T51 Dixon style tool holders?

[Bo’sunParticipant @bosun58570]

Is there a dimensional standard?

[Bo’sunParticipant @bosun58570]

Good morning,

In response to a previous topic of mine, I purchased an inexpensive T51 (as advertised) Dixon style tool holder from Amazon, hopefully to fit my Warco QCTP. I reasoned, that if it didn't fit, I hadn't lost much.

The tool holder duly arrived and appeared realy well made. It fitted one side of the QCTP perfectly, but the second side would barely clamp up. I'm guessing there's a dimensional issue?

Presumably (and I say that cautiously) there is some sort of dimensional standard for these? Anyone know where I can find one?

[DC31kParticipant @dc31k]

Start here:

https://www.model-engineer.co.uk/forums/postings.asp?th=135594

Continue here:

Google "dickson toolpost dimensions" and look at images.

Try a different combination of eccentric cams, sides and top-hat parts (number the holes 1 & 2, the cams 1 & 2 and the top-hats 1& 2. Try all possibilities).

[John HinkleyParticipant @johnhinkley26699]

I bought a Dixon type QCTP many years ago when I first bought my lathe. I had problems from the word go with the tool holders not clamping securely to the tool post. I traced the problem to poor machining of the top hat parts and ended up making new ones. After that, it worked ok-ish but I replaced it with a wedge type when we came back to the UK. So, the problem is solvable, if you can isolate the cause.

John

[Bo’sunParticipant @bosun58570]

Thanks for the replies.

All of the original tool holders supplied by Warco fit and clamp satisfactorily, so I'm reluctant to start swapping things around at this stage. I have however, got things to work with some narrow shims to improve the clamping force, so my initial thoughts are dimensional errors.

[Tony Pratt 1Participant @tonypratt1]

Your problem[s] will undoubtedly be poor quality & varying machined dimensions on the critical sizes, I changed to a wedge type and am well pleased.

Tony

[Bo’sunParticipant @bosun58570]

Yes Tony, "varying machined dimensions" does indeed seem to be the issue. Further investigation shows the (for want of a better word) ears, that the top hat clamps onto, are around 0.50mm thinner than ones that work. A narrow 0.47mm (that's what I had) shim bonded to each ear does the job. Not perfect or desirable, but at least I now have a useable tool holder that works in both positions.

[Dave DanielsParticipant @davedaniels93256]

I had the same 'effect' with mine.

Clamps on one face but not t'other. Well, they did but not very effectively.

If you faff about as I did swapping bits around to see just what the hell was going on you may find, as it appears Mr. Hinckley did, that the discrepancy lies with the ( WARCO ) tool-post parts. In my case was one of the pistons / top-hats.

I don't have a work-around. I only use one face at a time anyway. Now I know what the game is it doesn't cause me any problems. If I get really chokker with it I'll make another piston.

The two WARCO tool-holders clamp up at different 'angles of clamp' on the wrench depending on which face I use.

 

Summary:

I have 8 toolholders. 2 WARCO & 6 RDGT51

ALL fit on one clamping face.

The RDG holders don't clamp properly on the other.

The 2 WARCO holders need more clamping on the second face.

The effect follows the piston on face 2.

D.

 

 

Edited By Dave Daniels on 13/11/2020 11:31:42

Edited By Dave Daniels on 13/11/2020 11:32:11

[John Hall 7Participant @johnhall7]

I’ve just had the same problem…bought a QCTP from Warco (9009)for my WM250VF..then later bought some additional T51 tool holders from RDG…which don’t fit….well they fit, but do not clamp..

spoke to Warco who said they themselves actually had a bad batch which ended up in the scrap bin…so I guess the manufacturing tolerances for these amongst various manufacturers bust be none existent….so if you buy a QCTP…it’s better staying with the same supplier for additional tool holders as hopefully they should fit, and at least you can return them if there are problems…

anyone want any T51 tool holders from RDG?…Ive got 6 going cheap…🙄

[JasonBModerator @jasonb]

Depends where the problem is that is stopping the clamp going tight. A simple bit of linish/belt sander work got some of the ones I bought to fit.

[Anonymous]

The design of the Dickson toolpost system is over-constrained, so the holders need to be made to a high degree of accuracy over multiple dimensions to fit properly. Although I (mostly) don’t use a QCTP all my Dickson holders are genuine parts with one exception. The exception was made by A&R (I think) who was a toolmaker and at one time supplied holders after Dickson stopped making them. I think he ceased trading some years ago.

Andrew

[ChrisLHParticipant @chrislh]

I bought my QCTP many years ago at the Myford stand. When I was looking for extra toolholders a very kind soul on one of the stands told me to be careful as there were two dimensional “standards” with very little difference. I took his advice and all has been well since. What I never understood was why the two “vee” guides where a “vee” and a flat suffice for even the best quality lathes. In the latter case the dimensions are much less critical.

Sorry, I know this doesn’t help the OP.

