Lathe run out

[RobinParticipant @robin]

Wasn't sure if I wanted to admit it, but I do have a level, does that make me weird?

It is making me think I may want a floor mount I can adjust while looking at the bubble.

[Anonymous]

Posted by Chris Mate on 12/05/2021 19:45:17:

As soon as you bolt the lathe Headstock-to-Bed combination(Maybe new from factory) down to something, in most cases the cabinet, your bed twist is linked to that………..

Not really, it depends upon the lathe. My secondhand lathe came bolted to the manufacturers cabinet. Early on I had issues with it turning tapered at the headstock, although strangely not when boring. The consensus on the internet was that it was a bad idea to fiddle with the lathe to cabinet bolts. Instead I spent ages shimming and fiddling with the cabinet bolt down points to no avail. In the end it turned out (just like Hopper mentioned above) that I hadn't been careful enough when replacing the gap piece. Having triple cleaned the gap piece and refitted it according to the instructions I loosened all the hold down bolts and just let the lathe sit on the concrete floor. The lathe now turns parallel to a couple of tenths at the tailstock and a thou or so at the headstock. Not bad for a lathe that is over 40 years old and is unshimmed.

Andrew

[Anonymous]

Posted by Robin on 12/05/2021 20:25:06:

…………..I do have a level, does that make me weird?

No, but using the level across the tops of the prismatic guides doesn't tell you anything useful, as those surfaces play no part in controlling how the saddle moves, which is what you're really interested in. In addition the saddle is controlled by one prismatic guide, not by both.

Andrew

[Dave SParticipant @daves59043]

Whilst maybe not strictly correct placing it across both prismatic ways at both ends is at least consistent.

I think you can (initially anyway) assume the prismatic ways relationships do not alter along the bed – it there would be all sorts of fun with the tailstock/saddle relationship.

That implies that the reading should be the same at each end assuming the lathe is not twisted.
The photos show 2 quite different readings, so there is at least a bit of twist to look at.

Dave

[Mark Simpson 1Participant @marksimpson1]

I have the same machine, and also fought the taper for a frustrating time. I made jacking feet from M12 bolts as my floor is not surface plate quality… Things improved a lot and have stayed true… I bought an MT3 testbar and got it to .0005" over 15" (actually it worked out about .0007" over 30" when I turned the back axle for my TE)

If someones had the gap piece out they are a real b****r to get back properly. I use a DTI to see if the carriage lifts when passing over it… If the needle moves it's not bedded properly…. do it again. The mating surfaces are not as well ground as they might be.

At the end I faffed around with the tailstock to get it as close as possible… and I've left it alone… IF I need an offset (only needed it a couple of times) I use a 2" boring head from the mill in the tailstock on an MT3 arbor

Good luck, the basic lathe is fine (especially for the money) some of the accessories are "sub optimal"
oh and you'll have to pull the coiled leadscrew guard off to skim the backplates on the chucks

[HopperParticipant @hopper]

Posted by Robin on 12/05/2021 20:25:06:

Wasn't sure if I wanted to admit it, but I do have a level, does that make me weird?

It is making me think I may want a floor mount I can adjust while looking at the bubble.

 

 

Good start. I would first get it bolted down firmly to the floor. Then set it "level" (or at least the same bubble position) at both ends of the bed proper, not the removable gap piece. U-shaped shims slid in under the mounting bolts will do the job. Usually only takes a few thou here and there of shim. You will soon get a feel of how much shim causes how much movement of the bubble.

Once you have got it level, you can then repeat your turning test and see how it compares. Any further shimming to bring it to turn dead parallel can then be done.

Setting it level does not always absolutely guarantee parallel turning because as noted above, it is unknown if the tops of the inverted V ways are dead true to the angled load bearing surfaces at the front or the flat surface the carriage rides on  at the back. Plus these cheaper hobby lathes are often made from "green" castings that have not been aged to relieve casting stresses, so can move and distort a bit after being machined in the factory. Plus there can be the movemet of the carriage under the load of cutting forces. Also there is the factor of the removable gap piece being properly made and installed.

So your turning test will be the last double check just in case. Then, on with the tailstock but that is a different job.

