Boxford 280 lathe run out.

[Andy SprouleParticipant @andysproule22368]

Hi I’ve had this lathe for several years now and very happy with it,after a discussion with a friend I checked the run out on the lathe with the 3 jaw chuck on and off  it’s a D1-3 fitting.With the chuck off the front taper is 0.02 mm run out the face of that taper is 0.005mm run out, with the 3 jaw chuck on the run out is just slightly over 0.02 mm.Wondering how accurate it would have been from new and would other owners be concerned with this type of run out

[Martin ConnellyParticipant @martinconnelly55370]

Typically it is usual to assume that the runout of a three jaw chuck is not too important. Trying to remove a machined part from a 3 jaw self centring chuck and then replace it in exactly the same position is often a futile experience. Also the chances of the jaws giving the same run out for different diameters is low. If you have obvious (as in visual) run out of a three jaw chuck then some remedial work may be required but mostly they are used as is. If you want to put a part machined workpiece back in a chuck then an independent 4 jaw chuck can be used to achieve near zero run out so this is the path most people follow.

If you have a need to regularly hold lots of parts with low runout without needing to dial in a 4 jaw chuck then collets or soft jaws could be a good option. There are also times when turning between centres is a good technique to use but some people never need to do it.

Martin C

 

[Thor 🇳🇴Participant @thor]

Hi Andy,

I don’t have a Boxford 280 lathe but the run out on my old Compact 8 is less than the 0.02mm you get on the taper. A thread about the run out here. I assume you are already a member of the BoxfordLathe user group.

Thor

[Andy SprouleParticipant @andysproule22368]

Thank you both for taking the time to reply.I saw that thread on run out he was happy when he ended up with 0.02 mm run out.I am not a member of the Boxford group but will join up.When the 280 came from the factory I was wondering would there be no run out at all or what would have been acceptable to them.

[PeteParticipant @pete41194]

While it’s not a Boxford or a D1-3, the principles are exactly the same for any lathe since any spindle mounted chuck or work holder has to locate to the same points each time for both the radial and axial run outs. Try this video. https://www.youtube.com/watch?v=ii0Xbzl1kIw for how he re-ground his lathes spindle nose to much better than it was. That video will explain the importance of each surface the chucks locate to with the D series spindle mounting design. However an exact answer to your question is still not quite that simple. The spindle bearings and / or any adjustment to those needs to be verified as being 100% correct first. And any indicator checks are in fact only a static test. Many changes can occur once the spindle is under power and cutting loads are applied. And that’s when the spindle bearing condition or adjustment becomes even more important. Logically you need to properly access each of the interrelated components before concluding what may or may not require adjustment or further correction. I wouldn’t know the factory new Boxford lathe specifications for your spindle measurements, but I think your .02 mm / .00078″ is likely a little on the high side. Without question your Boxford would have been shipped with a proper certificate of accuracy and those numbers would certainly been listed. So finding anyone with the same lathe that still has there own certificate, (maybe on that Boxford group) should get you what the factory new numbers would have been. While very good, the .005 mm / .00019″ axial measurement and where you checked it is unimportant. It’s the face and it’s radial run out that has the holes for your cam lock studs to go through that is. That and the spindles internal Morse taper, although it’s only really important when taper tooling is being used in it. Ideally and with the D series design, the cams pull the chucks back plate taper fully onto the spindle taper until it also seats against that spindle face at the exact same time. So the spindles male taper ensures the chucks correct radial position, and that face gives the correct axial location for the chuck each time it’s mounted. Both have to be correctly sized to very high levels of precision on both the spindle and chucks back plate for each locating surface to properly work and fully contact each other as they should when the cams are fully tight.

And as others have mentioned, three jaw lathe chucks are mostly a convenient and easy work holding method. As long as the work is completed at a single chucking, then almost any run out number a seriously worn or even cheaper off shore chuck might have are almost irrelevant. Far too many seem fixated on wanting those very low run out numbers from there three jaw chucks. Yes of course it’s nice if you can get that, but absolute repeatability and perfection is still impossible. If you need better concentricity when re-chucking the work, then any standard 3 jaw with there hardened jaws isn’t the work holding method that should be used. And the radial run out number any chuck, face plate, collet etc may have is still only half of what’s really important. Just like checking that spindle face for it’s axial run out, then how true and parallel the jaw gripping surfaces or face plate may be to the lathe bed are also just as important. And few seem to ever check that. Without question the better brand name chuck manufacturers would be finish grinding those jaws in the completed chuck on rather specialized grinding equipment and making the extra effort to ensure those jaws are in fact square to the chuck face itself. With those much cheaper chucks, there exact alignment may be correct or not, and possibly no different than an already decent chuck with those worn or slightly tapered jaw faces.

 

[HuubParticipant @huub]

I you haven’t noticed the runout over the years, than obviously it is not so important for you.

