The Home Machinist!

I have a box of various (some expensive) inserts. If I were to try and make some
tool holders what would I make them out of. I have seen a copy of articles of guys
doing this .. but .. they made as assumption the reader knew what he was making
it out of.

Is CR fine ... I would rather use SS .. how about that.

One dumb question. Someone said that it should have a relief of about 8 degrees. Its
embarrassing to ask .. but .. does this mean that .. what the insert sits on should
slant DOWN towards the work 8 degrees or slant UP towards the work.

Quick answer: It depends on the inserts.

Relief is how much angle there is under the cutting edge, and that will vary by the type of insert.

Look up your inserts here to see what they are:
http://carbidedepot.com/formulas-insert-d.htm

You can also see what toolholders look like here:
http://carbidedepot.com/formulas-th-d.htm

Steve

cool .. thanks Steve

Neither cold rolled or stainless are a good choice for tool holders. The pressure of the cut will deform the seat rapidly, assuming you put them to work, and that results in broken inserts. For that reason, tool holders are heat treated, to resist compression, and often have a carbide anvil to help distribute the pressure (important when chip breakers are a part of the insert).

We'd be best served using an alloy that can be heat treated----4140, or even 1045 (medium carbon steel). Anything to permit hardening the area that accommodates the insert.

Don't guess at seat angles. Negative rake inserts are formed with no relief, relying on the rake angle to provide both side and front relief, so if your newly created tool doesn't have the required rake, they won't cut. By contrast, if you provide negative rake for positive rake inserts, they're not likely to hold up well because of lack of support of the cutting edge. Do your homework before setting out on this project.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

so ... on the chart pointed to by Steve .. it says that a P nomenclature requires
an 11 degree relief.

So .. is the relief angle already cut on the insert and the insert
sits flat on the holder. Or does the holder provide the relief angle.

The picture looks like the angle is on the insert .. but you talk as though
I can do it wrong ... providing the wrong relief (pos or neg) which would indicate
that making the tool holder wrong would be the problem.

I kind of thought I WAS doing my homework ... I'll tell ya what .. don't tell me .. but
point me to where that info is .. I think you will find .. that finding that simplistic info is
harder than you think. Trust me .. you think I like coming here asking you guys these really basic
simple questions ? I have a million questions in my head .. and I don't know even ONE
machinist friend that I can go to ... to ask questions ... YOU guys are my machinist friends.

Sorry .. Frustrating moment there .. grin

********************

Clearance or Relief Angle (e.g. "CNMG432" / "CCMT32.51")

Code Letter Angle Diagram
N 0°
A 3°
B 5°
C 7°
P 11°
D 15°
E 20°
F 25°
G 30°

The best thing you can do to get a clear understanding is to look at some insert holders, to see what I'm talking about.

The thing you're struggling with, it appears, is you're trying to confuse relief with rake. They are not one and the same. In other words, a negative rake insert has no relief. It is made with 90° corners (top to side, or bottom to side--- normally---there are exceptions). Relief, at the cutting edge, is generated by the rake angle of the holding tool.

By contrast, positive rake inserts generally are made with (too much) relief, but the holder compensates for the relief angle by, you guessed it, the rake angle. Thus, positive rake inserts tend to be much more fragile than negative rake inserts.

In so far as pointing you to a source where you can get the needed information, it's not likely to exist. These determinations are generally made by the insert making people, and not necessarily disseminated to the public at large. There is usually no need, for most folks don't make their own holders, often for good reason. They are a precision piece of work, one whereby an insert seats properly, exposing the right amount of the insert to the cut, and lending full support, so the insert isn't easily broken in use. The slightest deviation from a proper fit will often result in broken inserts, in particular if the seat gets distorted, as I mentioned previously. That's not to say you're not capable of duplicating such an effort, but if you're new at machining, it's not going to be easy, due in part to the compound angles that are involved, to say nothing of the critical geometry of the insert form itself. Yes, I realize that some are a simple 90° cut, but not all are.

I'm sorry I'm not more help, It could be that someone on the board has built holders and has the needed information. Perhaps they can step forward and offer assistance. I simply do not have the required knowledge. However, were I in need, I'd measure existing tooling to learn what is needed.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

The insert holders that I have that use clearance inserts set the insert flat/horizontal - since the clearance under the cutting edge is already part of the insert - and the relief angle is carried down the insert to provide clearance. The seat is flat and horizontal, and is the same size as the bottom of the insert to provide full support. The holder also has the supporting side (or sides) cut with the corresponding relief angle. Inserts that do not have a clearance angle sit angled downward.

