Dickson tool post

[Nitai LeviParticipant @nitailevi73768]

Hi

I have an original Dickson tool post which came with my Emco lathe.

I have a lot of holders, some original, some new from Bison and some Chinese. The Chinese ones fit great, the others are loose so I shimmed them. The wear is definitely in the post itself though.

I'm considering a new Bison or a Dickson tool post. I'm a bit concerned that my Chinese holders would be too tight… but not the end of the world.

I'm trying to see if there's a difference. I think the Bison is made in Poland, the Dickson is supposedly made in the UK, though probably not by the original Dickson company? I don't know.

The Dickson is a little more expensive, but local Bison prices are actually higher than ordering the Dickson from the UK.

The Bison has an extra "rod" sticking up from the post, I don't know what this is?

I see there are some Chinese made copies too. My Chinese holders are mostly good but did have a couple of annoying QC issues with a couple of them. The extra cost of a "real" Dickson or a Bison is worth the (maybe imaginary?) reassurance and major hassle of returning an international order if necessary.

Anyone compared the Dickson and Bison from Rotagrip?

I also think the Emco version is slightly different with a larger hole at the bottom. Maybe a little tricky to modify if the post is hardened…?

Thanks!

Edited By Nitai Levi on 24/09/2017 09:30:12

[Nitai LeviParticipant @nitailevi73768]

[Nick_GParticipant @nick_g]

.

I know Jason uses a genuine Dickson tool post and has many holders so he may be able to offer a better balanced opinion.

I had for a while a clone Dickson of far east origin and while the holders themselves seemed to be OK the actual tool post was truly awful and would unlock it's self just for fun. I can assure you that when it did such while parting off it was far from fun. – Many here though seem to have had no problem with them so perhaps I got a bad one.

I have no experience of Bison tool posts or holders but I have quite a bit of other tooling from Bison. I find them 1st rate and they are one of my 'go to' brands. e.g. I have new Bison and Pratt chucks. I although as a 'Brit' it pains me to say I regard the Bison as higher quality.

Nick

[JohnFParticipant @johnf59703]

Hi Nitai, I see no reason to replace the tool post completely, the only parts that can wear are the locking gams and the top hat shaped lock. As far as the Chinese / original or Bison toolholder's as concerned I would work so the originals fit and if there is an error it will surely be on the far Eastern ones. One of my tool posts it 40 years old and has been in daily use plus we have a Smart & Brown machine that came from the factory i worked in, it has the original Dickson tool post fitted in the 1960's when they originated and is still working fine.,

I have a mixture on my Myford and Emco lathes, some of the F/East holders I have had to modify, I don't buy them now but they are soft enough to machine with carbide to make them fit properly.

Going back to your question why not just replace the cams etc, Rotogrip do spares for the Bison ones but it would be wise to check sizes and compare to your original Dickson one. Have a look at the link below to see a chart to determine the size you have, on my Emco Super 11 it is the same as the Myford S.OO size.

**LINK**

There is also the chap who is making UK made versions of the Dickson, I have some of his holders and they are fine and indeed superior IMO to the imported ones.

Cheers John

PS All my tool posts are genuine original UK Dickson ones

PPS, The additional peg you can see on some models-usually the larger ones is a location peg, when fitting the tool post body you can add location holes in the top slide to ensure it is at 90deg or whatever you choose.

Edited By JohnF on 24/09/2017 10:26:00

Edited By JohnF on 24/09/2017 10:54:20

[mark smith 20Participant @marksmith20]

I use an emco toolpost that came with my lathe ,it isnt a Dickson copy as it doesnt have the cam type mechanism to engage with the toolholders. Does anyone know if spare holders are available for this style that fit as i only have 4 normal holders for it. The block is 55mm square and around 40mm high. Anyone have an idea when this style was made?

Edited By mark smith 20 on 24/09/2017 10:54:02

[Nitai LeviParticipant @nitailevi73768]

Thank you both.

Yes, since posting this thread I found the spares on Rotagrip and I'm wondering if the "lock pad" and/or the "lock bolt" can simply be replaced to fix it. The pad is cheap enough that I can just order to try. The bolt is not… but making an extra order later just for that is extra international shipping.

I thought maybe the vees themselves are worn from all the inserting and removing of the holders? Shimming the vees on the loose holders worked for now.

