My poor old BD920n

C-Bag said:
Thanks for the complete description. Many folks are one liners and with this kind of thing you cannot trouble shoot their process or help them. I’ve given up trying.

There are just two crucial mistakes. One was not seating the front bearing with a press. And the other super critical one is tough because you almost need the lathe to do it. Machine the back bearing mount to a slip fit. Pressing on the back bearing mean you will never be able to get proper pre load, period. It will either be to loose or to tight. I had to make a rig using my tail stock large live center and my drill press to CAREFULLY take off what turned out to be about .0012. Those couple of tenths are hard but crucial to make a slip fit. On mine the spindle is #3 MT so I bought a good name collet and a 1/2” reamer blank both on eBay.
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So are you saying I need to buy new bearings, or can I get away with re-doing the rear one?
 
It’s totally up to you. But if you used a hammer to get it apart or together for that matter I‘d spin them with no grease to see if they got dinged. I used pullers to get mine apart and kinda reversed the process to install the races. The front bearing I seated with the press and the back bearing slipped on after I re machined the spindle to let the bearing slip on.

I had struggled with horrible chatter and if I was lucky could take a .020 DOC. when I replaced the bearings with I think exactly the same Timken bearings like you and got the spindle straightened out and could actually get the pre load correct I could take a .080 DOC with no chatter and nice finish. Never was able to do that before and no matter what I did my finish sucked.

If you are going to pull it back apart do you have some V blocks or something you can check if the spindle is bent?
 
C-Bag said:
It’s totally up to you. But if you used a hammer to get it apart or together for that matter I‘d spin them with no grease to see if they got dinged. I used pullers to get mine apart and kinda reversed the process to install the races. The front bearing I seated with the press and the back bearing slipped on after I re machined the spindle to let the bearing slip on.

I had struggled with horrible chatter and if I was lucky could take a .020 DOC. when I replaced the bearings with I think exactly the same Timken bearings like you and got the spindle straightened out and could actually get the pre load correct I could take a .080 DOC with no chatter and nice finish. Never was able to do that before and no matter what I did my finish sucked.

If you are going to pull it back apart do you have some V blocks or something you can check if the spindle is bent?
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No. I think I -may- have just figured out at least some of my spindle issues. I'll post some pics and explain when I'm able.
 
JayUSArmy said:
Ok, so on the bearings. I used the ones I found recommended.. Timken 32007 bearings. Not the absolute highest quality money can buy, but from a reputable company as I understood it. I did clean them out as best as I was able prior to greasing and installing.
I used the “Red Tacky” #2 EP grease packed to my best guess of 50%, as recommended in the "Rebuilding the asian 9x20 Lathe" that originated on the yahoo group, though I think I still over packed it because grease has been squeezing out of the bearing guard.

Now, I mentioned my method of installing was likely an issue. To get the front (chuck side) all the way to the end, I had to take a copper (soft) rod against the inner diameter of the bearing and hammer it down bit by bit. This took a lot of patience and many many hours. This was also how I got the bearing races into place on the headstock, as I had already figured out that it was way out of alignment. It also occurs to me NOW that I could probably have rented some kind of puller from the local NAPA autoparts store that would have worked better and with less frustration. How I put on the rear one(both bearings were insanely tight to put on): I basically used the preload nut with a couple washers to apply pressure against the bearing and cranked it down until the nut bottomed out, then took it off and put more spacers against the bearing and repeated the process. The reason I suspect I may have damaged the bearings, is that I might have way over tightened them making sure that the rear bearing was fully seated.

Measuring runout on the lip of the spindle... I don't recall for sure right now (I'm at work), but I -think- it was under half of one thou.

For setting the preload, I basically had already gotten it super tight to where it was really stiff to turn, backed off the tension and let it run for 20-30min to warm up, then tried to follow the procedure in the Rebuilding book that I mentioned:



No matter how loose I set the preload, it wouldn't spin 1.5 times.. even with the spindle loose enough to rattle back and forth, but I think that may be due to having too much grease. It feels nice and smooth now, though, with no movement of the spindle that I can detect.

Thank you for taking the time to comment and give advice, I'll continue to update this thread as I make progress or get stuck.
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Just a few comments. Tony is steering you right; I agree that taking care of the spindle first is the priority.

Spindle bearings are a big deal. If I were you, I would not use standard bearings. Instead, I would at least go with an ABEC3/P6 class bearing like this and match the class in the rear spindle set. Grease only 25-30% of the bearing on installation and keep everything super-clean when you install them.

