Studer RHU 450 from the 1960s

[ole.steen]

Bruce!

I have just the other day bought a Studer RM-250 for a song in a reasonably complete but sorry state. I have yet to pick it up, as the snow prevents driving with heavily loaded trailers around here. I suspect the surplus hubs you have might fit this machine, I'll let you know in 3 weeks time or so, if you still have them for trade or sale..

Ole

 

[ballen]

Hi Ole,

I'll let you know in 3 weeks time or so, if you still have them for trade or sale.

I do have the hubs, and would be particularly interested in trading them for accessories for my RHU-450. So please get in touch after you have your machine. I suggest you send me an email, which you can do from my PM page.

PS: you will find some interesting information about the RM-250 here: Studer Grinding Machines - Anglo-Swiss Tools

Cheers,

 

[Richard King]

Bruce I saw you looking for a felt filter a few days ago. Not sure where I read it. I see on Amazon you can buy filter material. Also when felt was more popular when I way yonger we would buy what was called hard while felt but it was 1/2 think. I also know you can buy felt at craft store but I suspect the fibers are to coarse. The wool shirt suggestion ...umm..well.

I was thinking can you contact Studer and buy the correct one from them or get their recommended cloth. Hate to see you ruin a spindle bearing if it doesn't work correctly.
Amazon.com: Polyester Felt Filter Media Fabric Sheets - Cut your own Filters: Industrial & Scientific

 

[ballen]

Hi Richard,

Bruce I saw you looking for a felt filter a few days ago. I was thinking can you contact Studer and buy the correct one from them or get their recommended cloth. Hate to see you ruin a spindle bearing if it doesn't work correctly.

Glad you are still following my saga. I'm very happy with the ways, and they are behaving as desired, no sticking or other problems.

Studer answers my inquiries with the polite German equivalent of "sorry, we have no information or parts for that ancient product."

I found some filter material in a strange place. I buy vacuum cleaner bags for home in boxes of 20. In addition to the 20 bags, there is a piece of "filter felt" that goes in between the bag and the motor/fan air input, as well as a HEPA filter that goes at the motor/fan air output. The filter felt looked just right, not too dense but not too open, correct thickness, and a white color that will show up particles nicely. So I used a bit of that. I'll keep an eye on it, and change it if something better turns up.

I've measured the axial play (100 microns = 0.004") of the wheel spindle bearing. It's twice as large as it should be. So this weekend I will adjust it to the correct value. The instructions are very clear about the procedure, and it looks straightforward. I'll test it without a grinding wheel and monitor the temperature. Any suggestions or things to watch out for?

PS: the hydraulic pressure was lower (6.5 bar) than the manual suggested (7 bar). So I increased the pressure at the regulator to 7 bar. Bad idea!! Within about an hour I noticed that the oil had gotten warmer and less viscous. (I saw this first through the tell-tale oil eye that I installed to monitor the way oil.) After some googling I ran the regulator down to 6 bar, and that fixed it. Apparently if you set the pressure too high, then the pressure relief in the pump opens all the time, and the pump circulates oil back to the sump directly. This is not good: you want excess oil to go out the pressure regulator, after which it passes through an oil cooler, which increases the viscosity by cooling it. So I learned that it is a Bad Idea to set the pressure regulator too high. Fortunately I caught this mistake right away.

 

[ballen]

I pulled off the wheel spindle bearing cover to have a look inside. It's very nice design, and looks pristine. Here is "the big picture", drive pulley to the left, wheel taper to the right:

This is a closeup of the inside. The small spur gear drives an oil pump. The spur gear itself is driven by the short section of "worm gear" on the spindle. The oil pump pulls in oil from the bottom left copper tube in the photo. This comes from a rear compartment. The pump pushes the oil up the copper tube on the bottom right of the photo. The T-junction carries oil to a filter (under the black hex-head cap in the previous photo) where it goes into the main bronze bearing. Additional oil goes around the tube on the top of the photo, which is sealed shut at the left end, but has "weep holes" along it that drip onto the left side bronze bearing.

I spun the spindle shaft with an electric drill to verify the oil delivery.

