Repair guy

[Dr Stan]

It is true the quick cast method will give you a quick and fairly accurate means of measuring the taper. However one would still need "a set of quality dials" when setting up either the compound or the taper attachment at the proper angle to build the lap. As one who worked as a tool maker for a number of years before going to academia, I have indicators which are accurate up to .001 mm (.0000395 in). I certainly would not expect a home shop machinist to have one that accurate, but .0005" is certainly affordable for most.

[metric_taper]

That may be a 7 Morse taper. You can look up the specs in Machinery's Handbook. If you find the spindle is worn or not at the correct angle, you can recut it with a carbide insert boring bar. You can use the taper attachment, or swing the compound slide around to the correct angle. I like to use the compound for short angles.

Once you determine what the taper should be (the model G0749 is a #7MT) You can easily set the compound slide to the desired taper like this:
1- Put a bar in the chuck or collet and turn to get a full cleanup on the material diameter with a good finish. Diameter must be the same for the length of the turned part. Keep part in place until angle is set.
2- Calculate a right triangle for one side of the taper. Set up a dial indicator perpendicular to the turned part, on the side facing the operator. The compound slide is the hypotenuse, indicator stem is the short side and the part is the long side.
3- Adjust the angle of the compound until the dial indicator reads the number of the short side when the compound is dialed the length of the long side. Tighten compound slide in place.
4- Remove indicator and bar, add part to be turned and cutting tool, and cut taper. In this case, the part to be turned would be the spindle taper. No need for a toolpost grinder, just go over the surface several times with the carbide insert. Make sure the toolpost is tight, so it doesn't move during the cutting process.

I was hoping it would have been a 7MT, and used the data from Machinery Handbook a few weeks ago, and verified that it would slip through from the opening size. Grizzly was no help, as they had all the same documentation I did. The OEM lathe manufacture had 6MT for 4 different models of this lathe. Which Grizzly copied into their spec sheet. But with the 3-1/8" through bore, it clearly was wrong. I've had this lathe since new in 2004. What I've figured out, that it was made from every incorrectly machined part that instead of scrapping was put together and sold with a group of this same manufactured defective lathes. The lathe was never in their catalog, and I accidentally found it on their web site back then. It was cheep at $7000 for 5600 lbs weight (and in my budget). It does turn true, and with a 7.5HP can take very heavy cuts.

I've been reworking every issue (and there are many) as they come along. I just never checked this sleeve out with an indicator before. I only did this, as I put a 4MT test bar in this sleeve and found a killer amount of runout at the end of the bar. This traced it back to the sleeve not fitting the spindle. And I believe it to be the spindle that is the problem.

I did measure to the best of my metrology that the sleeve was 90mm at its major diameter, and had a 1:20 taper angle. The spindle I've not measured yet, as there is .2" in 4 inches, and I need to make a dial indicator holder, to hold the small 1" dial (.25 inch travel) indicator, that will fit inside the opening. I know I don't have to sweep all 4 inches to collect enough data on the taper.

This is now another project to make a holder for the indicator I have.

I don't believe the compound slide has enough travel to install the tool post grinder on and machine via this path, as this taper length is about 4.5 inches.
But I want to measure the sleeve more accurately first. I'm waiting on a bench center from eBay, that in conjunction with a sine plate I will determine the angle of this sleeve.

This sleeve is hardened, so it would have to be ground, if that is the path I go. But if it is the spindle opening, that is where I want this fixed, so I can say that it is a 90mm gauge metric taper of 1:20. Just in case I find tooling in the future, but I've not seen the DIN specs as they want money just to look at this.

Yes, the simple solution is to cut a new taper sleeve that fits the existing lathe as is. It's only job in life is to keep a center centered, and will not drive torque.

[metric_taper]

Do you have any runout when using the chucks? I'd mount the sleeve on an arbor mount a center and center it in a four jaw chuck and using a dog to drive I'd set up a grinding fixture on the tool post . Indicate the compound to the taper and then using a seperate indicator on the bottom of the compound. Then I'd take a test grind full length of the taper. If it cleans up all the blue dye I'd loosen and tap the compound about .002 at the tailstock end. Recut the grind measure the large end if it matches the taper in the head I'd stop and recheck the fit in the spindle. Easy to save your zero by just taking the arbor and part out from the centers. Remove the chuck and Ck the fit with blue dye. It may take awhile but you can fit it a few thousandth at a time. If the spindles out you'll need to recut the bore. Hopefully it's just the sleeve.

