I do it differently by putting my bar in a 4jaw to zero over the end and scalping the 60* with a tool bit..and then come in with my center drill.
Drill rod is not perfectly straight but often you can roll it on your surface plate and find a side that is near dead flat to mark that side and use it for checking.
The showing of how easily the drill rod deflects is important..If you can deflect the workpiece with two fingers then the tool bit or grinding wheel on the OD will deficit the part.
That youtube video is a FAIL for using a 3 jaw to center drill. Should be a 4 jaw independent as you state. I used the steady rest to center drill my bar as it was too large to clear the spindle hole. In my case, bevause I was going to turn the collars the center holes were not as critical as if one were relying on the factory surface of a piece of drill rod.
While I could have used a piece of drill rod, I was very interested in doing the job using 1890's toolroom technique and the rigorous application of geometry. I bought every book Lindsay sold on metalworking and have read them many times. I don't think I ever saw a multicollar bar, but it's the obvious extension of turning collars at each end.
I now have ebay test bars ground between centers for MT 0-4. So my old bar is superfluous except as a very difficult exercise in machining and a rehearsal for spindle grinding.
The +0/-0.0002" ABEC 7 spindle tolerance is consumed by a 33 F temperature change. That did me in on a solid bar. A hollow spindle will be worse. I'll try grinding some scrap wrist pins before I try to do the spindle.
I'm a little confused about how you are having such temperature problems. Rough the part and let it cool. Then finish with some cutting oil (if using HSS, I think that's what you said you used?) a sharp tool and a light cut and you should get almost no temperature rise.
If you mean grinding, that should be similar. If you're getting large temperature rises when finish grinding you have a wheel issue. Either the completely wrong wheel for the job or poor dressing. Possibly improper work speed or traverse rate also. And use coolant...
It might not be as much of a problem now. It was my first serious attempt at making a precision part. Never having had a shop class of any type, much less machining I was rather a babe in the woods. It made me *very* conscious of thermal expansion and contraction.
Prior to that the most precise job I'd done was to bore and bush the leadscrew pillow blocks on a much worn and abused a Sears 109. That actually went very smoothly despite the limitations of the machine and operator.
The +0/-0.0002" ABEC 7 spindle tolerance, is fairly close ( I thought it was +0 + .0002)
But that doesn't matter..Trying to celebrate an old lathe to .0002 anything is not worth the damage grinding on a lathe can do,
Having a simple test bar that is a half thousandth off should be close enough for such a lathe.
If you had a good surface plate you could scrape an aluminum level to be a temporary straight edge.
Yes, I sent that guy on eBay a message that selling wheels in the USA not including the RPM is leaving him open to a law suite.
A vitrified wheel should never be mounted with not having a blotter..That eBay guy does not seem to offer a blotter or mention them.
Yes, a 3" grinding wheel can kill you.
wheels are tested to + 50% RPM to see they will not blow up..and each production run of wheels is also tested to be sure something in the mix has not changed.
Find many great new & used options and get the best deals for 1/2/4X 3" Grinding Wheel Polishing Pad Abrasive Disc Metal Grinder Rotary Tool at the best online prices at eBay! Free shipping for many products!
Likely a guy who knows nothing about grinding selling wheels.
In my case, this is a new machine intended for small work i.e. <0.5" stuff and mostly brass.
I completely stripped the headstock today. The spindle bearing surfaces are 0.0001" and 0.0003" oversize for the ABEC 7 tolerances stated by the Torrington and Timken catalogs which stipulate a "line to line fit". In essence the spindle and housing tolerances are the same as the bearing ID and OD tolerances.
I have *zero* confidence I could hold such small cuts with a TPG even if I practice on a dozen junk wrist pins. Even using the compound to reduce the feed I simply don't have the control I'd want.
As an alternative I'm considering gluing a corundum whetstone to an angle plate, mounting that on the carriage and with the spindle mounted between centers, pressing the stone against the spindle. Naturally that will be slow grinding, but with the very little I want to take off, that seems an advantage. The whetstone will be flattened before use. Another variant would be to glue wet or dry to the angle plate.
I'm sure this is very unorthodox, but as the saying goes, "It's a poor workman who blames his tools." In my world view a "machinist" can do anything with anything given sufficient time. Not sure I'll live long enough to reach such status, but I am trying. I'll be doing all this work on my well used Clausing 4902.
Plan B if the ABEC 7 installation fails is to make and lap in a plain bearing. That has the advantage of having zero rotational error after lapping, but the nuisance of keeping it lubricated. On the other hand, I'm used to that on the Clausing.
I am going to fool around with the HF router as a TPG, but it's rather low priority. Just a possible means of doing the job.
A flattened whetstone should work about as well as any other method. I've used that one myself on spindle rebuilds. Keep it wet with mineral spirits and it won't load.
Using a grinder - especially a TPG on a lathe - for such a miniscule amount of material removal is folly, IMO. It would be very difficult and time consuming to even set the workpiece. Either hone or lap is the way I'd go for a few tenths or less removal on something where runout is crucial..
Thank you. It's very helpful to know that a pro has used the concept. When I realized how little metal I could safely remove I realized that I'd never be able to set that up with any TPG, much less a DIY router based TPG.
Because of the precision required for high speed bearings, I think the router has potential for the very few jobs for which one is likely to use one. But I'm going to design a mounting that provides reliable tenth or less infeed without relying on setting the compound at an angle. And that depends entirely on actually needing a TPG.
I just heard from a local friend who made a bunch of ring laps to sharpen his reamers. We messed around with his Nardini rebuild project yesterday. Next visit I'm going to study his ring laps.
After miking the spindle I am +0.0" on the rear journal and +0.0003" on the front journal. Not much. "'Tis but a scratch, but 'tis enough".
Making a ring lap for a single job is a *lot* of work for little benefit. So I'm going to do it free hand using a small whetstone.
The spindle will be mounted on my MT 2 test bar which will in turn be mounted in a 4 jaw and indicated to within a tenth. If the ways are accurate enough I'll support the end with the tailstock and a live center if I have one large enough. I may have to stop until I get a bullnose live center.
I was going to mount the stone on an angle plate until I realized I'd need to align it to within 33" of arc with the axis of rotation to keep taper under 1 tenth over the 5/8" width of the journals. No chance of doing that on a 60 year old Clausing. But I can feel the increase in drag when the stone is flat across the journal.
Next step is to make sure the stones are flat.
I will post a picture of John's ring laps when I see them.
We're a long way from my original query. However, the alignment issue is informative. I plan to make a steel mount for the HF router and shall be paying very close attention to developing a proper means of aligning it.
But for now I feel lucky. It's not as fearsome a job as I thought. Not trivial, but I was pretty terrified before I measured the spindle. Of course, there is the headstock housing to do. I ordered a 0.0001" dial bore gauge. Try as I might I couldn't repeat closer than a thou with a telescoping gauge.