Harold Hall QTCP, MEW 50, any one using it?

[Clive FosterParticipant @clivefoster55965]

Hi Bill

 

As requested a picture of the two “bent” styes of Armstrong type holder posed next to a round bar at more or less operating angle.  Various sizes and similar but different styles depending on maker.  These are for 1/4 square tool bits, shanks on these are nominal 1″ high and typically the sharp end will be about 5/8 to 3/4 above the support surface.  Usually the bit axis will be 90° to the work with any special shaping ground on the tip. A 3″ stick of HSS will usually do for 2 double ended bits.

 

Hope this helps.

 

Clive 

[John OlsenParticipant @johnolsen79199]

When I inherited my Myford it came with toolholders in the above style. The problem with them is that the amount of overhang gives good leverage for the cutting forces to shift the toolholder on the topslide. If you tighten up the toolpost nut to prevent this, it distorts the topslide, making it tight on its slide. This is of course a Myford shortcoming rather than the fault of the toolholders themselves. Similar toolholders were made without the built in rake for use on shapers, and they are very useful there.

 

regards

John

[Bill PudneyParticipant @billpudney37759]

Now I know, I’ve seen and used those, I just never associated them with “Armstrong”.  One of the reasons for doing what I did was to reduce overhang, both of parting off and cutting tools.  The Sieg C3 is not the most rigid of lathes and anything to help increase rigidity is welcome.

cheers

Bill Pudney

[adyParticipant @ady]

Reading through the thread I noticed that also another type of QCTP was
mentioned, namely the type having a cylindrical tool post with tool
holders nipping the post.

 

The old Drummonds used them, they are called Norman’s Patent.

 

 

The round post in the middle also has a deep thread which takes a (very rare now) indexing milling and gearcutting unit, so it was mounted directly on the compound.

 

A standard Drummond lathe and cast iron stand cost about 26quid, and if you wanted it, the gearcutting arrangement would cost you 30…so there aint many around.

 

[adyParticipant @ady]

I haven’t read the thread but I suppose I should mention that the simplest QCTP is a rear toolpost.

 

A one eighth tool

 

 

 

And a half inch tool

 

 

Both at dead centre, and no shimming required because the tool is upside down and cuts from the back, just swap ’em over.

Those of us with a reals mans lathe, like a Drummond with a slotted cross slide, can do these things.

Edited By ady on 15/12/2010 03:46:57

[John OlsenParticipant @johnolsen79199]

Bill, I suspect Armstrong was a maker, although the ones I have are mostly Jones and Shipman. The one exception is a parting tool holder by Ace. (Not to be confused with Acme, suppliers of dynamite to the Roadrunner )

 

The only one I have with the zero rake for a shaper is slightly too big to fit the toolpost on my 18 inch Alba. I wonder what sort of giant machine it would fit? It may yet get a few minutes on the other side of the shaper to make it useful, as other than the size of the shank it would be about right.

 

regards

John

[Clive FosterParticipant @clivefoster55965]

Bill, John

 

Armstrong from Armstrong Patent, which they were marketed as for many years.  Armstrong invented the beast and took out several patents from around the mid 1890’s to mid 1920’s.  Don’t know the specific patented features tho’ although the idea of pointing the tool upwards at a generic “little too large” rake angle was clearly important for easy grinding and tool material economy. 

 

The distorted top slide problem is pretty much inevitable on a small lathe with a simple clamp tool holder where all the pull forces go through the stud in the middle.  Stiffness depends on thickness and on small machines there just isn’t enough room for lots of metal.  I suspect 5″ or so centre height is about as small as you can go whilst retaining more than satisfactory stiffness.  Below that compromise is essential.  Obviously a slotted block type holder where all the clamping forces are within the block is better in this respect but obviously tool size is restricted and we are back to the dreaded shim type height adjustment.  The conventional QC is even worse it this respect as space for height adjustment can only be found by slimming things a bit more unless the holder proper is made to overhang the slide introducing its own set of problems.

 

Looking at my picture in a previous post it occurs to me that the bottom plate of a slot type holder could be dispensed with if using Armstrong holders in the configuration shown.  A solid trapezoidal pillar, as large as practicable, could be made with two sides angled to match the desired tool holder shank inclinations for turning and facing having two narrow overhanging ledges to carry the clamp screws.  The clamping forces should be well enough spread not to distort the slide.  Obviously only one holder at a time would be fitted hence some means needs to be devised for sufficiently accurate replacement so there is a certain inconvenience in that respect.  Clearly alternative mounts need to be arranged for boring and parting tools but the concept looks promising.

 

Talking about parting tools I’m amazed that no-one has produced for sale or as a DIY design a solid block with grooves and clamps to carry either the standard parting HSS blade or the modern insert holder blade.  Clearly it needs to be two pieces with a bolt on base so shims can be inserted to get the right centre height, a once only job with inserts and if you accept flat top grind on HSS blades.  This is probably the most rigid possible set-up, especially as it allows the deepest blade to be used.  Similar arrangements are accepted on rear tool posts so why not at the front?

 

Clive 

[Bill PudneyParticipant @billpudney37759]

Clive wrote….

 

“……….as a DIY design a solid block with grooves and clamps to carry either
the standard parting HSS blade or the modern insert holder blade.”

 

Like this you mean??  (scroll down).  I got the idea from GHT’s book, Model Engineers Workshop Manual

 

http://madmodder.net/index.php?topic=3823.0

 

Sorry but for some reason I cannot include photos here.

 

Cheers

Bill Pudney

[Bill PudneyParticipant @billpudney37759]

After my last post I went and had a look at the Albums section here.  Amazingly I managed to set up an album, I simply had been doing it incorrectly before……

Anyway have a look……..

cheers

Bill Pudney

[Author]

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