Large Indexable Insert Holder and Small Lathe

[kquiggle]

I have been wanting to try out a larger indexable insert holder on my small (7 X 10) lathe, just to see if there were any benefits. When I got a 20% discount offer I took the plunge and bought the tool below (Dorian MTGNR08-2A).

After some initial trials I conclude that I would not recommend this purchase for a small lathe. I'm posting this here for the benefit of anyone else contemplating a similar purchase.

Here's a short summary of my findings:

- fits my QCTP toolholder, but I had to modify the tool to get it to center
- tight fit (or no fit) for some cutting operations
- no major advantages, some disadvantages

For a more detailed overview with more photos see this link:

https://sites.google.com/site/lagad...athes-mills-etc/review---indexable-toolholder

P.S.

I'm not saying this is a bad tool, just that it is not a good fit for a small lathe.

 

[MachineTom]

The carbide inserts have been great for what they were designed for,Industrial use. No real thought given for small flimsy machines. Carbide can withstand high temperatures, and high pressures, but to do this the edges are honed, not to make them sharp but to make them dull. Because carbide is so hard, like other hard things it chips, so honed edges are what are made. But honed edges need more power to cut, more power, higher tool pressure, more vibration, none of these things appeal to a lightly constructed machine like you have.

Another thing that is common on carbide cutters is point radius, to give better life, a bigger radius is good, it also improves finish, but the larger the radius the greater the pressure on the cutter, more vibration, and more power needed. Those cutters look to have a 2-3/64 tip radius way to much for shallow cuts that your machine can handle. And last is speed SFM, because of the dull edges carbide needs much higher surface speeds to work. So a piece of 1" stock 1018 steel should be cut at 1000rpm 200SFM, feed at .008-.015 per rev, and a DOC of as much as the lathe can take on my 12" thats .050+.

There are special cutters known as up-sharp which could work but they are large and never on sale.It could be an expensive experiment.

 

[mc_n_g]

You probable picked one of the harder styles for a small lathe...a negative insert. Does not mean you cannot use them but they are not really meant for smaller lathes (unless you have some very good inserts). In general, negative inserts need good horsepower and a rigid machine.

Positive stype inserts are easier and more 'free' cutting than negative inserts. Positive inserts will only give you 2, 3 or 4 good corners (only on one side) where a negative insert can be flipped over and used.

You are going to see performance all over the board. You need to run carbide with a higher RPM and some require a minimum depth of cut.
If you buy inserts based upon price do not expect any performance unless they are a known brand which are surplus.

I have seen many times people poopoo carbide because their experience is not what they have heard. Wrong machines, wrong carbide style, wrong coating, wrong chipbreaker...and so on.

There are hundreds of carbide grades from the manufactures and most are specific to cutting select metals.

Just be cautious of what you have. Just like cars there are many makes and models for different roles.
Welcome to the carbide world.

 

[kquiggle]

It was an experiment on a number of levels, so I can't say I'm all that disappointed with the results. I believe you are right about the positive/negative insert comment. On the plus side, it seems to do a great job on brass.

My thinking is that carbide inserts and tools are generally designed with larger machines in mind, in production environments, but this does not mean they cannot be used successfully and to advantage on a small lathe. I plan to try more experiments when the state of my wallet and the sales prices coincide.

I'm hoping to hear from others on this forum who have used indexable tools - what worked and what didn't work. I feel it's as important to know about the failures as the successes so we know what to avoid as well as what to get.

 

[Woodster]

I use carbide all the time on my 7 X 14, but only 1 particular type of insert. I use a CCMT 06 style insert with either .2 or .4mm nose radius for both turning and boring as i can get them from work (part worn finishing tips, with plenty of life for what i do) and rarely have any problems. I turn Titanium, steel, ali and brass with no issues. Rigid set up, perfect centre height, minimum overhang for both tool and workpiece, reasonable speed (but not too fast) and reasonable feed, Soluable oil coolant (as much as you can) and not neat oil or WD40, max 1.5mm DOC, never let the tool dwell and ALWAYS take a spring cut as you will get more workpiece deflection than HSS tooling because Carbide inserts do not 'Dig in' like HSS.