Here is another photo of the same, where you can see the oil source on the bottom right in this picture:

Last but not least, here is a closeup of the base of the grinding wheel taper. Note the small hole in the bottom, where oil can run back into the wheel head sump. I wonder if a felt ring is missing here...

For the record, here is the procedure to adjust the spindle, where L is the nut closest to the wheel and R is the nut closest to the pulley. Each nut is locked with two hex-head setscrews.

Wheel --- L --- R --- Pulley

(0) Remove grinding wheel, open top
(1) Loosen lock on R
(2) Loosen R
(3) Loosen lock on L
(4) Tighten L until spindle no longer rotates
(5) Put dial indicator on left hand spindle end.
(6) Loosen L and tighten R until left hand spindle has moved 50 microns
(7) Fix L in this position. Be sure R is snug.
(8) Loosen R by 12mm on the circumferance and fix in place
(9) Do a test drive without grinding wheel for 30-60 min
(10) close top, replace wheel

It seems clear to me that the spindle has too much play, because with the wheel and belt remove, I can spin the spindle easily (very little friction). From what I have read, that means "too loose".

I won't do any adjustments until the weekend, but now I have a clear mental picture of what needs to be done, so I can think it through carefully first.

 

[Richard King]

It appears someone has tried to adjust the spindle bearings. One looks like it was tightened and one loosened if they are RHT. The spanner holes look swedged. I highly doubt the factory did that. Another thing is when loosening the set screws that no doubt have brass/bronze threaded shoes under them. There is a special way to loosen them.Loose the set screw about 1/8 to 1/4 turn, then take a blunt nose punch the fits inside the socket head and tap it with a light blow with a hammer. That will release the shoe so it will loosen easier. Another tip is to spin the spindle 360 degree's and use a cold roll steel punch and lightly tap the circumference of the OD of the nut, this helps the treads loosen too. Smart move on the filter. I like the oil filter idea. Be sure to follow the directions on tightening the drive belt/belt on the spindle. I love this thread! Rich

PS: I doubt there was felt in that hole as the oil drains fast and if it is plugged the oil would run into the coolant.It has a slinger and I suspect the wheel hub has one too flinging the coolant out toward the wheel.

It that an optical illusion on the lube pump gear. It looks like 2 of the teeth are bent about 7 Oh-clock on 2nd pic.

 

[ballen]

Richard, as always, thanks for your comments and tips. You are very perceptive.

I thought the same thing about the spanner holes. But then I rotated the spindle and all of the spanner holes look like this: slightly raised around the holes. (By the way, I did not know the word "swedge". I just looked it up in the dictionary!) The metal around the holes for the set screws is raised in the same way. Furthermore, these parts are blued and the bluing is undisturbed around the holes. And there are no burrs or scrape marks. So it just doesn't look as if Bubba has been in there. Can you think of a manufacturing process for these nuts that would leave those "swedge marks"?

You can't see it in these photos, but the number 7 is scribed onto each nut. One nut also has a reference line scribed onto it. I'll post some photos, perhaps that will provide some additional clues. Before I do anything intrusive, I'll take some pictures and notes to record the current positions of the nuts on the spindle, so I can easily compare before and after adjustment.

Thanks for the tips about loosening the shoes under the set screws and the nuts themselves. I didn't know this.

The little gear is fine. I don't know why a couple of teeth are blackened, there should not be any grease in here.

I have been through the Studer manual both in the English and German versions. There is NOTHING about how to tension the drive belt. This is a flat rubber belt, about 2mm (1/16") thick and about 40mm (1 1/2") wide. What do you suggest? (According to the drawing, that end of the spindle is supported with an NN3008 cylindrical roller bearing. Radial stiffness is 890N per micron. So a force of 90kg = 200 lbs radially will compress the bearing by 1 micron = 40 millionths of an inch).

I wasn't thinking about felt IN the hole, but instead an annular ring of felt in the outer groove. I'm not so worried about oil in the coolant as I am about coolant and grit getting into the spindle oil via that hole. But the hub does have what looks like a thread on the ID of the section that fits into the region around that hole. That must be the slinger, intended to carry coolant away from that hole.