 

Edited By Hopper on 13/05/2021 03:18:45

[RobinParticipant @robin]

Posted by Hopper on 13/05/2021 03:15:13:Good start. I would first get it bolted down firmly to the floor. Then set it "level" (or at least the same bubble position) at both ends of the bed proper, not the removable gap piece. U-shaped shims slid in under the mounting bolts will do the job. Usually only takes a few thou here and there of shim. You will soon get a feel of how much shim causes how much movement of the bubble.

I might get away with glue but drilling holes in her garage floor is not really on the cards, we have to keep this credible. She has X-ray vision and knows instinctively if I am hiding something.

I like Mark's M12 adjustable feet, but how does that square with your "few thou here and there"? How about three m12 feet and one fine thread foot at the lighter end? I have a set of M17x1.0 taps and die which need trying out.

Someone in New Delhi is selling MT5 alignment test bars for £70 including carriage on fleabay. Worth taking a chance?

[Ex contributorParticipant @mgnbuk]

Consider a lathe on a ship

All well and good, but lathes are not built on ships.

They are usually built in factories with concrete floors and precision levels are used duing the build process to a national or "house" standard. Using a precision level to put the machine back to the condition in which was was checked out at the factory should produce the same test sheet results.

Warco sell adjustable mounting feet

There are holes visible in the machine base that will take these and allow adjustment of the machine base on the floor.

Nigel B

[HopperParticipant @hopper]

Posted by Robin on 13/05/2021 10:56:05:

Posted by Hopper on 13/05/2021 03:15:13:Good start. I would first get it bolted down firmly to the floor. Then set it "level" (or at least the same bubble position) at both ends of the bed proper, not the removable gap piece. U-shaped shims slid in under the mounting bolts will do the job. Usually only takes a few thou here and there of shim. You will soon get a feel of how much shim causes how much movement of the bubble.

I might get away with glue but drilling holes in her garage floor is not really on the cards, we have to keep this credible. She has X-ray vision and knows instinctively if I am hiding something.

I like Mark's M12 adjustable feet, but how does that square with your "few thou here and there"? How about three m12 feet and one fine thread foot at the lighter end? I have a set of M17x1.0 taps and die which need trying out.

Someone in New Delhi is selling MT5 alignment test bars for £70 including carriage on fleabay. Worth taking a chance?

Crikey, you need to get 'er better trained. But that's a longterm project and beyond our remit here.

Four adjustable feet, the type with large round rubber or urethane etc pad at the bottom of each would do the job. Search for "machine feet adjustable" or "Machine Levelling Feet" and you have plenty to choose from. They come in different diamter mounting threaded studs to suit whatever holes are already in your cabinet base. They have two nuts on each threaded stud so can be adjusted to suit your needs. No need for ultra fine threads etc. Whatever they come with will do the job. Not as good as bolted down but better than perched on lumps of wood for sure.

I would not buy the test bar from India. Unknown quality — some are very poorly made — and not at all necessary to set up your lathe. The two turning tests I described earlier will do the job to a better standard.

Others here can probably recommend where to buy suitable machine feet in the UK and that should get you going.

[simondavies3Participant @simondavies3]

Posted by Robin on 13/05/2021 10:56:05:

Someone in New Delhi is selling MT5 alignment test bars for £70 including carriage on fleabay. Worth taking a chance?

It depends….the one that I bought was tri-lobed on a very coarse spiral down the bar, bent and (as far as it was possible to measure accurately across lobes) tapered. In essence, an expensive MT3 taper since that was the only functioning part. eBay agreed and refunded me immediately suggesting that my supplier might have already had some complaints…

The replacement from China (yes, I know, I never learn) appears straight and measures the same with my digital micrometer at each end but is not the finest piece of work. I use it with caution and remind myself that I didn't spend a fortune on it so shouldn't expect any more.

[RobinParticipant @robin]

After further investigation RDG Tools have an HBM 5MT LATHE PARALLEL TEST BAR for £79.50 incl., but the description next to it is for a 'tween centres bar so I would have to enquire what it actually is

[Tony Pratt 1Participant @tonypratt1]

You don't need a test bar, just shim the lathe until it cuts parallel.

Tony

[Lee Reynolds 1Participant @leereynolds1]

Alignment bars from India – yes it does depend.

