ABA FFK 350 Surface Grinder documentation

[rreng]

Hi

i've got an ABA surface grinder that i'm still missing documentation for. I was able to figure out basic functionality by myself (by taking it apart for re-painting it mostly), but when it comes to taking the grinding spindle apart, i'd prefer to have new bearings handy in order to swap those when i get around disassembling it anyways. I'm quite new to surface grinding (bought the grinder because it was dirt-cheap, and fixed it), but i experienced a difference in the grinding feel between a fairly cold and a pretty warmed up spindle. I tried both, and while cold the spindle grinds perfect, when warmed up it feels like the radial play of the spindle is becoming a little big. If let run without load for about 20 minutes it starts to make strange noises (which disappear under load) so i guess i've to deal with worn spindle bearings.

Maybe somebody here has the same machine and can provide me with some info?

The technical specs are pretty interesting... 350x150mm grinding area, hydraulic x travel actuating Y travel via a ratchet-drive in adjustable intervals, so it can basically surface an entire workpiece without much interaction all by itself.

As i'm waiting for the new bellows to be manufactured for the Y axis spindle, i thought i'd might figure out the rest of the machine.

Thanks for your efforts!!

Best regards, Ricardo

 

[Peter from Holland]

Hello ricardo

I gave you a drawing of the spindle already and because of work was not yet able to respond your further requist
It seems that you think you can buy new bearings and be done with it
But probbably you have plain bearings And probbably looking at the age of your machine they are gone
If you want to repair your spindle bearing assembly be aware you will have a steep learning curve
You first need to lapp your spindle Then the plain bearings are steel and have ID a tapered OD with 3 ridges on the OD The ID is bronze Probably electroplated So the old bearings have to be electroplated, machined to near size and then the whole assembly has to be finescrapped This is all very accurate labour that requiers at least some skills in those fields
What you can do
Make sure the housing is filled with the proper oil THIS IS VERY IMPORTANT
That oil is as thin as water (nI can look up the specs tomorrow)
Do not overfill it or it will come out of the bearings A bit under the middle of the eyeglass will do
The bearing has a worm wormwheel assembly to push it in the tapered bore of the housing to adjust play
The 3 ridges will give it a 3 lobed form
Adjust it till it has some drag Turn it on and watch it not getting hot
A good bearing will have less then 0.01mm endplay
I do not think yours can get that tight

Why I know all this
I just scrapped one that I bought 20 years ago with a bad spindle and now decided it is not worth the trouble to fix it

Peter

 

[rreng]

Hey Peter,

thank you for your reply! I went ahead and wrote this post before i sent you a message on the flanges - i didn't know that you might have some documentation on it at that time. Thank you very much for the drawing, as it helps me understand how the spindle bearings work, and that some adjustment can be made. I've found the adjustment screws, but still need some kind of how-to adjust them. There is a + and - painted with a permanent marker next to one of those adjusting screws, but i didn't experiment with those yet. I've read that pushing the spindle upwards by hand while measuring with an indicator to read out the movement is the way to measure on surface grinders. The bearings are well lubricated, though the oil isn't as thin as water as you said. I don't know if it's the right oil though. I've poured it into a clean bottle to check for dirt and measure how much oil is in there, it's about 1.3 to 1.5liters and the oil looked pretty good, so i filtered it and filled it into the machine again. I don't have oil coming out of the bearings yet, and the bearings don't feel so bad, it's just a change in surface finish that i'm experiencing between cold to warm - maybe the oil really is the wrong one (i'll swap it, once i find out which oil is the correct one), maybe the grinding wheel flange is just out of round a little. I don't have a wheel balancing jig yet, so i didn't feel like removing the wheel from the flange, nor was i able to check for balance. So it is possible that all i'm experiencing is just some harmonics from a fairly unbalanced grinding wheel once the oil gets warm enough to allow minor movements of the grinding spindle within its bearings.

The process of overhauling plain bearings is well known to me, and if i'd find them worn, i'd totally be in for it, BUT if they really are plain bearings, i'm pretty sure that i could get away with just adjusting them properly (for now). The machine was built in 1966, and has seen lots of use.... of course.

Do you might have pictures of the bearing assembly of the machine that you scrapped? I'd be curious to see it. I'll check the runout, but from what i've felt it's FAR below 1/100mm.

Thanks for all your help, i'll take some more measurements soon, and report back. From the feel of it i'm not sure in which direction i've to go yet. I guess the list is as follows:

1. check wheel for balance
2. check spindle for radial and axial play when a) cold b) hot
3. find out which oil is the correct one and fill that in
4. grind grind grind (hopefully)

 

[Peter from Holland]

I went to the scrap bin and then took some pictures


you see the spindle with the 2 extruding parts Those are the pumps that pump the oil through the bearing
At the front of the bearing the oil can return to the reservoir
picture 2 and 4 shows the housing with tapered ID for the plain bearing with the mecanism to adjust play on the bearing Worm and whormwheel with ID thread that grips the thread on the plain bearing

Third picture shows the tapered steel plain bearing with the 3 ridges and bronze plating inside
Those 3 ridges make 3 high spots in the bearing when adjusting This makes for more pumping action of the oil in the bearing

BTW the play in a bearing should be measured dry
With no oil on it Otherwise you measure the oilfilm

Peter

 

[rreng]

Hi Peter,

thank you, that clears things up a bit. I took the liberty to measure some stuff today. The spindle doesn't have any "runout", it runs super-smooth. However, i stopped the spindle, removed the grinding wheel flange and tested how far i could lift the spindle. I could lift it about 7-8/100mm. Thats not too bad for a plain bearing. Certainly not a "like new" condition, but neither worth overhauling already. Once i switch the spindle on it "jumps" to the middle of the "play" that i measured, thus builds up a good oil film as bearing surface and doesn't move with or without load. I've increased the oil level to about top of the eyeglass (took simple 10w30 engine oil which isn't best for this purpose, but works good enough for testing) and the noise i experienced when the spindle ran warm for a while without load disappeared completely.

From what i see the lack in surface quality that i'm experiencing most likely is from the rather unbalanced grinding wheel. I'll get a new one as this one got quite small already (about 150mm), and send it over to a friend for balancing (as i don't have a balancing jig YET). I'll report back on the outcome.

Thanks for your help again, i think i've got to come back on your offer of scanning the manual for me. I'd love to read about the bearing adjustment from the manual.

 

[Peter from Holland]

Worse than I thought
I cannot make it any nicer but 0.07mm endplay means the bearing is completly shot
The one I scrapped had less
A accurate plain bearing like on a grinding spindle has less as 0.01mm
It has to be so tight because grinding is a accurate proces The more play the more the spindle can wander
That tight you need to use very light oil otherwise the spindle gets too hot

Peter

 

[rreng]

I'm talking about radial play, while i think "endplay" means axial play. High rpm plain bearings need some space for the oil, though 7-8/100mm might be on the rather big end, it feels quite good though. I'll figure what to do next once i see the outcome of running a balanced grinding wheel instead of the unbalanced one i currently run.

 

[fxb]

Aba ff350