Good way to refit the "rotation locator pin" ?

This is the workhead base from a Studer RHU-450 cylindrical grinder that I am fixing up.



The round hole on the left-hand side is for a "locator pin" that is meant to index the workhead into the position where the rotation axis is parallel to the work table feed direction. After rescraping and realigning this is quite a bit offset from the correct location. So my question is, what's a good way to fix it?

The pin is 12mm (15/32") in diameter, case hardened and ground. At the end it tapers to 11mm (7/16") at a 1:20 ratio. I am not sure if the taper part is meant to be part of the location or just to help guide the pin into engagement.

One way to fix it would be to bore out the hole, glue in a cast iron plug with some loctite, then carefully locate the new hole, bore it out slightly undersize, then modify a 12mm reamer and pass it down. Or grind down an MT1 or Jarno 4 reamer (which have 1:20 taper ratios) and use that.

Another approach would be to bore out and roughen the hole, then turn the workhead+base assembly upside down, coat the locating pin with mold release, and fill the area around the locator pin with some steel-filled epoxy.

Is there a standard solution that works well?

Sounds like you want to screw up the pin location because you scraped the slide out of square. If the pin fits good now in the original location then I would assemble the work head with a test bar in spindle and with the index hole in the original location use the shim method we have discussed before to know how much you need to scrape off the opposite side. Doesn't the head have a scale so you can turn the head to different degree's stamped into it and the index hole is for setting the head at true parallel? And if you change the hole location the scale with not be aligned?

ballen --

I completely agree with Richard King, but I'll directly answer your question too: It's quite common today to "liquid shim" a hardened, precision-ground bushing into oversize holes in castings. If I recall correctly, both Diamant (the maker of Moglice and DWH compounds for the machine-tool makers) and SKC (one of Diamant's competitors) have published how-to-do-it papers on the subject . . . using their materials, of course. Both Diamant and SKC are German companies, I'm pretty sure.

I've done similar liquid-shim jobs using filled epoxies from a hardware or auto-supply store to pot-in-place commercial drill bushings. Unless one side of the joint is damaged and NEEDS repair, a potted-in-place bushing can be installed in either part; just choose the easier one. Release coat and damming materials are pretty easy to improvise.

John

Hi Richard,

I have the impression that the alignment hole is deformed but will take a good look at it and measure how far off it is with shims as you suggest. If the hole is just a little deformed then I have some TimeSaver lapping compound that I can use to lap it to a good fit.

Once the pin is a good fit then I can scrape the workhead so that it's correctly aligned with that pin in place. First will shim and measure it.

John, if the hole is badly deformed then I had been thinking of molding a socket that matches the pin. But if I understand you correctly you are suggesting making a steel bushing which fits the pin and then gluing that bushing into the correct location with liquid shim. That seems like a better approach than bedding the pin directly in the molding compound. Did I understand that correctly?

Yes, I'll pay attention that the scribed scale aligns to the mark. But the mark may have already been redone once so I could move it again if needed.

Cheers,
Bruce

Bruce --

I've done potted-in-place bushings myself, but have an old recollection of a how-to-use brochure from one of the many makers of wear-resistant catalytically-cured compounds showing an indexing pin bearing directly on their cured product. Can't recall which maker, but it's been long enough that that company has probably disappeared into ITW or Henkel by now.

With that out of the way, here's a link to an excerpt from SKC's catalog; take a look at the illustration directly above the page number on page 26: http://skc-technik.de/bilder/coatings_for_joint_faces.pdf

John

John Garner said:

Have an old recollection of a how-to-use brochure from one of the many makers of wear-resistant catalytically-cured compounds showing an indexing pin bearing directly on their cured product.

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OK, so not a crazy idea.

With that out of the way, here's a link to an excerpt from SKC's catalog; take a look at the illustration directly above the page number on page 26: http://skc-technik.de/bilder/coatings_for_joint_faces.pdf

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I assume that the black indicates the liquid shim. So this is showing a metal bushing fit over the indexing pin. The metal bushing is held-in/located by the liquid shim. This seems like a good way to go. It's what I will do if I need to relocate the pin or reform the socket.

