Setting lathe tool height using a prism

[Blogwitch]

Many years ago, when attending one of the model engineering shows, there was a chap selling what looked like a prism mounted on top of a bar.
The bar height was adjusted until a centre mounted in the spindle of the lathe became spot on with the centre of a graticule in the prism. It was very easy to see when this happened.

Once this setting was found and locked up, it was an easy exercise to very accurately set tool heights to exact spindle centre.

He had sold out of these ones by the time I got there, only having other prism related tools available.

Can anyone remember seeing them? Do you know how they work? How easy would it be to make one?

Many thanks in advance.

John

 

[goldstar31]

I seem to recall a lot of information on prisms in Smith's Advanced Machine Tool book. Sadly. in a bout of generosity, I sent it at my expense to a guy only to get banned. He disappeared from the scene- and that was that. Funny people!

However, 'Smith' is still free on the 'net. He solves the problems of tool heights on grinder periphery. Others simply make a table- ie Chaddock and Clarkson!

So - in my other world- prisms are used in the jigging of mangled car re-alignment. Graticules, prisms and lasers but necessary as cars are not aligned in a straight line any more. Again, steering geometry - Mercedes for one- was optically aligned.

In a further regression, two or more points arise. I have an optical punch and in yet another cubby hole, there is 'geometer's' Microscope on the lathe. I think that our 'Jim' from Kiwi Country managed to download it all from my instructions. Somewhere is lathe optical alignment- maybe is Schlesinger or Burley.

Interesting stuff. However, despite all this, I have a very technical 6" rule which serves my modest needs.

Cheers

Norman

 

[Blogwitch]

Norman,

The only reason I am looking to make one of these is my physical mobility, nothing more (old age creeping up on me).

From what I saw, I just looked from the side or top (can't remember exactly but it was very easy to see) and it was straight forwards from then on, just move the tool tip up or down until in perfect alignment.

I use a scribed line on an old height gauge at this time, but getting down to see when I have split the line with the tool tip is getting more difficult. That method gets me to within 0.001" of correct height, a little more precise than guessing when the ruler is perfectly vertical. I know squares could be used to check, but then things start to get complicated to see in a very small area.

John

 

[goldstar31]

I can only sympathise! Old age with its attendant other probs is a 'so and so'
Probably someone will be able to assist but I would be thinking about a height gauge made from a dial gauge with a flat elephant's foot rather than the normal ball affair.

Digressing further, I've unearthed a Martin Cleeve idea for a Boxford grinding shop mike affair. It is calibrated in 'tenths'.
Again, I've unearthed a sort of D bit which GHT used when he gave the words and music in constructing my little Versatlie Dividing Head.
For those unfamiliar, this has two worms and can play about with the classic division plate- with ONE hole.

Meanwhile, I'm still fiddling about with that Myford ML10's problem which has a tumbler trio of gears- as an addition.

Must be an easier hobby

Norman

 

[Blogwitch]

I have even tried one of these.

http://www.machine-dro.co.uk/edge-tech-pro-lathe-gauge.html

OK for normally mounted tips, but have come to the conclusion that when trying to set up a boring bar with a negatively raked fitted CCMT tip (which I use a lot) then it is rather difficult getting this tool to sit exactly on the extreme edge of the tip as it is pointing in a downwards direction.

Hence my search for an easy to see visual aid.

John

 

[SmithDoor]

There are two ways most machinist use is one use a center move cutter till at center
The way I use is just ruler off the cross slide.
Both are low cost and simple to use
For other machinist shop for speed just cut bock of Al or steel to right height
:thumbup:

Dave

Many years ago, when attending one of the model engineering shows, there was a chap selling what looked like a prism mounted on top of a bar.
The bar height was adjusted until a centre mounted in the spindle of the lathe became spot on with the centre of a graticule in the prism. It was very easy to see when this happened.

Once this setting was found and locked up, it was an easy exercise to very accurately set tool heights to exact spindle centre.

He had sold out of these ones by the time I got there, only having other prism related tools available.

Can anyone remember seeing them? Do you know how they work? How easy would it be to make one?

Many thanks in advance.

John

 

[goldstar31]

There are two ways most machinist use is one use a center move cutter till at center
The way I use is just ruler off the cross slide.
Both are low cost and simple to use
For other machinist shop for speed just cut bock of Al or steel to right height
:thumbup:

Dave

Might I suggest that you actually read and -digest- what I wrote?
John 'did' but his physical difficulties preclude adopting them.

 

[SmithDoor]

I am letting any know how my self and others did this

Dave

Might I suggest that you actually read and -digest- what I wrote?
John 'did' but his physical difficulties preclude adopting them.

 

[Blogwitch]

I actually did a write up on one of the forums showing many different types of setting 'perfect' height for tooling, including some of the faults that occur when you don't get it quite right.

As I said, I have tried them all, some are too long winded, like raising or lowering the tool tip and taking a cut across the face, some not very accurate, like the ruler method. They will do for most people if you are not too worried about quality and accuracy of cut, but I am, and because of the restricted access I now have is the reason I was asking about the prism system, which at this time, would be the only one I can consider because of the accuracy and ease of use. As I stated before, splitting a scribed line (max 0.002" thick) was perfect for me for many years, but now I cannot get down into the positions that I used to be able to.

If no one can give any help on this topic, then I will have to get out my box of prisms and see if I can design and make one myself. I was just hoping someone had all the data required.


John

 

[joco-nz]

Is this the text being referred to?
https://archive.org/details/textbookofadvanc00smituoft

 

[goldstar31]

Is this the text being referred to?
https://archive.org/details/textbookofadvanc00smituoft

Yes, James! The worked examples DO give a clear and concise 'apprenticeship' which you seek.

