Unwanted Taper ?

[Danuzzo]

Thank's for all the input. To answer goldstar's question. Yes the lathe was bolted down.

I cannot financially or wisely spend the money to buy fancy measuring equipment, so I cannot level a bed properly. Plus I would not know the proper methods for doing so. However, I do like Tony's idea of mounting pads with jack screws.

Another question. With these 7x mini lathes, would the chances of having an warped bed be less with a 7x10 vs a 7x16 (less chance for error??) Just curious.

 

[peterl95124]

at least here on the west coast 0.001" is called a "thou" and 0.0001" is called a "tenth" (!)
I've never heard a machinist use the term "mil", you do see it used in some specifications
outside of machining, for example "10 mil" plastic sheeting is 0.010", but never in machining
so 0.010" shim stock is "10 thou", not "10 mil".

I've never been able to get the head perfectly aligned with my lathe bed (tightening the bolts
changes the alignment, argh!!!), so for critical parts, e.g. a shaft that has to fit a ball-bearing,
I use very fine wet-or-dry paper to get a perfect fit over the length it has to slide over.
Fortunately I'm always building one-off model engine parts as a hobby, otherwise I'd have
to get a better lathe !!!

the only model engine part for which this tedium is an issue for me is valve stems,
but in that case I want a 2000-grit mirror polish finish in the end, so while using coarser
grits to approach the final diameter I monitor the taper (with a 0.0001" vernier mic)
and eliminate it that way.

HTH, YMMV, etc...

 

[goldstar31]

Thank's for all the input. To answer goldstar's question. Yes the lathe was bolted down.

I cannot financially or wisely spend the money to buy fancy measuring equipment, so I cannot level a bed properly. Plus I would not know the proper methods for doing so. However, I do like Tony's idea of mounting pads with jack screws.

Another question. With these 7x mini lathes, would the chances of having an warped bed be less with a 7x10 vs a 7x16 (less chance for error??) Just curious.

It doesn't do to bolt a lathe down- on a unknown surface. Unbolt it and use TWO sprit levels - one length ways one crossways. At least you will get somewhere - cheaply. Again, use a cheap laser pointer- through the spindle and also therough the tailstock after removing the poppet. I think the Model Engineer article 'Microscope on the Lathe is still on the net. Written by Exactus which was propably 'Ned' Westbury.

You should get some idea of what it is all about.
Again, get Georg Schlesinger's Measurement of Machine Tools- rather than inventing your own rather doubtful ways

 

[goldstar31]

at least here on the west coast 0.001" is called a "thou" and 0.0001" is called a "tenth" (!)
I've never heard a machinist use the term "mil", you do see it used in some specifications
outside of machining, for example "10 mil" plastic sheeting is 0.010", but never in machining
so 0.010" shim stock is "10 thou", not "10 mil".

I've never been able to get the head perfectly aligned with my lathe bed (tightening the bolts
changes the alignment, argh!!!), so for critical parts, e.g. a shaft that has to fit a ball-bearing,
I use very fine wet-or-dry paper to get a perfect fit over the length it has to slide over.
Fortunately I'm always building one-off model engine parts as a hobby, otherwise I'd have
to get a better lathe !!!

the only model engine part for which this tedium is an issue for me is valve stems,
but in that case I want a 2000-grit mirror polish finish in the end, so while using coarser
grits to approach the final diameter I monitor the taper (with a 0.0001" vernier mic)
and eliminate it that way.

HTH, YMMV, etc...

The only time that abrasive paper should be used is at the end of a scraping cycle when one papers the arris is raised creating the spots which should eventually gt 25 points/spots per square inch.

Thous? I also refere to gnat's cocks and midgie whiskers

 

[BaronJ]

Hi Peter,

I've never been able to get the head perfectly aligned with my lathe bed (tightening the bolts changes the alignment, argh!!!)

Assuming that your lathe is properly mounted on a rigid surface that cannot move or warp, the easiest way to set the lathe up is to use the two collar method, and use shims or jacking screws at the tailstock end to very slightly twist the bed so that each of the collars measure the same diameter.