No, all lathe chucks run true with the spindle. I replaced the original junk with Bison and Pratt Burnerd 4 Jaw.
The problem is a mis-matched taper between the sleeve and spindle. The sleeve bottoms out early, so I need to increase the angle of the spindle or decrease the sleeve. I want to end up with some sort of standard just in case there is future tooling (e.g. collet closer) I need to fix the one that is off.
If I go the path of making a new sleeve, I would machine in place a new center in the 3 jaw chuck, so it would run true to he lathe axis. At least I'm thinking in that direction. I would use a 4MT drill chuck arbor to hold the sleeve between centers. Hopefully the Jacobs taper is long enough to grab with a dog.

[metric_taper]

Not positive what your objective is. Are you trying to fix the head stock spindle taper or identify what it is? First off is there something wrong with the spindle? Does it have a problem from an accident? If the spindle in the lathe runs true the first thing is to identify the taper. Surely it is a standard unless someone has modified it. If you are trying to put it back to a standard taper you should find someone with a DuMore tool post grinder with accessory long axis slide of its own. They do exist and are used for truing precision machines after bearing changes. Been there done it! But the spindle taper should be where to start and go from there.

The accident is via the OEM manufacture of the lathe.
My objective is to fix what I believe to be a spindle manufacturing defect. From another web site, a tool and die guy believes I have a 90mm gauge 1:20 metric taper. He say's he's built tooling for this in the CNC industry.
I'm just now finding this problem with the lathe as I generally never do center work.

[metric_taper]

I hope I am reading the problem right.
My initial thought is, to clock the internal taper of the spindle to work out exactly what the taper is - decimal or inch - i.e, x fractional inch taper per y inch linear - or metric equivalent. Then, see if there is some way to set up the adapter by some means - mandrel of some sort and get it running true via a 4-jaw chuck... this is the awkward bit! Not sure yet quite what I'd do without the adapter actually in hand!
If that can work then the adapter can be clocked to see what the taper discrepancy is exactly, then set up for the correct taper and grind externally or even cut with a carbide insert even if hardened. Now, if this could improve things the next step could be to lap the adapter and spindle gradually together until the fit is correct - which would mean then having to always use that spindle taper/adapter combination for good. A good 1/10s indicator would be useful.
One other thought - if internal taper of spindle could be measured well enough - use that info to turn a new dummy adapter out of ordinary CRS and try and get that right for fit. If that worked then drill and ream for end to take a Morse dead center. It could serve even if not hardened.
Sorry long winded but sort of thinking aloud right now

The biggest problem with making a new sleeve, is I probably have to use the lathe chuck during the process, then unmount it, do a blue check, then mount it, and I bet this is many iterations.
I do have a tenths indicator, and that's my next project to make a rigid holder for it.
I'm retired, but time still keeps the shop door closed way too much. Still trying to finish a house addition from 2007.

Lots of idea from folks here, that is what I hoped for.

[metric_taper]

I've not done any lap work outside of a flat lapping plate.
Can you remove 4.5 thousands of material from a 90mm diameter. In my ignorance, I would think lapping is generally small "tenths" of material removal. And if I could remove this, I bet I would end up with the sleeve at an angle to the axis.

[ulav8r]

To lap, you would need to use a small lapping head on a boring bar type holder and use a taper attachment to move it from one end to the other. It would be practically impossible to hold a full lap on center to the precision you want. A tool post grinder with a long internal fixture would be easier to use because it would cut quicker.

[metric_taper]

It is true the quick cast method will give you a quick and fairly accurate means of measuring the taper. However one would still need "a set of quality dials" when setting up either the compound or the taper attachment at the proper angle to build the lap. As one who worked as a tool maker for a number of years before going to academia, I have indicators which are accurate up to .001 mm (.0000395 in). I certainly would not expect a home shop machinist to have one that accurate, but .0005" is certainly affordable for most.

I have .001mm indicators, BUT the dial indicator (Wright & Moore) with 1mm stem travel, is too long for the 90mm opening. The test indicators I have all have very short 3/8" arms, and I do worry about cosine error to check anywhere internal from the front edge.

I have a small dial indicator .01mm that can fit, but need to make a rigid setup. I just want to sweep the bore to see that the taper is consistent. Probably moot, as I need to regrind it. I need a starting point.

As my taper attachment needs some gib adjust and deburring of ways, in your opinion as a tool maker, can it hold the quality needed?
The right solution of removing the spindle is never going to happen, as it's too major of a tear down, and the cost of paying a tool and die machine shop is not in my desired expense. The tear down is the real excuse to machine it in place. I really can't wreck it unless I end up with a hyperbola or steps in the taper.

