Thread: Newby, HSS, or carbide + tools

Originally Posted by lather

stuart i understand what you mean, will need to get the actual specs to check if it sits above the posts lower surface when centered.

You're talking about the parting tool holder?

Originally Posted by lather

just thought about this, when using a parting tool is there any reason for using it at an angle.

You mean an angle other than 90 degrees to the spindle? Not that I can think of. You could do a little concave on one surface and convex on the other as you part off, but it would only be a little before the work would start to rub on the bottom corner of the blade.
I've draw a picture to show what would happen to the clearance if you tried to part into the end of a bar. It could of course be done if you ground the end to give clearance, but there are cheaper ways of machining this than using a parting tool

Stuart

Originally Posted by Stustoys

The reason the lathe have variation is because the center height doesn't matter. So they don't aim to get it right, just close. If what you are saying it true you wouldn't need tool height adjustment on "good" lathes.
The reason for the variation is there are (by my count) 14 machined surfaces that effect the center height of a lathe.

I hope I am explainging myself well enough

Stuart

Obviously the Chinese aren't using CNC machines for H&F's (etc) lathes. Would it be wrong to suspect a lot of their gear and techniques were either imported from the north of England or have been copied?

The H&F catalogues of a few years ago had a 'Daishin Champion' which is so similar to a Colchester that if you swapped the badges you would never know. Still a decent machine (I used one at TAFE), but then again they had a good design to copy

No doubt Colchesters had variance in centre height between machines, but that is to expected for a lathe made 40 or more years ago.....

oops I'm wrong.
There are only 2 machined surfaces that effect the center height of a lathe.
But there are 10 faces between the ways and the face that the toolholder sits on.
There are 16 faces total from the spindle axis to the tip of the tool(give or take a couple depending on how your lathe is made). 12 of them effect the "tool height" you need to get to center height. The other 4 are the "tool height" being the toolholder and the tool bit.
I assume they only machine the castings until the clean up and call it done. Its not a dimension that matters, as long as they don't go to "high"
Stuart

Hi,

Originally Posted by stustoys

well we agree until we get to here.
Tool height is actually centre height.

no it's not tool height is the last step in a chain and is the distance from the bottom of the toolpost slot to the lathes centre.

yes you are right stustoys, i shouldn't have described it that way.
Having a quick change toolpost allows you to correctly adjust the height of your lathe tools to be at centre height.
Yes they allow you to adjust the tool height until it matches the center height.
- no comment from me neccesary.
Centre height is not from the top of the bed ways to the headstock to the headstock spindles centre.
No that is what center height is.
yes your right again - i should have said that centre height is the distance from the top of the lathes bedways to the centre of the headstock spindle. This distance is also about half of the lathes swing.
Lathe swing is about double center height.
https://www.machineryhouse.com.au/products?stockcode=l183
scroll to specifications


then you aren't adjusting center height you are adjusting tool height

the tool height is the last step in a chain to bring the point of the tool to match the center height of the lathe.

The reason the lathe have variation is because the center height doesn't matter. So they don't aim to get it right, just close. If what you are saying it true you wouldn't need tool height adjustment on "good" lathes.
The reason for the variation is there are (by my count) 14 machined surfaces that effect the center height of a lathe.
I totally agree with you here. It would be pretty hard two find identical lathes with absolutely matching centre height even if they were made by cnc. Other factors why lathe tools need shimming or machining down is ie some 16mm tools from one factory may not be the same height as some 16mm lathe tools from another factory ie the latter factory tools could be 16.1mm. I know that the left and right hand tools from my carbide tool set from hare & forbes were different when i miked the ends. I believe this would probably be the same if they were branded for example (ie) vandurit or sandvik. Even carbide inserts from one manufacturer to another would probably be slightly different in thickness.

As a correction to my mention of boring height, i found my cd with the hercus book on it afterwards. Apparently this also applies to parallel turning tools. I am going to try and post the link or the pdf file here i hope it works. The info is on page 9 under 'height of cutting tools'. It is a handy reference book with a lot of info in it.
Thanks for the corrections stustoys.
I am off now to start a thread about quick change toolposts.
I hope i am explainging myself well enough

stuart

Steran, that looks like a very informative book. If there are any missing chapters can you scan them too? I know it is a bit cheeky to ask...

What page relates to centre height (I'm not too lazy to read it, just not much time at the moment)?

steran50 interesting read. I always set my poring bars high, on the theory that as they load up the cut is reduced so things wont break, I guess this may increase the chance of chatter though.
I wonder why they say set the parrallel turning tool high, maybe to reduce chatter?
I hope you're making a QC tool post


Gerbilsquasher Its page 14 of the book but page 9 of the pdf

Stuart

However it seems to relate more to the 'centre height' of the workpiece rather than the 'centre height' of the lathe...