# Rake angles



## Izzy (Sep 21, 2017)

I wanted to make my own insert tooling for my lathe and before I start I'd like to know the effect rake angle has when it's positive, negative or neutral I've tried doing some research but couldn't really find a solid answer. 
The inserts I happen to have, have a 25° clearance angle so I was thinking of doing a 10°-15° rake angle which would leave me 10-15° clearance. What is everyone's advice? I can provide any Info y'all might need I Wana get this done right the first time!


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## Bob Korves (Sep 21, 2017)

Here are a bunch of answers to your question:
https://www.bing.com/search?q=the+effect+on+cutting+of+rake+angle&pc=MOZI&form=MOZSBR


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## patmat2350 (Sep 22, 2017)

Rake... and "back rake"... which one?
Here's a thread on back rake: http://www.practicalmachinist.com/vb/general-archive/tool-back-rake-80591/


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## Kenny G (Sep 22, 2017)

Thanks for the diagram being a newbe this is the best diagram explaining the angles I have seen.


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## Izzy (Sep 22, 2017)

I guess I should be more specific with my question, good threads and good info but not quite what I was looking for. 
I'm going to be making a boring bar, a turning tool and a facing tool the lathe I have came with a whole bunch of 60° triangle inserts that have a flat face and 25° clearance angle but no tool to hold them so I'd like to make use of them. I'm thinking 10° rake but don't Wana over do the rake angle does 10° sound good? And for the boring bar what does everyone recommend I use, round stock or square stock? What's everyone else use at home? I'm still trying to come up with a design so I'm open to ideas...


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## Dave Paine (Sep 22, 2017)

My boring bars were purchased so the manufacturer has already done the angle-of-the-dangle machining.

The bars are round stock with a flat machined on the top.  I recommend this approach.  It allows me to clamp the bar in the correct position in the toolholder and a consistent position when I need to re-position the bar for various depth of boring.


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## Izzy (Sep 22, 2017)

These are the tips in question.


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## 4GSR (Sep 22, 2017)

With that style of inserts, you generally have a neutral top rake for the insert.  The problem you run into is the smaller the bar is, the more negative rake you have to put in the bar so the insert does not drag on the bottom side of the insert.  

Go to some of the manufactures website that sell small insert boring bars and study the pocket geometry for the inserts offered.  Some manufactures give angle information, some do not.  Check other manufactures, be suprise to the details you can get to make a boring bar to.  I would suggest using screw down inserts over the old generic ones like TPG's for boring bars.  The screws are available off of eBone for reasonable prices.


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## Izzy (Sep 23, 2017)

I honestly wouldn't have thought to check manufacturers websites! And honestly I'm only trying to make these inserts work because I have hundreds of them. My main reason for asking this question was because I made a facing tool to hold these at a neutral rake as a tester and I was getting quite a bit of chatter. I just used 3/4" cold rolled steel with an angle milled in and 6-32 screw to hold it. Tool was on center and just chattered horribly. I don't Wana spend a bunch of time on a boring bar and have it chatter like crazy too. I noticed the boring bars at work have a negative rake too why is that? Just better for boring or something more?


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## IanT (Sep 23, 2017)

Hi Izzy,

Couple of comments - which may (or may not help) you. I use inserted tooling for some things (parting and screw-cutting) - basically because it's easier to get the specific tool shapes I need. But for most stuff I still use HSS. Whilst there are clearly differences between inserts and HSS - I'm going to assume that the basics remain the same. 

When I grind a HSS tool - the "rake" used will vary depending on the type of material I'm going to cut. Not sure you mentioned what this was but I'll assume you want to machine some form of steel. You should therefore have some side and back rake - the combination of these two giving you the 'top' rake. How much rake you give is really also a compromise - as sharper tools tend to have shorter lives. You can look up rake angles for HSS tools elsewhere - but I only use a zero (neutral) rake when machining brass.

Remember that inserted tools were intended originally for industrial use and hobby machines are not as rigid as large commercial ones - so whilst negative rakes might get used in commerce they will generally not be much use to you in the home workshop - unless you are trying to machine something very sticky - like phos. bronze - and even then I'd only use them if I had real problems...

Hope this helps.

Regards,

IanT


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## IanT (Sep 23, 2017)

Sorry Izzy - just re-reading my post and I didn't make myself clear on one point.

Your inserts will have some rake built in I assume - and you do mention this. I was referring to the actual cutting angles involved - so if you are just asking about 'inclinations' of the inset holder itself - then a "neutral" angle on the holder, will give you whatever 'rake' is built-in to the cutting tip of the insert...

You need rake to cut steel well - decide how much you want/need and adjust your insert holder angle accordingly, based on the tip's rake.

Regards,

IanT


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## Tozguy (Sep 23, 2017)

Izzy said:


> I honestly wouldn't have thought to check manufacturers websites! And honestly I'm only trying to make these inserts work because I have hundreds of them. My main reason for asking this question was because I made a facing tool to hold these at a neutral rake as a tester and I was getting quite a bit of chatter. I just used 3/4" cold rolled steel with an angle milled in and 6-32 screw to hold it. Tool was on center and just chattered horribly. I don't Wana spend a bunch of time on a boring bar and have it chatter like crazy too. I noticed the boring bars at work have a negative rake too why is that? Just better for boring or something more?