It seems your chuck holder is mounted on the lathe spindle using bolts at the front. You could check if this mount has any play and use that play to decrease the spindle runout. As mentioned before, check your bearings first!

I have turned the register on the backplates of my chucks a bit larger so I can use the play to reduce the runout.

The runout of my (Chinese) 180 mm Sanou chuck was less than 0.01 mm when new (absolutely top). After 3 years of hobby (ab)use, it is now 0.025 mm worse case (not bad for a 3 jaw lathe chuck).

The runout of my (Taiwanes) 80 mm chuck is 0.05 mm worse case after 15 years of hobby (ab)use (acceptable for a 3 jaw lathe chuck).

[MacolmParticipant @macolm]

Only the two Camlock interface surfaces need to run true, being the taper and the adjacent flat face with the holes for the cam pegs. I would expect these to be better than 0.01mm TIR. Certainly on my Colchester Bantam they are better than that, but most of the other the faces have slight visible eccentricity.

[Robin DuftonParticipant @robindufton85682]

Are you measuring 0.020mm with the spindle running slowly with the machine warmed up, or are you grabbing the spindle and turning it by hand with the machine cold?

I’ve had to demonstrate a number of times that the numbers you see aren’t always trustworthy. Prime being someone who measured runout on a Bridgeport at 0.070mm and their eyes bulged when I pushed sideways on the spindle and doubled it.

[MacolmParticipant @macolm]

If you have a self-centring chuck mounted on a back plate which has some slack on the register, and also a morse taper extension adapter that runs true over that length where the chuck jaws will close, you may be able to rapidly get the chuck running very true as follows.

Fit the extension arbor inside the chuck, lightly nip the chuck jaws onto the true diameter, and similarly nip the chuck back plate fixings, then progressively tighten both up to the operating values. Hey presto, the chuck will be pretty true for that diameter. A lightly worn chuck will then be reasonably true over its full range of diameters. I have a four jaw self centring chuck mounted like that, and run out is very small indeed.

A custom device might be blank morse arbor threaded so that a mandrel can be fitted, and its diameter turned to the size you use most often. Then proceed as above to centre the chuck.

[Ian PParticipant @ianp]

Andy, its not completely clear what the two measurements you have shown in the picture actually are.

I assume the 0.02 is radial run out on the taper spigot but the other number (0.005mm) looks to be axial run out on the end face of the spindle which has nothing to do with the chuck mounting, The end face will be in fresh air when the chuck is mounted.

The important face is the large diameter one. Have you checked the axial run out of that?

Ian P

 

 

[Howard LewisParticipant @howardlewis46836]

Don’t get too obsessed by the numbers.

The results that you get will be different depending on how and when you measure.

Cold, rotated by hand will probably differ from cold under power, and again from what you find when the machine is warmed up and running under power.

Worn or maladjusted bearings will are unlikely to provide the accuracy, or repeatability, that you seek.

The acid test is does it cut parallel when warm ? Because that is what you ultimately want the machine to do.

A hot compnent will be larger than when it has cooled to ambient temperature.

That result might vary according to depth of cut, and or feed rate,since the forces involved will change.

To make any sense, the measurements need to be taken under conditions that are as consistent as possible.  (Which is why, in industry, Standards and Calibration rooms are temperature and humidity controlled , and measurements only traken after the component has been there for 24 hours to ensure that temperatues are all the same).

Eliminate as many variables as possible before recording any dimension or run out

HTH

Howard

[Martin ConnellyParticipant @martinconnelly55370]

I would just like to add that with a large boring bar and carbide inserts you can clean up the faces of chuck jaws without having to resort to a lathe mounted grinder. I bought a new set of standard (internal) jaws for a chuck I had that was missing them and did this as there was visible runout when first fitted. The caveat for any process like this on a three jaw chuck is that as soon as you move the jaws to another position there will likely be a measurable runout as there are so many factors that can change the runout.

Martin C

[Nigel BennettParticipant @nigelbennett69913]

I’ve just checked my Boxford 280. The radial runout on the internal MT bore is 0.02mm TIR but the outside tapered register is only 0.005 – the needle barely moves. Curious; you’d think they would be more or less the same.

I replaced the headstock spindle bearings with standard Timken bearings, which were not to the same high specification as the originals, which appeared to me to be a bit worn. £200 or so… about five years ago. I kept looking for some Gamet ones at the time (It was an option from Boxford), but even if I could have sourced them, they would probably have been ten times that price (if the price of similar-sized ones were any guide.)

[mgnbukParticipant @mgnbuk]

At work we have a Harrison VS330, bought s/h and unusually it came with it’s original documentation pack, including the test certificate. I was in work today & took a couple of pictures or the test certificate, the spindle bit is below :

The values are metric. Also included was  Talyrond readout of a test piece machined on the lathe & details of the standard the machine was built to :

The VS330TR is not much bigger than a Boxford 280, so the values should be a reasonable guide. The two machines amy well have been designed by the same chap – the Boxford designer came from Harrisons & I recall it being stated at the time that he had designed the M300.

