Rake angle on Cutting Tools…..memory tips???

[Chris TickTockParticipant @christicktock]

Has anyone come across some method to easily remember positive, neutral and negative rake angles. I have so far looked in vain.

Chris

[Chris TickTockParticipant @christicktock]

[Paul LousickParticipant @paullousick59116]

As the years pass by, I find it harder and harder to remember things but a text book or computer helps me remember things like rake angles.

Paul.

[Bob StevensonParticipant @bobstevenson13909]

Honestly Chris I think you are making too much out of this…..I have been turning most of my life and aquired my first real lathe about 40 years ago and I'm not really sure what 'positive' 'neautral' & 'negative' actually mean in lathe tool context ….I'm pretty sure that you don't need to either….just get a copy of 'The Amateurs Lathe' by Sparey and in there you will find the relatively few tool designs needed to make just about anything with excellent surface finish etc.

look in the book, grind up some HSS and get making clocks!…add more special tools as needed.

I spent a chunk of the morning in my clock club workshop making a centre arbor for my latest clock….I tried out a Pultra 10mm lathe which was used in WWII by Handley page to make rivets for the 'Halifax'….I really enjoyed myself and was able to get a brilliant finish using a 'knife' tool I keep in my box….touched up the edges with my 'Eze-Lap' and away we went. The only 'choice' I made was selecting a tool with some top rake suitable for steel.

Just get at it Chris, you'll be OK!

[Ian PParticipant @ianp]

Do you mean the actual numerical values, or the relationship of the angled faces with the workpiece?

This was meant as a straight question.

Ian P

[John ReeseParticipant @johnreese12848]

https://littlemachineshop.com/reference/rakerelief.php

[I.M. OUTAHEREParticipant @i-m-outahere]

Simples !

10-15 deg on everything except with a tool for brass or bronze as I don’t touch the top of the cutting tool so no side or back rake .

Easy way is to set up your grinder so the tool rest is at the centre height of the armature shaft then grind the end of a piece of square mild steel that is the same size as your tool bit , adjust the height to get the angle on the end something in the range i listed above and lock it down . You can grind 95% of the tool bits you will ever need at that setting and you will only need to fine tune the settings for something that is or can be problematic like stainless or copper .

Side cutting edge angle – I don’t bother as i just rotate the tool post around a little if i feel i need one but one thing to remember is that the angle between the front cutting edge and side cutting edge must be less than 90 deg so the trailing edge of the front cutting edge doesn’t rub -I usually just use the same clearance as the other edges as it is set up already on the grinder .

If you are into making clocks you will probably be machining brass most of the time and the most important thing with a tool for brass is that it has been honed to give a good smooth finish on the cutting edges and is razor sharp .

Sharpening tool bits or drill bits by hand isn’t difficult it is just a matter of understanding the technique and practicing it !

[JasonBModerator @jasonb]

If it's the actual angles for metals then print this which is basically the same as the LMS one linked to above and stick it behind your grinder. But don't get too hung up on it.

Edited By JasonB on 21/11/2019 08:09:48

[VicParticipant @vic]

There was a heated debate on another forum about rake angles etc. If you multiplied all the different “recommended” rake angles by the number of different tool shapes you would need 127 different tools as I remember. Much of the printed data about this is quite simply out of date and only really relevant if you are a production turner using one of the many carbon “tool” steels available 100 years ago. Bob has the right idea, just grind up some HSS and give it a try. It’s how I started. These days though, apart from “specials” I use a Tangential Tool or Insert tooling. Good luck.

[mechman48Participant @mechman48]

+1 for JasonB comments; as with Vic's comments I'm the same, the tangential tool or insert tooling does 98% of my machining.

George.

[Martin Johnson 1Participant @martinjohnson1]

If the O.P. is working in industry trying to make a profit or bonus by turning things out as quickly as possible, then rake angles, clearances etc. all matter.

If as I suspect he is working in a home shop. They really don't. I turn just about any material with the same set of tools – all ground by eye with a bit of clearance on the front and whichever side face is cutting. Put a few degrees of rake on the top and that does the job. Only exception is some brass which is better without the rake on the top – even then, most of the time I can't be arsed to change the tool.

My qualifications for such a gung ho approach? 50 years model engineering, 40 years as a chartered mechanical engineer.

Martin

[John HaineParticipant @johnhaine32865]

Just on the subject of tangential tools, a few years back I posted here how to grind the tool bit to get zero top rake for brass, a diligent search should find it. Having said that I've never bothered to grind one with the different angles and get by fine with the standard tool.

[Brian Sweeting 2Participant @briansweeting2]

Do what some tutors do, make a wooden model of the tool with all the angles on them along their uses.

[ZanParticipant @zan]

As long as you have clearance then many of the rake angles can be condensed into a very small number of iterations. If you look at the link and view the table, most of them give very similar numbers, and a lot give ranges, most of which cross over so single tools will cater for multiple materials.. the only real exception is for brass or plastics, but even with these I have successfully turned them with steel angle tools..

Most quoted angles are for industrial practise where time is critical to balance with tool life , far less important for us. In addition few so called high speed steel tools are now used in industry, they are too too slow and inaccurate (from a resetting point of view when re grind is needed, tips replace quickly to precise position) in this modern age of high speed production

I’m hearing so much about tangential tools it’s time I joined the family!

[Chris TickTockParticipant @christicktock]

Thanks all for posting your reply, all polite input is always welcome. I note some do not think understanding wether a cutting tool's rake angle is positive or negative is important. However soft metal such as brass has a different chip removal geometry han steel. The rake angle when drilling into brass is very important as the drill can lock into the brass, I suggest machining brass couls also introduce issues and therefore understandig the implications of rake angles is advisable.