I tried ordering from Rotagrip but there is a bug on the website for the international shipping so I'll try calling tomorrow and see if I can.

It would be annoying to have to modify a hardened post for the Emco which on a stock Dickson or Bison it seems that I would.

Thanks again

[Clive FosterParticipant @clivefoster55965]

The extra rod on the Bison is for indexing purposes should you need to rotate either the tool post or topside by specific angles on a regular basis. Many Dickson and industrial level clones also have them. All mine, Dickson OE and Rapid clones, do.

For example my topside lives at 25° angle off from perpendicular which suits my favourite zero2zero thread cutting method, gets the handles and dials out of each others way and makes for a more rigid setup as tool feed cutting forces don't have to go directly through two feed screws. In principle it would be useful if I had an indexing plate underneath the tool post to easily re-set the appropriate tool post rotation when I need to have the topside parallel to or perpendicular to the bed. I also have an angled treading tool that would benefit from such indexing. In practice I have my own adequately fast methods of getting things aligned so the pin is of little benefit to me.

I'm surprised you have sufficient wear on your Dickson post to affect its operation. Like JohnF I've seen some pretty old ones and none had significant wear. Even when new the original bearing surfaces in the locking system are on the slack side of free running. Intentionally so as a bit of float ensures that things will always pull up square on the locking surfaces without being impeded by the internals of the locking system. Also helps cope with the fine swarf which seems to magically build up inside. At leas it all comes apart easily to clean once you've figured the secret.

As has been discussed before the major issue with Dickson clone tool holders concerns tolerances on the back slide of the Tee slot that the locking device pulls on. The position of this surface has to be quite tightly controlled with respect to the spacing and depth of the female Vees so that the locking mechanism is working at appropriate angles to both hold strongly and lock securely. Being internal its a pain to measure. If the production process and fixturing isn't properly thought out its easy to end up with a bit too much variation leading to ill fitting tool holders.

Clive.

[Chris Evans 6Participant @chrisevans6]

My genuine Dickson tool post is over 25 years old and no signs of wear. Tool holders are a bit of a lottery for fit the genuine ones I have are good as are some cheap pattern ones from RDG. Other pattern holders from a reputable supplier that cost three times more than the RDG supplied ones had to go back.

[Nitai LeviParticipant @nitailevi73768]

I'm pretty sure this tool post came new with the lathe which would make it at least 35 years old. The lathe had a few worn parts (even though incorrectly described as "in wonderful condition&quot so I'm not so surprised that it's worn.

I'm almost positive it's the post because the "back" side, although a little looser than it should be, is significantly better than the "left" (more used) side, which simply doesn't grip the original holders or the new Bisons at all (i.e. the cam just keeps spinning.

Thanks!

[Clive FosterParticipant @clivefoster55965]

Although proper analysis of the Dickson tool post operation along with assessment of acceptable wear and tolerances would be more than a little tedious, albeit pretty straightforward, it doesn't seem unreasonably difficult to arrange some form of ad-hoc check system to verify if a particular tool holder will work in a satisfactory manner with a given tool post.

For practical purposes its safe to consider all the errors stacking up into the position of the inner edge of the Tee slot that the locking bar pulls on relative to the female Vee grooves. Consider an accurately made channel section the same width as the tool post with both channel tops and intervening base properly co-planar. If suitably sized rods were mounted accurately parallel on top of the channel arms at the same spacing as the tool post Vees a toolholder laid on top would seat properly on the rods and the height of the inner edge of the Tee slot relative to the base measured. Various ways to make the measurement. I'd probably slide a parallel thought the Tee slot and measure both sides with a depth micrometer. Hence the variation between holders can be established.

Typically for industrial quality T2 size Dicksons there is around 150° total travel on the operating spanner from full open to full closed. Assuming the ones I've used to be typical lock generally occurs at around 70° to 75° of spanner travel from full open. Empirically I'd suggest that the limits for satisfactory operation are probably around 65° to 80° of locking spanner travel. Clearly more than 90° is going to take it over centre and past lock whilst too small an angle won't give the appropriate relationship between the tangents of the cam and its bore at the contact line to jam and hold. I imagine that it might operate OK up to perhaps 85° of operating spanner travel but this would leave no margin for wear if made like that new.

