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Schaublin 135 cross slide has gone bananas

ValkmanFP4

Plastic
Joined
Mar 31, 2020
Hello fellow machinists,

I've encountered an issue with my Schaublin 135 lathe where the cross slide appears to be bowed/warped. The warp is approximately 0.08 mm high in the middle. This is measured on a surface table, not while on machine with the gib and nut installed. This is not due to wear as the cross slide rocks while upsidedown on a surface table. This warp is causing inaccuracies in my work, and I am seeking advice on the best approach to rectify this problem.

Could anyone share their experience or guidance on how to start fixing the issue? What should I aim to keep as reference surface? I have a scraper and access to a surface grinder.

Thank you in advance for your help and suggestions.
 
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Could you upload some pictures of your measurements and the setup? In general I guess it’s better to discuss this topic in the scraping/reconditioning forum. If it comes to that, I assume grinding and scraping is the way to go, but there are many many details to discuss.
 
Thanks for the responses.

Initially, I was pretty skeptical about taking "???"'s suggestion seriously, given we're talking about cast iron here. But curiosity got the better of me, and after a deep dive online, I stumbled upon methods used for straightening warped engine blocks. The idea of baking a part at 250 degrees Celsius for 6 hours felt like using a sledgehammer to crack a nut for my situation, so I leaned towards experimenting with applying force instead. I've attached couple images, first one with black numbers showing the measurements related to zero. The cross slide was on a surface table while doing the measurements. All values are positive with 10 micron resolution. Notice how it seems to be high around the nut. Luckily the slide is standing on its corners steadily and doesn't pivot on three points.

Initially, I pressed down right on the red cross, propping the slide at the far ends. The measurements improved. On the second go, aiming slightly off-center to balance out the chuck side's numbers. Ended up using a modest 2-3 metric tons of force. The slide did a bit of a dramatic bow, about 0.10 - 0.20 mm under the "straight" line, almost doubling the initial warp but flipped direction.

I'm more than happy with this for now. Earlier I was able to put a 0.05 mm feeler gauge under the slide, but now it's tight and doesn't even sound hollow when knocking with a hammer. I'm tempted to give it 'one more try', but I've got this sneaky feeling I might end up turning the slide into a high-end seesaw. I can later scrape the ways and grind the top if needed. But man, having a manual 50 ton hydraulic press is sweet when you want to use accurate numbers with high force. I played around with more and more displacement until I could see the indicator not returning to its initial value.

Hope this helps anyone in similar situation.
 

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Think you would want to do something to relieve any stress induced by the original bend and the subsequent straightening.
Some serious research seems called for here.
Further after the stress relief, for sure one would want to re- establish / verify the “ truth” of the geometry of the slide.
I find the “ bend” interesting, not what I would expect from a seasoned casting on a high end machine. Shouldn’t be any forces acting on that part to cause it to bend.

Cheers Ross
 
Seeing the effort needed to tweak this part, I'm convinced that regular use wouldn't bend it out of shape. There's no sign of any big knocks or damage on the machine either. Grinding it down to flatness would mean shaving off a lot, and who's to say it wouldn't just warp again due to material removal? Given its age, it's moved from being top-of-the-line to just a trusty old workhorse. While it might deserve a full check-up down the line, for now, we're keeping it running and getting the job done. Opting for a full stress-relieving heat treatment in a furnace right now would essentially necessitate a complete rebuild, which isn't where I want to get this into.

I plan to double-check the measurements later to make sure everything's still in line. Overthinking it just adds unnecessary stress.
 
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I have seen many times parts like that getting bowed due to stress caused by the casting itself. Over the years the stress relieves and the part bows.Now you pushed it back I think the internal stress is back again. Heat treatment does not completely the trick, time does the trick here . It's cast iron not steel. I expect the part to get bowed again over time.
I think scraping was the best option here. The real experts are in the recondition forum here.
 
Note: heat treatment is not the only process that can relieve part stress.
Selective peening on the under side surfaces , shot peening, thermal cycling, or vibration treatment are some processes that might be employed. I am sure there are others.
I agree that scraping is the best finishing process once the stress has been addressed.
Cheers Ross
 
Late to the party, but… I would have accepted the slide as it was without adding more unpredictable stress by a press and just rescaped it. Likely it would have been flat and stayed that way for some time. Now that it’s been pressed, who knows what the newly introduced stress will do.
 
I’m not sure if this is the case or not, but @Richard King explained that before scraping the bottom of a mill table, the upper side has to he ground in order to relief stress caused by work hardening, then the bottom can be scraped avoiding bowing (I hope I describe it correctly). Not sure if it has anything to do with this case, but introducing more internal stress does not seem the way to go. Again, the experts for this topic are in the machine reconditioning forum…
 
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The inability to directly measure internal stress in a workshop is a concern. Without concrete measurements, determining when stress is fully relieved is guesswork. Heat treatment stands out as a method offering some predictability in stress relief, contrasting with other techniques that seem more heavily influenced by unpredictable factors.

It appears the part had inherent stress from its manufacturing process, especially noticeable at its thinnest points. Given the part's non-uniform shape, any residual stress likely contributed to its deformation over time, considering it's been over 40 years since its manufacture. While it's uncertain if the stress was fully relieved initially, the pressing may have introduced additional stress, though its impact is likely minimal. The improvement is evident, and it's reasonable to assume this isn't the only component in the machine with residual stress. Overall, the situation has been positively addressed. If scraping or grinding is now done, it will require much less material removal. Should re-scraping become necessary in e.g. five years, it likely won't be the only maintenance task the machine will need.
 
I’m not sure if this is the case or not, but @Richard King explained that before scraping the bottom of a mill table, the upper side has to he ground in order to relief stress caused by work hardening, then the bottom can be scraped avoiding bowing (I hope I describe it correctly). Not sure if it has anything to do with this case, but introducing more internal stress does not seem the way to go. Again, the experts for this topic are in the machine reconditioning forum…
Tables with t-slots for workholding and vises can indeed deform the table when tightened, introducing stress.
 
Late to the party, but… I would have accepted the slide as it was without adding more unpredictable stress by a press and just rescaped it. Likely it would have been flat and stayed that way for some time. Now that it’s been pressed, who knows what the newly introduced stress will do.
Thanks for the input. In its original shape, it would've required grinding both the top and bottom, probably milling deeper dovetails, grinding the cross slide nut for fit (it's already very close to the cross slide bottom), making or buying a new gib and scrape everything into final fit ... probably only to notice that the saddle requires work, too.
 
You should messure the sliding surface independetly from the top
The top may be bowed hollow rough Whatever
That in itsself has no influenze on the performance
Bleu the bottem sliding surface and see how that is That is the important bit
Or put it on a surface table and see where and how much of feeler gauge you can stick between table and slide

peter
 
You should messure the sliding surface independetly from the top
The top may be bowed hollow rough Whatever
That in itsself has no influenze on the performance
Bleu the bottem sliding surface and see how that is That is the important bit
Or put it on a surface table and see where and how much of feeler gauge you can stick between table and slide

peter
Yes, that's true. But as said, I was able to verify the top measurements with the sliding surface ones .. A 0.05 mm feeler gauge was going under the cross slide very close to where it was 0.05 high measured from the top. I might do a bluing to see where the current contact is.. but based on how it rotates on the surface table, it's making contact in the four corners and somewhat showing what we're seeing in the measurements.
 








 
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