Chuck Runout

[doubletop]

I purchased a new lathe last year and until now haven't needed to make much use of the 4 Jaw chuck. During the week I needed to make some new main driver crank pins for the Simplex loco I'm refurbishing. Anyway, it needed the 4 jaw to ensure they were truly concentric. Running a 550 revs there was a noticeable vibration and the 4 jaw chuck body looks like its running eccentrically.

I decided to do some checks with the DTI but I've no idea what should be expected so here's a video of the results and I'm sure you guys are going to put me right.

http://www.youtube.com/v/avA4yc0ZBVg

DTI resolution is 0.0001" so each unit of major scale = 0.001"

Pete

 

[vcutajar]

Pete I am no expert but I think I saw the 4 jaw chuck backplate wobbling. Maybe the backplate face which mates with the chuck needs to be faced.

Vince

 

[vcutajar]

Pete

Did you check the face of the backplate with the DTI? Just my impression.

Vince

 

[doubletop]

Vince

I checked the video and see what you mean. I know there are a few of these lathes out in our community and hoping the experts will be able to advise what should be expected.

No I haven't checked the face. I'm reluctant to disassemble the chuck until I've spoken to the vendor. The video is really for their benefit so I can show them the problem. I've posted here for an unbiased opinion.

Pete

 

[Blogwitch]

Pete,

Just to put you on the straight and narrow and to allay a few of your fears.

1. The outside faces of backplates and chucks can be almost anywhere, they are only rough machined to within a few thou. All the slots and other things are done after the chuck has been mounted onto a jig, and so should be within close tolerances.

2. A four jaw is like working with a faceplate with something mounted on it, it is inherently unbalanced, purely because of the way they work and are assembled, so expect vibration at higher revs.

3. Have you done your chuck setups yet? This is for your self centring scroll chucks. Insert a good quality bar into the chuck and tighten up. Put a pop mark on the outside edge on the headstock nose, adjacent to one of the D1-4 locating holes and then put the chuck onto the nose fitting. Number the pins on the chuck. Check the runout on the bar in the chuck. Note down the runout and pin number adjacent to the pop mark on the nose fitting. Move the chuck around one locating pin, and try the runout again, note this down. Repeat for all four locations, and it should show that in one position, the runout will be better than the other three. Mount the chuck into that position, recheck the runout, and if it is still the best, put a mark on the chuck in line with the marked headstock mounting hole. Always mount the chuck in this aligned position.

I have done this with all my chucks and even the faceplate and four jaw, without the runout check of course, just to make sure that the nose fittings always go into the same position on the lathe.

With self centring scroll chucks, you should always, as well, find out which key hole gives the best results with runout when tightening. Most chucks will have a '0' mark on the master key hole for that chuck which was used when making it, but if not, find the best key hole yourself and mark it up, and always use that one hole for final tightening.


John

 

[doubletop]

Thanks John

At least you didn’t say “OMG”, which is a good start. I had realised the back and edge of the back plate would not be good reference points but I did the checks for completeness, lest somebody would ask “have you checked the back and edge of the back plate?” I realise that the chuck should probably come off the back plate and the register tested but I don’t want to disturb it until the vendor has come back to me.

I had attempted to get the 4 jaw in balance by truing up the test bar. It’s clear that during the manufacturing process they’ve balanced the chuck as it has had some weight removed on the front face by machining a small recess. I took the view that as they had done that it should run pretty well when the jaws were set the same.

On the three jaw, although the jaws are marked 1, 2, 3 but for some reason the chuck isn’t. Setting the test bar using the “0” key hole I tried all 9 combinations of jaws and camloc positions (mine is a 3 pin camlock) until I found the best combination and then marked the jaw positions and backplate/nose location. That’s the setting I’ve used in the video.

Pete

 

[Chitownmachine]

Well looking at the video, I agree with the other guys, but you need to seperate the chuck from its mating plate and indicate off a machined surface....for example, the bore of the plate and the machined face of the plate. You are indicating off of what looks like a cast or rough machined chuck plate which dosen't "really" have to be concentric as long as the bore is and the bolt holes are good....the IMPORTANT things to chuck concentricity are bore of plate concentric, face of plate flat, mounting holes are equal distant from the center of the bore. Just a few things to think about. If the bore is ok and face is out of whack, take a facing cut till the plate is true. Lemme know how it goes.