I'm glad you like this thread. For me it's very important, because in this project, knowledge is everything. By being patient and asking questions, I've benefited from your expertise and that of others here. That's the main reason that I post pictures and wait a few days before I do something new.

Thanks again!

 

[ballen]

I adjusted the wheel spindle bearing. In the end it was easy, if I do this again it will take half-an-hour. But the first time it required some on-the-job learning.

Initially, I followed the instructions to the letter, but after I was done, when I rotated the spindle by hand it felt tighter in some orientations and looser in others. And when I measured the axial free play, it was much less than the intended 50 microns (0.002").

It turned out that the issue was the locking screws for the two nuts. When tightened, these locking screws shift the positions of the nuts by a small amount. It's not much, but enough to reduce or even eliminate the axial play and clearance. Once I realised this, the adjustment went more easily.

The spindle/bearing are not completely symmetric under rotation. I don't know if this is normal, or the result of a abuse or damage in the past. I now have it set so that the axial play is between 50 and 60 microns, depending upon the orientation of the shaft. (Previously it was around 110 microns. The manual calls for 50 microns.)

Before I made any adjustments, I marked the positions of the two nuts for comparison. After the adjustments, both had moved on their circumference by about 8mm. These adjusting nuts are about 60 mm in diameter, so have a circumference of about 190mm. I think they are a 1.5mm thread. So the amount that I moved the nuts was about 8/190th of 1.5mm, which is about 60 microns. This is completely consistent with the before/after axial clearance.


After adjusting the spindle, I ran it (without the wheel) for an hour without any issues. It is smooth and quiet, and the temperature rise is about 10C/20F.

One difference that is significant: the spindle oil tell-tale now shows an oil level almost halfway up (when the spindle is running):

Before I adjusted the spindle bearing, there was nothing visible in this window, even though spindle oil was flowing. That's because with the increased clearance, the oil flowed through the bearing so quickly that none of it "backed up" for the tell-tale window.

This weekend I'll do some more grinding, and see if having the correct spindle bearing clearance makes a difference in the finish.

Richard, can you give me some advice about the correct tension for the drive belt? It is 1mm x 35mm x 940mm. I can easily twist it 45 degrees in the middle, 90 degrees with some effort.

Cheers,
Bruce

 

[Richard King]

When I said it in the thread I was thinking roughly 1/8 deflection each way in the center of the pulleys. I have just got an education on belt deflection. I figured I should know, so I just spent an hour researching it. I discovered things like span length or distance from center of one pulley to the other and deflection force, etc.
It seems the rule of thumb on a V or flat belt is 1/64" of deflection for every 1" span distance. saw one diagram where they lay a straight edge on top of the belt and use a ruler and in the center of the span press down on the belt to get the deflection.

Before I was thinking it had a bronze bushing on each side and if you got it to tight it might burn the bearing ad score it. Now you said it is a ball bearing then the tension is probably not as important. Also I would start out using the 1/64 method and with the wheel mounted run it under load for about 1 hour and shut it off and then start it up again and see if it slips when it's hot. I am thinking you might want to ask "Carbide Bob" as he runs a grind shop and many grinders like Heald use flat belts. I also found this book that appears to be in German that is about flat belts. Dubbel: Taschenbuch fur den Maschinenbau - Google Books Rich

 

[ballen]

Hi Richard,

It seems the rule of thumb on a V or flat belt is 1/64" of deflection for every 1" span distance.

While you were researching this, so was I. I found this document about the 1 x 35 x 940mm flat belts:

https://www.bearingsrus.co.uk/pdf_downloads/flatbelt.pdf

It specifies a power rating for a particular belt width and pulley size, with a static tension of 12kg per cm of belt width. In this case since the belt is 3.5cm wide, it should be under a tension of 42 kg = 92 lbs. Since the belt comes into and leaves each pulley, that means that to get this tension, I would need to pull the motor with a force of 84kg = 184 lbs, then tighten the belt. It seems high, but then....

Before I was thinking it had a bronze bushing on each side and if you got it to tight it might burn the bearing ad score it. Now you said it is a ball bearing then the tension is probably not as important.

