed, I had it running at 200 RPM. The power feed was set very low and took 25 minutes to travel the half casting distance, overall it took 1 hour to complete both cuts, that included the casting end change.
I could most probably have got away with a much higher speed and feed, but I didn't want to take any chances. You only get one go at it.
I just sat back with a fag and a cup of coffee, while the machine got on with the job.




Here is the casting swapped over for the second cut. I set the casting straight longtitudinally by eyeballing the back edge and lining it up with one of the t-slots. That should get it within a couple of thou of being true, and that is close enough for this job, as I do not need to take anything off using the outer edge of the cutter.




The finished run, and I have put on an arrow to show the end of the old cut and the start of the new.




Here is a close up of the join. It looks rather mismatched, but after measuring all over the area, no detectable mismatch could be found, so no problems on that score.
After checking the whole run length I was delighted to find that my 0.001" tolerance was well within limits.
Punch the air, kiss the dog and after getting all the loose hair out of my mouth, time for a fag and another coffee.




I restarted just after lunch, and set up the rear side of the casting, and without changing the height of the cut, the next two cuts were carried out just like the first side. Now starting to sweat, to see if my measurements and calculations were correct, as this was the side with the biggest measured sag error, 0.011".




I needn't have worried, it turned out exactly the same as the other side, except for the very extreme left hand end (1/2"), that had dropped to within 0.002" tolerance. That was accepted by me because that was the thinnest end of all the measurements. In fact, if I had put 1 more thou on the cut, that would also have been within my limits. But it doesn't matter anyway, the saddle should never be needed to go that far back.




I did do a slight deviation on the fourth cut. Under where the head sits there was a machined area, to enable a stable flat area for the clamp down bolts. It meant that I had to feed the cutter in to that depth before carrying on to the end.



So that is the casting machined up to a good standard, with an added bonus. When I took the clamps off after the final machining run, there was no rock on the casting. Whether it stays that way will only be known in the future.

But, this was only the first part of the job.
As I was discussing this machining exercise with Darren, an article appeared in Model Engineers Workshop, showing how to make and fit tapered jib strips for this very machine. So that will be the topic for the next bit of this post.

I can now stop sweating, and maybe get a bit of sleep tonight.

Bogs

[Brass_Machine]

Rock on John! 

Eric

[Stilldrillin]

Nowt much I can say...... 

By `ek I`m enjoying this project. Thanks John.   

[bogstandard]

Eric,

I haven't enjoyed myself like this for many months, it must be the challenge, plus what little adrenalin rush I have left.
It was almost as good as getting a little engine up and running.

SD,

Not many techniques or methods shown in these posts, and of course there are most probably dozens of other ways it could have been done. This version is what I was happy with, and I'm glad you are enjoying it.



This little exercise has shown just how far out of wack these little lathes can be, and still be able to turn materials, not very well, but they do achieve it. I hope by the end of the project, it will be just as accurate, if not better, than a lot of the more expensive machines on the market, with the only thing being expended is a bit of time and a small amount of raw materials.

Looking at the whole process now, I reckon this part of the job could be done in about 3 hours, from running lathe to running lathe.

50% there, the next bit (and adrenalin rush) awaits.

Bogs

[sbwhart]

Great Job John

 

 
Stew

[rleete]

Man, I am sooooo jealous of Darren.

[Baldrocker]

Just how many years of experience do you have Johnjavascript:void(0);
Please keep sharing.
BR

[Bernd]

John,

Nice piece of work.    I'm going to have to check my Grizzly lathe. I think it has problems to. But not right now.

Lets see if I understand this. When you took the two cuts you just used your eye ball to line it up parallel ,no indicator or other devise used?

Bernd

[bogstandard]

BR

Industry wise, 40+ years.
Me wise, about 50+ years. I was playing about with technical things from a fairly early age.

But machining was only a very small part of it.
Problem solving and lateral thinking is more in my line, plus many years on the tools.

But I never give up learning, if a young sprog comes along and tells me or shows me something I have never come across before, then I will take notice of him/her, just as much as if it was a very experienced person. We all have something to offer.

The problem now is remembering everything, and getting it all passed over before it is all forgotten.

We need to preserve our heritage and skills, before we all turn into a country of shopkeepers, accountants and lawyers.


Bernd,
I did not need to have it any more accurate than a few thou, due to the fact the jib strip face doesn't go all the way back to the main casting body. I just needed a machined area for the narrower jib strip to run on.

When I moved the casting from one end of the table to the other, the cutter was moved out of the way in the Y axis. The casting was then put to the other end of the table, lightly clamped down, and then tapped by hand, so that when eyeballed along one of the machined side edges of the casting, the edge was aligned with one of the edges of the t-nut slots. By aligning by eye over a long length like this, you can usually get to within a few thou of being parallel to the table. But it doesn't work if you are cross eyed. It is better if you can do it with just one eye, I normally take out my glass one, but you could just close one of yours.

The clamps were then tightened up and the cutter moved back into position for carrying on with the cut.

C-O-C attached to describe by piccy. Once you do it you will wonder what all the fuss was about.

Someone also mentioned about this in a post the other day, but can't for the life of me remember who. It might have been Rog.


Bogs