 

[mu38&Bg#]

Carbide for small machines is all about insert selection. There are plenty of sharp edge, small nose radius inserts out there, most are specifically made for screw machines. Most inserts intended for finishing operations are also suitable, but optimum SFM can still be high. You really have to study the catalogs to get what you want. There are positive rake inserts that provide low cutting forces and are suitable for a wide variety of steels. The Dorian catalog does a decent job of explaining geometry. Some catalogs get into specifics about rake angle and lands.

Woodster I have to disagree with the spring pass. Many insert geometries simply rub on a spring pass. If you are getting nice chips on a spring pass I think you're taking far too much on the finish pass and are seeing the result of machine deflection, not the inserts ability to cut. On my 10" machine inserts never cut on a spring pass. CCMT alone doesn't describe anything about the insert other than basic shape. You'll need manufacturer and grade to determine the cutting edge geometry.

I just bought some Sandvik DCET 2(1.5)00-UM grade 1025. These have very sharp edges and a very small nose radius. I just tried them on a piece of 4140 annealed and they cut very nicely at moderate speeds and low feeds. I normally use Sandvik DCMT 2(1.5)1-UM 1125. When used at recommended feeds and speeds (read screaming fast for a manual machine) they leave a bright and shiny finish, but cut OK at more manageable feeds and speeds.

The negative holder was a start in the wrong direction. 3/8" holders probably fit the 7x10's better.

I would suggest Sandvik DCGT 2151 or 2150 in UM or UF grade 1125. Put it in a matching 3/8" holder, for D inserts an SDJCR-06. If you prefer triangle (T) or 80° diamond (C) just change the first letter of the insert accordingly. You'll have to check the catalog as not all the designations are the same or available in every insert shape, if you want a 80° diamond you'd get CCMT 2151-UM or UF. The finish insert (UF) has a smaller minimum depth of cut while the medium insert (UM) has a larger maximum depth of cut. I use Sandvik __GX-AL for aluminum.

Greg

 

[mc_n_g]

I don't know if you have a small mill or not but making a lathe insert holder for TPG 221 or 222 or even 321/322 styles. The last number represents the radius of the nose. There are plenty of resources available to go over the particulars.
The TPG is nice as it is simple triangle without a hole. The insert is positive style so you can only use the top 3 corners. The main focus would be a clamping mechanism after milling a pocket. There are several websites that show different designs for making insert holders.
If you don't have a mill you can buy a holder relatively cheap from some the hobby type online stores.
If you pick generic inserts use C2 grade for non-steels and use C5/C6 for steels. C5 would be more for roughing where C6 is for finishing. You can normally find these inserts for $2-$5 each. You can get a pack of 10 for probably $20-$30 dollars.
That is probably the simplest way of getting into it with a 'basic' carbide insert. If an insert is coated most likely it is for steel or stainless. There are a few coatings for aluminum but with these cheap inserts you probably will not find that too much.
I run HSS ground blanks, multiple types/shapes of carbide inserts, and HSS ground inserts. It all depends upon what I am cutting and what lathe I am using. Carbide = fast speeds.
You would like to find a set where all holders take the same insert style. This way you only need one shape of insert but would need to by different grades for materials.

There is a lot too it and you most likely started with the negative insert style and it just does not perform on a small lathe. You need high RPMs and chip shield to keep the chips from welding to your skin.

 

[kquiggle]

Thanks for all the good comments everybody.

I do have a mill and have considered making my own insert holders - if anyone has done this and has some recommendations please chime in. Anyone have an opinion on purchased versus home made insert holders - the holders I have seen advertised seem pretty high priced for what you are getting.

 

[Niels Abildgaard]

Been there
Done that
Made pictures

http://www.homemodelenginemachinist...urning-inserts-small-manual-lathe-long-10175/

 

[mu38&Bg#]

I've drawn some insert holders but have not made any yet. I buy from Ebay and have several name brand holders now having paid between 15 and 30USD each. Even the import sets are a decent place to start. http://www.shars.com/products/view/2763/38quot_Indexable_Carbide_Turning_Tool_Set

 

[kquiggle]

Wow - great responses.


