Lathe run out

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

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

16mm. Yeah that should take the weight!

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

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

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

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

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.

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.

Just for info the horizontal alignment of the headstock is normally adjustable on these lathes, I had to align my Bailiegh PL1340 headstock as when turning a piece of 50mm aluminium it was about 0.1 mm out over 150mm!

The lathe was second hand but hardly used. There are jacking screws on the back of the headstock to help.

ian

Still waiting for parts I have been trying to come up with some test I can apply while I screw adjust the feet.

I put in a wiggler to project the spindle rotation axis to the far end of the bed.

Then view from above and from the side with digi-cam...

It seems to be improving all by itself but I think it will twist wildly out of shape the moment I stress it.

It needs to be locked down

That long thin bar is so flexible it is telling you nothing reliable. Stick with the standard tests as described.

I'm not so sure... the wiggler tip is steady in the same position whether spinning or not. It has to be on the spindle axis. There is no other sensible place it could be.

I just dropped the tailstock down to alignment by taking it out and cleaning it below with Scotchbrite, brake cleaner and a roll of kitchen towel. Vast amounts of foundry sand, cast iron dust and Gobi desert replaced with clean oil.

I will have to take the saddle off and give it the same treatment before I can trust it, before it grinds my bed down to unuseable

Robin, I have a very similar lathe, albeit Axminster branded. It sits on the wonky flagstones of a 200 year old cellar, using eight (four per pillar) 80mm diameter rubber feet on M12 studs (I got them from WDS I think):

I was lucky enough to have to have the generous help of a professional engineer (the late John Stevenson) in setting the machine up. He spent half an hour muttering, twiddling the nuts and checking the ways with a level before announcing 'that's good enough'. No shimming or anything like that, and it was indeed 'good enough' - it turns parallel between centres to < 0.01mm over 400mm. The lathe weighs about 600kg, of which I reckon about 100-120 kg is in the stand and the rest in the machine - so it's the tail wagging the dog - but it seems to work.You'll get there! It won't twist after it's been set up properly - at least mine hasn't.

Your method of projecting the spindle axis by holding a piece of what looks like rolled BMS in a 3-jaw is, unfortunately, not good . For starters, the bar cannot be relied on to be round/straight and the chuck won't hold the bar dead on axis anyway. Then there's gravity. You need to think about what exactly you're measuring and why. And re-read what others have said upthread.

Another Robin.

That looks familiar

It's a nice machine, just needs a bit of fettling. You chose well

I am. (Based on 50 years of aligning machinery ranging from sewing machines to power station turbines. )

Plus, if the headstock spindle is a tad out of alignment with the as-yet unaligned bed, at the end of that four foot bar it's going to be waaaaay out. Which puts your tailstock alignment out by the same amount if you set it to the wiggler point.

Do what the professionals do, set your tailstock alignment as close to the chuck as possible. Preferably after the bed has been aligned.

And please be very careful spinning that unsupported bar under power. It can bend and whip around with catastrophic results if spun at more than absolute snails pace.

The department I supported at work (RGT then EGT then eventually Siemens) used alignment mandrels for years, we had to make them as large a diameter as possible because of sag. We calculated the effects of diameter and material and wall thickness to get them to have as low a sag as possible but it was always there. We ended up with aluminium alloy mandrels with diameters that reduced along their length, staring off about Ø200 then a section of about Ø150 until we had a mag base type rod in the end. The sag was lowest when the diameter was as large as possible and wall thickness did not need to be very high. As soon a laser alignment became available we bought into it immediately. So I have to say Hopper is 100% correct here, your long and slender mandrel will have measurable sag that will be there regardless of spinning or not. So side to side may be OK but up and down no chance.

Machine tool setting was done with optical systems for years to avoid sag like this and we had one at work that we could not use on most of our setups because of there being no way to mount it. When we got the laser based systems we gave the optical system to the local astronomy society.

Martin C

Further to Martin’s note ... It’s worth looking at Dr Schlesinger’s little book:

Testing Machine Tools

Downloadable, thanks to our editor’s alter-ego, here: **LINK**

http://www.stubmandrel.co.uk/workshop/13-dr-schelsinger-s-limits

Jump to page 9 of the book.

MichaelG.

Although, Schlesinger is probably way too much information to be of much use to a beginner. But perhaps nice to know the background and just how far you can disappear down the rabbit hole if so inclined.

The other "bible" if you are interested in such things is the classic book "Machine Tool Reconditioning" by Edward Connelly. It is more of a hands-on "how to" book for shop-floor machine tool fitters. But not available for free download and getting expensive to buy in hard copy these days. I bought mine in the US in the 1980s for what seems a laughable pittance today.

As I pointed out before, the Myford ML7 User's Manual PDF is available for free and has all the home hobbyist needs to know about setting up a new lathe in good condition to turn parallel. It's a very basic process if you stick to it.

.

... Which is why I wrote:

Further to Martin’s note: ... Jump to page 9 of the book.

That short section is important, and Schlesinger apparently had it sussed in 1902

MichaelG.