If you measure the travel of the locking system it should be possible to sort out whether any given holder will lock in place properly. Obviously much easier if you have a known good one to start with but shimming, as Nitai does, should give you a start if nothing works. Ultimately if it is wear in the tool post everything reflects back onto the thickness of the locking bar.

So if Nitai makes a new locking bar, or just builds up an old one with weld, suitably thicker on the tool post side the clamping range will be pulled back towards the tool post and everything should work again.

Clive.

[Clive FosterParticipant @clivefoster55965]

Further to my previous post it will be self evident that the angular travel of the locking spanner is a simple and effective criteria to decide whether or not a particular toolholder is likely to work properly in particular tool post. Often this will be more than sufficient but its purely functional assessment and bereft of hard dimensional numbers.

No substitute for numbers if you really need to figure out whats going on and what is wrong. Seen a lot of money wasted in my professional life when folk chased the empirically obvious without stopping to verify the numbers. Correction an error with compensating error only gets you so far.

Clive.

[John MCParticipant @johnmc39344]

I have Dickson tool posts on my lathes with some genuine and some"foreign" tool holders. Never had a problem with them being gripped by the tool post. What I have seen though is distortion of the top hat shaped part that pulls the holder in to the tool post. This component is somewhat thin walled where the hole that the cam passes through. Seemed to be a problem with the smaller versions of the tool post. Worth checking I think as the most likely culprit to insecure clamping. The posts are case hardened so would, I suggest, need a huge amount of work to "wear out".

I've also checked the dimensions of a number of my tool holders, genuine vs copy, significant variation in dimensions except for the angle of the "angled" dimensions and their positions , all the same as near as I could measure. The tool posts have no problem gripping any of them.

The checking and repair for the problem I have suggested was the job of the apprentice at an engineering company I worked at many years ago.

[Nitai LeviParticipant @nitailevi73768]

OK, some progress… I have no idea why I didn't do this before

I switched the two lock pads. Since they are symmetrical I may have also put them upside down without noticing. There is definitely a difference. The "left" (looser) side it less loose and the "back" side is looser than before. The "left" is now better than the "back", but it's not exactly reversed. So wear in the lock pads is definitely part of it, plus either wear in the vees and/or putting upside down had something to do with it.

I can make new ones but it's not that fast. I'll check the ones from Rotagrip. The photo looks like the Bison version, which is different and won't work, but it's just the same stock photo for all sizes and models. I'll check with them tomorrow. For £13 it's worth buying instead of making.

Thanks again

[Martin DowingParticipant @martindowing58466]

@Clive Foster

Very good discussion. I would add that it might be difficult to establish *fully open* position accurately by observing behavior of cam itself. As they are locking both ways, it is easier to check an angle between 2 *fully closed* positions and divide it by 2 to get value needed for your discussion. For me this angle is a little bit over 180 deg.

I have this toolholder, sold to me by Myford Nottingham 15 years ago. The only problem was broken cams (parting tool jam on backgear did the trick). I have recently made more beefy ones, but with all dimensions on the business side left intact. More metal could be left on the other side, because T-slot of holding unit permitted that. As for now they are working brilliant, made of BDMS. The locking bar with eccentric must be hardened however for item to last.

Edited By Martin Dowing on 27/09/2017 10:07:45

[Russ BParticipant @russb]

If the vee's are worn, then just like a lathe bed, the wear will be concentrated more in one spot, and I bet at the top and bottom, they aren't worn at all.

Get a precision ground "anything big enough" (vee block or other setting tool?) and test the faces of the vee's for flatness.

I'd be tempted to have a go at making my own cams, or perhaps making some slightly thicker top hats if the vee's or cam has worn a bit??

[Clive FosterParticipant @clivefoster55965]

Martin

I agree that it might be a bit difficult to establish fully open positions by observing the behaviour of the cam itself. However on factory Dickson and industrial quality clones the angular travel of the locking spanner is limited by contact between the locking device and the thick washer / spacer that sits on top of the tool post under the hold down nut. The primary purpose of the thick washer is to ensure that the nut doesn't interfere with the locking system. However its large enough to encroach on the space occupied by the grooved collar into which the height setting thimble on the tool post fits so the collar has to be cut away for clearance. On my T2 size posts that washer is 1 1/2 " (nominal) diameter and the collar cutaway is such that only 150° or so of movement is possible. I believe the cutaway is asymmetric relative to the cam so that almost full travel is reached on the opening side but rather less on the locking side. Presumably other sizes are similar in geometry.