Niels: Nice write-up; wish I had read it earlier; some good links there too.

dieselpilot: Nice tip on the Shars set - very tempting.

Much appreciated everyone.

 

[robcas631]

The carbide inserts have been great for what they were designed for,Industrial use. No real thought given for small flimsy machines. Carbide can withstand high temperatures, and high pressures, but to do this the edges are honed, not to make them sharp but to make them dull. Because carbide is so hard, like other hard things it chips, so honed edges are what are made. But honed edges need more power to cut, more power, higher tool pressure, more vibration, none of these things appeal to a lightly constructed machine like you have.

Another thing that is common on carbide cutters is point radius, to give better life, a bigger radius is good, it also improves finish, but the larger the radius the greater the pressure on the cutter, more vibration, and more power needed. Those cutters look to have a 2-3/64 tip radius way to much for shallow cuts that your machine can handle. And last is speed SFM, because of the dull edges carbide needs much higher surface speeds to work. So a piece of 1" stock 1018 steel should be cut at 1000rpm 200SFM, feed at .008-.015 per rev, and a DOC of as much as the lathe can take on my 12" thats .050+.

There are special cutters known as up-sharp which could work but they are large and never on sale.It could be an expensive experiment.

I recently bought a Flycutter set with HSS inserts. Using the internet, I looked up how to properly sharpen them, and there was a lot of emphasis on back rake and relief angle. More importantly creating the proper point radius. So, I turned on the grinder and gave it a go. Well I must have taken good notes because I created a mirror like finish with the first two bits I ever made.

 

[kquiggle]

I'm planning more experiments with carbide, but I'm definitely a fan of HSS. My grinding skills still aren't all they should be, but I think the process is pretty forgiving. Thinking back to high school shop - you can do a pretty amateur job and still get decent cutting results. Plus, there are many times when being able to make a special purpose cutting tool is very useful.

 

[dbs]

Take a look at WWW.Plastools.com. They have several styles of holders that take 0 degree rake inserts and their holders are made to hold the insert like a positive insert holder(nose with a down tilt). I've used the 3/8" holder on a 7x10 and now on a 9x20 lathe without any problems. There are LOTS of so called negative rake inserts available to fit there holders, they give you 6 cutting sides and the cost is less than most positive inserts. I find the finish on most cuts to be about the same, for the same sfpm, as I get with HSS. Good luck on your hunt for holders and inserts. Dave

 

[kquiggle]

By an odd coincidence, I recently purchased a toolbox at a garage sale and found a bunch of inserts in one of the drawers. It's quite an interesting assortment (see photo below); some of them look damaged, but others look unused.

Might be time to try them out on a home made insert holder.

 

[MachineTom]

One way to use inserts is to modify the insert holder to directly mount on the tool post. In this case it is a radius grooving tool, the holder was cut so the original end was not used, and I just made an on-edge style tool holder.

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[kquiggle]

MachineTom - that's a very clever mod. If I run across some auction bargains along those lines I may give it a try.

 

[Niels Abildgaard]

That Machine Tom strategy is very smart.
It has been a pleasure to understand.
Took some time.
More of that kind please.

 

[mu38&Bg#]

At first glance the large holder looks like a good idea. I was going to do this, but found that most take large inserts. If your lathe can't handle the extra depth of cut a larger insert offers, you might end up spending the money on larger more expensive inserts. Inserts for grooving/cutoff, and threading tools are often the same size regardless of holder size, so it's not a concern. Just don't buy a 5-6mm wide cut off holder for a small lathe. i shop for inserts before holders.

Kquiggle, did you look for positive rake negative inserts to fit your holder? I'm sure they are out there. A finishing insert would be worth trying. Dorian lists several. Do you know exactly which insert you tried?

Greg

 

[kquiggle]

The insert I tried was a TNMG222. I don't know that positive rake inserts would help, as I believe the toolholder has a negative rake in the insert holder.