I used to sell Moglice and have used it several times. You need to make the shim or pour the socket a minimum 1/16" ,062" per side bigger and I would either buy, make, or regrind the pin. Then spray the pin with a wax release agent. I would explore reaming hole before recommending using a Moglice product. Call or write
About Diamant: 13� years of success and experience I met and sold Moglice products in Taiwan with the at that time president Achim Shultz who has retired. It is a good product, but it's not a cure all. Studer now has another product similar they use in the bedways on their epoxy poured bases. Preparation is the key to having a successful pour. So practice doing it dry a few times.

This is the procedure you use to make the flat shim. same procedure but different then a bushing.
Moglice P5 injection on flat ways - YouTube

Shaft bushing....what you would do but on a small scale after aligning test bar.
Moglice P5 - Inject Application for Columm - YouTube

again similar project for ideas.
DIAMANT Plasticmetal - Repair Bearing Set - YouTube

Bruce --

Found it! See Figure 28 in the link, which is from Diamant's distributor of Moglice in the US: Replication Materials in New Machine Architecture

John

As much as I love Mogice / SKC. I'd never pot it in, for a direct fit against a pin. In my experience, you would always have a hardened ground socket, that would receive a hardened shot pin. I have a Mazak procedure for aligning multi pallets. This is on Horizontals, with 6 -8 pallets.

They have Grub / Set screws so you can tune alignment. Tune the socket alignment. Then you pot them in with magic mud.
Despite John's example, I've never seen a steel pin, up against magic mud. It's always a shot pin into a Steel hardened socket.

Rich's 1/16" per side is in the order.. I'm at what looks like a 25mm drill bush in a 30mm hole. The gap is potted.

Regards Phil.

Hi John,

John Garner said:

Found it! See Figure 28 in the link, which is from Diamant's distributor of Moglice in the US: Replication Materials

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Wow, that is EXACTLY the locating pin case, with the locating pin set directly in the Moglice. Thank you!

When I am done scraping the tailstock base, I will get back to this locating pin. Before I decide what to do, I need to examine the condition of the locating hole and see how far off it is. Then I'll decide how to proceed.

Well I had a better look at what is going on. It turns out that the problem was not with the location/indexing pin at all. Here is the workhead, the base with rotary shaft, and the indexing pin:



The indexing pin has at most 5 microns = 0.0002" of slop. So that's OK. But the "locating" part of the rotary shaft (which I am pointing to with the hex wrench here):



is 21.98mm (so 0.02mm under nominal size of 22mm) whereas the bore in the workhead is 0.03mm OVER nominal size" (the bore gauge is zeroed at 22.000mm)



This means that the difference in diameter between the rotary shaft and the bore is 0.05mm = 50 microns = 0.002" of slop.

Since the rotation axis and indexing pin are 7cm = 3" apart, this translates to an error at the end of my 400mm = 16" test bar of 0.290mm = 290 microns = 0.011".

I find this very annoying. After my scraping and adjustments, typical errors at the end of the test bar are a few microns, so this is fifty times more! The rotary shaft appears to be the original part, even stamped with the correct machine number:



Should I try and fix this, or is the point that the workhead always needs to be "trammed" so there is no point in making it better? If I do want to fix this, the bore in the workhead appears to be parallel/circular to a few microns, so I could turn a larger rotary shaft and lap it to fit. Or is there a better way, something like some stiff split plastic O-rings that could be fit into grooves in the existing rotary shaft, which would force the rotary shaft to center in the bore and eliminate the radial free play? This "bearing" only gets rotated by hand, and not that often, so a ring made of the right kind of plastic would probably not wear out in my lifetime.

(One idea to take up the clearance would be to wrap the locating part of the rotary shaft with teflon plumbers tape. It's an excellent lubricant and won't be under enough pressure to cold-flow significantly. But I think it's too thick: nominally 75 microns = 0.003".)

I'd agree your centre pin or Fulcrum, is the cause of your pointing error. How ever that 0.02 undersize or clearance on a 22mm bore. That would have to be there for a running / rotational fit. Any tighter, that's likely to bind. It's a steel on cast Iron fit. It need's some amount of clearance to work / still rotate.

I'm half handy at grinding, have several machines my self, but more importantly I've witnessed really good grinder operators.

They don't trust those dowel pins. They will put you in the ball park, better than 0.0005"/ 6". You can re-ream those. But each and every one will keep a lump of lead / brass / bronze to tweak in a parallel grind. You also have the taper adjustment on the table, to dial in, an un-supported work head, that's not true.