I took a chance and paid £80 for an MT5 one with Express delivery (Arrived in 5 days)!

There seemed to be several suppliers and I was lucky.

Mine measured OK and the results matched those done by a professional, with an ex Harrison works real thing, on my M300 the week before.

My only criticism would be the lack of proper centers in each end, but still worth the money I think.

[Howard LewisParticipant @howardlewis46836]

In your position, I would not worry about fixing the cabinet to the floor. You could fit adjustable feet, and adjust the level using those. Some cast iron lathe stands have tappings for just that purpose..

If you have to concentrate your efforts on shimming between the lathe feet and the cabinet. to remove twist from the bed, you need to read how to do it as per Ian Bradley in "The Amateur's Workshop" or the "Myford 7 Series Manual" as a guide to where to adjust the feet.

If you don't like shimming, you can use studding and nuts between the lathe and cabinet. One nut each side of the cabinets holds the studding captive, while a nut above and below each lathe foot provides the adjustment to take twist out of the bed.

Ian Bradley advocates leaving the Headstock end alone and making all the adjustments at the Tailstock end..

Once twist is out bof the bed , the machine should cut parallel on an supported bar (Follow Ian Bradley's advice and only take fine cuts, on a reasonably thick bar, to minimise risk mof the cuttingb pressures deflecting bthe bar.

If, after this, the lathe cuts a taper when working between centres, it is possible that the Tailstock is offset across the bed. To check, and if correct this, firstly you need two good centres. The hard one goes in the Tailstock, and it is worth trimming up the soft one in the Mandrel, immediately before use.

Fit an alignment bar (Or a substantial bar known to be straight and parallel. ) into the four jaw chuck and adjust the jaws until the DTI shows it to be running absolutely true..

Mount a DTI (The more sensitive, the better ) in the Toolpost, at centre height and set to Zero. Move the Saddle to the end of the bar, and note the reading Unless the Headstock is out of alignment, the reading should still be Zero..

Then mount the Alignment Bar between centres and set the DTI, still at centre height, to Zero. Move the Saddle to the tailstock end of the bar and note the reading..

If the reading is anything but Zero, use the adjusting screws to move the Tailstock, (lock one against the other each time ) until the DTI reads Zero at both ends of the travel of the Saddle.

You can check the centres for being at the same height.,by bringing them together so that they grip a thick feeler gauge or steel rule, placed vertically between the centres. If the centres are at the same height, the feeler will be vertical. If it is not, the centres are not at the same height. Hopefully this will not be the case, since your lathe appears to be fairly new.

Unless the error produces large taper errors, with a prismatic bed, you might be better to live with it.. Scraping or shimming the flat underside, might introduce other errors because of the prismatic way, so sleeping dogs may best be left to lie. Totally correcting the error may be difficult.

Howard

Howard

[RobinParticipant @robin]

Posted by Howard Lewis on 13/05/2021 23:35:17:

In your position, I would not worry about fixing the cabinet to the floor. You could fit adjustable feet, and adjust the level using those.

Sounds good and I agree with this Ian Bradley bloke, fix the headstock, adjust the tailstock. However, I won't be reading his book because education is for young people with their lives ahead of them, not for old gits living on anti-stroke meds.

I like shopping with my granddaughter, drawing CAD on my computer, and exporting that CAD to the machine tools in the garage.

This week I have bought a hoverboard, made some machine feet, and ordered some steels to fit those feet to the bottom of the lathe cabinet. One foot in each corner, one tie bar across the middle to stop the bed sagging like a hammock.

Once made and fitted I will reawaken this "Topic" and I will be most grateful if you could be here clutching your copy of "The Amateur's Workshop" just in case it all goes horribly wrong, as it probably will, confidence being that feeling you get just before you understand the problem

[Pete RimmerParticipant @peterimmer30576]

I make adjustable machine feet by welding large thick washers to the heads of bolts The washers go against the floor and I use flanged nuts underside of the feet, unless the feet are themselves tapped.

As for putting the level on the flat tops of the prisms – This won't allow for wear but it will let you see if the bed has twist. T

he prisms will have been ground in the same setup as the ways (or at least they should have). There's no other efficient way to do it.

[HopperParticipant @hopper]

Nice work. I think you will need a second nut on each screw to enable you to adjust and then lock in position. Or are you doing something tricky there?