Chris

[Ian PParticipant @ianp]

I'm even more baffled now

[Chris TickTockParticipant @christicktock]

Posted by Ian P on 21/11/2019 20:59:57:

I'm even more baffled now

Probably my typos but put simply if the rake angle is important when drilling brass is it also important when turning brass on a lathge…this is a question not a statement?

chris

[Mark P.Participant @markp]

I tend to grind all mine at about 10°, works for me.

Mark P.

[Ian PParticipant @ianp]

Posted by Chris TickTock on 20/11/2019 21:36:56:

Has anyone come across some method to easily remember positive, neutral and negative rake angles. I have so far looked in vain.

Chris

My bafflement is not the facts about rake angles but more about your last reply where you mention polite polite input and then say some (people here presumably) do not understand rake angle being important.

Your original question was far from clear, initially I took it that you wanted to know how to improve your memory, then I wondered if you were trying to clarify the terminology of the tool geometry.

To answer your last question, yes, rake angle is important

Ian P

[Ian PParticipant @ianp]

Posted by Mark P. on 21/11/2019 21:48:31:

I tend to grind all mine at about 10°, works for me.

Mark P.

Go on then Mark, is that positive or negative and is that for steel or brass?

Ian P

[I.M. OUTAHEREParticipant @i-m-outahere]

Chris,
This video will explain a lot even though he doesn’t talk about brass it does somewhat explain what the various angles do.

The reason you don’t really need any rake angle on a lathe bit for brass is because the chip fractures easily not because of the tool pulling itself into the workpiece like a drill bit does and a lathe holds the tool more rigidly than a drill press .The rake angles really help to pull the chip away and make them curl -if you try machining something like aluminium with no side rake or even a negative rake you will see there is a build up of material in front of the cutting edge – the tool is essentially forming a bulldozer blade and pushing material ahead of itself .

I would also take a look at the Clickspring channel on youtube especially if you are into making clocks as there are are some really good tips there !

 

 

 

 

https://youtu.be/__A2xtLF0AU

 

Edited By XD 351 on 22/11/2019 01:50:33

[JasonBModerator @jasonb]

Posted by Chris TickTock on 21/11/2019 21:27:07:

Posted by Ian P on 21/11/2019 20:59:57:

I'm even more baffled now

Probably my typos but put simply if the rake angle is important when drilling brass is it also important when turning brass on a lathge…this is a question not a statement?

chris

Unlike some here I have never modified a drill bit for brass or used specific ones made for the job, just use the same ones that I do for every other metal, may just take a bit more care when enlarging a hole but that's all. So just like the replies to your question it can matter but is not really that critical for the average guy in his shed.

Like others I don't grind tools specifically for different metals, the most I am likely to do is use a **GT for non ferrous and **MT for ferrous but even then I will use **GT on steel and iron. With HSS then I'll just give the top a few degrees and use it on everything. I don't even have a fancy tool rest just the poor basic one that came with the 6" bench grinder so all grinding done by eye and not measured. So a tool that I have ground up to a special shape for use on say brass will also get used on steel or iron if I need the same shape or the profile altered and the top surface left untouched.

When it comes to milling I had always used the same geometry milling cutters but have taken to using specific ones for non ferrous in some cases but don't have duplicates of all even if the sizes and shapes were available but can still cut metal without problems.

The other advantage of the higher rake **GT inserts when used on brass and the harder bronzes is that you don't get covered in a shower of fine chips as the swarf comes on in curls. Can't see much wrong with the finish from a CCMT with it's positive geometry compared to HSS. Notice how the insert tooling also throws the swarf away from the surface being cut so that there is less chance of it affecting the finish.

 

Edited By JasonB on 22/11/2019 07:32:40

Edited By JasonB on 22/11/2019 07:35:02

[ChrisBParticipant @chrisb35596]

I use TNMG inserts (negative) on all materials I use – stainless, brass, steel, alu, and they cut well and with a good finish. Most of the times the finish comes out like a burnished mirror finish. Down side is I cannot machine very small diameters as the tool creates quite a lot of side pressure, and it does not give a good finish with spring passes – but what I mean to say is, it all depends on the application – maybe rake angles come to play most when turning small parts etc but not much for larger work – my limited experience opinion.

So I would experiment with tool geometry, materials, speeds and feeds and find what suits my application best, as probably no book will have your exact conditions (type of lathe/tools/etc) and work requirements. I opted for TNMG inserts because as a beginner I was going to ruin a lot of inserts until I get a good feel of my lathe, so having 6 cutting edges on one insert and the negative insert being more robust, it made a good compromise.

[Ron LadenParticipant @ronladen17547]

With the bit of experience I have picked up so far I dont get hung up on the angles and when I grind a HSS tool I just go with what looks about right and it always seems to work. I am starting to lean more towards insert tooling though, I have MT inserts for general turning and my parting is an insert tool plus I am about to get some GT inserts for non ferrous.

One thing that did jump out at me on Jasons link and the LMS link to recommended angles for different metals was the 35 degree back rake for aluminium, the tools I have ground and used have nothing like that probably around 15 degrees not that I have measured but they have seemed to work ok.

Edited By Ron Laden on 22/11/2019 08:57:39

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 22/11/2019 07:02:14:

.

The other advantage of the higher rake **GT inserts when used on brass and the harder bronzes is that you don't get covered in a shower of fine chips as the swarf comes on in curls. Can't see much wrong with the finish from a CCMT with it's positive geometry compared to HSS. Notice how the insert tooling also throws the swarf away from the surface being cut so that there is less chance of it affecting the finish.

.

Nice demonstration, Jason

MichaelG.

[Author]

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