HTH

Nigel B.

 

[PeteParticipant @pete41194]

Yes the correct carbide replaceable tips that are resistant to cutting edge damage during interrupted cuts could be used to lightly re-bore the chuck jaws. But that’s not the full story of how it would need to be done for anyone attempting this for the very first time. First visualize how the jaws operate and are retained within the chuck body itself. For any mechanical object to move or slide within another, there has to be a certain amount of clearance. With a lathe chuck, those would be between the chuck jaw slots, jaws and the tenons and grooves on even the best and most expensive chucks made. And those non optional clearances are what allow the chuck jaws under those tightening loads to very slightly tilt backwards with the external jaws until they fully bottom out within whatever those clearances allow. And even more so for short work that is less than the length of the jaw faces. It’s for that reason various methods of preloading the jaws so there in there normal fully tightened position before those jaws are re-machined or reground. That way they will come out true and parallel to the lathes bed ways and concentric to at least that diameter they were re-machined or reground at. It would be a waste of time trying to re-true the chuck jaws without doing so. And even more so with a worn chuck. In fact you might end up with even more run out and / or far less gripping force on those chuck jaws if it’s done incorrectly. Without that preload, the jaws will bounce in and out within those clearances during each rotation of the chuck as there being re-bored or reground.

About the best video I know of about preloading and grinding jaws would be this one. https://www.youtube.com/watch?v=xYKBBApx6c8. It’s done from the perspective of using logical and known directional forces for how 3 jaw chucks actually work and how the internal and external chuck jaws are tightened to. And yes he’s using a proper tool post grinder which few of us will have. But the set up and methods will have no difference if you chose to re-bore the jaws instead. The ubiquitous Dremel tools are well known as have rather poor spindle bearings, I’ve still used mine to regrind chuck jaws with decent success as long as I properly dressed the grinding wheel first and take extremely light depths of cut with multiple spark out passes.They can be made to work, but it’s obviously very slow and far from ideal. To add to his findings in that video about which pinion is the most accurate after regrinding. I have a couple of very accurate and for there size quite expensive Emco chucks. In the short user manual each came with, Emco were quite specific about keeping all the parts in the exact same positions the chuck was originally ground to including each of those pinions. And the pinion location on mine that the chuck manufacturer used when the final finish grinding was done is stamped with a noticeable 0 mark as it’s master pinion, and that one gets used for the best concentricity.

With the limited amount of chuck literature I’ve managed to find, the manufacturer’s don’t seem to stress just how important cleaning of the chucks internals really is. A one time I never cleaned any of my chucks either. At least not until I managed to break a a jaw tooth from trying to force the jaws past whatever chips and debris were inside it. Fortunately that one was a relatively tiny and inexpensive chuck, so that lesson could have cost me a lot more. But no chuck no matter how accurate when new will continue to produce the same accuracy unless it’s kept fairly clean. And as that video points out, you would need to do so before any re-boring or grinding was being done, and for some very good reasons.

[Andy SprouleParticipant @andysproule22368]

Thank you for all the replies very interesting and informative.As Huub pointed out”It seems your chuck holder is mounted on the lathe spindle using bolts at the front. You could check if this mount has any play and use that play to decrease the spindle runout. As mentioned before, check your bearings first!”These bolts were not fully tight and with a bit of light tapping and fully tightning the reading on the taper is 0.006 mm and the flat face with the holes for the pegs 0.008mm.

[Andy SprouleParticipant @andysproule22368]

Watched a video on YouTube of a guy testing an industrial  boxford he used a  three foot length of three by two under the chuck and got 0.02 mm  lift was wonder what you thought of method and result?Its at 2.20 mins

[Clive Brown 1Participant @clivebrown1]

As Archimedes once said; “Give me a lever long enough…..”

[PeteParticipant @pete41194]

It’s a classic method used to check bearing clearance. But I’d keep it in mind that he’s checking a larger lathe with much heavier bearings and spindle than might be common for most of us. So a shorter length of lever on a smaller machine is all that’s needed. All your really checking on a sleeve or roller bearing head stock is how much clearance or slack there is in either bearing type between the spindle and bore with sleeve type bearings, or internal clearance within a roller bearing that might be due to wear or being slightly out of adjustment. So your taking up whatever clearance and squeezing out any lubrication film that’s there. Any extra force isn’t needed beyond that.

It’s also a good check if the lathe may or may not need that adjustment, so any extra clearance doesn’t necessarily mean it needs new spindle bearings. The axial end float of the spindle would be another important check. But the lathe should also be fully up to normal bearing and spindle temperatures before these checks or you may get incorrect measurements between a room temperature machine verses one that’s warmed up. Imo adjusted .001″ too loose is multiple times better than .001″ too tight. 🙂

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