NUMOBAMS 8x16 (NU-210G) Lathe Review

[Susquatch]

@opensourcefan - your thread came off the rails a bit there and I apologize for my role in that.

I confess that I am a bit confused. I re-read your entire thread to try and make sense of things.

Normally, when a lathe produces a taper that close to the chuck, it is not the Chuck's fault unless the chuck is loose. No matter how badly a part is held in a chuck, and no matter how badly the chuck is attached to the spindle, and no matter how out of round the chuck is etc, the part will turn concentric to the spindle, not the chuck. A better chuck will only help hold a part more closely to the axis of the spindle.

In my mind, there are only three possibilities.

1. The axis of the spindle is not aligned to the axis of the bed.

2. The tool holder is moving up/dwn or In/out while it moves on the bed.

3. The chuck or the part held in the chuck is loose and moving around.

I expect this might sound like Greek to you, but think about it. With a good lathe that is setup properly, and a really crummy 3 jaw chuck, you can put a chunk of square stock in the chuck, and turn a perfect cylinder with no taper. When the tailstock is not used, tapers at the head only happen when the spindle axis is not aligned with the axis of the tool travel - which should be the same as the axis of the bed.

You cleaned up that chuck and I think it's probably ok now.

But I don't think your head and/or ways are aligned properly.

 

[Susquatch]

@opensourcefan - one more thing. As I understand it, this character "Sam" lured you away from Ali to his own website. If that happened on eBay or Amazon, that supplier would be in really big trouble. I'd wager that the same thing applies at Ali.

This gives you lots of leverage. I'd suggest two things here. Find out what Ali's policies are on that front. If they are as I expect, and if you have copies of his correspondence luring you away, you can have a very different conversation with Sam. If you are pissed off enough, I'd go straight to Ali with that info.

 

[opensourcefan]

UPDATE

Okay so he finally agreed that the head is out of alignment. He is sending me a new Sanou 3 jaw chuck as compensation for the issues and I'm going to fix it.

Saga is over. I feel better now.

 

[opensourcefan]

@Susquatch

Yep agree, it was always the head alignment, I never believed for a second that it was the chuck but they did. Took forever to convince them otherwise.

 

[Susquatch]

UPDATE

Okay so he finally agreed that the head is out of alignment. He is sending me a new Sanou 3 jaw chuck as compensation for the issues and I'm going to fix it.

Saga is over. I feel better now.

I'm glad you are happier. Do you have a plan yet for how to go about fixing it? If not, post a few photos of how your head and bed are attached to each other.

 

[opensourcefan]

I'm glad you are happier. Do you have a plan yet for how to go about fixing it? If not, post a few photos of how your head and bed are attached to each other.

Just 4 bolts behind some electrical housings that need to be pulled. All the electrical needs to be hung out to get that section off.

Going to ever so lightly loosen 3 with the 4th just a touch tighter so when I "tappy tap tap" it'll pivot a bit and not go too far outta whack.

I'll first use my .001" dial indicator followed up by my .0001". Going to use the bar I last turned which is still undisturbed in the chuck. It'll have to do until I find an MT5 Test Bar.

 

[YYCHM]

Going to use the bar I last turned which is still undisturbed in the chuck.

Doesn't that bar have a taper since you turned it already?

 

[opensourcefan]

Doesn't that bar have a taper since you turned it already?

Yes

The taper was cut in relation to the ways. If I align the back end of the cut piece it will be aligned with the ways.

I have completed the first round of alignments in the absence of having a longer test bar. I wasn't able to tap it into position as the relationship between the way seats on the head and the bed ways wasn't accurate. Each time I tightened up the bolts it all went to crap again. So I ended up shimming the head both vertically and laterally. It's now .002" within 4". I can live with that untill I get my bar.

I think this proved that it was built this way and wasn't a bump during shipping or whatever.

 

[Susquatch]

Yes

The taper was cut in relation to the ways. If I align the back end of the cut piece it will be aligned with the ways.

I have completed the first round of alignments in the absence of having a longer test bar. I wasn't able to tap it into position as the relationship between the way seats on the head and the bed ways wasn't accurate. Each time I tightened up the bolts it all went to crap again. So I ended up shimming the head both vertically and laterally. It's now .002" within 4". I can live with that untill I get my bar.

I think this proved that it was built this way and wasn't a bump during shipping or whatever.

Just 4 bolts behind some electrical housings that need to be pulled. All the electrical needs to be hung out to get that section off.

