What am i doing wrong?

[lazylathe]

Hi All,

Following on from the last thread about aligning my lathe....

It was recommended that i bolt all four corners down for stability.
That has been completed and i levelled the lathe again while bolting down the corners carefully.

All is good in that department now! ;D

I did have the test bar and dial indicator mounted when i tightened down the bolts.
The indicator did not change it's reading.
This leads me to believe it is the headstock that needs to be adjusted.
Am i correct in assuming this?

Now comes the part that confuses me...
Since the lathe is levelled and bolted down, how do i shim the feet to reduce the value of the readings?
Do i have to do it all at the same time and the bolting down part comes last?

I will recheck the readings and post the results here.

Andrew

 

[BillC]

Cut a selection of various thickness shims to do the shimming/bolting down. There are usually jacking bolts in the feet next to the bolt-down holes to adjust the feet height.

What you are doing is tedious and there is no shortcut to properly setting up a lathe. I rarely bolt one down but I'm dealing with larger machines. The stand type bench lathes should be shimmed and bolted down as you are doing....

BillC

 

[lazylathe]

Thanks Bill!

Why would the values not change when i was bolting the lathe down?
Seems counter productive to add shims.
Would the readings not have changed when i was levelling the lathe?

These are the readings i got after bolting down using the MT2 test bar.

Vertical measurements:
Headstock = 0.000 Tailstock = -0.0015 and +0.0005

Horizontal measurements:
Headstock = 0.0005 Tailstock = 0.0035

Andrew

 

[Mainer]

There are a couple of premises involved in all this:

1. At the factory, the lathe bed was machined to be straight and parallel when it is bolted down to a flat surface.

2. At the factory, the headstock, as mounted on the lathe bed, has its axis in line and parallel to the lathe bed.

So, what you're trying to do is recreate the factory conditions in your shop. #2 is built into the lathe and unless you mess with it or something Dreadful occurs, alignment of the headstock to the bed can be assumed to be correct. Not always, but it can be taken as valid until definitely proven otherwise.

#1 is where the problems may arise. In its "normal" condition the lathe bed wants to be straight. Trouble begins when you start bolting it to a bench which, unless the bench happens to be a very large surface plate, will not be flat to any degree of precision. So you happily bolt down the lathe to your less-than-flat bench and what happens? The lathe bed gets twisted. At the thousandth-of-an-inch scale of things, cast iron is remarkably rubbery. It's easy to put a twist of a few thousandths of an inch into a lathe bed without trying very hard.

If the lathe bed is twisted, it will turn taper, not parallel. Depending on the direction of the twist, the taper will be large at the headstock end and small at the tailstock end, or vice-versa. So, what you need to do, fundamentally, is make sure that when you bolt down the lathe you don't inadvertently introduce any twist into it.

One way to check if the bed is twisted is with a precision level at both ends of the bed. There is nothing mystical about a lathe being level --leveling is just a convenient way to check for twist.

Another way is Rollie's Dad's Method, which IMO is more accurate than leveling.

Three points determine a flat plane. The difficulty comes when you start bolting down that fourth lathe leg, which can crank in a twist to the bed. To fix that, you need to need to shim that 4th leg so when the mounting bolt is tightened nothing moves. By convention, shimming is done at the tailstock end. It's a matter of test, shim, test, adjust shim, test, adjust, etc. until it's correct. As BillC says, it can be a tedious process.

It sounds as though you aren't very far out now though. You may be "good enough" already.

 

[bambuko]

This might be of interest to you:
Follow a Myford Lathe Rebuild

Chris

 

[lordedmond]

If the indicator is not moving when you alter the shims ant the TS end ,what have you bolted it down to? , to me ( I did go to bed early last night , and new batteries have been installed ) the bed is stiffer that the stand/bench you have it bolted to with mine on a Myford stand its easy to move the bed with the jacks

If this is the case then the stand is moving not the bed


Stuart

 

[lazylathe]

Thanks for all the answers and help!

I have deduced from all the comments that it is the top of the stand that is lacking in rigidity!

The stand itself is from a steel bookshelf that i cut down to the correct height.
So that is very rigid and has bracing and supports built into it.

The top on the other hand is two sheets of 1mm pressed steel with hardwood sandwiched between the steel sheets.
I am beginning to presume that the "Hardwood" is not that hard after all and is deforming when i tighten down the lathe anchors.

Moving on from this would a thick steel sheet on top of the original top help?
I would also have to add steel sheeting underneath to prevent the bolts from digging into the original base.

How do others that use wood for their lathe stands counteract this??
Any good leads on where to get steel sheets from in Ontario, Canada would be most helpful!

Thanks,

Andrew

 

[bambuko]

That is rigid (relatively speaking):

(from the web page I have linked to before) - notice the size of lump of iron the bed is fixed to ;D

Steel bookshelf, even with hardwood is (for the purposes of supporting the lathe) as good as a piece of jelly :big:

Chris

 

[lazylathe]

Hi Chris,

I have read that link before, thanks.
Along with 99% of what is on the Myford pages...

I know a lot of guys here use wood for their lathe benches and have great success with them.

For one i know i would not be able to carry such a chunk of steel!!
And the cost would be outrageous...