Here is a snapshot of the spindle drawing:

The bearing is an NN3008 bearing. It's not a ball bearing, it's a 2-row cylinder bearing. It's rated for a dynamic radial load of 43kN = 4500 kg and the radial stiffness is 890N/micron. So a force of 84kg = 820 N will deflect it a bit less than a micron!

Given that the spindle is adjusted for a clearance of 5 microns at the wheel side, a 1 micron deflection at the pulley end should not be problematic.

Bottom line: unless you spend your time doing one-arm pushups, or use a pry bar for tensioning, it would be hard to overtension the belt. That's probably why the manual doesn't talk about it!

I also found this book that appears to be in German that is about flat belts.

I'll have a look at that tomorrow. I'll also set up a scale and tension the belt to something a bit less than half the value above, just to play it safe.

I'm done roughing out my test bar on the lathe (drawbar stub, short MT5 taper, extraction nut, 32mm x 370mm straight). I still need to decide what thread to put on the drawbar end, I left a 20mm stub there. Hopefully I'll have time this weekend to grind it. I'm very excited about being able to use gage blocks to hit the MT5 taper "on the nose".

PS: the test bar is to help me with headstock and tailstock alignment. Remember that's what started this thread? I am slowly working my way back to it, just with some detours along the way.

Cheers, Bruce

 

[Richard King]

Heck I re-read the thread and found the manuals...Studer RHU45 manual English.pdf - Google Drive

All the answers are in there it seems. One says the belt tension us governed by springs...and it shows all the grinding info. I did see they explain how to set the machine on a steel plate and leveling instructions. I would say until you get the machine on the ground it is futile trying to get a good finish. Rich

 

[ballen]

Hi Rich,

All the answers are in there it seems. One says the belt tension us governed by springs.

Could you please tell me what page or section you found that in? I've searched the same manual and not found any reference to the belt tension. And as far as I can tell, there are no springs related to that belt.

I did some grinding on the short MT5 test bar today. The finish is getting better:

(The machine is still on a pallet, but it will come down by the end of this month.)

This grinding took much longer than it should have because I keep making mistakes.

- First off, I forgot that I had removed and replaced the wheel when adjusting the spindle bearings, so forgot to dress the wheel again. The finish was awful.

- Put too much pressure on the tailstock spring, galled center hole, bad finish and off-center

- Moved the table the wrong way to take out taper, and made it worse!

- Found that my test bar is too long (500mm overall) to allow use of the tailstock-mounted dresser.

- Infed to the bar, and couldn't figure out why I wasn't hitting it. Then realised that I had forgotten to switch on the headstock. Had to remove about 1mm (0.040") of diameter to clean off the resulting scar on the backside of the bar.

- Started getting a terrible finish and rubbing because the wheel had gotten clogged from removing all that material

- Forgot to move the coolant nozzle after dressing the wheel, see 'BAD FINISH' above.

Fortunately I have not ruined the bar, although the straight part will be about 31mm in diameter, not 32 as planned.

I need to grind the taper part further because I need to go right up to the extraction thread. I tried it with a full-width wheel but the corner had broken down. So I need to dress the wheel so that only the last 3mm (1/8") is cutting and then try and blend that.

 

[sfriedberg]

ballen, I have had days like that myself. The bright side is that you probably won't make most of those mistakes again.

 

[Richard King]

Bruce running a cylindrical grinder is like driving a car. It takes practice and care. I can help you fix it but your GRIT has made this happen. WE (on PracticalMachinist.com) can help and make suggestions, but YOU are the force behind this marvelous thread! Thank You!

In many machines they have a counter weight that pulls the wheel head backward so it takes the backlash out of the nut and so the wheel can't pull forward and you have immediate response to the inward feed. Others have you lower the back of the machine or out of level to do the same thing and let gravity do the job. I read that about the springs in the first machine on your list. It was a lapper I think. I did not find that in the bigger machine link. Ballen I am so Glad Charles made this a Sticky as this information will help people with Studers till Kingdom Come. Be sure to put your real name on the here someplace so people will thank you. :-) Rich

PS: Thank You Bruce - This is the kind of thread Practical Machinist deserves not some of what we have seen on here lately. The way I read the rules when I signed up "This is a Forum for professionals and for professional machines". Thanks to Don ( Milicron) also!!