Going to ever so lightly loosen 3 with the 4th just a touch tighter so when I "tappy tap tap" it'll pivot a bit and not go too far outta whack.

I'll first use my .001" dial indicator followed up by my .0001". Going to use the bar I last turned which is still undisturbed in the chuck. It'll have to do until I find an MT5 Test Bar.

OK, sounds to me like you know what is needed.

Personally, I'm not a fan of the MT5 test bar method anyway. It depends on a perfectly machined MT5 socket in the spindle and a perfectly machined test bar.

A solidly mounted chuck and a piece of 1-1/2" pipe 12" long firmly mounted in the chuck will actually work better. Many machinists use an 8 inch pipe, and some even use round bar.

Then cut a dumbbell contour into the pipe. It does not need to be deep - just enough so you can traverse the bar end to end without cutting in the middle. The purpose is to avoid any possibility of moving or springing the cross-slide.

The reason for pipe instead of bar is to reduce the amount the bar droops under its own weight. But for short lengths a regular bar will work just fine.

When you start the process of cutting the two ends and measuring the taper, take very very fine cuts to avoid deflecting the bar with tool pressure. A very very sharp hss tool works better for this because carbide likes a bit of pressure. There are carbide bits that don't, but it's just easier to sharpen a special hss bit.

There are lots of videos on the web. Just be careful to consider how your head is mounted and how to properly adjust it. They will typically be called "levelling" the lathe. So make sure you find one that actually means taking the twist out of the bed AND THEN adjusting the axis of the spindle to be parallel to the axis of the bed. Here is one by Joe Pie.

 

[Rauce]

Personally, I'm not a fan of the MT5 test bar method anyway. It depends on a perfectly machined MT5 socket in the spindle and a perfectly machined test bar.

I’ve found that MT test bars are very accurate for the cost. The MT5 test bar I just purchased for my lathe rebuild is consistent on diameter on the straight section to .0003” over 10”. Seated in the spindle taper the TIR at the far end of the bar is .0006”.

 

[Susquatch]

I’ve found that MT test bars are very accurate for the cost. The MT5 test bar I just purchased for my lathe rebuild is consistent on diameter on the straight section to .0003” over 10”. Seated in the spindle taper the TIR at the far end of the bar is .0006”.

That's good. But even knowing that about your bar doesn't help the guy who has no idea how good the MT on his spindle is.....

For those that do, it's just fine.

But I prefer the certainty of an in chuck test bar the first time a lathe spindle is aligned.

 

[trlvn]

Yes

The taper was cut in relation to the ways. If I align the back end of the cut piece it will be aligned with the ways.

I'm really confused by the above. We believe the axis of rotation of your lathe is misaligned with the bed (horizontally) as the machine cuts tapered parts. The amount of misalignment is 1/2 the change in diameter for a given distance from the head. Wouldn't you have to effectively use Rollie's Dad's Method to measure the tapered part after changing the head alignment?

I have completed the first round of alignments in the absence of having a longer test bar. I wasn't able to tap it into position as the relationship between the way seats on the head and the bed ways wasn't accurate. Each time I tightened up the bolts it all went to crap again. So I ended up shimming the head both vertically and laterally. It's now .002" within 4". I can live with that untill I get my bar.

I think this proved that it was built this way and wasn't a bump during shipping or whatever.

I thought you stated earlier that you had verified that the axis of rotation was parallel with the bed in the vertical plane? If so, why are you having to shim vertically now? Is it possible your shims have fixed the horizontal alignment but screwed up the vertical?

Did you take the head fully off the machine to check for burrs or chips?

Craig

 

[Rauce]

That's good. But even knowing that about your bar doesn't help the guy who has no idea how good the MT on his spindle is.....

For those that do, it's just fine.

But I prefer the certainty of an in chuck test bar the first time a lathe spindle is aligned.

You’ll know how good the MT in the spindle is when you put the bar in. Any runout seen on the bar will be some combination of error in the bar + error in the spindle. If say the TIR is .001” at the furthest point from from the spindle along the bar then assuming the diameter of the bar is consistent, the bar is true to the spindle bore to .0005” along the length (+/- any variation in the diameter/2)

The certainty of a test bar like you described is great but often when aligning the headstock you don’t have the benefit of the machine in question running in order to make such a bar that’s matched to the machine/chuck etc. in question.

 

[Susquatch]

Wouldn't you have to effectively use Rollie's Dad's Method to measure the tapered part after changing the head alignment?

Or any other equivalent method...... Rollie's dad and I had a fight over my sister once so we don't get along. I prefer regular geometry.

