Quick change tool holder – what is this groove for?

[HopperParticipant @hopper]

Here's a picture of a Swiss-made SPI holder of similar type. You can see the machining marks on the bottom surface of the tool slot. Looks like it was ground in this case, (or perhaps face milled?), with the face of a dish wheel or similar. With half-round grooves provided to clearance the edge of the wheel (or cutter?) It still looks to me like the one in the OP was made in a cheap copy of this technique where a dovetail cutter was run down the length of the slot. Cheap and cheerful.

[Michael BriggsParticipant @michaelbriggs82422]

For reference here are a couple of photographs of a recently manufactured Bison tool holder, my older ones have different colour screws and the top and bottom external faces are not ground.

[Raymond AndersonParticipant @raymondanderson34407]

Michael Briggs, The undercut on my Bison's are very similar to yours, only my ones don't appear to be quite so deep,but are still radiused.

Maybe there is a small radius on the op's ones ? just not showing in the pic. Just can't see Bison making a toolholder with such a wonderful "stress riser "

If indeed it turns out to be a plain undercut , then you should do as suggested and contact Bison – Bail.

[Michael BriggsParticipant @michaelbriggs82422]

Hello Raymond, the depth of undercut varies on mine and there are other small differences depending when or perhaps where they were made. I think there is a radius on the original photograph that is difficult to see. Michael

[Raymond AndersonParticipant @raymondanderson34407]

Hi Michael B, just had a check of my Bison's and you are correct, the undercut looks to vary slightly from one holder to the next.. All still Radiused of course.

If there is a Radius on the one in the op's pic It is just not showing up. Some of my ones appear to have slightly different Radii. They are maybe cut using custom tooling which varies in Radii from one to the other, or maybe even a modified Dovetail cutter.

[Neil WyattModerator @neilwyatt]

Hate to rain on the parade, but a bit of image enhancement and it's clear the OP's holder has a radiused corner just like Michael Briggs's.

[Raymond AndersonParticipant @raymondanderson34407]

You've not rained on anyone's parade Neil. Good to get it confirmed that there is a Radius.

[HopperParticipant @hopper]

LOL, so it's just the chamfer that is sharp edged? We'd better call off the lawyers and leave Bison alone then.

[mrbuilderParticipant @mrbuilder]

Sorry everyone, was away from my computer until now… Yes being the owner of the original photo, I can confirm that it has a radius on the inside (as Neil has blown up). So mine look like the version Michael Briggs posted but his have a nicer finish on the faces.

Funny how sometimes you're talking about the same thing from a different perspective! Sorry it's blown out of proportion.

Yes Hopper just the chamfer, so I'm guess whatever tool they use to clean up the edge created that.

For me my question still stands on why it is there to begin with (i.e. the undercut with a smooth radius) particularly on the vee holders, I've contact Bison to find out. I have some genuine Dickson's coming and from what I can see from the photos they don't have this 'feature' at all.

[mrbuilderParticipant @mrbuilder]

Thought it might be helpful to close this out

Posted by Paul Lousick on 17/11/2016 04:21:25:

Probably an undercut to remove any radius corner made by the cutter and to allow the lathe tool to seat against the bottom and side faces.

Paul is correct, according to Bison this is their reason.

Posted by mrbuilder on 18/11/2016 21:04:10:

Or if perhaps if guys use vee holders to hold square tools as well (which I have seen occasionally)…

As is this, for why they have the same feature on their vee holders.

[mark costello 1Participant @markcostello1]

Because v holders can be also used for turning and facing tools.

[mrbuilderParticipant @mrbuilder]

Posted by mark costello 1 on 22/11/2016 18:09:06:

Because v holders can be also used for turning and facing tools.

Yes that is their reason. Sorry if it was not clear but my above post was a statement not a question.

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