Full travel of the locking cam requires 180° rotation. A system capable of this will inevitably be able to go right round in a full circle. I guess the original designers considered positive stops desirable to ensure things couldn't be set up so as to just lock at 180° as such would present a very real risk of things working over centre in use, thus unlocking the tool, if sufficiently out of specification components were fitted.

In a practical world you don't have to be terribly exact. Just wanted to put out some (hopefully) typical and fairly easily estimable numbers for the behaviour of a system that is working properly. The one Nitai has clearly isn't right so I figured some information on what is normal would help nail down where the problem lies.

Clive.

[Nitai LeviParticipant @nitailevi73768]

Thanks.

The difference between the two locks and the change from replacing the cams convinced me the problem is likely to be in the cam rod or pad. I ordered the parts, it's not worth it making them myself.

Posted by Clive Foster on 27/09/2017 13:57:22:

However on factory Dickson and industrial quality clones the angular travel of the locking spanner is limited by contact between the locking device and the thick washer / spacer that sits on top of the tool post under the hold down nut.

This created a sneaky disguise for the problem at first.

The original holders felt like they locked i.e. I did feel a solid end to the rotation of the locking rod when tightened, but something felt off, wasn't sure what. I then noticed the top of the locking rods was touching the washer, which made me think it should be smaller. I checked with the washer off and then noticed I could pretty easily rotate the locking rod a full circle repeatedly. There was a difference in resistance throughout its rotation but kept moving. At the end of the movement (when touching the washer) it was just locked enough that it seemed ok but it wasn't really locked.

[EmgeeParticipant @emgee]

MarkSmith. the toolholder and tool post are both original equipment from an Emco 5 cnc lathe, there were 3 types and I believe yours are the later type with an offset dovetail, the other types had a central dovetail. Both had holders for use in the boring mode which are opposite handed to the mode shown in your pictures.

The Emco Compact 5 cnc MK1 model were sometimes fitted with an Emco badged toolpost similar in design to the Dickson snail type securing method.

Emgee

[geoff walker 1Participant @geoffwalker1]

Hi All,

Interesting thread this one even though the Dickson theme has been covered a lot.

I bought mine from A and R precision from Coventry who I believe made Dickson holders for Myford until they, A and R, went into liquidation. I had heard a lot about this company and was of the opinion that if they made them for myford then they were likely to be a top quality tool post and holders.

Well it is but I still had problems and had to make adjustments to the two "top hat" locks. Without the adjustments the cam travel was very short and it just didn't feel right. I took each of the two "hats" and carefully reduced the thickness of the "brim" with a small flat needle file. I removed a small amount from each side, about 10 thou, checking each side with a micrometer. This allowed the cam to rotate to a more comfortable and secure locking position. Of course care needs to be taken you don't go too far.

Hope this may be of help to others experiencing the same problem

geoff

[mechman48Participant @mechman48]

I have a 'Bison' QC tool post on my WM250V-F bought at an 'auto/machine boot sale where one or two dealers appear. I had to make a new tool post stud to fit and it suits me fine. I have a variety of holders, 20 so far, of from varying makers, Chinese, some with a 'M' or 'W' stamped on them depending on how you look at them, & some bought from dealer at Harrogate ME exhib' all fit the tool post snugly & so far none has let me down re. rigidity.

​George.

[Nitai LeviParticipant @nitailevi73768]

Just an update. I got a couple of replacement parts from Rotagrip (pads and bolt). They are better, but when the Bison is good, the others (especially the new Chinese ones) are too tight i.e. it's hard to slip them on, it's really borderline.

It varies depending on the side I put the pads, so I use the looser side and this is about an ok compromise for both. Modifying all my tight ones is not realistic since I have a lot of them and I already shimmed the originals.

If I did it over again I would probably get only Dickson and Bison holders and use the new pads on the tight side. Maybe one day I'll do that, remove the shims and sell my Chinese ones. For now I'm using the compromise.

Although you can see the Bison and Dickson holders are better made, in practice it doesn't really make any difference. I only don't like the Chinese parting tool holder, really worse design.

Edited By Nitai Levi on 09/10/2017 08:51:35

[Author]

Posts