Lathe tool holder needed or it’s identification.

[Jim GardnerParticipant @jimgardner97734]

I find that I could do with some extra tool holders for my Colchester Bantam. Despite searching the web for hours, all I get are general descriptions rather than what I need. I though I had found the correct one at Zoro Tools (Type 1 is a match in all dimensions they give, which does not include angles). Unfortunately they told me that holder was specific to their tool post.

I did find one article that suggested Colchester changed form their own post, to Dickson, and that may be what I have.

Could anyone help by telling me exactly what my tool holder is so I can search, or if they know of any retailer that sells them please?

Dimensions are, length 73mm, overall width 31mm, height 43mm. Tool slot varies between 18-22 height and 14mm wide.

[Jim GardnerParticipant @jimgardner97734]

[John HaineParticipant @johnhaine32865]

Dickson type. RDG may stock?

[EmgeeParticipant @emgee]

See this page at Lathes UK for some dimensions of Dickson toolholders.

**LINK**

If you can't find the type needed you could make your own on the mill, 1 of the important dimemsions is the between V's centres, keeping the rest to your existing toolholder sizes should be straightforward machining.

Emgee

[Martin ConnellyParticipant @martinconnelly55370]

I have made some of these holders with one V. I think two Vs is over constraining and as a result allows the holders to take up different positions when put on the mount. Due to machining tolerances the two Vs can never be identically spaced from one holder to the next or to the mounting block. This means that either V may be the one that controls the position of the holder when it is mounted or it may be the two outer faces or the two inner faces and it is impossible to predict which it will be. The single V works as well as the twin V for rigidity and has better repeatability of position.

Martin C

[EmgeeParticipant @emgee]

Posted by Martin Connelly on 06/09/2023 08:22:20:

I have made some of these holders with one V. I think two Vs is over constraining and as a result allows the holders to take up different positions when put on the mount. Due to machining tolerances the two Vs can never be identically spaced from one holder to the next or to the mounting block. This means that either V may be the one that controls the position of the holder when it is mounted or it may be the two outer faces or the two inner faces and it is impossible to predict which it will be. The single V works as well as the twin V for rigidity and has better repeatability of position.

Martin C

The statement that the 2 V's will be at different dimensions is acceptance of poor machining practise, perhaps you can get away with the support given by 1 V in contact but heavier cutting could find it a weakness.
Why did Dickson, Bison and others gp to the additional cost and adopt 2 V's if 1 is sufficient ?

Emgee

[Clive FosterParticipant @clivefoster55965]

Martin

Despite appearances the Dickson 2 see system is never over constrained. The system will always take up a properly spaced 3 point location, or rather 2 lines and maybe a point even if there are dimensional errors. The only constraint is that the Vees be parallel and of sufficiently similar angle to achieve line contact on at least one face. Which makes manufacture much easier as parallelism is easy to achieve in any competent jigging and set up for final grinding.

Really accurate depth setting, as needed with one V and a point so that the male and female Vees achieve full line contact on both sides, is not so easy. Tolerance on the point or flat height relative to the Vee is very small. Theoretically zero if the male and female Vees are exactly the same angle. Tightening the female angle a bit probably adds tolerance but reduces stability if taken too far. Had some optical mounts in the lab using a version of the single Vee and flat system. Using in an interferometer set up showed repeatability to be insufficient for the task.

If you analyse the Dickson setup it's clear that one side of one pair of male and female Vees produces the line contact needed for vertical and tilt stability. The minimum point contact needed for rotational stability could be anywhere on the other Vees and the system must work. In practice scuff marks show that any professional standard Dickson set gives line contact on two opposing sides of two Vees. I suspect that the female Vee angles may actually be a touch different to the male ones.

Tool tip positional variation depending on which side of the Vees do the guiding is immaterial out in the real world. It must clearly be very small

Interestingly scuff mark positions differ depending on who made the toolpost and holder. I have a Rapid Original post on one lathe and a real Dickson on the other with industrial quality tool holders from a variety of makers. I blued things up when I was having rigidity issues to see what was going on and it was quite clear that different holder / tool post pairings had different contact line positions.

Eventually I twigged that my rigidity issues were due to the thickness of the bottom collar on the height setting device varying between holder makes. If the collar is too thick it cannot properly enter the snail like slot below the hex of the locking device. So the locking force acts to bend the setting screw rather than pull the holder tightly agains the toolpost. It didn't help that several of my holders had acquired bent setting screws in a previous life. Testimony to the attempts of unthinking gorilliods to substitute brute force for careful examination and sorting of the problem.

