QCTP dilema?

[Bo’sunParticipant @bosun58570]

Thank you Clive, for an excellent summary of the various designs.

I've opted for the Dixon type sold by Warco for the WM240. If it doesn't work, they can have it back. After all, they recommend it for that lathe.

Thanks to everyone for the comments. Greatly appreciated.

Bo'sun

[SteviegtrParticipant @steviegtr]

Posted by Bob Unitt 1 on 20/03/2020 11:55:00:

I have a 40 year old old Myford/Dickson QC toolholding system on my 254S. How hard would it be to make my own holders on the 254 and a VMB mill, are accurate drawings available anywhere and what's the best material to make them from (for pretty light usage) ?

Edited By Bob Unitt 1 on 20/03/2020 11:55:37

I have just bought a length of square stock, to have a go at copying the ones I have. Just need a dovetail cutter now.

Steve.

[not done it yetParticipant @notdoneityet]

If it doesn't work, they can have it back. After all, they recommend it for that lathe.

Of course it will work. Of course they would recommend – they are selling it, aren’t they? I never believe all the bovine excrement in advertising hype.🙂 Sliced bread is always best, so they say….

Question might be: Is it the best choice? Only time and experience will tell.

[Neil WyattModerator @neilwyatt]

I have a ridiculously simple quick-change toolpost design in my head.

At some point I'll make it and astound the engineering world!

Neil

[thaiguzziParticipant @thaiguzzi]

Posted by Graham Stoppani on 20/03/2020 06:00:53:

Last year I replaced my Dickson type tool holder with a wedge type one from ARC Eurotrade. Very happy with the new tool holder. My reason for changing was the old tool holder had too much play in it that allowed the tools to deflect downwards slightly while cutting. The wedge design by its nature takes up any slack when you tighten it which the Dickson type does not.

I like the wedge type too, mainly because extra toolholders are so easy to make.

But, re the Dickson design, i have to completely disagree. When clean and in tolerance, it is a great tool. I don;t baby my machines and have never had a problem, from my pro days 30 years ago with Colchesters to my current hobby days with a Boxford.

Clive as per usual, makes some very valid points above.

[clivelParticipant @clivel]

Posted by Clive Foster on 20/03/2020 08:32:38:

…

In my view the steadily increasing use of carbide insert tooling which doesn't need easy height setting to compensate for sharpening means its time to re-consider alternatives to conventional QC posts. Especially for home builds. Slotted block posts are easily made and, if easy to change, would be an acceptable alternative to conventional QC systems.

Richard Smith described an interesting tooling system for carbide inserts in the November 2016 issue (#248 ) of MEW: "A carbide insert based quick change tooling system for the lathe" subsequent articles included further details and expanded on the system.

I have been contemplating doing something similar for myself but haven't persevered as my diamond toolholder handles most of my needs for now.

I was wondering if anyone else had given this system a try?
Clive

[Henry BrownParticipant @henrybrown95529]

Interesting stuff, especially Clive's well written and informative thoughts. I have the standard tool post and can't help but wonder if there is a trade off of rigidity against tool change convenience. For me I'm not sure I'd see any real benefit but a new toy is always attractive!

When I was on the handles the capstans were the only machines with QCTP, all the centre lathes and turret lathes used four way (standard) tool posts but we didn't have any indexible tools back then, all brazed carbide.

[Clive FosterParticipant @clivefoster55965]

Posted by Neil Wyatt on 20/03/2020 15:42:27:

I have a ridiculously simple quick-change toolpost design in my head.

At some point I'll make it and astound the engineering world!

Neil

Show me yours and I'll show you mine!

Seriously I've been mimbling over the rotating centre "stud" concept for many years out of conviction that there ought to be a way to make it a practical home shop build proposition for the inexperienced. Neil was kind enough to publish a letter and concept diagram of how it could be done on a SouthBend / Boxford et al T slotted top-slide in MEW rather more years ago than I want to admit to.

The fundamental issue has always been how to come up with a universal concept that does not require the lathe to be modified. The special Tee nut in the aforementioned concept being possibly acceptable but modifying the topslide on a lathe with the usual screwed in toolpost stud is not.

A month or three ago the penny finally dropped and I realised that if the stud were a hollow tube with the bottom end stoutly closed it could be held down by a socket cap screw inside the tube. Interposing a T shape bush allows the screw to be securely tightened whilst still permitting rotation. Probably sensible to close the top end with a solid stub to keep the dirt out and provide more than the relatively thin tube wall for the tommy bar to act on.

Rotation indexing can be done via a suitably notched or drilled plate sitting below the assembly. I imagine the centre bolt would be tight enough to hold it secure but it should be no great trouble to shape it to seat positively against the side(s) or end of the topslide. If only a couple of rotational positions were acceptable drilling a hole or two to take a pin, as per Dickson posts, might not be considered objectionable. Fitting indexing holes directly in the topslide does make the assembly lower. The hollow castellated nut screwing into the block that does the actual holding down is probably most appropriately made using a pipe thread.

Finding space for a sufficiently solid construction might be an issue on machines much below 3" centre height. However its worth noting that for small machines the disadvantages of the Norman post disappear if height setting is abandoned and the toolblock simply sat down on the topslide. Either directly with a rotation index plate interposed. When all is said and done a Norman is about the easiest system to make. It would be wise to drill and tap the top of the centre post so a clamp down screw and washer could be added to positively hold it down if things look like getting hairy. Interrupted cuts spring to mind.

The fundamental inconvenience of block posts is that HSS tools need shimming to compensate for geometry changes after sharpening. Quick interchange blocks let you do the shimming by measurement on the bench rather than on the machine. If you make a suitable setting jig and have your shims sorted that will be about as easy, and almost as fast, as setting up a conventional QC system on the machine.

Clive

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