OK, but... The purpose of that bar is to evaluate spindle alignment. You cannot do that using the tailstock. Therefore, your half thou with the tailstock is not a valid measurement.
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What's this 9.5" long Test bar telling me?
- Thread starter YYCHM
- Start date
OK, but... The purpose of that bar is to evaluate spindle alignment. You cannot do that using the tailstock. Therefore, your half thou with the tailstock is not a valid measurement.
Actually, I think the purpose of this test bar is to evaluate tailstock alignment. I think the bar is fine. Tomorrow I'll mount it in a chuck and check headstock alignment....
Ummm actually we are gunna have to agree to disagree on that.
To check tailstock alignment you use a bar that has centers on it.
To check spindle alignment you use a bar with an MT5 taper and you do not use the tailstock.
Alternatively, you can test spindle alignment by putting a bar in the chuck, but then you have to cut the bar so that it is concentric with the axis of the spindle. I wouldn't be cutting that bar if I were you.....
No Craig. Maybe a sketch will help.
- upper diagram shows alignment reference. Red line is lathe axis. Black arrow shows TS coincident to the end of the bar
- lower diagram shows HS out of alignment relative to lathe axis. TS meets end of bar. But it is displaced towards rear of lathe & would cut a taper if HS was brought into alignment
- upper diagram shows alignment reference. Red line is lathe axis. Black arrow shows TS coincident to the end of the bar
- lower diagram shows HS out of alignment relative to lathe axis. TS meets end of bar. But it is displaced towards rear of lathe & would cut a taper if HS was brought into alignment
Attachments
For sure take up @RobinHood on his nice offer to check the bar on his Glorious Granite. Trust me, I'll be next in line! LOL
But I'd like you to do a more static test that has nothing to do with runout which I am assuming means you are rotating the test bar? That may be required at some point as @Mcgyver is showing tohelp diagose bar trueness or socket condition, but is one step ahead IMO
- insert in HS socket
- place DTI on center of bar (9:00 position viewing from TS side) on HS end & also make a felt pen reference mark there
- Lock down everything that can move except bed axis travel (lock cross slide, compound, DTI mag...)
- zero the needle
- traverse down to end of bar. What is the reading? Lets say its 0.002". So something is out but could be several different things at this point. Traverse to mid bar & record reading. Is it half the amount (0.001") or something different?
- ideally on this same spindle clock setting you should be able to repeatedly traverse back & forth & get the same numbers. Is there deviation or drift every time you hand crank or do the numbers stay the same?
- Lightly tug on the saddle & watch the needle, does it move or is it pretty stable?
- this is just an aside but even assuming a perfect test bar I wonder what saddle wear would look like on indicator readings because the needle is going to run up the bar section OD & needle plunger will record this as displacement. I have no idea what condition your lathe is but I'm visualizing this would happen.
But I'd like you to do a more static test that has nothing to do with runout which I am assuming means you are rotating the test bar? That may be required at some point as @Mcgyver is showing tohelp diagose bar trueness or socket condition, but is one step ahead IMO
- insert in HS socket
- place DTI on center of bar (9:00 position viewing from TS side) on HS end & also make a felt pen reference mark there
- Lock down everything that can move except bed axis travel (lock cross slide, compound, DTI mag...)
- zero the needle
- traverse down to end of bar. What is the reading? Lets say its 0.002". So something is out but could be several different things at this point. Traverse to mid bar & record reading. Is it half the amount (0.001") or something different?
- ideally on this same spindle clock setting you should be able to repeatedly traverse back & forth & get the same numbers. Is there deviation or drift every time you hand crank or do the numbers stay the same?
- Lightly tug on the saddle & watch the needle, does it move or is it pretty stable?
- this is just an aside but even assuming a perfect test bar I wonder what saddle wear would look like on indicator readings because the needle is going to run up the bar section OD & needle plunger will record this as displacement. I have no idea what condition your lathe is but I'm visualizing this would happen.
Attachments
And now I will eat my own words about bed wear effect. It would have to be substantial to register an indicator reading of significance. See sketch over on the other lathe alignment post. No not that post, the other one.... the OTHER other one. THIS ONE lol
canadianhobbymetalworkers.com
NUMOBAMS 8x16 (NU-210G) Lathe Review
Using my favourite design tool for piping - Engineering Power Tools Plus Edition (check it out) https://pwr-tools.com/new_pwr-tools/ I picked 1-1/4" Sch40 as a largest size that would fit in most large hobby lathes. I also solved for 1/2" that would likely fit in a 7/8" collet. 15" length of...
canadianhobbymetalworkers.com
Former Member
Guest
I'm going to ask a strange question, why use the bar in the first place? I do not use my mt taper to hold work in the headstock as all you are determining is if your mt taper is correct, provided of course if your bars is correct to start. I am concerned with my holding methods. Chuck(s), collet(s) each individual one if I'm going to be OCD, as these points will effect my ultimate accuracy and not the MT in my spindle (unless of course you are using a drawbar and mt collet).
