SAG12 Transmission Teardown

My lathe was slipping in all its forward speeds, and I finally got the time to tear into it. Since there seems to be little info out there about what I was in for, I decided to document as well as I can manage what I come across, so that others can take the journey with me and grubby their hands in a virtual fashion.
I've only begun at this point, but there is enough to post. I've put a link on my site at gizmowizard.com.
I've found some wasted parts, and a burned up forward clutch coil. I'm shipping the coil to Larry Norman today, and in the coming weeks plan to strip the rest to make sure I've found all the damage and clean everything up for reassembly.
Stay tuned for more!

Gizmo,

Well done! I am very glad you are going to this effort to record your rebuild, it is the one part of my Sag 12 that worries me a little, though no problems so far! (errr..well sometimes when you flick it into reverse it takes its time )

I have never seen a manual that describes any "how to", just the parts book, so you are doing us a good service! I wonder if there ever was a service manual for these lathes?

re. the shims in the clutches. I wonder if the shims are required to obtain an airgap when the clutch is not magnetised? (I need to study your photos more).I am only familiar with the single plate type, which run a 0.2mm airgap when the magnet is 'off'.

I know plastic shims are sometimes supplied with the single plate clutches we used, they are just another material used for shims, not meant as a wear surface or anything.

Best wishes with the rebuild.

If I can offer one piece of advise (which you may well know) cleanliness is the most important thing, aside from getting all the parts in good order. It isn't that difficult either.

The system I have worked out for myself is to pre clean, inspect, stone, machine, renew everything before assembly, so at assembly time you are only working with clean bench, parts, tools and hands.

I would be washing all the parts intially for inspection. At this time you want to do all your stoning etc, feel for dings on the shafts, plates etc - don't be stoning anything once it is clean!

Once you are happy with the parts, wash them again in fresh cleaner, blow them off, putting the parts in zip lock bags (or similar) until assembly time. Do this so everything is ready, including fasteners, gaskets etc, then clean your tools too, plus of course your hands.

Don't put clean parts down on a bench - have a stack of newspaper on hand, so you can keep putting down clean paper to lay clean parts on.

And have paper towels or clean rags, don't even think about using the grimy ones you dismantled with.

I would scrub the housing with a water soluble degreaser inside and out (use brushes, bottle brushes etc), checking/stoning all the gasket surfaces, then use a water hose to wash it out.
It should be absolutely clean.

My method is to then spray with WD40, then blow out with air, including all the tapped holes etc. Stick a large rubbish bag or similar over it when you aren't working on it. (It looks surprisingly sludgy inside!)

Have an oil can or squeeze bottle with perfectly clean hydraulic oil ready for assembly time.

Dirt, grit etc will kill a piece of machinery like this, and yet it is often neglected. In fact I know people who are proud of their rough and ready approach, they think it is part of their skill! However, fine machinery and dirt won't last the distance....

Thanks Peter
I contemplated for a bit whether or not I should wait until all was clean and spiffy before I took the photos, but decided that it was just another avenue for procrastination. I've rebuilt things in the past, planning to document the process, but found myself at the finish line with no photos. So this time I decided to have the camera on hand for the dissassembly as well as the reassembly, and post the photos as they are available. A grand vision would include the creation of a "how to" manual, perhaps in pdf format for download, but I can't commit to the time that would require at the moment. So right now all I have is photos of alarmingly filthy parts.
I always laugh at auto repair manuals with photos of the underside of cars, clearly taken from cars that haven't yet escaped the factory. Why are my cars so dirty?
Yes, it's surprisingly sludgey. I think the black may be partly burned oil residue from the forward clutch, which has been running hot for who knows how long. And some of the black is from wear on the steel parts too, I suppose.
At any rate, they will be clean as can be when it's back together, hopefully for the next forty years or so.
It did occur to me that the plastic shim had some purpose related to the magnetic design of the clutch. It is definitely in the flux path, so it may be there to lessen the load on the needle thrust bearing, as well as establish the axial clearance between the coil and hub bearing arrangement.
The only air gap I see is a radial clearance between the stationary coil and the rotating hub, visible in my fourth photo. The hub is built as a wheel, with a heavy rim and hub, separated by relatively thin spokes. My working theory at this point is that when the coil is engergized, the stack is drawn together by the flux bridging the radial gap between the rim and hub. One result of this design is that the thickness of the plates is not critical to their effectiveness, and another is that the radial gap between the hub and coil is fixed and not subject to wear.
I've no idea how the single disk clutches are put together, any more than I did the multi-disk units a week ago. I assume they are entirely different.

Nice work. I have the cover off my SA12 at the moment and need all the help I can get. I bought the lathe knowing that it has a couple of slipping clutches.

Where do you intend getting the new clutch plates. Are you having them laser cut or made some other way. What material should the be made from.

Terry

Gizmo,

You have raised an interesting question - how do these clutches work?

I wonder if you can energise one to test your theory?

I think you could be right.

