Lathe Carbide Insert Tools

[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.

[jjr2001]

Yes I do use the green wheels for carbide. I have an 8" Delta grinder and one of the wheels is the green carbide grinding wheel and the other is a fine aluminum oxide that I use for HSS. The tool grinder that I built has a diamond wheel for HSS and Carbide grinding.
The diamond wheel is finer and gives a better finish on the carbide but for my purposes the good ole green wheels work fine.

cheers, JR

[Meinthailand]

Many thanks JR.

MeInThailand

[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

[Toolmaker51]

Excerpted, as I tend to do. Not diluting, more to centralize reply to comments of the post.

Yes green wheels for carbide. ...and fine aluminum oxide that I use for HSS. The diamond wheel is finer and gives a better finish on the carbide but for my purposes the good ole green wheels work fine. cheers, JR

Properly dressed green wheels can produce virtually honed carbide cutting edges, often too fine. Carbide removes material with a sort of deformation action, not dependent on 'sharpness' compared to HSS that shears. With excess clearance they weaken measurably. Detect chips with side of a thin brass or tin shim-like leaf across the cutting edge. Those cause interfering chip streams, that pile up fused to the edge and cause increased chipping. A razor edge is difficult to maintain in alloys and nonferrous materials. However, diamond finishing can produce correct shape and being 'polished' reduces friction at higher rpms/ finer feeds/ cleanup cuts.
Used carefully, the diamond stick hones are sufficient. Hone strokes should be in one direction; away from edge to prevent unintentional rounding off. Not easy to make each stroke consistent.
Better yet make a honing guide. Simple block with set screws to hold tool, appropriate angles for front-side clearances and same reliefs. Apply this with a flat marble tile and wetted wet/ dry paper, about 400-600 grit, yes they are silicon carbide and will dress cemented or insert carbides readily. A desired radius is best 'swung' or 'swept' across, clearance first, then edge clearances, then the reliefs. Same single direction applies, and across entire length of paper, a few will visibly alter the edge. Might be a wet honing tray in HMT.net to search out, recall it has a battery operated pump from a desk fountain too. But isn't under 'hone', 'honing'...or 'wet'.

When inserts were more clamp on than retained by screw, we'd use them up as nubs brazed or silver soldered to a shank of cold rolled. Still works, but holes weaken remainder sooner. Great when durable form tools are needed. Like remnant metal, carbide isn't scrap until you can't hold it anymore.

jjr2001 commented "...learn something new every time, visit Homemadetools.net". His "I's" removed intentionally [not in the gory sense].
We ALL do.