Head Stock alighment

[leeharrysouth]

Hi all,
I have an 05 eldorado and the headstock is out of alignment with the bed. I need to realign it but not sure what to do about the taperd pins at the base of the headstock. Others have written that they simply removed one and no longer used it or that they drove the original pin in after realignment as far as it would go and thats it. My question is has anyone experianced problems with headstock moveing after alignment without both pens rightly inserted. I have a Jet 36 inch lathe that has no pins and it doesent seem to show any problems with movement. Any help will sure be appreciated.

leeharrysouth

[fastlanecafe]

When I bought my used Quadra lift model, the owner had disassembled it for shipping and for some reason had removed the lathe column casting rather than just the mill head assembly. When I reassembled the machine I aligned the headstock to the cross slide table and then put the pins back in place. I suggest you remove the pins ( mine were threaded so you could put a little bolt in them and use it to pull them out) and loosen the bolts a bit/ Then use a rubber mallet to move the headstock into alignment. Tighten the bolts a bit at a time and re-check after each sequence to be sure the head is not shifting. Once you have the bolts tight and the headstock is aligned, drop the pins back in- if they won't go in, DO NOT drive them in- this will move the headstock. If you have a selection of tapered reamers or can borrow one, just ream the hole and insert the pins. A tack weld at each corner is a quicky, but not so attractive way of doing the same thing. The bolts will probably hold the head in place without the pins as well.

[dgapilot]

You might want to replace the bolts. There have been many reports of the cheap Chinese bolts stretching and not holding torque. As stated above, once in alignment and properly torqued, if the pins don't go in, ream the holes and oversize the pins (if necessary)if there is room.

[dahui]

This brings up an interesting question. I thought my headstock was out of alignment because I get about .002 taper over 1 inch of travel when I turn anything. The diameter is smaller at the headstock end and it is very consistent.

So, I used "rollie's dad's method" to check the alignment. Essentially putting a piece of drill rod in the chuck and taking readings near the headstock and then another reading down the rod about 12 inches. You do some math and the result should give you the ammount of misalignment. After doing my calculations I only had .0005 diference 12 inches apart. I don't think I could move anything and get much closer than that. I also have an 8" wrist pin from a top fuel dragster that is ground to within .0001 down it's entire length. I tried using this as well (even though it was shorter) and got measurements consistent with the drill rod readings.

So the question remains, why am I getting a reverse taper?

I don't mean to hijack so I will also ask how you measured the headstock alignment and if maybe I'm doing something wrong.

[leeharrysouth]

dahui,
I measured my headstock twist in three ways. First I did a fine cut on a piece of cold rolled steal about eight inches long. It showed a taper of about .004 over its entire lenth. Larger at the tail stock end. I did this a few times with consistant results. I then placed a large ream in the foure jaw and ran a dial indicator along its lenth with the cross table. Again, got about the same results. I finally used John strannons (I think thats the name) book and checked things with a piece of drill rod while utilizing a spider at the locknut end of the spindle shaft. All gave about the same results. I showed no problems with headstock tilt using the same proceedures so I dont think there is a problem with the chuck jaw alignment. I cant figure any other cause of this problem than the headstock alignment. I think I will just remove one pin and line things up for a few cuts and see what happens. I dont plan on re-reaming the pin hole. I think I will just leave the pin out. John strannon said he had no pins on his headstock. My Jet lathe is not pined either. My main concern is paint chips when I shift things around. Dont want to throw the tilt off any. Paint just falls off this machine when you look at it.

By the way I have always enjoyed your web page. Noticed that it has not been updated for a long time. Do your still work with your shoptast or have you moved on to other machines.

Leeharrysouth

[HuFlungDung]

I cringe every time I read of guys re-aligning their headstocks. It is almost as though the factories are run by such imbeciles that they can do everything except dowel the headstock properly onto the ways.

The assumption of the newbie is that the lathe bed is an immutable frame of reference, as though nothing could possibly affect that massive casting. Well, that is not so. The lathe bed is easily twisted like a licorice twist. It is up to you to untwist it when you set it up. Commonly the lathe position is roughed in with a precision level at two extreme ends of the bed. This gets you in the ballpark.