I was thinking that the stationary coil worked across its face and pulled everything together axially - hence the need for the correct airgap between the heavy 'wheel' and the coil (enough so the parts don't touch when not magnetised, but as close as possible).

But working through the 'overhanging' rim of the coil carrier, onto the heavy 'wheel' would be much better. You can tell I don't understand magnetism.

-I wonder if you are noticing much difference between plate widths? Could you record what a 'good' plate width is, and how much variation you found?

I am especially interested in the reverse clutch. Everyone I know seems to use the reverse clutch to slow the spindle down, and I have never heard of any problems. It would be interesting to see if yours have suffered any. I don't do this anymore.

I wonder if you want to tee-in a pressure gauge to your lower oil pump? I have sometimes thought this would be worthwhile - to run a nylon tube up and mount a gauge where it is visible.

Graziano agents in NZ told me the pressure should be 3-5 ATM, which I suppose is 45-75 psi)

-One other thought - I think all the gearbox shafts are drilled almost full length, to supply oil to the bearings. These holes will need to be scrupulously cleaned, as will all the oil pipes and pump itself. There must be some stuff in there that you don't want pumped into those clutch needle bearings!!

This is a particular problem with mechanisms that have died and contaminated their oil - people forget to clean out oil coolers, pipes etc - and the whole problem starts over again.

Gizmo, not trying to tell you how to do the job, just in case its handy for anyone else in the future.

I've got everything apart now, bagged and tagged and inspected for damage. It looks like all I need, other than a lot of cleaning, is one thrust stack, a snap ring, and thrust washer. The thrust washer is the only thing I'll have to make, but it doesn't look too scary.
Larry Norman has rebuilt my fried forward clutch coil, and I should have it back within a few days. He's awesome, and a wealth of knowledge on all things SAG12.
I had anticipated having to replace clutch plates, and had planned to find a laser house to make them after making a dxf file for them. I'll still do the dxf, just because I can, but I'm no longer planning to replace any plates. Many of my plates are scored, because my trans was run dirty for a while, I suspect, but I plan to lap them smooth and put them back in. They don't seem to be worn in thickness to any significant degree. I think that the design of this machine relies on the viscosity of the oil to carry the torque between the plates. As the magnet pulls them together, the oil layer gets very thin very quickly, but if the oil is clean the plates shouldn't wear at all. Larry reports that he has customers with job-critical SAG 12s who drain their oil regularly and pump it through an automotive-type oil filter, since the lathe just has a screen for the job. That said, scored disks were not the cause of my slipping problem, the fried coil was.
My reverse clutch was working fine, dirt and all, but it is the one that has a wasted snap ring and thrust washer.
I'm still scratching my beard over what initiated the various modes of failure in my transmission. Did the coil go bad, get hot (plenty of evidence for that) causing other parts to fail? Or was it some other chain of events? I suppose I may never know for sure. Whatever the cause, I had dirt flowing in the oil, and dirt kills. And yes, I plan to take particular care cleaning out all of the oil passages. Larry emphasized this also.
A pressure gage would be a great idea, and I think I have the parts laying around to rig one, at least temporarily to get a read on things.
I've also worked out a nearly complete bearing interchange chart which I'll add to my site soon. It looks like the only one that may not be available anywhere is the roller thrust bearing within the clutch assembly itself. Mine is intact, so I'll resusitate it, as it appears I have no option anyway.
I've worked with a variety of magnetic assemblies, from simple reed switches to YIG-tuned microwave oscillator assemblies. I've found that you have to scrub simple magnetic attraction notions out of your head and replace them with flux-path based ones. A magnet generates a field, and it wants to form a loop. Whatever ferromagnetic material that will close the loop will be drawn onto the components that make up the loop and held there. It appears that the most ferromagnetically contiguous piece in the clutch stack assembly it the thick plate on top of the plate stack. When it carries the flux, it squeezes the stack, and will do so with a force relatively independent of the thickness of the plates.
One brilliant aspect of the SAG12 clutch is the fact that the coil is stationary, and yet the parts that they engage are rotating. Pulling that off is a neat trick, the likes of which would never happen on "Monster Garage".
More photos in a few more days..

Gizmo,

Re. the thrust bearings. I had a quick look in my Graziano parts book and they list 'INA' Bearings and part numbers.

There seem to be three different sizes used, and 3rd gear has a slightly different thrust washer at one end, but that is in the INA catalogue also.

I have an old 'INA' catalogue here, and they list all the thrust bearings, they are standard sizes.

I also checked the roller bearings, they are listed in the catalogue, but designated "special sizes". It seems to be the lengths that are special, not the diameters. There seem to be four different roller bearings (maybe more).

Have you tried INA? They are available here in NZ, so you should have them over your way!

The thrust bearing I'm referring to is inside the clutch assembly, and isn't shown on the Graziano parts list, or at least the one I have. It is the one shown in my photo titled "shim stack", is 42mm ID, just shy of 55 OD, and 3mm thick. My INA catalog isn't new, but it's newer than my lathe! If your parts/list and or INA catalog shows a number for this bearing, please let me know what it is!
All of the thrust bearings and needle rollers shown in the Graziano parts diagram (page 31 of mine) are apparently still available from INA.
Since the Graziano parts diagram doesn't show the clutch assembly level parts, I'll make a diagram to add to my page. Another item on my to-do list!