I'm discounting the degree referencing ring thing. Wouldn't you have to move that by near a degree or more too notice? You'd be hard pressed to scrape an Axis Too & From, One degree out of alignment

Sorry everyone for not following the thread day to day. Ballen wrote me again....so much wasted brain power about the pin. I had assumed you had opened the head swivel already.

I believe the head stock saddle riding edge surface was ground cockeyed. I would scrape it parallel to bar when it is assembled. Phil has a point about the clearance. The steel shaft and cast iron will get rusty if left alone. Ballen being a perfectionist can make a Nylatron or Delrin bushing and press it in and no clearance. I seldom worry about this as most of my customers use the tailstock and use a dead centers on the ends.

The dead headstock center will never see an elliptical error if it is off so little. That's why Studer made it that way and as Phil said you can turn the swivel plate to compensate for taper on shafts. The point here is are you going to grind shafts independent of the tailstock?

Now if your going to grind using the head-stock only then you have to have everything aligned.

I am a firm believer in bringing things back to original condition and leaving the head not on zero on the scale seems wrong to me. As I have written before the machine builders scrape the headstock last after the get the TS aligned or that's the way I do it on the machines I rebuild. The TS is always worn more and on a grinder if I am not going yo install a wear strip under the head and tail stock and leave it Iron on Iron.

Reminds me of a class I taught years ago for Gallmeyer & Livingston and they were testing the mag chuck and back fence making it parallel to the ways so it could grind slots, flatness and squareness. Charlie Galmeyer the owner said to me. I have no idea what the machine owner is going to use the machine for, so I scrape the machine perfect in all directions. Many times I ask the machine owner ...are you going to grind slots? or just grind flatness? If they are not going to grind slots I can save a lot of time by not checking squareness of column and wheel spindle.

(learned the hard way when I taught a class in Boston...I am sure I asked the student about grinding slots on his micro surface grinder he brought to the class as a project...he said I never asked and he complained I didn't know what the Fk I was talking about, so now I am going to show all students on here and in person explaining both methods so here is no confusion.

If it were a crankshaft grinder there would be only one answer...2 test bars would need yo be within .0001" in 6" or they would grind egg shaped.

So Ballen what are you going to grind on the machine? I have no idea...as they others don't either. Unless I missed you saying that. I hate to teach 1/2 assed ways as I am a perfectionist too when it comes to scraping precision. Rich

Hi Richard,

Thanks for looking at this again! If the index pin is supposed to bring me within 0.0005" in 6", then I should fix the slop in the steel shaft. Right now it's at about 0.004" in 6". I know that I need to tweak it in the end (I have a brass tapper that I use for this) but I feel like it should be closer from the start.

Richard King said:

I believe the head stock saddle riding edge surface was ground cockeyed. I would scrape it parallel to bar when it is assembled.

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I did that! Then I discovered that it was way off parallel, and when I looked more closely, the problem was the slop in the steel shaft. But in fact it does line up OK with the marks on the scale, the error from the slop is about 0.002" and not visible.

Ballen being a perfectionist can make a Nylatron or Delrin bushing and press it in and no clearance.

Click to expand...

Ok, that sounds good to me. I can get Delrin easily but I have never done no-clearance plastic bushings. What sort of wall thickness should I make the bushing with, and how much interference should it have on the OD or ID? The ID of the cast iron hole is 22.03mm = 0.867"

The point here is are you going to grind shafts independent of the tailstock?

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I want to also be able to hold and grind parts in a 3-jaw chuck and in collets (the machine has both).

Yes, I tend to be a perfectionist. Given that I am scraping everything into really good alignment, I figure I might as well get the head stock saddle right. And I can't do that with the slop in the steel shaft .

I am a firm believer in bringing things back to original condition and leaving the head not on zero on the scale seems wrong to me.

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It will be on zero! As I said, I was wrong about the index-pin being off.

The TS is always worn more

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On mine the tailstock is (way!) high. So I am doing it the other way, getting the HS lined up and then scraping the TS down to it. I think that the machine might have gotten a brand new tailstock at some point, because the number on the TS does not match the rest of the machine. And the new TS was never fitted properly to the machine.

So Ballen what are you going to grind on the machine? I have no idea...as they others don't either. Unless I missed you saying that.

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Richard, I don't know yet. I got the machine to learn how to use a cylindrical grinder. The test bar that I made is getting a lot of use, and once I have the machine back together the first order of business will be making a shorter version plus MT5 adaptors/holders for tooling.

