My new Harrison lathe

[God mode restorations]

Just wondered as i didnt see any posts in regards to that. I you should show that as its the bit people dont know about or understand

I understand that . Unfortunately for me I am dyslexic so I struggle with words and explaining things to people in a way that they understand. It's the reason why I dont show all the process.

 

[Pete.]

Surly if the compound is sloped and you cut using it the tool will not remain on the centre line of the spindle axis

That's true, and we already mapped the compound ways to the base so we know that the ways on this machine are co-planar to the swivel but bear with me and I'll explain why it doesn't matter nearly as much on a lathe as on a milling machine/grinder or jig bore for example.

 

[mtt.tr]

That's true, and we already mapped the compound ways to the base so we know that the ways on this machine are co-planar to the swivel but bear with me and I'll explain why it doesn't matter nearly as much on a lathe as on a milling machine/grinder or jig bore for example.

i see to error is very small as its indirect just wondered what efforts where made to prevent it

 

[Pete.]

As I said we up-turned the compound base on my surface plate and ran a 1um dial gauge over it.

Anyway, look at the example below. Let's assume a compound base of 8" diameter (which is about the size of the one in question). We'll put in an imaginary 20 thou over 8" out-of-plane between the base and the ways. This is already an unthinkable amount because despite having almost no wear IF it did have that much wear or warp then it would need machining at the very least and even the most ignorant person couldn't scrape 20 thou off one side of a 8" base unwittingly his arm would fall off first.

Ok so you can't see it but I've drawn two parallel lines 10 thou apart (because we're working with radius not diameter) then I've drawn a red line from the centre to the edge of the 4" radius 10 thou low. We'll turn an imaginary 100 thou, 1" and 4" diameter with this imaginary compound and measure the linear difference between a diameter turned with a dead flat perfectly true slide versus one which is out of plane by 10 thou over 4". As you can see the differences in radius are infinitesimal. The worst is 13 millionths of an inch. Of course you can't even turn to a hundredth of that amount so that discrepancy is, literally, nothing in turning terms it's actually less than most surface finishes you could expect. Even the leadscrew on the lathe, when new, would not be made to that accuracy unless you were using something very special. On top of that you have tool deflection under load - that's going to be in the several thousandths of an inch, not millionths.

The worst effect that it can have is if you were setting up and cutting tapers with a sine bar, but even then the numbers are very small and if you're looking for that accuracy you should be grinding, not turning.

Just to add that this doesn't hold true for the cross slide ways. Those will always be 'on axis' with the spindle so long as 1. the tool is set to spindle centre height in the centre line and 2. the ways are actually straight. On a cross-slide the most important thing is that the ways are truly perpendicular to the spindle axis, except for a slight specified allowance for 'dishing'.

 

[Pete.]

Now, on a milling machine, the total opposite is true. If your table is not co-planar to the underside ways you'll cut a taper in the part, same for the cross- x and y top and bottom ways. If your x- and y-axis ways are not totally perpendicular, you'll machine out-of-square features in the part. If your y- and z- axis ways are not perpendicular with an allowance for droop, you'll machine steps in the part when facing off with multiple passes with an end mill. If your ways are concave, you'll mill the part concave. It's a lot more complicated.

 

[Pete.]

Another quick example. Lets say your were turning a part, parallel or shallow-tapered like a taper pin, using the compound around 200 thou diameter and using 4" of slide travel. In the 'extreme' example of the ways being 20 thou out of plane to the swivel base your diameter would be half a thou out over 4". If you used a far more realistic figure of 2 thou over 4" out-of-plane the error drops to just 2 hundred-thousandths. Spencer's compound base is far less than 2 thou.

 

[hermetic]

Just found this thread, you have one of Heckmondwikes finest there! What a machine, You are making a cracking job of the refurb It has quite a few similarities to my Covmac, which is from the early forties, I shall be watching this from now on, another great machine saved!

 

[pressbrake1]

I do everything by hand fizzy.

Ive heard that rumour too

 

[mtt.tr]

Ive heard that rumour too

I say matron

 

[God mode restorations]

Just found this thread, you have one of Heckmondwikes finest there! What a machine, You are making a cracking job of the refurb It has quite a few similarities to my Covmac, which is from the early forties, I shall be watching this from now on, another great machine saved!

View attachment 201109

Thanks hermetic.
Yes she is a awesome machine.
Your machine looks a nice bit of kit.

 

[God mode restorations]

Today's task was to clean the bottom half of the tailstock ready for measuring.
I set piece up on the surface plate with three adjustable Jack's. This will allow me to dial in the four corners so I know its level. Measurements are taken with the dti.
And as I thought and as you would expect its low on the front and back edges. 25 thou . So a good days scraping and nearly there.

 

[God mode restorations]

That's one side complete. Tough stuff this.

 

[God mode restorations]

Finally finished.
That was the hardest bit of cast I have ever scraped. Literally one pass and then sharpen tool again. Coupled with the fact that there is a lot of trams lines that the scraper gets caught on.

 

[dobbslc]

Great work! So if I were to run my finger nail along that surface would I be able to feel the scraping marks?
Does it produce swaff?

 

[God mode restorations]

Great work! So if I were to run my finger nail along that surface would I be able to feel the scraping marks?
Does it produce swaff?

You can Just about feel it. Once the scraping is completed it gets a slight stoning. This is done every pass to deburr the scrapes

 

[Spark plug]

That was the hardest bit of cast I have ever scraped. Literally one pass and then sharpen tool again.

I scraped a surface plate once like that, it was akin to self inflicted torture, I feel your pain.

 

[God mode restorations]

I scraped a surface plate once like that, it was akin to self inflicted torture, I feel your pain.

Definitely torture. As much as I enjoy scraping. This piece was testing my strength.

 

[minimutly]

Did I read that right - 25though wear front and back? So looking at it you scraped all or nearly all the way out both ends, 25 thou at the peak?

 

[God mode restorations]

Did I read that right - 25though wear front and back? So looking at it you scraped all or nearly all the way out both ends, 25 thou at the peak?

Yes. I should of used a surface grinder. I have one but it's not a home. A good two days work.

 

[God mode restorations]

Did I read that right - 25though wear front and back? So looking at it you scraped all or nearly all the way out both ends, 25 thou at the peak?

That was supposed to be 2.5 thou not 25 thou my mistake