lathe tool sizes

[chris mcnicollParticipant @chrismcnicoll83540]

hi there, i have a Harrison L2 lathe as shown **LINK** and im after getting some new tools for it, would you buy indexable or buy blanks and make your own? i have checked the centre and it looks like 1/2" shank tools are correct size, now would i be best buying next size down and shimming them up or just going for the 1/2"

probably silly questions but im new so please be kind.

chris

[chris mcnicollParticipant @chrismcnicoll83540]

[JasonBModerator @jasonb]

Whatever you go for you will have to do some shimming to get the tip dead on ctr height. Indexable tools will be metric shank so 12mm rather than 12.7mm (1/2" ) and by the time you have ground some top rake onto a 1/2" square HSS blank it too will be lower.

J

[Bob StevensonParticipant @bobstevenson13909]

I like the biggest, ie., thickest tools that can be fitted because I'm a self confessed 'flexfreak'……ALL lathes flex to some degree which spoils the quality of finish and ease of cutting etc. The thicker the tool with minimal overhang the better the turned quality of the surface…..

I've made my own cutting tools from HSS blanks since I was a youngster at school (so I have had some practice now!) and never really got on with indexable, or removable insert type but they do have their adherents who get reasonable results……..

…….Might be a plan to get some of each and see how you go!

[Neil WyattModerator @neilwyatt]

Tools need to match your technique rather than your lathe. The same goes for speeds and feeds.

If you are a 'gentle' machinist then you won't ever have issues with using small tools and wonder what the fuss is about, and vice versa.

If you are used to HSS then you will get poor results with carbide and again vice versa, at least unless you bear with them and 'unlearn' your old technique and developed a new one.

Even this isn't the whole story as the style of insert you use, the geometry of your grinding, the sharpness of the tool and the condition of the lathe all play a part as well.

Ultimately most tools that will fit in a lathe can be made to work satisfactorily if the lathe can run fast enough and is rigid enough for the tool (you can always slow down or reduce cut for a weedy tool).

Toolpost capacity is an indication of the size of tool your lathe is expected to use. With inserts in particular it is possible to 'dial in' material, insert type, feed, speed and depth of cut and expect to get good results – but only if your machine is up to the task, and the results may take you out of your comfort zone (I know ripping off swarf with carbide flat out even on my small lathe is quite scary!)

Ultimately, what gives the best results for YOU can only be discovered by experiment and experience.

Neil

[VicParticipant @vic]

I'm with Bob, bigger is better but half inch tools look to be about right for that lathe Chris. My favourite is a tangential tool holder which doesn't need shimming as height adjustment is built in. I also don't shim my insert tool holders either, I've just epoxied the correct spacer to the bottom of each tool holder so they're permanently on centre height.

[BazyleParticipant @bazyle]

"Toolpost capacity is an indication of the size of tool your lathe is expected to use"

Beg to differ. It is just an indication of the maximum size some dick will put in 'cos he thinks it makes him more 'professional'. Do you drive around with 5 people permanently in your car just because the manufacturer said it is a 5 seater?

Put a centre in and move the (empty) toolholder over next to it. Measure the actual space available for a tool. That shows that anything bigger is just a waste of money as it will have to be ground down.
Then just get some 1/4 in HSS 'cos it is cheaper and quicker to grind to shape and if it flexes it will give you the chance to learn better technique.

[Nick_GParticipant @nick_g]

.

Obviously physics state that bigger will me more rigid.

But as model engineers we spend a good deal of our time by default making quite small parts. This means at times we will need smaller tools to enable them to be able to get into the required work area.

This is most noticeable when a tailstock live center is perhaps engaged. – I have a small bodied extended point one which helps. But even they have limitations and I have found myself grinding down the tool around the cutting area in order to gain access to the work.

Nick

[AjohnwParticipant @ajohnw51620]

Posted by Bazyle on 29/07/2016 09:49:32:

"Toolpost capacity is an indication of the size of tool your lathe is expected to use"

Beg to differ. It is just an indication of the maximum size some dick will put in 'cos he thinks it makes him more 'professional'. Do you drive around with 5 people permanently in your car just because the manufacturer said it is a 5 seater?

Put a centre in and move the (empty) toolholder over next to it. Measure the actual space available for a tool. That shows that anything bigger is just a waste of money as it will have to be ground down.
Then just get some 1/4 in HSS 'cos it is cheaper and quicker to grind to shape and if it flexes it will give you the chance to learn better technique.

