Jet mini lathe alignment issues

[ebrannon]

I recently arrived at my winter quarters with my Jet mini lathe. I noticed that the tailstock does not align exactly, and when I tried to drill a hole, it made a larger whole than the bit, so it must be out of alignment. ( I did the Al Hockenbury test of seeing if the tailstock made a circle on a piece, and it does).

I have been seeing if the subject has been covered already, but only found a few suggestions on testing alignment.

Any of you with Jet Mini lathes have any suggestions? Mine is way out of warrantee.

Ed

ps- as a side note, I have replaced the bearings in this lathe 2 times. I now notice that when I use the tail stock on a longer piece (say 12"), their is a slight rumbling noise. Wondering if this the reason the bearing keep going out.

 

[Bill Boehme]

The sound could be an indicator that the bearings are worn out. More likely though the rumbling sound is an indicator that there is excessive axial play in the spindle.

First, brinelling is what usually makes bearings wear out on woodturning lathes in my opinion. If you are using too much tailstock pressure, that will cause the bearings to wear out early. "Too much" tailstock pressure means anything more than light to moderate pressure. If you are trying to "seat" a spur drive with tailstock pressure then you have gone way too far. When you installed the new headstock bearings, did you check the axial play and apply a very light preload? Since you have replaced bearings previously, you are familiar with the procedure for removing the handwheel. When reinstalling, apply just enough preload to take out the axial play while still being able to spin the spindle without any significant amount of friction increase from the unloaded condition. After some wearing in, it may be necessary to increase the preload.

 

[john lucas]

The first thing I would do is check to see if the headstock is on solid and aligned with the tailstock. I can't remember right now how the headstock is installed on that lathe but if it has screws I would loosen all of them and see if it shifts any. If it does pull up the tailstock and align it and tighten them back down. If it isn't installed this way then ignore what I just said. 🙂

 

[Wayne Spence]

Align the tailstock with the tailstock spindle retracted and then check the alignment with the spindle extended at least 3/4 of its length. This may be what BB refers to as axial play.
I too have replaced the bearings on my jet mini twice with no change in the alignment. The first time the bearings had to be changed because someone (not me but a family member) tried to drive out the spindle with the set screw fully engaged. No I did not shoot them but I thought about it.

 

[Fred Belknap]

Make sure it is solid and level before doing to much. I'm not familiar with smaller lathes but on larger lathes it will cause a misalignment between the head stock and the tail stock.

 

[Bill Boehme]

The first thing I would do is check to see if the headstock is on solid and aligned with the tailstock. I can't remember right now how the headstock is installed on that lathe but if it has screws I would loosen all of them and see if it shifts any. If it does pull up the tailstock and align it and tighten them back down. If it isn't installed this way then ignore what I just said. 🙂

It has four hex head cap screws and I believe that it also has alignment pins so there is no wiggle room.

Align the tailstock with the tailstock spindle retracted and then check the alignment with the spindle extended at least 3/4 of its length. This may be what BB refers to as axial play.
I too have replaced the bearings on my jet mini twice with no change in the alignment. The first time the bearings had to be changed because someone (not me but a family member) tried to drive out the spindle with the set screw fully engaged. No I did not shoot them but I thought about it.

Congratulations on showing great restraint. 😀 If it is a family member then no crime would have been committed -- at least not in Texas.

I was referring to the headstock spindle and not the tailstock quill. Axial play is free play along the spin axis as opposed to free play crosswise which would be called radial play. What I meant was that the spindle could have slight looseness along the spin axis such that it could be moved in and out of the headstock by a few thousandths of an inch -- not necessarily enough to see, but enough to feel or hear. When the handwheel is installed, it needs to be tightened enough to take up the slack, but not so tight that it adds unnecessary friction.

Make sure it is solid and level before doing to much. I'm not familiar with smaller lathes but on larger lathes it will cause a misalignment between the head stock and the tail stock.

The Jet and most other mini lathes like it are very solid, but it is still a good idea to follow your suggestion for a host of other good reasons. Trying to do anything when whatever you are working on is not well supported and wobbling is a pain.

 

[ebrannon]

fixed

I removed the head stock and gave it a cleaning and re installed. I found it had just enough movement to allow me to bring the alignment back to center without having to shim. I made sure the spindle was property tightened so their was no play and not too much pressure.

I did not realize you could over tighten from the tail stock quill. The clamp block on the bottom is not the stock block, but rather a larger square aftermarket piece that gives more surface area and bite, so I possibly I be over tightening. Also, I am not sure the bearings are super high quality on these small lathes.

Thanks for the good advice. Back at it today.