The final test is the free running mandrel held in the spindle taper or chuck. Now, it is seldom possible to find a perfectly straight shaft 12" long, or if you do have one, to find a chuck that will accurately hold it concentric with the spindle axis. A bit of wobble could skew your analysis if you are not careful.

So typically, one must first ascertain the condition of the chuck. Place a piece of precision ground round in the chuck, and run a dial test indicator on it. Grab the piece or apply leverage to it to deflect it with moderate pressure. If the chuck jaws are in good condition, the piece will consistently spring back to the start reading. If you apply leverage and the piece moves and stays moved, then the chuck jaws are tapered, and gripping (most likely) on the back and looser on the front. I'm assuming that the chuck has been properly mounted and is secure on the spindle nose.

Because the lathe is not yet set up, you don't want to grind the jaws yet. So you have to figure a way to ensure 6 point contact (if using a 3 jaw chuck) of the shaft in the chuck. One way is to use a couple of rings of soft copper wire between the jaws and the test bar. For example, you could strip the insulation off of some solid 14-2 or 12-2 house wire and use that. Form a ring long enough to go round the mandrel. Position one ring in a jaw serration near the back end of the jaw, and the other in a jaw serration near the front of the jaw. Using the jaw serrations makes it easier to hold the wire, but is not a pre-requiste. When you clamp down on the test mandrel, the soft copper will yield, and hopefully, squash enough to actually get 6 points of contact on the test mandrel.

Now the test mandrel can be cut. I would probably use a piece of 1.5" or larger stock, and maybe 6 to 8" long in front of the jaws, and undercut an area, leaving two raised areas on the test bar, about 1/2" wide, one area right at the outermost end, the other right near the jaws. Now, get a sharp finishing tool and take a very light cut on both areas of the test mandrel without permitting any movement of the cross slide or compound. That means you should have already checked the gibs for snug fit in both these areas before the test cut.

Now, using a screw micrometer and not a digital caliper, measure the smoothly turned test areas. If you can't turn the surfaces smooth, then you don't know enough about tool grinding, and you'll need to pause, and go study up

The difference in diameters will reflect the true state of the lathe bed. If the outermost test area is larger than the area nearest the chuck, then the lathe bed is twisted, it is low at the tailstock end, on the operator's side of the machine. Adjust the foot screw or shim that corner of the bed. This is a delicate adjustment, so a screw adjuster is highly recommended.

How much to adjust? It would be proportional to distance. If the lathe bed is 10 times longer than the distance between your test cut areas, then a .002 measured difference might be .010 to .020" elevation of the foot screw. Write down what you did in your adjustment, and take another test cut. Even a newbie should be able to get pretty close in half a dozen trial cuts. The trial cuts are only .002" deep, you don't want to create excessive deflection during the test cuts which will fool you.

The ultimate test is boring a cylinder. While most guys can fiddle and fudge with files and sandpaper on the outside of a piece to bring it in spec, it is a lot of trouble to polish a bore straight and true, . If you bore a hole about 4" deep in a 4" diameter heavy wall pipe, and measure the inside diameter at both ends (with the piece still chucked), and get the same results, the lathe setup is good. Unfortunately, most newbies cannnot accurately measure an ID, but again, using an ID indicator, you should be able to detect taper. Set the dial tip at centerline height, and run it along the back side of the bored hole. Testing in this area will show double the actual alignment error of the lathe bed.

So small errors in taper can be easily corrected by proper adjustment of those ordinary looking screws on the feet of your lathe. Leave the dowel pins in the headstock alone.

Now, you're ready to do the tailstock alignment tests. Do NOT adjust the levelling screws of the lathe bed for tailstock problems. Adjust the push-pull screws in the base of the tailstock itself.

[smallblock]

Bed twist would be pretty hard on one of those machines, unless the machine was bolted to a very solid table that was not flat. People complain about various issues such as soft fasteners etc., but the castings on these things are really thick. On my old 17-20 model, I pulled it all apart and re-painted it, and the base casting weighed in at about 150#- almost as much as my Atlas lathe completely assembled.

