Lathe not turning true

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Angela S

Member
Joined
Jun 26, 2019
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182
Location
Seattle
Hello,

I recently purchased my first lathe. It is a Turncrafter Commander 10 in. Variable Speed Midi Lathe. The lathe is not turning true. If I put the spur center in the head stock and the live center in the tail stock, the spur center point rotates around the live center point. I do not know how to fix this and any suggestions would be greatly appreciated.
 
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Sounds like an alignment problem - something discussed on another post this week.

Start by putting your spur drive in the headstock and the 60deg cone live center in the tail stock. Extend the tailstock quill as far as it will go, and then bring the tailstock up so that the two points are close together. The two points should just touch each other, but it is possible, and even likely, that there will be some mismatch. These lathes come in two boxes, and you have to install the headstock onto the body of the lathe/bedways, and it is very common for the initial installation to not be properly aligned.

Look carefully at where they come together. If they are aligned vertically, but out of alignment horizontally, its an easy fix. Use the appropriate allen wrench that came with the lathe to loosen the four socket-head screws that attach the headstock to the bedways - loosen them just enough that you can gently rotate the headstock to align the point of the spur drive with the point of the live center, and then retighten the screws.

It is also possible for the misalignment to be in the vertical plane. That's the worst-case scenario and its harder to fix. If the point of the spur drive is too low, you can loosen the four screws as described above, add shims under the headstock, and then tighten them back down. However, if the point of the spur drive is too high, then the problem is with the machining. In that case, my suggestion would be to get on the phone with Penn State customer service (call them on the phone - that works far better than using e-mail) to discuss returning the lathe for a replacement.
 
Did you have the tailstock quill locked?
Are the Morse taper receivers and the centers clean in both the head and tail stocks before you insert the centers?

If yes to both, then some adjustment may be needed. How large is the "orbit" of the spur center tip around the live center tip?
 
monophoto said:
Sounds like an alignment problem - something discussed on another post this week.

Start by putting your spur drive in the headstock and the 60deg cone live center in the tail stock. Extend the tailstock quill as far as it will go, and then bring the tailstock up so that the two points are close together. The two points should just touch each other, but it is possible, and even likely, that there will be some mismatch. These lathes come in two boxes, and you have to install the headstock onto the body of the lathe/bedways, and it is very common for the initial installation to not be properly aligned.

Look carefully at where they come together. If they are aligned vertically, but out of alignment horizontally, its an easy fix. Use the appropriate allen wrench that came with the lathe to loosen the four socket-head screws that attach the headstock to the bedways - loosen them just enough that you can gently rotate the headstock to align the point of the spur drive with the point of the live center, and then retighten the screws.

It is also possible for the misalignment to be in the vertical plane. That's the worst-case scenario and its harder to fix. If the point of the spur drive is too low, you can loosen the four screws as described above, add shims under the headstock, and then tighten them back down. However, if the point of the spur drive is too high, then the problem is with the machining. In that case, my suggestion would be to get on the phone with Penn State customer service (call them on the phone - that works far better than using e-mail) to discuss returning the lathe for a replacement.
Click to expand...

My tail stock has a little give to the left and right. So, I can move it to meet up with the spur center.
 
Thank you for the ideas so far. I am not sure I explained the main issue well. When I have a pen mandrel in the head stock, the end of the pen mandrel moves up and down significantly. I thought my mandrel was bent, I purchased a new mandrel and it still moves. I use a mandrel saver when turning pens and this reduces the issue some, but I still get a slight center on the end furthest from the head stock.
 
What you described, the tip of the spur centre scribing a circle around the dead centre is as Gary said, a bad centre (very likely) or it isn't seated correctly. If the headstock/tailstock were misaligned the spur drive point would spin at a point beside the live centre. Get a dead centre for $5 or $10 from Grizzly or you favourite supplier and repeat the tests. https://www.grizzly.com/products/Grizzly-HSS-Lathe-Center-MT2/H5789 . If you don't have a 60º cone live centre for the tailstock get one at the same time. Don't use a cup centre to hold the end of a mandrel. https://www.grizzly.com/products/Grizzly-Live-Center-MT2-with-Taper-Bearings/G5686
You'll be ready for the day when you want to turn between centres. If after trying the dead centre you still have the point scribing a circle around the tail stock centre call PSI and ask for the service technician.
 
Angela S said:
My tail stock has a little give to the left and right. So, I can move it to meet up with the spur center.
Click to expand...

That seems to be a common concern with Turncrafter lathes. I've heard the same complaint from other Turncrafter owners, and I know it's true in my 12" Turncrafter. The bottom of the tailstock has a rectangular protrusion that fits into the gap in the bedways; in theory, this aligns the tailstock, but the machining in Turncrafter lathes is a bit casual, and that protrusion tends to be a fraction of a millimeter too narrow.

