I have a question about lathe alignment

[Tozguy]

I'm writing this from my sick bed. It seems I have a lot of time to think right now.
I have always had about .004" to .006" taper over a 6" long cut. I have leveled my lathe but I have a theory why it may not stay level. This is a South Bend 9" lathe. It is mounted on a nice shop built steel cabinet bench with a top made of .125" steel. Where I think the problem may be is, this lathe is in a shed beside my home. The floor is 3/4" particle board sub-flooring on 2 X 8 joists 8 ft long. With the heavy machines, this floor has some give or "bounce". If I lift one corner of the lathe bench even .050" it throws the level out. I don't believe it is possible to keep things level on this floor. Now to my question. The lathe only need to be level to itself ( not the world. They put them on ships in a shop and the ship is not always level to the earth). Short of rebuilding the shop, I am wondering if placing a 40" X 20" steel plate 1/2" or thicker on the bench top and then mounting the lathe on the plate if that would help solve the problem of constant changing of the leveling. The lathe could be aligned to the very stiff plate and remain constant. Am I way out in left field in this thinking?

Mark, I think that you are on the right track by wanting to build a 'boat' under the lathe. However a 1/2'' solid steel plate would not be as stable as a 2'' laminated wood base. I would look at some heavy plywood (maybe the furniture making guys here could guide us as to choice of plywood) laminated to 2'' thick using epoxy. Then if the 'boat' needs to be moored to what is below it then a three point connection would be all I would use (like for surface plates). That way the cabinet and floor are free to twist and warp without stressing the lathe.

Once the lathe is aligned in all its parts there wood be (pun intended) nothing to upset it.

Trying to reinforce the floor is akin to trying to freeze the ocean so I would not go that route.

I hope you are getting well and will be back in your shop soon.

 

[kvt]

Yes machines on ships etc are not always level with the ground/water etc. But the mounting platform is always solid. Thus They do not really move on them. Then level the lathe to the mounting platform. I.e. If the platform such as a garage floor is on a 5 degree slop, then I would ensure that whatever I mounted my lathe to was also at the 5 degree or leveled to level, Then mount the lathe and level to that to the platform. As long as the lathe is leveled to the solid object. Then the it is level or at least that is what I have seen/read in some things. As I was doing a lot of research when I got my first 10" lathe. and it seems to work out. that way.
Also if what you are saying that you line the head stock and tail stock up when close then you move the tail stock farther away and it is off and the more you move it the worse it gets. Then there are two possibilities. One would be bed twist, but normally do not see it being that much out of alignment, The second one would be the head stock is out of alignment

That is just my 2 cents as I am also fairly new at this. I though I was very lucky after doing one shimming and getting this results over 9.5 inches Here is both ends.

 

[Technical Ted]

I used a machinist level to level the cabinet on the floor ( I know that is probably useless). I then leveled the bed on the cabinet and still cut a taper ( around .003" over 5 inches. That along with the tail stock lines up at the spindle but not at the other end of the bed is what made me think the head stock may be off.

I agree with the others and you that your foundation isn't ideal, but it sounds like you've got more issues than just your floor. When you say the tail stock is off at the other end, is it off horizontally, vertically, or both? Both would indicate a bed twist. Vertically would indicate bed wear or a head stock pointing up or down, etc.....

I don't know about your 9" SB, but on my 15" SB the head stock is aligned to the bed by one of the V ways so you would think as long as it was assembled when clean and free of burrs it should be aligned. But, also look at it this way... it's your spindle that needs to be aligned, not necessarily your head stock, so has someone disassembled/replace the head stock bearings? Are they worn and out of alignment with the head stock? If someone home brewed some replacement head stock bearings at some point, it's possible they are off.

Just throwing ideas out there in an attempt to help,
Ted

 

[Mark_f]

Mark, I think that you are on the right track by wanting to build a 'boat' under the lathe. However a 1/2'' solid steel plate would not be as stable as a 2'' laminated wood base. I would look at some heavy plywood (maybe the furniture making guys here could guide us as to choice of plywood) laminated to 2'' thick using epoxy. Then if the 'boat' needs to be moored to what is below it then a three point connection would be all I would use (like for surface plates). That way the cabinet and floor are free to twist and warp without stressing the lathe.

Once the lathe is aligned in all its parts there wood be (pun intended) nothing to upset it.

Trying to reinforce the floor is akin to trying to freeze the ocean so I would not go that route.

I hope you are getting well and will be back in your shop soon.

I agree with the others and you that your foundation isn't ideal, but it sounds like you've got more issues than just your floor. When you say the tail stock is off at the other end, is it off horizontally, vertically, or both? Both would indicate a bed twist. Vertically would indicate bed wear or a head stock pointing up or down, etc.....

I don't know about your 9" SB, but on my 15" SB the head stock is aligned to the bed by one of the V ways so you would think as long as it was assembled when clean and free of burrs it should be aligned. But, also look at it this way... it's your spindle that needs to be aligned, not necessarily your head stock, so has someone disassembled/replace the head stock bearings? Are they worn and out of alignment with the head stock? If someone home brewed some replacement head stock bearings at some point, it's possible they are off.

Just throwing ideas out there in an attempt to help,
Ted

Thank you all for all the good information. Rebuilding / re-enforcing the floor is not an option as I would have to tear down the building to do it. But I like the idea of setting a thick wooden base under the lathe and leveling to that.