This is done by taking a fine cut, a couple of thou, across both collars without altering the cross slide in any way.

My two collar test bar is an 8" inch (200 mm) length of 20 mm diameter hydraulic piston rod with two 20 mm thick aluminum rings, 40 mm in diameter locktited onto it 6" inches (150 mm) apart.

 

[fcheslop]

An often overlooked problem with the OP machine is that the bolting down pads (feet) are not machined correctly by the factory and if you merrily go bolting it down without at least giving them a cursory looking at it twists the machine
Iv skimmed a couple in the past for people when I had the facilities to do so and they were 0.025 or there abouts out
There are many ways to skin a cat my preference is to use test bars although Im lucky and made them when I had the equipment to do so on a cylindrical grinder
Again look at Bogstandards Darrens lathe write up the pics may well be missing but the methodical approach still holds true
The two collar method is in the Myford book I posted a link to although Iv not seen any acknowledgement that he/she has looked into it
Horses and water
cheers

 

[goldstar31]

From my shenanigans with my Myford Motor problem- now solved- I am setting the lathe up again.
The Myford manuals for ALL the 7 series are available on the net to down load. The 2 ring thing is there.

Taking Frazer's comments about skimming lathe feet, it may not be practical for some workers.
I must, however, agree with both him and John Baron about 'getting the bed' level, out of twist and probably suggest that dear old Tom Walshaw's book - writing as Tubal Cain in Simple Workshop Devices has a technique to hold his lathe on penny washers and nuts and studding. He lived in the English Lake District and the level of his lathes etc in his workshop actually moved.

I did A Level Physical Geography and was a member of a mountain rescue team! My home dates to Anglo Saxon times and Roman times as well as being undermined in later times. So it is on a concrete float and so is my newer worksop. So one CAN drop a slurry of concrete which automatically levels itself. So my lathe is going back to a reasonably level and solid base. Isn't education useful

Of course, the lathe and stand are really too heavy to move at my age and I'm using steel rollers and a pinch bar made from a pneumatic drill end. Brute force and bloody ignorance ?

 

[Cogsy]

Hi,

Let’s get real here. addressing the above points in order:

1) Your example of machining a valve stem with 1/2 thou/inch taper and a total end-to-end discrepancy of 0.025mm (1 thou) suggests a machined stem length of 2 inches - a full sized I.C. engine valve. If you are intending to make critical engine components for your car, holding a taper over 2 inches is the least of your problems (in real a production environment such items would be rough turned on a lathe then ground to size - much quicker, easier and more precise)

Ok, 1-1/2" stem then, which takes the difference in stem diameter down to almost 0.02mm, still well outside the tolerance I like for my valve stems (to be honest I look for < 0.01mm variance over the entire stem length on valves). I would think a 2" valve stem would be a Brigss and Stratton size, maybe a motorbike, but certainly far from full size 'normal' I.C. for a car. At least all the ones I've ever worked on.

2) Your second point above considers two bearing journals 3 inches apart. As I’m sure you already know, no-one would ever seriously attempt to make a shaft to the journal diameter along its entire length - you would machine one journal to size, move along and machine the second journal to size then machine the shaft in between to about 10-20 thou under the journal size (and leave it rough turned - don’t waste time, effort and money putting fine finishes where they are not required)

What I was meaning here was a single cylinder (say a hit and miss) style crankshaft, not a multi-throw. One that uses ball bearings as main bearings. The bearing needs to be pressed onto the shaft and at least be a 'good' fit along the entire length, while things like gears, flywheels and even outboard bearings (for some designs) get placed along the 3" shaft-end so it needs to be on-size for it's entire length.

The issue with machine accuracy breaks down in to two sets of criteria: Accuracy over short distances, and accuracy over long distances. For most of us, accuracy over short distances (less than 1/2 inch) covers 99% (often 100%) of a hobby user’s requirements. Unless you make full sized pistons for 3 litre car engines, I cannot imagine anyone actually needing to hold 1/2 thou over 3 inches

All the best
Ian

Obviously I disagree with this (as you can see above) and I have a theory that the measuring system we use might have something to do with it. To imperial users, a thou seems like a tiny amount but to metric users that's more than 2 full graduations on our measuring tools. When I'm machining for a critical dimension, like a bearing fit for example, I'm aiming to hit my number spot on but I will normally tolerate +/- one hundredth of a millimetre. So my 'normal' working tolerance on a precision part is within about 0.0004". So having each crankshaft half of a hit and miss to 1/2 a thou along it's length seems perfectly reasonable to me.

