Testing bearing/contact surface between a carbide insert and the holder

[maxime.levesque]

After ordering a set of turning carbide insert holders and noticing a defective one (the insert would simply not screw into place), I did another attempt before giving up, with another seller, and received a set that was even worst.

3 out of the 7 holders in the set had a gap greater than 0.1mm under their tip, I was able to slide a 0.1mm feeler gauge under it, I have attached a photo to illustrate the issue.

The nice thing about SCamazon, is that items can be returned at no costs, so there is only loss of time, but in my case the time spent was a good learning opportunity.

I realise that holders are more difficult to fabricate than I thought, the bearing surfaces under the insert needs have maximum contact, if you have a fraction of the surface that is in contact, you will get that fraction of the rigidity.

The fact that heat hardening can introduce distortion, adds another level of complexity, I suppose the only way to guaranty maximal contact surface is to have grinding as a last step.

I've have ordered holders from a seller that is higher in the food chain, not a top name brand, but one that has a name a reputation that is worth preserving. I also ordered others from an ebay seller that was praised on this site, I'll be doing a bit of "metrology" before I even put them to use.

Feeler gauge test, perhaps a test with Prussian blue, if the contact surface is decent it's a good start, as for hardness test, I wish I had a Rockwell hardness tester !

 

[RaisedByWolves]

Have you checked to see that it’s not the inserts causing this.

If you think heat treat will cause that much distortion, look into how the inserts themselves are made.

It will be an eye opener.

Our kennemetal holders are pretty beat up, I’ll have to check them for this and report back.


ETA: I checked our K insert holders and all of my BG holders.

Our K holder is butchered beyond belief with the backer literally falling apart and still works ok.




And only one of my BG set has any appreciable gap, but until now I hadn’t really even thought about it.




This makes me wonder if it is a perceived problem or a confidence issue.

Granted, you want your new tooling to be good right out of the box, and at least one of yours is truly suspect, but how much does this really effect insert performance?

 

[maxime.levesque]

Have you checked to see that it’s not the inserts causing this.

Good point, I did put the inserts on my granite plate, it appeared dead flat, no rocking.

If you think heat treat will cause that much distortion, look into how the inserts themselves are made.

Whatever flatness distortion would occur during the sintering of inserts, could easily corrected with grinding.

This makes me wonder if it is a perceived problem or a confidence issue.

Granted, you want your new tooling to be good right out of the box, and at least one of yours is truly suspect, but how much does this really effect insert performance?

I haven't done any calculations of the loss of stiffness, but an insert with no support underneath is in effect a cantilever beam. One only needs to look at the design of cantilever structures in construction to get an idea how much weaker cantilevers are compared to structures with full support underneath.

Given that losses of rigidity is cumulative, and that the "law of the weakest link" applies,: when rigidity is lost at the tip of the cutting tool, it doesn't matter if the holder is held by 4 tons of metal.

 

[aliva]

Could you put an anvil under the insert and and use a longer screw?

 

[Liljoebrshooter]

Lap the bottom of the insert on a diamond lap.
Joe

 

[OTmachine]

One of the reasons that I mainly use HSS and brazed cemented carbides. I have found it difficult to find good inserts source due to the infrequency of my purchases. Got used to “quality“ inserts, (Kennametal, VR-Wesson, Valenite), when I worked for companies. Cannot justify the cost for the mostly one-off parts that I make / repair in the home shop. I have and still like the TPG style inserts using the adjustable CBT chip breakers.

 

[Bentley18]

Hi all. I've read a lot of posts on this forum but haven't posted much if at all, if any. I've been in the cutting tool business since 1981 and over the years I've learn much. You could also see if the insert clearance is matched with the clearance in the holder. if the clearance on the insert is less than the clearance in the holder the tool will not seat properly. You can get away somewhat if the insert clearance is more the the holders clearance.

 

[OTmachine]

Hi all. I've read a lot of posts on this forum but haven't posted much if at all, if any. I've been in the cutting tool business since 1981 and over the years I've learn much. You could also see if the insert clearance is matched with the clearance in the holder. if the clearance on the insert is less than the clearance in the holder the tool will not seat properly. You can get away somewhat if the insert clearance is more the the holders clearance.

But, I believe that the insert would be closer to the locating surface at the tip, not allowing the .1 mm thickness gage to be inserted, if this were the case. I could be wrong.

 

[matthewsx]

Sounds like you found the answer to your other thread.

How cheap should one get with carbide tool holders ?

I made a few insert lathe tools, and they worked just fine. I showed them to a real machinist, and he said that the next time I was around real machinists, I should keep my stupid homemade tools to myself. I asked him if I should buy a Sandvik or Kennaetal tool, and he said that they will work...

www.hobby-machinist.com

Honest suggestion, chuck some stock up in your lathe and take a few cuts then let us know how it performs. For grins, buy a quality holder and inserts and compare.

I've never done this test with my carbide, but I do find HSS more than suitable for most of my work. Industrial quality insert holders are available fairly cheap on eBay used. Buy non-counterfit inserts from reliable tooling suppliers if they don't come with the tool. If you have a local industrial tool supplier a trip there on your lunch break would probably be worthwhile.

@davidpbest literally wrote a book on this subject.

About my book "Introduction to Indexable Tooling for the Metal Lathe"

Some of the members here on Hobby-Machinist ask questions about my book “Introduction to Indexable Tooling for the Metal Lathe”. So, I thought I would post some sample pages from the book, to give an overall flavor of the writing style, and include the complete Table of Contents as an attachment...

www.hobby-machinist.com

Cheers,

John

 

[extropic]

@maxime.levesque
I've bought numerous Chicom turning insert tool holders and haven't noticed or thought to check for the clearance you've discovered.
However, I will be into it, like white on rice, when I get back to my home base.
I agree that it's a problem that needs to be addressed, not sluffed off.
I sure hope my collection is in good shape. I never expected the sort of problem you discovered. That's what you get for being diligent.
Good catch.