D1-4 on a PM1340

[Tired&Retired]

Here is my best advice to you, and I mean it with helping you foremost in mind. I would stop what you're doing and replace the spindle. Do not modify your chuck tapers because there is a good chance they have an accurate female taper at this point and it is likely they will work fine on an accurate spindle taper.

In my opinion, it was a mistake to grind that spindle. Matt is complicit in this and I hope he makes good by sending you a replacement spindle because it should have been good in the first place.

So you are saying that all four (4) chucks I checked in the video, with each having 0.002", 0.004", 0.006", and finally 0.008" gaps, respectively, are ALL just fine? As someone here mentioned earlier, if it was the spindle taper that is bad, then wouldn't there be logical to assume that all four of the chucks would gap roughly the same? Of course, they could ALL be bad, and the spindle taper be bad as well. With my luck.....

Uhhh. Using 3000 grit on anything is NOT grinding. Have you ever wet sanded a car's paint job? If you started out using 3000 grit, you would die from old age before you got the job done. And that is simply automotive paint, not hardened metal you are trying to "remove" material from. 3000 is normally used only to remove the haze that you get from using 1500 or 2000 grit. Which is basically the minute scratches that the coarser grits leave behind. Extremely fine grits are NOT for gross material removal. You use the coarser grits for that and always start from the coarsest you believe you need and gradually work up to the finest grit. Use too coarse a grit to start off with, and you WILL regret it. Heck, just using 3000 grit after using something like 400 grit would wear you right out trying to get the finish you are after. Start off with 3000 grit? Heck, hope you are retired and lots of time on your hands.

Heck, I polished the aluminum cradles on my vette when I had it in the shop for a drivetrain upgrade. You just cannot start with something like 3000 grit as that would do nothing but remove just the highest microscopic "burrs" on the metal and nothing more without making a lifelong career at it. Look at the pics I enclosed of closeups of the taper. All my polishing did was to deburr the presumed microscopic rough high spots off the metal as you can still see the original pits of the metal plainly visible. Had appreciable metal been removed, you would see a completely uniform glossy mirror like surface on the metal left over by that 3000 grit abrasive. Not to mention it would have taken an enormous amount of time to get there.

If that very light polishing I did has ruined the spindle taper, as you seem to be convinced of, then if that much metal was removed to ruin it, then in what way would it be ruined? How much metal would need to be removed to take it out of manufacturing tolerances?

Heck, for that matter Matt told me he has worked on actually grinding spindle tapers in the past with success, and recommended that I use a much coarser grit than that 3000 I have used, because the 3000 grit would take me forever to remove any appreciable metal. I don't believe he would steer me wrong about how best to resolve this problem with the lathe I bought from him. Do you?

So, with all due respect, I just do not agree with your opinion that the spindle taper has been ruined. Not saying you are wrong, just that I do not believe that to be the case right now.

As for getting a replacement spindle, only if I feel confident that it is necessary. At this point, replacing the spindle seems like it would be a hell of a lot of work to correct something that could likely be fixed a whole lot easier. And as for the suggestion of replacing the entire lathe that was offered a little while back, well, seriously? Maybe you enjoy the time and effort necessary to pull the lathe off the table and put it into the back of the pickup truck, recrate it, take it for pickup by UPS (they cannot get a large truck up our driveway), then wait till a replacement comes in and then do the reverse to put the new one in, but I surely don't. Honestly, if that were the case, I would probably just use the lathe as a horizontal polisher on rods and poles and be done with it.

That being said, thank all of you for your suggestions and offers of help. I AM reading everything, but honestly I cannot act on it all. I am looking for the best and easiest solution even though the two might possibly be mutually exclusive.

 

[Tired&Retired]

Yea, I suspect that one is going to be a bit of work, but totally doable. It takes very little material removal on the taper to get a big movement along the Z axis.

It's the same spindle, your mounting each of the chucks too. That the gap is different for each chuck strongly implies that the chucks are what vary in size. Even if the spindle is a on the MMC (max material condition) side of the tolerance, the chucks are clearly not all the same size.

