Sheldon Sebastian 13" Gear Head Headstock Issue

[4GSR]

I thought about this a little more. The front bearing issue is not from an improperly fitted cup. This is from a bearing running loose over time. When I say loose, it may have only been a half thousandth to a couple of thousandths loose, hard to say. There is a fine line on adjusting this bearing arrangement. Always start off with the adjustment tight. Not so tight the spindle does not turn easily. Run the spindle as a medium RPM say 350-375 for this lathe. When the bearing housings get warm to touch, back off the adjustment about a 1/8 of a turn. Run again and see if the temperature goes down a little. This is where a digital thermometer can be helpful. If it goes down a little, and it should, Takes some cuts and see how it does.
You want the bearings adjusted to where is -0- zero running clearance in the bearings. Trying to adjust using a .0001" dial indicator is not going to work. May help in determining of the bearings are loose, but that's about it. Ken

 

[4GSR]

Running the spindle in the 600 or 900 RPM range is not going to help you any, in adjusting the bearings, since it runs hot (100-160 deg. F) in these ranges anyways in normal use on this lathe. Another inherited issue with this lathe. After about 40 hours of running, if still hot when running in the 350-375 RPM range, back off the spindle nut another 1/8 of an turn. And run another 40 hours. If no change in temperature, it should be good. Next is watching the cutting pattern in your work. Of course, the lines you are getting are not going to go away until you rework the saddle to the bed ways. Okay? What you want to look for is linear lines in the work piece. This will either relate to gear teeth or the rollers in the bearings. Hopefully, neither of these will show up. Ken

 

[Jahue]

I assumed the same thing, however the patten is perfectly uniform no matter where on the bed the tool is cutting. If I move the saddle out and use my big boring bar the lines show on the inside. If I cut near the end on a very long bar they show. And the pattern is exactly the same the entire length of cut. Wear in the saddle would change the pattern, given that the machine would not have worn consistently. So the pattern showing absolutely uniform over the entire length means it can't be wear in the ways. The pattern also shows up if I hand feed the saddle and put the feed in neutral taking out the apron worm gear entirely. I have also adjusted all the gibs. I know the ways are worn, because the machine is noticeably tighter near the far end. But I still get the pattern there.

 

[4GSR]

It's in your saddle. It starting to have enough wear that it is riding high on top of the ways instead on the vee as it should. If you have a mill, go in and mill the relief at the bottom of the vee a little deeper and maybe a few thousandths wider, too. Next look for the ridges that are starting to show up on the edges of the vee's and flat. Take a flat file and carefully file them flush with the adjacent surfaces. Then lightly hone the surfaces to get rid of any high spots missed. Go back together and try some cuts and see if you get better results. Ultimately, this needs to be rescraped and fitted. Since you said the bed has some wear, this would be a waste of time to try to rescrape and fit without regrinding the bed.

As I've said many time over, your spindle bearings are fine for now. Spindle bearing like the tapered roller type when worn or damage from excessive use create a whole different set of issues that show up on your work piece. And I don't see that in the posted pictures.

Ken

 

[Jahue]

I will check it, however the other machine I have which is identical has a crap ton more wear and abuse on in, and it doesn't show the same thing. It cuts beautifully. I still wouldn't think that wear in the saddle would produce a perfectly uniform pattern in the work down the entirety of the bed.

 

[4GSR]

Check it out and let us know what you find. Also check the leadscrew and see if it is bent. It could be lifting the carriage a tenth or two causing the lines in the work. The worm in the apron that rotates off of the lead screw could be causing some funny things that show up on the work piece rather its feeding or not. It could be moving the carriage around. Just have to go down a list and mark off things that you check.

Is your other lathe a Sheldon Sebastian Lathe, too?

 

[Jahue]

I went back and checked the saddle, I haven't fully pulled the saddle but looking from both ends there appears to be about .002" of v in the saddle before relief groove. I also checked against the tailstock flat to see how much drop there is in the ways between the tight section and the section near the headstock. over the 24-28" near the head stock the ways drop maybe .0005 once you get to the tight section near the far end the drop.. or rise from the front is about .003" So near the headstock it is lower but its consistently lower. I checked this by putting a mag bas on the saddle and indicating off the tailstock flat.

 

[Jahue]

Yes the other lathe is exactly the same, oddly enough the serial numbers are only about 75 apart.

 

[4GSR]

Okay. Pull the lead screw and put up in your other lathe and see how bad of runout you get.

I know you posted over on PM, I watch over on that forum, too. You received some good responses from over there, too. Keep at it. You'll get to the root of the problem some day. If not, sell it, buy something else and move on. Ken

 

[Jahue]

A partial update, the other machine I have access to is A-6 the one i'm working on is an A-5 identical except for the length. So I can't pull the leadscrew and swap them. But I have attempted to run some other diagnostics. The pattern shows up in all chucks new Bison 3 Jaw, Buck 6 Jaw, and 4 jaw. I haven't checked the 4 jaw this go around but I have in my previous tests. Yesterday I put a long bar in on the machine and maxed out the distance I used a high precision live center. On the end closest (last 1inch) to the live center the pattern appears to go away, as the tool cuts the pattern appears about 1.5-2" from the far end and is present the remaining distance. I checked a few things late last night but they seem inconclusive thus far. I pulled the support block for the leadscrew and with my hand at the lower speed held the leadscrew to keep it from whipping and made a cut near the headstock mostly to see if the leadscrew was in a bind. The pattern was still visible. I also tried the threading lever... still there. I then pulled the leadscrew completely and hand feed the best I could at a constant speed... and it seems to go away, I won't say yet that its gone, its hard to be consistent when hand feeding the apron. I'm going to try and rig up a small motor to see if I can drive it without the leadscrew more constantly.

It's worth noting that I also quickly indicated the leadscrew near the gearbox and it runs out about .003, without the support on the other end, the other end runs out enough to see by eye. I did check the leadscrew with a very high end level (the straightest surface I could find) and it appears to be straight, even by eye it doesnt seem to be bent... I also did the roll test and it has no discernible wobble.

My bigger question is, can I detect with a .0001 indicator the wobble in the saddle if I measure off the ways? Or is there a way to isolate and narrow it down to either the spindle or the saddle?