You should use a press to install the front bearing. If you don't have one, almost any auto repair or machine shop does and will probably do it for free or really cheap. It might even be worth taking the spindle (once you confirm it is straight) to a machine shop and have them turn the rear of the spindle for the slip fit Tony mentioned. At the same time they may be able to press the bearing on for you. Do whatever you have to do to get the bearings installed properly.

The "spin the chuck to adjust preload" is how the Emco factory does it. They do this with the lathe cold; that is, no warm up. If the lathe and bearings are hot and you adjust preload that way then the preload will NOT be right. Remove the belt, slip the lathe into neutral and adjust it cold to get 1 to 1.5 revolutions of the chuck that is spun as hard as you can by hand. As cheesy as this method sounds, this is how an Emco engineer described the process and it works. My Super 11 runs cool and has zero run out at the spindle.

Once you get the spindle sorted, the quickest and easiest way to align the headstock is to turn a piece of 12L14 mild steel that is about 3/4 - 1" OD with about 4" sticking out of the chuck and without tailstock support. You can use a 3jaw for this. Use a sharp, properly ground HSS tool for this and take a 0.010" deep cut all the way down the rod to remove the skin. Then take a 0.003" deep cut to smooth it out, and then take a 0.001-0.002" deep cut and strive for a good finish. Measure the OD at the chuck end, the tail end and the middle. All readings will be the same when the headstock is aligned with the ways. If the readings differ, adjust the headstock and repeat your test cuts until you have the same OD all the way down the rod. It is my belief that test cuts are the most accurate way to do this.

Good luck and listen to Tony.
 
I’m humbled Mike. I’m just a hack that kept trying to fix the problems piecemeal and getting piecemeal results. Not until Savarin and Bi11 and others described how to go through the headstock bearings the right way did I decide to get serious. Early on it would have been nice to have things right but I wasn’t doing critical and precise work and honestly I was buying into the general disdain for my Chinese cheapo copy and not expecting much. I do sometimes wish I would have been able to find better bearings but at the time for whatever reason they were 3x’s what you listed. I paid around $30ea. For my Timken NOS’s.

I am no expert and not presenting myself as such. All I’m doing is regurgitating as accurately as my old gray matter can remember what I learned here and found once applied finally worked. I’m the one a fault for bad spec’s now, not the lathe.
 
C-Bag said:
I’m humbled Mike. I’m just a hack that kept trying to fix the problems piecemeal and getting piecemeal results. Not until Savarin and Bi11 and others described how to go through the headstock bearings the right way did I decide to get serious. Early on it would have been nice to have things right but I wasn’t doing critical and precise work and honestly I was buying into the general disdain for my Chinese cheapo copy and not expecting much. I do sometimes wish I would have been able to find better bearings but at the time for whatever reason they were 3x’s what you listed. I paid around $30ea. For my Timken NOS’s.

I am no expert and not presenting myself as such. All I’m doing is regurgitating as accurately as my old gray matter can remember what I learned here and found once applied finally worked. I’m the one a fault for bad spec’s now, not the lathe.
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What you are doing is giving the OP good information, Tony. Experience counts.

My experience is only with an Emco Compact 8, the lathe upon which most of these 9" lathes are based, but it is not the same. I would defer to you and others like you.
 
Ok, I just bought some better bearings. Once I get them, I'm going to get rent a bearing press and pull the spindle again. I -think- I understand the principal of the v-block check of the spindle for being bent: basically place the blocks on a reference surface, on the ends of the spindle. Put an indicator in the middle and if it's NOT bent, the gauge should read the same as the spindle is rotated around. Am I missing anything? If the spindle is bent, is it a total loss or is there a way to correct it?
 
Yup, you’ve got the idea. if it is bent it is trash IMHO. There is no way I know of to fix it. I think the grizzly G4000 is the same lathe. They are the ones I’ve bought parts for my 9x20 through them. Looks like it’s $150 for a new. Hopefully you won’t have to go that route.
 
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C-Bag said:
Yup, you’ve got the idea. if it is bent it is trash IMHO. There is no way I know of to fix it. I think the grizzly G4000 is the same lathe. They are the ones I’ve bought parts for my 9x20 through them. Looks like it’s $150 for a new. Hopefully you won’t have to go that route.
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Please note I had a brain cloud and put G4003, it’s actually the G4000.
 
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