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The Diamond Tool Holder

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thaiguzzi26/01/2019 07:01:31
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555 forum posts
130 photos
Posted by Clive Foster on 20/01/2019 13:53:00:

ega

If downwards projection of the toolbit is an issue with tangential holders the simple answer is to switch to an Armstrong style!

As the video linked in the first post implies, but doesn't actually state, at the cutting edge tangential and armstrong tool holders are functionally identical devices. The only primary difference is that the armstrong bit requires two grinds for most tool shapes whilst the tangential bit gets away with one. If you have the grinding jig. The armstrong bit also consumes its cutting edge at every grind so it gets narrower and shallower over time whilst the tangential tool regenerates the edge in the same place with every grind. Of course an armstrong bit does not need a jig, although a simple angled fence can be helpful, and sharpening on the front of the wheel using the hollow ground method is trivially simple.

The real genius behind the Eccentric Engineering tangential toolholder was the realisation that the toolholder and uber simple sharpening jig combination added up to a price / performance / perceived value ratio corresponding to a successfully marketable product. Realising that there was also a touch of "new to this generation" novelty to provide serious marketing impact and keep the idea fresh was important too.

Well done that man. Seriously. Heck I almost bought one.

Fact is an equivalent simple, one universal angle, sharpening jig can be devised to use with armstong holders. With equally effective results given a simple half page instruction sheet explaining the hollow grind on front of the wheel method and how to hone the tool to keep it sharp. Possibly a footnote on packing up for various rake angles too. Which pretty much don't matter for the home shop guy so long as the thing is sharp and has some clearance.

But no one has ever made a go of a lathe tool sharpening jig for home shop guy. Southbend tried but theirs was too clever and too complex. Good tho'. Price / performance / perceived value being all wrong for a commercial product especially with everyone saying its dead easy to grind an ordinary tool. Which it is if you have someone to show you but un-mentored and working from books is a different matter if things don't click quickly. Especially if you don't know how much of a cut you ought to be able to peel off with a sharp tool. I've yet to see a written description of basic lathe tool sharpening that rates better than not very good from the solo novice viewpoint.

Doesn't help that the Americans never officially seemed to twig that the rocker in their obnoxious lantern tool posts is unnecessary when an armstrong is used. Simply roughly shim and change the tool bit projection for fine height adjustment. So the poor old armstrong system got tarred with the lantern brush.

Clive.

Edited By Clive Foster on 20/01/2019 13:54:32

As always, Clive is right on the money.

I have a Bison QCTP (Dickson clone with 19 holders) that is on my lathe 96% of the time. I have the original 4 way tool post that is used 1% of the time and a home made lantern tool post sans rocker holding an Armstrong holder for those awkward lack-of-space jobs or one-off tool bits for the other 3%.

As you can see, i find the lantern/Armstrong far more useful than the 4 way.

XD 35126/01/2019 07:21:35
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1309 forum posts
111 photos

Has anyone tried using the tangential tool with a brazed carbide on a square tool shank ? I have a couple of these tool holders from eccentric but rarely use them as I use carbide insert tooling for the most part but have always wondered if a chunk of carbide brazed onto the end of a piece of square stock then ground the same as the tool steel bit would work .

John Haine26/01/2019 07:46:59
2590 forum posts
133 photos

In this thread **LINK** a few years back I gave details on how to work out the angles to get different clearances. Thanks to Michael Gilligan I can now find old posts!

Vic26/01/2019 09:48:55
2203 forum posts
10 photos
Posted by XD 351 on 26/01/2019 07:21:35:

Has anyone tried using the tangential tool with a brazed carbide on a square tool shank ? I have a couple of these tool holders from eccentric but rarely use them as I use carbide insert tooling for the most part but have always wondered if a chunk of carbide brazed onto the end of a piece of square stock then ground the same as the tool steel bit would work .

Not sure, it might work. Someone gave me several broken 1/4” solid carbide end mills so I tried one of those once ground in the Eccentric tool and it works great on hard stuff. I turned some HSS with it the other week.

John Pace26/01/2019 10:25:11
149 forum posts
148 photos

I silver soldered this 1/8 inch carbide shank into a suitable size square piece,the edge is milled out about half the diameter and the piece soldered in ,it seems to work best if left as a round shank.The round piece fits neatly between the clamp.

The one on the left is ground to conform the the square shank ,because carbide chips easily when ground to the acute angles of the diamond tool a shallower angle is needed at the top and both the sides need a little grinding for clearance.

Useful for harder materials and maybe cast iron.

John

007.jpg

mark costello 126/01/2019 19:38:36
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534 forum posts
12 photos

I have made a carbide tool bit to use in a tangential tool holder. I have used it on hard plastics. I have not used it on steel yet.tangential carbide tool.jpg

John Reese27/01/2019 00:06:30
772 forum posts

With that high rake angle I bet it cuts very well in the beginning but will not last long. Sharp points like that on carbide are prone to chipping.

John McNamara27/01/2019 13:23:07
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1306 forum posts
113 photos

Hi John Pace.

GMTA I made the same toolbit using the carbide shank from a PCB drill, PCB drills are so tiny to hold up they are made from very fine grain carbide. Tough too.

I milled a piece of key steel of the correct size and silver soldered in place.

Been using it for a couple of years. The ten degree angle you normally use for the Diamond tool can be reduced to around 5 deg by angling the template. More robust for heavier work. However it will work fine as standard.

Regards
John

John Pace01/02/2019 19:36:01
149 forum posts
148 photos

Posted by John McNamara 7/01/2019 13:23:07

Hi John Pace.

GMTA I made the same toolbit using the carbide shank from a
PCB drill, PCB drills are so tiny to hold up they are made from
very fine grain carbide. Tough too.

I milled a piece of key steel of the correct size and silver
soldered in place. Been using it for a couple of years. The ten
degree angle you normally use for the Diamond tool can be reduced
to around 5 deg by angling the template. More robust for heavier work.
However it will work fine as standard.

Regards
John

Hi John,

I don't use the supplied fixture to sharpen the toolbits,some while ago
I bought 10 off 1/4 square toolbits from J&l supplies they were on offer
at about 80p each 10% cobalt.
Both ends are sharpened as can be seen in the photo .I had this process
scribbled out on a piece of paper and have tidied if up here for use
on the Quorn grinder or tool grinders with similar axis. This may be useful
for others wishing to do this.The self centering 2 inch four jaw chuck is
from Chronos and makes this much easier to do.

Having 20 ground ends if one is dulled it goes in the grind box and
a fresh one fitted.

The carbide tips that are ground similar to a CCMT shape only need regrinding
on the top until the are worn down enough that the sides need doing again.
Grinding the carbide is best done towards the cutting edge to avoid chipping.
These days the tangental toolholder gets the most use.

John

Diamond toolholder toolbitsCarbide tip grindingHSS grinding

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