The chucks will be the easiest to adjust.

For example, opening the chucks taper diameter by .002" will move the chuck .008" closer to the spindle.

Here's the calculation:

Tangent(7.125)(.008)(2)=.001999

Where 7.125° is the taper angle, .008" is the distance you need to move the chuck and (2) converts it from radius to diameter.

The chuck that's only .002" from fitting, would only need the diameter opened up by .0005". You could accomplish that with about 5-10 second of polishing with 220 grit.

Tangent(7.125)(.002)(2)=.000499

Well a bit technical mathematically for my old brain, but sounds like this may be the best path for me to take.

I do like the suggestion about using the tail stock to hold the MT5 test rod in place, as I really didn't like the idea of the weigh of a nearly free standing chuck spinning around at even slow speeds. Even just having one just drop on my foot would pretty much ruin my day. Not to mention that rod flailing around that the chuck is wrapped around.

My attitude when running the lathe is that the SOB will kill me if I let it.

So I am trying hard not to let it get the chance.

Thanks!

 

[Ken226]

Perhaps its just a little tolerance stacking, combined with a couple chucks that are a bit outside of the acceptable tolerance range.

According to this, from Pratt Burnerd Chucks, the taper large end is 2.5005" with a tolerance of +.0005 -.000. So, a diameter from 2.5005" up to 2.501" is acceptable.



I can't find anything indicating that the taper in the chuck would have a different tolerance. I hate making assumptions, but in the absence of evidence to the contrary, if i assume the hole in the back of the chuck is toleranced the same. 2.5005" +.0005 -.000, the hole diameters from 2.5005" to 2.501" are within spec.




So, if your spindle happens to be on the maximum material condition side of that tolerance with a diameter of 2.501", it would still technically be within spec. In that case, a chuck with a taper diameter of 2.5005" would be withing spec as well.


Using a little simple trig, that .0005 diameter difference on the tapers results in a spindle face gap of .002". Everything is within spec, but on opposite sides of the tolerance allowance. This jives well with the info a couple pages back published by Rohm chucks.


Now if your spindle taper is on the MMC side of the tolerance @ 2.501" AND one or more of those Chinese chucks/backplates have a taper that happens to be undersized, even by just a little, you have a bigger gap.
In the case of a MMC spindle nose and a chuck that has a hole within spec @ 2.5005", leaves a gap of .002"
In the case of a chuck has a hole that is .001" under minimum spec, you would have a gap of .006"
If the chuck has a hole that is .0015" under minimum, the gap would be .008".

.0015" of diameter can be polished off quickly with a little emery cloth.

Don't polish off too much though. You don't want zero gap, you want a gap of around .001".

Up to .002" is acceptable, but no less than .0008". On my chucks, I aim for .001, which closes up with about 20ft lbs of torque on the cams.

 

[Dabbler]

@Tired&Retired I have finally gotten to your video.

So you are saying that all four (4) chucks I checked in the video, with each having 0.002", 0.004", 0.006", and finally 0.008" gaps, respectively, are ALL just fine?

-- Absolutely you have proven the chucks' backing plates are at fault. There is no question in my mind about this and if I were there I'd do the same tests. After seeing the results, here's what I'd do in my shop were this the case:

First I'd take 4000 grit emery paper and a wooden stick, like a paint stirrer, and run the spindle at 1000 rpm, and polish the entire spindle taper.

Ok guys before you flame me let me explain --

Using 4000 grit for polishing is only going to take the peaks of all those scratches off of the taper. With 5 minutes work, and changing the paper to fresh a lot, you'd be very diligent to take one tenth off the taper. Use 6000 grit if you are squeamish. This will help eliminate any 'hangs' on the taper. Why wood? because it won't change the taper at all, not one bit. I've been honing inside and outside tapers for 40 years using similar techniques, in order to get sub tenths accuracy. I've done this many times on outside Morse tapers , to repair peoples drill chuck tapers, etc.

This isn't going to fix your problem, however, this is just 'insurance' so the next operations will work well.

