Fixing Darren's lathe

[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

[SPiN Racing]

Very very nice!

Quite impressive!

(Adds research on a side cutter to the list of "just might need it some day" tooling.)


Watching you measure this reminds me of how I have to measure a Rotor housing on a rotary.
Same basic thing I spose.
THe rotor housing is hourglass shaped (sorta) and it is around 3" thick on one variant of the engines.
The engine is assembled like a dagwood sandwich with long tension bolts.
Thing is.. the aluminum housings that are sandwitched between cast iron.. can compress over time.
Sooo They need measured all around the circumfrence, to make sure thy are within the factory race tolerances.  There can be no more than .0023" of variance between measure points.
Junk housing if its out of tolerence. Usually if out of tolerence the chrome liner is worn through on the inside.

[bogstandard]

Spin,

A mic and a DTI can become your super efficient eyes and fingers if used correctly. They can show you the most minute detail of a part that just cannot be detected by normal senses, and they very rarely make a mistake.

A side and face cutter is one of those tools that I use to get me out of a scrape now and again. But not essential.

There are other ways I could have used to obtain the same effect. A quickie knock up, upside down flycutter would achieve the same results. You could use a normal flycutter if you can run your machine in reverse.

It is called cat skinning. Many ways of doing the same job.

Bogs

[Darren]

John that is looking real good I have to say...

You did all that with a slitting saw  learn something new every day, thankfully. Hard bit is hanging on to all these new learnt titbits.

I've had that lathe for over two years, so hopefully the casting has settled somewhat in that time.
Is two years enough? And does breaking the skin cause further stress releases?

Anyways, every time you post further teasers of progress cast a ray of wonder and excitement. It will be interesting how my perception of the machine will alter after abusing using it again
 

[Bernd]

John,

That's kind of what I thought you had done, but wasn't sure.

The Grizzly has the same kind of bed as what your working on. I'm sure it has some of the same problems. I've had this lathe for almost ten years. I'm sure it's not up to speck.

I've got some interesting things I liked to try to do with this lathe, but that would be  .

Bernd

[bogstandard]

Darren,

It was a side and face cutter, slightly different to a normal slitting saw. A slitting saw cuts on the circumerence edge, a side and face is as it says. I used the side cutting bit to carry out the machining.

http://en.wikipedia.org/wiki/Milling_cutter

Without knowing what the casting has gone thru during it's life, it is difficult to say whether machining it will cause any changes. You can only hope and assume what will happen. Even some normal materials have wierd reactions when you take the outer skin off. Gauge plate is renowned for bending like a banana if you just machine one side.

I am hoping, by the time I have finished doing all sorts of bits and adjustments to this little treasure, it will act in a completely different way to what you are used to.

Bernd,

Just get your mic and go along the bed as I did initially, no need to strip it down, just in places you can get to. That will show you straight away whether you have the same sort of problems.

Even though these lathes are fairly cheap to buy, it looks like that with a little bit of work, they can be made to be worth their weight in gold.

Bogs