View Full Version : Tangential Tool Surface Finish

02-19-2009, 08:36 AM
I have been playing with a tangential tool holder on and off since fall. It is great for roughing, but I cant get a decent finish from it. I have tried various combinations of feeds and speeds. changing the angle of the tool post. cutter above and below center. Nothing seems to help. Any suggestions would be appreciated.



02-19-2009, 08:50 AM
Add a small tool nose radius?

Lew Hartswick
02-19-2009, 10:29 AM
Add a small tool nose radius?
Yep. Just roundover the "corner" all the way down the length of the bit.

02-19-2009, 11:19 AM
Rounding the corner of the bit is a help, as is honing the cutting edges.

You'll notice the bit's top, because it is hollow ground, touches on two opposite corners when held against a flat. I use 1500 grit carbide paper on a flat and tip the bit around those corners so the cutting edge touches, then hone lightly; repeat for the other edge by tipping the other direction. If you don't over-do this it can be honed a couple times between sharpenings.

With a well honed bit, try cutting from left to right, taking 3 thou or less - my experience is that this produces the best finish using the tangential. Cutting from right to left, much heavier cuts are possible with somewhat poorer finish.

Also, the tangential's high rake can cause it to self-feed on brass and some types of aluminum, especially on heavier cuts (which produces a scalloped finish). Try reducing the angle of the bit's top to avoid this.

Edit: A slip of paper cut to width and inserted in the bit slot helps prevent the bit being driven down the slot by interrupted cuts.


02-19-2009, 11:28 AM
I think you will need to remove the back rake that is on the top of the cutter. The photo shows there is back rake and I believe it would cut better with "0" rake. You may have to redisign your fixture to hold the cutter while sharpening.

Many times a back rake will cause the tool to draw into the work and give a rough finish. It will exagerate any slop in the crossfeed and compound dovetails. Also, higher rpm and slower feed may help.

02-19-2009, 12:10 PM
To simplify it on my cutters I round off the leading edge first then grind the end last. That way I don't bugger the new edge by fat-fingering the round-off on the grinder. Honing is also a good suggestion.

There are also a lot of shapes the cutter can take. The diamond being the natural and repeatable one, but experimenting shows anything is possible (though not necessarily repeatable following a regrind). Case in point, I ground a form for turning an Acme-like screw to be used as a hobb and it worked well. The helix angle was built into the tool holder.

02-19-2009, 12:26 PM
Those tangential cutters , I have 4 of them for my Lathe, I had them made up along with some special stainless grooving tooling by a local tool shop (my friend works there OOPS I mean used to he is layed ioff but now has time to make me tooling at a decent price) Anyhow i thought these cutters were only for finish ing light cuts?? I wonder how they will work on stainles steels>

02-19-2009, 12:52 PM
Thanks for the advise. The biggest improvement was made by a radius on the leading edge. honing helped also. I tried various rake angles, but the steeper angle helped, at smaller angles the side was dragging the material. I now can get a much nicer finish with a .010 DOC at 550 RPM (fastest the ole P&W will go) and a nice slow feed.

05-04-2009, 01:50 AM
The other thing you can do is sharpen a round bar that will create a broad curve. I just chop off pieces of HSS drill bit since local shops don't sell bits in round format, though bigger shops may. This is covered in the brochure that comes with the tool, or the video.

Ian B
05-04-2009, 06:54 AM
Maybe I'm missing something, bu doesn't standard tool geometry apply equally well to normal or tangentially-held toolbits? If the front & side clearances, top rake & nose radius etc presented to the work are the same, then the results should be the same.

This is why rounding the corner would be effective - just as it is for a conventionally-held tool.

I can see the convenience of only having to sharpen the "end" of the tool (the face that governs the rake), but against this you're stuck with one profile. I use a Jones & Shipman toolholder, which has top rake built in, and allows for different nose profiles. It has its advantages & disadvantages too.


05-04-2009, 10:25 AM
Looks like the same set-up used in a W & S box cutter tool. Great for roughing and finishing. I have a gauge somewhere with all of the angles to grind / regrind the tool bit. I like the tool bits with some Molybdenum in 'em, like the old Mo-Max tool bits.

06-30-2010, 12:12 PM
I know this post is somewhat dated but after 30 some odd years I picked up A Diamond holder from Baycom for cutting gummy metal. It wasn't cheap but I really don't like making tools and heaven knows I've made my share over the last 40 years!

Here's what I found:

It works well enough just following the info on the box but it leaves a semi-smooth finish, not great in my book.

I took one of my own HSS 1/4" bits and put a 1/32" round nose the entire length of the leading edge on my homemade slow speed (250 rpms) with a 1200 grit flat face diamond wheel on it. That's all, I didn't hone the cutter in any other way, just used a Norton fine wheel on my conventional grinder to Diamond's specs.

This made a night and day difference in the cut. I tried 'junk' steel (you know the gummy stuff with different degrees of hardness throughout it) plus aluminum, brass, 303, 304 stainless, etc. Each one gave me, not just a good but an excellent finish. The gummy metals easily finished better than my carbide inserts and when I ran my thumb nail down them they were smooth with no ridges.

The trouble with the Diamond tool is that it doesn't have a nose. You simply can't cut with a dead sharp cutter and expect good results. There is too much stress on the cutter point. Anyone who cuts threads knows this, you sharpen a 60 degree threading tool and by the time you're finished with the first few passes you can see the cutter tip is dull if you inspect it with a magnifier.

I cut different depths and the Diamond tool tip now lasted longer also. The tool I got was for the Aloris quick change holder on my Maximat Super11 and V10P lathes.

I won't be giving up my carbide inserts, when things have to move along fast you just can't beat them! The Diamond holder does have a place though for those times when I have difficult metals to cut or when I want 1018 to look like 12L14 and also on my little Sherline CNC.

The other good thing about the Diamond holder is the cutting action creates less stress on light lathes. Now that I know what it's about and its limitations I'll be getting one for my Sherline as well.

I think it's a good tool for those who are just learning machining also, especially those having trouble with grinding HSS bits, which by the way, give a better cut than inserts in many metals when you're not flooding the part with coolant.