Fingering the Plate - More T and C Stuff

[Anorak Bob]

The workhead on the Hercus No.1 grinder has some modifications. Peter Fou..., the fellow I bought it from, replaced the 24 position indexing plate with an adjustable 12 position version. One of my favourite cutters is an eight flute endmill that desperately needs a sharpen. I wouldn't mind having a crack at making an indexer along the lines of the original but there may be a few issues that need addressing.

The idea behind the adjustable finger is to enable the precise alignment of the cutting edge in relation to the grinding wheel. Peter achieved the adjustment by means of a slotted indexing plate and a rigid plunger. Hercus provided a spring loaded adjustable finger. The finger could have been the Achilles's heel in the design. Gary at Eccentric Engineering ( Diamond Tool Holder ) said that his Hercus No.1 T + C workhead had also been modified. Whether the issue is with the spring steel and its installation or the shape and engagement of the pawl in the indexing plate, I don't know. These machines appear thin on the ground and the chance of finding one with the original indexer might be even thinner.

The spring steel on the finger in the catalogue images looks short and therefore I imagine stiff. It has to be flexible enough to rise up out of the vee and rigid enough that it stays in place. The spindle is lockable by means of a thumb screw operated cotter. Not that grinding should dislodge the finger.

I have been thinking of doing away with the spring steel and making the finger rigid with the springing occurring in the square head instead.

Has anyone had experience with this type of indexer ( Cincinnati's Milicron grinder had a somewhat similar set up but the indexer ratcheted one way ) and if so could they share that experience?

Bob.

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[Michael G]

I think you could be right Bob - if the spring got bent by a ham fisted operator the location would become a bit more arbitrary.
Rather than a spring though, how about something like this.
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If you made up an end piece with a rounded end (either a sphere or a cylinder) and adjusted it properly it would probably locate beautifully - if you really wanted a spring the plunger could have a little give to it to reduce the need to have the adjustment spot on.

Michael

[Anorak Bob]

I think you could be right Bob - if the spring got bent by a ham fisted operator the location would become a bit more arbitrary.
Rather than a spring though, how about something like this.
296791
If you made up an end piece with a rounded end (either a sphere or a cylinder) and adjusted it properly it would probably locate beautifully - if you really wanted a spring the plunger could have a little give to it to reduce the need to have the adjustment spot on.

Michael

Hello Michael,

The De-Sta-Co probably clamps closed with enough clamping force to bend the spindle and I'd end up manning an oar in Bryan's boat.:)

I could use something gentler like the plunger on the Hercus milling slide's indexer but it provides no tangential adjustment. The now self exiled Pete F suggested forgetting the indexer and only using a finger to support the cutter, as is done on both his Clarkson and Darex, by the flute but there could be a time when the object being ground is not finger supportable ie flats on a shaft...

Bob

[Bryan]

Bob those toggle clamps can be adjusted for pressure.
Not the most elegant solution, granted. More my sort of fix than yours. :)
One argument against pivoting the block would be wear, but probably not a concern for occasional use.

Plenty of room aboard SS Rooted Machines, but the less the merrier.

[Michael G]

Bob those toggle clamps can be adjusted for pressure.
Not the most elegant solution, granted. More my sort of fix than yours.

(And obviously mine too)
One of the things that would worry me about a spring loaded plunger (whether a leaf type or a plunger type) is that unless the stiffness of the spring was right there is a possibility of the plunger being cammed out of the v slightly.
A toggle clamp (but adjusted for near zero pressure) would be a positive stop so you would have greater certainty that the geometry you are grinding would be spot on.
The type of finger that Pete is thinking of is another way around the problem and again because the direction of grind is pushing against the supporting finger there is better certainty of the ground geometry.

Michael