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"Grinding" a small spindle for ABEC 7 bearings

rhb

Aluminum
Joined
Apr 27, 2019
Location
A small town in central Arkansas
After lots of investigation and thought I think I'm ready to "grind" the spindle and thought it might prove useful to document the method and results here.

I've determined that I need to remove 0.00005-0.0001" from the rear journal and 0.00025 - 0.0003" from the front journal to bring them within the +0.0/-0.0002" ABEC 7 spindle tolerance.

Because of the extremely light cuts I've concluded that a tool post grinder is neither needed nor desirable. Instead I intend to hand work a small whetstone against the journals while the lathe is running much as one would a file. The rear journal will just get the medium Arkansas stone. The front will start with the corundum stone and finish with the Arkansas stone. Both stones have been lapped flat using silicon carbide paper on a surface plate. I plan to run at minimum speed and measure often. When the front journal gets to a tenth oversize I'll switch to the Arkansas stone.

The spindle is mounted on an MT 2 test arbor which has been wrapped with copper wire and placed in a 4 jaw independent chuck. It will be indicated to a tenth or less TIR. The chuck jaws look to be in excellent shape with no discernible wear.

I considered a number of other approaches and this seemed the most controllable. Maximum drag corresponds to being parallel to the existing surface.

Reg
 

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What is the spindle out of?

Am I right to guess it's a small lathe and you want to put class 7 bearings in it? Are you sure you won't introduce some errors by "filing" on the journals?
 
It's an "unmentionable" I bought to make custom gun screws. When I started clocking it after arrival and spotted the ways my ideas changed. *Everything* I've checked has been within new toolroom specs except the bearings. My Clausing 4902 is rather large for making 3.5 mm RF connector gauges and much too worn to fight that battle.

I'm not*certain* of anything other than I'm going to try. I considered the popular youtube "shoe shining" with wet or dry method, but don't have any confidence in that maintaining roundness. I don't currently have the ability to make 3 point roundness tests, but that's a good use of the LVDTs I just bought.

I may well fail, but if for under $2k and a bit of sweat equity I have the equal of a $21K Levin I'll be *very* happy.

The human fingertip is an amazing instrument. If the existing journals are out of round I should feel it running at <60 rpm.

I have to make an adjustable inside lap to do the housing, and on reflection I may switch to an adjustable outside lap for the spindle. It's not that much more work. And I just got a piece of Versa-bar plate. The catch with that is the need to achieve less than a tenth taper over 3/4" on an old machine.

I called several machine shops in Little Rock. When I stated a 2 tenths tolerance they all said they couldn't do that and gave me the name of another shop. I stopped when the cam grinder shop I was referred to didn't answer their phone and I found complaints they took over 2 months to grind a cylinder head.

I won't actually attempt this for a couple of days. I *really* want it to come out right.
 
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Somewhat depends on if I can find the box of junk wrist pins or something else of suitable precision. Random 25 cent a pound scrap yard stock is, well, questionable. The precise stuff, such as my chromed hydraulic shaft off cuts are rather large. I may just take a deep beath and hope I don't have to buy a new spindle.

The only thing that makes me consider this is the extremely small cut.

I'm dragging my feet as much as I can stand.
 
Ahh, I found you other thread, now I understand:


I think you're getting bearing tolerance class and shaft/housing fits confused, here's what your looking for:


You're existing shaft/housing is probably in the tolerance range for a lathe spindle but putting ABEC 7 bearings in a China LSO is probably not going to give you the results your looking for, there are way too many other variables that make up runout and spindle to bed alignment to consider.

As an aside I put Barden angular contact bearings in my little Emco C5 lathe years ago that did tighten it up and make it run truer so it might help in your case but I wouldn't hold my breathe.
 
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Those charts were the motivation for that thread. If you'd looked farther you'd have seen the conclusion.

Look at the scan from the Torrington catalog in post #6 in that thread.

The motivation for replacing the bearings is that and the tailstock are the *only* things I've found that aren't within two tenths. I've now spent many hours doing various tests. The headstock vertical alignment is a bit off, so I'll need to scrape the headstock, but that's not difficult. The tedious part will be installing and removing it.

With the spindle stationary I was able to align the headstock to within a tenth the length of the bed measuring at 1" intervals. Either my test bar just happens to match the ways or they're straight.

I have less than a tenth TIR on the spindle surfaces (face, periphery and taper). The sole issue is misalignment with respect to the axis of rotation. That ranged from 0.0005" to 0.0015" from revolution to revolution with the OEM bearings.

I've spotted the dovetail bed with a straight edge. The rear way is flat the full length. The front way has slight highs at the ends. The operator stopped the grinding stroke a little too soon? That won't be much trouble to correct by hand. Far less work than reconditioning a used machine.

The preceding comments on using an outside lap have me in a bit of a quandary. I must make a lap for the housing and it's not a lot more work to bore the inside to make an outside lap for the spindle.

But I'm curious to see how the stones work in practice. I think I'll try taking off a tenth on the front journal with the Arkansas stone as an experiment and test that for errors just to see how that works out. I've got indicators I can set up to check for out of round.