Normally, its not a problem in turning - the slight misalignment may cause slight asymmetry in the turning, but it's not enough to bother anything. Where it can be a problem is in drilling. To avoid the problem, make sure that the live center is firmly seated in the tailstock quill (which really means that you need to extend the quill just a bit - perhaps no more than 1/16 inch so that the live center taper is firmly seated. Then, before starting to drill, face off the end of the blank, and use the corner of a skew chisel to cut a slight conical dimple that is exactly centered on the axis of rotation. Finally, move the tailstock to the left until the drill bit centers in that dimple before locking down the tailstock.
 
monophoto said:
That seems to be a common concern with Turncrafter lathes. I've heard the same complaint from other Turncrafter owners, and I know it's true in my 12" Turncrafter. The bottom of the tailstock has a rectangular protrusion that fits into the gap in the bedways; in theory, this aligns the tailstock, but the machining in Turncrafter lathes is a bit casual, and that protrusion tends to be a fraction of a millimeter too narrow.

Normally, its not a problem in turning - the slight misalignment may cause slight asymmetry in the turning, but it's not enough to bother anything. Where it can be a problem is in drilling. To avoid the problem, make sure that the live center is firmly seated in the tailstock quill (which really means that you need to extend the quill just a bit - perhaps no more than 1/16 inch so that the live center taper is firmly seated. Then, before starting to drill, face off the end of the blank, and use the corner of a skew chisel to cut a slight conical dimple that is exactly centered on the axis of rotation. Finally, move the tailstock to the left until the drill bit centers in that dimple before locking down the tailstock.
Click to expand...


This is a great tip. Thanks!
 
Sounds that from your description, all the issue is with the headstock spindle...the Morse taper to be exact and or the spur drive itself and have nothing to do with the tailstock if indeed the center point of the spur drive is rotating around the center point of the live center.

Have you tried reversing the spur center with the live center? Does the point of the live center now in the headstock revolve or orbit around the spur(in the tailstock? If so, check out the Morse taper in the headstock for debris as suggested...If no debris, call PSI. The Morse taper may not be on axis with the spindle.

A pen mandrel extending that far from the headstock may very well have some deflection of its own.
I doubt the spur drive that came with your lathe is the Cadillac of spur drives and may very well be the culprit.
Curly 's comments above go for me too.
Good luck figuring out the issue and on to great turning!
 
A suggestion. Do this with the lathe OFF.
Using a pointed pencil across the tool rest, rest the point against the inside of the morse taper. Turn the headstock spindle by hand and observe if the point remains against the inside of the taper.
This will show if the taper is not turning concentric.

If you have or have access to a dial indicator this is much easier to check.
 
Be careful you dont put too much pressure on the end of the mandrel when cinching up the tailstock as this will cause or make worse a bow in the mandrel shaft. If it has a bow with just enough pressure to trap the end of the mandrel it may have been damaged and needs replaced.
 
Find someone with a metal lathe and have them come over with their test gauge to check your head stock for runout. What you are describing of the tip of the spur making a small circle is called runout and is not an alignment problem. Measure on the OD of the shaft and the ID of the taper. You should see at most 3/1000" from high to low measurement. If the OD is good and the ID isn't, it was improperly machined and the manufacturer needs to fix it. If the OD and ID are off it's either bad machining or bad bearings. Both need addressing by the manufacturer.

Most likely it's something on the taper keeping the spur from seating correctly. Make sure the taper on the lathe is clean and try another dead center. You should not be able to see the tip move.


Sent from my iPad using Penturners.org mobile app
 
Dan is right here, this is not an alignment problem.
The first thing to check is the Morse taper in the headstock spindle. Being a new lathe, it could be just in need of a good clean. They might have coated the inside with rustproofing compound, this can be cleaned off using white spirits or thinners, and a rag wrapped around a piece of dowel, once you have it clean, give it a wipe with some clean light oil with some lint free rag.
If you have the internal mt completely clean, and you are still getting the same runout, it looks like it is indeed a manufacturing issue, which should be addressed with a replacement lathe.
 
All possible solutions have been pretty much explained and suggested, is unfortunate that when we buy a new lathe we expect them to be working right and accurate but don't despair, this has been the most common issue/problem when purchasing anew lathe, regardless if you a new to it or not, off-course, an experienced turner that decided to upgrade or downgrade their lathe is normally confronted with this exact issue, they already know the normal tests to perform and what to do to align or minimise the problem but still, some of them can not improve the situation and have no choice than return the lathe or exchange it, so, what I'm trying to say is that, you are not alone on the issue, I know that this doesn't solve your problem but at least makes you aware, these problems with new lathes are a lot more common than it should, unfortunately...!

Good luck,

Cheers
George
 
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