 

[MichaelMouse]

I removed the head stock and gave it a cleaning and re installed. I found it had just enough movement to allow me to bring the alignment back to center without having to shim. I made sure the spindle was property tightened so their was no play and not too much pressure.

Let's think. Rumbling, two sets of bearings replaced, drive not aligned with the tail. Sounds like you had an axial alignment problem, alright. When you align, it's not just the points from drive and live meeting, it's whether the axis through the entire spindle aligns with the axis through the tail. If it doesn't, and you tighten the tail heavily, it'll lead to the problems you've been having, for sure.

Wondering why the headstock doesn't wedge to align firmly with the ways, so that only the tail needs messing. Shouldn't be that difficult to engineer.

 

[Bill Boehme]

That's right, MM, and it is not a trivial matter to measure or correct since it involves more than just angular correction, but also lateral and vertical adjustment. I haven't tried this, but a length of drill rod that fits snugly all the way through headstock and tailstock without binding might work. You would know that everything is in perfect alignment when the tailstock can be moved from one end to the otherwithout binding.

Sometimes we get overly concerned about alignment. For turning between centers, it is not really important.

 

[MichaelMouse]

That's right, MM, and it is not a trivial matter to measure or correct since it involves more than just angular correction, but also lateral and vertical adjustment. I haven't tried this, but a length of drill rod that fits snugly all the way through headstock and tailstock without binding might work. You would know that everything is in perfect alignment when the tailstock can be moved from one end to the otherwithout binding.

Sometimes we get overly concerned about alignment. For turning between centers, it is not really important.

They make the double MT, which will do the same from half-way through. To preserve alignment on my tailstock I dimpled the metal so I wouldn't have to glue a shim.

Worth the effort, even though things will spin between points, because loading the bearings off-axis is a killer.

 

[Bill Boehme]

I didn't want to mention the double ended MT because alignment tolerances would need to be on the order of .0005 inches for a good fitting at both ends. No woodturning lathe can meet that sort of precision unless somebody has spent a lot of serious time fine tuning things. I would guess that most woodturning lathes would be considered doing well at a couple orders of magnitude less precise. It would not be doing your lathe sockets in the spindle and tailstock any favors to try forcing them together with this unnatural double ended beast as a starting point for getting everything aligned.

 

[MichaelMouse]

Fortunately most people don't "force" precision. They creep up on it gently. Well, except SWMBO who's the archetype for the "bigger hammer" school.

 

[john lucas]

I don't know Bill, It would take a 3/8" rod to go through the heastock and tailstock and it will have quite a bit of flex as you move out. I don't think that would work. Good idea though.

 

[Bill Boehme]

I don't know Bill, It would take a 3/8" rod to go through the heastock and tailstock and it will have quite a bit of flex as you move out. I don't think that would work. Good idea though.

I was thinking about something like hardened drill rod and making sure that it floats freely all the way through, but I have not actually tried it. On my lathes the alignment appears to be pretty good. I have a Crown lamp auger that is 3/8" diameter. I have a stub hollow Morse taper insert that I modified with holes on the side to clear chips that helps to give a close clearance hole at both ends of the tailstock. I should also get another one for the spindle MT socket so that I would have four close clearance holes for the rod. This would be the real acid test for quasi-perfect alignment.

I am in a funk that my slick new Robust doesn't have a hole in the handwheel that is large enough for a lamp auger -- it appears to be about 1/4 inch diameter. I guess that I'll have to replace it with a Delta midi 🙄 ( just kidding)

MM, I don't know how many folks are of the "bigger hammer" persuasion, but I do know that an overwhelming majority of those who want to borrow my tools because their <enter name of tool here> is broken fall into that category.

 

[john lucas]

For interest sake when I go to the shop this morning I'm going to try your technique. I have a lamp auger but also think I have some drill rod unless I've already cut it up to make tools. I can't remember if my new Delta 46-460 has a 3/8" hole or something smaller through the headstock. I guess I'll find out.
I do have 3/8" collets with #2 morse taper. I could install one of those. I can put an indicator on to see how much it sags.

 

[Bill Boehme]

For interest sake when I go to the shop this morning I'm going to try your technique. I have a lamp auger but also think I have some drill rod unless I've already cut it up to make tools. I can't remember if my new Delta 46-460 has a 3/8" hole or something smaller through the headstock. I guess I'll find out.
I do have 3/8" collets with #2 morse taper. I could install one of those. I can put an indicator on to see how much it sags.

OK, but don't forget that it is not a cantilevered rod since it is supported at both ends. Any sag would be in the center, but straightness of the rod and deviation from flatness of the lathe bed are liable to obscure what you actually want to measure.

Here is a link to a PDF table of beam deflection formulae.