Mount your 4 jaw chuck, and dial in the largest round stock you can manage. You want it to be very well centred, but not necessarily perfect. the round stock has to protrude the depth of your 3 jaw chuck jaws, plus, say 1/2 inch. For example a 2" cold rolled bar 6" long with 3" protruding.

Then clamp your 3 jaw chuck on this with the camlock pins removed.

Now dial in your taper on the backing plate of your 3 jaw chuck, using the 4 jaw adjustments. It can be out a thou if you like as this won't matter too much, but ten thou would not so good...

Now you will need a dowel, say 1" diameter, 6" long and you put 1000 grit emery paper around the half of it protruding enough you can grasp it. Run your lathe at about 300 rpm, and 'rock the paper lightly until you get even contact. Polish the taper for a few minutes and see if you get starry pattern on it. If that is the case, then your inside taper was never ground or poorly ground. If it is bright and shiny, well it was ground wrong. not impossible for an offshore backing plate.

If you are determined to fix the problem yourself, then do this:

You are going to repeat the following steps a lot of times, in order to be careful. Do not rush these steps...

Reinsert your camlock pins.
Remove the assembly by releasing the camlock on the 4 jaw. I use masking tape to ensure I remount using the same pins.
Mount the assembly as a 3 jaw chuck (taking care to hold up the assembly to prevent cocking of this heavy assembly]
Note how close you are getting using your feeler gauges.
- when your tightest is very close you remove it and check how far your are away when the backing plate is 'half tight'.
- your goal is to get that around 3 or 4 thou, or as close as 2 thou won't hurt.
Flip the assembly around so the 4 jaw chuck is mounted. Check that your 3J taper is close to concentric, and fix if necessary.
Rehone using progressively higher grit counts until you have your 2 to 4 thou 'half tight.

When you are at a good spot, you will find that your tightening will be fairly easy, and then suddenly get harder.
This is a sign that you are seating on the flat. You can check with a strong light to be sure there is no light at any point between your backing plate and the spindle flat.

-- That's what I'd do, after all this is all fun, right?

Then I'd repeat it for all my backing plates.

 

[Cadillac]

Did you ever try mounting the chucks without the pins in it? I know you can’t pull them in but maybe the pin holes are to short and not allowing the chucks to seats? I’d just check all avenues first before sanding the spindle.
Another thing is in your video you showed a gauge on all the critical surfaces. To me the flutter was about equal including the inner taper. That would say to me the problem is in the spindle or the bearings. Seeing as your have fitment problems it’s probably the n the spindle.

 

[Ken226]

^^^^^^^^^
Dabbler gave good advice. That's what I do as well.

If fact, when I buy a backing plate that was made[Edit] Offshore, I just assume that It will need done. It pretty much always needs done if unless your buying $$$ stuff.

 

[Tired&Retired]

OK, some more food for thought with the above posts.

FYI, I broke out the torque wrench and I am getting roughly 25 ft/lbs when I tighten down the camlocks by hand. So I tried torquing to 30 lbs on the 3 jaw chuck and I was unable to get a 001.5 feeler gauge anywhere between the backplate and the spindle face. So things were looking up!

Then I tried the 4 jaw chuck, which has the largest gap of 0.008". Best I could do is to bring the gap down to around 0.006". BTW, both chucks were a bit more difficult to get off of the spindle after the torquing. I have a 5C chuck and ER40 chuck that are just barely larger in diameter than the spindle, and I already have to work at getting them off of the spindle. Not really keen on having to use a pry bar on them.

Thinking of the above mentioned gap on the 4 jaw chuck, as per the recommended procedure by Dabbler, if I am unable to get the 4 jaw chuck to fit properly on the spindle with that large of a gap, is even "truing" up the jaws going to help much? Unfortunately the 4 jaw chuck is the worst of the bunch concerning the gap I have been talking about. Since the jaws don't hold a shaft or rod at a single point of contact, but along the contact surfaces of the jaws, wouldn't there be the possibility of front to back wobble in the work piece if the backplate of the chuck and spindle face aren't exactly parallel? So even if I got the single plane diameter of the shaft or rod concentric on that one plane in the 4 jaw chuck, won't the rest of the shaft be wobbling around in relation to that plane because of the gap at the backplate/spindle faceplate surface being transferred to the jaws? Or am I missing something here? I can see this in my mind easier than I can explain it in words. But I don't always trust my mind lately.