Actually, it becomes rather advanced- as I have intimated earlier.

Once you realise that there are more suitable lathe tools and the drawings are not quite so pretty as today, he is as sound as a bell.

Norman

 

[joco-nz]

Cool. I found a more accessible PDF version of this if anyone is interested.
Use this google search to find things.

 

[Niels Abildgaard]

My carbide tipped boring bar and its adjusting.
The small cylinder is 25.14mm long and that is the measure from compound to centerline

http://i.imgur.com/z4S76ir.jpg

http://i.imgur.com/EP4H3kI.jpg

 

[Blogwitch]

Neils,

A good solution for your boring bars.

Unfortunately, I have used a set of CCMT mounted bars for many years that have the tip mounted in a down tip configuration, negative rake, that allows the largest possible bar to fit into the hole being bored, for rigidity. It was for this reason I started to use them for all my boring, except for some very large tipped boring bars that I have.

Because of this tip configuration, a 'touching' method cannot be used, because of the tips' downwards slope, if you touch on, then the setting gauge cannot be at the very edge of the tip. As stated before, I use a visual system of getting the correct height on all my lathe tooling, and it is now becoming difficult for me to use.

Looks like I will have to bite the bullet and design and make my own.

Many thanks for the help offered.

John

 

[rodw]

I bought a couple of laser modules something like one of these
http://www.ebay.com.au/sch/sis.html...id=121212852782&&_trksid=p2057872.m2749.l2658

I was going to make a Dan Gelbert laser edge finder for a mill. One day.

I wonder if one of these held in the chuck would help? If need be, mount a battery behind it so you can run the lathe to take out any inaccuracies.

Not what you are looking for but maybe it will make alignment easier.

 

[goldstar31]

Further to Rod's comments about lasers prompts me to add thoughts of the past.
The first was Peter Rawlinson in ME and how he used cheap lasers to set up. Sorry, I was in communication with Peter but it's a long time ago.

The second is or was Centrecam which appeared in M E or MEW and utilised a program using a cheap web cam.
The program again used graticules( my reference to car body alignment again). Actually, I bought the program use from ? Ian Trethowan? but despite promises, he never developed the software.

So you may get a few clues to see the tool tip using a cheap webcam. It is worth Googling Centrecam again

I'm still interested

Norman


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Further search 'here' indicates that several members here were using CentreCam

 

[Blogwitch]

Rod,

The laser setup would be of no use, the accuracy just isn't there for the setup I require, unless I could get a line at most 0.002" wide. plus it would have to be projected onto something, a problem I have now with my scribed line.

Norman,
The camera idea I though about a while back when a friend mounted one onto his lathe to have a look at his surface finishes. In fact I have already got a couple of those types of cameras, but to me, it looked rather awkward with cables and displays hanging about, plus I would have to make a very high precision graticule to fit over the front, whereas with a prism I could just score a fine line across one of the back faces with a height gauge.

I might seem very negative when it comes to every other methods, but I am trying to see problems before they occur, and nothing as yet comes close to the accuracy and ease of use as a prism.

So sorry lads, seeing no one else has replied, I am going it alone, but if I do succeed, then I am sure I will show it.

I looked at the prisms I already have, the size I want to use is mounted into a high precision periscope affair, so I will have to go to see if my friend has any that are dismounted as I think the one I have can be used for something more important.

John

 

[goldstar31]

I'm in the midst- or mists of trying to hear stuff via my mobile onto my hearings aids- but stopping and starting it- remotely.
However I passed Maplins and they have USB microscopes - for £30 and I have a dead laptop. Thought that there couldn't be too much cabling. My thoughts were looking at the negative angles which you use in your boring.

Now that I have tamed my little ML10, it is all worth a punt.

Off to see my favourite heart surgeon and obviously he is doing stents -remotely. Might pick up an idea

Regards


N

 

[Blogwitch]

That's the problem Norman.

Something that should only be a lump of metal say 1/2" diameter by say 6" high has, by your way of thinking, turned into a PC next to the lathe, cables and camera knocking about around the toolpost and spindle.

Anyway, contacted my friend, but he only has what I have, so two 10mm 90degree mirrored on the long face prisms have now been ordered from China, so as soon as they arrive, plans in my head will be put into metal. I have plans for two, one for use on the cross slide and one for use down onto the bed for tips that extend too far in front of the cross slide. Both should be able to cope with normal and upside down tooling.

Less than 10 pounds lost if it doesn't work, hopefully, many years of ease of use if it does.

BTW Norman, my hearing aids are also bluetooth enabled, so is my car. I can access my mobile when I care to use it (about once a month) but when I contacted the hearing aid suppliers about getting data sent from the bluetooth in my car (sat nav, radio etc) I got no reply. All they seem to be interested in is listening to the TV or mobiles, and charge the earth for doing it. THEY are deaf to everything else.

John

 

[goldstar31]

Thanks, John. My thoughts on 'computers' in this instance were to adopt a redundant and ready to throw out ancient laptop. I suppose that some bright spark could rig a tablet with its own battery. Time will tell.
I'm certainly curious about this suggestion about prisms. Laughingly, I'm a member of rather odd Chinese /Far Eastern 'organisation'

As for hearing aids, I'm indented to you- and I ordered a 'gubbins' yesterday to fit my Old Geyser's mobile. You know the thing, built to accept idiotic operators with arthritic fingers-- and brains.

So I am clearly more than interested in what transpires.

Regards

Norman