 

[ballen]

Richard, Sfriedberg,

Thanks for the encouraging words. The analogy with driving a car is a good one. I think it might also be similar to the kinds of mistakes one makes when first learning to use a lathe, thinking out the workholding, order of cuts, and developing a feel. Anyway, mistakes are how one learns, and I'm sure I'll make plenty more

Rather than doing any more grinding, I spent some time measuring the bar. One of the center holes was galled and had shifted 30 microns (0.0012") off center. I was able to clean it up and move it back to within a few microns of center by putting a 60-degree burr into a lathe chuck and a center into the tailstock and then applying pressure in the right direction. (I've ordered a couple of center laps but they won't arrive until the end of the month.)

I eventually figured out what went wrong. The problem was that my improvised 'drive dog' was pulling the bar to one side. So I made a better one that does not exert any forces other than rotational ones. The starting point was a piece of 15mm (5/8") thick aluminium.

The drive pin is a 3mm (1/8") steel pin pressed into the aluminium. The hole for the screw is 6mm (1/4"). This will allow me to grind off the end of the bar by about 10mm (3/8").

I'll make a corresponding balance piece for the opposite side of the drive plate, and then see if I can get the test bar straight and concentric to a micron.

Richard, there is a fair amount of backlash in the cross feed of my machine, but it's not a problem, I'm accustomed to taking it up in the approach. The next time I have the wheel head off, I can adjust the cross feed nut to take up the free play. And eventually I'll put some glass scales and a DRO on the machine. But that's for the future, first I need to learn to use it.

I'll come back here once I have the test bar finished, probably next week.

 

[ballen]

Well it took a while to finish the test bar! I have been very busy with work the past months and not had much time to spend on the Studer. But I have made some progress and am getting better with it.

First, I think I understood what might have caused the wear/galling along the long ways in the first place. I think part of the problem is that the hydraulic/bedway oil got overheated and lost some of its lubricating ability. Why? It turns out that early versions of the Studer RHU-450 were built with no oil cooler. Later versions of the machine had an oil cooler but no forced air circulation through that oil cooler. Even later versions had an oil cooler AND a blower fan (mounted on the back of the hydraulic pump motor) to circulate air through that cooler. So I suspect that overheating hydraulic/bedway oil was a chronic problem with these machines, but that Studer might have only realised this after the machines had been in the field for some years and showed signs of excessive bed wear. Note that this is purely speculation!

My machine is a model with an oil cooler but without a blower fan. When I left it running for a number of hours, the oil got hot enough that the viscosity changed significantly. So my solution was to add a thermostatically controlled blower fan to the oil cooler. I used a centrifigual blower because they are quiet and move a large air volume. This is mounted in a folded aluminium box on the back of the oil cooler, which pulls cool air through a "cold" passage in the bottom of the oil cooler.

The air inlet is on the far side, so not visible in the photo below. The rectangular opening that you see below is the air outlet, which blasts the cold air upwards, behind the oil cooler.

This cold air is blown in the upwards direction into a plastic shroud which redirects the cold air out of the "hot" part of the oil cooler and back to the "outside world".

From the outside the addition of a blower fan does not change the appearance, but it moves a lot of air over the oil cooler.

To control the blower fan I used a standard W1209 programmable thermostat. The temperature sensor/probe is located on the inlet of the oil filter, and the thermostat is set to maintain a hydraulic oil temperature of 30 Celsius = 86 Farenheit. I installed the thermostat in the place previously occupied by an (unused) accessory power connector. This also lets me monitor the oild temperature when the machine is running.

The second modification is the addition of an oil filter on the pressure valve return line, before the oil cooler. I just didn't like the fact that there was nothing in the system to polish small particles from the oil. I used a Wix 51413 spin-on hydraulic filter, mounted in an accessible location near the top of the machine. This is a 11 micron microglass filter rated for 120 liters/minute with a 30 bar burst pressure. I deliberately used a filter without a bypass value and connected it with a plastic hose that will split if the pressure ever gets above a few bar.