 

[Blogwitch]

Sorry about that Pete, I should have said three pins not four, exactly the same as mine.

You might find that the recess in the front of the chuck is where they normally stick their badge, and it has most probably dropped out somewhere. All my chucks have them.

Sometimes the jaw numbers aren't marked very clearly, or just the '1', or maybe are very tiny, but the C-o-C at the bottom shows where they are normally located.

With regards to the vibrations, if it isn't an out of balance item mounted on the spindle then you should check your lathe foot mountings. My lathe has six mounting holes, four under the head and two under the tail (as far as I can remember without looking), and is supported on bolts, with their heads as the feet, and mine has never vibrated like that since it has been in position and levelled, and it isn't even bolted down, just the weight of the lathe holding it there. Except for the gearbox whine, if you felt my lathe whilst running, you could hardly tell if it was running, it is that smooth.

Check your motor pulley whilst running, and see if it is that which is vibrating or out of line. Is yours the 9 or 18 speed model? Mine has four pulley grooves in each sheave and is the 18 speed version, so if yours is the 9 speed then it could be different to mine.

Other than that, I can't suggest much more than has already been mentioned.

John

 

[doubletop]

Thanks guys

As suggested; I do need to separate the chucks from the back plates and test them, but until the vendor gets back I'll leave as is. I think that, as the nose seems OK, it is just about the chucks and back plates. The vendor did say they had a test rig for chucks

The thing about the 4 jaw is it is very visibly eccentric. The vibration doesn't occur with anything but the 4 jaw and it isn't really moving the lathe and stand its just the resonance going through the machine. Other than that its on a pretty flat surface. When they laid the new garage floor they used a laser level.

You may be right about the label, the 3 jaw has one but the 4 jaw doesn't.

Its the 18 speed model set to the low range, as you know John it isn't the easiest to switch ranges.

I'll go out and re-check the jaw numbering, but I think I checked with the magnifier lamp.

Pete

 

[ShedBoy]

I did not know about jaw numbering when I first got my lathe (AL335A). A nieghbour put me on the right track when he watched me changing jaws over one day. Repeatability is excellent now. Original chuck has never been apart but is probably due for a clean.

Brock

 

[coopertje]

Hello Pete,

Recently I had a similar issue after mounting a Rohm chuck on a Chinese back-plate. The back-plate was machined on the lathe, this ensures a maximum accuracy. When running at higher RPMs and when using the chuck I had vibrations in the machine and the surface finishing of a test part was terrible. I checked my lathe the same way as you did and there was no issue here, the complete spindle (inside, outside and front) was within 0.002mm. I took the chuck from the backplate and put it in my milling table with the camlock facing upward. Put the DTI in the mill and measured the angle of the inner adapter (move down for 5mm, check the difference on the DTI and calculate the angle using the tangent). I found that it was 1.5 degrees off!! Ok, problem found. The result of this angle mismatch is that the back-plate does not centrate on the lathe spindle cone but more or less on the 3 studs of the camlock system. I think its wise to check this on your lathe, as you probable know repeatability of chinese products is not their strong part. May explain why your 3 jaw is ok and your 4-jaw not. To solve this set-up your top support of the lathe with the DTI running over the spindle cone. When it is absolutely zero, mount the back-plate on your 3-jaw and re-machine the inner taper of the back-plate. Take away as less as possible, you do not want your cone to become too big!! When the fitting is ok, mount the back-plate on your lathe and machine the adaptor ring for the 4-jaw yourself. I do this with all my adaptors and chucks unless they are from a well know quality brand.
Hope this helps, good luck and regards Jeroen

 

[doubletop]

Hello Pete,

........................solve this set-up your top support of the lathe with the DTI running over the spindle cone. When it is absolutely zero, mount the back-plate on your 3-jaw and re-machine the inner taper of the back-plate. ...................