Appropriate adjustment to collar thicknesses and new screws where needed sorted the problem. As I recall matters real Dickson collars are thinnest, Rapid maybe 15 thou thicker and the worst "unknown" make almost 40 thou thicker. By the time that one arrived and failed to fit anything I was aware of the problem so rectification was swift. The screw would have failed the EU cucumber specification!

One thing I've never understood about Dicksons is how they manage to accumulate fine swarf inside so quickly. Popping apart to clean is dead easy so its no great chore to do regularly but where does it all come from?

Clive

Edited By Clive Foster on 06/09/2023 10:08:57

[Richard MillingtonParticipant @richardmillington63972]

If you tool post height is 43mm:

T0, S0,

https://www.rotagriponline.com/index.php?option=com_virtuemart&page=shop.browse&category_id=244&Itemid=29&redirected=1&Itemid=29

T51 from RDG although you may have to alter the slot which the piston engages to pull it in.

[Bo’sunParticipant @bosun58570]

Well Richard, that's a relief. I'm obviously not the only one to experience such a problem. I have a couple of Warco tool holders, and a couple of "T51" tool holders from Amazon where the cam either doesn't engage, or is only just in effect.

The solution was some strips of metal about 0.3mm thick and 4mm wide, stuck into the slots with JB Weld. Some tight packing was required until set, to ensure a minimal adhesive thickness.

A small dab of paint reminds me which tool holders have the mod, so that I fit them to the tool post with a little more care.

[Simon Williams 3Participant @simonwilliams3]

I don't think the tool post holder height is the deciding factor, it's the centre distance of the vee slots and the height of the tool post itself that determines what to call it. As ever, Tony at lathes.co.uk has the definitive chart here but they seem to be an "S" number not a "T" number.

If the overall length of the holder is 73 mm, then that makes the vee centres credibly 63 mm, which in turn identifies the variant as a T63, previously known as a T1. I have several, all are 43 mm high though they have a variety of tool slots mostly 19 mm though some will accept 22 mm.

That's a re-badged Dickson quick change tool holder sold as an alternative to the four way tool post Colchester also offered. I fancy the business about there having been an alternative tool post is a choice between a four way and the Dickson style. Whether Colchester badged Dickson or made their own others may know, but I can say that I have tool holders which have the original Colchester part number, also genuine Dickson ones and I've bought no-name equivalents including the relatively cheap Indian ones and they all fit the toolpost without any debate about the accuracy of the vee spacing. No wobble.

As for Zoro's suggestion that their tool holders only fit their tool post, I think that's probably them being cautious. I have at least one of their holders, fits my tool post perfectly fine. I believe my tool post is as originally supplied by Colchester, though the badge has worn off long since. But the lathe came from AEA Harwell, so I doubt if they bought anything other than the manufacturer's recommendation.

HTH Rgds Simon

edited see strikethrough first paragraph

Edited By Simon Williams 3 on 06/09/2023 14:11:52

[Simon Williams 3Participant @simonwilliams3]

A quick blip on the googlenet revealed we've been here before:

Dickson Tool holders

and also that Dickson were part of the same group as Colchester so it would be pretty natural for a simple re-badge exercise.

Rgds Simon

[Simon Williams 3Participant @simonwilliams3]

And just to finish off, here's the answer to the "S" or "T" prefix riddle:

Snip from Cutwel (Bison) Catalogue

[Martin ConnellyParticipant @martinconnelly55370]

Clive, doesn't your third paragraph prove my point? The two lines of contact on opposing sides of two Vs is the same as two lines of contact on one V. By having them separated by a relatively large distance and clearances between the tool holder and central block the tool holder can take up different positions, much like putting a part in a lathe chuck and not getting repeatability. Using one V and a positive fixed stop at the other end gives better repeatability. Even with one V the weak point in the setup is likely to be the small cross section of the piston pulling in the tool holder either side of the cam hole. Since my stop on the unused V is a Loktited grub screw I can adjust the position of the holder so that the pull in cam over-centres (toggles) to lock the holder in place and does not just rely on friction of the cam on the plunger. It always bothered me that the pull in cam on the various bought tool holders I have all ended up with the cam in a different position when tightened up and only one or two over-centred the cam.

The only good reason for two Vs on a tool holder is so that it can be used on multiple faces of the centre block without changing the basic geometry. Manufacturers do not need to make left and right handed holders and stockists do not need to hold two "hands" with the chance of people ordering the wrong one.