Other improvements for making the test bar include this swing-back dresser from one of the other members here. My earlier attempt at making the test bar taper failed because I had not realised that a strip along the left-hand end of the grinding wheel had broken down. This dresser makes it easy to clean up the wheel if needed without losing any of the settings/geometry.

I also picked up a pair of nice snap gauges on Ebay. This one is a 1-2" Federal Testmaster which makes it very easy to measure and eliminate taper.

So here is the finally-completed part: a test bar with a (short) MT5 taper and a 400mm=16" cylinder. The bar is round and straight to about 2 microns (slightly less than 0.0001". It fits the taper perfectly (which you can tell from the feel but which I also checked via bluing).

I still need to cut a drawbar thread onto the 20mm stub at the right end. I'm going to use this test bar to help me get the workhead and tailstock properly aligned.

 

[ballen]

I started this thread in part because the geometry of the machine is not correct. The tailstock is higher than the work spindle, and the work spindle is closer to the front of the table than the tailstock. In the course of investigation, the need for new oil pockets in the ways came up, and that became a priority.

Now that the oil pockets and oil system are sorted out, I am back to fixing the geometry. First I followed Richard's suggestion of seeing what shims would be needed to make everything right. It needed:

- tailstock 0.002" = 50 microns shim towards the front of the table

- workhead lifted 0.004" = 100 microns on the right side and 0.005" = 125 microns on the left side.

My plan was to first scrape the workhead to bring it forward 0.002" and to tilt it down on the right by 0.001", and then to scrape in the tailstock to match. But as I was preparing for this, I then found the real cause of the misalignment.

I had removed the workhead, disassembled, cleaned and deburred the mount, and then checked it on a surface plate.

I had expected the test bar to point upwards as it had on the machine, but instead it pointed slightly *downwards*, about 30 microns = 0.0012" in 300mm = 12".

This pointed a finger at the table as the reason for the misalignment.

Then I measured the table, indicating it as it slid by on the machine. BINGO! It was level in the middle (orange section labeled level) but dropped down about 30 microns = 0.0012" on the left back and 70 microns = 0.003" on the left front. This makes the table tilt up and to the right, making the workhead also tilt up and to the right, resulting in the test bar being too high at the tailstock. Here is a picture showing those measurements (but after removing the swivel table)

Now what was responsible for the swivel table drooping down? I feared that it was bedway wear, but fortunately that was not the case. I first pulled off the swivel table and then indicated the fixed table below. Here is the fixed table:

On the left, as shown in the photo above, it is 5 microns = 0.0002" low in the front, and 12 microns = 0.0005" high in the back. But that is not enough to explain what I was seeing earlier.

Finally I investigated the swivel table. (My surface plate is not big enough to hold the entire swivel table, so this took a while.) It turns out that the TOP of the swivel table is flat to within a few microns, but the BOTTOM is not. When the bottom of the swivel table was ground, it appears that the area under the workhead got ground 130 microns = 0.005" too thin! So when the swivel table is clamped down, this pulls the left side of the swivel table down, making the workhead spindle point up and to the right.

I'm going to see if I can find a local shop that can clamp the swivel table upside down (as shown in the photo above) and regrind the bottom. They'll need to take about 0.005" = 130mm off to clean it up.

I wonder how it got like this. I suspect that someone rebuilt or reconditioned the machine and screwed this up. I can't imagine that it left the factory like that.

Cheers,
Bruce

PS: since only one pad on the swivel table is really messed up, an alternative might be to use a steel-filled adjustment material like DWH 310 fluid to "add back" the missing material. If I can find a 1-meter surface plate I could use that as a master for molding.

 

[dian]

check on the minimum thicknes of the epoxy filler. you can mix it yourself, btw.

 

[Richard King]

You would be better to find a rebuilder or someone with a bigger surface plate then the swivel plate so they or you can scrape one side of the plate before you grind it. Scraped for contact not PPI so you can hit the opposite side of plate area you scrape when on the surface plate and hear a thud or solid noise everywhere you hit.