I did lots of turning on machines that would make a Harrison look like a toy with nothing other than 5/16 HSS. The machines had an advantage though. Enough tools height to use a holder that held the bit at an angle. For very heavy turning with very heavy feeds a superweld with up to a 1" shank would be used. Not much call for it though.

Some auto work used 1/2" hss and these often had extremely poweful motors fitted as lots of things were made with one cut.

I generally use 1/4 HSS at home but do have some 5/16" as well. That size might be a good idea if you intend to fully use say a 1HP motor at normal HSS turning speeds but even with extreme cuts rake angles can reduce the loads a lot. Bigger sizes can also be handy for boring bars, say 1/2" but beyond what that can do a boring bar is a better option. The HSS can be handy for internal screw cutting, coarse threads with a narrow dia but they do flex.

As a suitable for most things I would suggest these to get you started

**LINK**

They are long enough to get a "tool" on each end and in my experience made out of good stuff. He also offers them in 6mm but for confidence the 8mm is likely to be a better bet.

John

–

[BazyleParticipant @bazyle]

John makes a good point about boring tools being bigger – but that is because they often need a lot more length to get down a cylinder casting.

[Clive FosterParticipant @clivefoster55965]

Posted by Ajohnw on 29/07/2016 15:46:38:

Enough tools height to use a holder that held the bit at an angle.

John

Armstrong, AndyCraft, J&S are commonly found brands for toolholders of this style. Much to be said for them in the home shop as they provide plenty of support letting you use smaller tool blanks. They don't need positive rake angles ground onto the top so are as economical as tangential types. Need to flatten off the built in top rake, around 7° I think, for some materials tho'.

They also make a fairly effective poor boys substitute for a quick change system if you leave the holder mounted up and change tool bits with reference to a tool tip height gauge. The projection repeats when changing if the tool tip is on centre. I prefer the optical type of tool height gauge. Easily made and can be used at a distance if thigns get in the way of directly bringing the tool tip up to the line.

I like the J&S pattern holder. The bit holder is lower than the base of the shank so you can use next size up tooling. Total projection is more than with the Armstrong and Andycraft styles. Sometimes an advantage, sometimes not.

There was an articel by Jacques Maurel describing home made equivalents in a recent MEW.

Clive.

[MWParticipant @mw27036]

I think logic would be that you should aim to own a good range of small tools for internal turning and thread cutting, and with external turning you can afford to go a little bigger, but it doesn't really matter alot if you're only taking small cuts, obviously a bigger tool normally means a bigger cutting face.

I find that the "general use size" for me is around 3/8" maybe 1/2" tool steel on some occasions, i know other production workshops where the same rule applies. I have never had a use for a tool any bigger than 16mm square. ever. 1" square is simply ludicrous, it isn't necessary for all but the most titanic of lathes. 

Michael W

Edited By Michael Walters on 29/07/2016 19:57:47

[AjohnwParticipant @ajohnw51620]

The ones we used were made on site Clive. I can't remember the angle. They were made to suite the lathe with about 3/4" of the tool bit sticking out and set on height by simply winding in against a 6" rule with the clamping screw loose. Easy if done several times daily. Also easy to loose the knack eventually too.

They were pretty simple to make. I suspect instructors wanted them for friends etc as every lathe had one fitted so why make more. Simply file up and harden a drift a touch bigger than the tool bit. Drill a suitably sized hole to drift out and part drill a little way down at a size that just clears the diagonal of the drift. It's just used to centralise the drift. Then hammer it through and remove the guide drilling. Then add a clamping screw hole – an unbreko type screw would be best as the soft ones will mushroom over.

I suspect I would mill the drift these days. I think the hole was sized to leave around 1/16" flats in the corners to support the tool bit after it was drifted out. Maybe a bit more on 5/16 bits. Too much and no chance of driving a drift through. I suppose people could mill up a stepped drift but they do need to be tapered a touch otherwise it would be impossible to get them out. Not too much taper as they may "drift" off.

To be honest I often think about this style of holder when I look at all of my quick change holders. I used to have a whole selection of shapes in a tobacco tin. A boxford has 1" centre height directly above the compound slide and I suspect that may be sufficient. It's easy enough to shorten 100mm tool bits. Grind a bit of a groove round them, hold in a vice and give it a whack with a hammer. Result 2 50mm toolbits. HSS doesn't like being bent.

The angle I seem to remember is 15 degrees. However I would have though 10 would be fine as the main effect is to lead the swarf away from the work. Screw cutting tools are just flattened off at what ever angle it is. The big advantage the arrangement has is that the tool isn't weakened by grinding on back rake and easy height setting.

John

–

[Author]

Posts