 

[goldstar31]

Today's gripping episode is the installation of my 'new' Myford and its ort of desecrated metal stand by cutting the floor of my wooden workshop floor. The concrete screed is fairly level- if one ignores the great circle sailing or whatever. I did it in about 1945 and gues that it still applies

The deivery guys had sort of plopped the original metal stand and the new Myford onto the 4 studs which I had earlier screwed down with nothing more that studding, nuts and penny washers.
Chucking a decent spirit level along the bed indicated that it was pointing almost due North but as a basis to turn things-- I could forget it! So I unbolted the top holding bolts and sang 'I;m forever Blowing bubbles' because it was dead easy to crank up with a spanner underneath the feet- and in a few minutes, the bubble was spot on in 4 directions. I simply bolted the feet down.
Frankly, is that all there is to it, please? I'd forgotten.

 

[IanN]

Today's gripping episode is the installation of my 'new' Myford
:
Frankly, is that all there is to it, please? I'd forgotten.

I believe you should have had a glass of Bushmills between achieving a level state and the final tightening

All the best,
Ian

 

[IanN]

:
to be honest I look for < 0.01mm variance over the entire stem length on valves
:
What I was meaning here was a single cylinder (say a hit and miss) style crankshaft, not a multi-throw. One that uses ball bearings as main bearings. The bearing needs to be pressed onto the shaft and at least be a 'good' fit along the entire length, while things like gears, flywheels and even outboard bearings (for some designs) get placed along the 3" shaft-end so it needs to be on-size for it's entire length.



Obviously I disagree with this (as you can see above) and I have a theory that the measuring system we use might have something to do with it. To imperial users, a thou seems like a tiny amount but to metric users that's more than 2 full graduations on our measuring tools. When I'm machining for a critical dimension, like a bearing fit for example, I'm aiming to hit my number spot on but I will normally tolerate +/- one hundredth of a millimetre. So my 'normal' working tolerance on a precision part is within about 0.0004". So having each crankshaft half of a hit and miss to 1/2 a thou along it's length seems perfectly reasonable to me.

Hi Cogsy,

Thanks for taking the time to reply - as you point out, we probably work in two different environments and have different expectations and histories and so have differing points of view. My view point:

I was taught to use a mill and a lathe in 1969 and my first employer (while paying lip service to SI units) manufactured everything in Imperial units - during my time there I purchased a full set of Imperial measuring equipment and tooling. My next employer was "metric". I purchased a full set of SI unit measuring equipment and tooling. I just work better in thous than mils and to this day resent having to buy every "tool of the trade" twice

I am past retirement age but I still teach engineering apprentices (and lecture in engineering at a university) and so my view point is purely practical, so answering your points:

1) Why on earth would you turn the entire length of a valve stem to such tight tolerances when only half of the stem actually runs in the valve guide?

I based my comment on valve stems on many years experience of Mr Weslake's beautiful BLMC A series engine which had valve guides around an inch long (depending on engine version) - the critical fit of a valve stem is over less than half its length, the rest of the stem is surrounded by spring or manifold gas. I agree that if you are in industrial manufacture you would grind the stem to size along its entire length, but as a "Home Model Engine Machinist" this target is quite unnecessary

2) I agree with you entirely that bearings, journals, etc require accurate diameter shafts, but gears, eccentrics, etc are always fitted with collets, cotters, keys, or grub/set screws. Please don't tell me you press fit everything along a shaft machined to a single dimension!

Finally, the units we work in have absolutely no relevance - it is the physical distance that matters

I hope we may agree to differ on these points. As I said in an earlier post, there are two types of lathe owner, the sort who makes stuff and has a machine capable of doing what they want, and the sort who pursues accuracy and precision as a goal in itself. As a hobby, both are perfectly acceptable.