I agree that the error from slightly different mounting positions is going to be small but if you are using CNC that small error is unwanted as tool tables become less accurate mainly along the Z axis. Also for someone making their own holders the process of making two accurate parallel Vs is the hardest part. If it can be reduced to just making one V it is much easier.

Martin C

[Michael GilliganParticipant @michaelgilligan61133]

For anyone sufficiently interested:

I gave a link to the patent, on this page**LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=174393

MichaelG.

[Nigel McBurney 1Participant @nigelmcburney1]

you could try the second hand machinery dealers,used genuine Dickson toolholders are not cheap as they are always in demand,

[EmgeeParticipant @emgee]

Posted by Martin Connelly on 07/09/2023 08:51:42:The only good reason for two Vs on a tool holder is so that it can be used on multiple faces of the centre block without changing the basic geometry. Manufacturers do not need to make left and right handed holders and stockists do not need to hold two "hands" with the chance of people ordering the wrong one.

I agree that the error from slightly different mounting positions is going to be small but if you are using CNC that small error is unwanted as tool tables become less accurate mainly along the Z axis. Also for someone making their own holders the process of making two accurate parallel Vs is the hardest part. If it can be reduced to just making one V it is much easier.

Martin C

Martin

On the Emco toolpost I have the dovetails are offset, this means you need 2 types of toolholder, the tool fixing screws and adjuster are reversed top to bottom for the boring tool position.

Toolsetting tables on a cnc program are normally generated by determining the offset in Z and X axis with the cutting tool fitted to and always remaining in that numbered holder, so if the tool remains in the holder no difference will be found when the toolholder is changed during a program run.

I agree cutting 1 V slot is much easier but only 1 move of the table needed to cut the second V parallel to the 1st.

Emgee

[DC31kParticipant @dc31k]

Posted by Michael Gilligan on 07/09/2023 09:28:52:

I gave a link to the patent, on this page**LINK**

Unless I am mistaken, that appears to be for a four-way indexing toolpost. I would be interested to see a patent for the quick change post.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by DC31k on 07/09/2023 10:19:14:

Posted by Michael Gilligan on 07/09/2023 09:28:52:

I gave a link to the patent, on this page**LINK**

Unless I am mistaken, that appears to be for a four-way indexing toolpost. I would be interested to see a patent for the quick change post.

.

It does indeed … Strange that nobody commented before

I might have another look this evening

MichaelG.

[Martin ConnellyParticipant @martinconnelly55370]

Emgee, the problem with two Vs is poor repeatability of positioning when fitting the tool holder to the block. It's a bit like the boat in a lantern tool post. It doesn't self level under the pressure of the clamping screw due to friction. The same is true for refitting something in a 3 jaw chuck. Friction stops the part from fully self aligning in the jaws. A tool holder mounted on two Vs is the same, pulling the holder into the block with the piston does not cause the holder to always take up the same position because of friction and because absolute perfection in manufacturing cannot be achieved, there are manufacturing tolerances in the holders and the mounting block. It is interesting to look at the design Harold Hall came up with for a home made QCT. It follows similar lines to what I am suggesting regarding a single V. Looking from above it follows the similar tooling practice for locating parts with two holes that use a round dowel for position and a diamond dowel for rotation. In the case of a tool holder as it is pulled in it rotates round the pivoting point of the V (or a dowel in HH's design) and up against a hard stop.

Martin C

[EmgeeParticipant @emgee]

Martin

With a good quality toolblock the user shoudn't experience what you suggest, I have been using the system on 2 cnc lathes for a few years and never experienced such issues.

Emgee

[Jim GardnerParticipant @jimgardner97734]

Interesting replies and thank you all for them. Opinions are obviously varied, to the point that some people say they are easy to make, while others disagree.

Certainly for now, I will continue looking, specifically at Dickson tool holders.

[Michael GilliganParticipant @michaelgilligan61133]

Right … This is the patent that I should have linked : **LINK**

https://worldwide.espacenet.com/patent/search/family/010123251/publication/GB1215583A?q=dickson%20donald%20john

I had both of them, and evidently selected the wrong one

It doesn’t say much about the manufacture of the tool-holders, but it does put them in their original context, and is interesting for that.

MichaelG.

.

There may be more, but I’ve never found it/them

[DaggersParticipant @daggers]

If you would like to see what is involved measuring and making Dickson tool holders have a look at Jon’s Workshop on youtube he goes through measuring and manufacture, might be of some interest.

Type in “Jon’s workshop tool post” in Youtube

Note— did try to used the Youtube embed button but the instructions shown do not match my Youtube.

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