Lathe Carbide Insert Tools

[jjr2001]

Here are a few of my favorite insert tool bits for the lathe:

The first two on the left are shop made using 3/8" 1018 steel. Nothing special except that I like to put an insert on each end of the tool blank. With that config I can turn to a shoulder either left or right depending on the tool and then just remove and replace the tool holder on the 90 degree side of the tool post (parallel with bed) and the same tool (opposite end) will face the end of the part that is being turned.

The pair in the middle are purchased tool holders for small triangular inserts but I machined the blank end to handle an insert also. This converts it to my kind of tool that cuts from both sides of the QCTP.

The pair on the right is another set of shop made tools. They are also 1018 3/8 steel with small square inserts for facing and chamfering on the back end.

The tool at the top was too large for my lathe but it works fine now. The last two pictures show this tool in better detail. It is commercial in manufacture but I milled it down to 1/2" thick so it would fit my tool post. Probably too large for my little lathe but great for roughing. I will grind the inserts with little to no nose radius and just re-grind it when it breaks. Great for removing scale on hot rolled steel.

Cheers, JR

[Paul Jones]

JR,
I like your modifications by machining the blank end of the tool holder to handle another insert and all the additional position options this provides. Great idea about regrinding old inserts and re-purposing these for removing scale on hot rolled steel.

By the way, I had to replace all my imported QCTP tool holder set screws with USA made dog point set screws. The original ones that came with the tool holders didn't last long and set screw cup points tend to mar the tool holders. Dog point set screws hold well and don't mar the tool holder surfaces.

Paul

[jjr2001]

Thanks Paul, I checked all of the QCTP holders that I have to verify that they were in fact dog point. They are all dog points, however it seems that the quality is a bit lax. The dog is not flat! I guess that is why they are leaving marks on my tools. I will keep an eye out for a box lot special and pick up at least 50 of them.


John

[Toolmaker51]

Thanks Paul, I checked all of the QCTP holders that I have to verify that they were in fact dog point. They are all dog points, however it seems that quality is a bit lax. The dog is not flat! I guess that is why they are leaving marks on my tools. I will keep an eye out for a box lot special and pick up at least 50 of them.
John

Besides Allen Co, probably best manufacturer for socket head screws of any variety is Brighton-Best. They've been purchased by an offshore corporate structure; however I detect NO reduction in quality from first box [early 70's] I ever used against a box I depleted just days ago. https://www.brightonbest.com/contact.html. They have a distributor network but justifies specifying them in your order.
Most fastener houses list continent an item is sourced from or quality level. SHSS are equivalent to Gr8. You want alloy steel, NOT stainless. A bit of anti-seize on the threads will let them burnish in use and last forever, MOL.

Per Machinists Handbook, flat set screws are available in
1. actual flat point and chamfered thread.
2. [full] dog point extending a cylindrical portion beyond thread less than minor diameter roughly 3x thread pitch in length
3. half dog point, identical features but cylindrical length is roughly 1/2 as long.

re QCTP's; If you replace screws insure screw length engages all available threads in holder. 100 and 200 AXA's meant for smaller shanks may not get 100% when dog point begins in female threads of holder. I recommend flat points as they bear on threads and point to largest degree possible.

A lot of insert tooling is softer than what was standard a few years ago and dents represent that. Dents cause alignment to shift when screw point seeks that 'pocket'. Stone top of shank enough to flatten out 'rim' of the craters. There also is tendency to over tighten. Alleviate both with cleanly sheared steel strapping or blue shim stock .010+/ .254mm+ thick.
During set up they'll slide smoothly while minimal tension is administered by set screws, after which are tightened. Needless to ever be more than comfortably applied by that size short arm Allen wrench.

[jjr2001]

Thank You Toolmaker51.
I learn something new every time I visit Homemadetools.net....And in just this one reply there are a number of great points.

Thanks again, John

[Meinthailand]

Hi jjr2001 and thanks for sharing this with us. A couple of questions if I may?

Do you actually grind broken carbide inserts to make them useable again?

What are "dog point" set screws?

Many thanks.

[Paul Jones]

Meinthailand,

Google for "dog point set screw images" (but without the quotation marks) and you will see what these look like. The ends of the set screw are flat and without a thread so when tightened down on the tooling, the set screw leaves practically no marks on the tooling. I use the word "images" in most of my google searches because I find it easier to first see what I am looking for than click and read, only to find it is not what I am looking for.

Paul

[Meinthailand]

Hi Paul and thanks for the quick response.

I assume these are to hold the tool in the toolpost not the carbide insert in the tool.

Thanks also for the google search tip. It works a treat.

MeInThailand

[jjr2001]

Hello MeInThailand,
Yes I do grind broken and even new carbide inserts for my mini lathe. Most of the ones I have picked up on eBay have a fairly large radius for my little machine (7"x16" mini lathe). I have also purchased some in tooling lots that would not work at all due to the geometry. (some of them are just weird). Anyhow I will make up a piece of cold rolled steel and mount the insert on that temporarily and then grind it to what ever I need at the moment. For turning aluminum and brass I will grind them pretty sharp and not put much of a radius on the cutting edge. Works great for me in my little hobby shop.

Cheers, JR

[Meinthailand]

Many thanks JR. Sounds like a great boon to be able to do that.

Sorry for my ignorance but do you use a green grit grinding wheel like the ones we used to use in the days of brazed-on carbide tips?

Thanks MeInThailand.