All the best,
Ian

 

[peterl95124]

Hi Peter,



Assuming that your lathe is properly mounted on a rigid surface that cannot move or warp, the easiest way to set the lathe up is to use the two collar method, and use shims or jacking screws at the tailstock end to very slightly twist the bed so that each of the collars measure the same diameter.

thanks BaronJ, but what i wan't able to communicate correctly is that it is the bolts that hold the lathe
head to the lathe bed that I can't tighten without upsetting the alignment of the head. I have to set the head
at an unaligned angle, then tighten the bolts, then re-measure the taper, lather-rinse-repeat, it's awful.
I'm pretty sure my lathe bed is too short and stocky to bend.

 

[goldstar31]

The question which has rattled through what might pass as a brain is 'Why do people in their ( hopefully) right minds. disturb the setting of the headstock and spindle.

It is only when I have had to strip the lathe down to correct a worn bed. Then, in the care of a Myford 7 Series, the settings were set in the factory NOT to be disturbed by us lesser mortals.

Would someone explain why?

Again, there is no reason to have a bed truly horizontal other than the ease of setting up. A lathe on a ship goes with the waves like the rest of us

Cheers


Norman

 

[BaronJ]

Hi Peter,

thanks BaronJ, but what i wan't able to communicate correctly is that it is the bolts that hold the lathe
head to the lathe bed that I can't tighten without upsetting the alignment of the head. I have to set the head
at an unaligned angle, then tighten the bolts, then re-measure the taper, lather-rinse-repeat, it's awful.
I'm pretty sure my lathe bed is too short and stocky to bend.

Sorry I misunderstood !
In that case I would remove the head and make sure that the underside that contacts the bed was clean and flat, doing the same for the bed surface where the head sits. No shims or anything else under there unless the manufacturer put it there.

Align the head using a known straight bar in the chuck to the tailstock. Nip the head down. That should get you in the ball park.

From here its very much measure and adjust as needed to get everything as near true as you can.

As far as the bed bending, don't kid yourself ! I've seen cast iron cylinder heads bend without too much effort !

Good luck, it won't be easy but patience wins.

 

[goldstar31]

Of course Baron is right, it actually needs a test bar which in this case is either a No2 or 3 Morse taper.
However, mine is 6" long so that I can detect a deflection of half a thous. If however we all go back to the Propositions of Euclid( which all remember, adding a length of piping to extend the levverage we can move the spindle minutely. If course. we all know this and we can do this minute compensation that Myford does to allow for the pressure exerted by the lathe tool.
No it ain't the book but that is what happens.

And the Best of Luck

Norman

 

[JCSteam]

Frazer, Norman, and indeed John (Bogstandards, how is his health by the way? anyone know?). This thread is a bit of da-ja-vu for me. The three mentioned members, have been at the receiving end of me chasing my tail with incorrect technique and measuring equipment. I currently have my lathe in pieces as it needed a good clean an repaint, plus there were a number of issues that needed to be addressed, (me half nuts for one). A recent house move was a prime opportunity to "Start again", and do it right this time. Though before with Frazers assistance and fettling, the now +80 year old lathe could still hold a 1thou taper over 4" length, through summer and winter, and could be dialled in even more accurately if I wished, (for a day before the humidity changed and say goodbye settings).
The Myford ML4 was bolted to a wooden kitchen worktop (not ideal), on M8 threaded bar cut to length. and bolted to the wooden top, with washer and nut under and above the mounting feet. The lathe could be slightly twisted to level the bed, then subsequent test cuts taken on a piece of solid bar prodruding unsupported 4" from the chuck., As already mentioned, cuts of only a thou or less a time, and when close to desired tolerance a spring cut is taken, whereby the lathe turned off, the saddle retracted, then another cut taken at the same setting, (ie don't move the handle for the cross slide or the compound).

This eliminates any spring in the material your cutting or the tool, the heavy cuts you are taking will be compounding the taper effect, ease off and go slow.