Cheers,
Bruce


PS: I suspect that I may have a sloppy rotation pin in the swivel table also. That's not good because it makes it hard to hit angles spot on using gauge blocks. So I may do the delrin bushing there also.

Ballen have you considered the height or centerline of the wheel head and if the wheel head spindle is parallel (or slightly higher on spindle side of wheel-head) to the work-head and tailstock? You may have written in the other thread...maybe you should add a link to the other thread to this one..so the story can continue. This is so much more interesting then some of the "other" one lately. Your machine is not a made up thread.

Richard King said:

Ballen have you considered the height or centerline of the wheel head and if the wheel head spindle is parallel (or slightly higher on spindle side of wheel-head) to the work-head and tailstock? You may have written in the other thread.

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I have thought about this, and it is mentioned in the other thread, but I have not made the measurements. It's not so easy to do that because both end of the wheel head spindle are tapered, so I need to turn some measuring rings with a tapered ID and a constant cylindrical OD to make the measurement.

Because I have been lowering the HS and TS, I am pretty confident that I will have to lower the wheel spindle center height. That's "easy" because it's a universal cylindrical grinder so there is an intermediate plate which I can remove and grind or have ground. I can also shim this before grinding if needed to remove any left-right tilt. Since it's universal the other axis can be adjusted parallel, no problem.

I'm not worried about that, because the Studer spec calls for a wheel centerline that's within 100 microns = 0.004" of the height of the HS/TS axis. That's easy: most of the other specs on the machine are 2-4 microns = 0.00008" - 0.00015".

Coming back to the topic of this thread, I decided rather than messing with fitting a Delrin bushing, I am first going to try molding an insert onto the existing rotary shaft. If this doesn't work out then I will just turn a new shaft from some pre-tempered 42CrMo4 (ANSI 4140) and do a delrin bushing as we discussed above. I'm using some SKC-60 (this is like moglice) that I already had from a previous project, from SKC-Gleittechnik.

I made a 7mm (9/32") hole that goes up the center of the rotary shaft:



with a 6mm (1/4") cross drilling at the top that joins it:



and I turned down an intermediate region by 4mm (5/32") in diameter. I won't be able to get to it until this weekend, when I'll knurl this where the molding compound is going to touch it to give it some "teeth" then put it into place and inject from the center hole. There's enough clearance to push out the air around the remaining stubs.

Don't forget to mold release the hole. You did say the hole was concentric right? Plan on adding a lubricant after? Or is the SKC self lubricated like Moglice is?
When I used to do the tight fit's with Mogice I polished or rubbed the wax in as if I was polishing a car. I would re-think the plate you are grinding. I would grind it parallel and not tapered. If it is tapered a lot , when you swiveled it one end will rise and one end will drop. Then when you dress the wheel it will be tapered.

Like I said if it's a small amount, probably won't matter, but if it's a lot it would. How wide is the wheel ? I used to scrape the Vee & Flat ways if the test bar or ring your making indicated parallel to the table travel. I would leave the Vee side (left on most grinders) high as that's where the grit wears the machine more, so as it wears it gets better. I would think .0002" per 1". What does Studer say on their spec sheet? Rich

PS. Just looked at the shaft and cross hole. Is the hole drilled on the bottom ? I used to pump in Moglice in the bottom so it would force out the air as it flowed up the hole.
Be sure to seal the bottom outside end with duc tape as if it is like Moglice liquid it will leak like water.

Hi Richard,

Richard King said:

Don't forget to mold release the hole.

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I have a spray can of mold release wax which I purchased from SKC at the same time as the SKC-60. It works well.

You did say the hole was concentric right?

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I gauged the diameter in several directions all along the length. It looks good to a few microns, around say 0.0001". Otherwise I'd be worried about getting the pin out again.

Plan on adding a lubricant after? Or is the SKC self lubricated like Moglice is?

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It has molybdenum disulfide or some a similar lubricant embedded in the material. After curing it's hard and very slippery. You are supposed to use it with oil, but I think once it's lubricated it will be good for at least a few thousands spins. That's enough for at least a few years.

When I used to do the tight fit's with Mogice I polished or rubbed the wax in as if I was polishing a car.

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OK, I'll do the same. I can use a Dremel with a cloth wheel to buff the inside of the hole.

I would re-think the plate you are grinding. I would grind it parallel and not tapered. If it is tapered a lot , when you swiveled it one end will rise and one end will drop. Then when you dress the wheel it will be tapered.

