I think I understand what the mod us, it is when using a tool that is still below centre hight when the QCTP is screwed up to its highest point, so this mod lifts it up that bit higher allowing for the tool to then be at centre hight.

But I could be wrong

Allan

Lifting a QC holder above its design range will almost certainly compromise rigidity.

My method is to slip a piece of sharp inside corner angle beneath the undersize tool. The side of the angle fills the gap between the tool and the back of the holder helping to keep the tool centralised under the hold down screws. If you simply space an undersize tool up there will be a gap between tool and holder when the screws are set central on the tool. Significantly less rigid and mch harder to get the tool dead parallel to the holder.

I make my angle by welding suitable size bar or plate offcuts together for most appropriate combination of lift and backside spacer. Alternative way of backside spacing is to drop sharp angle over the top of the tool. If you use alloy it will protect the ends of the screws from mushrooming and, allegedly, give a better grip than steel on steel.

The original posters reference to shims is misleading. Objective is to bring the tool tip to within the adjusting range of the QC system. You only need one one thickness of space for each size of too small tool blank.

Clive.

This is of course what they do in modern machines – no need for QCTP's.

Why grind up a 12mm x 12mm tool blank when all you may want is a 3mm wide bull nosed tool to give a specific profile which can be ground from a 3mm x 3mm blank. This is when it makes sense to use a small blank which may then be outside the adjustment range of a QCTP.

The samllere lathes generally won't take the old style holders that were used in the past to hold small bits as the gap in teh toolpost is not that deep.

As for loosing rigidity, probably not an issue for this use as you are hardly likely to be taking large cuts with small 3×3 and 4×4 tool bits. Agreed you would not want to do it with a large roughing tool taking 0.100" deep cuts.

J

There is another problem with the QCTH's that I have (and others that I've seen) in that they are designed for larger HSS tools (and not the smaller section ones I prefer to use – mostly 3/16th). The screws that hold the tool in place do not allow you to place a small tool securely at the outside edge of the holder (which means that holder itself often gets in the way) and the tool is not supported or guided by the back edge of the holder either. The height adjustment problem wasn't a problem for me, as I made a new (lower) block to mount the QCTH block on…

One solution to both these problems is to make a split 'shoe' that fits the QCTH slot and has a groove in it to fit the tool. This not only lifts the tool but also allows it to be gripped at the edge of the tool holder. You still need a 'shoe' per QCTH or you lose the utility of having multiple holders set-up. I tried this approach but still wasn't happy with the bulk/size/overhang of the QCTH system I have (which is just a simple budget one).

So I've taken a different route and I'm in the process of moving my smaller tooling to a 'Rose' tool-block system, which currently looks like it will be a good solution for me (e.g. suit my smaller machines and general size/type of work).

Regards,

IanT

+1 for Jason's comments.

If the QCTP is the correct size for the lathe then there'll be clamping meat above lathe centre height as well as the tool thickness and the support shelf thickness below centre height.

If you think about it, there's little difference between this situation and a thicker boring bar twice as thick with a smaller cutter with resultant cutting edge at the centre of the boring bar.

Here the boring bar is 7/16" and the toolbit 1/4" diameter. You can also see how much of the clamping surfaces is above centre height to support the setup.

In the case of my size SOO Dickson QCTP, I have toolholders from 3 different sources each with different thicknesses of lower shelf. For small tooling it makes sense to use the holders with the thickest support shelf.

HTH

Jon

I think your photo shows the problem of holding a smaller tool (in a larger QCTH) quite well Jason.

When machining a shoulder, you either have to extend the tool out to the depth (+) of the shoulder (not always possible) or move the tool out flush to the edge of the holder – where the tool holding screws will only be acting on the very edge of the tool and where it's very easy to have it move (as I discovered the hard way).

Regards,

IanT

Yes it does Jason – I'm not sure what others here would call it but it's what I referred to as a "shoe" earlier.

Yours is a more elegant design, mine was simply slit from the 'working' end to about two thirds way down (e.g. I didn't drill the lengthways hole).

Regards,

IanT

I have two "shoes" similar to the one in Jason's drawing sized to hold 1/4" and 3/16" square HSS tooling in Dickson T2 size tool-posts. Mine are solid with 6 short grub screws to hold the tool in place and long enough that two tools could be held, one at each end, if so desired. I think the solid construction and grub screw tool retention is arguably superior to the split version shown by Jason as the tool stays firmly mounted when the holder is removed. On the other hand Jason's version is better in that it lets you change out the tooling using one holder rather than needing a holder for each tool.

The grub screw fixing also lets you grind the tool in the holder giving more to hold onto. Especially nice when doing short tool bits for boring bars, which is probably the most common thing I use mine for. Never tried mounting up two tools as it looks a right pain to set up, unless you adjust the tool post when flipping, as one tool is inverted with respect to the other. Obtained somewhen in the last 20 – 30 years as I neither made of purchased them.

Clive.

.

An excellent solution, Niels

Thanks for the picture

MichaelG.

.

One might reasonably assume that the toolholder block was custom-made to suit those tools.

… and also … being a nice simple unit, the whole block could be easily shimmed to increase height,

[yes, I'm aware that negative thickness shims are scarce]

It depends where your priorities lie; I suppose [*], but

I wanted to give praise where I thought it was due.

MichaelG.

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[*] I would gladly sacrifice some convenience of adjustability for a compact device with good stiffness.

Edited By Michael Gilligan on 01/03/2017 08:47:33