The same should be doable with the mini lathe so long as you are not planning on it been moved often. remove the rubber pads, and bolt directly to studding fixed to the workbench. get the bed as level as possible even by crude means such as a builders level. check and check again. Then begin your cutting, take a 10thou cut 1" from the end of the bar, and stop 1" from near the chuck. now your material will be less likely to spring when you take your 1thou cut, do a spring cut as described above after the initial cut then measure both ends with a micrometer.

Report back what you find after you do the above, this is working to a tolerance of 0.0005" which unless you have to achieve something of greater accuracy for whatever your machining will suffice for most machining applications, it certainly did for me for......blimey that's going back two years now. The lathe set up has made parts that have paid for the lathe in full so the only cost to me now are the additional tooling, rotary table, fixed vertical slide, myford milling vice, lots of rusty hammers and files ect ect that I bought for £80. Even then some of it was sold to recover the cost. levelling me with some tool restoration to do and hadn't cost me a penny. BUT!!! Do spend money on good measuring equipment that will measure down to half the tolerance you want, or learn to live with the tolerance you can measure, ie micrometer only measures to 0.0005" then you can only realistically set up to a 0.001" tolerance.

Don't disturb your headstock unless you really have to, it'll never just bolt straight back on perfect, how do I know.....3nights in my garage says that haha

I hope this is of some help to you, and take it from someone who HAS been in your shoes a few years ago you will get there, just need to be realistic with the tool you have, and the tolerance you want to achieve.

Regards

Jon.

 

[goldstar31]

Thanks JCSteam for the mention.
I'm glad that you are trying to start up again after your move.
Me? I'm in lockdown and unable to get out of my bungalow and gardens- for the future.
Being a widower, it is quite boring. So really, part of the family gets my food and my daughter in Leeds keeps in telephone contact.

With the help of John Baron and a friend from Sunderland, I have been able to get the sort of new Myford working. It's aligned now and the motor- a split phase one- is running. My Sieg C4 is stagnating now that I can find my shed warmer. I've just fitted the George Thomas ratchet 4 way tool post and next is the rear inverted tool post. Where my chuck spanners are now are missing so I'll have to make a new set. I can cobble one up to make a decent set. I've got the Quorn going and the Stent will soon be employed.

The difficulty now is getting metal. There is Argoshield gas in the Mig and that's about it. I'm or was a certifield welder after I retired and it solves a lot of almost insoluble problems at this difficult time.
Keep well and keep safe


Cheers

Norman

 

[JCSteam]

Well Norm, if your bored up there I have some castings for a dividing head, sat under the bench that need finishing off, and I can get the extra materials from work (yes still working making plastic sheet, and Perspex face shields). Ill drop them at your doorstep next time i'm passing haha.

Keep safe old friend.

Jon

PS I was told Noggin end are still selling mail order.

 

[goldstar31]

Thanks John but I already have 2 Dividing heads and 2 rotary tables.

Actually I can use my one hole dividing plate to get ANY number. Using TWO acme threads!

Thanks again

Norman

 

[terryd]

at least here on the west coast 0.001" is called a "thou" and 0.0001" is called a "tenth" (!)
I've never heard a machinist use the term "mil", you do see it used in some specifications
outside of machining, for example "10 mil" plastic sheeting is 0.010", but never in machining
so 0.010" shim stock is "10 thou", not "10 mil".

I've never been able to get the head perfectly aligned with my lathe bed (tightening the bolts
changes the alignment, argh!!!), so for critical parts, e.g. a shaft that has to fit a ball-bearing,
I use very fine wet-or-dry paper to get a perfect fit over the length it has to slide over.
Fortunately I'm always building one-off model engine parts as a hobby, otherwise I'd have
to get a better lathe !!!

the only model engine part for which this tedium is an issue for me is valve stems,
but in that case I want a 2000-grit mirror polish finish in the end, so while using coarser
grits to approach the final diameter I monitor the taper (with a 0.0001" vernier mic)
and eliminate it that way.

HTH, YMMV, etc...

Hi Roger,

glad to hear that about your terminology, but I've heard serveral machinists in The US use those terms (mil) on Youtube videos so I assumed that it as always thus the case

TerryD