Making Dickson QCTP holders

[Rickabilly]

Hello All,

It's not uncommon to see guys here making QCTP tool holders, what I've not seen is anyone making Dickson style holders,

They are more common here in the UK I figure,

My Colchester Mascot came to me with no compound slide but with a hydraulic copying attachment which had it's own QCTP on a very short offsetting slide, I mounted it in the normal toolpost position thinking the offsetting slide would allow thread cutting and with the intent of fitting a taper turning attachment for any taper turning also I was going to build this in a way as to allow basic copy turning too but not using the complex hydraulic copy turning attachment for various reasons.

So QCTP mounted the only problem was I only had one standard holder... Not ideal.... Ebay to the rescue, nope not this time, it was my plan until a little research found holders for my unusually large QCTP (about 125mm across the main block) were going to cost from £45 up to who knows what, some were £70 each buy it now, So I decided not to buy them ever, instead I'd make them.

The first step was to measure what size these were and find a specification or maybe even a drawing, the most critical dimension is the pitch centres of the locating "peaks" luckily I had that one holder so all i did was clamp two identical ground dowells into the valleys in the holder measure the distance across the outside of the dowells and take away one dowell diameter. After all the setting up the measurement was exactly 100mm, Hmmm how would I remember such an obscure number.

To the Internet...
After a few hours searching I lost interest in finding a sketch and went to plan b, I made my own, it's all pretty simple stuff, the only tricky part was in getting the "t" slot at exactly the same height vs the locating valleys as this is critical to the clamping force available, not to worry as "I have a plan".

But right now I'm out of time so I'll get back to this later, photos then.

regards
Rick

[Mayhem]

Dave J made a bucketload of holders: http://www.metalworkingfun.com/thread-1291.html

I'm wanting to make some too: http://www.metalworkingfun.com/thread-26...l#pid55197

Like you, I couldn't find any dimensions of the critical parts.

[Rickabilly]

Sorry Dave, I didn't realise this had been done before, thanks for letting me know though Darren, I can now assume folks know a little more about these great little tool holders, well... mine aren't so little... as this particular set are for my Colchester Mascot so are about 125mm Long and can hole 1" square shanked tooling.

regards
Rick

[Rickabilly]

Hello All,
So the photos I promised from last time,
First I quick shot of My toolpost and "offsetting slide", the large knob on the top left hand side of the QCTP is the offsetting handwheel, it drives through a worm and wheel arrangement to turn a short leadscrew the moves the toolpost along a very short dovetail slide, this gives about 10mm or approximately 3/8" of travel, it's pretty hard going too but it allows for most thread cutting without need of a compound slide,
    When it came to measuring the pitch between the two locating grooves, I used the two dowel method described above, it's a version of measuring a thread via wires,
       

Given that the Mascot is my go to machine for heavy roughing and general abuse my holders need to be made of something decent so I went straight to a piece of 2" square EN24 Alloy steel, It's hard enough as supplied and can be further hardened as required, it's not nice to cutting tools, but is absolutely machinable, so the right stuff for this job, especially as I had a leftover piece from a Job I had recently done. I'm not going to show bandsaw shots as I'm sure you've all spent enough time looking at a saw cutting through a chunk of steel, I cut the steel into a little pile of blanks all 125mm long except the last one as the off cut would have been useless I decided to make an over length holder for some as yet unknown purpose, but when I need it, well, I'll show it off then, It's as good a time as any to mention that the original holders were higher than mine, at about 2.5" high, they didn't need to be and I did some measuring to ensure adequate clamping etc, before finally going with a 50mm height.

The next step was to block them all down to a nice accurate 50mm square , (once again boring so no pics) 

I took four blocks and lined them up neatly in my milling vise, as it was nicely trammed and I have power feeds on all axes on my Mill, I decide to use the cross feed rather than the long feed for most of the job,
As a result I could leave the vise in it's standard orientation, this made the accuracy of the distances between the vees easier to obtain as I have an "Anti climb" control on my long axis which removes all backlash from the long feed screw, which allows for climb milling normally but also means the the dial on the handwheel reads true regardless of which direction it was last turned.
So I got about the process of roughing and finishing the deep groove in the centre, leaving the Tee-slot "wings" till last, the groove is also toleranced but not as tightly as the position of the Vees so I did the deep central groove first, so that I could find it's centre when setting up for cutting the Vees, I centered on the slot after swinging the vertical head to 45 degrees, and by using the tilted tool to cut the champhers on edges of the groove, I easily found it's centre. By setting up this way you can acheive 141% accuracy as the angled cut is that much wider than a square cut would be, this means by use of a keen eye and a good steel rule you can achieve very much tighter tolerances than you might expect.

       

Finally it's just a matter of moving the table 50mm one way and then back by 100mm to get the correct spacing for the vee grooves, I cut the grooves all but 0.3mm to depth before rechecking centrality and finishing both groves with a fresh endmill,

I'll get back to work now and give a little bit more in a few days as time allows.

Best regards
Rick

[awemawson]

As you say that particular style of Dickson tool post with the off set feature was the one intended for hydraulic copy turning and was supplied standard with the Hepworth tracing accessory.

I made loads of Dickson 'T2' holders out of EN8 years back when I still had a horizontal mill, and I must say it's use made things much easier. You can't have too many holders :)

[Mayhem]

(08-03-2016, 11:49 PM)Rickabilly Wrote: Sorry Dave, I didn't realise this had been done before, thanks for letting me know though Darren, I can now assume folks know a little more about these great little tool holders, well... mine aren't so little... as this particular set are for my Colchester Mascot so are about 125mm Long and can hole 1" square shanked tooling.

regards
Rick

Mine will accept 1 1/4" shank tools

[krv3000]

brill

[Rickabilly]

(08-04-2016, 06:27 AM)Mayhem Wrote:

(08-03-2016, 11:49 PM)Rickabilly Wrote: Sorry Dave, I didn't realise this had been done before, thanks for letting me know though Darren, I can now assume folks know a little more about these great little tool holders, well... mine aren't so little... as this particular set are for my Colchester Mascot so are about 125mm Long and can hole 1" square shanked tooling.

regards
Rick

Mine will accept 1 1/4" shank tools

As did the original holder I got with the toolpost, but  25mm shank is plenty big enough for anything I do and I couldn't justify buying big enough material to gouge out 1 1/4" + clearance slot with meat left to support the cutting forces, so I limited myself to 25mm ,

I haven't seen bigger tools needed since my steelworks days where we would sometimes use 2" square section HSS in the big roll turning lathes.

Rick

[Mayhem]

I wonder if the dimensions are the same?

[Mayhem]

I actually checked mine, using a couple of endmills in place of dowel pins. The distance between the centre of the v grooves is exactly 100mm. Looks like we have then same tool holders.