[RobinParticipant @robin]

Posted by Hopper on 16/05/2021 11:14:07:

Nice work. I think you will need a second nut on each screw to enable you to adjust and then lock in position. Or are you doing something tricky there?

Why, thank you

I have 1 1/2" x 3/4" steel bars coming which I will drill and tap to take the weight. Those large m16 nuts are mere locknuts.

Have to get my 15" tap wrench out, biggest I have, unless this is about to turn into another jolly shopping opportunity

[RobinParticipant @robin]

Posted by Pete Rimmer on 16/05/2021 11:10:48:

I make adjustable machine feet by welding large thick washers to the heads of bolts The washers go against the floor and I use flanged nuts underside of the feet, unless the feet are themselves tapped.

I have never had much luck with welding, Never found the right darkness in the mask. Lord knows I have tried.

My son has TIG and MIG and doesn't think there is a problem

[HopperParticipant @hopper]

16mm. Yeah that should take the weight!

Drill your holes a bit oversize to make the tapping easier.

[Howard LewisParticipant @howardlewis46836]

Once you have the adjustable feet in place, you are ready to start taking any twist out of the bed.

Ian Bradley explains much better than I can but here goes. He is talking about adjusting the lathe relative to the bench, but in your case you are adjusting the cabinet.

Put a piece of largish round bar in the chuck,, (Say 1"minimum, dia, but 1.5" would be even better, so that it sticks out for at least 6" Do not support with a Steady ir the Tailstock.

(Imperial since those are the units with which we are most likely to have been familiar through our lives )

Take a light skim along the bar.to clean up.

Leaving a short, say 1/2" area at each end, take a cut over the central area, to produce a "cotton Reel" effect. Only needs to be about 0.100" deep max, so may need more than one cut.

Take another very light cut, not more than 0.002" over the two collars.

Measure the larger diameters, at each end.

Preferably with a micrometer rather than a digital calliper, so that the "feel" is the same for all measurements.

If you have to use a digital calliper, push the jaws into contact with your hand, not the thumbwheel.

If the diameter of the collar at the outer end of the bar is larger; the foot at the FRONT of the TAILSTOCK end needs to be extended VERY slightly, to raise the lathe at that point..

Take another very light cut over the collars

Remeasure.

If necessary, readjust and repeat light cuts can measurements until both diametrs are the same.

The bed should then be free from twist, and the lathe no longer cut tapers.

Bear in mind that on long work, even between centres, cutting forces will deflect the bar so that the central diameter may be smaller than at the ends, so finishing cuts need to the smallest possible, with a sharp tool, mounted exactly on centre height.

For this sort of job, it would be better to use a travelling steady, to support the work close to the cutting tool.

HTH

Howard

 

 

Edited By Howard Lewis on 16/05/2021 12:23:11

[Howard LewisParticipant @howardlewis46836]

There is the possibility that the above may not work!

The cabinet could be so stiff that it will not dlflect.

If so, you will have to work between the feet of the lathe and the cabinet.

Just use tthe same technique.

Making riser blocks, and using studs and nuts will be the easier method rather than trying to find shimm which give exactly the Zero twist.

keep us posted!

Howard

[RobinParticipant @robin]

Posted by Hopper on 16/05/2021 11:55:54:

16mm. Yeah that should take the weight!

Drill your holes a bit oversize to make the tapping easier.

I must confess, I am not blessed with a vast assortment of drill bits, "a bit over 14mm" to choose from

[RobinParticipant @robin]

Posted by Howard Lewis on 16/05/2021 13:21:23:

There is the possibility that the above may not work!

The cabinet could be so stiff that it will not dlflect.

I think I am okay on that one, but keep checking

The cabinet is two plinths and a drip tray.

When I took the twisting force out by putting a roller under the right-hand end, the taper reversed itself.

The correct adjustment is there to be had, all I have to do is find it.

[larry phelan 1Participant @larryphelan1]

Have been trying that all afternoon, still no better in my case.

How much shim can be inserted between the lathe and the cabinet ?, dont want to crack the feet.

Seems like Robin and I have the same problem, just in opposite directions !

Will sleep on it and attack it again tomorrow.

[Author]

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