[John Hall 7Participant @johnhall7]

My problem is that the RDG holders do not clamp…the distance from the piston face to the holder face is larger than the Warco holder…

when the cam is turned the piston does not push out far enough to engage on the holder face, and the cam can be turned fully round…

They would probably be fine with a RDG QCTP…

RDG we’re doing a good deal some time ago so I bought 6, but have only recently got round to using them…If I’d have know the problem then, I would have just bought one to try the fit…Hind sight..etc..Hopefully this may  pre warn anyone doing the same..

The Warco holders have now doubled in price…It was a while ago that I bought the originals 🙄

[JasonBModerator @jasonb]

Had that too on a couple. I sacrificed a Woodruff cutter to thin down the inner edge that the piston pulls against. If doing it again a cheap carbide Tee or Woodruff cutter from the likes of Ali may stand up better.

It is not just pushing out far enough but you also need to ensure it pulls up enough to go round as far a sother holdes allow as it will come loose if not.

[DalboyParticipant @dalboy]

My original tool post was from Warco when I brought my lathe, I have ordered from them again. But I did buy from Ebay a set of 4 T51 holders and found no problem with them holding in either of the two positions.

I did measure the Warco ones, and they matched what the seller was supplying. And these were supplied from their UK address

[John Hall 7Participant @johnhall7]

Yes, I wrongly assumed they would all be the same…🙄

Hopefully the ones I’ve just ordered from Warco fit ok…

[JasonBModerator @jasonb]

I have always found the angled surfaces OK but problem is either the red area touches the post before the angled faces make full contact, linish the red area down. Or the area shown green needs to b emachined away as either the piston won’t reach or cannot be tightened enough to hold.

[Michael GilliganParticipant @michaelgilligan61133]

At the risk of being a pedantic old ****, may I suggest that the name Dickson be included somewhere in the title of this topic … it might make future searching a little easier.

MichaelG.

[JasonBModerator @jasonb]

Maybe as the last few posts relate to holders from RDG and it is mostly about copies of the original it is best left as is, another case of two “standards”

[Michael GilliganParticipant @michaelgilligan61133]

As you wish, Jason

’though they should really know better !

MichaelG.

[JasonBModerator @jasonb]

Possibly a case of someone objection to them using Dickson in much the same way they are not keen on others using Myford in a product description.

John seems to have found the thread OK after 4 years anyway and as the new search does not just look at thread title like the old one did it is less of an issue.

[Michael GilliganParticipant @michaelgilligan61133]

As you wish, Jason

[Martin ConnellyParticipant @martinconnelly55370]

The issue of over constraint on these tool holders led me make one that only had one V and an adjustment screw in place of the other V. It was a proof of concept tool holder and it works fine. It can be adjusted to allow the plunger to retract to the point where it toggles properly which is something the purchased ones clearly fail to do.

Martin C

[Martin Connelly]

On Martin Connelly Said:

The issue of over constraint on these tool holders led me make one that only had one V and an adjustment screw in place of the other V. It was a proof of concept tool holder and it works fine. It can be adjusted to allow the plunger to retract to the point where it toggles properly which is something the purchased ones clearly fail to do.

 

Martin C

 

2 vees are a pain to manufacture but IF made correctly they work fine, looking at your offering it’s easier to make but I’m not liking the single location vee close to the cutting tool end and the clamp behind it with no 2nd vee further outboard to support alignment and resist pivoting. Just my first impressions and hardly a problem in hobby machining, who knows what would happen under a heavy cut.

Tony

 

[Martin ConnellyParticipant @martinconnelly55370]

In order to lift off the single V something would have to give, either the piston or the lips that it pulls on or the V of the tool holder, I think the tool post is a harder steel so unlikely to be the thing that moves. Since the piston cam is over-centred as it is adjustable that is not going to rotate to a position where it is loose, which is a possibility with two Vs and a cam that is not able to go slightly over centre and so is unable to effectively toggle.

The issue with two Vs is that if there is any deviation from the exact dimension between them, even if within tolerance, on either the tool holder, the tool post or both then you cannot predict which V the tool holder will settle on and be high on the other. This is the over constraint in the design that has been mentioned. It is like the difference in stability of a tripod and a four legged table on an uneven surface. It is possible to set up the tool to a zero, take the tool holder off and replace the tool holder and find it is no longer at the previous zero point. It is similar to the problem of taking something that has just been turned out of a chuck then putting it back in and finding it is not running true. Friction prevents the small movements needed for things to settle in the same position. It can also be compared to the location of something on a jig where if you have two round pins to go into two round holes you will have a problem but if one of the pins is lozenge shaped and oriented correctly then parts fit on and come off easily but are correctly restrained, not over constrained. Basic jig and tool design philosophy, no more constraint than is needed.

The issue of not being adjustable for the purpose of toggling the cam is that you can get the cam pulling up the piston in different positions due to manufacturing tolerances. If you filed a bit out of the hole in the piston to get a toggling action for one tool holder then the next tool holder you try might let the cam go over centre but not pull the piston tight enough.

Martin C

Have you ever looked at Harold Hall’s quick change tool post design? He only had a single vertical location point (that was cylindrical as opposed to being a V for easier manufacture).

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