Gizmo,
Sorry, you are right - they don't show the clutch break down. The thrust bearings I was looking at are between the "clutch cone" and the "clutch".

My manual must be a little different from yours, though, as it is on page 20. There are 53 pages total.

Each "exploded" parts drawing, with part numbers, is a fold-out page in the manual, followed by a page with the part number and description, folllowed by another page showing the assembled view in cross section, once again with part numbers.

Here's a result of some reverse-engineering on the clutch assembly

I've done it all up in SolidWorks. It provides a nice way to "see inside" and reveals that the axial gap is determined by the thickness of the thrust stack. Perhaps the teflon washer is a shimming mechanism to set the gap, and/or the axial clearance of the assembly.
I still have to do an exploded view. That's next.
One note here- mine is apparently an "early" machine, I think it was made in 1966. The serisl number, over on the far right side of the ways, is SAG12=N853. Later machines, according to Larry, have ball bearings in the clutch assembly.
I have DXF files of both plates up and available for download on my site. Just click on the thumbnail of the plate, and the link will appear.

I've got a REV A version of a drawing to show exploded and section views of the clutch asembly on my http://www.gizmowizard.com page now, along with a partially annotated parts list for the whole transmission with bearing interchange info.
I've got the case cleaned up now, and now it's time to scare up some tidbits to put it back together.

Anyone with a Graziano Sag12 owes the Gizmowizard a vote of thanks. Keep up the good work. I now look daily to see if there is a new download.

Thanks Paul

Gizmo, I just got a box of Sag clutch parts, If you can measure the thrust bearing or washers you need I most likely have them and would be glad to send them to you. I just talked to Larry Norman today and he helped me figure out how to remove the spindle. He is pretty knowledgable, said he went to Italy and learned some things from the factory,didn't ask him how long ago that was.One thing of interest to Sag owners is he said that the headstock should run hot like almost too hot to touch to get the tolerance they claim by tightening the preload on the front bearing.Mine runs cool? Tryed to link to your website but was unavaliable. Thanks for sharing your project, I will try to get some pictures of the jig to remove the headstock. Jim

Got to your website Gismo, Great job Thanks Jim

My website has been iffy ever since I posted that big pdf file. I don't understand why that would impact anything, and it may be unrelated. At any rate I'm trying to figure out the cause of the intermittent outage. Keep trying!

Paul. I don't know if I am getting through on the private message thing but there are 3 sizes of thrust washers. I think the 54.7 od and42 id is the one you want but I see a couple of larger ones and smaller one that looks a little rough. Send a mailing address. Jim

It's back together and running!
I've got a new string of photos on the SAG12 page from my website at www.gizmowizard.com.
It now snaps to full speed in any direction, and I'm making chips again. Wheee!
Next project, please!
I made a significant discovery while cleaning up the oil pump, which explains with little doubt what caused my trans to fail.
The pump is a conventional vane type, driven off the end of the input shaft. As you look at the pump, it turns counterclockwise. The right side of the pump is the suction side, pulling oil up from the sump through the strainer. The left side of the impeller chamber is the pressure side, with a port that feeds the fittings leading to the countershaft and output shaft, as well as the drilling connected to the pressure switch. The pump chamber is closed by a round plate that screws on with three equally spaced screws.
The input shaft gets its oil directly from the impeller chamber, by way of a slot milled in the backside of this cover plate, and then through the hollow axis of the pump and directly into the shaft. The orientation of the slot that feeds the input shaft is critical, as it has to connect the core of the pump to the pressure side of the chamber.
Can you guess now how the cover of my lathe was intalled by the last nimrod that put it together? Yep, the slot connected the input shaft to the suction side of the pump. No wonder it ran hot! It's a wonder it survived at all....
I've confirmed all this with Larry Norman, who says that there should be an index mark on the cover and pump body to line up. Mine had no such markings, but it does now.
Many thanks to all who pushed me on through this project, especially Larry for the clutch coil rebuild, and Jim Moser for the tidbits made of 100% unobtainium.

Nice job Paul,and and great documentation. Looks simple when it is all back together, lots of little pieces in there. Havn't had time to exchange spindles yet, I'll get some pictures when I do. Thanks for the show and tell, Jim

Fantastic work Paul.

I have had the top of my gearbox for some time now but haven't had time to get to fix it due to working six days a week.

Hope to be able to get to it in the next five or six weeks. Will then have the task of getting new plates (and/or rewind).

Thanks again

Terry

Paul,

Well done - excellent job! And thanks very much for recording the operation for our benefit!! Easy to say, not so easy to do!

Interesting about the oil pump. I will be checking...

I like the dish washer photo

I wonder what you did in place of the missing spacer washer - teflon was it?