Jeroen

Got it thanks. It took a couple of reads for the bit above. But then realised what you were getting at. Set the topslide angle to that of the nose cone and use that to face off the 4 jaw back plate inner cone angle.

Pete

 

[coopertje]

Thats exactly what I mend. Sorry if it was unclear :-\

Regards Jeroen

 

[rkepler]

But then realised what you were getting at. Set the topslide angle to that of the nose cone and use that to face off the 4 jaw back plate inner cone angle.

I've made a couple of D1-3 adapters (I'm assuming that's what you have), and find that getting the angle right is a real PITA. On remachining one the problem is going to be getting the right angle at the correct major diameter so the backplate can be tested against the spindle. On mine I'd bore the depth first (.500 minimum, non-critical but I'd go .510) set the taper (3"/ft or 7 deg 7 1/2 min but really whatever your spindle has) and cut the taper max diameter out to approaching the 2.1250" spec. Somewhere around 2.1" I'd pull the backplate, blue the spindle nose and see where it was on the angle, you'd get a fair test at this point. (Really, at this point I cheat as I have another spindle nose against which to test). Correct the angle, take a little bit off (I paint the taper with marker or blue and nibble until it's gone) and test again. Once you think you're close to the right diameter you can start testing the fit against the spindle face with some Plastigage - put one piece on the center of the 3 flats and look for .001 clearance when tight. Squishing them flat is acceptable as long as you're close to the max torque you want to apply to the cams - what you're looking for is for the spindle taper to center the backplate and the face to make sure that it's square. I think a D1-3 fit is right when I have to pop it with the heel of my hand to make it release after undoing the cams.

If you end up playing with the taper cut so much that you his the spindle face w/o contacting the taper you can just take a little facing cut to narrow up the taper again. I've had to do that with a couple of import plates that were overcut.

 

[doubletop]

Good news; it looks like I won't need to do any machining. I sent the vendor the link to the video and they are going to take the 4 jaw back and sort it for me. I think you've confirmed for me that what I'm getting on the 3 jaw is what should be expected.

I won't see it again for over a week but when I get it back I'll do the same test and show you the result.

Pete

 

[vcutajar]

That is good news.

Vince

 

[doubletop]

Packed off to the vendor over the weekend, probably shipped north today. I'll let you know the verdict.

Pete

 

[Blogwitch]

Pete,

Packed off to the vendor over the weekend, probably shipped north today.

That's the advantage of where I live, only a few miles to the vendor, any problems and it is a face to face confrontation, and issues get fixed on the spot.

You must have read somewhere on here that I actually refused my lathe after I assembled it because I had a few issues with it.

They rebuilt a new one at the factory and modded it to my specifications, then I went there and gave it a good dose of looking over. They then brought it to my house and swapped them over.

I also made on the deal as well, they gave me a spare 3 jaw chuck, so I now have two, one with normal jaws and one with soft jaws permanently fitted, plus a few other little sweeteners.

It always pays to complain if something isn't to your liking.


John

 

[doubletop]

John

I do recall you saying you'd had a few issues with yours and the vendor had sorted it for you. Fortunately, you've got the background and experience to know what's right and whats not. I haven't used a lathe like this since I used a clapped out Boxford at school, so no way of knowing what to expect.

Are you sworn to keep quiet on the issues you experienced, lest they get a worldwide run of complaints, or can you share?

Pete

 

[Blogwitch]

Most were to do with build quality.

At one time, there was a worldwide shortage of these machines, and it looked like mine had been made up with some reject parts fitted and painted up with a Turks head brush in an attempt to make it look good, just to try to clear the backlog of orders. A major ding on the slideway, casting voids showing under where the toolpost sat, etc etc.

But my main issue was with the safety equipment fitted.

With the fitted chuck guard, you could only turn a maximum of 11", not the 17" that was advertised. They fitted a much larger industrial chuck guard on the new machine and that cured that fault.

The other main issue was the telescopic spring sleeve that covers the leadscrew. With it fitted, it did not allow the saddle to go forwards enough to let me work with the faceplate, in fact, with the topslide and saddle fully forwards, the tool tip was still 3" short of the faceplate. They removed the guard on my new machine.

Those last two faults are most probably still present on your machine.

John