This does not address holders much, but does discuss inserts fairly well.

http://www.ccpa.org/pdf/B212_4.pdf

_________________
Standards are so important that everyone must have their own...
Logan 10x24 Lathe, RF-30 Mill, 20 Ton Press
Disclaimer: I'm just a guy with a few machines...

I finally found some answers. Found two good articles about guys making
their own.

Here were the links and the pertinent info that I found.

http://bbs.homeshopmachinist.net/showthread.php?t=39130
http://www.metalwebnews.com/howto/toolh ... older.html

I understand that some of this is these guys opinion ...

I make my tool holders from 1/2" square mild steel HRS stock. A couple feet of stock and a few enjoyable hours making chips and you can have all the holders you want. Don't waste money on fancy steel - mild steel is just as rigid. See Machinery's Handbook 24 ed pp 448 - the modulus of elasticity is about the same for all steels. Sure, the tool post clamping screws mar the top surface of the relatively soft material but so what! It's not as strong as tool steel but if you bend/break a 1/2" square tool holder, the loss of the holder will be the least of your problems. See the Drawing


The TNMPxxx series of inserts is a so-called positive/negative rake insert. The insert is made so that if it was mounted flat, it would have +10 degrees rake. If it's mounted so it's nose droops down 5 degrees, it would then have 5 degrees clearance and 5 degrees rake - reasonable values for most machining. These inserts also have a hole through the center for mounting which is countersunk on both sides of the inserts. Some inserts such as the TNMG series look at first glance as if they are positive/negative type but a more carefull examination reveals that the chip control groove does not go right out to the edge. These are, in fact, 0 rake inserts.

Thanks for the charts and links ... everything really did help.

Mike

This only works fine on a small lathe. I argued with the guy when he wrote it. Some people there is no way you can tell them anything. In my opinion this isn't good advise at all. My insert holders are all store bought industrial quality and have served me well for at least 20 years. I don't have to make a bunch of holders and stock them for when they fail in a heavy cut. Listen to Harold he knows what he is talking about.

Richard W.

lol ... how can you not listen to Harold .. he's like some ancient book. You can't argue with
experience like that. Every now and then he gets upset when someone argues about
not needing to do it the right way .. he doesn't care if you do it right or not .. just don't say
that it doesn't matter .. grin.

rats.. he's standing behind me .. isn't he ?

but as far as the holder goes .. it was just interesting to see how other people did it .. and to
see what they made them out of. And a pretty good talk of rake and relief.

I just have a few boxes of different inserts .. that it would be fun to try out .. and 90bucks for
a new holder is prohibitive for just messin around. I think .. like a lot of guys .. I work more
ON my tools than I do using my tools to make things.

When you guys envision a tool failing .. you see an important piece of work being destroyed.
I don't think I have ever had an important piece of work in my machine .. I just like
having fun and learning.

Mike

I'm ready.

I share Richard's thoughts, and I outlined perfectly well why. If you've used negative rake for roughing, on a machine that is capable of moving stock, you'll understand the point in question. Cutting pressure is so extreme that the insert is pressed in to the holder. That's the reason carbide anvils are often employed. Once that has occurred, the tool is, for all practical purposes, useless.

While being pressed in doesn't sound like it's much of a deal, the real problem comes from the uneven deformation of the seat, greater at the point of the cut. That causes the insert, when installed to not bear at the point, where support is most needed. The slightest amount of pressure applied to the tip breaks the insert. That generally won't happen to hardened holders, although a crash can still deform the seat.

The real issue with making one's own tool holders isn't that it can't be done. They're made by people every day. Hell, I've made tool holders, even from mild steel. I just don't see them as a tool satisfactory for long term application. Those I've made were job specific, and used but one time only. Adequate for the purpose, but woefully inadequate for the long haul.

The entire point of this post is that to address the real issues as if they are just imaginary isn't doing anyone a service. That's what has been overlooked by the linked article. Sure, you can mount an insert, and even put it to use, but what real good is it? It isn't reliable if you index, so there's no guarantee that the dial settings won't be lost, and if the seat deforms, as I've suggested, there's no guarantee that the insert won't be broken.

It's pretty simple. If a setup will tolerate an insert tool that isn't troubled by not being heat treated, it's most likely that the task at hand would be far better addressed by using HSS instead of carbide, anyway.

All too many look upon insert tooling as a dodge, to avoid learning to grind HSS tools. In most cases, they don't benefit in the slightest, as most small machines can't take a cut that warrants the use of carbide. The only real benefit would be in machining either abrasive or hard materials, where HSS has limitations.

I've never been keen on guys that treat learning things properly with contempt. Some of the people involved in that forum do just that, wearing cheat methods as a badge of honor. They are free to think and do as they wish, but they certainly won't earn my respect in the process.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.