The second issue, turned between centers, ends are good, center is off. This is simple cutting defection or over pressure defection caused by excessive tail stock pressure. A follow rest helps with removing that (or at least most of that).
Now if I have determine that my spindle has "zero" run out at both ends, using a spider at both ends to center a "perfect" test bar for zero run out (this way the bar is spinning concentric and true), I would now use this to align the headstock. At which point holding methods need to aligned to this.
The second issue, turned between centers, ends are good, center is off. This is simple cutting defection or over pressure defection caused by excessive tail stock pressure. A follow rest helps with removing that (or at least most of that).
Now if I have determine that my spindle has "zero" run out at both ends, using a spider at both ends to center a "perfect" test bar for zero run out (this way the bar is spinning concentric and true), I would now use this to align the headstock. At which point holding methods need to aligned to this.
Peter, the issue your diagram presents is why its better to sweep the bar with an indicator (at location) than run the indicator along it.
If one follows the method I described, socket condition, spindle taper accuracy doesn't matter. It doesn;t matter how true the bar is to the spindle. This approach is preferred because it bypasses sources of error and just measures spindle aligment to the bed (or at least the path the carriage takes over the bed).
I made a specialty spindle for doing the sweep shown below. Worth it for reconditioning, but a lot of effort for very occasional use. You could get the same results by clamping a precision angle plate on the compound then using an indicator in a surface gauge held to the vertical surface, move, or sweep, the indicator tip over the bar
If one follows the method I described, socket condition, spindle taper accuracy doesn't matter. It doesn;t matter how true the bar is to the spindle. This approach is preferred because it bypasses sources of error and just measures spindle aligment to the bed (or at least the path the carriage takes over the bed).
I made a specialty spindle for doing the sweep shown below. Worth it for reconditioning, but a lot of effort for very occasional use. You could get the same results by clamping a precision angle plate on the compound then using an indicator in a surface gauge held to the vertical surface, move, or sweep, the indicator tip over the bar
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And now I will eat my own words about bed wear effect. It would have to be substantial to register an indicator reading of significance. See sketch over on the other lathe alignment post. No not that post, the other one.... the OTHER other one. THIS ONE lol
NUMOBAMS 8x16 (NU-210G) Lathe Review
Using my favourite design tool for piping - Engineering Power Tools Plus Edition (check it out) https://pwr-tools.com/new_pwr-tools/ I picked 1-1/4" Sch40 as a largest size that would fit in most large hobby lathes. I also solved for 1/2" that would likely fit in a 7/8" collet. 15" length of...
Good stuff Peter.
I did a LOT of looking on line last night for something that explains what headstock alignment was all about to send to @YYCHM (and a million others). There were things out there, but nothing I wanted to give a reference to. So I guess we have to keep trying ourselves.
No, not that other one, the other other one! LOL!
Rauce
Ultra Member
Couple thoughts from me…
To accurately check for bow in a shaft the V blocks you put a shaft on do not need to be matched or “precision” v blocks, nor do the blocks need to be on a precision surface.
Also regarding the centers in these types of test bars, I’m confidant that they are manufactured by cylindrically grinding between centers. Centerless grinding is not a suitable process for something that needs to be ground straight. Centerless grinding will grind a consistent OD but will not correct a bow in a shaft.
To accurately check for bow in a shaft the V blocks you put a shaft on do not need to be matched or “precision” v blocks, nor do the blocks need to be on a precision surface.
Also regarding the centers in these types of test bars, I’m confidant that they are manufactured by cylindrically grinding between centers. Centerless grinding is not a suitable process for something that needs to be ground straight. Centerless grinding will grind a consistent OD but will not correct a bow in a shaft.
Hey @YYCHM , I actually ordered a bar like yours a few days before you did.
So many members were vouching for it that I decided to get one just to play with to see how it compared to cutting collars which is my favoured way to do it.
They say it's never a good idea to evaluate something you don't trust before you even start. But I figured I could overcome my bias. I like to think I'm open minded enough to do that. Of course, my bride says otherwise......
At any rate, despite ordering a few days before you, mine had been showing late for a week now. Today, they outright cancelled it and issued a refund. Not good for my attitude at all......
How are you doing with yours? I never heard any more from you after your last post on Saturday.
Btw, I did see on their website that they advertise the bar for tailstock alignment. I can see ways to do that, but I think it's an outright application error on their part given that there are so many better cheaper ways to do it. I'd be very interested to hear how you make out using it for that. At my stubborn old age I know I can always learn something new or different whenever I finally burn my prejudices.......
So many members were vouching for it that I decided to get one just to play with to see how it compared to cutting collars which is my favoured way to do it.
They say it's never a good idea to evaluate something you don't trust before you even start. But I figured I could overcome my bias. I like to think I'm open minded enough to do that. Of course, my bride says otherwise......
At any rate, despite ordering a few days before you, mine had been showing late for a week now. Today, they outright cancelled it and issued a refund. Not good for my attitude at all......
How are you doing with yours? I never heard any more from you after your last post on Saturday.