I will look into what options i have that are readily available to me.

On another note i chucked up a bit of aluminium rod to do a test cut.
Faced the end and centre drilled it.
Extended it out 6 inches and took light finishing cuts at high speed to get a great surface finish.
Measured it at both ends and it is fatter at the tailstock end.
0.1mm difference over 6 inches.
0.0038 inches difference according to the micrometer. ( that took a while to figure out!)

My plan is to build stuff close to the headstock!!! :big:
Just joking!!! ;D

Anyway i will look into my options.
I have attached some pics of the bench.

Andrew

 

[lordedmond]

Andrew

Is that the setup in the lathe that you are using to test the ability to turn parallel ?

that is not the way to do it , you do not use the TS to support the out board end

to check the bed you turn a test bar held in the chuck only let it sick out say 8 inches take very light cuts ( to avoid springing the bar ) and use a 1 inch dia bar, measure that at the chuck and the free end ( no ts support ), then shim as required.

When you have that correct then centre the bar ends and turn another test bar between centres ( having first trued up the live soft centre ) this time you will adjust the TS to achieve the required result ( do not alter the bed shiming )


If I have mis read your pics the its my bad

Stuart

BTW think about that lamp with its CF lamp you can run int strobe effects, I personally use 25w 12 volt halogen lamp ( with a suitable transformer ) with integral reflector easy to make the body as you have a lathe

 

[lazylathe]

Hi Stuart,

At the moment i do not have any thick stock, only some fairly thin aluminium rods.
So this was just a test to see what it would cut and the variances.

I have been checking with a MT2 test bar and using that for the measurements.
Hoping that doing it this way for initial measurements the results will be repeatable.
Again since the bar stock i have is thin and fairly flexible and sags a lot when extended from the chuck jaws,
i thought the solid test bar would give better results.

Hopefully this week i will pick up some 1 inch bar stock and be able to do it the correct way.
What type of metal is best for this?? Alu or CRS??

Before i do all of this i must first sort out the base that the lathe is going to be bolted onto.
What would be a good thickness of plate to use without going overboard??
I do not have the set up to drill holes through super thick steel sheets.

As for the light i just changed it today since the old filament light blew.
I also installed a new fluorescent above the lathe and have yet to tidy up the cables...
The light is a lot better there now!

Andrew

 

[steam58]

A piece of tubing or pipe would be better for the test cuts.

 

[lazylathe]

I have found a solution to mount the lathe onto.

At work we use some man made material for our work tops.
I am not sure what it is made from but it is green, extremely heavy and dense and has virtually no flex on the 8 foot long sections.
It is virtually impossible to cut with regular blades and requires diamond tipped carbides to cut it really nicely. All other blades dull really quickly and tend to melt if the speed is too high.
Since i will be using a 4 foot section i think it will be okay.

What i was thinking was this:

Keep original top, drill large diameter holes through the top to have access to lathe mounting bolts.
Bolt new green top to original top.
Then level and adjust lathe that is only bolted to the new green top.

If anyone sees any potential flawas in this please let me know!

Andrew

 

[duckman]

Is that a surface plate your lathe is bolted to, or a very flat piece of steel, if yes and its not a 5 day job strip your lathe down to a bare bed, clean your table top and turn the bed over then using as big a surface gauge as you have indicate the bottom of the bed mounts, you will probably find a variation where it rest on the plate, when you bolt it down you force the bed to sit on these spots, this where you can force in a distortion. The other thing that can be done is if you have 4 dti's and mag bases mount 1 over each hold down bolt then loosen the hold down bolts and see where it rises up. Hard bolting a lathe down can cause a lot of distortion, thats why you need to be very, very careful when bolting a lathe down. Just my $.02 worth I've only been rebuilding machinery for the last 38 years, machining, scraping, wiring, hydraulics, pneumatics, and any thing else to get the job out the door.

 

[lazylathe]

Hi Duckman,

Thanks for the reply!
No it is not a surface plate. I mentioned earlier that it was hardwood sandwiched between two 1mm steel plates.
The hardwood was compressing causing the distrotion to not go away due to the fact that the lathe is more rigid than the support base.
So i am hoping the composite stone top will help counteract this effect and allow me to bolt the lathe down.

Unfortunately i do not own 4 DTI's... Only two, if i did that is an excellent way of doing it!
You mention hard bolting down a lathe.
Is there another option to bolting it down?
Bambuko talked a while back about the Hardinge way of bolting a lathe down using 3 points and springs.
I have four mounting bolts and no springs...

All i want to do is get passed this hurdle so that i can actually try to make something...
It is very frustrating!
What i am trying now is to shim the lathe and use Rollie's dad's method to test a bar and see when i can get close to zero readings by shimming.
When that is done then i will start to tighten the bolts and hopefully the readings will stay the same.

If this does not work then i will be looking for a thick steel sheet to bolt it onto tor try and get the readings to an acceptable level.

Andrew

Here are the readings from a quick adjust last night.
These are my readings:
Horizontal-
Headstock = 0.0005
Tailstock = -0.0025 and +0.0005

Vertical -
Headstock = 0.0000
Tailstock = +0.0015 and -0.0015