When I said the tail stock was off the farther out it goes, it is off horizontally. The headstock does set on a V way. I know the history of the lathe and it is all original and has never been rebuilt or torn down. I think I remember checking the headstock clamps on the bottom once and they were not really tight and I tightened them some. Maybe there is some small crap (technical term) got under it.

When I am better, I think I will get a wood top 1 1/2" to 2" thick and put the lathe on it. I also think I will lift the headstock and clean under it and put it back on and then see what I have. I have done the bearing test ( prying up ) and it is good. This taper is the only problem I have ever had with this lathe. When I leveled it, I never noticed any bed twist. The previous owners ( father and then son) are not skilled enough to have even noticed this problem. They used it very lightly and owned it most of its existence.

Before I do all this, I was thinking about putting a 3MT test bar in the spindle and using an indicator, check the top for level with the bed and the side for straightness with the bed. If you all think this is a good check, I can order a test bar.

Thank you all for your ideas and responses. You have been very helpful.

 

[kvt]

Test bar will help and can also be used between centers, to help with tail stock alignment as well.
one of the things I was thinking of is put a solid piece under table, legs or what ever you lathe is on. Jut to make sure it does not try to sink into or through the Partical board at some point. Will also help control the movement from the floor xfer to the lathe. Just something I was thinking about As wife is thinking maybe I should get a building for our backyard to put my stuff in.

 

[Mark_f]

Test bar will help and can also be used between centers, to help with tail stock alignment as well.
one of the things I was thinking of is put a solid piece under table, legs or what ever you lathe is on. Jut to make sure it does not try to sink into or through the Partical board at some point. Will also help control the movement from the floor xfer to the lathe. Just something I was thinking about As wife is thinking maybe I should get a building for our backyard to put my stuff in.

You pose an interesting question. Would it be just as effective to put a thick wood pad between the cabinet and floor as to put the wood pad between the cabinet and lathe?

 

[Technical Ted]

You pose an interesting question. Would it be just as effective to put a thick wood pad between the cabinet and floor as to put the wood pad between the cabinet and lathe?

Personally, I think I would want it as close to the lathe as possible to eliminate all the variable movement that might happen in the cabinet, etc.. But, either way would be better than what you have now.

A test bar is a handy thing to have. I made one for my lathe. Yes, they are great for aligning the tail stock and also for checking to verify the lathe is level and there is no bed twist.

Since you know your tail stock is off, if I were to use it on your lathe to check things, I think I would put the end of it in a four jaw chuck using some aluminum or copper pieces between it and the jaws so I could easily indicate both ends while holding on to it with enough force to keep it aligned. So, if you have a 12" test bar, indicated dead on, on both the chuck and far end, you will have something running concentric with your spindle. From there, you can set up a surface gauge base (or whatever) and a test indicator and run the base along the edge of your V ways and indicate on the test bar to check for alignment of your ways to head stock that way. You may have to stone off any burrs or high spots on your ways to get a good reading. In your case, you are looking for thousands not tenth's of a thousands (since your taper is so bad) and this might prove to be a quick check to help locate the problem. Also, as mentioned previously, the bed has to be level to remove all twist before using this technique.

I would also suggest you log (write down in detail) all of the test and results as you make tests on a pad or in a notebook. Accurate data and a systematic approach is the best way to track problems like this down. I can't rely on my memory when doing a lot of troubleshooting like this! So setup, measure, log the results and soon you will be able to put two and two together and determine the issue(s) that is causing this taper.

Good luck,
Ted

 

[Glenn Brooks]

Mark, it seems nobody is willing to comment on your question about headstock misalignment. I've been chasing a similar problem with taper on my old 12" Utilathe, and found some relief by adjusting torque on the four headstock bolts. Also discovered the headstock has been shimmed at some point in the past. Further, doing reasearch on this on a rebuilders forum, I discovered some comments that suggest that headstock bolt torque does indeed affect taper. Which makes sense if you consider drawing the right front edge of the spindle down and away from the lathes true centerline will certainly create a taper in long work.

Can't hurt to experiment with removing the headstock and looking for debris bits underneath, then remounting. Or alternatively, just loosen the appropriate bolts and take a series of cuts to see if you can improve the situation.

Glenn

 

[Tozguy]

You pose an interesting question. Would it be just as effective to put a thick wood pad between the cabinet and floor as to put the wood pad between the cabinet and lathe?

I too feel that it is better directly under the lathe. Bear in mind that it should be an 'engineered' wood slab that is stable and rigid. It was not under a lathe but I have used 18 ply birch plywood that you could almost use for a pool table.

Re the taper, once you have the base sorted, I would not assume that anything is aligned and take the time to check and clean everything. Follow recommended alignment procedures in the proper sequence.

 

[woodchucker]

I would get some 2x4 or (4x4 preferred) , and put them on the floor running perpendicular to the joists. Extend it to one joist past your table in both directions, then put the table on those. Obviously you will need to put cross bars between them to stabilize them (if using 2x4). This will support the lathe on more than just the OSB, which has lots of give, now you are supporting on multiple joists. That's all I think you need to remove most of the floors flexibility.
After mounting it, give it about 2 weeks to settle. before leveling everything. I would makes some really nice clean cuts on the ends, seal the ends with epoxy, then seal the whole thing with ZINSSER BIN PRIMER which is shellac based and will help to prevent moisture from changing the wood drastically from humidity. It will still change, but not much given the 3.5 " cross section that a 4x4 is.