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

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Chris TickTock20/11/2019 21:36:56
222 forum posts
8 photos

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

Chris

Paul Lousick20/11/2019 22:13:08
1212 forum posts
502 photos

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 Stevenson20/11/2019 22:40:30
313 forum posts
6 photos

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 P20/11/2019 23:02:55
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2246 forum posts
90 photos

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 Reese20/11/2019 23:21:24
798 forum posts

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

XD 35121/11/2019 00:32:13
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1362 forum posts
118 photos

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 !

JasonB21/11/2019 08:08:54
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Moderator
16530 forum posts
1759 photos
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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

Vic21/11/2019 09:27:39
2330 forum posts
12 photos

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.

mechman4821/11/2019 16:15:53
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2518 forum posts
377 photos

+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 121/11/2019 16:37:54
128 forum posts
1 photos

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 Haine21/11/2019 17:45:27
2693 forum posts
138 photos

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 Sweeting21/11/2019 18:24:22
385 forum posts
1 photos

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

Zan21/11/2019 19:26:38
135 forum posts
5 photos

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 TickTock21/11/2019 20:47:41
222 forum posts
8 photos

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 P21/11/2019 20:59:57
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2246 forum posts
90 photos

I'm even more baffled now

Chris TickTock21/11/2019 21:27:07
222 forum posts
8 photos
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.21/11/2019 21:48:31
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605 forum posts
6 photos

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

Mark P.

Ian P21/11/2019 21:49:40
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2246 forum posts
90 photos

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 P21/11/2019 21:50:49
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2246 forum posts
90 photos
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?devil

Ian P

XD 35122/11/2019 01:50:05
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1362 forum posts
118 photos
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

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