Btw, I did see on their website that they advertise the bar for tailstock alignment. I can see ways to do that, but I think it's an outright application error on their part given that there are so many better cheaper ways to do it. I'd be very interested to hear how you make out using it for that. At my stubborn old age I know I can always learn something new or different whenever I finally burn my prejudices.......
Hey @YYCHM , I actually ordered a bar like yours a few days before you did.
So many members were vouching for it that I decided to get one just to play with to see how it compared to cutting collars which is my favoured way to do it.
They say it's never a good idea to evaluate something you don't trust before you even start. But I figured I could overcome my bias. I like to think I'm open minded enough to do that. Of course, my bride says otherwise......
At any rate, despite ordering a few days before you, mine had been showing late for a week now. Today, they outright cancelled it and issued a refund. Not good for my attitude at all......
How are you doing with yours? I never heard any more from you after your last post on Saturday.
Btw, I did see on their website that they advertise the bar for tailstock alignment. I can see ways to do that, but I think it's an outright application error on their part given that there are so many better cheaper ways to do it. I'd be very interested to hear how you make out using it for that. At my stubborn old age I know I can always learn something new or different whenever I finally burn my prejudices.......
Still tinkering trying to make sense out what I'm seeing. Mounting the test bar in my 3J didn't prove anything.
Will take the bar to @RobinHood to measure up when I get a chance.
If you want to try ordering again, these guys delivered within 10 days via DHL.
This is the same vendor @trlvn ordered from.
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In this mode the test bar is basically a nice long dowel pin. If your HS was perfectly aligned & the chuck gripped with 0.002" runout, then the test bar would reflect that runout. If your HS is misaligned & the chuck grips the same 0.002" runout, you will have some combined measurement condition. If the chuck had 0.001" runout but mounted at some angle to the spindle nose, it would be different again. The effects masking and/or exaggerating one another depending on direction & extent, which is is therefore impossible to prove much of anything. That's why its important to try & start at the beginning & proceed in a stepwise logical order introducing one variable or accessory at a time.
Think about this measurement process kind of like like vectors. We have a misalignment condition A and B which are independent, but result in measurement outcome C.
But just knowing C, we really have no idea (within reason) how much A or B is influencing our measurement. Conceivably we could have two problems, A & B opposing each other resulting in zero C (if only life worked that way LOL). So if A represents headstock alignment & B represents chuck alignment, one can visualize other 'vectors of influence' like bowed test bar or twisted lathe bed & the sketch becomes even more complex. I'm not saying there is anything wrong with chucking a test bar, but just have a sense of what the test is about.
Just got a call from Amazon. Apparently refunds from India are "complicated". I need to wait for another notification before I can place another order.
I like that @RobinHood offered to help you. He seems like a really cool guy! I'll be anxiously awaiting the results.
More tinkering.......
I scrubbed out the spindle taper with a wire brush and wiped down the taper and test bar with a clean cloth. I then set the test bar in the spindle taper with a light tap of a wood mallet.
Now I'm seeing nil runout at either end of the test bar and a 3 thou. discrepancy along the length of the test bar. I clocked the spindle through 0, 90, 180, and 270 deg. and got the same 3 thou. discrepancy along the length all in the same direction.
3 thou. headstock alignment issue?
I scrubbed out the spindle taper with a wire brush and wiped down the taper and test bar with a clean cloth. I then set the test bar in the spindle taper with a light tap of a wood mallet.
Now I'm seeing nil runout at either end of the test bar and a 3 thou. discrepancy along the length of the test bar. I clocked the spindle through 0, 90, 180, and 270 deg. and got the same 3 thou. discrepancy along the length all in the same direction.
3 thou. headstock alignment issue?
Without seeing your setup, it's hard to say. But if runout is zero, I'd say that head alignment is the most likely explanation. 3 thou over 18" is not unexpected though.
Also, that bar of yours is a big one. Depending on where and how you measured, it might even be gravity.
But ya, if concentricity (runout) is good, then end to end varience is usually because the spindle isnt parallel to the bed. So the question IS how are you measuring that?
Also, that bar of yours is a big one. Depending on where and how you measured, it might even be gravity.
But ya, if concentricity (runout) is good, then end to end varience is usually because the spindle isnt parallel to the bed. So the question IS how are you measuring that?
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I would assume the 0.003" discrepancy from directly in front. You should also measure from directly on top. So if directly on top measures zero, you have no droop. Then either your head stock is slightly out of alignment or your bed has twist. Remove any twist from your bed (you should be using the Starrett 199 level). And like @Rauce mentioned, you could have wear.
9.5" long, 1" dia. test bar.
The bar you linked to me was bigger than that.
But OK, so I'd prefer to see you use a dial test indicator with the needle pointing down as @PeterT showed earlier to measure that. Those regular indicators sometimes have a lot of force in the spring. As small as that force is, it can bend the bar.
But what you are seeing right now is NOT gravity.
You should also test along the top to evaluate nod. You might see gravity there.
You are doing great.