[leeharrysouth]

Huflungdung's input is very much appreciated. Allot of good input. I understand that without a level bed no other adjustments should be attempted. I also agree that a bed of this size and weight will twist. Even if it is short in lenth. After reading this I am going to go back and recheck my bed with a precision level. I dont agree with the asumption that these machines always come from the factory with a well aligned headstock. I have known and read of too many people with asian machines that did have to align there headstock. All said, I did level my bed as well as possible. It is not perfect, but, within a few degrees all around. I leveled the table as close as possible with its screw adjusters and then shimed the bed until all was as close as possible for me. I guess screw adjusters could be installed under the bed, but,, it would be a fair job considering that the lathe would have to be lifter off the table. One must also consider the fact that the table supplied with the machine is not that sturdy itself. I reinforced my table with side and back plates to stiffen things up and it did help allot. So, my question is that with the machine leveled as close as possible (that is possible for me) and with a good chuck should the headstock be the next logical step? The bed is certainly a good argument and something to look very hard at.

leeharrysouth

[HuFlungDung]

All I'm suggesting is that you don't be paranoid about levelling the bed if a slight adjustment of the levelling screw will fix the problem.

I've had 7 lathes, from a 15" Clausing, to a 28" Hungarian lathe with a 8000lb bed and a couple of CNCs and never suspected that the headstock was misaligned. I simple level them, then do the test cuts as described and fine tune the adjustment.

A CNC could get hammered hard enough in a crash that it will move the headstock, so I'm told they have ready provision for making adjustments should the need arise. Manual lathes, not so much.

Yes, I've read of hundreds of guys 'fixing their headstock alignment' with all sorts of makeshift ideas. If you've got one of these 'adjusted specials', you might have to 'put it back to factory' so that you can check what was really the matter.

When you understand what you are doing, and how sensitive the lathe bed is to twist, you won't question what I said to do. It would have to be a really gross error before I would even question the headstock alignment.

Little beknownst to the newbie, there are plenty of reasons that you might see taper on the work, and none of them have to do with how straight the lathe is. There is differential flexure of the part, tool wear, chucking misalignment, tailstock alignment and workpiece and tool length expansion from heat that all work against you.

Once you get it set close as per the above instructions, then work with it a while and think about trends in how the machine is performing. If it bores a straight hole, but turns taper between centers, then don't mess with the levelling screws.

[leeharrysouth]

Ok. I am open to any suggestion that will save work and re-work. So, I am going to approch this agian from the start. Not now (too many other projects going on)but, in the future. I will recheck the bed and get it as close to zero bubble on the level as I can. Once that is achieved I will set the chuck with copper wire, place a piece of 1.5 dia. crs about ten inches long and take a cut. Now, lets say that I am still out in taper. Do you recommend that I shim the bed to correct this taper even if that throws the previous level off. In other words the lathe may cut straight, but, the bed is off a minor amount to make it cut straight?

Thanks, leeharrysouth

[HuFlungDung]

Yes, the levelling is only a beginning point. You can hope that the casting was relaxed and sitting flat on four points at the factory, but there is no guarantee that it was, or that it has not sprung a little since, due to stress changes as the casting ages. If they poured it a week ago and its on your workbench today, it may drift a bit.

But the original straightness of the bed sitting on the grinder is what you want to restore. Maybe they shimmed it, the machinist was too tired to fix it, so he let it go. You just don't know So when he unclamped it, it sprung back and wouldn't be truly level in its relaxed state.

Your concern is how it performs for you, rather than some ideal of perfect levelness. Perhaps a used machine, slightly worn, might gain a bit more useful life by purposely tweaking the levelling screws to put it back straight in the area in which it gets used the most.

Nobody I know uses an engine style lathe to turn long straight cylinders as long as the lathe bed. They use cylindrical grinders and rests to do that. So if your lathe will turn straight cylinders about 4 to 6 inches long in any one setting, that is really all you need to achieve because most of your parts will likely have different diameters over lengths greater than those.

[leeharrysouth]

Thanks, Ill give it a go.

leeharrysouth