I've got piece of ductile iron bar that I can treppan to make both a QCTP holder for the HF router and a combination inside and outside lap. Likely I'll never use the router TPG, but it's cheap and might prove useful one day.
 
It is tough to come in and take one or two tenths off a part diameter or ID with the best grinding machines for getting concentricity and straightness with that little stock. An abrasive paper may be the better solution with taking great care that you don't measure while the part is still warm.

We used to lap precision reamers with a closable collar device and lapping compound to get down to a few millionths but that seems way overkill for your project.
 
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Yup...

I see from this and the other thread you like to ask lot's of questions and type a lot but when the answers come in they go right over your head and you explain (in great detail) how you've already got it all figured out.

So you're tying to convert a HF 7x12 LSO into a toolroom lathe to make screws for firearms?

This should be locked.

I'm out.
 
I called several machine shops in Little Rock. When I stated a 2 tenths tolerance they all said they couldn't do that and gave me the name of another shop. I stopped when the cam grinder shop I was referred to didn't answer their phone and I found complaints they took over 2 months to grind a cylinder head.

I think what the meant is they couldn't remove that little material from the existing diameter. If the shaft was new and .005" oversize it wouldn't have been a problem.
 
As long as the questions are related to the process, it's not an inappropriate topic. It is a good idea to check for roundness before just using the whetstone. An external lap may help correct an out of round condition, but as with any other operation: it's important to be able to check and quantify whether an improvement is being made or not.
 
Yup...

I see from this and the other thread you like to ask lot's of questions and type a lot but when the answers come in they go right over your head and you explain (in great detail) how you've already got it all figured out.

So you're tying to convert a HF 7x12 LSO into a toolroom lathe to make screws for firearms?

This should be locked.

I'm out.

Well at least the OP is trying to do something interesting, and causes us no harm.

I have a friend who would do something similar and make it work. If you don't try, you'll never know your, or a machines limitations.

And there is a good market for firearm fasteners.

What's the worse that could happen? OP gets a slip fit and uses Loctite.

Loctite has been my savior on multiple occasions.
 
I called several machine shops in Little Rock. When I stated a 2 tenths tolerance they all said they couldn't do that and gave me the name of another shop. I stopped when the cam grinder shop I was referred to didn't answer their phone and I found complaints they took over 2 months to grind a cylinder head.

The shop I've used locally Electronic Chrome and Grinding ( https://www.ecgrinding.com/ ) would grind under size, then build that up with chrome prior to finish grinding. I've never had them do that, cos' the shafts I have ground are new. But plenty of people do.

Last time I was there, there was a whole shelf of Ducati cranks waiting to be ground/chromed/ground
 
Yes, cutting undersize, chrome plating and regrind is almost a standard repair method for bearing journals. I've used that method on journals of shafts even up into the mid double digit ton range. I'll be using it again on some hydraulic spools from my surface grinder before too long.
 
I have sent Centerless grinder spindle to Inter-motion and they ceramic coated the journals and not chrome plated them. I have also Chromed them too, but Ceramic works better. https://www.inter-motion.com/
I also have had these guys chrome and re-Babbitt shoes. GCH.
 
Rich,I haven't seen the ceramic coating before. Having seen millwrights at work, I'd be more than a little worried about fragility. For a precision spindle rebuild however, I expect millwrights shouldn't be within a country mile. I looked at your link but there's nothing about the ceramic coating process. I will do some googling.
 
I dialed the test bar in the 4 jaw to a tenth and have made a few brief passes with the medium Arkansas stone. I can see the effect of the stone, but can't measure it. So I broke for lunch and will resume later.

On the finger feel aspect, I noticed that I had not completely flattened one face of the Arkansas stone.

I'm seeing about a tenth variation miking the journal. I initially assumed that was just the inevitable errors trying to mike a tenth, but I'm going to check that after lunch.

I did test the Clausing spindle bore and it has less than a tenth TIR, but I'll probably recheck that too.

There's no need for this level of precision for gun screws, but I do a lot of electronics dabbling using 3.5 mm series connectors. For those those the tolerances are 1-2 tenths. An out of spec connector can destroy the connector it's mated to. At the $100+ each prices and the labor of tearing an instrument apart to replace the connector that's a serious concern. And for some of my gear it's not actually possible to replace them except in a factory setting.

I bought a batch of 100x SS right angle M-F SMA adapters from a reputable supplier on ebay. The connectors could not be mated with each other. They would mate with other connectors, but the tolerance stack for the M & F ends would not let them mate. I'd like to have some gauges, but can't afford the prices Maury charges. I missed a Maury A027A set of gauges I'd planned to snipe on ebay. I've not seen another set in several years.

My real interest is the process of doing work at this level. Can I do it? The machine is just an excuse. The tailstock is total junk both by design and manufacture. After watching a short youtube video of an ebay seller operating a Levin I'm seriously considering installing a feedscrew and graduated collar for the tailstock offset as well as the ram feed. I'd already planned to do that on the ram, but I'd never seen the offset feed that the Levin had. I thought is was very cool.

I view the basic machine as a semi-finished set of parts. I'd love to have my Clausing reconditioned to toolroom specs, but that would be both expensive and a *lot* of work. It's just fine as is for ordinary work.
 








 
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