Let it be known, in case anyone hasn't figured this out yet, I am NOT a machinist. Never even stayed at a Holiday Inn Express.

 

[Dabbler]

Hi 'Tired - Unless you are registering against the front flange - that is you only touch the taper - you won't get good finishes and you won't have the full strength and rigidity of the spindle. Especially for parting it will make a big difference.

You won't make things worse by polishing the back plates. it only can get better. The only care you have to take, and why I recommended wood - is to not alter the angle of the taper in the backing plate. Even if it is wrong, you haven't made it worse.

Based on your measurements in the video, your 4 jaw chuck will be working well within expectations for a hobby machine if you seat it against the flange. Your 3 jaw chuck won't be quite as good, but that's what you get with mid-range offshore chucks. - Frankly I've seen worse. Even on a brand new offshore 3J chuck seating properly.

I think we can get really good performance out of your collet chuck once it is seated well. There are ways to make it better, but out of the scope of this thread.

P.S. - you only 'true up' 4j chuck jaws in extreme cases of wear and neglect. Truing up 3J chucks is out of your skill range today, but perhaps soon you can consider working on it.

 

[Tired&Retired]

Did you ever try mounting the chucks without the pins in it? I know you can’t pull them in but maybe the pin holes are to short and not allowing the chucks to seats? I’d just check all avenues first before sanding the spindle.
Another thing is in your video you showed a gauge on all the critical surfaces. To me the flutter was about equal including the inner taper. That would say to me the problem is in the spindle or the bearings. Seeing as your have fitment problems it’s probably the n the spindle.

When setting up the camlock pins in the chucks, I always would put them where it seemed optimum, and then try them one extra turn in, and then one extra turn out to make certain I had them correctly positioned. If the holes were drilled short, I would think I would not be able to run the pins in that extra turn?

I guess it is certainly possible that I have multiple problems. The spindle could be machined incorrectly, and ALL of the chucks not being machined correctly, neither. Honestly, of all the chucks I have, I would have thought that the Precision Matthews name brand 4 jaw would be the closest to being a perfect fit. After all it is supposed to be made in Taiwan, and claimed to be "high precision". But I am just not seeing that, I guess.

I asked Matt for a proven GOOD backplate for the D1-4 spindle so I could have something to use as a test reference, but he did not make any offer to supply something like that to me. I would certainly return it, but I guess he just doesn't have something like that available.

Sigh, I have wanted a larger lathe for a long time, and was REAL excited about getting one finally. But that is really losing it's luster right now.

Actually this headache started even before that when I bought a "Chinabay" lathe that sounded real nice but turned out to be a real bucket of thrown together defective components. Sent it back and got a full refund, then now I had my appetite whetted decided to take a big step upwards in price and hoped for quality with something better. Please don't ask me how that is working out for me. I have been on the internet since something like 1997 and have never resorted to profanity in writing. I sure would hate to break that streak now.

 

[Ken226]

Fix your 4 jaw first. It's your most useful chuck, and can be used to fix the rest.


To fix the 4 jaw, do this:

Take a measurement in the 4 jaw chuck that your about to start polishing, for future reference.. use a parallel or something precise as a spacer. This will enable you to keep track of how far you need to go later, while your sanding. The spacer will allow your caliper jaws to measure the same spot in the taper, now and later



put your 3 jaw on the lathe and chuck up a piece of bar stock. Preferably 1" or more.

Turn your 4 jaw around backwards and mount it to the bar. Indicate it to center, remove the studs from the back, and start polishing the inside of the taper with emery cloth.

Stop occasionally, grab your spacers and take a measurement. Once your removed about .001", test fit it. Now, you'll have an idea of how long it took to remove .001", and how much further you need to go.

I'll go shoot a quick video for ya.