I'm not sure that the steel used in the boring bars where you work are cold rolled steel. Chatter can have a number of causes and a flexible holder is one of them. Ordinary screws don't cut it either. Good insert holders and screws are expensive for a reason.

If your neutral rake facing tool chattered I would not blame the rake angle to start with. Continue to work towards getting satisfactory cutting with those inserts on ordinary turning and facing. Learn what it takes to get them to work before going to boring.

This is a general purpose beginner kit I use with similar inserts. Square shanks and neutral top rake. Note the extra screws because they are special.


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## Fallriverbryan (Sep 23, 2017)

Maybe you could make a round holder for your inserts.   Then, you can make adjustments to your rake angles by turning the bar in your holder. All the boring bars have seen include about 3 degrees of back rake and work well for me in stainless steel.

Sent from my SM-G950U using Tapatalk


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## 4GSR (Sep 23, 2017)

Here's a drawing for a small boring bar I made may years ago to fit a bunch of surplus insert I have on hand.  It came out okay, not perfect, did get the job done I needed it for.


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## Bob Korves (Sep 23, 2017)

The type of steel and whether it is hardened or not will not change the flex characteristics at all.  All steels, in all tempers, have about the same elastic modulus.  If you want a more rigid boring bar, you must go to carbide.  Edit:  And/or go to a bigger diameter bar...


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## 4GSR (Sep 23, 2017)

Here's a picture of the boring bar I made to the drawing posted in my previous post.  One thing you have to remember, you should cut the insert pocket with a tapered end mill that has an angle that matches the angle of the insert.  That angle will be either 7 degrees or 11 degrees, depending on the insert style, TCMT or TPMT and all of it's variations.  Ken


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## Izzy (Sep 23, 2017)

@Tozguy I know the boring bars at work aren't crs that's just what I used for the facing tool. I would assume boring bars would be made out of a hardenable material to try an control flex/chatter as best as possible.
The tool I made looks identical to the tools you posted I'll take a pic so y'all can see what I came up with
Unfortunately the tip doesn't have any built in rake angles or chip breakers or anything like that just a nose radius and I measured 25° back clearance (I think that's what it's called) 
@4gsr I like that boring bar and that's kinda what I was shooting for so I might just use that idea lol


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## Izzy (Sep 23, 2017)

This is the tool I made...


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## Izzy (Sep 23, 2017)

Here's a new design I just tried out, 10° rake. Seems to cut much smoother, chip isn't as hot either.


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## 4GSR (Sep 23, 2017)

Izzy said:


> Here's a new design I just tried out, 10° rake. Seems to cut much smoother, chip isn't as hot either.
> 
> 
> 
> ...


Okay, on TP_ style insert for turning tools, Angle one or the back rake is generally 0 degrees.  The side cutting or the edge of the insert that is getting the cut, that angle is generally set at 5 degrees.  That's why the TP_ insert has 11 degrees side angle to it.  So you almost have it right.  Since it is cutting, I wouldn't mess with it.  Go for it!


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## Tozguy (Sep 23, 2017)

Izzy, glad you are making progress. What material are you cutting? Hot chips might be a good thing if it keeps the tool and work cooler.


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## Tozguy (Sep 24, 2017)

This article has some relevant info about rake angle (among other things):

http://www.sandvik.coromant.com/Sit...s/global/technical guides/en-gb/C-2920-23.pdf


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## Rockytime (Sep 24, 2017)

Dave Paine said:


> My boring bars were purchased so the manufacturer has already done the angle-of-the-dangle machining.
> 
> The bars are round stock with a flat machined on the top.  I recommend this approach.  It allows me to clamp the bar in the correct position in the toolholder and a consistent position when I need to re-position the bar for various depth of boring.



I've done the exact thing. They work flawlessly. No more brazed boring bars!


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## Izzy (Sep 30, 2017)

@Tozguy I'm just cutting regular old mild steel. Nothing fancy lol


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## crazypj (Oct 1, 2017)

I very rarely use carbide tooling nowadays but looks like bit isn't supported properly. Try 1/8" thick 'chip breaker' on top as well to spread clamping load.
learning how to shape and sharpen HSS will teach you more about how uncritical tool angles really are on hobby machines.
I remember when 'we' tried ceramic tooling at factory, didn't have a machine fast enough or rigid enough to use it and ended up going back tp brazed carbide for most general purpose work
Same principle applies to our hobby machines. 
I totally understand wanting to use the inserts you have but you may be better off finding out exactly what they are and 'e-baying' them


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## Izzy (Oct 1, 2017)

The rake angle made a pretty big difference actually, my machine seems to be sensitive to small changes maybe it's got something to do with it being an older belt driven friction bearing machine but it seems to be cutting ok now. Chatter ended up being the screw had came loose haha live and learn.


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