I do like that I'm learning new things, I just wish I had the skill to implement with zero defects.

[Dr Stan]

Yes the taper attachment can be adjusted to hold an accurate taper and you are correct that 4 1/2 thou is a bit much to lap. Doable but far from fun as you'd have to recut the lap & recharge it several times to maintain any semblance of accuracy. So it looks to me like you need to work on the taper attachment as the first step. I'd also only use the taper attachment to cut in one direction. A tool post grinder with a high speed internal spindle would be close to ideal, but not many have such an item. I've worked in commercial shops which did not have even an OD tool post grinder.

Your best option is to buy a hard turning insert for the boring bar, then use layout dye to see your progress. Another possibility is to MacGyver an attachment to use a die grinder (not a Dremmel) for the internal grinding. Keep in mind the grinding wheel & the work need to be counter rotating otherwise you'll just skip across the surface. You also need to true up & dress the wheel while mounted in the grinder before any grinding. Cover every bare surface you can and remove and clean the wipers when finished.

I did not previously mention this, but I've had extremely bad experiences with Jet, but nowhere close to what you've been through. I think you're right in that they threw together a bunch of poorly manufactured parts and slapped a "can't pass this up price" on them and sold them to generate some income at the expense of the consumers. BTW I'm sure they are out there, but I've never seen a metric tapered spindle bore in the US.

[metric_taper]

Yes the taper attachment can be adjusted to hold an accurate taper and you are correct that 4 1/2 thou is a bit much to lap. Doable but far from fun as you'd have to recut the lap & recharge it several times to maintain any semblance of accuracy. So it looks to me like you need to work on the taper attachment as the first step. I'd also only use the taper attachment to cut in one direction. A tool post grinder with a high speed internal spindle would be close to ideal, but not many have such an item. I've worked in commercial shops which did not have even an OD tool post grinder.

Your best option is to buy a hard turning insert for the boring bar, then use layout dye to see your progress. Another possibility is to MacGyver an attachment to use a die grinder (not a Dremmel) for the internal grinding. Keep in mind the grinding wheel & the work need to be counter rotating otherwise you'll just skip across the surface. You also need to true up & dress the wheel while mounted in the grinder before any grinding. Cover every bare surface you can and remove and clean the wipers when finished.

I did not previously mention this, but I've had extremely bad experiences with Jet, but nowhere close to what you've been through. I think you're right in that they threw together a bunch of poorly manufactured parts and slapped a "can't pass this up price" on them and sold them to generate some income at the expense of the consumers. BTW I'm sure they are out there, but I've never seen a metric tapered spindle bore in the US.

Thanks Stan
If this lathe would have been a standard catalog item from Grizzly I think it would have been much better.

And my Jet lathe had many problems as well. Biggest problem is it is a bench. So not rigid for parting operations. I fixed that by bolting it to a 2" thick slab of steel. But I found issues with the headstock bearings not having oil ports drilled from the built in oil sight glass reservoir. the sight glass always showed it was full.

I do have a TPG, I've used it to fix the tail stock quill on this lathe in question. The original quill was machined wrong for a 4MT taper, where it would not seat. As the tang geometry was totally screwed up, and hardened, Grizzly sent me the one off their "parts" lathe. But it was .003 to large for the bore of the tail stock, so I used the TG to machine it to size. Lots of little problems, but so far nothing that prevent accurate work, that was until I found this sloppy sleeve.
My bigger "tool hole" is metrology equipment and surface plate skills (another Enco 2'x3' back when sold with a stand for $200 delivered). This is what I'm working on currently, as fixing this has shown me both a skills and tool deficit.

The TPG I purchased many years ago from Enco, was for a 16" lathe, but I used it on my 10" as that is the size they sold (was on sale at less then $1200). It was made in the old USSR in Czechoslovakia. It has an internal grinding adapter.

So my issue will be getting the right wheel(s) for this, as it only came with one. Darn, another task to unmount the one on the adapter, and measure, and hopefully find metric stones with the right internal and external dimension.

I have a 6x12 surface grinder, and I know that every time I use it, I see I need to learn more about wheels, their hardness for the task at hand, as well their grit size. I just don't do it often enough, and what ever repair I do, seems to work with what I have.

Now I just got to get some time in the shop working this problem. I'm hoping the sleeve is correct, as TPG the spindle hole will let me keep trying to fit it versus a major setup change.

I can understand doing the grinding in one direction. The taper attachment is pushing/pulling on what was the fixed thrust bearing of the telescoping cross feed shaft, and I know there is dead-band in this.