 

[Susquatch]

You’ll know how good the MT in the spindle is when you put the bar in. Any runout seen on the bar will be some combination of error in the bar + error in the spindle. If say the TIR is .001” at the furthest point from from the spindle along the bar then assuming the diameter of the bar is consistent, the bar is true to the spindle bore to .0005” along the length (+/- any variation in the diameter/2)

The certainty of a test bar like you described is great but often when aligning the headstock you don’t have the benefit of the machine in question running in order to make such a bar that’s matched to the machine/chuck etc. in question.

I don't agree with that.

The whole point of making a bar in the spindle that is being aligned is to check the alignment of the spindle. A known bar is not required and need not be matched to anything.

Edit - Much as I don't like Rollie's dad, you can google it to see how it works. But the bottom line is that a rotating spindle should cut a perfect cylinder if the cutting tip is moving on a path that is parallel to the axis of the spindle. That's the whole operating principle of a lathe. If it doesn't cut a cylinder, then the two axis (spindle & bed) are not parallel. Easy peasy.

 

[Rauce]

I don't agree with that.

The whole point of making a bar in the spindle that is being aligned is to check the alignment of the spindle. A known bar is not required and need not be matched to anything.

What I meant by “matched” is that (unless I’m misunderstanding you) as soon as you remove your bar from the chuck it’s going to be somewhat difficult to put it back in the chuck with exactly the same alignment to the spindle. Leaving it in the chuck and the chuck on the machine while you align the headstock might be an option here but not always, which is where a cyclindrically ground MT test bar with precision that’s easily measured is better. You don’t need the machine to be operational to cut a test bar and you can take it in and out of spindle as many times as you need and it will be in alignment with the spindle within tenths every time. And in between removing it and reinstalling it you can remove the headstock to scrape or shim or whatever until you get aligned to your satisfaction.

 

[opensourcefan]

@Susquatch

I like the idea of not having to buy a bar specifically for this machine. The dumbbell shape seems better than dragging my indicator all the way back and forth watching it ride the surface imperfections. Maybe a 3" pipe over 15" or so would work?

I'll wait for the new chuck to arrive.

 

[opensourcefan]

UPDATE - Electrical Quality

So during my disassembly I had to remove most of the electrical. While doing so I had two terminals fall off their wires. One connection fell out of the 3 pin connector for the rpm gauge and one on the power on off switch. I'm sure I'll discover more during round two of the alignment.

 

[PeterT]

@opensourcefan I didn't read through your entire post, but you might find link below of interest. Specifically post #28. My contribution on this subject is somewhat repetitive to what I've typed elsewhere on this forum, some copy-pasted. I'm growing weary of headstock rotation deniers & YouTubers that regurgitate the same Google results whether it makes sense or is applicable.

- sounds like you found the vertical bolts that secure the HS to the bed, but there may be other adjustment screws or 'alignment systems' which set the HS rotation relative to the bed. This is highly lathe dependent and what seems to be often the case, undocumented in the lathes own parts manual. If it was incorrectly set at the factory and/or has come out of alignment, then yes unfortunately leaves the task of fixing it. HS alignment has nothing to do with chucks.

- I'm not sure why the resistance to MT-ended test bars other than the usual (expense) which of course is a personal decision. In my case I found an inexpensive one on Ebay that is very accurate for this purpose. If it helps matters, they have utility for HS alignment TS alignment & rotary table centering.

- I'm not opposed to cutting coupons to validate things, but (IMHO) its best reserved as a final / tuning / validation step when you have eliminated other, potentially larger error sources by simple measurement. Others have a different opinion & that's fine. If you visualize what is happening with either bed twist or HS is misaligned is the cutting edge is either drifting above or below the rotation axis of the coupon as it traverses. So its not quite as simple as just removing material because the cutter & material are responding differently no different than if you set your tool too low or high in normal cutting. Now I imagine this effect diminishes as you converge on correct geometry. There are many paths to arrive at the desired end result. I'm just suggesting something that seems logical & efficient to me.

Lathe Headstock Alignment

How then would you check the alignment of the HS and then proceed to correcting twist? ie how do you tell if the misalignment is from the headstock or a twist in the bed.

www.homemodelenginemachinist.com

 

[YotaBota]

Hoping all works out for you and that a new chuck makes up for all the aggravation.

I know MT is supposed to be standard but if you have one company making MT stuff using metric machines and one company using inch machines is there not a chance the MT could differ enough between the two that it could be measured? That would also include the competency of the programmer and to what decimal place they programmed the machine cutting the MT.