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Good point, I'll grind it parallel. My expectation is that the wheel spindle is already very close to level, because the wheel slide ways still have their scraping marks and oil pockets, but I'll check it carefully. First though I want to get the HS and TS properly aligned.

How wide is the wheel?

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My widest wheels are 25mm = 1". The flange and wheel guard can go up to 30mm = 1 1/4". According to the manual the machine can take wheels up to 50mm = 2" wide, but I don't have the flange and wheel guards for that so will stick to 25/30mm.

I used to scrape the Vee & Flat ways if the test bar or ring your making indicated parallel to the table travel. I would leave the Vee side (left on most grinders) high as that's where the grit wears the machine more, so as it wears it gets better.

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Makes sense. The vee is left on this machine. But I am really hoping that the Vee and flat are OK as they are, because scraping them in will take a lot more care and skill than getting the HS and TS right. I'm not feeling ready for that, so hoping it's not needed.

I would think .0002" per 1". What does Studer say on their spec sheet?

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I just had a look. Studer specs the wheel spindle parallel to the table to within 30 microns in 400mm (0.001" in 16"). That's 0.00007" per inch.

The height difference between wheel spindle and work spindle should be less than 100 microns (0.004").

Just looked at the shaft and cross hole. Is the hole drilled on the bottom ? I used to pump in Moglice in the bottom so it would force out the air as it flowed up the hole. Be sure to seal the bottom outside end with duc tape as if it is like Moglice liquid it will leak like water.

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The central hole is at the bottom of the pin, and the cross hole is at the top. The SKC-60 is more like soft butter or cold honey than like water. So I'll have the HS and pin upside down when I pump it full using a cartridge gun to generate the pressure. This way the opening will fill from the bottom, and push the air out the top. Then when it's full, I'll put a piece of duct tape over the hole to keep the SKC-60 inside, and I'll turn the HS the right way around. Then let it all sit for 24h. The SKC-60 is thick enough that it won't leak out of the 0.002" clearance between the pin and the hole. At least that's the plan.

Cheers,
Bruce

PS: here's a couple of action photos from when I was working on the HS and TS. The corner groove wasn't quite wide/deep enough for scraper clearance so I used a 3mm = 1/8" cutter to improve that. Also I had so much material to remove to get the alignment right on the front rail that I milled off most of it before scraping. The tailstock was impossible to clamp well so I was taking multiple shallow cuts.

Looks like you got it figured out. :-)

I used to do this. After I got the head aligned and scraped right, I would grind or mill and scrape the outside of the part so there was an original side I could use next time or to test fast without using the test bar. I also did that on large milling machines with box ways that needed the saddle side ways square to table travel. When the saddle was out being milled I would have the clearance surface on the opposite side of the saddle way machined parallel so I could indicate their when scraping squareness and not have to mount a square on the table. I would also cover that parallel surface with a sheet metal cover so it would not get painted or dinged up. Rich

Hi Richard,

Richard King said:

Looks like you got it figured out. :-)

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Coming from you, that's reassuring. I've done this exactly 0 times before. Whereas I bet that you lost count about forty years ago!

I used to do this. After I got the head aligned and scraped right, I would grind or mill and scrape the outside of the part so there was an original side I could use next time or to test fast without using the test bar.

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That's a good idea. I don't want to mess with the front of the HS but on the back there's a flat landing pad for a collet-closing attachment. I could mill or scrape that into alignment with the spindle axis. It would save me from putting in and taking out the test bar.

I also did that on large milling machines with box ways that needed the saddle side ways square to table travel. When the saddle was out being milled I would have the clearance surface on the opposite side of the saddle way machined parallel so I could indicate their when scraping squareness and not have to mount a square on the table. I would also cover that parallel surface with a sheet metal cover so it would not get painted or dinged up.

Click to expand...

Got it. I'll look at the different parts to see if there's a good place to mill/grind/scrape a reference surface.

PS: I thought you'd comment on my scraping on the underside of the TS. I removed 80 microns = 0.003" of tilt by step scraping, but after refining it found I had gone 20 microns = 0.001" too far. So then I step scraped off about 10 microns then refined to get the last ten. I know it's not as good as it could be, but since I have to lower the TS to the right height I will get to practice it again. Will probably mill off most of the material then scrape it in. But won't do this until the HS is completely finished, including the index pin and rotary shaft.