If not shimming, a warped plate to grind it straight won't haopen. Once the one side is ground to clean up, flip it over and grind the scaped side. Also have them grind the positive side the stocks align to, Be sure to measure before so you know. As you will need to lower the wheelhead so its axis is close to the HS & TS. You can look at Studer spec sheet or George Sleshinger book Testing the Machine Machine Tools that can be found in Scibbs dot com. . I do not like the long test bars. Did you check lift on them? Seems 1/2 the length would be better. Test the Work Head bearings? I cant read the orange on the table top, use black marker please. The table top should be scraped 0 0 frt to back left , middle, and right side or .0002" high Wheelhead side when down. I have pics of one i did in old laptop back home. Im 2 days drive from home now.

The pics are from the last Studer I scraped at Minnisota Grinding in 2015. RICH

Pic's are on a Myford and Studer I scraped. 3 rd pic is how I scraped and measured the table top of Studer. The 2nd pic is lining up the HS & TS with 2 test bars. 4 th and 5th are just some other pic's. They were in the PM folder, luckily.

 

[ballen]

Hi Rich,

Thanks for checking in, especially from on the road! Having you here gives me the ability to fix this, which I could not manage on my own.

You would be better to find a rebuilder or someone with a bigger surface plate then the swivel plate so they or you can scrape one side of the plate before you grind it. Scraped for contact not PPI so you can hit the opposite side of plate area you scrape when on the surface plate and hear a thud or solid noise everywhere you hit.

Yeah, that makes sense. I'll see if I can find a 1 meter plate near me.

If not shimming, a warped plate to grind it straight won't haopen. Once the one side is ground to clean up, flip it over and grind the scraped side. Also have them grind the positive side the stocks align to.

You mean the front edge of the swivel table, correct? I'm confident that it is straight because if I put a dial indicator on it and clock the swivel table straight, this front edge shows maybe one micron of variation over the entire length as the table travels by. One micron is 0.00004". I'm actually inclined to leave that front surface alone, because it's pretty damn good already. Unless the grinder is really good it will make it worse!

As you will need to lower the wheelhead so its axis is close to the HS & TS. You can look at Studer spec sheet or George Sleshinger book Testing the Machine Machine Tools that can be found in Scibbs dot com.

Fortunately this is less demanding than many of the standards for cylindrical grinders. Here is the spec reproduced from a Studer spec sheet:

It calls for the wheelhead axis to be within +-100 microns height of the workhead axis. So if I get lucky it will still be OK. Otherwise I can grind one of the mounting plates underneath the wheelhead to lower that if needed. I think those are small enough to fit on my surface grinder.

I do not like the long test bars. Did you check lift on them?

That's a good idea. I calculated that they should droop 5 microns over the entire length. Can I measure this by pushing up on the end with approximately half the weight of the straight part? Is that what "checking the lift" means?

Seems 1/2 the length would be better.

Yeah, eventually I will make a shorter one, or a hollow one. Its fun to grind tapers on the machine. What's a good length?

Test the Work Head bearings?

Yeah. Those are (barely!) within the Studer spec. 1 micron = 0.00004" of runout at the nose, about 4 microns = 0.00016" at 150mm = 6" from the nose.

I cant read the orange on the table top, use black marker please.

Sorry about that. The numbers that I wrote on the table top were from measuring it moving by a fixed indicator, BEFORE I removed it from the fixed table underneath. The point is that it was twisted by being clamped down. Once I got it onto the bench I tried rocking/swivel tests along it with my (smaller) surface plate. As far as I can see, the swivel table top IS flat and not twisted. But I will see if I can find a big surface plate and check it better.

3 rd pic is how I scraped and measured the table top of Studer.

Rich, how did you print the bottom of the swivel table to scrape it? Did you print it from the fixed table underneath? Probably I should try that, just to see what the print looks like.

Cheers,
Bruce

PS: any idea how the bottom of the swivel table could have gotten messed up like this? Just to be sure that I have found the real problem, I think that I will put the swivel table back on with a 125 micron = 0.005" shim under the front left corner and a 75 micron = 0.003" shim under the middle of the left side, just to PROVE that this is the source of the geometry problems. It will only take an hour and will give me some further confidence that I am not barking up the wrong tree.